Free electron transfer—relations between molecule dynamics and reaction kinetics

Abstract

Electron transfer in non-polar media (alkanes, alkyl chlorides) exhibits some essential peculiarities. For instance the reaction of hetero-substituted aromatics with parent solvent radical cations results in the parallel formation of metastable donor radical cations and fragmentation products, in comparable amounts. The fragmentation products originate from a dissociative donor radical cation which decays extremely rapidly, i.e., in a few femtoseconds. This phenomenon is explained in terms of intramolecular dynamic motions which cause changes of the electron density (pi- and n-orbitals) in dependence on the deformation angle between the substituents and the aromatic ring. Hence femtosecond dynamics is reflected in the nanosecond time range and can be observed with real-time spectroscopy. Therefore, the process is named free electron transfer (FET) which corresponds to an unhindered electron jump occurring in the first approach of the reactants. This dynamic controlled process is compared with the classical electron transfer theories which are based on equilibrium kinetics. From the FET mechanism some new aspects for chemical reaction kinetics can be derived (critical review, 69 references).

Charge transfer reactions from tryptophan and tyrosine to sulfur-centered dimer radical cation in aqueous -sulfuric acid medium: a pulse radiolysis study

“…5A) which could be because of and 600 nm) have not been affected by oxygen in agreement with radical cation nature. [3,27] Similarly, absorption band for tyrosine radical at 410 nm was not affected by oxygen as it is O-centered radical. [26] However, tyrosyl radical absorption at 340 nm was found to decay at a faster rate in presence of oxygen (k = 8.02 × 10 8 M À1 s À1 ) (Fig.…”

“…Earlier, solute radical cations produced on radiolysis have been suggested to form such radical cation-anion pair in 1-chlorobutane solvent. [3,27] On the basis of experimentally observed transient absorption spectra, kinetic traces, and literature, a general reaction mechanism (Eqs. 5-8) is assumed for the reactions studied in the present work: SO 4 •¯þ TH for NAM; TrpH; TyrOH and Phe…”

“…to produce solute radical cation of several compounds, especially phenols, was reported earlier. [1][2][3] However, protonation state and redox properties of organic solutes are affected by pH in aqueous solution. As the acidity of the medium is increased (pH decreased), the oxidation of solutes becomes difficult and deprotonation of the produced radical cation becomes less favorable depending on its pKa.…”

“…However, distinct steps of formation of solute radical cation and subsequent deprotonation to produce solute radical and proton in non-aqueous media are reported exhaustively. [1][2][3] Electron transfer from solutes to radical cation of the solvents (CCl 4 , CH 2 Cl 2 , 1-C 4 H 9 Cl, etc.) to produce solute radical cation of several compounds, especially phenols, was reported earlier.…”

Influence of inhomogeneous distributions on charge transfer in micro-nano optoelectronic conversion systems

“…及由国内超快光谱研究领域的知名 专家撰写的专业著作 [23,24] . 这种对重整化能的处理类似于在描述黏性溶剂 中小分子之间的电子转移过程中发展起来的简化模 图 2 自由电子转移中相关过程的时间尺度 [15] Figure 2 Time range of processes relevant in free electron transfer (FET) [15] 图 3 (网络版彩色)蛋白质动力学的特征时间尺度及其对应的功能 于反应-扩散方程 [42,43] , 在动态不均匀分布模型中, 学的行为 [3] . 这也意味着光合作用反应中心里电子转 移反应是强烈地受蛋白质动力学影响的, 而非蛋白 图 5 (网络版彩色)细菌光合作用反应中心的野生型及各种突变型结 构(a) [3] [47] Figure 5 (Color online) The cofactor arrangement of wild-type bacterial photosynthetic reaction centers (a) [3] and schematic representation of the relative free energies of P + B A  and P + H A  from wild-type reaction centers and eight mutants (b) [47] 质简单的对电荷分离进行响应.…”