@article{khan_eaker_bowden_dickey_2014, title={Giant and switchable surface activity of liquid metal via surface oxidation}, volume={111}, ISSN={0027-8424 1091-6490}, url={http://dx.doi.org/10.1073/pnas.1412227111}, DOI={10.1073/pnas.1412227111}, abstractNote={Significance We present a method to control the interfacial energy of a liquid metal via electrochemical deposition (or removal) of an oxide layer on its surface. Unlike conventional surfactants, this approach can tune the interfacial tension of a metal significantly (from ∼7× that of water to near zero), rapidly, and reversibly using only modest voltages. These properties can be harnessed to induce previously unidentified electrohydrodynamic phenomena for manipulating liquid metal alloys based on gallium, which may enable shape-reconfigurable metallic components in electronic, electromagnetic, and microfluidic devices without the use of toxic mercury. The results also suggest that oxides—which are ubiquitous on most metals and semiconductors—may be harnessed to lower interfacial energy between dissimilar materials.}, number={39}, journal={Proceedings of the National Academy of Sciences}, publisher={Proceedings of the National Academy of Sciences}, author={Khan, Mohammad Rashed and Eaker, Collin B. and Bowden, Edmond F. and Dickey, Michael D.}, year={2014}, month={Sep}, pages={14047–14051} }
 @article{chen_bowden_2013, title={Electrochemical characterization of dehaloperoxidase adsorbates on COOH/OH mixed self-assembled monolayers}, volume={703}, ISSN={["1873-2569"]}, DOI={10.1016/j.jelechem.2013.05.023}, abstractNote={Electrochemical characterization of Amphitrite ornata dehaloperoxidase, a monomeric hemoglobin, adsorbed on COOH/OH-terminated alkanethiolate mixed self-assembled monolayers (SAMs) is reported. Adsorption was achieved by simple electrode exposure to low ionic strength protein solution at pH 6.0, and cyclic voltammetry (CV) was employed to measure surface concentration, electron transfer rate, and formal potential under anaerobic conditions. Surface concentration values determined by CV were found to be inversely proportional to scan rate, a behavior that is different than that observed for electron transfer proteins such as cytochrome c. We attribute this behavior to a dynamic heterogeneous adsorbate layer that permits some fraction of the molecules to undergo reorientation during a CV scan. A model was proposed that classifies adsorbates among three populations with respect to their most stable orientations, namely, electroactive adsorbates, latent electroinactive adsorbates capable of undergoing reorientation to electroactive states, and electroinactive adsorbates. Electrochemical results and the proposed model are discussed in terms of the tertiary structure and surface properties of dehaloperoxidase and are compared to the docking and electron transfer reactions of the myoglobin/cytochrome b5 system. Examination of the effects of ionic strength and mixed SAM composition provide support for the proposed model.}, journal={JOURNAL OF ELECTROANALYTICAL CHEMISTRY}, author={Chen, Thomas K. and Bowden, Edmond F.}, year={2013}, month={Aug}, pages={23–28} }
 @article{d'antonio_chen_turner_santiago-capeles_bowden_2013, title={Voltammetry of dehaloperoxidase on self-assembled monolayers: Reversible adsorptive immobilization of a globin}, volume={26}, ISSN={1388-2481}, url={http://dx.doi.org/10.1016/j.elecom.2012.10.011}, DOI={10.1016/j.elecom.2012.10.011}, abstractNote={Abstract Dehaloperoxidase (DHP), a monomeric hemoglobin, was adsorptively immobilized under low ionic strength conditions on binary self-assembled monolayers composed of OH- and COOH-terminated alkylthiols. Voltammetry of its Fe(III)/Fe(II) reactions revealed adsorbed DHP to be electroactive and native under both anaerobic and aerobic conditions. The chemically reversible nature of the adsorptive immobilization was established from voltammetric desorption/re-adsorption experiments. Cyclic voltammetric determination of electroactive surface concentration uncovered an unusual inverse scan rate dependence that was rationalized by means of Hoffman's dynamic docking electron transfer model [Z.-X. Liang et al., J. Am. Chem. Soc. 126 (2004) 2785]. This result represents the first evidence for dynamic docking control of protein electron transfer in an electrochemical setting.}, journal={Electrochemistry Communications}, publisher={Elsevier BV}, author={D'Antonio, Edward L. and Chen, Thomas K. and Turner, Abigail H. and Santiago-Capeles, Lisandra and Bowden, Edmond F.}, year={2013}, month={Jan}, pages={67–70} }
 @article{edward l. d'antonio_bowden_franzen_2012, title={Thin-layer spectroelectrochemistry of the Fe(III)/Fe(II) redox reaction of dehaloperoxidase-hemoglobin}, volume={668}, ISSN={["1873-2569"]}, DOI={10.1016/j.jelechem.2011.12.015}, abstractNote={Dehaloperoxidase-hemoglobin (DHP A; isoenzyme A) is a globin from the annelid Amphitrite ornata that displays enhanced peroxidase activity compared to other myoglobins and hemoglobins. In this study, anaerobic thin-layer spectroelectrochemistry was used to measure formal reduction potentials (E°′) for the Fe(III)/Fe(II) redox couple of DHP A from pH 5.0 to pH 7.0. The value of E°′ determined at pH 7.0 (100 mM potassium phosphate buffer under ambient temperature), +0.202 ± 0.006 V vs SHE, gives DHP A the most positive Fe(III)/Fe(II) reduction potential among known intracellular globins (approximately 150 mV and 50 mV higher than typical myoglobins and hemoglobins, respectively). This finding is particularly distinctive in light of DHP A’s enhanced peroxidase activity, a function that is commonly carried out from the Fe(III) state, which is favored by more negative reduction potentials. For example, horseradish peroxidase has a formal potential that falls 0.47 V negative of the DHP A value. Using available crystal structures, two major energetic factors involving the distal histidine (H55) have been identified that appear to account for the unusually positive DHP A reduction potential. First, H55, which is positioned ∼1 Å further away from the heme iron than distal histidines in hemoglobin and myoglobin, displays a diminished capacity to serve as the hydrogen bond acceptor for a ligated water molecule, resulting in destabilization of the Fe(III) state relative to a common globin. The more distant positioning of H55 from the heme iron also imparts to it a conformational flexibility, which is linked to the electron transfer reaction. In its internal (closed) conformation, H55 hydrogen bonds with and stabilizes an iron-ligated H2O molecule, whereas in its external (open) conformation, H55 hydrogen bonds to a heme propionate resulting in a 5-coordinate heme iron. A thermodynamic cycle that links the conformational change to electron transfer is shown to be consistent with a positive shift in reduction potential if the open conformation is differentially favored by the Fe(II) state, a proposal that is supported by the available crystallographic data.}, journal={JOURNAL OF ELECTROANALYTICAL CHEMISTRY}, author={Edward L. D'Antonio and Bowden, Edmond F. and Franzen, Stefan}, year={2012}, month={Mar}, pages={37–43} }
 @article{d’antonio_d’antonio_de serrano_gracz_thompson_ghiladi_bowden_franzen_2011, title={Functional Consequences of the Creation of an Asp-His-Fe Triad in a 3/3 Globin}, volume={50}, ISSN={0006-2960 1520-4995}, url={http://dx.doi.org/10.1021/bi201368u}, DOI={10.1021/bi201368u}, abstractNote={The proximal side of dehaloperoxidase-hemoglobin A (DHP A) from Amphitrite ornata has been modified via site-directed mutagenesis of methionine 86 into aspartate (M86D) to introduce an Asp-His-Fe triad charge relay. X-ray crystallographic structure determination of the metcyano forms of M86D [Protein Data Bank (PDB) entry 3MYN] and M86E (PDB entry 3MYM) mutants reveal the structural origins of a stable catalytic triad in DHP A. A decrease in the rate of H2O2 activation as well as a lowered reduction potential versus that of the wild-type enzyme was observed in M86D. One possible explanation for the significantly lower activity is an increased affinity for the distal histidine in binding to the heme Fe to form a bis-histidine adduct. Resonance Raman spectroscopy demonstrates a pH-dependent ligation by the distal histidine in M86D, which is indicative of an increased trans effect. At pH 5.0, the heme Fe is five-coordinate, and this structure resembles the wild-type DHP A resting state. However, at pH 7.0, the distal histidine appears to form a six-coordinate ferric bis-histidine (hemichrome) adduct. These observations can be explained by the effect of the increased positive charge on the heme Fe on the formation of a six-coordinate low-spin adduct, which inhibits the ligation and activation of H2O2 as required for peroxidase activity. The results suggest that the proximal charge relay in peroxidases regulate the redox potential of the heme Fe but that the trans effect is a carefully balanced property that can both activate H2O2 and attract ligation by the distal histidine. To understand the balance of forces that modulate peroxidase reactivity, we studied three M86 mutants, M86A, M86D, and M86E, by spectroelectrochemistry and nuclear magnetic resonance spectroscopy of 13C- and 15N-labeled cyanide adducts as probes of the redox potential and of the trans effect in the heme Fe, both of which can be correlated with the proximity of negative charge to the Nδ hydrogen of the proximal histidine, consistent with an Asp-His-Fe charge relay observed in heme peroxidases.}, number={44}, journal={Biochemistry}, publisher={American Chemical Society (ACS)}, author={D’Antonio, Edward L. and D’Antonio, Jennifer and de Serrano, Vesna and Gracz, Hanna and Thompson, Matthew K. and Ghiladi, Reza A. and Bowden, Edmond F. and Franzen, Stefan}, year={2011}, month={Nov}, pages={9664–9680} }
 @article{d’antonio_d’antonio_thompson_bowden_franzen_smirnova_ghiladi_2010, title={Spectroscopic and Mechanistic Investigations of Dehaloperoxidase B fromAmphitrite ornata}, volume={49}, ISSN={0006-2960 1520-4995}, url={http://dx.doi.org/10.1021/bi100407v}, DOI={10.1021/bi100407v}, abstractNote={Dehaloperoxidase (DHP) from the terebellid polychaete Amphitrite ornata is a bifunctional enzyme that possesses both hemoglobin and peroxidase activities. Of the two DHP isoenzymes identified to date, much of the recent focus has been on DHP A, whereas very little is known pertaining to the activity, substrate specificity, mechanism of function, or spectroscopic properties of DHP B. Herein, we report the recombinant expression and purification of DHP B, as well as the details of our investigations into its catalytic cycle using biochemical assays, stopped-flow UV-visible, resonance Raman, and rapid freeze-quench electron paramagnetic resonance spectroscopies, and spectroelectrochemistry. Our experimental design reveals mechanistic insights and kinetic descriptions of the dehaloperoxidase mechanism which have not been previously reported for isoenzyme A. Namely, we demonstrate a novel reaction pathway in which the products of the oxidative dehalogenation of trihalophenols (dihaloquinones) are themselves capable of inducing formation of oxyferrous DHP B, and an updated catalytic cycle for DHP is proposed. We further demonstrate that, unlike the traditional monofunctional peroxidases, the oxyferrous state in DHP is a peroxidase-competent starting species, which suggests that the ferric oxidation state may not be an obligatory starting point for the enzyme. The data presented herein provide a link between the peroxidase and oxygen transport activities which furthers our understanding of how this bifunctional enzyme is able to unite its two inherent functions in one system.}, number={31}, journal={Biochemistry}, publisher={American Chemical Society (ACS)}, author={D’Antonio, Jennifer and D’Antonio, Edward L. and Thompson, Matthew K. and Bowden, Edmond F. and Franzen, Stefan and Smirnova, Tatyana and Ghiladi, Reza A.}, year={2010}, month={Aug}, pages={6600–6616} }
 @article{serrano_davis_gaff_zhang_chen_d'antonio_bowden_rose_franzen_2010, title={X-ray structure of the metcyano form of dehaloperoxidase from Amphitrite ornata: Evidence for photoreductive dissociation of the iron-cyanide bond}, volume={66}, journal={Acta Crystallographica. Section D, Biological Crystallography}, author={Serrano, V. S. and Davis, M. F. and Gaff, J. F. and Zhang, Q. and Chen, Z. and D'Antonio, E. L. and Bowden, E. F. and Rose, R. and Franzen, S.}, year={2010}, pages={770–782} }
