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Microscopic Origin of Different Hydration Patterns of para-Nitrophenol and Its Anion: A Study Combining
Carlos Bistafa1,2,3, Yukichi Kitamura2,3, Masataka Nagaoka2,3
1Institute of Physics , University of São Paulo , Rua do Matão, 1371 , Cidade Universitária, São Paulo-SP 05508-090 , Brazil.
Abstract:
A theoretical study of the solvatochromic shifts of para-nitrophenol ( pNP) and para-nitrophenolate anion ( pNP-) in aqueous solution is presented using a QM/MM methodology with molecular dynamics simulation. The optimized structures in aqueous solution are obtained using both the polarizable continuum and the free-energy gradient methods. For pNP, the calculated redshifts at the CASPT2 (12,10) level are, respectively, 0.71 and 0.94 eV, in good agreement with the experimental ones (0.80-0.83 eV), whereas for pNP-, they are small. The difference between the solvatochromic shifts of pNP and pNP- is calculated as 0.71 eV in good agreement with the experimental one (0.79-0.81 eV). Finally, these shifts are understood in terms of the solvent effect on the solute structure, accurately calculated by the present theoretical treatment.
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