Hybrid QM/MM molecular dynamics simulations for an ionic SN2 reaction in the supercritical water: OH− + CH3Cl → CH3OH + Cl−

A hybrid real space quantum mechanical/molecular mechanical (RS‐QM/MM) method has been applied to an ionic SN2 reaction (OH− + CH3Cl → CH3OH + Cl−) in water solution to investigate dynamic solvation effects of the supercritical water (SCW) on the reaction. It has been demonstrated that the approaching process of OH− to methyl group is prevented by water molecules in the ambient water (AW), while the reaction takes place easily in the gas phase. Almost the same solvation effect on the dynamics of OH− is observed in the SCW, though the bulk density of water is substantially reduced compared with that of the AW. It has been shown that the solvation of the SCW around the OH anion is locally identical to that of the AW due to the strong ion‐dipole interactions between OH− and water molecules. At the transition state, the QM/MM simulations have revealed that the excess electron is quite flexible, and the charge volume, as well as the fractional charges on atoms, vary seriously depending on the instantaneous solvent configurations. However, it has been found that the solvation energy in the SCW can be qualitatively related to the HOMO volume of the system by Born's equation. © 2002 Wiley Periodicals, Inc. J Comput Chem 24: 209–221, 2003

[1]  W. L. Jorgensen,et al.  Comparison of simple potential functions for simulating liquid water , 1983 .

[2]  Scott F. Smith,et al.  Theoretical examination of the SN2 reaction involving chloride ion and methyl chloride in the gas phase and aqueous solution , 1985 .

[3]  R. Hernandez,et al.  Stochastic Dynamics in Irreversible Nonequilibrium Environments. 1. The Fluctuation−Dissipation Relation , 1999 .

[4]  Hideaki Takahashi,et al.  Real Space Ab Initio Molecular Dynamics Simulations for the Reactions of OH Radical/OH Anion with Formaldehyde , 2001 .

[5]  H. Kramers.  Brownian motion in a field of force and the diffusion model of chemical reactions , 1940 .

[6]  Wu,et al.  Higher-order finite-difference pseudopotential method: An application to diatomic molecules. , 1994, Physical review. B, Condensed matter.

[7]  W. Kohn,et al.  Self-Consistent Equations Including Exchange and Correlation Effects , 1965 .

[8]  E. Pollak,et al.  Variational transition state theory for electron transfer reactions in solution , 1996 .

[9]  Jacopo Tomasi,et al.  Molecular Interactions in Solution: An Overview of Methods Based on Continuous Distributions of the Solvent , 1994 .

[10]  D. R. Hamann,et al.  Pseudopotentials that work: From H to Pu , 1982 .

[11]  M. Aida,et al.  An ab initio MO study on the hydrolysis of methyl chloride , 1999 .

[12]  W. J. Caspers.  On the exchange potential , 1964 .

[13]  J. Tomasi,et al.  Ab initio study of ionic solutions by a polarizable continuum dielectric model , 1998 .

[14]  Martins,et al.  Efficient pseudopotentials for plane-wave calculations. , 1991, Physical review. B, Condensed matter.

[15]  P. Rossky,et al.  Molecular Simulation of a Chemical Reaction in Supercritical Water , 1994 .

[16]  O. Kajimoto.  Solvation in Supercritical Fluids: Its Effects on Energy Transfer and Chemical Reactions. , 1999, Chemical reviews.

[17]  Lewis W. Flanagin,et al.  Temperature and Density Effects on an SN2 Reaction in Supercritical Water , 1995 .

[18]  J. Hynes,et al.  Reactive modes in condensed phase reactions , 1981 .

[19]  P. Rossky,et al.  Dynamics of chemical processes in polar solvents , 1994, Nature.

[20]  I. Tuñón,et al.  Molecular dynamics simulations of elementary chemical processes in liquid water using combined density functional and molecular mechanics potentials. I. Proton transfer in strongly H-bonded complexes , 1997 .

[21]  A. Zunger,et al.  Self-interaction correction to density-functional approximations for many-electron systems , 1981 .

