Wayne F. Reed

Polyelectrolytes from polysaccharides: selective oxidation of guar gum- a revisited reaction

The aim of this work was to study the properties of the carboxylated polyelectrolyte obtained from guar gum. The C-6 alcohol functions of galactose units side chains were oxidized first by GO-ase to aldehyde groups and then to carboxylic groups by halogen oxidation. The enzymic oxidation step was followed by the Dische method, by viscosity and light scattering measurements. With regard to previous reports, some changes were introduced in the two-step reaction, in order to prevent polymer degradation. Several characteristics of the carboxylated polyelectrolyte have been studied, such as molecular weight distribution, degree of substitution, viscosity, intrinsic viscosity determined by the isoionic method, radius of gyration, charge parameter and apparent intrinsic persistence length. The charged macromolecule formed from native guar showed all the typical characteristics of a polyelectrolyte. The viscometry results indicate that carboxylated guar has a much higher viscosity in low salt content than the native polymer, which improves its thickening properties.

Temperature and ionic strength dependent light scattering of DMPG dispersions

The temperature dependence of the intensity of light scattered by aqueous dispersions of the anionic lipid DMPG (dimyristoyl phosphatidylglycerol) was studied at different ionic strengths. The lipid main transition, gel-liquid crystal, is clearly detected by a sharp decrease in light scattering. As expected, the temperature of the main transition (Tm) was found to increase with the increase of the ionic strength. For low ionic strength, a DMPG second temperature transition, termed the ‘post-transition’, can be monitored by both an increase in light scattering and a decrease in conductivity. Zimm plot analysis indicates that below Tm the liposomes tend to aggregate, and show a negative second virial coefficient A2, and particles of large molecular weight. At the main phase transition, parallel to the decrease in light scattering, there is an increase in the sample conductivity, A2 becomes positive and the particle molecular weight decreases, indicating that the vesicles become disaggregated. Moreover, at the post-transition (Tpost) A2 becomes very small, perhaps slightly negative, and the molecular weight increases again. Both the main and the post transitions were found to be reversible. In contrast to the main transition, the post-transition could not be detected by spin labels placed either at the membrane surface, or in the bilayer core. While the mechanism of increased ionization at Tm could be related to the melting of the hydrocarbon chains, the mechanism for the possible counterions recondensation at Tpost is far less clear.

Polyelectrolyte properties of proteoglycan monomers

Light scattering measurements were made on proteoglycan monomers (PGM) over a wide range of ionic strengths Cs, and proteoglycan concentrations [PG]. At low Cs there were clear peaks in the angular scattering intensity curve I(q), which moved towards higher scattering wave numbers q, as [PG]1/3. This differs from the square root dependence of scattering peaks found by neutron scattering from more concentrated polyelectrolyte solutions. The peaks remained roughly fixed as Cs increased, but diminished in height, and superposed I(q) curves yielded a sort of isosbestic point. Under certain assumptions the static structure factor S(q) could be extracted from the measured I(q), and was found to retain a peak. A simple hypothesis concerning coexisting disordered and liquidlike correlated states is presented, which qualitatively accounts for the most salient features of the peaks. There was evidence of a double component scattering autocorrelation decay at low Cs, which, when resolved into two apparent diffusion ...

Monte Carlo study of titration of linear polyelectrolytes

An off‐lattice Metropolis Monte Carlo algorithm with reptation is used to find the average fractional ionization ᾱ as a function of pH for a generic ionizable linear polyelectrolyte in a salt solution. The polyelectrolyte is treated as a threefold rotational isomeric state model polymer; each unit can bear a negative charge or not with intrinsic ionization constant pKa. Debye–Huckel screening is assumed between the charges. For computational convenience, the dielectric constant of the polymer is taken to be that of the solvent. The number of units N was either 50 or 100. Monte Carlo results were collected for various Debye screening lengths at six combinations of number of chain units N, bond angle θ, and Manning parameter when fully charged, ξ0. For four of the combinations, ξ0 was 1 to take partial account of counterion condensation. These runs had N and θ of 50 and 1°, 50 and 70°, 100 and 1°, and 100 and 70°. The fifth combination had N=50, θ=70°, and ξ0=2.85. The sixth had N=50, θ=27.34°, and ξ0=0.72,...

Monte Carlo electrostatic persistence lengths compared with experiment and theory

An off‐lattice rotational isomeric state model Monte Carlo algorithm for a polyelectrolyte with Debye–Hueckel screening and no hard core repulsion is used to generate short (up to 150 unit) chains at (1) different ionic strengths, (2) varying uniform charge densities, and (3) pH–pK0 governed ionization. The mean square radii of gyration are related to the apparent total persistence lengths of the polyelectrolytes via the wormlike chain model. Near the random coil limit the apparent electrostatic persistence length varies approximately as the inverse square root of the ionic strength and linearly with charge density. The persistence length behavior is very similar in cases (2) and (3). These approximate power laws agree well with those found experimentally for hyaluronate and variably ionized polyacrylic acid. The original electrostatic persistence length theory, which does not contain excluded volume effects, predicts power law exponents which are twice these. Corrections due to polyelectrolyte excluded v...

