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PubMed1977

A field-dissociation relation for polyelectrolytes with an application to field-induced conformational changes of polynucleotides.

An extension to polyelectrolyte solutions of Onsager's field-dissociation relation for weak electrolytes can be derived in a simple way. It is found that, except in the limit of zero ionic strength, a strong applied electric field prevents counterion condensation from proceeding to completion. The extent of incompleteness initially varies linearly with the applied field. The field-dissociation relation can easily be incorporated into the theory of ionic effects on the stability of ordered polynucleotide structures, whereupon a dependence of the stability on field strength emerges. An explicit calculation for a co-operative transition of the DNA melting type is presented, and it is concluded that for sufficiently low ionic strengths, a field of the order of 10 kV/cm may be able to induce melting by lowering the Tm by a few degrees. The threshold effect found experimentally by Pörschke, and particularly the observed linear dependence of the threshold field on the logarithm of the ionic strength, appears here as a simple consequence of the linear increase of the stabilization free energy with the logarithm of ionic strength.

Chemical Phenomena↗
PubMed1978

Electro-optical studies on synthetic polyelectrolytes. IV. Electric polarizability and conformation of poly-N-methyl-2-vinylpyridinium bromide in aqueous solution.

Measurements of the relaxation time on aqueous solutions of the title polyelectrolyte as a function of the concentration and of the molecular weight show that its conformation at very high dilution can be better accounted for by a weakly bending rod or wormlike chain model, with persistence length ranging from 200 to 400 A. The analysis of the field strength dependence of the electric birefringence yields electric polarizability values which increase sharply with the dilution and are not significantly dependent upon the molecular weight. This has been tentatively interpreted on the basis of the theories derived by Oosawa and by Mandel and Van der Touw. The partially flexible model proposed by the latter authors allow to identify the electric polarizability calculated from electro-optical data to the specific dielectric increment measured in the high frequency range; both parameters appear to be molecular weight independent. The electric polarizability obtained from the Kerr effect would be originated in the induced dipoles caused by the delocalization of the bound counterions along rigid subunits whose length seems however to differ from the persistence length.

Birefringence↗
PubMed1978

Limiting laws and counterion condensation in polyelectrolyte solutions. V. Further development of the chemical model.

Counterion binding to polyelectrolyte chains is formulated as a chemical reaction Mz (free) leads to Mz (bound). Expressions for the chemical potentials of free and bound counterions are set equal to obtain the reaction equilibrium. The results are equivalent to those in the previous paper of this series. An additional result obtained here is that a polyion holds its bound counterion layer with a strength on the order of 100 kcal/(mole cooperative unit). The method is then applied to the calculation of the polarizability along the chain due to the bound (condensed) counterions.

Electrolytes↗
PubMed1979

Concentration dependence of equivalent conductivity of polyelectrolyte.

Equivalent conductivity of aqueous solutions of alternating copolymer of iso-butyl vinyl ether and maleic acid, [poly(iso BVE-co-MA)] was studied, especially its polymer-concentration dependence. Various species of counterions such as quaternary ammoniumions (NMe4+, NEt4+, NPr4+, NBu4+) and divalent ions (Ca2+, Sr2+, Ba2+) were employed besides alkali metal ions. The applicability of Manning's conductivity theory was examined for the case of univalent counterions at various degrees of neutralization (beta). A major discrepancy against the theory was observed at beta = 1.0, while a comparatively good agreement was found at beta around 0.5. This suggests that the rod-like polyion model, which is the basis of the theory, is applicable near beta = 0.5, where polyions are most expanded. The low conductivities in the case of quaternary ammonium counterions suggested the ion-binding due to hydrophobic interaction with alkyl side chains. Molecular weight dependence was not appreciably observed near beta = 0.5 similarly to usual polyelectrolytes, but it appeared slightly at beta = 1.0.

Journal Article↗
PubMed1979

Divalent paramagnetic counterions site binding in polyelectrolyte solutions. Analysis of the frequency dependence of the water protons magnetic relaxation and the characteristic parameters of "site binding".

Chemical shift and relaxation time measurements on the water protons in polyelectrolyte solutions containing divalent paramagnetic counterions have shown the existence of three types of counterions: - site bound with loss of water molecules and partial or complete release of the electrostriction in the first hydration sphere, - atmospherically trapped with no change in hydration, - free. The overall stoichiometry of the two former is in agreement with Manning's fraction of condensed counterions. A complete analysis of the frequency dependent contribution of site bound counterions to the water protons relaxation times leads us to interesting conclusions on the modifications of the first hydration shell and on the life time of site binding.

Journal Article↗
PubMed1980

Dielectric behavior of linear polyelectrolytes.

The dipolar correlation function for a system of counterions diffusing on the surface of a polyelectrolyte cylinder is computed. Repulsive coulombic interactions between the counterions are taken into account. Lateral dissociation and reassociation to the cylinder is treated microscopically. Numerical calculations needed to obtain quantitative results for the long time behavior are presented. The model dependence on its parameters is interpreted with special emphasis on parameter values typical of DNA.

