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 AND353 K

Monte Carlo simulations at temperatures of 293 and 353 K have been per formed 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 interactio ns. The structure of the solvated ions is discussed in terms of radial density functions and coordination number, angular and energy distrib utions. A neutron diffraction study was also carried out on a solution of the same concentration at 298 K. The method of isotopic substituti on 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+ c oordination and the water structure. Comparison of the former with tho se 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 cop per species in solution. In addition, the neutron diffraction and isot opic substitution (NDIS) results show that the H-bond structure is str ongly perturbed by the presence of a high concentration of ions.