MOLECULAR-DYNAMICS SIMULATIONS OF ZINC IONS IN WATER USING CHARMM

Molecular Dynamics simulations of a zinc ion with 123 and 525 TIP3P-wa ter molecules were carried out with CHARMM using two different Lennard -Jones parameter sets for the Zn2+ ion. The results were compared to p ublished experimental and simulation data. Good agreement was found fo r radial distribution functions, number of hydrogen bands, and diffusi on coefficients. Experimental radial distribution functions were bette r reproduced by the original CHARMM22 parameter set than by the parame ter set modified by Stote and Karplus. Diffusion coefficients were fou nd to depend on the system size rather than on the parameter set used and were better reproduced by the larger systems. The divalent zinc io n exerts a strong influence on its hydration shell as indicated by the high first peak of the radial distribution function. Water molecules in the vicinity of the zinc ion show a slight deformation of the O-H b ond length and of the H-O-H bond angle as compared to pure water. No w ater molecules from the first hydration shell were exchanged during 1 ns of MD simulation.