 @article{nakano_yoshitake_yamashita_bowden_2007, title={Cytochrome c self-assembly on alkanethiol monolayer electrodes as characterized by AFM, IR, QCM, and direct electrochemistry}, volume={23}, ISSN={["0743-7463"]}, DOI={10.1021/la063697w}, abstractNote={With the advantage of carbodiimide coupling chemistry, horse heart cytochrome c (cyt c) has been covalently immobilized onto self-assembled monolayers (SAMs) from 11-mercaptoundecanoic acid (MUDA) developed on single-crystal or polycrystalline gold substrate surfaces. The cyt c immobilized substrates thus prepared have been characterized by atomic force microscopy (AFM); we have succeeded in obtaining surface topographical images down to single-protein resolution. AFM imaging has also shown densely packed, uniform protein monolayer formation that is highly suggestive of self-assembly of cyt c molecules on MUDA SAMs. Covalent attachment of cyt c has been further evidenced by reflection-absorption FT-IR as well as microgravimetric analysis using a quartz crystal microbalance (QCM). In the latter, the specific MUDA and cyt c surface concentrations were determined to be 0.86 +/- 0.11 nmol cm-2 (n = 5) and 28 +/- 12 pmol cm-2 (n = 5), both of which agree fairly well with their theoretical counterparts. The obtained QCM chips having the cyt c/MUDA/Au interfacial structure were found to be capable of the direct electrochemistry of the surface-attached cyt c molecules. Cyclic voltammetric measurements on the chips gave particular redox waves showing characteristics of surface process. The electroactive protein surface concentration was determined to be 7.2 +/- 4.8 pmol cm-2 (n = 6); it was almost consistent with values found in literature, while it was limited to 26% in magnitude for the QCM data. This was deemed to have arisen from the orientation variation of the surface-confined cyt c molecules and is discussed briefly.}, number={11}, journal={LANGMUIR}, author={Nakano, Koji and Yoshitake, Tadateru and Yamashita, Yasunori and Bowden, Edmond F.}, year={2007}, month={May}, pages={6270–6275} }
 @article{xu_bowden_2006, title={Determination of the orientation of adsorbed cytochrome c on carboxyalkanethiol self-assembled monolayers by in situ differential modification}, volume={128}, ISSN={["0002-7863"]}, DOI={10.1021/ja054219v}, abstractNote={The contact domain utilized by horse cytochrome c when adsorptively bound to a C(10)COOH self-assembled monolayer (SAM) was delineated using a chemical method based on differential modification of surface amino acids. Horse cytochrome c was adsorbed at low ionic strength (pH 7.0, 4.4 mM potassium phosphate) onto 10 microm diameter gold particles coated with HS(CH(2))(10)COOH SAMs. After in situ modification of lysyl groups by reductive Schiff-base methylation, the protein was desorbed, digested using trypsin, and the peptide mapped using LC/MS. Relative lysyl reactivities were ascertained by comparing the resulting peptide frequencies to control samples of solution cytochrome c modified to the same average extent. The least reactive lysines in adsorbed cytochrome c were found to be 13, 72, 73, 79, and 86-88, consistent with a contact region located up and to the left (Met-80 side) of the solvent-exposed heme edge (conventional front face view). The most reactive lysines were 39, 53, 55, and 60, located on the lower backside. The proposed orientation features a heme tilt angle of approximately 35-40 degrees with respect to the substrate surface normal. Factors that can complicate or distort data interpretation are discussed, and the generality of differential modification relative to existing in situ methods for protein orientation determination is also addressed.}, number={21}, journal={JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, author={Xu, Jishou and Bowden, Edmond F.}, year={2006}, month={May}, pages={6813–6822} }
 @article{petrovic_clark_yue_waldeck_bowden_2005, title={Impact of surface immobilization and solution ionic strength on the formal potential of immobilized cytochrome c}, volume={21}, ISSN={["0743-7463"]}, DOI={10.1021/la0500373}, abstractNote={Four different self-assembled monolayer (SAM) electrode systems were examined electrochemically in order to better understand surface charge effects on the redox thermodynamics of immobilized horse heart cytochrome c (cyt c). Neutralization of protein surface charge upon adsorption on anionic COOH-terminated SAMs was found to cause substantial changes in the formal potential, as determined by cyclic voltammetry. For cyt c immobilized on negatively charged surfaces, the formal potential shifted to more negative values as the ionic strength was decreased, which is opposite to the trend displayed by solution cyt c. In contrast, immobilization to uncharged interfaces resulted in an ionic strength dependence for cyt c that is similar to its solution behavior. The results provide insight into the importance of surface charge on the formal potential of cyt c.}, number={14}, journal={LANGMUIR}, author={Petrovic, J and Clark, RA and Yue, HJ and Waldeck, DH and Bowden, EF}, year={2005}, month={Jul}, pages={6308–6316} }
 @article{el kasmi_leopold_galligan_robertson_saavedra_el kacemi_bowden_2002, title={Adsorptive immobilization of cytochrome c on indium/tin oxide (ITO): electrochemical evidence for electron transfer-induced conformational changes}, volume={4}, ISSN={["1388-2481"]}, DOI={10.1016/S1388-2481(01)00299-5}, abstractNote={Abstract The adsorptive immobilization and electrochemistry of horse and yeast cytochrome c on indium/tin oxide (ITO) electrodes is reported. Near-monolayer coverage was achieved in pH 7 phosphate buffers of ionic strength equal to 10 and 50 mM, respectively, for the horse and yeast species. The layers exhibit very well-behaved voltammetry and are stable on the timescale of hours to days. Cyclic voltammetry revealed quasireversible behavior that is a product of both electron transfer (ET) kinetics and ET-induced conformational changes. A square scheme mechanism linking the redox states and the conformational states is proposed. Using a simple ET kinetic model that adequately describes the voltammetry at higher scan rates, a standard ET rate constant of 18 s −1 was determined for adsorbed horse cytochrome c . With decreasing scan rate, we observed a limiting peak separation of approximately 10 mV, an example of unusual quasireversibility (UQR) that we attribute to the effect of conformational changes. Finally we note that the intrinsic cytochrome c ET rate on ITO is some 6 orders of magnitude less than for gold.}, number={2}, journal={ELECTROCHEMISTRY COMMUNICATIONS}, author={El Kasmi, A and Leopold, MC and Galligan, R and Robertson, RT and Saavedra, SS and El Kacemi, K and Bowden, EF}, year={2002}, month={Feb}, pages={177–181} }
 @article{leopold_bowden_2002, title={Influence of gold substrate topography on the voltammetry of cytochrome c adsorbed on carboxylic acid terminated self-assembled monolayers}, volume={18}, ISSN={["0743-7463"]}, DOI={10.1021/la011456c}, abstractNote={Interfacial investigations of a protein monolayer electrochemical system, equine cytochrome c (cyt c) adsorbed to carboxylic acid terminated self-assembled monolayer (COOH SAM) modified gold electrodes, were performed. Electrochemical, spectroscopic, and scanning probe microscopy techniques were utilized to explore the influence of gold topography in the cyt c/COOH SAM/gold system. COOH SAMs were prepared from 14-mercaptotetradecanoic acid and 11-mercaptoundecanoic acid on a variety of substrates including evaporated, bulk, single crystal, and epitaxially grown gold on mica. These substrates encompassed a wide range of surface roughness. As the topography of the gold became smoother, SAMs exhibited an increased ability to block a solution probe molecule, indicative of a lower level of defectiveness. At the same time, after exposure to equine cyt c deposition solutions, the extent of adsorption and the magnitude of the electrochemical response of the adsorbed cyt c decreased significantly with increasingly smooth substrates. The results show cyt c adsorption and electrochemistry to be intimately related to the density of defects in the SAM, which in turn are largely dictated by the topography of the gold substrate. This hypothesis is supported by experiments in which the density of defects in the SAMs was controlled on each type of gold substrate using intentional roughening/smoothing procedures as well as through the use of mixed SAMs. Results are interpreted in terms of the topographically dependent acid/base properties of the COOH SAMs, which can limit the electrostatically driven adsorption of cyt c and the effectiveness of the protein's electronic coupling at the differently textured SAM surfaces.}, number={6}, journal={LANGMUIR}, author={Leopold, MC and Bowden, EF}, year={2002}, month={Mar}, pages={2239–2245} }
 @article{leopold_black_bowden_2002, title={Influence of gold topography on carboxylic acid terminated self-assembled monolayers}, volume={18}, ISSN={["0743-7463"]}, DOI={10.1021/la011683e}, abstractNote={Film permeability and double layer capacitance (Cdl) results are reported for mercaptotetradecanoic acid self-assembled monolayers (C13COOH SAMs) on gold substrates spanning a range of topography. Whereas film permeability was observed to decrease with increasing substrate smoothness, indicative of lower defect density in the SAMs, the capacitance, unexpectedly, was observed to increase as the topography became smoother. To explain these results, a simple structural model is proposed in which the extent of hydrogen bonding (H-bonding) among carboxylic acid endgroups is related to the underlying gold substrate topography. The model predicts that more extensive H-bonding will occur as substrates become smoother which, in turn, impacts the dielectric properties of the film. The model also provides an explanation for the discordant pKa results that have heretofore been reported for COOH SAMs. Altered surface acidity of up to 3 pKa units appears to be attributable to substrate topography.}, number={4}, journal={LANGMUIR}, author={Leopold, MC and Black, JA and Bowden, EF}, year={2002}, month={Feb}, pages={978–980} }
 @article{nahir_bowden_2002, title={Measurement of the rate of adsorption of electroactive cytochrome c to modified gold electrodes by electrochemical impedance spectroscopy}, volume={18}, ISSN={["0743-7463"]}, DOI={10.1021/la020144m}, abstractNote={The electrochemistry of a system containing a surface-confined electroactive species is characterized by electrochemical impedance spectroscopy, and the results are displayed on a Cole−Cole plot. The rate of adsorption of electroactive horse-heart cytochrome c to a carboxythiol-modified gold electrode is experimentally monitored by continuously measuring the change in the magnitude of the pseudocapacitance, which is directly proportional to the amount of adsorbed protein. The time dependence of the adsorption of cytochrome c to the thiol-modified gold electrode shows a significant period of diffusion-controlled behavior. Limitations on the frequency of measurement are outlined in relationship to the magnitude of the standard rate constant of the electron-transfer reaction.}, number={13}, journal={LANGMUIR}, author={Nahir, TM and Bowden, EF}, year={2002}, month={Jun}, pages={5283–5286} }
 @article{goldstein_leopold_huang_atwood_saunders_hartshorn_lim_faget_muffat_scarpa_et al._2000, title={3-Hydroxykynurenine and 3-hydroxyanthranilic acid generate hydrogen peroxide and promote alpha-crystallin cross-linking by metal ion reduction}, volume={39}, ISSN={["0006-2960"]}, DOI={10.1021/bi992997s}, abstractNote={The kynurenine pathway catabolite 3-hydroxykynurenine (3HK) and redox-active metals such as copper and iron are implicated in cataractogenesis. Here we investigate the reaction of kynurenine pathway catabolites with copper and iron, as well as interactions with the major lenticular structural proteins, the α-crystallins. The o-aminophenol kynurenine catabolites 3HK and 3-hydroxyanthranilic acid (3HAA) reduced Cu(II)>Fe(III) to Cu(I) and Fe(II), respectively, whereas quinolinic acid and the nonphenolic kynurenine catabolites kynurenine and anthranilic acid did not reduce either metal. Both 3HK and 3HAA generated superoxide and hydrogen peroxide in a copper-dependent manner. In addition, 3HK and 3HAA fostered copper-dependent α-crystallin cross-linking. 3HK- or 3HAA-modifed α-crystallin showed enhanced redox activity in comparison to unmodified α-crystallin or ascorbate-modified α-crystallin. These data support the possibility that 3HK and 3HAA may be cofactors in the oxidative damage of proteins, such as α-crystallin, through interactions with redox-active metals and especially copper. These findings may have relevance for understanding cataractogenesis and other degenerative conditions in which the kynurenine pathway is activated.}, number={24}, journal={BIOCHEMISTRY}, author={Goldstein, LE and Leopold, MC and Huang, XD and Atwood, CS and Saunders, AJ and Hartshorn, M and Lim, JT and Faget, KY and Muffat, JA and Scarpa, RC and et al.}, year={2000}, month={Jun}, pages={7266–7275} }
