Conformational transition polyelectrolytes

Extensive data are given in the Uterature for the potentiometric titration of polymer acids which may be used to study the behaviour of polyelectrolyte systems under different conditions. For poly(a-D) galacturonic acid there are few data of this kind, especially in connection with the occurrence of a conformational transition induced by pH variations, or with the effect brought about by the addition or the exchange of counterions. Since for a polyacid not exhibiting a conformational transition in the course of titration, pK K denoting the apparent dissociation constant) increases monotonously with degree... 

Conformational Transitions in Polyelectrolyte Networks Induced by Electric Fields... 

Biochemical processes are among the most challenging and interesting reaction systems. Due to the nature of the constituents involved, macromolecules such as nucleic acids or proteins, the processes to be analyzed do not follow a simple physicochemical model, and their mechanism cannot be easily predicted. For example, well-known reactions for simple molecules, e.g., protonation equilibria, increase in complexity for macromolecules due to the presence of polyelectrolytic effects or conformational transitions. Because the data analysis cannot be supported in a model-fitting procedure (hard-modeling methods), the analysis of these processes requires soft-modeling methods that can unravel the contributions of the process without the assumption of an a priori model. 

Kiriy A, Gorodyska G, Minko S, Jaeger W, Stepanek P, Stamm M (2002) Cascade of Coil-Globule Conformational Transitions of Single Flexible Polyelectrolyte Molecules in Poor Solvent. J Am Chem Soc 124(45) 13454... 

The water-insoluble PMAA-poly(N-ethyl-4-vinylpyridinium bromide)polyelectro-lyte complex (5 l) formed at pH < 4 becomes soluble if the excess PMAA in the polyelectrolyte complex is ionized110. The solubility of the polyelectrolyte complex is apparently connected with the appearance of high negative charges of the complex particles and is accompanied by a conformational transition of PMAA in excess. It has been proposed that the water-soluble polyelectrolyte complex consists of the nucleus formed by bound base and acid units. This structure is retained in solution due to unbound parts (sequences) of ionized PMAA. 

In all cases, however, the potentiometric plots of PMA reveal an anomaly at around a 0.15, which is absent in the titration curve of poly(acrylic acid) or other vinyl polyelectrolytes so far studied. The anomalies have been attributed by Leyte and Mandel to a conformational transition of cooperative character taking place in the PMA chains over a narrow range of a-values (5). This anomalous behavior of PMA samples of different t5q)e and amount of chain stereoregularity over a given range of degree of neutralization has been confirmed using... 

External polymers can also be employed to control leakage of entrapped solutes. Adsorption of the hydrophobic polyelectrolyte poly(2-ethylacrylic acid) on phosphatidylcholine membranes causes the disruption of vesicle membranes (Figure 4.32) with small changes in pH (7.4—>6.5). The surface polyelectrolyte undergoes a well-defined conformational transition from an... 

A further application of time-resolved fluorescence measurements is in the study of conformational dynamics of polymer chains in solution. Fluorescence anisotropy measurements of macromolecules incorporating suitable fluorescent probes can give details of chain mobility and polymer conformation (2,14). A particular example studied in this laboratory is the conformational changes which occur in aqueous solutions of polyelectrolytes as the solution pH is varied (15,16). Poly(methacrylic acid) (PMA) is known to exist in a compact hypercoiled conformation at low pH but undergoes a transition to a more extended conformation at a degree of neutralization (a) of 0.2 to 0.3 (1 6). Similar conformational transitions are known to occur in biopolymer systems and consequently there is considerable interest in understanding the nature of the structures present in model synthetic polyelectrolyte solutions. 

Water soluble synthetic polyelectrolytes have attracted increasing attention in recent years, mainly because of their wide utility in industrial applications, and also because of their resemblance to biopolymers. PolyCmethacrylic acid), PMA, a wea)c polyelectrolyte, exhibits a mar)ced pH induced conformational transition. A wide variety of techniques have been employed to gain more information on the nature of the conformational transition of PMA, these techniques include viscometry, potential titrimetry,(1-5) Raman spectrometry,(6) calorimetry,(7-9) electrical conductometry,(10) dilatometry,(11) H NMR linewidth,(12) viscoelastic studies,(13) )cinetics of chemical reactions, (14) small-angle neutron scattering,(15) pH jump,(16,17) and fluorescent probing.(18-27)... 

In order to extend earlier wor)c, several positively charged luminescent probes, tris(2,2 -bipyridine) ruthenium(II) complex, Ru(bpy)3, Auramine 0, Au 0, 1-pyrenebutyltrimethyl ammonium bromide, C PN and 1-pyreneundecyltrimethylammonium iodide, PN have been employed to monitor the nature of the conformational transition of PMA over the pH range of 2 to 8, from A states into B states. The purpose of the present wor)c is, to investigate the intermediate states in the uncoiling process of PMA polymer coil with increasing pH and to study any effects that are induced by polyelectrolytes on the photophysics and photochemistry of cationic... 

CONCLUSIONS This Study shows that fluorescence probing techniques are useful and powerful tools for investigation of conformational transitions of polyelectrolytes as induced by cationic surfactants, pH or other means. Studies on the interaction of cationic probes with polyelectrolytes provide useful information on the intermediates that lie between A states and B states. It is concluded that the conformational transition induced by pH is a progressive process over several pH units. Studies on the interaction of cationic surfactants with PMA at pH 8 show that the aggregates formed are large loose structures, while the interior of the aggregate has a hydrophobicity that is similar to that of a micelle. 

Benegas JC, Pantano S, Vetere A, Paoletti S. Polyelectrolytic aspects of the thermodynamics of conformational transitions k carrageenan in formamide. Biopolymers 1999 49 127-130. 

Conformational Transition in Polyelectrolyte Molecules Influence of Osmotic Pressure of Counterions... 

These two examples show that the theoretical description of conformational transition in polyelectrolyte macromolecules is of great importance. The study of conformational transition in polyelectrolyte molecules is also very important from the fundamental point of view. 

Let us consider now the intermediate case—the conformational transition in polyelectrolyte macromolecules of finite size dissolved in a solution of finite concentration. 

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