Monte Carlo simulations and neutron diffraction studies of the peptide forming system 0.5 mol kg-1CuCl2–5mol kg-1NaCl[ndash ]H2Oat 293 and 353 K

Abstract

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 CuII solvation phenomena correctly, three-body terms were incorporated, based on abinitio 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 (63Cu and 65Cu) 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 CuII coordination; both techniques show evidence of direct contact between Cu2+ and Cl− and indicate [Cu(H2O)5Cl1]+ 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.