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

Abstract

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: Δ_rH_m ^θ = −114.9 ± 1.42 and Δ_fH_m ^θ = −1608.3 ± 11.6 kJ mol⁻¹. For copper–alanine compound, a complete set of thermochemical parameters were calculated: Δ_rH_m ^θ = −18.0 ± 0.9; Δ_fH_m ^θ = −2490.4 ± 4.3; Δ_DH_m ^θ = 597.2 ± 17.7; Δ_MH_m ^θ = 771.9 ± 18.7; Δ_gH_m ^θ = 627.1 ± 22.3 and 〈D〉 (Cu−L) = 156.8 ± 5.7 kJ mol⁻¹. Based on Δ_rH_m ^θ 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.