N-Salicylideneaminoacidato copper(II) complexes as galactose oxidase model compounds

[CuL·B]^q model systems, where L²⁻ is the tridentate Schiff base ligand formed by the condensation of salicylaldehyde with alanine, B is imidazole, q=−1, 0 and +1, are optimized at B3LYP/6-31G* level of theory. Their electronic structure is described in terms of Mulliken population analysis and reactivity indices of Fukui. The total energy of [CuL·B]^q species increases with the electron removal. The reactivity indices suitable for the alcohol (sugar) adducts formation (CuO_sugar and O_phenoxylH_sugar interactions) are in the neutral molecule as well as in the singlet cation. Despite the similar trends in Cu–O_phenoxyl bonding and significant O_phenoxyl spin density in triplet cation, the catalytic mechanism of sugars oxidation proposed for the galactose oxidase cannot be used in our system because the [CuL·B]⁺ formation is energetically unfavorable. The imidazole nitrogen deprotonation is more probable than of the alanine ternary carbon atom.