The Experts below are selected from a list of 5172 Experts worldwide ranked by ideXlab platform
Stephen E Harding - One of the best experts on this subject based on the ideXlab platform.
-
Full hydrodynamic reversibility of the weak dimerization of vancomycin and elucidation of its interaction with VanS monomers at clinical concentration
Nature Publishing Group, 2017Co-Authors: Mary K. Phillips-jones, Ryan Lithgo, Vlad Dinu, Richard B. Gillis, John E. Harding, Gary G. Adams, Stephen E HardingAbstract:Abstract The reversibility and strength of the previously established dimerization of the important glycopeptide antibiotic vancomycin in four different aqueous solvents (including a medically-used formulation) have been studied using short-column sedimentation equilibrium in the analytical ultracentrifuge and model-independent SEDFIT-MSTAR analysis across a range of loading concentrations. The change in the weight Average Molar Mass M w with loading concentration was consistent with a monomer-dimer equilibrium. Overlap of data sets of point weight Average Molar Masses M w(r) versus local concentration c(r) for different loading concentrations demonstrated a completely reversible equilibrium process. At the clinical infusion concentration of 5 mg.mL−1 all glycopeptide is dimerized whilst at 19 µg.mL−1 (a clinical target trough serum concentration), vancomycin was mainly monomeric (
-
physical characterisation of the rhamnogalacturonan and homogalacturonan fractions of sugar beet beta vulgaris pectin
Carbohydrate Polymers, 2010Co-Authors: Gordon A Morris, Mariechristine Ralet, Estelle Bonnin, Jean Franois Thibault, Stephen E HardingAbstract:Abstract Acid extracted sugar beet (Beta vulgaris) pectin was subjected to enzymatic hydrolysis using fungal pectin methyl esterase (f-PME) and two endopolygalacturonanases (PGs I and II). From the hydrolysate, the RG-I fraction was separated and purified by chromatographic techniques. This RG-I fraction was shown to be of high weight Average Molar Mass (188,000 g/mol), but low intrinsic viscosity (36 ml/g), which is consistent with a random coil conformation (Lp = 1.4 nm). The HG fraction was prepared by mild acid hydrolysis of acid extracted pectin. The HG fraction was found to have a relatively low weight Average Molar Mass (20,000 g/mol), but a rather high intrinsic viscosity (77 ml/g), which is consistent with the HG fraction being rigid in solution (Lp = 9.8 nm). Lower Molar Mass pectins are richer in HG regions and pectins of higher Molar Mass are richer in RG-I regions. We conclude that the degradation of the HG region has an important impact on intrinsic viscosity, but less on Molar Mass and the inverse is true for the degradation of RG-I region. This has important consequences in terms of the functionality of sugar beet pectin molecules.
-
physical characterisation of the rhamnogalacturonan and homogalacturonan fractions of sugar beet beta vulgaris pectin
Carbohydrate Polymers, 2010Co-Authors: Gordon A Morris, Mariechristine Ralet, Estelle Bonnin, Jean Franois Thibault, Stephen E HardingAbstract:Acid extracted sugar beet (Beta vulgaris) pectin was subjected to enzymatic hydrolysis using fungal pectin methyl esterase (f-PME) and two endopolygalacturonanases (PGs I and II). From the hydrolysate, the RGI fraction was separated and purified by chromatographic techniques. This RG-I fraction was shown to be of high weight Average Molar Mass (188,000 g/mol), but low intrinsic viscosity (36 ml/g), which is consistent with a random coil conformation (Lp = 1.4 nm). The HG fraction was prepared by mild acid hydrolysis of acid extracted pectin. The HG fraction was found to have a relatively low weight Average Molar Mass (20,000 g/mol), but a rather high intrinsic viscosity (77 ml/g), which is consistent with the HG fraction being rigid in solution (Lp = 9.8 nm). Lower Molar Mass pectins are richer in HG regions and pectins of higher Molar Mass are richer in RG-I regions. We conclude that the degradation of the HG region has an important impact on intrinsic viscosity, but less on Molar Mass and the inverse is true for the degradation of RG-I region. This has important consequences in terms of the functionality of sugar beet pectin molecules. © 2010 Elsevier Ltd. All rights reserved.
