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Study of Water and Dimethylformamide Interaction by Computer Simulation

Joao Manuel Marques Cordeiro and Luiz Carlos Gomide Freitas^
Departamento de Fisica e Quimica, Faculdade de Engenharia de Ilha Solteira - UNESF,
CP 31 - 15385-000 - Ilha Solteira-SP, Brazil
^ Departamento de Quimica Universidade Federal de Säo Carlos ,
CP 676 - 13565-905 Säo Carlos-SP, Brazil
Z. Naturforsch. 54 a, 110-116 (1999);

[received November 19, 1998]

Monte Carlo simulations of water-dimethylformamide (DMF) mixtures were performed in the isothermal and isobaric ensemble at 298.15 K and 1 atm. The intermolecular interaction energy was calculated using the classical 6-12 Lennard-Jones pairwise potential plus a Coulomb term. The TIP4P model was used for simulating water molecules, and a six-site model previously optimised by us was used to represent DMF. The potential energy for the water-DMF interaction was obtained via standard geomeU*ic combining rules using die original potential parameters for the pure liquids. The radial disU-ibution functions calculated for water-DMF mixtures show well characterised hydrogen bonds between the oxygen site of DMF and hydrogen of water. A structureless correlation curve was observed for the interaction between die hydrogen site of the carbonyl group and die oxygen site of water. Hydration effects on the stabilisation of die DMF molecule in aqueous solution have been investigated using statistical perturbation theory. The results show that energetic changes involved in the hydration process are not sttong enough to stabilise another configuration of DMF than die planar one.

Key words: Monte Carlo Simulation; Solvent Effects; Statistical Perturbation Theory; Hydration of Peptides.

1. Introduction