Journal Article↗
PubMed1980

The development of an equation for the potentiometric titration of linear polyelectrolytes using a site model.

An equation for the potentiometric titration of linear polyelectrolytes is derived by considering neighbor interactions of ionizable groups and the association equilibria between ionized groups and counterions. The first, second, ... and lth neighbor interactions are directly introduced into the equation, and additional neighbor interactions together with interactions between the ionizable groups and simple salt ions are taken into account as perturbed electrostatic potentials. It is observed that the approximation which includes the second or third neighbor interaction is sufficient for description of the potentiometric titration. Good agreement between predictions of the present theory and experiment is obtained for isotactic and syndiotactic poly(acrylic acids).

Journal Article↗
PubMed1980

New method for simultaneous measurement of frequency spectra of complex dielectric constants of polyelectrolyte solutions.

A high-speed and high-accuracy measurement of relaxational frequency spectra of complex dielectric constants of polyelectrolyte solutions with a high conductivity was realized by a new digital signal processing technique. In this method, a sum of sinusoidal waves of geometrical series of frequencies is utilized as a multifrequency excitation signal and demodulation of the resulting response is carried out simply by addition and subtraction of digital signals in a minicomputer. This new technique is superior to the conventional cross correlation method using the fast Fourier transform in that it greatly reduces the processing time and avoids effectively the influence of a quantization error. The result for a DNA solution obtained by this method is presented to demonstrate the utility of this method.

Journal Article↗
PubMed1980

A conductance stopped-flow study of polyelectrolyte systems. Dynamic conformational change of synthetic macroions and their complexation with neutral polymers.

Two dynamic phenomena of polyelectrolyte systems, namely the rapid conformational changes of weak polyelectiolytes (polyacrylic acid (HPAA) and polyethylenimine, induced by pH-jump) and the complexation of HPAA with polyvinylpyrrolidone are first investigated by means of the conductance stopped-flow (kappa-SF) technique. The pH-induced relaxations observed by mixing an aqueous solution of HPAA or polyethylenimine with water containing a tiny amount of alkali or acid, are safely ascribed to the conformational transition of the macroions between the compact "coil" and the stretched "rod" forms. The relaxation times are large at high degrees of neutralization and for "rod" conformation. Tentative values for the thermodynamic parameters of the dynamic conformational changes are obtained and discussed. The reaction rates of the polymer complex formation and dissociation of HPAA with polyvinylpyrrolidone are also determined using the kappa-SF method. The association constant and the rates of formation and dissociation are 1.84 x 10(3) M(-1), 9.4 x 10(4) M(-1) s(-1) and 51 s(-1) at 10 degrees C, respectively. We then derive the thermodynamic parameters from the above results.

Journal Article↗
PubMed1981

Dielectric behavior of polyelectrolytes II. The cylinder.

The dipolar correlation function for a system of coupterions diffusing on the surface of a polyelectrolyte cylinder is computed. The influence of screened coulombic repulsions on the dielectric increment is determined. Dissociation and reassociation of the counterions to the cylinder is treated microscopically and the coupled bulk diffusion is solved in the presence of the Poisson-Boltzmann potential. It is found that the correlation function contains a small, fast decaying, molecular weight independent part arising from diffusion around the cylinder and a large, slowly decaying, molecular weight dependent part arising from diffusion along the cylinder axis. The dissociation-reassociation kinetics can play a large, possible dominant, role in determining the relaxation rates.

Journal Article↗
PubMed1981

The binding of divalent metal ions to polyelectrolytes in mixed counterion systems. II. Dextransulfate-Mg2+ and dextransulfate-Ca2+ in solutions containing added NaCl or KCl.

Measurements of magnesium and calcium ion activities in solutions of the polyelectrolyte dextransulfate, with added sodium chloride or potassium chloride are presented. A two wavelength dye spectrophotometric method is used. Dextransulfate concentrations Cp (expressed as moles sulfate ion/litre) vary between 0.001 and 0.007, total ionic strengths between 0.005 and 0.08 mole/XXX. Divalent metal ion concentrations are varied between 0 and 1.2 Cp. The results for the metal ion activities are expressed in the form of parameters theta2 = C2/Cp (C(2bp) = bound divalent metal ion concentration) and K2 = theta2/(C2-C2b). For each divalent/univalent counterion pair the values obtained for theta2 and K2 as a function of C2,Cp, and ionic strength are compared to predictions of the "two variable theory" developed for these mixed counterion systems by Manning. This comparison shows that the observed decrease in theta2 with increasing ionic strength at fixed C2 and Cp is generally well predicted by the two variable theory. The extent of divalent ion binding at a given C2, Cp, and ionic strength is largest for the Ca/Na counterion combination, and lowest for the Mg/K combination.

