PROTON CHEMICAL-SHIFT OF WATER IN THE LIQUID-STATE - COMPUTER-SIMULATION RESULTS

Molecular dynamics simulations have been employed to determine the relative proton magnetic resonance (H-1 NMR) chemical shifts of water in liquid state. The proton chemical shifts were obtained as a sum of the average electrostatic and van der Waals contributions. In order to compute these contributions, the Buckingham-Marshall-Pople treatment of the electrical field effect on proton magnetic shielding was used. The SPC/E model for water was studied at temperatures of -10, 25, and 100-degrees-C, and the H-1 NMR chemical shifts were found to be in good agreement with experimental data. The dependence in the values of the chemical shifts upon the number of molecules involved in their evaluation was examined in detail. In general, the nearest neighbors of a molecule gave rise to particularly large deshielding effects, whereas more distant molecules were found to increase shielding. The method employed can be utilized in the calculation of proton-shielding changes in any liquid for which the appropriate intermolecular potentials are available.