Interfacial Bond-Breaking Electron Transfer in Mixed Water鈥揈thylene Glycol Solutions: Reorganization Energy and Interplay between Different Solvent Modes

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• 作者：Oksana Ismailova ; Alexander S. Berezin ; Michael Probst ; Renat R. Nazmutdinov
• 刊名：The Journal of Physical Chemistry B
• 出版年：2013
• 出版时间：July 25, 2013
• 年：2013
• 卷：117
• 期：29
• 页码：8793-8801
• 全文大小：385K
• 年卷期：v.117,no.29(July 25, 2013)
• ISSN：1520-5207

文摘

We explore solvent dynamics effects in interfacial bond breaking electron transfer in terms of a multimode approach and make an attempt to interpret challenging recent experimental results (the nonmonotonous behavior of the rate constant of electroreduction of S₂O₈^{2鈥?/sup> from mixed water鈥揈G solutions when increasing the EG fraction; see Zagrebin, P.A. et al. J. Phys. Chem. B 2010, 114, 311). The exact expansion of the solvent correlation function (calculated using experimental dielectric spectra) in a series predicts the splitting of solvent coordinate in three independent modes characterized by different relaxation times. This makes it possible to construct a 5D free-energy surface along three solvent coordinates and one intramolecular degree of freedom describing first electron transfer at the reduction of a peroxodisulphate anion. Classical molecular dynamics simulations were performed to study the solvation of a peroxodisulphate anion (S₂O₈2鈥?/sup>) in oxidized and reduced states in pure water and ethylene glycol (EG) as well as mixed H₂O鈥揈G solutions. The solvent reorganization energy of the first electron-transfer step at the reduction of S₂O₈2鈥?/sup> was calculated for several compositions of the mixed solution. This quantity was found to be significantly asymmetric. (The reorganization energies of reduction and oxidation differ from each other.) The averaged reorganization energy slightly increases with increasing the EG content in solution. This finding clearly indicates that for the reaction under study the static solvent effect no longer competes with solvent dynamics. Brownian dynamics simulations were performed to calculate the electron-transfer rate constants as a function of the solvent composition. The results of the simulations explain the experimental data, at least qualitatively.}