A calorimetric investigation into copper–arginine and copper–alanine solid state interactions

Complexes of formula CuCl2 · 2arg and CuCl2 · 4ala (arg = arginine; ala = alanine) were prepared at room temperature by a solid state route. The metal–amino acid solid state interactions were studied by i.r. spectroscopy and solution calorimetry. For both complexes, participation of the carboxylate group as well as nitrogen in coordination are inferred, based on the i.r. data. For the copper–arginine compound, the calculated thermochemical parameters are: ΔrHmθ = −114.9 ± 1.42 and ΔfHmθ = −1608.3 ± 11.6 kJ mol−1. For copper–alanine compound, a complete set of thermochemical parameters were calculated: ΔrHmθ = −18.0 ± 0.9; ΔfHmθ = −2490.4 ± 4.3; ΔDHmθ = 597.2 ± 17.7; ΔMHmθ = 771.9 ± 18.7; ΔgHmθ = 627.1 ± 22.3 and 〈D〉 (Cu−L) = 156.8 ± 5.7 kJ mol−1. Based on ΔrHmθ and dissolution enthalpy values, a stronger intermolecular solid state interaction can be inferred for the arginine complex, than for the alanine one complex, probably due to the formation of intermolecular hydrogen bonds in the former.