TY - JOUR TI - Phase equilibrium for the hydrogenation of polystyrene in CO2–swollen solvents AU - Xu, Dawei AU - Carbonell, Ruben G. AU - Roberts, George W. AU - Kiserow, Douglas J. T2 - The Journal of Supercritical Fluids AB - Polystyrene (PS) can be hydrogenated using a heterogeneous catalyst suspended in a solvent swollen by supercritical carbon dioxide (scCO2). Various phase equilibria are involved in this system. First, the application of scCO2 to a solution of PS can cause the polymer to precipitate. Therefore, the effect of CO2 pressure and temperature on the phase behavior of various solvents containing dissolved PS was investigated, leading to the selection of decahydronaphthalene (DHN) for in-depth study. It was found that the CO2 pressure required to precipitate PS from DHN increased with the temperature. The volume of solutions containing various concentrations of PS in DHN increased considerably as the CO2 pressure was increased. Volume expansions of 35–40% were obtained between 40 and 150 °C and between 3 and 9 wt.% PS. Moreover, calculations using the Peng–Robinson equation of state showed that the H2 concentration in the liquid phase was higher in CO2–swollen DHN than in the pure solvent, at a constant H2 partial pressure. The rate constant for PS hydrogenation was found to be higher in CO2–swollen DHN than in the pure solvent. DA - 2005/5// PY - 2005/5// DO - 10.1016/j.supflu.2004.09.004 VL - 34 IS - 1 SP - 1-9 J2 - The Journal of Supercritical Fluids LA - en OP - SN - 0896-8446 UR - http://dx.doi.org/10.1016/j.supflu.2004.09.004 DB - Crossref KW - hydrogenation KW - polystyrene KW - supercritical carbon dioxide KW - phase equilibrium KW - Peng-Robinson ER - TY - JOUR TI - Small Peptide Ligands for Affinity Separations of Biological Molecules AU - Wang, Guangquan AU - Salm, Jeffrey R. AU - Gurgel, Patrick V. AU - Carbonell, Ruben G. T2 - CHEMICAL ENGINEERING TRENDS AND DEVELOPMENTS AB - This chapter contains sections titled: Downstream Processing in Biopharmaceutical Production Affinity Chromatography Advantages of Small Peptide Ligands Combinatorial Peptide Libraries Screening of One-Bead-One-Peptide Libraries Characterization of Peptide Ligands Future Challenges and Opportunities References DA - 2005/// PY - 2005/// DO - 10.1002/0470025018.ch3 SP - 63-83 ER - TY - JOUR TI - Structural mechanism of oxidative regulation of the phosphatase Cdc25B via an intramolecular disulfide bond AU - Buhrman, G AU - Parker, B AU - Sohn, J AU - Rudolph, J AU - Mattos, C T2 - BIOCHEMISTRY AB - Cdc25B phosphatase, an important regulator of the cell cycle, forms an intramolecular disulfide bond in response to oxidation leading to reversible inactivation of phosphatase activity. We have obtained a crystallographic time course revealing the structural rearrangements that occur in the P-loop as the enzyme goes from its apo state, through the sulfenic (Cys-SO(-)) intermediate, to the stable disulfide. We have also obtained the structures of the irreversibly oxidized sulfinic (Cys-SO(2)(-)) and sulfonic (Cys-SO(3)(-)) Cdc25B. The active site P-loop is found in three conformations. In the apoenzyme, the P-loop is in the active conformation. In the sulfenic intermediate, the P-loop partially obstructs the active site cysteine, poised to undergo the conformational changes that accompany disulfide bond formation. In the disulfide form, the P-loop is closed over the active site cysteine, resulting in an enzyme that is unable to bind substrate. The structural changes that occur in the sulfenic intermediate of Cdc25B are distinctly different from those seen in protein tyrosine phosphatase 1B where a five-membered sulfenyl amide ring is generated as the stable end product. This work elucidates the mechanism by which chemistry and structure are coupled in the regulation of Cdc25B by reactive oxygen species. DA - 2005/4/12/ PY - 2005/4/12/ DO - 10.1021/bi047449f VL - 44 IS - 14 SP - 5307-5316 SN - 0006-2960 ER - TY - JOUR TI - Nonequilibrium model for sorption and swelling of bulk glassy