Revealing Ligand Deprotonation and Speciation Pathways in Cu(II)–Glycine Aqueous Solutions via Liquid-Jet X-ray Photoelectron Spectroscopy Supported by ab-initio Calculations

Abstract

We present an integrated methodology combining photoemission spectroscopy, chemical speciation modeling, and ab initio calculations to investigate aqueous solutions of copper chloride salts mixed with glycine. This system is of interest due to the role of amino acid–metal interactions in biological and environmental contexts. Speciation simulations based on chemical equilibrium models reveal the formation of Cu−(Glycine)₂ and Cu−(Glycine)⁺ complexes, with relative abundances that depend on initial ion concentrations. N 1s photoemission measurements indicate that the complexation processes involve deprotonation of glycine’s amino group, enabling copper to coordinate with the -NH₂ and -COO⁻ functional groups. Simulated Cu 2p photoemission spectra considering Cu−(Glycine)₂ and Cu−(Glycine)⁺ molecular compounds found by speciation reproduce both the main line and satellite features observed experimentally. These results provide detailed insight into copper–amino acid coordination and demonstrate the strength of combining spectroscopic data with advanced theoretical modeling to unravel speciation and electronic structure in complex aqueous environments.