 @article{smalley_chalfant_feldberg_nahir_bowden_1999, title={An indirect laser-induced temperature jump determination of the surface pK(a) of 11-mercaptoundecanoic acid monolayers self-assembled on gold}, volume={103}, ISSN={["1089-5647"]}, DOI={10.1021/jp983325z}, abstractNote={The indirect laser-induced temperature jump (ILIT) method is used to determine the acidity (pKa) of monolayers composed of 11-mercaptoundecanoic acid (MUA) self-assembled on vapor-deposited gold film electrodes in contact with either 0.10 or 1.0 M ionic strength NaClO4 electrolyte solutions. The ILIT technique may be used to measure the pKa of a surface-attached acid because the magnitude of the ILIT response is related to the potential gradient at the electrode/electrolyte interface which is, in turn, related to the extent of ionization of the acid. The relevant data are the potentials of zero ILIT response versus pH. A simple two-layer model of the acid-modified electrode/electrolyte interface and Gouy−Chapman double layer theory (modified for the onset of dielectric saturation effected by the large concentration of charge present at this interface when a substantial fraction of the carboxylic acid moieties are ionized) were employed to analyze these data. This analysis gives pKa = 5.7 ± 0.2 at 0.10 M ionic strength and pKa = 4.4 ± 0.2 at 1.0 M ionic strength while the total concentration of MUA comprising the self-assembled monolayer is determined to be essentially the same at both ionic strengths, averaging (5.4 ± 0.3) × 10-10 mol/cm2. Reasons for the observed variation of pKa with ionic strength are discussed.}, number={10}, journal={JOURNAL OF PHYSICAL CHEMISTRY B}, author={Smalley, JF and Chalfant, K and Feldberg, SW and Nahir, TM and Bowden, EF}, year={1999}, month={Mar}, pages={1676–1685} }
 @article{huang_cuajungco_atwood_hartshorn_tyndall_hanson_stokes_leopold_multhaup_goldstein_et al._1999, title={Cu(II) potentiation of Alzheimer A beta neurotoxicity - Correlation with cell-free hydrogen peroxide production and metal reduction}, volume={274}, ISSN={["0021-9258"]}, DOI={10.1074/jbc.274.52.37111}, abstractNote={Oxidative stress markers as well as high concentrations of copper are found in the vicinity of Aβ amyloid deposits in Alzheimer's disease. The neurotoxicity of Aβ in cell culture has been linked to H2O2generation by an unknown mechanism. We now report that Cu(II) markedly potentiates the neurotoxicity exhibited by Aβ in cell culture. The potentiation of toxicity is greatest for Aβ1–42 > Aβ1–40 ≫ mouse/rat Aβ1–40, corresponding to their relative capacities to reduce Cu(II) to Cu(I), form H2O2 in cell-free assays and to exhibit amyloid pathology. The copper complex of Aβ1–42 has a highly positive formal reduction potential (≈+500–550 mV versus Ag/AgCl) characteristic of strongly reducing cuproproteins. These findings suggest that certain redox active metal ions may be important in exacerbating and perhaps facilitating Aβ-mediated oxidative damage in Alzheimer's disease. Oxidative stress markers as well as high concentrations of copper are found in the vicinity of Aβ amyloid deposits in Alzheimer's disease. The neurotoxicity of Aβ in cell culture has been linked to H2O2generation by an unknown mechanism. We now report that Cu(II) markedly potentiates the neurotoxicity exhibited by Aβ in cell culture. The potentiation of toxicity is greatest for Aβ1–42 > Aβ1–40 ≫ mouse/rat Aβ1–40, corresponding to their relative capacities to reduce Cu(II) to Cu(I), form H2O2 in cell-free assays and to exhibit amyloid pathology. The copper complex of Aβ1–42 has a highly positive formal reduction potential (≈+500–550 mV versus Ag/AgCl) characteristic of strongly reducing cuproproteins. These findings suggest that certain redox active metal ions may be important in exacerbating and perhaps facilitating Aβ-mediated oxidative damage in Alzheimer's disease. Alzheimer's disease thiobarbituric acid-reactive substance reactive oxygen species dichlorofluorescein bathocuproine disulfonic acid bicinchoninic acid phosphate-buffered saline Oxidative damage in the neocortex coincides with Aβ accumulation both in Alzheimer's disease (AD)1 (1Hensley K. Hall N. Subramanian R. Cole P. Harris M. Aksenov M. Aksenova M. Gabbita S.P. Wu J.F. Carney J.M. Lovell M. Markesbery W.R. Butterfield D.A. J. Neurochem. 1995; 65: 2146-2156Crossref PubMed Scopus (689) Google Scholar) and in Aβ amyloid-bearing transgenic mice (2Smith M.A. Hirai K. Hsiao K. Pappolla M.A. Harris P. Siedlak S. Tabaton M. Perry G. J. Neurochem. 1998; 70: 2212-2215Crossref PubMed Scopus (522) Google Scholar), but the mechanisms of oxidation are unknown. The possibility that Aβ accumulation causes oxidation, perhaps by radical formation (3Hensley K. Carney J.M. Mattson M.P. Aksenova M. Harris M. Wu J.F. Floyd R.A. Butterfield D.A. Proc. Natl. Acad. Sci. U. S. A. 1994; 91: 3270-3274Crossref PubMed Scopus (1093) Google Scholar), has been explored, but the nature of the chemistry involved in generating Aβ-associated oxidation products such as lipid peroxides (4Mark R.J. Lovell M.A. Markesbery W.R. Uchida K. Mattson M.P. J. Neurochem. 1997; 68: 255-264Crossref PubMed Scopus (708) Google Scholar) remains to be elaborated. In culture, Aβ-induced neurotoxicity is characterized by elevated cellular H2O2 and is combated by antioxidants such as vitamin E and catalase (5Behl C. Davis J.B. Lesley R. Schubert D. Cell. 1994; 77: 817-827Abstract Full Text PDF PubMed Scopus (2052) Google Scholar). The origin of the toxic H2O2 is unknown. Recently, we reported that Fe(III) interacts directly with Aβ1–42 and Aβ1–40 to produce H2O2 and TBARS formation in a cell-free manner in vitro, through reduction of the metal ion (6Huang X. Atwood C.S. Hartshorn M.A. Multhaup G. Goldstein L.E. Scarpa R.C. Cuajungco M.P. Gray D.N. Lim J. Moir R.D. Tanzi R.E. Bush A.I. Biochemistry. 1999; 38: 7609-7616Crossref PubMed Scopus (1036) Google Scholar), suggesting that a source of the H2O2 that mediates toxicity in cell cultures exposed to Aβ is extracellular. Cu(II)and Fe(III) have been found in abnormally high concentrations in amyloid plaques (≈0.4 and ≈1 mm, respectively) and AD-affected neuropil (7Lovell M.A. Robertson J.D. Teesdale W.J. Campbell J.L. Markesbery W.R. J. Neurol. Sci. 1998; 158: 47-52Abstract Full Text Full Text PDF PubMed Scopus (1828) Google Scholar), and copper-selective chelators have been shown to dissolve Aβ deposits extracted from AD post-mortem brain specimens (8Cherny R.A. Legg J.T. McLean C.A. Fairlie D. Huang X. Atwood C.S. Beyreuther K. Tanzi R.E. Masters C.L. Bush A.I. J. Biol. Chem. 1999; 274: 23223-23228Abstract Full Text Full Text PDF PubMed Scopus (450) Google Scholar). Therefore, these metal ions may be important cofactors in Aβ-associated oxidative damage. Importantly, we have also reported that the generation of both Cu(II) and Fe(III)-mediated TBARS is greatest for Aβ1–42 > Aβ1–40 ≫ rat Aβ1–40 (6Huang X. Atwood C.S. Hartshorn M.A. Multhaup G. Goldstein L.E. Scarpa R.C. Cuajungco M.P. Gray D.N. Lim J. Moir R.D. Tanzi R.E. Bush A.I. Biochemistry. 1999; 38: 7609-7616Crossref PubMed Scopus (1036) Google Scholar). This rank order is of interest because it mirrors the relative participation of the peptides in amyloid neuropathology, and because the most active one (Aβ1–42) is overproduced in familial AD (9Scheuner D. Eckman C. Jensen M. Song X. Citron M. Suzuki N. Bird T.D. Hardy J. Hutton M. Kukull W. Larson E. Levy-Lahad E. Viitanen M. Peskind E. Poorkaj P. Schellenberg G. Tanzi R. Wasco W. Lannfelt L. Selkoe D. Younkin S. Nat. Med. 1996; 2: 864-870Crossref PubMed Scopus (2282) Google Scholar). Rats and mice do not develop amyloid (10Vaughan D.W. Peters A. J. Neuropathol. Exp. Neurol. 1981; 40: 472-487Crossref PubMed Scopus (69) Google Scholar), even in mice transgenic for familial-AD linked mutant presenilin that overexpress endogenous mouse Aβ1–42 (11Duff K. Eckman C. Zehr C. Yu X. Prada C.M. Perez-tur J. Hutton M. Buee L. Harigaya Y. Yager D. Morgan D. Gordon M.N. Holcomb L. Refolo L. Zenk B. Hardy J. Younkin S. Nature. 1996; 383: 710-713Crossref PubMed Scopus (1325) Google Scholar), probably due to the three amino acid substitutions in their homologue of Aβ (Arg5 → Gly, Tyr10 → Phe, and His13 → Arg) (12Shivers B.D. Hilbich C. Multhaup G. Salbaum M. Beyreuther K. Seeburg P.H. EMBO J. 1988; 7: 1365-1370Crossref PubMed Scopus (388) Google Scholar). Although Fe(III) mediates and potentiates Aβ1–40 toxicity in cell culture (13Schubert D. Chevion M. Biochem. Biophys. Res. Commun. 1995; 216: 702-707Crossref PubMed Scopus (143) Google Scholar), it is not clear whether this is due to metal interaction with the peptide or due to a nonspecific increase in reactive oxygen species (ROS) generation within the cell. Redox active metal ions, such as Cu(II) and Fe(III), play an obligatory role in generating ROS, and in mediating ROS-induced damage (e.g. the Fenton reaction) (14Halliwell B. Gutteridge J.M.C. Biochem. J. 1984; 219: 1-14Crossref PubMed Scopus (4577) Google Scholar, 15Stadtman E.R. Oliver C.N. J. Biol. Chem. 1991; 266: 2005-2008Abstract Full Text PDF PubMed Google Scholar). Similarly, the Cu(II) and Fe(III) enhancement of dichlorofluorescein (DCF)-reactive oxygen species generated by Aβ25–35 treatment of post-mitochondrial rat cerebrocortex (16Bondy S.C. Guo-Ross S.X. Truong A.T. Brain Res. 1998; 799: 91-96Crossref PubMed Scopus (126) Google Scholar) could be due to catalytically enhanced ROS generation within the tissue, rather than due to metal interaction with the peptide. Cu(II) causes the peptide to aggregate to a greater extent than Fe(III) (Aβ1–42 > Aβ1–40 > rat Aβ1–40) (17Atwood C.S. Moir R.D. Huang X. Bacarra N.M.E. Scarpa R.C. Romano D.M. Hartshorn M.A. Tanzi R.E. Bush A.I. J. Biol. Chem. 1998; 273: 12817-12826Abstract Full Text Full Text PDF PubMed Scopus (945) Google Scholar), a property that may be related to the relative affinities of the metal ions for Aβ. We hypothesize that if such redox active metal ions bind to Aβ peptides with high affinity and become more oxidizing, they may potentiate Aβ-induced cytotoxicity. Furthermore, if the redox competence of Aβ is responsible for its neurotoxicity, then toxicity should be greatest for Aβ1–42 > Aβ1–40 > rat Aβ1–40. Aβ1–42 has been reported to be more neurotoxic than Aβ1–40 (18Doré S. Kar S. Quirion R. Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 4772-4777Crossref PubMed Scopus (294) Google Scholar), but a comparison of the neurotoxicity of these three peptides, or the effects of Cu(II) upon the potentiation of their respective toxicities in culture, has not yet been reported to our knowledge. Here we report that, in the presence of Cu(II), Aβ is indeed redox-competent (Aβ1–42 > Aβ1–40 ≫ rat Aβ1–40), and that a series of electron transfer reactions occur when Cu(II) binds to Aβ, including reduction to Cu(I) and consequent O2-dependent, cell-free peroxide formation. These changes correlate with a striking potentiation in the neurotoxicities of the respective Aβ species in cell culture, supporting an extracellular origin for the H2O2that mediates Aβ-induced toxicity. These data suggest that formation of an Aβ-copper complex may be a pathophysiological interaction, and a new target for therapeutic interdiction in AD. Aβ peptides 1–40 and 1–42 were synthesized by the W. Keck Laboratory, Yale University, New Haven, CT. Confirmatory data were obtained by reproducing experiments with Aβ peptides synthesized and obtained from other sources: Glabe Laboratory, University of California, Irvine, CA; Multhaup Laboratory, University of Heidelberg; U.S. Peptides, Bachem (Torrance, CA); and Sigma. Rat Aβ1–40 was synthesized and purified by the Multhaup Laboratory. For the EPR experiments, Aβ1–40 was synthesized at the University of Queensland. Aβ1–28 and Aβ25–35 were purchased from U.S. Peptides, Bachem, and Sigma. Aβ40–1 was purchased from Bachem, and also synthesized by the Multhaup Laboratory (giving corroborating results). Aβ peptide stock solutions were prepared in water treated with Chelex-100 resin (Bio-Rad) and quantified, according to established procedures (17Atwood C.S. Moir R.D. Huang X. Bacarra N.M.E. Scarpa R.C. Romano D.M. Hartshorn M.A. Tanzi R.E. Bush A.I. J. Biol. Chem. 1998; 273: 12817-12826Abstract Full Text Full Text PDF PubMed Scopus (945) Google Scholar). Cu(II)-Gly stock solutions were used to prevent metal-hydroxy and metal-oxy polymers that form in neutral metal ion solutions and were prepared by mixing National Institute of Standards and Technology (NIST) standard copper with glycine at metal/ligand molar ratio of 1:6. Other reagents are from Sigma, unless otherwise mentioned. Assays were performed using a 96-well microtiter plate (Costar), based upon a modification of established protocols (19Landers J.W. Zak B. Am. J. Clin. Pathol. 