A fragment molecular-orbital-multicomponent molecular-orbital method for analyzing H/D isotope effects in large molecules

被引:25
作者
Ishimoto, T
Tachikawa, M
Nagashima, U
机构
[1] Natl Inst Adv Ind Sci & Technol, Res Inst Computat Sci, Tsukuba, Ibaraki 3058561, Japan
[2] CREST, Japan Sci & Technol Agcy, Kawaguchi, Saitama 3320012, Japan
[3] Yokohama City Univ, Grad Sch Sci, Quantum Chem Div, Kanazawa Ku, Yokohama, Kanagawa 2360027, Japan
关键词
D O I
10.1063/1.2151897
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
We have developed a fragment molecular orbital (FMO)-multi-component MO (MC_MO) method to analyze isotope effect due to differences between the quantum effects of protons and deuterons for large molecules such as proteins and DNA. The FMO-MC_MO method enables the determination of both the electronic and the protonic (deuteronic) wave functions simultaneously, and can directly express isotope effects, including coupling effects between nuclei and electrons. In our calculations of two polyglycines, which serve as prototypes for biological molecules, by this method, we clearly observed the geometrical relaxation induced by the H/D isotope effect in the intramolecular hydrogen bonding portions of the molecules. The H/D isotope effect on the interfragment interaction energy, including that of the hydrogen bonding parts, was also demonstrated: the hydrogen bond was weakened by replacement of hydrogen with deuterium. We also developed electrostatic potential approximations for use in the FMO-MC_MO calculations, and the accuracy of the energy differences induced by the isotope effect was independent of the approximation level of the FMO-MC_MO. Our results confirmed that the FMO-MC_MO method is a powerful tool for the detailed analysis of changes in hydrogen bonding and interaction energies induced by the H/D isotope effect for large biological molecules. (c) 2006 American Institute of Physics.
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页数:9
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