polymer films with Supercritical carbon dioxide AU - Carla, V AU - Wang, K AU - Hussain, Y AU - Efimenko, K AU - Genzer, J AU - Grant, C AU - Sarti, GC AU - Carbonell, RG AU - Doghieri, F T2 - MACROMOLECULES AB - A new procedure is introduced for the calculation of solubility isotherms of plasticizing agents in glassy polymer matrices with particular application to the case of absorption of supercritical gases in bulk glassy polymer films. The model presented is an extension of the nonequilibrium thermodynamics for glassy polymers (NET-GP) approach, modified to allow for the calculation of the effects of pressure, temperature, and gas concentration on the glass transition. Mass sorption and one-dimensional swelling behavior are analyzed for the carbon dioxide (CO2)−poly(methyl methacrylate) (PMMA) system at high pressure. A quantitative comparison is presented between the model performance and experimental data measured using quartz crystal microbalance (QCM) and high-pressure ellipsometry (HPE). DA - 2005/11/29/ PY - 2005/11/29/ DO - 10.1021/ma0506684 VL - 38 IS - 24 SP - 10299-10313 SN - 1520-5835 ER - TY - JOUR TI - Density-induced phase separation in poly(ethylene-co-1-butene)-dimethyl ether solutions AU - Li, D AU - McHugh, MA AU - Zanten, JH T2 - MACROMOLECULES AB - Dynamic light scattering measurements are reported for poly(ethylene-co-20.2 mol % 1-butene) (PEB10) in dimethyl ether (DME) at 110−170 °C and pressures to 2500 bar. The cloud-point curve for the PEB10−DME system exhibits both low- and high-pressure upper consolute solution temperature (UCST) branches. The polymer infinite dilution translational diffusion coefficient, D0, increases with increasing temperature and decreasing pressure as expected. The observed variation of D0 is inversely proportional to the solvent viscosity, indicating that the polymer coil hydrodynamic size is independent of temperature and pressure. The dynamic second virial coefficient, kD, which represents a balance between thermodynamic interactions and hydrodynamic forces, displays values that lie within the bounds expected for ϑ and good solvent conditions. While the low-pressure UCST is classical in that the polymer−solvent interactions become unfavorable upon approach to this phase boundary, the high-pressure UCST branch exhibits anomalous behavior wherein polymer−solvent interactions improve as this phase boundary is approached. Such behavior suggests that the phase separation is entropic in origin and is driven by unfavorable mixing effects. DA - 2005/4/5/ PY - 2005/4/5/ DO - 10.1021/ma048166y VL - 38 IS - 7 SP - 2837-2843 SN - 1520-5835 ER - TY - JOUR TI - Observation of polymer chain contraction near the overlap concentration AU - DiNoia, TP AU - Park, IH AU - McHugh, MA AU - Zanten, JH T2 - MACROMOLECULES AB - Department of Chemical Engineering, Johns HopkinsUniversity, Baltimore, Maryland 21218; Department ofPolymer Science & Engineering, Kumoh National Universityof Technology, Kyungbuk, Korea; Department of ChemicalEngineering, Virginia Commonwealth University,Richmond, Virginia 23284; and Department of Chemicaland Biomolecular Engineering, North Carolina StateUniversity, Raleigh, North Carolina 27695-7905Received June 9, 2005Revised Manuscript Received August 2, 2005 DA - 2005/11/1/ PY - 2005/11/1/ DO - 10.1021/ma051216u VL - 38 IS - 22 SP - 9393-9395 SN - 1520-5835 ER - TY - JOUR TI - Characterization of microcellular biodegradable polymeric foams produced from supercritical carbon dioxide solutions AU - Cotugno, S AU - Di Maio, E AU - Mensitieri, G AU - Iannace, S AU - Roberts, GW AU - Carbonell, RG AU - Hopfenberg, HB T2 - INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH AB - The formation of foams of biodegradable poly(ε-caprolactone) (PCL) from CO2 solutions in molten PCL was investigated. This study included characterization of the CO2 diffusion and equilibrium solubility in molten PCL in contact with supercritical CO2 (scCO2). Experiments were performed at 70, 80, and 90 °C at CO2 pressures up to 25 