1958; 29: 590-592Crossref PubMed Scopus (68) Google Scholar). Polypeptides (10 μm) or vitamin C (10 μm), Cu(II)-glycine and Cu(I) indicator (250 μm), either bathocuproine disulfonic acid (BC) or bicinchoninic acid (BCA, 4,4′-dicarboxy-2,2′-biquinoline), were coincubated in Dulbecco's phosphate-buffered saline (PBS: 1.19 mm CaCl2, 0.6 mm MgCl2, 2.7 mm KCl, 1.4 mmKH2PO4, 137 mm NaCl, 7.68 mm Na2HPO4, pH 7.4), at 37 °C. Absorbances were then measured using a plate reader (SPECTRAmax Plus, Molecular Devices). In control samples, both metal ion and indicator were present to determine the background buffer signal. Absorbance of metal ion and peptide present in the absence of indicator were taken to estimate the contribution of light scattering due to turbidity. The net absorbances (A) were obtained by deducting the absorbances from these controls from the absorbances generated by the peptide and metal in the presence of the indicator. Cu(I) concentrations (μm) were calculated as A × 106/M, where M is the known molar absorption coefficient (m−1cm−1). For Cu(I)-BC, M = 12,250 at 483 nm; and for Cu(I)-BCA, M = 7700 at 562 nm. Cyclic voltammograms were obtained at room temperature (22 ± 2 °C) on air-equilibrated solutions using an EG&G PARC potentiostat, model 263A. The electrochemical cell incorporated an indium/tin oxide working electrode (Donnelly Corp.) of 0.32-cm2 area, a platinum auxiliary electrode, and a Ag/AgCl (1 m KCl) reference electrode. Indium/tin oxide electrodes were pretreated by successive 30 min sonications in Alconox solution (8 g/liter), 95% ethanol, Milli-Q water, and PBS, pH 7.3, followed by overnight equilibration in PBS. The peptide solution was prepared by first dissolving Aβ1–42 with sonication in double-distilled water to 300 μm, after which the peptide solution was added to Dulbecco's phosphate-buffered saline without calcium or magnesium (Sigma) to a final concentration of 100 μm. Background voltammograms were first acquired in buffer on each new electrode used, followed by examination of Aβ1–42 (100 μm) in buffer, CuCl2 (17 μm) in buffer, and Aβ1–42 (100 μm) with added CuCl2 (17 μm) in buffer. The possibility that the formal potentials measured were for surface-adsorbed complexes cannot be excluded, and, in fact, the wave shapes (Fig. 3, lines c and d) are suggestive of involvement by adsorbed species. Further investigation is planned to resolve this issue. Aβ1–40 (0.42 mg) was dissolved in 300 μl of PBS buffer (20 mmNa2HPO4, 20 mmNaH2PO4, 150 mm NaCl, pH 7.4) to which CuCl2 (as indicated) was later added. Q-, X-, and S- band EPR spectra were recorded on a Bruker ESP300E EPR spectrometer; the magnetic field and microwave frequency were calibrated with a Bruker ER-035M gaussmeter and an EIP 548B microwave frequency counter. Quantitation of the Cu(II)-Aβ1–40 EPR resonance was performed by a comparison method (20Pilbrow J.R. Hanson G.R. Methods Enzymol. 1993; 227: 330-353Crossref Scopus (17) Google Scholar) using an X-band dual TE104rectangular cavity with TEMPO as reference sample. The individual cavities have different modulation amplitudes, which can be calibrated, and different microwave magnetic strengths (B1), which was overcome by measuring standard and reference samples in each cavity. The doubly integrated areas are proportional to the spin concentration and were normalized for the anisotropic probability <g 12> and instrument settings. The relative areas can then be used to calculate the concentration of Cu(II)-peptide that produces the residual spectrum. The anisotropic spectra of the Cu(II)-AB1–40 complexes were measured at 130 K using a flow-through cryostat. Spin Hamiltonian parameters were extracted from the spectra with the XSophe/Sophe computer simulation software suite (21Wang D.M. Hanson G.R. J. Magn. Reson. A. 1995; 117: 1-8Crossref Scopus (118) Google Scholar). Buffers were demetallated with Chelex 100 resin. Rat embryonic day 17 forebrain neuronal cultures were grown at 95% O2, 5% CO2, 85% humidity for 4 days in serum-free NeurobasalTM medium with B-27 supplement (Life Technologies, Inc.), 20 μml-glutamate, 100 units/ml penicillin, 0.1 g/ml streptomycin, and 2 mml-glutamine. On the fifth day (treatment day), the medium was replaced with serum-free NeurobasalTM plus l-glutamine without B-27 supplement (vehicle medium). Stock solutions were mixed in vehicle medium to a final concentration of peptide or copper-glycine. Experimental trials were done in triplicate wells. Viable cells were counted manually using a 1-mm2 grid (10× objective) stained with either calcein-AM (Live/DeadTM assay, Molecular Probes) or trypan blue. Data were analyzed using one-way analysis of variance followed by post-hocStudent-Newman-Keuls method and/or Student's t test. Significance level was set at p < 0.05. The colorimetric H2O2 assay was performed in a 96-well microtiter plate (SpectraMax Plus, Molecular Devices), according to a modification of an existing protocol (22Han J. Yen S. Han G. Han P. Anal. Biochem. 1996; 234: 107-109Crossref PubMed Scopus (21) Google Scholar). Polypeptides (10 μm) or vitamin C (10 μm), Cu(II) (1 μm), and a H2O2 scavenging agent, tris(2-carboxyethyl)phosphine hydrochloride (Pierce, 50 μm), were co-incubated in PBS buffer (300 μl), pH 7.4, for 1 h at 37 °C. Following incubation, the unreacted tris(2-carboxyethyl)phosphine hydrochloride was detected by 5,5′-dithiobis(2-nitrobenzoic acid) (Sigma, 50 μm). The amount of H2O2 produced was quantified based on the formula: H2O2 (μm) =A × 106/(2 × L ×M), where A is the absolute absorbance difference between a sample and catalase-only (Sigma, 100 units/ml) control at 412 nm; L = the vertical pathlength, corrected automatically by the plate reader to 1 cm; M is the molecular absorbance for 2-nitro-5-thiobenzoate (14,150m−1 cm−1 at 412 nm). For the DCF assay, 5 mm of 2′,7′-dichlorofluorescin diacetate (Molecular Probes) in 100% ethanol was de-acetylated by 0.01m NaOH for 0.5 h, 200 units/ml horseradish peroxidase was then added, and the DCF solution was neutralized and diluted to 200 μm by PBS before use. Then 20 μm DCF, 10 μm Aβ1–42, and 1 μm Cu(II)-glycine were co-incubated at 37 °C for 20 min in PBS. Catalase (1000 units/ml) with or without heat inactivation (100 °C for 30 min) was used to validate the signal. The fluorescent readings were recorded by a Packard 96-well fluorocounter (485 nm excitation; 530 nm emission). Where the O2 tension of the buffers were manipulated, the buffer vehicle was continuously bubbled for 2 h at 20 °C with 100% O2 to create conditions of increased O2tension, or purged with argon (Ar) to create anerobic conditions, prior to the addition of vitamin C or polypeptide. To establish whether Aβ reduces Cu(II) to Cu(I), we used three independent methods. In the first approach various Aβ peptides, vitamin C (as a positive control), and other control polypeptides were incubated with Cu(II)-glycine chelate. Cu(I) formation was monitored using a chromogenic Cu(I)-trapping agent, BC. Aβ1–42 and Aβ1–40 were the only tested peptides found to reduce significant amounts of Cu(II) to Cu(I) (generating 6 and 3 μm, respectively) during the 1-h incubation period (Fig. 1). Cu(II) was not significantly reduced (<1 μm) by rat/mouse Aβ1–40, reverse sequence human peptide (Aβ40–1), amylin, insulin, Aβ1–28, or Aβ25–35 (Fig. 1). Since it has been pointed out that BC could also bind to Cu(II), potentially altering its reduction potential and cause artifactual estimates of Cu(I) (23Sayre L.M. Science. 1996; 274: 1933-1934Crossref PubMed Scopus (35) Google Scholar), we corroborated the apparent Cu(II)-reducing properties of Aβ1–40/2 by comparing the assay results using BC to those obtained with another Cu(I) detection agent, BCA. The apparent amounts of Cu(I) generated by Aβ1–42 and Aβ1–40 using either BC or BCA were in excellent agreement (Fig. 1, inset). Secondly, EPR spectroscopy was used to measure residual Cu(II) remaining after incubating stoichiometric ratios of CuCl2with Aβ1–40. This peptide caused a loss of the Cu(II) signal (76%), in relative agreement with the corresponding Cu(I) detected in the bioassays above. The detection of Cu(I) by BC assay, at levels roughly comparable to those estimated from loss of the EPR signal for Cu(II), suggests that the EPR signal was not disappearing due to formation of antiferromagnetically coupled (S = 0) dicopper species. Experimental EPR S-band spectra (Fig. 2) and X- and Q-band spectra (data not shown) establish that copper binds very tightly to these peptides. Fig. 2 A shows that an approximately equimolar mixture of Aβ1–40 and CuCl2 produces a single Cu(II)-peptide complex. The multiple resonance signal shown in the EPR spectrum for copper-peptide (Fig. 2 A) is for a single Aβ-bound Cu(II) species that is paramagnetic. Spin quantitation employing a dual mode TE104 X-band rectangular cavity revealed that this EPR signal accounted for 24% of the added Cu(II), consistent with 76% of the Cu(II) being converted to EPR-silent species, very likely Cu(I). There was no evidence of free, uncomplexed Cu(II) remaining after addition of the peptide, since unbound Cu(II) itself gives a different multiple resonance signal. The loss of 76% of the Cu(II) signal upon incubation with Aβ1–40 is compatible with peptide-mediated reduction of Cu(II) to diamagnetic Cu(I), which is undetectable. Computer simulation of the experimental spectrum of Aβ1–40 with an axially symmetric spin Hamiltonian and the g andA matrices (g ∥, 2.295;g ⊥, 2.073; A ∥, 163.60, A ⊥, 10.0 × 10−4cm−1) yielded the spectrum shown in Fig. 2 B. Expansion of the M I = −1/2 resonance revealed nitrogen ligand hyperfine coupling. Computer simulation of these resonances indicated the presence of at least three nitrogen atoms. The magnitude of the g ∥ andA ∥ values also suggest a tetragonally distorted geometry, which is commonly found in type 2 copper proteins (24Frausto da Silva J.J.R. Williams R.J.P. The Biological Chemistry of the Elements. Clarendon Press, Oxford1991Google Scholar), and together with the Blumberg Peisach plots, are consistent with a fourth equatorial ligand binding to copper via an oxygen rather than a sulfur donor atom. Thus, the coordination sphere for the copper-peptide complex is CuN3O1. The third line of independent evidence to support Aβ-dependent reduction of Cu(II) was the electrochemical behavior of Cu(II), assessed in the presence and absence of Aβ by cyclic voltammetry (Fig. 3). This revealed that Aβ1–42 (line c) gives rise to a voltammetric response with a formal reduction potential of approximately +500–550 mV (versus Ag/AgCl) in phosphate-buffered saline alone. This is an extraordinarily high positive potential, which suggests a Cu(I) oxidation state that is highly stabilized by the peptide. Our buffers, even after careful preparation and filtration through Chelex-100 resin, were found routinely to possess ≈0.1 μm copper background contamination, as assessed by inductively coupled plasma analysis (8Cherny R.A. Legg J.T. McLean C.A. Fairlie D. Huang X. Atwood C.S. Beyreuther K. Tanzi R.E. Masters C.L. Bush A.I. J. Biol. Chem. 1999; 274: 23223-23228Abstract Full Text Full Text PDF PubMed Scopus (450) Google Scholar). To determine whether interaction with this trace quantity of metal ion was responsible for the electrochemical response of Aβ, we added CuCl2 (17 μm) to the solution. This increased the magnitude of the response from the Aβ1–42 solution (line d), consistent with this potential being characteristic of a copper-Aβ complex. Background voltammograms of the PBS vehicle did not produce such peaks (line a), and Cu(II) in PBS showed only a Cu(II/I) peak in the reduction wave at ≈−80 mV (line b) along with the return oxidation wave. This reduction process was not observed when Cu(II) was added to Aβ1–42, consistent with the complete reaction of Cu(II) with Aβ. Since Cu(I) can in principle reduce O2, we tested Aβ peptides in the presence of Cu(II) (1 μm) for direct production of H2O2. We found that peroxide was indeed formed in these solutions, the amount of H2O2 produced in 1 h by the various Aβ and control peptides was greatest for Aβ1–42 (10 μm) > Aβ1–40 (7.5 μm) ≫ rat Aβ1–40, Aβ40–1, Aβ25–35, Aβ1–28, insulin, and amylin (≈0 μm) (Fig. 4 A), paralleling the amounts of metal reduction by the same peptides (Fig. 1). Validation of these results was achieved by coincubating Aβ with catalase, which abolished the H2O2 signal in a dose-dependent manner, and also by performing a corroborating assay using dichlorofluorescein (data not shown). To investigate whether the formation of H2O2 by Aβ was due to the specific reduction of O2, we studied the generation of H2O2 by Aβ1–42, Aβ1–40, and vitamin C under different O2 tensions in the presence of 1 μm Cu(II) (Fig. 4 B). The presence of vitamin C was used as a control measure to estimate the maximum amount of H2O2 that could be detected in the buffer vehicle by the non-protein generation of Cu(I). This experiment confirmed that there was a significant dependence of H2O2 production upon the O2tension. The presence of either Aβ1–42 and Aβ1–40 generated significantly more H2O2 (Aβ1–42 > Aβ1–40) than vitamin C under any O2 tension studied, and generated H2O2 under low O2 tension where vitamin C produced none. Under ambient and argon-purged conditions in this system, the reduction of Cu(II) alone by the positive control, vitamin C, was insufficient to produce detectable H2O2. Therefore, Aβ facilitated the reduction of O2 more than would be expected by the interaction of the Cu(I) reduced by Aβ with passively dissolved O2. Hence, Aβ acts not only to reduce metal ions, but also to trap molecular O2 to form H2O2. These data also suggest that copper cycles between the oxidized and reduced forms when bound to Aβ, since the presence of 1 μm Cu(II) was sufficient to produce a catalytic amount (10 μm) of H2O2 in 1 h, consistent with redox cycling and multiple electron donation events from Cu(I) to molecular O2. We examined Aβ1–42 (10 μm) in Cu(II) (1 μm in PBS, pH 7.4) for evidence of O2− formation over a 1 h incubation. Neither of the O2−-selective detection reagents hydroethidium (20 μm, Molecular Probes), nor nitro blue tetrazolium (NBT, 0.1 mm) detected O2− formation from Aβ, using