Polymerized surfactant vesicles: kinetics and mechanism of photopolymerization

Formation of vesicles, prepared from styrene-containing surfactants [ H 2 C = C H C 6 H 4 N H C 0 2 (CH2)lo] [C,6H,,]N+[CH3]2,Br(1) and [n-C1SH~IC02(CH2)2]2N+[CH,] [ 2C6H4CH=CH2],C1(2), has been verified by static and dynamic light scattering and electron microscopy. Hydrodynamic diameters, DH, of vesicles 1 and 2 decreased with increasing sonication times to plateau values of 2100 and 1450 A. Vesicles prepared from 1 proved to be unstable on standing for a few hours, whereas those made from 2 remained stable for weeks. Weight-averaged molecular weights of vesicles prepared from 2 were determined to be 1.0 X lo* g/mol. Irradiation of 2 in ethanol or in vesicular form by a 450-W Xe lamp or by 15-11s bursts of 266-nm laser pulses a t an energy of 0.1-2.0 mJ/pulse led to the disappearance of styrene absorbances. Rates of monomer disappearances were considerably slower in ethanol than in vesicles. Polymerization rates for vesicular 2 were found to be independent of vesicle concentration but depended linearly on the applied laser energy. Conversely, rates in ethanol depended on the concentration of monomeric 2. Transient absorption spectra for 2 in ethanol and in vesicles, determined by laser flash photolysis, indicated the formation of styrene triplets (300 nm in E t O H and 320 nm in vesicles) and ground-state depletion at 250 nm. The time dependence of ground-state depletion was related to radical formation and propagation. Free-radical lifetimes and propagation times were assessed to be 17 ms h 37% and 1 ms & 62%, respectively. Time-resolved fluorescence anisotropies indicated a much faster rotation of 2 in ethanol (0.3 ns) than in vesicles (0.97 ns). Upon polymerization the styrene groups in vesicles lost all rotational mobility. These experimental data for vesicle photopolymerization have been accounted for in terms of a model which considers intravesicular surface reactions. In addition to correctly describing vesicle polymerization behavior, the model also provides an experimentally measurable quantity which relates average polymer chain length (determined to be 20 f 30% monomers/chain) to the quantum efficiency of free-radical formation and other easily obtainable parameters.

Automated batch characterization of polymer solutions by static light scattering and viscometry

Using a programmable mixing pump, light scattering flow chamber, refrac- tive index detector, and single capillary viscometer, the batch (unfractionated) charac- terization of polymers in solution has been automated. Three different schemes to produce polymer concentration gradients were used, and values for weight average mass Mw, root mean square radius of gyration ^S 2 & 1/ 2 , second virial coefficient A2, and intrinsic viscosity (h) were determined for a broad distribution sample of poly(vinyl pyrrolidone) (PVP) and a narrow fraction of poly(ethylene oxide) (PEO). High concen- tration experiments on the PVP also allowed determination of the third virial coefficient A3. The method has several advantages over traditional manual methods in terms of accuracy, sample preparation, and amount of labor required.

Light scattering power of randomly cut random coils with application to the determination of depolymerization rates

The scattering of light by a dilute monodisperse population of random‐coil molecules is approximately described by the well‐known function P(θ)=(2/u2)(e−u+u−1), where u=R2gq2, Rg is the radius of gyration of the random coils, and q=(4πn/λ)sin(θ/2) is the magnitude of the scattering vector. We show that if the molecules in this population undergo random scission, then P(θ) is still given by the above formula where, however, u is now equal to R2goq2+r, where r is the average number of scissions per molecule in the originally monodisperse population and Rgo is the original radius of gyration. It is suggested that this could be useful for determining depolymerization rate constants, and for investigating whether various forms of scission are actually random. Results from initial experiments which apply the theory to the acid hydrolysis of hyaluronic acid are presented. The rate constants found are in reasonable agreement with values in the literature.

Cleft Formation upon Polymerization of Surfactant Vesicles

Vesikel aus (I) besitzen einen hydrodynamischcn Radius von 425 A (Laserstreuung) und ein mittleres Molekulargewicht von 2.3- 107, die sich durch Photopolymerisation nicht andern.

Monte Carlo test of electrostatic persistence length for short polymers

A Metropolis Monte Carlo program with reptation is used to generate sample configurations of short electrically charged polymers with thermally distributed Debye–Huckel electrostatic energies. The polymer is a three fold rotational isomeric state model with bond angle θ between 5° and 90° and number of units N between 10 and 225. To compare the resulting root‐mean‐square (rms) values for radius of gyration S, and end‐to‐end length R, to theory, we use a wormlike chain with contour length L equal to the stretched out length of the polymer, the same total charge, and an intrinsic persistence length set so that, for large N, for specified θ and L, S agrees with the rotational isomeric state model. The results are compared with the predictions for S, with correction for finite L, of Odijk [J. Polymer Sci., Polymer Phys. Ed. 15, 477 (1977)]. They are then compared with three attempted corrections for excluded volume: (1) Odijk and Houwaart [J. Polymer Sci., Polymer Phys. Ed. 16, 627 (1978)]; (2) correction (1)...