Dissolution Behavior of Optical Isomers of fac-Tris(aniono)cobalt(III) of Some α-Amino Acids in Water

Abstract

Abstract fac-Tris(aniono)cobalt(III) of d-alanine, d-valine, d-leucine, l- and d-prolines, and l- and d-serines was synthesized, and the separation of the diastereoisomers of these chelates was attempted. The solubilities of these isomers in water were determined over the temperature range of 5 to 55 °C. The thermodynamic parameters of solution at 25 °C, such as the free energy (ΔGs°), enthalpy (ΔHs°), and entropy (ΔSs°), were estimated from the temperature dependence of the solubilities. Also, the dissolution behavior of these chelate in water was considered in terms of these thermodynamic parameters. Plot of ΔHs° against TΔSs° gave separate correlation lines for the groups comprising less soluble chelates and more soluble chelates. An increase in the solubility within the respective groups was caused by an increase in TΔSs°. Both ΔHs° and TΔSs° for the chelates of less hydrophobic glycine and serine were larger than those for the chelates of more hydrophobic amino acids.