Dissertation > Mathematical sciences and chemical > Chemistry > Physical Chemistry ( theoretical chemistry ),chemical physics > Structural Chemistry

Theoretical Study of the Dynamics of Electron Transfer in Biomolecular System

Author LiuJiFeng
Tutor LiXiangYuan
School Sichuan University
Course Physical and chemical
Keywords Electron transfer Tryptophan and tyrosine Rate Constants Reaction Mechanism Solvent effect
CLC O641
Type PhD thesis
Year 2004
Downloads 332
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This article is divided into two parts: The first part is the Summary of electron transfer theory, in this section, the authors of the foundation and theoretical models of electron transfer theory developed in the nineteen fifties and Marcus non-adiabatic electron transfer rate The classic formula calculated by the constant discussion of the factors affecting the electron transfer rate constant and its calculation method; In the second part, the author of ab initio ab initio method level between molecules in biological molecular modeling system adiabatic electron transfer reactions, molecular within the non-adiabatic electron transfer reaction intermolecular photoinduced electron transfer reaction mechanism was studied, and calculated the electron transfer reaction rate constants in the system. Chapter design? - Carbon-centered radicals the molecule (H2NCH? CHO) O2 oxidation model reaction. The application of an external electric field induced charge localized molecular orbital track with the charge given domain induced double-well potential curve calculated from the reaction system. Theoretical calculations show that the polar solvent effect significant role in promoting the charge separation of the electron transfer process: (1) fluctuations in polar solvents promote the transition state electron transfer occurs near the equilibrium in the product, the aqueous solution RC = 1.01; (2) an aqueous solution, the activation barrier of the reaction system is greatly reduced, only about half of the gas phase; (3) an aqueous solution of the heat of reaction is reduced to half of the gas phase. Analyzing the reaction according to the size of the redox reaction center distance between the size and electronic transfer coupling matrix element is adiabatic electron transfer process, the obtained electron transfer rate constant of 7.087 (10-12 M-1 calculated adiabatic electron transfer theoretical model by Marcus s-1. theoretical study shows that the electron transfer reaction is very slow, in the thermodynamic conditions, the electron transfer reaction occurs possibility is very small in the third chapter, the authors consider the solvent effect and mechanism of deprotonation of the three non-adiabatic electron transfer reaction mechanism between tryptophan and tyrosine (1) electron transfer the receptor isolated system the interaction between theoretical studies have shown both in the gas phase or in aqueous solution, not deprotonated positive the ion radical system high activation barrier for electron transfer reaction, the reaction is difficult to occur; (2) double-deprotonated anion radical electron transfer reactions of low activation barrier system, the transition state of the reaction equilibrium in the reactant attached lt; WP = gt; near, is an exothermic reaction, can occur spontaneously in the gas phase and the aqueous solution; (3) a third electron transfer mechanism, indol-the positive ionic moiety deprotonated form a neutral radical, then after proton transfer / electron transfer or electron transfer / proton transfer two-step process to generate product Theoretical calculations show that in aqueous solution proton transfer occurs first, and then electron transfer reaction path dominant theoretical study of the three mechanisms proven deprotonated mechanism of electron transfer control action, and to clarify the solvent effect caused by the rationality of the multi-step reaction mechanism and double deprotonation reaction mechanism (4) methylene chain as indole and phenol bridge system methylene number from 2-5 system electron transfer coupling matrix element effects of electron transfer coupling matrix element with the electron transfer to the relationship between the distance between the centers of the receptor, found both relationship exists between exponential decay, according to the fitting exponential curve ask? value than the value of the experimental forecast. (5) studies have shown that hydrogen bonding interactions between the indole and phenol NH bond on the indole ring in the oxidant after oxidation, under the influence of a polar solvent, can easily deprotonated. formed after the deprotonation of a more stable complex system, to drive the reaction forward as a whole. theory experimental study explains why oxidant easier oxindole The group become positive ions, and the next driving force of the electron transfer reaction (6) tryptophyl tyrosine dipeptide system bridge conformation on electron transfer kinetics of theoretical studies have shown different bridge the heat of reaction of the body conformation system, the internal reorganization energy and electronic coupling matrix element are quite different conformational changes of the bridge will affect the electron transfer kinetics of factors, thereby affecting the electron transfer rate. fourth chapter, the authors try to use HF and complete active space self-consistent field (CASSCF) investigated tryptophan and DNA Bases with 4 - nitroquinoline 1 - oxide (4NQO) the interaction between the light-induced electron transfer process between them, from theory to help understand 4NQO carcinogenic. theoretical study of these systems have little knowledge of theoretical calculation studies have shown that (1) there are two hydrogen bond interactions between tryptophan and purine bases with 4NQO, a The proton acceptor is a group of the the 4NQO molecule heterocyclic NO, another germplasm sub receptor is the the 4NQO molecular nitro, tryptophan or purine bases NH key molecule as a proton donor. (2) of tryptophan and 4NQO CASSCF calculations show that the formation of the most stable hydrogen bond complex system, the system first, two singlet excited state and the first excited triplet state of the charge-separated state to be described in the appropriate light irradiation conditions, the system can a direct light-induced electron transfer reactions of the lowest triplet state of the system is the 4NQO part of localized excitations state (3) guanine and 4NQO??? CASSCF calculations of the complex system, the effects of substituents on the system singlet excitation energy, and found that the substituents are independently a hydrogen atom, a methyl group, tetrahydrofuran, and the pentose group, the first singlet excited state are charge-separated state, the system from the ground state to the first excited singlet state of the transition energy decreases in turn, the transition can be estimated with the experimental electron transfer induced spectral absorption corresponding to the transition energy is consistent. Theoretical calculations show that 4NQO not only with the DNA base interactions, lt; WP = gt; tryptophan and between similar interaction, thus containing tryptophan anticancer protein structure and function relationship will certainly help to understand the solvent effect is the emphasis and difficulty in the electron transfer reaction. fifth chapter, the author introduces to this theoretical laboratory recently developed nonequilibrium solvation and new theoretical and computational model of the spectral shift correction, and has the effect of solvent probe called coumarin 153 system in 44 solution of the spectral data the radius of the fitting. system solvent cavity radius is obtained with the slope of the line fitting the new formula gives 3.7-3.9? cavity radius calculated using the van der Waals volume; Lippert-Mataga formula to a cavity radius is 4.6-4.9?, indicating that the new nonequilibrium solvation formula the prediction spectral shift is reliable fitting of the experimental data results and comparison with Lippert-Mataga formula.

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