MPa. The effective mutual diffusivity of CO2 in molten PCL was measured as a function of the CO2 pressure. The data revealed a dramatic increase in apparent effective diffusivity at elevated pressure, likely related to the formation of fluid bubbles, phase-separated from the previously homogeneous, molten PCL solution of CO2. Microcellular PCL foams were produced by starting from an equilibrium CO2−PCL solution at 70 °C over a wide range of initial pressures (from 6.9 to 32 MPa) by quenching down to foaming temperatures (from 24 to 30 °C) followed by rapid depressurization to atmospheric pressure. Foam structures were characterized by scanning electron microscopy, and cell sizes and density were determined quantitatively. The various foam structures were analyzed and interpreted in connection with the independently measured kinetics and equilibrium of CO2 sorption in PCL by considering the effects of starting pressure and foaming temperature on bubble nucleation and growth. DA - 2005/3/16/ PY - 2005/3/16/ DO - 10.1021/ie049445c VL - 44 IS - 6 SP - 1795-1803 SN - 0888-5885 ER - TY - JOUR TI - Hydrogenation of polystyrene in CO2-expanded solvents: Catalyst poisoning AU - Xu, DW AU - Carbonell, RG AU - Kiserow, DJ AU - Roberts, GW T2 - INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH AB - Organic solvents expanded with supercritical carbon dioxide can be excellent media for hydrogenation reactions. However, catalyst poisoning by CO formed via the reverse water-gas-shift reaction occurs during many hydrogenations in the presence of CO2. In this research, the hydrogenation of polystyrene in CO2-expanded decahydronaphthalene was studied in a batch reactor using two hydrogenation catalysts, 5%Pd/BaSO4 and 65%Ni/Al2O3/SiO2. The 5%Pd/BaSO4 catalyst deactivated at 150 °C and CO2 pressures of 250−2250 psig (1.8−15.6 MPa). Approximately 50 ppm CO was present in the CO2-rich light phase after about 10 h at 150 °C, 750 psig H2 pressure, and 2250 psig CO2 pressure. A model that incorporates CO poisoning was developed to describe deactivation of the Pd/BaSO4 catalyst. The 65%Ni/Al2O3/SiO2 catalyst was more active for ring hydrogenation than 5%Pd/BaSO4, and very little CO was formed in the presence of CO2. The Ni catalyst deactivated in the presence of CO2 at 180 °C, possibly due to H2O formed in a methanation reaction. DA - 2005/8/3/ PY - 2005/8/3/ DO - 10.1021/ie040243q VL - 44 IS - 16 SP - 6164-6170 SN - 0888-5885 ER - TY - JOUR TI - Effect of food matrix and cell growth on PCR-based detection of Escherichia coli O157 : H7 in ground beef AU - Taylor, TM AU - Elhanafi, D AU - Drake, M AU - Jaykus, LA T2 - JOURNAL OF FOOD PROTECTION AB - The purpose of this work was (i) to investigate the feasibility of a previously reported upstream processing method for PCR template preparation to facilitate the detection of Escherichia coli O157:H7 from ground beef and (ii) to assess the impact of cell growth (no growth in the matrix versus growth in the matrix) on molecular detection limits. Two food matrices (autoclaved and raw ground beef) were evaluated in all studies. For no-growth experiments, 10-g meat samples were inoculated with 10(2) to 10(7) CFU/g E. coli O157:H7 and then homogenized. The homogenates were processed to remove large particulates and inhibitors using a two-phase upstream processing method consisting of two sequential centrifugation steps, the second of which used titanous hydroxide to facilitate bacterial immobilization. After upstream processing, sample concentrates were extracted for DNA isolation and amplified by PCR. For growth experiments, 10-g meat samples were inoculated at 1 CFU of E. coli O157:H7 per gram, allowed to grow to 10(2) to 10(7) CFU/g, and then processed for PCR assay. Cell recoveries after upstream processing ranged from 15.9 to 77.6% and were not facilitated by the use of titanous hydroxide, as compared with a saline control (P > 0.05). Bacterial cell recovery and PCR detection limits were similar when comparing autoclaved ground beef and raw ground