The Experts below are selected from a list of 127494 Experts worldwide ranked by ideXlab platform
Michael J. Hageman - One of the best experts on this subject based on the ideXlab platform.
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Estimation of Recombinant Bovine Somatotropin Solubility by Excluded-Volume Interaction with Polyethylene Glycols
Pharmaceutical Research, 1995Co-Authors: Cynthia L. Stevenson, Michael J. HagemanAbstract:Purpose . The potential to estimate protein solubilities, with limited protein, by excluded-Volume Interactions was evaluated using polyethylene glycols (PEG) and recombinant bovine Somatotropin (rbSt). Methods . Solutions of rbSt were prepared at concentrations significantly below saturation solubility. Subsequently, varying amounts of PEG were added to force protein precipitation. Following centrifugation, the protein concentration in the supernatant was assayed by reversed-phase HPLC, where a logarithmic relationship between solubility and % PEG was observed. Results . An apparent protein solubility in the absence of PEG was determined by extrapolation and compared well with values measured by conventional approaches. Slopes of log solubility versus % PEG curves were consistent with excluded-Volume principles and depended on the molecular weight of the PEG used. Furthermore, the precipitation process proved to be reversible, allowing for recovery of intact protein. Solubility-pH profiles obtained in the presence of PEG greatly reduced the quantities of protein needed and compared favorably with profiles in the absence of PEG. Conclusions . Thus, it appears feasible and practical, with certain limitations, to obtain solubility estimates of proteins by Volume-exclusion methods with limited supplies of protein.
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Estimation of recombinant bovine somatotropin solubility by excluded-Volume Interaction with polyethylene glycols.
Pharmaceutical research, 1995Co-Authors: Stevenson Cynthia L, Michael J. HagemanAbstract:Purpose. The potential to estimate protein solubilities, with limited protein, by excluded-Volume Interactions was evaluated using polyethylene glycols (PEG) and recombinant bovine Somatotropin (rbSt).
Jeff Z. Y. Chen - One of the best experts on this subject based on the ideXlab platform.
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Tennis-ball state of a self-avoiding wormlike polymer on a spherical surface
EPL (Europhysics Letters), 2011Co-Authors: Wu-yang Zhang, Jeff Z. Y. ChenAbstract:Using Monte Carlo simulations of a wormlike chain that contains the excluded-Volume Interaction, we demonstrate that a directionally anisotropic state exists at high surface coverage, when the chain is confined to a spherical surface. The isotropic-anisotropic transition has first-order characteristics and can be compared with the isotropic-nematic transition observed in lyotropic polymer systems, both driven by the excluded-Volume Interaction. Unlike a nematic state, the anisotropic state observed here displays the so-called tennis-ball conformation, coupling the polymer-segment orientation preference with positional order.
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Surface-Induced Liquid Crystal Transitions of Wormlike Polymers Confined in a Narrow Slit. A Mean-Field Theory
Macromolecules, 2007Co-Authors: Jeff Z. Y. Chen, D. E. Sullivan, Xiangqun YuanAbstract:On the basis of a mean-field treatment of semiflexible polymer chains, we analyze the structure of long wormlike polymers sterically confined between two parallel, structureless walls separated by a distance W. With the Onsager excluded-Volume Interaction between polymer segments, the system displays three phases, uniaxial, biaxial, and condensed, depending on the polymer density and W. We have also determined the induced attractive force acting on the walls, mediated by the Onsager excluded-Volume Interaction between polymer segments.
Stevenson Cynthia L - One of the best experts on this subject based on the ideXlab platform.
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Estimation of recombinant bovine somatotropin solubility by excluded-Volume Interaction with polyethylene glycols.
Pharmaceutical research, 1995Co-Authors: Stevenson Cynthia L, Michael J. HagemanAbstract:Purpose. The potential to estimate protein solubilities, with limited protein, by excluded-Volume Interactions was evaluated using polyethylene glycols (PEG) and recombinant bovine Somatotropin (rbSt).
Cynthia L. Stevenson - One of the best experts on this subject based on the ideXlab platform.
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Estimation of Recombinant Bovine Somatotropin Solubility by Excluded-Volume Interaction with Polyethylene Glycols
Pharmaceutical Research, 1995Co-Authors: Cynthia L. Stevenson, Michael J. HagemanAbstract:Purpose . The potential to estimate protein solubilities, with limited protein, by excluded-Volume Interactions was evaluated using polyethylene glycols (PEG) and recombinant bovine Somatotropin (rbSt). Methods . Solutions of rbSt were prepared at concentrations significantly below saturation solubility. Subsequently, varying amounts of PEG were added to force protein precipitation. Following centrifugation, the protein concentration in the supernatant was assayed by reversed-phase HPLC, where a logarithmic relationship between solubility and % PEG was observed. Results . An apparent protein solubility in the absence of PEG was determined by extrapolation and compared well with values measured by conventional approaches. Slopes of log solubility versus % PEG curves were consistent with excluded-Volume principles and depended on the molecular weight of the PEG used. Furthermore, the precipitation process proved to be reversible, allowing for recovery of intact protein. Solubility-pH profiles obtained in the presence of PEG greatly reduced the quantities of protein needed and compared favorably with profiles in the absence of PEG. Conclusions . Thus, it appears feasible and practical, with certain limitations, to obtain solubility estimates of proteins by Volume-exclusion methods with limited supplies of protein.
Hiroshi Takano - One of the best experts on this subject based on the ideXlab platform.