-
dynamic light scattering as a relative tool for assessing the molecular integrity and stability of monoclonal antibodies
Biotechnology & Genetic Engineering Reviews, 2007Co-Authors: Ulf Nobbmann, Malcolm Trevor Connah, Brendan Fish, Paul Varley, Chris Gee, Sandrine Mulot, Juntao Chen, Liang Zhou, Fei Sheng, Stephen E HardingAbstract:Abbreviations used: AUC: analytical ultracentrifugation, DLS: dynamic light scattering, HPLC: high performance liquid chromatography, PCS: photon correlation spectroscopy, QELS: quasi elastic light scattering, PDI: polydispersity index, kDa: kiloDalton, SLS: static light scattering, M W : weight Average Molar Mass, S: Svedbergs, IgG4: immunoglobulin G subclass 4, Fab: fragment antigen binding, T M : melting point temperature. Biotechnology and Genetic Engineering Reviews Vol. 24, 117-128 (2007)
Gordon A Morris - One of the best experts on this subject based on the ideXlab platform.
-
physical characterisation of the rhamnogalacturonan and homogalacturonan fractions of sugar beet beta vulgaris pectin
Carbohydrate Polymers, 2010Co-Authors: Gordon A Morris, Mariechristine Ralet, Estelle Bonnin, Jean Franois Thibault, Stephen E HardingAbstract:Abstract Acid extracted sugar beet (Beta vulgaris) pectin was subjected to enzymatic hydrolysis using fungal pectin methyl esterase (f-PME) and two endopolygalacturonanases (PGs I and II). From the hydrolysate, the RG-I fraction was separated and purified by chromatographic techniques. This RG-I fraction was shown to be of high weight Average Molar Mass (188,000 g/mol), but low intrinsic viscosity (36 ml/g), which is consistent with a random coil conformation (Lp = 1.4 nm). The HG fraction was prepared by mild acid hydrolysis of acid extracted pectin. The HG fraction was found to have a relatively low weight Average Molar Mass (20,000 g/mol), but a rather high intrinsic viscosity (77 ml/g), which is consistent with the HG fraction being rigid in solution (Lp = 9.8 nm). Lower Molar Mass pectins are richer in HG regions and pectins of higher Molar Mass are richer in RG-I regions. We conclude that the degradation of the HG region has an important impact on intrinsic viscosity, but less on Molar Mass and the inverse is true for the degradation of RG-I region. This has important consequences in terms of the functionality of sugar beet pectin molecules.
-
physical characterisation of the rhamnogalacturonan and homogalacturonan fractions of sugar beet beta vulgaris pectin
Carbohydrate Polymers, 2010Co-Authors: Gordon A Morris, Mariechristine Ralet, Estelle Bonnin, Jean Franois Thibault, Stephen E HardingAbstract:Acid extracted sugar beet (Beta vulgaris) pectin was subjected to enzymatic hydrolysis using fungal pectin methyl esterase (f-PME) and two endopolygalacturonanases (PGs I and II). From the hydrolysate, the RGI fraction was separated and purified by chromatographic techniques. This RG-I fraction was shown to be of high weight Average Molar Mass (188,000 g/mol), but low intrinsic viscosity (36 ml/g), which is consistent with a random coil conformation (Lp = 1.4 nm). The HG fraction was prepared by mild acid hydrolysis of acid extracted pectin. The HG fraction was found to have a relatively low weight Average Molar Mass (20,000 g/mol), but a rather high intrinsic viscosity (77 ml/g), which is consistent with the HG fraction being rigid in solution (Lp = 9.8 nm). Lower Molar Mass pectins are richer in HG regions and pectins of higher Molar Mass are richer in RG-I regions. We conclude that the degradation of the HG region has an important impact on intrinsic viscosity, but less on Molar Mass and the inverse is true for the degradation of RG-I region. This has important consequences in terms of the functionality of sugar beet pectin molecules. © 2010 Elsevier Ltd. All rights reserved.
Bernadette Charleux - One of the best experts on this subject based on the ideXlab platform.
-
comprehensive modeling study of nitroxide mediated controlled living radical copolymerization of methyl methacrylate with a small amount of styrene
Macromolecules, 2009Co-Authors: Julien Nicolas, Krzysztof Matyjaszewski, Laura Mueller, Charlotte Dire, Bernadette CharleuxAbstract:This article presents a comprehensive kinetic study of the SG1 nitroxide-mediated copolymerization of methyl methacrylate with a small percentage of styrene using the PREDICI software. The aim of this study was to confirm the results from a previous publication showing that a living polymerization can be achieved for this system. The PREDICI simulations based on the penultimate unit effect model were also able to give a better insight into the complex mechanism of nitroxide-mediated controlled radical copolymerization. The model showed the copolymerization kinetics and the evolution of the number Average Molar Mass, the fraction of living and dead chains, and the concentration of the four types of alkoxyamines and propagating radicals with monomer conversion. It was applied for different initial percentages of styrene and different initiator concentrations.