beef, but cell recoveries were highly variable for raw ground beef samples in which E. coli O157:H7 cells were allowed to grow before processing for detection. Overall, PCR detection limits approximated 10(3) CFU/g of ground beef for all treatments. These results indicate that use of model food systems may not always provide an accurate replication of real-world conditions when evaluating PCR detection limits. DA - 2005/2// PY - 2005/2// DO - 10.4315/0362-028X-68.2.225 VL - 68 IS - 2 SP - 225-232 SN - 1944-9097 ER - TY - JOUR TI - A simple method for the direct detection of Salmonella and Escherichia coli O157 : H7 from raw alfalfa sprouts and spent irrigation water using PCR AU - Johnston, LM AU - Elhanafi, D AU - Drake, M AU - Jaykus, LA T2 - JOURNAL OF FOOD PROTECTION AB - The U.S. Food and Drug Administration recognizes that raw seed sprouts are an important cause of foodborne disease and is now recommending that either spent irrigation water or final product be screened for Salmonella and Escherichia coli O157:H7 as a means of assuring the safety of product intended for consumption. In an effort to streamline such testing efforts, a simple method to preconcentrate pathogens from sprouts and spent irrigation water was investigated to facilitate the direct (without prior cultural enrichment) detection of pathogens using the PCR technique. Alfalfa sprouts and spent irrigation water were seeded with Salmonella enterica serovar Typhimurium and E. coli O157:H7 at 10(-1) to 106 CFU/g or CFU/ml, respectively. Samples were blended (sprouts only) and then centrifuged at high speed to sediment the total bacterial population. The precipitate was processed for DNA isolation, PCR amplification, and amplicon confirmation by Southern hybridization. Mean pathogen recoveries after centrifugation ranged from 96 to 99% for both pathogens in both matrices. Using primers targeting the invA gene for Salmonella Typhimurium and the stx genes of E. coli O157:H7, it was possible to detect both pathogens in alfalfa sprouts at seeding concentrations as low as 10 CFU/g. PCR detection limits for both pathogens from spent irrigation water were 10(-1) CFU/ml, the equivalent of 100 CFU/liter of water. Because spent irrigation water is constitutionally simple, it is particularly well suited for bacterial concentration by simple centrifugation steps. In this study, progress was made toward development of a rapid, inexpensive, and sensitive method for the detection of sprout-associated pathogens that is relevant to current industrial practices and needs. DA - 2005/11// PY - 2005/11// DO - 10.4315/0362-028X-68.11.2256 VL - 68 IS - 11 SP - 2256-2263 SN - 1944-9097 ER - TY - JOUR TI - Hexamer peptide affinity resins that bind the Fc region of human immunoglobulin G AU - Yang, H AU - Gurgel, PV AU - Carbonell, RG T2 - JOURNAL OF PEPTIDE RESEARCH AB - Abstract: A family of linear hexapeptides composed of histidine on the N‐terminus followed by aromatic amino acid(s) and positively charged amino acid(s) has been identified through a three‐step screening of a synthetic solid phase library. These peptides were able to recognize human immunoglobulin G (HIgG) through its Fc region, and their selectivity to Fc is comparable to Protein A. This is the first known report of short peptides that are able to bind HIgG by recognizing its Fc portion. One of the ligands from the identified family, HWRGWV, was examined for its ability to isolate HIgG from complex mixtures. It was found that HWRGWV possessed the potential to purify HIgG from complete mammalian cell culture medium containing 10% fetal calf serum with purity comparable to commercially available resins, but using milder elution conditions. HWRGWV bound all HIgG subclasses and IgGs from bovine, mouse, goat, and rabbit. The broad affinity spectrum as well as its Fc recognition ability may be useful in capturing and detecting both polyclonal and monoclonal antibodies. DA - 2005/12// PY - 2005/12// DO - 10.1111/j.1747-0285.2006.00342.x VL - 66 SP - 120-137 SN - 