Enhanced water affinity of histidine by transition metal ions

This is the authors' abstract. We don't add key points for this paper.

Transitional metal ions widely exist in biological environments and are crucial to many life-sustaining physiological processes. Recently, transition metal ion such as Cu²⁺, Zn²⁺, Ni²⁺, have been shown can increase the solubilities of aromatic biomolecules. Comparing with Cu²⁺, Zn²⁺ shows less enhancement to the solubilities of biomolecules such as tryptophan (Trp). On the other hand, Zn²⁺ has a higher concentration in human blood plasma and appears in protein the most among transition metal ions, clarifying whether Zn²⁺ can enhance the solubilities of other aromatic amino acids is significantly important. Herein, we observed that the solubility of aromatic amino acid histidine (His) is greatly enhanced in ZnCl₂ solution. Based on first principle calculations, this enhancement of solubility is attributed to cation-$π$ interaction between His and Zn²⁺. Our results here are of great importance for the bioavailability of aromatic drugs and provide new insights for the understanding of physiological functions of Zn²⁺.