xanthine (1 mm) with xanthine oxidase (0.015 units/ml) in PBS as a positive control. To prove that Aβ-mediated H2O2 formation is metal-ion dependent, H2O2 production by Aβ1–42 in the presence of copper-selective chelators was assayed (Fig. 4 C). The presence of 200 μm BC or diethylenetriaminepentaacetic acid abolished Aβ-mediated H2O2 formation in the presence of 1 μm Cu(II). Triethylenetetramine dihydrochloride only decreased the formation of H2O2 by ≈50%, indicating that high affinity copper chelators may only be able to interrupt these interactions if they have sufficient stereochemical access to the bound copper atom. We tested the consequences of Cu(II)-Aβ interaction upon the survival of primary neuronal cultures. We found that the combination of Aβ1–42 with Cu(II)-glycine (each at 10 μm) significantly potentiated Aβ neurotoxicity (70% cell death in the presence of copper, 40% in its absence) (Fig. 5 A). The presence of catalase slightly rescued the toxicity of the peptide alone (30% cell death), but entirely rescued the fraction of Aβ1–42 toxicity that was enhanced by Cu(II), indicating that the potentiation of toxicity induced by the presence of Cu(II) was mediated by H2O2. Catalase could not completely rescue the toxicity of Aβ1–42, even when catalase was used at higher concentrations (2000 and 3000 IU, data not shown). Since Cu(II)-glycine alone was not neurotoxic, these results strongly support the possibility that Cu(II) interaction modifies Aβ leading to enhanced H2O2-mediated neurotoxicity. The inability of catalase to completely rescue the neurotoxicity caused by Aβ1–42 suggests that other neurotoxic mechanisms that are not mediated by H2O2 may contribute up to 25% of the lethality observed. To confirm that Cu(II)-enhanced toxicity of Aβ was mediated by extracellular H2O2 production, we studied the effects of Cu(II)-glycine supplementation upon the toxicity of the other biologically occurring Aβ species in primary neuronal culture, comparing human Aβ1–42 and Aβ1–40 to rat Aβ1–40 (Fig. 5 B). In the absence of additional Cu(II), Aβ1–42 was observed to be more neurotoxic than both human and rat Aβ1–40, whose lethal effects were indistinguishable and marginal at the concentrations tested (10–25 μm). However, whereas additional Cu(II) (10 μm) dramatically increased the toxicities of human Aβ1–42 and Aβ1–40, additional Cu(II) did not enhance the toxicity of rat Aβ1–40. The Cu(II)-induced potentiation of Aβ toxicity therefore followed the relationship of Aβ1–42 > Aβ1–40 ≫ rat Aβ1–40, which parallels both Cu(II) reduction, and the Cu(II)-mediated generation of H2O2, by the same peptides. Taken together, these data argue that Cu(II) enhances the neurotoxicity of Aβ substantially through the cell-free generation of H2O2. The experiments described above establish that Cu(II) is reduced by Aβ peptides, that Cu(I) mediates O2-dependent cell-free H2O2 generation, and that these properties directly correlate with the Cu(II)-mediated potentiation of Aβ neurotoxicity in cell culture. Previously, we showed that concentrations of Cu(II) at = 1 μm induce the aggregation of Aβ (17Atwood C.S. Moir R.D. Huang X. Bacarra N.M.E. Scarpa R.C. Romano D.M. Hartshorn M.A. Tanzi R.E. Bush A.I. J. Biol. Chem. 1998; 273: 12817-12826Abstract Full Text Full Text PDF PubMed Scopus (945) Google Scholar) and generation of TBARS reactivity (6Huang X. Atwood C.S. Hartshorn M.A. Multhaup G. Goldstein L.E. Scarpa R.C. Cuajungco M.P. Gray D.N. Lim J. Moir R.D. Tanzi R.E. Bush A.I. Biochemistry. 1999; 38: 7609-7616Crossref PubMed Scopus (1036) Google Scholar). The amounts of aggregation (17Atwood C.S. Moir R.D. Huang X. Bacarra N.M.E. Scarpa R.C. Romano D.M. Hartshorn M.A. Tanzi R.E. Bush A.I. J. Biol. Chem. 1998; 273: 12817-12826Abstract Full Text Full Text PDF PubMed Scopus (945) Google Scholar), TBARS reactivity (6Huang X. Atwood C.S. Hartshorn M.A. Multhaup G. Goldstein L.E. Scarpa R.C. Cuajungco M.P. Gray D.N. Lim J. Moir R.D. Tanzi R.E. Bush A.I. Biochemistry. 1999; 38: 7609-7616Crossref PubMed Scopus (1036) Google Scholar), production of Cu(I) and H2O2, as well as Cu(II)-enhanced neurotoxicity, are all greatest when generated by Aβ1–42 > Aβ1–40 ≫ rat/mouse Aβ1–40. This relationship also correlates with the relative participation of these peptides in amyloid pathology (10Vaughan D.W. Peters A. J. Neuropathol. Exp. Neurol. 1981; 40: 472-487Crossref PubMed Scopus (69) Google Scholar, 25Kang J. Lemaire H.G. Unterbeck A. Salbaum J.M. Masters C.L. Grzeschik K.H. Multhaup G. Beyreuther K. Muller-Hill B. Nature. 1987; 325: 733-736Crossref PubMed Scopus (3957) Google Scholar), and in familial AD-associated Aβ processing (9Scheuner D. Eckman C. Jensen M. Song X. Citron M. Suzuki N. Bird T.D. Hardy J. Hutton M. Kukull W. Larson E. Levy-Lahad E. Viitanen M. Peskind E. Poorkaj P. Schellenberg G. Tanzi R. Wasco W. Lannfelt L. Selkoe D. Younkin S. Nat. Med. 1996; 2: 864-870Crossref PubMed Scopus (2282) Goo}, number={52}, journal={JOURNAL OF BIOLOGICAL CHEMISTRY}, author={Huang, XD and Cuajungco, MP and Atwood, CS and Hartshorn, MA and Tyndall, JDA and Hanson, GR and Stokes, KC and Leopold, M and Multhaup, G and Goldstein, LE and et al.}, year={1999}, month={Dec}, pages={37111–37116} }
 @article{el kasmi_wallace_bowden_binet_linderman_1998, title={Controlling interfacial electron-transfer kinetics of cytochrome c with mixed self-assembled monolayers}, volume={120}, ISSN={["0002-7863"]}, DOI={10.1021/ja973417m}, abstractNote={ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTControlling Interfacial Electron-Transfer Kinetics of Cytochrome c with Mixed Self-Assembled MonolayersAsma El Kasmi, Jean Marie Wallace, Edmond F. Bowden, Sophie M. Binet, and Russell J. LindermanView Author Information School of Science and Engineering, Al Akhawayn University Ifrane 53000, Morocco Department of Chemistry, North Carolina State University Raleigh, North Carolina 27695-8204 Cite this: J. Am. Chem. Soc. 1998, 120, 1, 225–226Publication Date (Web):January 14, 1998Publication History Received1 October 1997Revised21 November 1997Published online14 January 1998Published inissue 1 January 1998https://doi.org/10.1021/ja973417mCopyright © 1998 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views1092Altmetric-Citations208LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (44 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information SUBJECTS:Alcohols,Charge transfer,Fungi,Interfaces,Peptides and proteins Get e-Alerts}, number={1}, journal={JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, author={El Kasmi, A and Wallace, JM and Bowden, EF and Binet, SM and Linderman, RJ}, year={1998}, month={Jan}, pages={225–226} }
 @article{clark_bowden_1997, title={Voltammetric peak broadening for cytochrome c/alkanethiolate monolayer structures: Dispersion of formal potentials}, volume={13}, ISSN={["0743-7463"]}, DOI={10.1021/la960650+}, abstractNote={Anomalous peak broadening is a persistent feature observed in the cyclic voltammetry of cytochrome c (cyt c) adsorbed on COOH−alkylthiolate/Au self-assembled monolayer electrodes. The origins of this broadening have been explored through variation of the electroactive cytochrome c surface concentration (Γ). Cytochrome submonolayers were prepared using two different methods. In the first method, submonolayers were created by partial desorption of an electroactive cyt c monolayer by exposure to higher ionic strength buffers. The apparent voltammetric properties of these submonolayers were dependent on Γ, exhibiting decreasing formal potentials, increasing electron-transfer rates, and decreasing peak widths as Γ → 0. On the other hand, submonolayers prepared according to the second method, in which partial desorption of a preadsorbed blocking monolayer of electroinactive porphyrin cyt c was followed by adsorption of active cyt c to the unblocked sites, exhibited opposite trends, i.e., increasing formal potentials and decreasing electron-transfer rate as Γ → 1. These results are indicative of a heterogeneous population of cyt c adsorbates on the SAM/Au surface due to a distribution of interfacial environments and adsorption energies. Peak broadening under reversible electrochemical conditions has been specifically attributed to a thermodynamic distribution of cyt c differential adsorption energies (i.e., ferri- vs ferro-cyt c). Fitting based on a Gaussian distribution of formal potentials resulted in a standard deviation, σ(E°‘), of 40 mV for the cyt c/HOOC(CH2)11S/Au system. Physical models based on intrinsic surface heterogeneity and adsorption-induced heterogeneity arising from steric exclusion are proposed to explain the dispersion of formal potentials.}, number={3}, journal={LANGMUIR}, author={Clark, RA and Bowden, EF}, year={1997}, month={Feb}, pages={559–565} }
 @article{bowden_1997, title={Wiring mother nature: Interfacial electrochemistry of proteins}, volume={6}, number={1997}, journal={Electrochemical Society Interface}, author={Bowden, E. F.}, year={1997}, pages={40–44} }
 @article{glenn_bowden_1996, title={Diffusionless Electrochemistry of Cytochromeb5Adsorbed on a Multilayer Film Electrode}, volume={25}, ISSN={0366-7022 1348-0715}, url={http://dx.doi.org/10.1246/cl.1996.399}, DOI={10.1246/cl.1996.399}, abstractNote={A multilayer film electrode has been developed that is well-suited for diffusionless electron transfer studies of acidic proteins. The multilayer electrode is comprised of trypsin-solubilized cytochrome b5 adsorbed electrostatically to a self-assembled HO2C(CH2)7SH/gold substrate via an intervening bridging layer of cationic poly-L-lysine.}, number={5}, journal={Chemistry Letters}, publisher={The Chemical Society of Japan}, author={Glenn, Julie D. H. and Bowden, Edmond F.}, year={1996}, month={May}, pages={399–400} }
 @article{anderson_bowden_pickup_1996, title={Dynamic Electrochemistry:  Methodology and Application}, volume={68}, ISSN={0003-2700 1520-6882}, url={http://dx.doi.org/10.1021/a1960015y}, DOI={10.1021/a1960015y}, abstractNote={ADVERTISEMENT RETURN TO ISSUEPREVReviewNEXTDynamic Electrochemistry: Methodology and ApplicationJames L. Anderson, Edmond F. Bowden, and Peter G. PickupView Author Information Department of Chemistry, University of Georgia, Athens, Georgia 30602 Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695 Department of Chemistry, Memorial University of Newfoundland, St. John's, Newfoundland, Canada A1B 3X7 Cite this: Anal. Chem. 1996, 68, 12, 379–444Publication Date (Web):June 15, 1996Publication History Published online15 June 1996Published inissue 1 January 1996https://doi.org/10.1021/a1960015yCopyright © 1996 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views3716Altmetric-Citations84LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (763 KB) Get e-AlertsSUBJECTS:Adsorption,Electrodes,Gold,Peptides and proteins,Redox reactions Get e-Alerts}, number={12}, journal={Analytical Chemistry}, publisher={American Chemical Society (ACS)}, author={Anderson, James L. and Bowden, Edmond F. and Pickup, Peter G.}, year={1996}, month={Jan}, pages={379–444} }
 @article{nahir_bowden_1996, title={The Distribution of Standard Rate Constants for Electron Transfer Between Thiol-Modified Gold Electrodes and Adsorbed Cytochrome c}, volume={410}, DOI={10.1016/0022-0728(96)04551-2}, abstractNote={Abstract The magnitude of the total rate constant of an electrochemical reaction at small overpotentials is shown to depend on the exponentials of the distance between the electron donor and acceptor, the reorganization energy, and the formal potential of the reaction. When a population distribution of one or more of these three parameters exists, the effect on the measured standard rate constant can be illuminated by using small-amplitude a.c. electrochemical impedance spectroscopy. Assuming a Gaussian distribution of the logarithm of the standard rate constants, the results from the system of cytochrome c molecules adsorbed on thiol-modified gold electrodes yield a standard deviation of approximately 0.5 for log k°/kavg°. The peak broadening of reversible voltammograms is related to a comparable distribution of formal potentials.}, journal={Journal of Electroanalytical Chemistry}, author={Nahir, T.M. and Bowden, E.F.}, year={1996}, pages={9–13} }
 @article{clark_stephens_bowden_daub_1995, title={Electrochemical reduction of the phytotoxin cercosporin}, volume={389}, ISSN={1572-6657}, url={http://dx.doi.org/10.1016/0022-0728(94)03835-q}, DOI={10.1016/0022-0728(94)03835-q}, number={1-2}, journal={Journal of Electroanalytical Chemistry}, publisher={Elsevier BV}, author={Clark, Rose A. and Stephens, Treva R. and Bowden, Edmond F. and Daub, Margaret E.}, year={1995}, month={Jun}, pages={205–208} }
