Michel Mandel

The influence of chain-flexibility on the colligative properties of polyelectrolyte solutions

The neglect of chain flexibility in Mannings theory of polyelectrolytes is assessed. For a flexible polyelectrolyte-the uniformly charged wormlike chain-counterion condensation is unaffected but colligative properties need to be modified. The relevant dimensionless parameter is (κLT)-1 where κ-1 is the Debye-Huckel radius and LT is the sum of the bare and electrostatic persistence lengths.

In situ breakage of turnip yellow mosaic virus RNA and in situ aggregation of the fragments. Analysis of successive stages

Abstract In situ breakage of TYMV-RNA was investigated by treating TYMV at various pH values and ionic strengths for various periods of time. It was concluded that: (1) The number of chain breaks increased with the pH and with the time of treatment; (2) the breakage phenomenon was not an all or none process; (3) the RNA fragments formed aggregates in situ , the average sedimentation rate of which decreased with increasing pH values; (4) kinetic analysis of the in situ breakage process revealed three successive stages: (a) an initial one in which the sedimentation of the RNA fragments decreased progressively; (b) a second stage in which aggregation of the fragments led to a reversal of this decrease and aggregates of increasing sedimentation rate appeared; (c) a final stage, characterized by a disintegration of the RNA aggregates; (5) the rate of aggregation depended on the pH, the ionic strength, and the history of the virus. The possible mechanisms underlying the successive in situ processes are discussed.

Influence of some factors affecting the stationary value of the electric birefringence of aqueous solutions of poly(styrene sulphonates) in the presence of 0.01 mol dm–3 NaCl

The stationary values of the electric birefringence obtained by applying rectangular pulses to aqueous Na-poly(styrene sulphonates)–0.01 mol dm–3 NaCl solutions have been studied for five different samples of polyelectrolytes ranging from Mw= 1.8 × 105 to 12 × 105 g mol–1. The corresponding Kerr constants determined at low electric field strengths were not linearly dependent on the polyelectrolyte concentration in the concentration region explored, which covered both the the dilute and semi dilute regimes. The specific Kerr constant at infinite dilution increased with molar mass to the power 0.7. In the semi-dilute regime a scaling law was found of the form (K/K*)∼(C/C*)0.8, where K* is the Kerr constant in the dilute concentration regime extrapolated to the critical concentration C*. This concentration and molar mass dependence cannot yet be fully understood in terms of proposed theories. The study of the field strength dependence of the electric birefringence indicates that smaller parts of the chain contribute to the orientation mechanism responsible for the induced macroscopic anisotropy. It is likely that progressive deformation of the more or less flexible chains by high electric fields also plays a role.

Thermal stability of turnip yellow mosaic virus RNA: effect of pH and multivalent cations on RNA deaggregation and degradation

Light scattering studies of RNA isolated from turnip yellow mosaic virus (TYMV) revealed a molar mass of 1.9.10(6) g mol-1, which is close to the value of 2.0.10(6) g mol-1 published for intact genomic TYMV RNA (2M RNA). However, gel electrophoresis under denaturing conditions demonstrated that only 30-40% of this native RNA was 2M RNA. Sucrose gradient centrifugation revealed the occurrence of a series of smaller RNA size classes, the mass ratios of which were greatly influenced by the pH of the solution and the presence of EDTA. These results suggest that native TYMV RNA preparations originally contain a mixture of intact RNA particles and of aggregates of RNA fragments with the same molar mass of about 2.10(6) g mol-1, and that the size classes are intermediates in the deaggregation process of the degraded genomic TYMV RNA. The native RNA displayed pH-dependent deaggregation and degradation. The degradation process of 2M RNA followed (pseudo) first-order kinetics. Lower degradation rates were observed for RNA depleted of divalent cations and polyamines. For depleted 2M RNA an enthalpy of activation of about 100 kJ mol-1 and an almost zero entropy of activation was calculated. Similar values were also found for depleted E. coli ribosomal RNAs and depleted MS2 RNA, demonstrating that all RNAs are equally vulnerable to degradation. In the presence of multivalent cations the activation enthalpy for 2M TYMV RNA degradation increased to 150 kJ mol-1 and the entropy of activation to 150 J K-1 mol-1, indicative for a different degradation mechanism.

The electric polarizability and the Kerr constant of a Gaussian charged polyelectrolyte chain in solution

Abstract With help of a very simple model an expression is derived for the electrical polarizability arising from the perturbation by an electric field of the distribution of counterions for a Gaussian charged macromolecule in solution. With this electric polarizability a corresponding Kerr constant is found for the same kind of chain, neglecting contributions of permanent dipole moments and atomic polarizabilities. Whereas the electric polarizability thus derived is proportional to the square of the molar mass M of the chain, the Kerr constant increases linearly with M.

Some remarks on the dynamics of charged macromolecules in solution

With reference to experimental results obtained by dynamic light scattering and electric birefringence decay it is shown that, for aqueous solutions of a highly charged macromolecule with a relative flexible backbone, in the presence of an excess low molar mass salt monovalent cations and anions, the dynamics of the charged macromolecules in the absence of an external force are comparable to what is expected and found for conventional but uncharged macromolecules in good solvents. It is concluded that under these conditions it may be assumed that the charged macromolecules move, in a first approximation, in a continuum constituted by both the solvent and the low molar mass salt, and that the coupling between the motions of polyions and small ions is weak. A calculation based on a simple model, in which the fundamental asymmetry between polyions and small ions is explicitly taken into account, however, leads to the conclusion that such a coupling may in principle be expected although it is not excluded that it is rather weak. The calculation also justifies the experimentally found linear concentration dependence of the macromolecular cooperative diffusion coefficient in dilute solutions and the decrease of the corresponding slope with increasing salt concentration.

Aggregation in solutions of poly-gamma-benzyl-L-glutamate monitored by static and dynamic light scattering

Abstract We have studied dilute and semidilute solutions of poly(γ-benzyl- l -glutamate) in 1,2-dichloroethane by static and dynamic light scattering. The aggregational behaviour of the semiflexible polymer is evidenced in both static and dynamic scattering, and is sensitive to the temperature and the polypeptide molecular weight. In particular, both the reciprocal specific scattering intensity and the effective decay rate of the dynamic correlations exhibit a minimum as a function of the concentration. The slope of effective diffusion coefficient versus the square of the scattering vector displays an anomalous maximum as a function of the concentration which can also be attributed to aggregation. The experimental evidence is compatible with head-to-tail dimerization of the polymer as the concentration increases.

On The Interpenetration Effect Of Two Homogeneous Polymers Differing In Molecular Weight In a Good Solvent

A study of the osmotic second virial coefficient A of mixtures of two chemically identical polymers differing in molecular weight in a good solvent has been performed. We have measured A as a function of the relative composition of the dissolved polymers for ten different combinations with molecular weight ratios varying from 1.8 to about 100. The experimental results were compared to the predictions of more than ten different theories. None of them can satisfyingly describe the behaviour of A in the whole region of molecular weight ratios. Our results show that when the two polymers have about the same size they behave like quasi-hard spheres and in the other limit of large size differences an interpenetration of the smaller molecule into the larger one is probable.