Development of New Cd2+ and Pb2+ Lennard-Jones Parameters for Liquid Simulations

ALEXANDRE S. DE ARAUJO; MILTON T. SONODA; OSCAR E. PIRO; EDUARDO E. CASTELLANO

JOURNAL OF PHYSICAL CHEMISTRY B

Año: 2006

1089-5647

We present new Lennard-Jones parameters for Cd2+ and Pb2+ ion-water interactions and a general methodology to obtain these parameters for any ion. Our strategy is based on the adjustment of ion parameters to reproduce simultaneously experimental absolute hydration free energy and structural properties, namely g(r) and coordination numbers, obtained from X-ray liquid scattering and QM/MM calculations. The validation of the obtained parameters is made by the calculation of dynamical properties and comparing them with experimental values and theoretical results from literature. The transferability of parameters is checked from the calculation of thermodynamic, structural and dynamical properties cited above with four different water models. The results obtained for Cd2+ and Pb2+ show an overall agreement with reference values. The absolute hydration free energy calculated with TIP3P, SPC/E, SPC and TIP4P water models presents, respectively, percent differences of 3.8%, 3.0%, 4.3% and 7.2% for lead(II)  and 8.3%, 8.4,%, 10.2% and 14.1% for cadmium(II) when compared with experimental values. Ion-water mean distance and coordination numbers for the first coordination shell are in good agreement with experimental and QM/MM results for both ions. The Cd2+ ion presents a higher diffusion coefficient compared with Pb2+ despite its lesser atomic radius, indicating a more persistent first coordination shell for the cadmium(II) ion, a result confirmed with calculations of mean residence time of water molecules in the first coordination shell.