@article{roberts_voinov_schmidt_smirnova_sombers_2016, title={The Hydroxyl Radical is a Critical Intermediate in the Voltammetric Detection of Hydrogen Peroxide}, volume={138}, ISSN={0002-7863 1520-5126}, url={http://dx.doi.org/10.1021/JACS.5B13376}, DOI={10.1021/jacs.5b13376}, abstractNote={Cyclic voltammetry is a widely used and powerful tool for sensitively and selectively measuring hydrogen peroxide (H2O2). Herein, voltammetry was combined with electron paramagnetic resonance spectroscopy to identify and define the role of an oxygen-centered radical liberated during the oxidation of H2O2. The spin-trap reagents, 5,5-dimethyl-1-pyrroline N-oxide (DMPO) and 2-ethoxycarbonyl-2-methyl-3,4-dihydro-2H-pyrrole-1-oxide (EMPO), were employed. Spectra exhibit distinct hyperfine patterns that clearly identify the DMPO(•)-OH and EMPO(•)-OH adducts. Multiple linear regression analysis of voltammograms demonstrated that the hydroxyl radical is a principal contributor to the voltammetry of H2O2, as signal is attenuated when this species is trapped. These data incorporate a missing, fundamental element to our knowledge of the mechanisms that underlie H2O2 electrochemistry.}, number={8}, journal={Journal of the American Chemical Society}, publisher={American Chemical Society (ACS)}, author={Roberts, James G. and Voinov, Maxim A. and Schmidt, Andreas C. and Smirnova, Tatyana I. and Sombers, Leslie A.}, year={2016}, month={Feb}, pages={2516–2519} }
 @article{schmidt_dunaway_roberts_mccarty_sombers_2014, title={Multiple Scan Rate Voltammetry for Selective Quantification of Real-Time Enkephalin Dynamics}, volume={86}, ISSN={["1520-6882"]}, DOI={10.1021/ac501725u}, abstractNote={Methionine-enkephalin (M-ENK) and leucine-enkephalin (L-ENK) are small endogenous opioid peptides that have been implicated in a wide variety of complex physiological functions, including nociception, reward processing, and motivation. However, our understanding of the role that these molecules play in modulating specific brain circuits remains limited, largely due to challenges in determining where, when, and how specific neuropeptides are released in tissue. Background-subtracted fast-scan cyclic voltammetry coupled with carbon-fiber microelectrodes has proven to be sensitive and selective for detecting rapidly fluctuating neurochemicals in vivo; however, many challenges exist for applying this approach to the detection of neuropeptides. We have developed and characterized a novel voltammetric waveform for the selective quantification of small tyrosine-containing peptides, such as the ENKs, with rapid temporal (subsecond) and precise spatial (10s of micrometers) resolution. We have established that the main contributor to the electrochemical signal inherent to M-ENK is tyrosine and that conventional waveforms provide poor peak resolution and lead to fouling of the electrode surface. By employing two distinct scan rates in each anodic sweep of this analyte-specific waveform, we have selectively distinguished M-ENK from common endogenous interfering agents, such as ascorbic acid, pH shifts, and even L-ENK. Finally, we have used this approach to simultaneously quantify catecholamine and M-ENK fluctuations in live tissue. This work provides a foundation for real-time measurements of endogenous ENK fluctuations in biological locations, and the underlying concept of using multiple scan rates is adaptable to the voltammetric detection of other tyrosine-containing neuropeptides.}, number={15}, journal={ANALYTICAL CHEMISTRY}, author={Schmidt, Andreas C. and Dunaway, Lars E. and Roberts, James G. and McCarty, Gregory S. and Sombers, Leslie A.}, year={2014}, month={Aug}, pages={7806–7812} }
 @article{barrios_d’antonio_mccombs_zhao_franzen_schmidt_sombers_ghiladi_2014, title={Peroxygenase and Oxidase Activities of Dehaloperoxidase-Hemoglobin from Amphitrite ornata}, volume={136}, ISSN={0002-7863 1520-5126}, url={http://dx.doi.org/10.1021/ja500293c}, DOI={10.1021/ja500293c}, abstractNote={The marine globin dehaloperoxidase‐hemoglobin (DHP) from Amphitrite ornata was found to catalyze the H2O2‐dependent oxidation of monohaloindoles, a previously unreported class of substrate for DHP. Using 5‐Br‐indole as a representative substrate, the major monooxygenated products were found to be 5‐Br‐2‐oxindole and 5‐Br‐3‐oxindolenine. Isotope labeling studies confirmed that the oxygen atom incorporated was derived exclusively from H2O2, indicative of a previously unreported peroxygenase activity for DHP. Peroxygenase activity could be initiated from either the ferric or oxyferrous states with equivalent substrate conversion and product distribution. It was found that 5‐Br‐3‐oxindole, a precursor of the product 5‐Br‐3‐oxindolenine, readily reduced the ferric enzyme to the oxyferrous state, demonstrating an unusual product‐driven reduction of the enzyme. As such, DHP returns to the globin‐active oxyferrous form after peroxygenase activity ceases. Reactivity with 5‐Br‐3‐oxindole in the absence of H2O2 also yielded 5,5’‐Br2‐indigo above the expected reaction stoichiometry under aerobic conditions, and O2‐concentration studies demonstrated dioxygen consumption. Non‐enzymatic and anaerobic controls both confirmed the requirements for DHP and molecular oxygen in the catalytic generation of 5,5’‐Br2‐indigo, and together suggest a novel oxidase activity for DHP.}, number={22}, journal={Journal of the American Chemical Society}, publisher={American Chemical Society (ACS)}, author={Barrios, David A. and D’Antonio, Jennifer and McCombs, Nikolette L. and Zhao, Jing and Franzen, Stefan and Schmidt, Andreas C. and Sombers, Leslie A. and Ghiladi, Reza A.}, year={2014}, month={May}, pages={7914–7925} }
 @article{schmidt_wang_zhu_sombers_2013, title={Carbon Nanotube Yarn Electrodes for Enhanced Detection of Neurotransmitter Dynamics in Live Brain Tissue}, volume={7}, ISSN={["1936-086X"]}, DOI={10.1021/nn402857u}, abstractNote={This work demonstrates the potential of nanoscale carbon electrode materials for improved detection of electroactive neurotransmitter dynamics in the brain. Individual multiwalled carbon nanotubes were synthesized via chemical vapor deposition, spun into yarns, and used in the fabrication of disk microelectrodes that were subsequently characterized using scanning electron and atomic force microscopies. The carbon nanotube yarn electrodes were coupled with fast-scan cyclic voltammetry and used to discriminately detect rapid neurotransmitter fluctuations in acute brain slices. The results demonstrate that the distinct structural and electronic properties of the nanotubes result in improved selectivity, sensitivity, and spatial resolution, as well as faster apparent electron transfer kinetics when compared to the conventional carbon-fiber microelectrodes typically used in vivo.}, number={9}, journal={ACS NANO}, author={Schmidt, Andreas C. and Wang, Xin and Zhu, Yuntian and Sombers, Leslie A.}, year={2013}, month={Sep}, pages={7864–7873} }