Computational and crystallographic study of hydrogen bonds in the second coordination sphere of chelated amino acids with a free water molecule: Influence of complex charge and metal ion

Hydrogen bonds of glycine complexes were calculated using quantum chemistry calculations at M06L-GD3/def2- TZVPP level and by analyzing the crystal structures from the Cambridge Structural Database (CSD). One hydrogen bond where amino acid plays the role of the H-donor (NH/O), and two where it plays the role of the Hacceptor (O1/HO, O1 is a coordinated oxygen atom, and, O2/HO, O2 is a non-coordinated oxygen atom) were investigated. The calculations were done on octahedral nickel(II), square pyramidal copper(II), square planar copper(II), palladium(II), and platinum(II) glycine complexes with different charges adjusted using water(s) and/ or chlorine ion(s) as the remaining ligands. For NH/O hydrogen bond, interaction energies of neutral complexes are the weakest, from - 5.2 to - 7.2 kcal/mol for neutral, stronger for singly positive, from - 8.3 to - 12.1 kcal/ mol, and the strongest for doubly positive complex, - 16.9 kcal/mol. For O1/HO and O2/HO interactions, neutral complexes have weaker interaction energies (from - 2.2 to - 5.1 kcal/mol for O1/HO, and from - 3.7 to - 5.0 kcal/mol for O2/HO), than for singly negative complexes (from - 6.9 to - 8.2 kcal/mol for O1/HO, and from - 8.0 to - 9.0 kcal/mol for O2/HO). Additionally to the complex charge, metal oxidation number, coordination number, and metal atomic number also influence the hydrogen bond strength, however, the influence is smaller.