 @article{jenns_scott_bowden_daub_1995, title={ISOLATION OF MUTANTS OF THE FUNGUSCercospora nicotianaeALTERED IN THEIR RESPONSE TO SINGLET-OXYGEN-GENERATING PHOTOSENSITIZERS}, volume={61}, ISSN={0031-8655 1751-1097}, url={http://dx.doi.org/10.1111/j.1751-1097.1995.tb02350.x}, DOI={10.1111/j.1751-1097.1995.tb02350.x}, abstractNote={Fungi in the genus Cercospora produce a singlet-oxygen-generating photosensitizing toxin cercosporin, which plays an important role in the ability of these fungi to parasitize plants. Previous studies demonstrated that resistance to cercosporin was associated with the ability of the fungus to reduce and detoxify cercosporin transiently. In order to characterize the mechanism of cercosporin resistance further, two types of mutants were isolated. One set of mutants was selected directly for sensitivity to cercosporin. Six cercosporin-sensitive mutants were isolated. Five of the mutants were totally inhibited by cercosporin as well as by five other photosensitizers, methylene blue, toluidine blue, eosin Y, rose bengal and hematoporphyrin. These five mutants were also deficient in cercosporin-reducing ability. The sixth cercosporin-sensitive mutant was only partially inhibited by cercosporin. This mutant was unaltered in cercosporin-reducing ability and in its response to the other photosensitizers. In order to test hypotheses concerning the mechanism of cercosporin reduction, a second set of mutants was selected for general deficiency in cell surface-reducing capability by screening for the inability to reduce two tetrazolium dyes (p-tolyltetrazolium red and 2,3,5-triphenyltetrazolium chloride) of similar redox potential to cercosporin. Dye-reduction-deficient mutants were unaltered in their resistance to cercosporin and in cercosporin-reducing ability. We conclude that cercosporin resistance of these fungi is strongly correlated with the ability to reduce cercosporin. However, cercosporin-reducing ability is separable from the general ability to reduce external electron acceptors.}, number={5}, journal={Photochemistry and Photobiology}, publisher={Wiley}, author={Jenns, Anne E. and Scott, Donna L. and Bowden, Edmond F. and Daub, Margaret E.}, year={1995}, month={May}, pages={488–493} }
 @article{ryan_bowden_chambers_1994, title={Dynamic Electrochemistry: Methodology and Application}, volume={66}, ISSN={0003-2700 1520-6882}, url={http://dx.doi.org/10.1021/ac00084a015}, DOI={10.1021/ac00084a015}, number={12}, journal={Analytical Chemistry}, publisher={American Chemical Society (ACS)}, author={Ryan, Michael D. and Bowden, Edmond F. and Chambers, James Q.}, year={1994}, month={Jun}, pages={360–427} }
 @article{scott_bowden_1994, title={Enzyme-Substrate Kinetics of Adsorbed Cytochrome c Peroxidase on Pyrolytic Graphite Electrodes}, volume={66}, ISSN={0003-2700 1520-6882}, url={http://dx.doi.org/10.1021/ac00080a004}, DOI={10.1021/ac00080a004}, abstractNote={ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTEnzyme-Substrate Kinetics of Adsorbed Cytochrome c Peroxidase on Pyrolytic Graphite ElectrodesDonna L. Scott and Edmond F. BowdenCite this: Anal. Chem. 1994, 66, 8, 1217–1223Publication Date (Print):April 15, 1994Publication History Published online1 May 2002Published inissue 15 April 1994https://doi.org/10.1021/ac00080a004RIGHTS & PERMISSIONSArticle Views280Altmetric-Citations64LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (737 KB) Get e-Alerts Get e-Alerts}, number={8}, journal={Analytical Chemistry}, publisher={American Chemical Society (ACS)}, author={Scott, Donna L. and Bowden, Edmond F.}, year={1994}, month={Apr}, pages={1217–1223} }
 @article{nahir_bowden_1994, title={Impedance spectroscopy of electroinactive thiolate films adsorbed on gold}, volume={39}, ISSN={0013-4686}, url={http://dx.doi.org/10.1016/0013-4686(94)00209-6}, DOI={10.1016/0013-4686(94)00209-6}, abstractNote={Results from electrochemical impedance spectroscopy measurements of gold electrodes, which were modified by immersion in solutions of alkanethiols and other sulfur-containing derivatives, are reported. Three cases were investigated: a capacitive system, a completely covered and a partially covered electrode. A proposed model considers both through-film and at-defect electron transfer paths, and is compared with experimental results}, number={16}, journal={Electrochimica Acta}, publisher={Elsevier BV}, author={Nahir, Tal M. and Bowden, Edmond F.}, year={1994}, month={Nov}, pages={2347–2352} }
 @article{nahir_clark_bowden_1994, title={Linear-Sweep Voltammetry of Irreversible Electron Transfer in Surface-Confined Species Using the Marcus Theory}, volume={66}, ISSN={0003-2700 1520-6882}, url={http://dx.doi.org/10.1021/ac00087a027}, DOI={10.1021/ac00087a027}, abstractNote={A theoretical analysis suggests a relationship between an observed reaction rate constant and a differential rate constant, which is related to the Marcus theory of electron transfer. Consequently, assumptions from the Marcus theory are used to derive an expression for the current as a function of overpotential during linear-sweep voltammetry in the case of kinetically irreversible electron transfer between an electrode and a surface-confined redox species. A method for the extraction of kinetic parameters from experimental current vs potential data is also described. The application of this procedure is demonstrated in the electron transfer between gold electrodes and strongly adsorbed cytochrome c through a self-assembled alkanethiolate monolayer}, number={15}, journal={Analytical Chemistry}, publisher={American Chemical Society (ACS)}, author={Nahir, Tal M. and Clark, Rose A. and Bowden, Edmond F.}, year={1994}, month={Aug}, pages={2595–2598} }
 @article{reeves_song_bowden_1993, title={Application of square wave voltammetry to strongly adsorbed quasireversible redox molecules}, volume={65}, ISSN={0003-2700 1520-6882}, url={http://dx.doi.org/10.1021/ac00054a006}, DOI={10.1021/ac00054a006}, abstractNote={The theory and application of square wave voltammetry to surface-confined quasi-reversible redox molecules (Ox+ne - =Red) is described. Theoretical voltammograms were calculated based on the following assumptions: (1) stable redox states ; (2) monolayer or less surface coverage; (3) equivalent surface sites and adsorbates; (4) non adsorbate-adsorbate interactions; (5) no diffusional contributions to the current; and (6) Bulter-Volmer electrode kinetics. A working curve strategy based on peak separation between positive-scan and negative-scan net current voltammograms was developed to facilitate the semiquantative determination of electron-transfer rate constants}, number={6}, journal={Analytical Chemistry}, publisher={American Chemical Society (ACS)}, author={Reeves, James H. and Song, Shihua. and Bowden, Edmond F.}, year={1993}, month={Mar}, pages={683–688} }
 @misc{song_clark_bowden_tarlov_1993, title={CHARACTERIZATION OF CYTOCHROME-C ALKANETHIOLATE STRUCTURES PREPARED BY SELF-ASSEMBLY ON GOLD}, volume={97}, ISSN={["0022-3654"]}, DOI={10.1021/j100126a037}, abstractNote={ADVERTISEMENT RETURN TO ISSUEPREVArticleCharacterization of cytochrome c/alkanethiolate structures prepared by self-assembly on goldShihua Song, Rose A. Clark, Edmond F. Bowden, and Michael J. TarlovCite this: J. Phys. Chem. 1993, 97, 24, 6564–6572Publication Date (Print):June 1, 1993Publication History Published online1 May 2002Published inissue 1 June 1993https://doi.org/10.1021/j100126a037RIGHTS & PERMISSIONSArticle Views1514Altmetric-Citations340LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (2 MB) Get e-Alerts}, number={24}, journal={JOURNAL OF PHYSICAL CHEMISTRY}, author={SONG, S and CLARK, RA and BOWDEN, EF and TARLOV, MJ}, year={1993}, month={Jun}, pages={6564–6572} }
 @article{hilgen-willis_pielak_bowden_1993, title={Dramatic stabilization of ferricytochrome c upon reduction}, volume={51}, ISSN={0162-0134}, url={http://dx.doi.org/10.1016/0162-0134(93)85036-8}, DOI={10.1016/0162-0134(93)85036-8}, abstractNote={By combining measurements of the free energy of denaturation of the C102T variant of Saccharomyces cerevisiae iso-1-ferricytochrome c with determination of the formal potentials for the native and chemically-denatured states we have determined the free energy of denaturation of the ferro form of the protein. We report that the simplest of all chemical modifications, addition of an electron, increases the stability of ferricytochrome c by approximately 10 kcal mol-1 at 300 K, pH 4.6. This makes reduced cytochrome c one of the most stable proteins yet investigated.}, number={3}, journal={Journal of Inorganic Biochemistry}, publisher={Elsevier BV}, author={Hilgen-Willis, Sharon and Pielak, Gary J. and Bowden, Edmond F.}, year={1993}, month={Aug}, pages={649–653} }
 @inproceedings{bowden_clark_willit_song_1993, place={Pennington, NJ}, series={Proceedings / Electrochemical Society}, title={Protein Monolayer Electrochemistry: A Strategy for Probing Biological Electron Transfer Kinetics}, booktitle={Proceedings of the Fifth International Symposium on Redox Mechanisms and Interfacial Properties of Molecules of Biological Importance, 1993}, publisher={The Electrochemical Society}, author={Bowden, E.F. and Clark, R.A. and Willit, J.L. and Song, S.}, editor={Schultz, F. and Taniguchi, I.Editors}, year={1993}, pages={34–45}, collection={Proceedings / Electrochemical Society} }
 @article{collinson_bowden_1992, title={Chronoabsorptometric determination of adsorption isotherms for cytochrome c on tin oxide electrodes}, volume={8}, ISSN={0743-7463 1520-5827}, url={http://dx.doi.org/10.1021/la00046a032}, DOI={10.1021/la00046a032}, abstractNote={ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTChronoabsorptometric determination of adsorption isotherms for cytochrome c on tin oxide electrodesMaryanne Collinson and Edmond F. BowdenCite this: Langmuir 1992, 8, 10, 2552–2559Publication Date (Print):October 1, 1992Publication History Published online1 May 2002Published inissue 1 October 1992https://doi.org/10.1021/la00046a032RIGHTS & PERMISSIONSArticle Views148Altmetric-Citations24LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts Get e-Alerts}, number={10}, journal={Langmuir}, publisher={American Chemical Society (ACS)}, author={Collinson, Maryanne and Bowden, Edmond F.}, year={1992}, month={Oct}, pages={2552–2559} }
 @article{daub_leisman_clark_bowden_1992, title={Reductive detoxification as a mechanism of fungal resistance to singlet oxygen-generating photosensitizers.}, volume={89}, ISSN={0027-8424 1091-6490}, url={http://dx.doi.org/10.1073/pnas.89.20.9588}, DOI={10.1073/pnas.89.20.9588}, abstractNote={Fungi that are resistant or sensitive to the singlet oxygen-generating toxin cercosporin were assayed for their ability to detoxify it by reduction. Cercosporin reduction was assayed microscopically by using bandpass filters to differentiate between fluorescence emission from cercosporin and reduced cercosporin. Hyphae of the resistant Cercospora and Alternaria species emitted a green fluorescence, indicative of reduced cercosporin. Hyphae of nonviable cultures and of cercosporin-sensitive fungi did not reduce cercosporin. Sensitive fungi occasionally reduced cercosporin when incubated with reducing agents that protect against cercosporin toxicity. Cercosporin could not be efficiently photoreduced in the absence of the fungus. Cercospora species were also resistant to eosin Y but were sensitive to rose bengal. Microscopic observation demonstrated that Cercospora species were not capable of reducing rose bengal but were capable of reducing eosin Y. These observations were supported by in vitro electrochemical measurements that revealed the following order with respect to ease of reduction: cercosporin >> eosin Y > rose bengal. The formal redox potential (E 0') of cercosporin at pH 7.5 was found to be -0.14 V vs. the normal hydrogen electrode. We conclude that Cercospora species protect themselves against cercosporin by the reduction and detoxification of the toxin molecule.}, number={20}, journal={Proceedings of the National Academy of Sciences}, publisher={Proceedings of the National Academy of Sciences}, author={Daub, M. E. and Leisman, G. B. and Clark, R. A. and Bowden, E. F.}, year={1992}, month={Oct}, pages={9588–9592} }
 @article{scott_paddock_bowden_1992, title={The electrocatalytic enzyme function of adsorbed cytochrome c peroxidase on pyrolytic graphite}, volume={341}, ISSN={1572-6657}, url={http://dx.doi.org/10.1016/0022-0728(92)80490-u}, DOI={10.1016/0022-0728(92)80490-u}, abstractNote={Cytochrome c peroxidase (CCP) is a well characterized redox enzyme which can serve as a model for understanding the electrocatalytic function of adsorbed enzymes. Rotating disk electrode (RDE) voltammetry and cyclic voltammetry were used to show that CCP adsorbed on edge-oriented pyrolytic graphite reduces H 2 O 2 electrocatalytically in a manner similar but not identical to solution CCP. Bulk electrolysis and Koutecky—Levich analysis of RDE data proved that the observed amperometric signal corresponds to the unmediated 2e − reduction of H 2 O 2 to water. The pH dependence of the enzyme—substrate kinetics of adsorbed CCP were similar to those for solution CCP at pH ≤ 6 but showed some differences at pH > 6. RDE studies in solutions of varying ionic strength show that CCP remains strongly adsorbed to pyrolytic graphite even at high ionic strength. Preliminary cyclic voltammetry experiments revealed that adsorbed CCP is reversibly inhibited by inhibitors of solution CCP.}, number={1-2}, journal={Journal of Electroanalytical Chemistry}, publisher={Elsevier BV}, author={Scott, Donna L. and Paddock, Robert M. and Bowden, Edmond F.}, year={1992}, month={Dec}, pages={307–321} }
