Counterion dynamics, intramolecular

The most important achievement of this work is the observation of greatly reduced intramolecular ET rates in the presence of chemically inert counterions. The dynamic counter-ion control of the ET rate could be observed because the studied electron transfer reaction was veiy weakly exothermic. Therefore, even in the case of the large organic cations and relatively weak electrostatic interactions, the condition Xionic > AG was satisfied, and the evolution along the slow coordinate of the Sumi-Marcus theory, that is, the diffusion of the cation, could become the rate-determining step. 

Abstract Aqueous solutions of star-like polyelectrolytes (PEs) exhibit distinctive features that originate from the topological complexity of branched macromolecules. In a salt-free solution of branched PEs, mobile counterions preferentially localize in the intramolecular volume of branched macroions. Counterion localization manifests itself in a dramatic reduction of the osmotic coefficient in solutions of branched polyions as compared with those of linear PEs. The intramolecular osmotic pressure, created by entrapped counterions, imposes stretched conformations of branches and this leads to dramatic intramolecular conformational transitions upon variations in environmental conditions. In this chapter, we overview the theory of conformations and stimuli-induced conformational transitions in star-like PEs in aqueous solutions and compare these to the data from experiments and Monte Carlo and molecular dynamics simulations. 

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