Solubility enhancement of aromatic amino acids and peptides in aqueous solution of divalent transition-metal cations - QENS study

Abstract

Generally, the solubility of aromatic amino acids decreases in solution containing multivalent transition-metal ions, such as Cu2+, Pt2+, Pd2+and Co3+, due to the formation of complex precipitates. Surprisingly, we have observed considerably enhanced solubility of tryptophan (Trp) in CuCl2 aqueous solution with a high local concentration of Cu2+ at the surface of Trp [Phys. Rev. Lett. 117, 238102 (2016)]. The solubility increases by 2-5 times that of Trp in pure water. Based on first principle calculations, this unexpected phenomenon is attributed to the strong interaction between Cu2+and the aromatic ring in Trp, referred to as cation–? interaction which modifies the electron distribution of the aromatic ring in Trp and increases the water–aromatic ring interaction.