 @article{collinson_bowden_1992, title={UV-visible spectroscopy of adsorbed cytochrome c on tin oxide electrodes}, volume={64}, ISSN={0003-2700 1520-6882}, url={http://dx.doi.org/10.1021/ac00037a028}, DOI={10.1021/ac00037a028}, abstractNote={ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTUV-visible spectroscopy of adsorbed cytochrome c on tin oxide electrodesMaryanne. Collinson and Edmond F. BowdenCite this: Anal. Chem. 1992, 64, 13, 1470–1476Publication Date (Print):July 1, 1992Publication History Published online1 May 2002Published inissue 1 July 1992https://doi.org/10.1021/ac00037a028RIGHTS & PERMISSIONSArticle Views1190Altmetric-Citations62LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (900 KB) Get e-Alerts Get e-Alerts}, number={13}, journal={Analytical Chemistry}, publisher={American Chemical Society (ACS)}, author={Collinson, Maryanne. and Bowden, Edmond F.}, year={1992}, month={Jul}, pages={1470–1476} }
 @article{collinson_bowden_tarlov_1992, title={Voltammetry of covalently immobilized cytochrome c on self-assembled monolayer electrodes}, volume={8}, ISSN={0743-7463 1520-5827}, url={http://dx.doi.org/10.1021/la00041a004}, DOI={10.1021/la00041a004}, abstractNote={ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTVoltammetry of covalently immobilized cytochrome c on self-assembled monolayer electrodesMaryanne Collinson, Edmond F. Bowden, and Michael J. TarlovCite this: Langmuir 1992, 8, 5, 1247–1250Publication Date (Print):May 1, 1992Publication History Published online1 May 2002Published inissue 1 May 1992https://doi.org/10.1021/la00041a004RIGHTS & PERMISSIONSArticle Views1363Altmetric-Citations196LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (492 KB) Get e-Alerts Get e-Alerts}, number={5}, journal={Langmuir}, publisher={American Chemical Society (ACS)}, author={Collinson, Maryanne and Bowden, Edmond F. and Tarlov, Michael J.}, year={1992}, month={May}, pages={1247–1250} }
 @article{tarlov_bowden_1991, title={ELECTRON-TRANSFER REACTION OF CYTOCHROME-C ADSORBED ON CARBOXYLIC-ACID TERMINATED ALKANETHIOL MONOLAYER ELECTRODES}, volume={113}, ISSN={["0002-7863"]}, DOI={10.1021/ja00005a068}, abstractNote={ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTElectron-transfer reaction of cytochrome c adsorbed on carboxylic acid terminated alkanethiol monolayer electrodesMichael J. Tarlov and Edmond F. BowdenCite this: J. Am. Chem. Soc. 1991, 113, 5, 1847–1849Publication Date (Print):February 1, 1991Publication History Published online1 May 2002Published inissue 1 February 1991https://doi.org/10.1021/ja00005a068RIGHTS & PERMISSIONSArticle Views928Altmetric-Citations320LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (471 KB) Get e-Alerts Get e-Alerts}, number={5}, journal={JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, author={TARLOV, MJ and BOWDEN, EF}, year={1991}, month={Feb}, pages={1847–1849} }
 @article{willit_bowden_1990, title={Adsorption and redox thermodynamics of strongly adsorbed cytochrome c on tin oxide electrodes}, volume={94}, ISSN={0022-3654 1541-5740}, url={http://dx.doi.org/10.1021/j100384a048}, DOI={10.1021/j100384a048}, abstractNote={ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAdsorption and redox thermodynamics of strongly adsorbed cytochrome c on tin oxide electrodesJames L. Willit and Edmond F. BowdenCite this: J. Phys. Chem. 1990, 94, 21, 8241–8246Publication Date (Print):October 1, 1990Publication History Published online1 May 2002Published inissue 1 October 1990https://doi.org/10.1021/j100384a048RIGHTS & PERMISSIONSArticle Views297Altmetric-Citations84LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts}, number={21}, journal={The Journal of Physical Chemistry}, publisher={American Chemical Society (ACS)}, author={Willit, James L. and Bowden, Edmond F.}, year={1990}, month={Oct}, pages={8241–8246} }
 @article{thorp_brudvig_bowden_1990, title={Proton-coupled electron transfer in[(bpy)2Mn(O)2Mn(bpy)2]3+}, volume={290}, ISSN={0022-0728}, url={http://dx.doi.org/10.1016/0022-0728(90)87440-u}, DOI={10.1016/0022-0728(90)87440-u}, abstractNote={In this paper we report the electrochemistry of 1 [(bpy) 2 Mn(O) 2 Mn(bpy) 2 ] 3+ (1, bpy=2,2'-bipyridyl) at edge-oriented pyrolytic graphite (EOPG) and tin-doped indium oxide. These surfaces appear to mediate proton-coupled electron transfer; it is also clear that both forms of 1 adsorb at these surfaces under certain conditions}, number={1-2}, journal={Journal of Electroanalytical Chemistry and Interfacial Electrochemistry}, publisher={Elsevier BV}, author={Thorp, H.Holden and Brudvig, Gary W. and Bowden, Edmond F.}, year={1990}, month={Sep}, pages={293–301} }
 @article{sorrell_martin_bowden_1989, title={A novel, functional variant of cytochrome c. Replacement of the histidine ligand with arginine via site-directed mutagenesis}, volume={111}, ISSN={0002-7863}, url={http://dx.doi.org/10.1021/ja00184a074}, DOI={10.1021/ja00184a074}, abstractNote={ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTA novel, functional variant of cytochrome c. Replacement of the histidine ligand with arginine via site-directed mutagenesisThomas N. Sorrell, Patrick K. Martin, and Edmond F. BowdenCite this: J. Am. Chem. Soc. 1989, 111, 2, 766–767Publication Date (Print):January 1, 1989Publication History Published online1 May 2002Published inissue 1 January 1989https://doi.org/10.1021/ja00184a074RIGHTS & PERMISSIONSArticle Views112Altmetric-Citations38LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (309 KB) Get e-AlertscloseSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts}, number={2}, journal={Journal of the American Chemical Society}, publisher={American Chemical Society (ACS)}, author={Sorrell, Thomas N. and Martin, Patrick K. and Bowden, Edmond F.}, year={1989}, month={Jan}, pages={766–767} }
 @article{paddock_bowden_1989, title={Electrocatalytic reduction of hydrogen peroxide via direct electron transfer from pyrolytic graphite electrodes to irreversibly adsorbed cytochrome c peroxidase}, volume={260}, ISSN={0022-0728}, url={http://dx.doi.org/10.1016/0022-0728(89)87165-7}, DOI={10.1016/0022-0728(89)87165-7}, abstractNote={where E is the enzyme, S is the substrate, and P is the product. Various immobilization strategies such as adsorption, entrapment, and covalent attachment have been described. Surface coverage can range from submonolayers to trapped enzyme layers many pm thick. Reaction (2), the net electrode reaction, may involve direct electron transfer between the enzyme and the electrode [l-3], or it may be mediated ]1,2,41. We are interested in the direct electron transfer reactions of redox proteins and enzymes which have been immobilized on electrode surfaces by adsorption. In previous work, we have described the voltammetry of irreversibly adsorbed cytochrome c, an electron carrier protein, on tin oxide electrodes [5,6]. In the present paper, initial results are reported for direct electron transfer to an irreversibly adsorbed heme enzyme, cytochrome c peroxidase (CCP), on edge-oriented pyrolytic graphite (EOPG). This 34.1 kDa (kg mol-‘) enzyme catalyzes the 2 e-/2 H+}, number={2}, journal={Journal of Electroanalytical Chemistry and Interfacial Electrochemistry}, publisher={Elsevier BV}, author={Paddock, Robert M. and Bowden, Edmond F.}, year={1989}, month={Mar}, pages={487–494} }
 @inbook{collinson_willit_bowden_1989, title={Electron Transfer Reactions of Irreversibly Adsorbed Cytochromes on Solid Electrodes}, ISBN={9781461278658 9781461305576}, url={http://dx.doi.org/10.1007/978-1-4613-0557-6_7}, DOI={10.1007/978-1-4613-0557-6_7}, booktitle={Charge and Field Effects in Biosystems—2}, publisher={Springer US}, author={Collinson, Maryanne and Willit, James L. and Bowden, Edmond F.}, year={1989}, pages={69–79} }
 @inbook{willit_bowden_1988, title={Electrochemical Reactivity of Strongly Adsorbed Cytochrome c}, ISBN={9781461595366 9781461595342}, url={http://dx.doi.org/10.1007/978-1-4615-9534-2_4}, DOI={10.1007/978-1-4615-9534-2_4}, booktitle={Redox Chemistry and Interfacial Behavior of Biological Molecules}, publisher={Springer US}, author={Willit, James L. and Bowden, Edmond F.}, year={1988}, pages={63–76} }
 @article{senaratne_bowden_1988, title={The electrode reaction of Euglenagracilis cytochrome c-552 at edge-oriented pyrolytic graphite}, volume={157}, ISSN={0006-291X}, url={http://dx.doi.org/10.1016/s0006-291x(88)80976-8}, DOI={10.1016/s0006-291x(88)80976-8}, abstractNote={The direct electron transfer reaction of Euglena gracilis cytochrome c-552 at edge-oriented pyrolytic graphite electrodes was determined by cyclic voltammetry to be quasi-reversible, stable and reproducible. The presence of a persistent layer of irreversibly adsorbed cytochrome c-552 on the electrode surface was detected in these experiments. Heterogeneous electron transfer rate constants for both the diffusing and adsorbed forms of the protein are reported, and mechanistic aspects are addressed. The applicability of cytochrome c-552 as a complementarily charged analog of eucaryotic cytochrome c in interfacial bioelectrochemical studies is discussed.}, number={3}, journal={Biochemical and Biophysical Research Communications}, publisher={Elsevier BV}, author={Senaratne, Vinitha and Bowden, Edmond F.}, year={1988}, month={Dec}, pages={1021–1026} }
 @article{bowden_dautartas_evans_1987, title={Chemical and mechanical properties of redox polymer-modified electrodes}, volume={219}, ISSN={0022-0728}, url={http://dx.doi.org/10.1016/0022-0728(87)85031-3}, DOI={10.1016/0022-0728(87)85031-3}, abstractNote={A model is developed to describe the coupling of the mechanical and electrochemical thermodynamics of redox polymer film conversion for systems in which there is a net change in the charge per redox site associated with this redox conversion. The electrostatically forced intrusion of compensating charge, in the form of ions of the supporting electrolyte, into the polymer film is predicted to result in non-Nernstian behavior because of the finite void volume within the film and the finite molar volume of the charge-compensating ion. The physical consequences of this phenomenon are the forced swelling of the polymer film, a process which in the presence of crosslinks (either covalent or ionic) requires energy input in excess of that needed to carry out the simple electron transfer to/from the redox sites. This energy is consumed in doing work against the elastic framework of the crosslinked polymer matrix, and when couched in terms of an elastic deformation, may be considered reversible in the thermodynamic sense. The model developed here treats only the simplest of such mechanical coupling in that reversible, isotropic stress-strain is proposed to account for the non-Nernstian thermodynamics of these redox polymer films.}, number={1-2}, journal={Journal of Electroanalytical Chemistry and Interfacial Electrochemistry}, publisher={Elsevier BV}, author={Bowden, E.F. and Dautartas, M.F. and Evans, J.F.}, year={1987}, month={Mar}, pages={49–69} }
 @article{dautartas_bowden_evans_1987, title={Chemical and mechanical properties of redox polymer-modified electrodes}, volume={219}, ISSN={0022-0728}, url={http://dx.doi.org/10.1016/0022-0728(87)85032-5}, DOI={10.1016/0022-0728(87)85032-5}, abstractNote={The thermodynamics of thin films (< 200 nm) of plasma-polymerized vinylferrocene (PPVF) deposited on various substrates have been examined in aqueous and non-aqueous electrolytes by controlled potential coulometry. The Nerst plots (E vs log[cFc+/cFc0]) of these data give slopes in the range of 120–150 mV/decade. Scanning electron microscopy of thicker films (> 400 nm) shows that significant physical damage can occur during electrolysis. These and related observations suggest that the super-Nersntian behavior may be related to stress induced by the forced incorporation of the anion of the supporting electrolyte, as is required to maintain electroneutrality within the films. A mechanical/electrochemical model is employed to explain the origin of the excess free energy required to convert ferrocene sites to ferrocenium sites within the PPVF films.}, number={1-2}, journal={Journal of Electroanalytical Chemistry and Interfacial Electrochemistry}, publisher={Elsevier BV}, author={Dautartas, M.F. and Bowden, E.F. and Evans, J.F.}, year={1987}, month={Mar}, pages={71–89} }