-
first nitroxide mediated controlled free radical polymerization of acrylic acid
Macromolecules, 2003Co-Authors: Laurence Couvreur, Catherine Lefay, Bernadette Charleux, Joel Belleney, Olivier Guerret, Stephanie MagnetAbstract:Controlled poly(acrylic acid) homopolymers were synthesized for the first time by direct nitroxide-mediated polymerization of acrylic acid. The polymerizations were performed in 1,4-dioxane solution at 120 °C, using an alkoxyamine initiator based on the N-tert-butyl-N-(1-diethyl phosphono-2,2-dimethyl propyl) nitroxide, SG1. The kinetics were controlled by the addition of free nitroxide at the beginning of the polymerization and the optimal amount was 9 mol % with respect to the initiator. In this case, whatever the initiator concentration, all polymerizations exhibited the same rate and conversion reached 85−90% within 5 h. Although the rate constant of propagation of acrylic acid is very large, its reactivity is moderated by a low activation−deactivation equilibrium constant between active macroradicals and SG1-capped dormant chains. Various alkoxyamine concentrations were investigated to target different Molar Masses. At high initiator concentrations, the number-Average Molar Mass, Mn, increased linear...
-
controlled free radical miniemulsion polymerization of styrene using degenerative transfer
Macromolecules, 1999Co-Authors: Muriel Lansalot, Jean-pierre Vairon, Bernadette Charleux, Celine Farcet, Rosangela PirriAbstract:Controlled free-radical polymerization of styrene was performed in aqueous dispersed medium using a degenerative transfer process with iodine atom exchange. The transfer agent was the commercially available perfluorohexyl iodide. Its efficiency was shown to be low in conventional batch emulsion polymerization since polymer had Molar Mass higher than expected. This was explained by a slow rate of diffusion of the perfluorinated transfer agent through the water phase, from the monomer droplets to the active latex particles. This problem was overcome by using a batch miniemulsion process. In that case, 100% efficiency of the chain transfer agent was reached, and the experimental Molar Masses fit well with the theoretical ones. With that technique, the transfer agent could be directly located in the polymer particles without transportation. Moreover, when using a continuous addition of monomer, a linear increase of the number-Average Molar Mass with conversion was observed.
Fredereic Bonfils - One of the best experts on this subject based on the ideXlab platform.
-
Rapid quantification and characterization of the pyrolytic lignin fraction of bio-oils by size exclusion chromatography coupled with multi-angle laser light scattering detector (SEC-MALS)
Journal of Analytical and Applied Pyrolysis, 2019Co-Authors: Miguel Ruiz, Jérémy Valette, François Broust, Fredereic BonfilsAbstract:Abstract A rapid method was developed to characterize the Pyrolytic Lignin (PL) fraction of flash pyrolysis bio-oils, based on size exclusion chromatography (SEC) coupled to differential refractive index (DRI) and multi-angle laser light scattering (MALS) detectors. Two beech wood bio-oils with different PL content were used in the study. The first was produced with a single-stage condensation system (BO), while the second was an organic fraction collected in the first stage of a two-stage condensation system (F1). PL was isolated from both the BO and F1 bio-oils by the water precipitation method. Our results suggested that quantification of the pyrolytic lignin fraction of bio-oils can be performed by the SEC-MALS-DRI method provided that the specific refractive index increment (dn/dc) is known, and the integration interval is carefully chosen. Average Molar Mass (Mn) values for the BO and F1 samples were 580 ± 50 Da and 890 ± 50 Da, respectively. Our results indicated that the condensation system and the water precipitation method affect the Average Molar Mass of isolated PL oligomers.
Olof Dahlman - One of the best experts on this subject based on the ideXlab platform.
-
characterization of the Molar Masses of hemicelluloses from wood and pulps employing size exclusion chromatography and matrix assisted laser desorption ionization time of flight Mass spectrometry
Biomacromolecules, 2001Co-Authors: Anna Jacobs, Olof DahlmanAbstract:The Molar Mass parameters for arabino-4-O-methylglucuronoxylans, arabinohexenuronoxylans, 4-O-methylglucuronoxylans, hexenuronoxylans, and galactoglucomannans extracted from wood and pulps have been determined. To characterize different types of hemicelluloses, delignified wood (spruce, pine, larch, aspen, and birch) and chemical pulps (unbleached and totally chlorine-free bleached) were extracted with dimethyl sulfoxide (DMSO) or alkaline aqueous solutions. Size exclusion chromatography (SEC) with off-line matrix-assisted laser desorption ionization time-of-flight Mass spectrometry (MALDI-MS) were employed to characterize the Molar Masses. The hemicellulose extracts were separated by SEC into fractions each containing components with a narrow range of Molar Masses and the Average Molar Mass of each fraction subsequently determined by MALDI-MS. The Molar Mass parameters for the hemicelluloses were then calculated on the basis of the SEC distribution curves and MALDI-MS spectra. As expected, in most cases ...
