Thesis (M.Sc.)--Chulalongkorn University, 2013

The reactivity of terminated sulfur atom within the thiosulfate (S₂O₃²-) ion involving in chemical reactions was investigated by the properties of molecular hydration shell obtained from the ab initio quantum mechanical charge field molecular dynamics (QMCF MD) simulation. The average geometry indicated the significant effect of explicit water molecule on the reduction of S_S length, reflecting in the splitting peaks of the spectrum for the stretching mode of this bond (v(SS)). A further investigation on a simple model with various theoretical levels exhibited the hydrophobicity of the S_S bond. The evaluation of molecular coordination number was sensitive with the radius of atomic hydration spheres, obtained from vague boundaries of the first peak in the atomic radial distribution functions. The number of actual contacts specified 6.8 water molecules interacting to the thiosulfate ion, and 2.4 extra waters located in the molecular hydration shell forming H-bonds network with bulk. The mean residence times for the water ligands distinguished the asymmetric strength of hydration shell into a weaker sulfur and three stronger oxygen sites, instigating the terminated sulfur atom as the active site involving in chemical reactions.