[22]  F. Grozema,et al.  Combined Quantum Mechanical and Molecular Mechanical Methods , 1999 .

[23]  D. Laria,et al.  Solvation effects on a model SN2 reaction in water clusters , 1996 .

[24]  Phillip E. Savage,et al.  Organic Chemical Reactions in Supercritical Water. , 1999, Chemical reviews.

[25]  Tricia D. Shepherd,et al.  Chemical reaction dynamics with stochastic potentials below the high-friction limit , 2001 .

[26]  P. Rossky,et al.  Hydration effects on SN2 reactions: an integral equation study of free energy surfaces and corrections to transition-state theory , 1989 .

[27]  J. V. Eerden,et al.  Free energy calculations on systems of rigid molecules: An application to the TIP4P model of H2O , 1999 .

[28]  Wu,et al.  Ab initio molecular-dynamics simulations of Si clusters using the higher-order finite-difference-pseudopotential method. , 1994, Physical review. B, Condensed matter.

[29]  Y. Saad,et al.  Finite-difference-pseudopotential method: Electronic structure calculations without a basis. , 1994, Physical review letters.

[30]  T. Arias,et al.  Iterative minimization techniques for ab initio total energy calculations: molecular dynamics and co , 1992 .

[31]  Barnett,et al.  Born-Oppenheimer molecular-dynamics simulations of finite systems: Structure and dynamics of (H2O)2. , 1993, Physical review. B, Condensed matter.

[32]  Jacopo Tomasi,et al.  A new integral equation formalism for the polarizable continuum model: Theoretical background and applications to isotropic and anisotropic dielectrics , 1997 .

[33]  P. Hohenberg,et al.  Inhomogeneous Electron Gas , 1964 .

[34]  K. Kobayashi.  Norm-conserving pseudopotential database (NCPS97) , 1999 .

[35]  K. Morokuma,et al.  An MO study of SN2 reactions in hydrated gas clusters: hydrated hydroxide [(H2O)nOH-] + hydrated methyl chloride [MeCl(H2O)m] .fwdarw. methanol + chloride + (n + m)water , 1985 .

[36]  P. Rossky,et al.  Continuum Electrostatics Model for an SN2 Reaction in Supercritical Water , 1995 .

[37]  R. Pierotti,et al.  A scaled particle theory of aqueous and nonaqueous solutions , 1976 .

[38]  Car,et al.  Unified approach for molecular dynamics and density-functional theory. , 1985, Physical review letters.

[39]  J. Tomasi,et al.  Ab Initio Study of the SN2 Reaction CH3Cl + Cl- → Cl- + CH3Cl in Supercritical Water with the Polarizable Continuum Model , 1997 .

[40]  J. Tomasi,et al.  Ab initio study of solvated molecules: A new implementation of the polarizable continuum model , 1996 .

[41]  Fumio Hirata,et al.  A hybrid approach for the solvent effect on the electronic structure of a solute based on the RISM and Hartree-Fock equations , 1993 .

[42]  Hideaki Takahashi,et al.  A hybrid QM/MM method employing real space grids for QM water in the TIP4P water solvents , 2001, J. Comput. Chem..

[43]  Tomoya Ono,et al.  Timesaving Double-Grid Method for Real-Space Electronic-Structure Calculations , 1999 .

[44]  G. Cardini,et al.  Microsolvation effect on chemical reactivity: The case of the Cl−+CH3Br SN2 reaction , 2001 .

[45]  Arai,et al.  Density-functional molecular dynamics with real-space finite difference. , 1995, Physical review. B, Condensed matter.

[46]  M. Born.  Volumen und Hydratationswärme der Ionen , 1920 .

[47]  J. Gao,et al.  A priori evaluation of aqueous polarization effects through Monte Carlo QM-MM simulations. , 1992, Science.

[48]  Hideaki Takahashi,et al.  A Density Functional Study for Hydrogen Bond Energy by Employing Real Space Grids , 2000 .