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Relaxation and Self‐Diffusion of a Polymer Chain in a Melt
AIP Conference Proceedings, 2004Co-Authors: Katsumi Hagita, Hiroshi TakanoAbstract:Relaxation and self‐diffusion of a polymer chain in a melt are discussed on the basis of the results of our recent Monte Carlo simulations of the bond fluctuation model, where only the excluded Volume Interaction is considered. Polymer chains are located on an L × L × L simple cubic lattice under periodic boundary conditions. Each chain consists of N segments, each of which occupies 2 × 2 × 2 unit cells. The results for N = 32, 48, 64, 96, 128, 192, 256, 384 and 512 at the Volume fraction φ ≃ 0.5 are examined, where L = 128 for N ⩽ 256 and L = 192 for N ⩾ 384. The longest relaxation time τ is estimated by solving generalized eigenvalue problems for the equilibrium time correlation matrices of the positions of segments of a polymer chain. The self‐diffusion constant D is estimated from the mean square displacements of the center of mass of a single polymer chain at the times larger than τ. From the data for N = 256, 384 and 512, the apparent exponents x r and xd, which describe the power law dependences of...
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Self-Diffusion of a Polymer Chain in a Melt
Journal of the Physical Society of Japan, 2003Co-Authors: Katsumi Hagita, Hiroshi TakanoAbstract:Self-diffusion of a polymer chain in a melt is studied by Monte Carlo simulations using the bond fluctuation model, where only the excluded Volume Interaction is taken into account. Polymer chains, each of which consists of N segments, are located on an L × L × L simple cubic lattice under periodic boundary conditions, where each segment occupies 2 ×2 ×2 unit cells. The results for N =32, 48, 64, 96, 128, 192, 256, 384 and 512 at the Volume fraction φ≃0.5 are reported, where L = 128 for N ≤256 and L =192 for N ≥384. The N -dependence of the self-diffusion constant D is examined. Here, D is estimated from the mean square displacements of the center of mass of a single polymer chain at times longer than the longest relaxation time. From the data for N = 256, 384 and 512, the apparent exponent x d , which describes the apparent power law dependence of D on N as D ∝ N - x d , is estimated to be x d ≃2.4. The ratio D τ/ seems to be a constant for N = 192, 256, 384 and 512, where τ and denot...
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Relaxation Mode Analysis of a Single Polymer Chain in a Melt
Journal of the Physical Society of Japan, 2002Co-Authors: Katsumi Hagita, Hiroshi TakanoAbstract:Relaxation modes and rates of a polymer chain in a melt are studied by Monte Carlo simulations of the bond fluctuation model, where only the excluded Volume Interaction is taken into account. Polymer chains, each of which consists of N segments, are located on an L × L × L simple cubic lattice under periodic boundary conditions, where each segment occupies 2 ×2 ×2 unit cells. The results for N =32, 48, 64, 96, 128, 192, 256, 384 and 512 at the Volume fraction φ≃0.5 are reported, where L = 128 for N ≤256 and L =192 for N ≥384. The relaxation modes and rates are estimated by solving generalized eigenvalue problems for the equilibrium time correlation matrices \( C_{i,j} (t) = \frac{1}{3} \langle \bar{\mbi{R}}_{i} (t) \cdot \bar{\mbi{R}}_{j} (0) \rangle\) of the coarse-grained relative positions \bar R i of segments of a polymer chain defined by \(\bar{\mbi{R}}_{i} = \frac{1}{n} \sum_{k=1}^{n} \mbi{R}_{(i-1)n+k}\), where R k denotes the position of the k th segment relative to the center of mass of the polym...
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Relaxation of a Polymer Chain Confined in a Tube
Journal of the Physical Society of Japan, 1999Co-Authors: Katsumi Hagita, Hiroshi TakanoAbstract:Relaxation modes and rates of a single polymer chain confined in a straight tube by repulsive walls are studied by Monte Carlo simulations of the bond fluctuation model, where only the excluded Volume Interaction is taken into account. The relaxation modes and rates are estimated by solving generalized eigenvalue problems for the equilibrium time correlation matrices C ∥ i , j ( t ) = c and \(C^{\perp}_{i,j}(t) = \frac{1}{2}\langle \mib{r}_{i}^{\perp} (t) \cdot \mib{r}_{j}^{\perp} (0) \rangle_{\rm c}\), where z i and r i ⊥ are the components of the position vector of the i th segment parallel and perpendicular to the tube axis, respectively, and z c is the parallel component of the center of mass of the polymer chain. For the parallel component, the behavior of the p th slowest relaxation rate λ ∥ p of a polymer chain of N segments agrees with the scaling prediction λ ∥ p ≃λ b ( g p / N ) 2 for g p / N ≪1, where λ b and g are the slowest relaxation rate wit...
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Molecular Dynamics Study of Relaxation Modes of a Single Polymer Chain
Journal of the Physical Society of Japan, 1997Co-Authors: Hidetomo Hirao, Sachiko Koseki, Hiroshi TakanoAbstract:Relaxation modes and rates of a single polymer chain with the excluded Volume Interaction is studied by molecular dynamics simulations. The variational method for the estimation of the relaxation modes and rates proposed by Takano and Miyashita [J. Phys. Soc. Jpn. 64 (1995) 3688] is generalized to cases where the detailed balance condition is not satisfied and applied to the results of the present simulations. The relaxation modes and rates estimated by the generalized method describe the behaviors of the autocorrelation functions of relative velocities and relative positions of the segments well. For a polymer chain with N segments, the behavior of the p th slowest relaxation rate λ p with p / N ≪1 is consistent with the theoretical prediction λ p ∝( p / N ) 2ν+ 1 , where ν is the exponent for the size of a polymer chain in good solvent.
