SOLVATION OF 1,4,7,10-TETRAAZACYCLODODECANE IN AQUEOUS-SOLUTION AS STUDIED BY THE MONTE-CARLO METHOD

The solvation structure of 1,4,7,10-tetraazacyclododecane (cyclen) in aqueous solution has been investigated using the Metropolis Monte Carl o scheme. Simulations have been carried out for a system containing 20 2 rigid particles, including one cyclen molecule, which is fixed at th e center of the cube. With a volume of 201 water molecules at 298 K an d 1 atm plus additional space occupied by the cyclen molecule, a perio dic cubic volume of side length 18.28 Angstrom was yielded. A cyclen-w ater pair potential has been developed based on nb initio calculations , while the MCY potential was employed to describe water-water interac tions. Three hydration layers around the cyclen have been monitored an d named the nearest-neighbor, inner hydration, and outer hydration she lls. The corresponding numbers of water molecules lying in each shell are 2, 6, and 54, respectively. The two nearest neighbors are bound to the ligand cavity, one above and the other below the ligand plane, po inting one hydrogen atom to the center of the cavity. It was also foun d that each of them was solvated by three of the six molecules in the inner hydration shell of cyclen. In addition, significant solvent stru cture around the cyclen molecule has been observed up to 8-9 Angstrom from the molecular center.