Monte Carlo simulations and neutron diffraction studies of the peptide forming system 0.5 mol kg-1 CuCl2-5 mol kg-1 NaCl-H2O at 293 and 353 K

Monte Carlo simulations at temperatures of 293 and 353 K have been performed for a 0.5 mol kg(-1) CuCl2-5 mol kg(-1) NaCl aqueous solution, which has been found to induce condensation of amino acids to peptides. Because pair potentials are insufficient to describe Cu-II solvation phenomena correctly, three-body terms were incorporated, based on ab initio derived potentials for CU2+-H2O-H2O and CU2+-Cl--H2O interactions. The structure of the solvated ions is discussed in terms of radial density functions and coordination number, angular and energy distributions. A neutron diffraction study was also carried out on a solution of the same concentration at 298 K. The method of isotopic substitution was applied to the copper(II) ions ((CU)-C-63 and (CU)-C-65) and to the water molecules (H2O and D2O) and results obtained for the CU2+ coordination and the water structure. Comparison of the former with those of the simulation shows that there is broad agreement for the Cu-II coordination; both techniques show evidence of direct contact between CU2+ and Cl- and indicate [Cu(H2O)(5)Cl-1](+) to be the prevalent copper species in solution. In addition, the neutron diffraction and isotopic substitution (NDIS) results show that the H-bond structure is strongly perturbed by the presence of a high concentration of ions.