 @article{bowden_dautartas_evans_1987, title={Chemical and mechanical properties of redox polymer-modified electrodes}, volume={219}, ISSN={0022-0728}, url={http://dx.doi.org/10.1016/0022-0728(87)85033-7}, DOI={10.1016/0022-0728(87)85033-7}, abstractNote={The redox thermodynamics of thin films (< 200 nm) of linear polyvinylferrocene (LPVF) deposited by spincoating on polished electrode substrates have been studied in tetra-n-butylammonium perchlorate + acetonitrile solutions. Three distinct regions of thermodynamic behavior were revealed through analysis of Nernst plots (E vs. log(cFc+/cFc0)) constructed from controlled potential coulometric data. For films which were 0–3% oxidized, super-Nernstian slopes with values dependent upon electrolyte concentration were attributed to Donnan equilibrium contributions to the electrode potential. This form of LPVF thus appears to function as a simple anion exchanger. Further oxidation (up to ca. 50%) is accompanied by a transition to a second thermodynamic region characterized by sub-Nernstian behavior which is interpreted in terms of an increasing association of ferrocenium/perchlorate ion pairs into dimers or higher order aggregates. Oxidation above 50% results in an abrupt return to super-Nernstian behavior, for which a mechanical/electrochemical model is proposed. In this third region, the LPVF film is envisioned to be a homogeneous network structure characterized by a high concentration of ionic crosslinks and a capability for sustaining electrochemically induced stress arising from the forced accommodation of neutralizing counterions. The transitions from one thermodynamic region to another are consistent with increasing film ion content as oxidation proceeds. The complexity in thermodynamic redox behavior of LPVF results from the substantial potential-dependent changes in film ion concentration (0 to 6 M) along with a relatively high degree of structural freedom due to the lack of covalent crosslinks.}, number={1-2}, journal={Journal of Electroanalytical Chemistry and Interfacial Electrochemistry}, publisher={Elsevier BV}, author={Bowden, E.F. and Dautartas, M.F. and Evans, J.F.}, year={1987}, month={Mar}, pages={91–115} }
 @article{willit_bowden_1987, title={Determination of unimolecular electron transfer rate constants for strongly adsorbed cytochrome c on tin oxide electrodes}, volume={221}, ISSN={0022-0728}, url={http://dx.doi.org/10.1016/0022-0728(87)80264-4}, DOI={10.1016/0022-0728(87)80264-4}, number={1-2}, journal={Journal of Electroanalytical Chemistry and Interfacial Electrochemistry}, publisher={Elsevier BV}, author={Willit, James L. and Bowden, Edmond F.}, year={1987}, month={Apr}, pages={265–274} }
 @article{moore_clausen_bowden_birzgalis_1987, title={In vivo measurement of tubular fluid ferrocyanide with carbon-fiber microelectrodes}, volume={252}, ISSN={1931-857X 1522-1466}, url={http://dx.doi.org/10.1152/ajprenal.1987.252.6.f1158}, DOI={10.1152/ajprenal.1987.252.6.f1158}, abstractNote={Techniques to construct carbon-fiber microelectrodes and to measure ferrocyanide ion concentration in single nephrons are described. The measurement involves polarizing an inert carbon-fiber microelectrode 500 mV positive with respect to a Ag-AgCl reference, while measuring the faradic current produced by the oxidation of ferrocyanide. A carbon fiber (5-7 micron diam) is heat sealed into a glass micropipette that is then sharpened, silanized, and electrochemically pretreated to minimize electrode degradation by protein. Circuit diagrams for an inexpensive voltage clamp-current monitor and a data sampling device are presented. The electrodes show a linear response to changes in ferrocyanide concentration in large and very small (20 nl) volumes in vitro. The electrodes were used in an electrochemical microassay to determine tubular fluid-to-plasma ferrocyanide concentration ratios and nephron filtration rates with proximal micropuncture samples. The results show excellent agreement with paired determinations using [3H]inulin. In vivo proximal tubule perfusion experiments show a rapid linear response to changes in tubular fluid ferrocyanide concentration. These electrodes permit rapid quantitative measurements of ferrocyanide concentration and water transport in the proximal tubule and may be useful in other biological systems.}, number={6}, journal={American Journal of Physiology-Renal Physiology}, publisher={American Physiological Society}, author={Moore, L. C. and Clausen, C. and Bowden, E. F. and Birzgalis, A.}, year={1987}, month={Jun}, pages={F1158–F1166} }
 @article{assefa_bowden_1986, title={Electron transfer reaction of cytochrome c peroxidase at tin oxide electrodes}, volume={139}, ISSN={0006-291X}, url={http://dx.doi.org/10.1016/s0006-291x(86)80277-7}, DOI={10.1016/s0006-291x(86)80277-7}, abstractNote={The unmediated one-electron reduction and reoxidation of ferric cytochrome c peroxidase at fluoride-doped tin oxide electrodes is reported. A long range interfacial electron transfer distance of 17 A is postulated by analogy to the Poulos/Kraut model for the cytochrome c peroxidase/cytochrome c electron transfer complex. The utility of the interfacial electrochemical approach for investigating cytochrome c peroxidase electron transfer behavior is discussed.}, number={3}, journal={Biochemical and Biophysical Research Communications}, publisher={Elsevier BV}, author={Assefa, Hanna and Bowden, Edmond F.}, year={1986}, month={Sep}, pages={1003–1008} }
 @inbook{bowden_hawkridge_blount_1985, title={Electrochemical Aspects of Bioenergetics}, ISBN={9781461294443 9781461323594}, url={http://dx.doi.org/10.1007/978-1-4613-2359-4_5}, DOI={10.1007/978-1-4613-2359-4_5}, booktitle={Comprehensive Treatise of Electrochemistry}, publisher={Springer US}, author={Bowden, Edmond F. and Hawkridge, Fred M. and Blount, Henry N.}, year={1985}, pages={297–346} }
 @article{bowden_hawkridge_blount_1984, title={Interfacial electrochemistry of cytochrome c at tin oxide, indium oxide, gold, and platinum electrodes}, volume={161}, ISSN={0022-0728}, url={http://dx.doi.org/10.1016/s0022-0728(84)80193-x}, DOI={10.1016/s0022-0728(84)80193-x}, abstractNote={Abstract Cyclic voltammetry has been used to study the heterogeneous electron transfer kinetics of horse heart cytochrome c in pH 7 tris/cacodylate media at several electrode surfaces. Reversible voltammetric responses (formal heterogeneous electron transfer rate constant>10−2 cm/s) were observed at bare gold electrodes and at tin-doped indium oxide semiconductor electrodes for certain experimental conditions. Quasireversible voltammetric responses were more typically observed at fluorine-doped tin oxide semiconductor electrodes, bare platinum electrodes, and at the indium oxide electrodes. Reaction rates at bare metal electrodes were strongly dependent on pretreatment procedures and experimental protocol. Reaction rates at metal oxide electrodes were strongly dependent on solution conditions, pretreatment procedures, and on the hydration state of the electrode surface. A general mechanistic scheme involving both interfacial electrostatic and chemical interactions is proposed for cytochrome c electrode reactions. The asymmetric distribution of surface charges on cytochrome c appears to play a dominant role in controlling electron transfer rates by its interaction with the electric field at the electrode surface. Electron transfer distances are also considered, and it is concluded that electron transfer between an electrode surface and the exposed heme edge of properly oriented cytochrome c molecules involves maximum distances of ca. 0.6–0.9 nm.}, number={2}, journal={Journal of Electroanalytical Chemistry and Interfacial Electrochemistry}, publisher={Elsevier BV}, author={Bowden, Edmond F. and Hawkridge, Fred M. and Blount, Henry N.}, year={1984}, month={Feb}, pages={355–376} }
 @article{bowden_cohen_hawkridge_1982, title={Anaerobic thin-layer electrochemical cell for planar optically transparent electrodes}, volume={54}, ISSN={0003-2700 1520-6882}, url={http://dx.doi.org/10.1021/ac00243a040}, DOI={10.1021/ac00243a040}, abstractNote={ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAnaerobic thin-layer electrochemical cell for planar optically transparent electrodesEdmond F. Bowden, David J. Cohen, and Fred M. HawkridgeCite this: Anal. Chem. 1982, 54, 6, 1005–1008Publication Date (Print):May 1, 1982Publication History Published online1 May 2002Published inissue 1 May 1982https://doi.org/10.1021/ac00243a040RIGHTS & PERMISSIONSArticle Views105Altmetric-Citations16LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (552 KB) Get e-Alerts Get e-Alerts}, number={6}, journal={Analytical Chemistry}, publisher={American Chemical Society (ACS)}, author={Bowden, Edmond F. and Cohen, David J. and Hawkridge, Fred M.}, year={1982}, month={May}, pages={1005–1008} }
 @article{bowden_hawkridge_chlebowski_bancroft_thorpe_blount_1982, title={Cyclic voltammetry and derivative cyclic voltabsorptometry of purified horse heart cytochrome c at tin-doped indium oxide optically transparent electrodes}, volume={104}, ISSN={0002-7863}, url={http://dx.doi.org/10.1021/ja00390a041}, DOI={10.1021/ja00390a041}, abstractNote={ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTCyclic voltammetry and derivative cyclic voltabsorptometry of purified horse heart cytochrome c at tin-doped indium oxide optically transparent electrodesEdmond F. Bowden, Fred M. Hawkridge, Jan F. Chlebowski, Eric E. Bancroft, Colin Thorpe, and Henry N. BlountCite this: J. Am. Chem. Soc. 1982, 104, 26, 7641–7644Publication Date (Print):December 1, 1982Publication History Published online1 May 2002Published inissue 1 December 1982https://doi.org/10.1021/ja00390a041RIGHTS & PERMISSIONSArticle Views1016Altmetric-Citations135LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (523 KB) Get e-Alerts Get e-Alerts}, number={26}, journal={Journal of the American Chemical Society}, publisher={American Chemical Society (ACS)}, author={Bowden, Edmond F. and Hawkridge, Fred M. and Chlebowski, Jan F. and Bancroft, Eric E. and Thorpe, Colin and Blount, Henry N.}, year={1982}, month={Dec}, pages={7641–7644} }
 @inbook{bowden_hawkridge_blount_1982, place={Washington, DC}, series={Advances in Chemistry}, title={The Heterogeneous Electron Transfer Properties of Cytochrome c}, ISBN={0841206619 0841223831}, ISSN={0065-2393}, url={http://dx.doi.org/10.1021/ba-1982-0201.ch007}, DOI={10.1021/ba-1982-0201.ch007}, abstractNote={The heterogeneous electron transfer kinetic parameters of horse heart cytochrome c were evaluated at pH 7.0. This work was directed at determining the formal heterogeneous electron transfer rate constant, k°′s,h, and the electrochemical transfer coefficient, α, at three different electrode surfaces: gold electrodes electrochemically modified with methyl viologen, fluoride-doped tin oxide optically transparent electrodes (OTEs), and tin-doped indium oxide OTEs. Kinetic parameters of cytochrome c were evaluated using samples in the totally oxidized and in the totally reduced forms. Kinetic effects arising from anion binding to cytochrome c were investigated for phosphate and chloride in the presence of the nonbinding buffer tris(hydroxymethyl)aminomethane-cacodylic acid. The kinetic parameters were determined using single potential step chronoabsorptometry at all three electrodes and using rotating disk electrode voltammetry at the methyl viologen-modified gold disk electrode.}, booktitle={Electrochemical and Spectrochemical Studies of Biological Redox Components}, publisher={American Chemical Society}, author={Bowden, Edmond F. and Hawkridge, Fred M. and Blount, Henry N.}, editor={Kadish, Karl M.Editor}, year={1982}, month={Jun}, pages={159–171}, collection={Advances in Chemistry} }
 @article{bowden_hawkridge_1981, title={Thin-layer spectroelectrochemical kinetic study of viologen cation radicals reacting at hydrogen-evolving gold and nickel electrodes}, volume={125}, ISSN={0022-0728}, url={http://dx.doi.org/10.1016/S0022-0728(81)80355-5}, DOI={10.1016/0368-1874(81)87175-4}, number={2}, journal={Journal of Electroanalytical Chemistry and Interfacial Electrochemistry}, publisher={Elsevier BV}, author={Bowden, Edmond F. and Hawkridge, Fred M.}, year={1981}, month={Aug}, pages={367–386} }
 @article{bowden_hawkridge_blount_1980, title={Heterogeneous electron transfer kinetics of sperm whale myoglobin}, volume={116}, ISSN={0022-0728}, url={http://dx.doi.org/10.1016/s0022-0728(80)80269-5}, DOI={10.1016/s0022-0728(80)80269-5}, abstractNote={Very little information has been reported describing the heterogeneous electron transfer kinetics of biological molecules at electrodes. We report here the first application of a recently developed spectro-electrochemical technique to the measurement of the heterogeneous electron transfer kinetics of a biological molecule, sperm whale myoglobin, at a methyl viologen modified gold minigrid electrode. The overpotential dependence of the heterogeneous electron transfer rate constant for the reduction of myoglobin at this surface gives rise to values of the formal heterogeneous electron transfer rate constant [ko′f,h=3.88 (±0.07)×10−11 cm/s] and the transfer coefficient [α=0.88 (±0.01)] for this electrocatalyzed process. The importance of studying the heterogeneous electron transfer kinetics of biological molecules lies in the fact that many physiological electron transfer reactions occur heterogeneously. Though myoglobin does not function in this manner physiologically, our initial study has been directed at this molecule owing to its stability and ready availability. It is expected that this technique will be applied to other optically transparent electrodes and other biological molecules thereby providing new insights into understanding biological redox reactions.}, journal={Journal of Electroanalytical Chemistry and Interfacial Electrochemistry}, publisher={Elsevier BV}, author={Bowden, Edmond F. and Hawkridge, Fred M. and Blount, H.N.}, year={1980}, month={Jan}, pages={447–457} }