XVIth International Workshop on
Quantum Systems in
Chemistry and Physics
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AB INITIO QM/MM-MD-FREE ENERGY GRADIENT (FEG) METHOD: FREE ENERGY LANDSCAPE OF GLYCINE ISOMERIZATION
Masataka Nagaoka1,2,†
1Graduate School of Information Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, JAPAN
2Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency (JST), Honmachi, Kawaguchi 332-0012, JAPAN
E-mail: mnagaoka@is.nagoya-u.ac.jp;
For the purpose to explore accurately the reaction paths for chemical reactions in solution or enzyme, we have proposed the free energy gradient (FEG) method [1] combined with ab initio QM/MM-MD calculation [2], i.e., the ab initio QM/MM-FEG method [3]. For two application, the method has been applied to the isomerization reaction of glycine in aqueous solution, i.e., the intramolecular proton transfer reaction from zwitterion (ZW-cis) to the neutral form (NF-cis) and other molecular structural changes among several NFs. Including the solvent effect explicitly by the ab initio QM/MM-FEG method, those stable-state structures were found different from those obtained in gas phase or by an implicit dielectric continuum model at the same ab initio QM level. Additionally, by the vibrational frequency analysis with the “free energy (FE)” hessian in solution, the calculated vibrational frequencies were in good agreement with the experimental ones in the range from low to middle frequencies of ZW. Furthermore, the FE of activation from ZW-cis to NF-cis was found in very good agreement with not only the estimation by the Car-Parrinello MD method but also the previous experimental one. It is concluded that the ab initio QM/MM-FEG method is promising and should provide a better description of chemical reactions in solution in comparison with a number of conventional approaches by using the mean field approximations [3]. For an application to enzymatic reactions, some recent results are also introduced.

[1] (a) N.Okuyama-Yoshida, M.Nagaoka, T.Yamabe, Int. J. Quantum Chem., Vol.70, 95 (1998); (b) N.Okuyama-Yoshida, K.Kataoka, M.Nagaoka, T.Yamabe, J. Chem. Phys., Vol.113, 3519 (2000); (c) M.Nagaoka, Y.Nagae, Y.Koyano, Y.Oishi, J. Phys. Chem. A, Vol.110, 4555 (2006).
[2] T.Okamoto, K.Yamada, T.Asada, Y.Koyano, N.Koga, M.Nagaoka, J. Comput. Chem, Vol.32, 932 (2011).
[3] (a) N.Takenaka, Y.Kitamura, Y.Koyano, T.Asada, M.Nagaoka, Theor. Chem. Acc., (2011) in press; (b) Y.Kitamura, N.Takenaka, Y.Koyano, M.Nagaoka, Chem. Phys. Lett., submitted.


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