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Polymer Size (polymer + size)
Selected AbstractsTransamination by Polymeric Enzyme MimicsHELVETICA CHIMICA ACTA, Issue 11 2003Wenjun Zhou Pyridoxamine was linked to a series of polyethylenimines (PEIs) with Mn=600, 1800, 10,000, and 60,000, both simply permethylated and with additional attached dodecyl chains. They were examined in the transamination of pyruvic acid and of phenylpyruvic acid, and showed MichaelisMenten behavior. The values of k2 and of KM determined showed only small variations with polymer size. Thus, the previously reported strong advantage of pyridoxamines attached to the Mn=60,000 PEI, relative to simple pyridoxamine alone, is seen to almost the same extent with the smaller PEIs. [source] Diffusion of semi-flexible polyelectrolyte through nanochannelsAICHE JOURNAL, Issue 7 2010Hongyan Gu Abstract The diffusion of sodium polystyrene sulfonate through polycarbonate nanochanels was studied in salt-free dilute aqueous solution. A stronger molecular weight dependence of diffusion was observed compared to free diffusion in dilute solution. Scaling exponentials relating polymer size to diffusivity were between Flory's theory (Deff , N,0.6) and Rouse's model (Deff , N,1), revealing a crossover regime from 3-D diffusion to 1-D diffusion. Diffusion was less hindered for the polyelectrolyte (Deff/D0), than for a rigid sphere, when the polymer/channel size ratio exceeded 0.2. This is attributed to elongated chains with reduced frictional hindrance. Simulation of the confined diffusion based on an elongated cigar model gave D , N,1 while the experimental results agree with D , N,0.94. For charged polyelectrolytes, the transition to 1-D diffusion therefore begins before the polymer radius of gyration exceeds the channel size contrary to model assumptions. We attribute this to the charged nature of the polyelectrolytes causing extended chain conformations. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Effect of polymer size and cosolutes on phase separation of poly(vinylpyrrolidone) (PVP) and dextran in frozen solutionsJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 4 2005Ken-ichi Izutsu Abstract The aim of this study was to elucidate the effect of the molecular weight of polymers on their miscibility in frozen solutions to model the physical properties of freeze-dried pharmaceutical formulations. Thermal analysis of frozen solutions containing poly(vinylpyrrolidone) (PVP) and dextran of various molecular weights was performed at polymer concentrations below the binodal curve at room temperature. Frozen solutions containing PVP 29,000 and dextran 10,200 showed two thermal transitions (glass transition temperature of maximally freeze-concentrated solution: Tg,) representing two freeze-concentrated amorphous phases, each containing predominantly one of the polymers. A combination of smaller polymers (PVP 10,000 and dextran 1,060) was freeze-concentrated into an amorphous mixture phase across a wide range of concentration ratios. Combinations of intermediate size polymers separated into two freeze-concentrated phases only at certain concentration ratios. Addition of NaCl prevented the phase separation of PVP and dextran in the aqueous and frozen solutions. Higher concentrations of NaCl were required to retain the miscibility of larger polymer combinations in the freeze-concentrate. The molecular weights of the component polymers, polymer concentration ratio, and cosolute composition are the important factors that determine component miscibility in frozen solutions. © 2004 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:709,717, 2005 [source] Functional water-soluble polymers: polymer,metal ion removal and biocide propertiesPOLYMER INTERNATIONAL, Issue 10 2009Bernabé L Rivas Abstract Water-soluble polymers have attracted much interest due to their potential applications in environmental protection engineering to remove harmful pollutants and in biomedicine in the areas of tissue engineering, within-body implants or other medical devices, artificial organ prostheses, ophthalmology, dentistry, bone repair, and so on. In this review, particular emphasis is given to the ability of water-soluble polymers with amine, amide, carboxylic acid, hydroxyl and sulfonic acid functional groups to remove metal ions by means of the liquid-phase polymer-based retention (LPR) technique that combines the use of water-soluble polymers and ultrafiltration membranes. The second part is dedicated to showing the potential application of functional water-soluble polymers and their polymer,metal complexes as biocides for various bacteria. These polymers and polymer,metal complexes show an efficient bactericide activity, especially to Gram-negative bacteria, Staphylococcus aureus reaching concentrations lower than 4 µg mL,1. This activity depends on polymer size, type of metal ion, contact time and concentration of polymer and metal ion. The discussion reveals that in the case of the LPR process the efficiency of metal ion removal depends strongly on the type of polymer functional group and the feed pH value. In general, two mechanisms of ion entrapment are suggested: complex formation and electrostatic interaction. In the case of the medical use of water-soluble polymers and their complexes with metal ions, the review documents the unique bactericide properties of the investigated species. The polymer-metal ion complexes show a reduced genotoxic activity compared with free metal ions. Copyright © 2009 Society of Chemical Industry [source] | ||||||||||