Hydrogen bond dynamics of methyl acetate in methanol

The interactions of methyl acetate in methanol have been studied by means of ab initio molecular dynamics simulations within the Car-Parrinello approach. These simulations have been shown to be particularly suitable to describe the H-bond dynamics of methyl acetate in water, leading to a complete characterization of the observed mono- and bi-dimensional IR spectra, reported by Candelaresi et al. [1]. Banno et al. [2, 3] have recently shown that the C=O stretching band of methyl acetate in methanol splits in a doublet as a consequence of the H-bond interaction as it occurs in water, although the position of the band differs in the two solvents. This behavior has been explained by considering the solvation structure and dynamics of methyl acetate in both solvents. Methyl acetate forms one or two H-bond in water solution, whereas in methanol it can interact at most with only one molecule. The H-bond effects on the spectroscopic properties of methyl acetate in methanol have been interpreted by wavelet transform analysis. An algorithm has been set up to correlate the C=O stretching frequency during the simulations with the function for the description of the H-bond, introduced by Pagliai et al. [4]. Since wavelet transforms localize the signal in the frequency and time domains, it is possible to obtain the frequency and the bond length of the C=O stretching at the same time step of the simulations. The Car-Parrinello molecular dynamics simulations, in conjunction with wavelet transforms, have shown to satisfactorily characterize the structural and vibrational properties of H-bonded systems, helping to elucidate at atomic level the interactions that take place in the sample dissolved in different media and their spectroscopic features. [1] M. Candelaresi, M. Pagliai, M. Lima, R. Righini, J. Phys. Chem. A 113 (2009) 12783-12790 [2] M. Banno, K. Otha, S. Yamaguchi, S. Hirai, K. Tominaga, Acc. Chem. Res. 42 (2009) 1259-1269 [3] M. Banno, K. Otha, K. Tominaga, J. Raman Spectosc. 39 (2008) 1531-1537 [4] M. Pagliai, G. Cardini, R. Righini, V. Schettino, J. Chem. Phys. 119 (2003) 6655-6662