1397-002X KW - affinity chromatography KW - Fc fragment KW - hexapeptide KW - immunoglobulin ER - TY - JOUR TI - Chemical functionalization of silica and alumina particles for dispersion in carbon dioxide AU - Visintin, PM AU - Carbonell, RG AU - Schauer, CK AU - DeSimone, JM T2 - LANGMUIR AB - The steric stabilization and flocculation of modified silica and alumina particle suspensions in condensed CO2 were studied. Silica particles (average diameters of 7 and 12 nm) were functionalized using chlorosilanes of the form CnF2n+1CH2CH2Si(CH3)2Cl (n = 8, 4, or 1) to give CnF2n+1-silica. Alumina particles (diameter of 8−14 nm) were grafted with C8F17CH2CH2Si(OEt)3 and chemically modified with perfluorononanoic acid to yield C8F17-alumina and C8F17COOH-alumina, respectively. Elemental analysis and thermogravimetric analysis on the derivatized particles were carried out, and surface coverage was calculated. The stabilization of these modified particles in condensed CO2 was quantified using turbidimetry. Particle stability was found to increase with increasing fluorinated tail length, temperature, and CO2 density. Unmodified particles and those modified with only −CF3 tails were unstable in condensed CO2. Stabilization in supercritical CO2 is continuous up to 24 h for the CnF2n+1-silica (n ≥ 4) particles and 96 h for the C8F17-alumina particles. The C8F17COOH-alumina particles gave a significantly higher graft density than the C8F17-alumina particles but are not as stable in CO2. The C8F17-alumina particles were stable at lower CO2 densities than the modified silica particles. This stability difference may be attributed to the precursor organosilanes being monofunctional (modified silica) versus trifunctional (modified alumina), producing different structures on the surface. DA - 2005/5/24/ PY - 2005/5/24/ DO - 10.1021/la047823c VL - 21 IS - 11 SP - 4816-4823 SN - 0743-7463 ER - TY - JOUR TI - Characterization of a peptide affinity support that binds selectively to staphylococcal enterotoxin B AU - Wang, GQ AU - Carbonell, RG T2 - JOURNAL OF CHROMATOGRAPHY A AB - The influences of mass transfer and adsorption-desorption kinetics on the binding of staphylococcal enterotoxin B (SEB) to an affinity resin with the peptide ligand, Tyr-Tyr-Trp-Leu-His-His (YYWLHH) have been studied. The bed and particle porosities, the axial dispersion coefficient and the pore diffusivity were measured using pulse experiments under unretained conditions. Adsorption isotherms for SEB on YYWLHH resins with peptide densities in the range from 6 to 220 micromol/g were measured and fitted to a bi-Langmuir equation. At peptide densities below 9 micromol/g and above 50 micromol/g, dissociation constants were lower (2 x 10(-3) to 7 x 10(-3) mol/m3), and binding capacities were larger (43-47 mg SEB/g). In the range from 9 to 50 micromol/g dissociation constants were larger (13 x 10(-3) to 24 x 10(-3) mol/m3) and capacities were lower (33-37 mg SEB/g). These observations are consistent with a transition from single point attachment of the protein to the ligand at low peptide densities to multipoint attachment at high peptide densities. The general rate (GR) model of chromatography was used to fit experimental breakthrough curves under retained conditions to determine the intrinsic rate constants for adsorption, which varied from 0.13 to 0.50 m3 mol(-1) s(-1), and exhibited no clear trend with increasing peptide density. An analysis of the number of transfer units for the various mass transfer steps in the column indicated that film mass transfer, pore diffusion (POR) and the kinetics of adsorption can all play an important role in the overall rate of adsorption, with the intrinsic adsorption step apparently being the rate determining step at peptide densities below 50 micromol/g. DA - 2005/6/17/ PY - 2005/6/17/ DO - 10.1016/j.chroma.2005.05.010 VL - 1078 IS - 1-2 SP - 98-112 SN - 1873-3778 KW - mathematical modeling KW - peptide affinity chromatography KW - peptide density KW - staphylococcal enterotoxin B ER -