Journal Article↗
PubMed1983

Ion binding or condensation to polyelectrolytes? A detailed comparison, on the example of sodium heparinate.

A modified Poisson-Boltzmann treatment is applied to aqueous solutions of sodium heparinate, in the presence of added salts (NaCl, LiCl, KCl, CaCl2). The results show that 23Na-NMR line widths for the counterions are determined nearly exclusively by Na+ in the immediate vicinity of the linear polyelectrolyte. Hence, two-state treatments, despite their crude character, can reproduce such experimental data rather well.

Journal Article↗
PubMed1983

Dielectric behavior of polyelectrolytes. III. The role of counterion interactions.

The role of the Coulomb forces between the counterions on the surface of polyelectrolytes on the dielectric response is analyzed. An estimate of the maximum dielectric increment (as a function of the number of counterions) is found as a function of the molecular length. The minimum-energy configuration of the counterions on a cylinder is found to be a double helix, suggesting the fundamental importance of electrostatic interactions in determining structure. Solutions of the dynamical equations for a few counterions indicate that a single mode dominates the relaxation which is enhanced by the inter-ion repulsions. A lower bound is found for this mode based on analysis of the system response for short lengths. Sum rules for the rates and amplitudes of the dipolar correlation function are derived and lead to an upper bound for the rate of the dominant mode. These bounds approach one another for the parameters characteristic of restriction fragments of DNA. This permits a prediction of the magnitude and time scale of the dielectric response.

Journal Article↗
PubMed1984

Interactions between ions and polyelectrolytes. A note on determination of ionic activities, with reference to a modified poisson-boltzmann treatment.

We compare the numerous available data on ionic activities, in the presence of polyelectrolytes, with evaluation of these quantities from a modified Poisson-Boltzmann equation in the framework of a cell model. This treatment gives an excellent description of the mean activity for various ions. The activity of counterions is well-predicted, that of co-ions is generally overestimated.

Journal Article↗
PubMed1987

Conductometric analysis of the competition between monovalent and divalent counterions in their interaction with polyelectrolytes.

A procedure is described for the analysis of the conductivity of solutions of anionic polyelectrolytes in which both mono- and divalent counterions are present. The method is based on analysis of the relation between the overall conductivity of the system and the conductivity of the individual monovalent cations which are only electrostatically (non-specifically) bound. The system is described in terms of the two-state approach, implying that the counterions are considered to be either fully bound to the polyion or completely free. The potentialities of the proposed method are explored by studying solutions of alkali polyacrylates with and without added zinc nitrate at several alkali nitrate concentrations. The results give a picture of the composition of the counterionic atmosphere around the polyion in systems with both mono- and divalent counterions present. To a certain degree, the divalent ion Zn(II) was found to be bound quantitatively by the polyion. The composition of the counterionic atmosphere around the polyion was largely independent of alkali nitrate concentration when the latter was present in not too large an excess with respect to both Zn(II) and the charged monomers.

Journal Article↗
PubMed1988

A new model of counterion condensation in polyelectrolyte solutions. III. Theoretical predictions of competitive condensation between counterions of different valences.

Our model has been extended for theoretical estimation of competitive condensation of counterions of different valences onto polyelectrolytes in solution. The estimations are compared with those obtained from Manning theory and with experimental data on counterion activity coefficients. The agreement with the data for sodium polystyrenesulfonate/MgCl2, CaCl2 is satisfactory.

Journal Article↗
PubMed1991

Polyelectrolytic aspects of the titration curve. The semi-flexible model.

An analysis is given of the theoretical approach to the quantitative description of proton dissociation curves for weak polyacids. The basic model of the counterion condensation theory has been used, with the modification reported in the preceding study (S. Paoletti, A. Cesàro, C. Arce Samper and J.C. Benegas, Biophys. Chem. 34 (1989) 301). In this paper we demonstrate the effect of relaxing the hypothesis of a rigid conformation on the polyelectrolytic properties of weak polyacids. As an application of the present approach, a description is given of the titration curves for two weak polyacids, poly(DL-glutamic acid) (PDLGA) and poly(L-aspartic acid) (PLAA).

Journal Article↗
PubMed1991

Polyelectrolytic aspects of the titration curve. pH-induced conformational transition of poly(L-glutamic acid): the semi-flexible model.

The cooperative conformational transition of poly(L-glutamic acid) induced by pH is monitored by the titration curves from literature. The polyelectrolytic approach described in the preceding article (A. Cesàro, S. Paoletti and J.C. Benegas, Biophys. Chem. 39 (1991) 1) is used to fit the experimental curves under various conditions of ionic strength and temperature, with the sole assumption that each polymeric state is characterized by a proper conformational flexibility. The helix-coil transition of the system becomes molecularly defined by the balance between the non-ionic conformational energy and the repulsive electrostatic energy of the two forms. Implications of the results of the theoretical model on the energetics of the cooperative order-disorder transition are discussed.

Journal Article↗