Equilibria of complexes in the aqueous cobalt(II)–N-(2-hydroxybenzyl)phenylalanine system and their biological activity compared to analogous Schiff base structures

Due to their excellent prospects in biological applications, Schiff bases and their complexes are a source of continuing interest. The present study examines the formation of four cobalt(II) complexes with the reduced Schiff base N-(2-hydroxybenzyl)phenylalanine (PhAlaSal) in alkaline aqueous solution by pH-metry. UV–Vis and ESI–MS studies confirmed the model of proposed species. Kinetic analysis indicated that the single- and bi-ligand cobalt(II) complexes transitioned from octahedral to tetrahedral structures. The Schiff base and its complexes detected under physiological pH were tested for antimicrobial abilities and compared with analogous structures of the Schiff base derivative, N-(2-hydroxybenzyl)alanine (AlaSal). The ability of these structures to influence cell growth was tested on L929 mouse fibroblasts and on cervix and gastric adenocarcinoma cancer cell lines. N-(2-hydroxybenzyl)phenylalanine demonstrates greater antimicrobial efficacy than N-(2-hydroxybenzyl)alanine but also higher cytotoxicity; however, it is nonetheless effective against cancer cells. In turn, AlaSal demonstrates low cytotoxicity for fibroblasts and high cytotoxicity for gastric adenocarcinoma epithelial cells at bacteriostatic concentration for Helicobacter pylori and Candida strains. The presence of these microorganisms in the gastric milieu supports the development of gastritis and gastric cancer; AlaSal therapy may be simultaneously effective against both. Due to their cytotoxicity, Schiff base complexes are not suitable for use against fungal and bacterial infections, but may effectively prevent cancer cell growth. DATA AVAILABILITY: Data will be made available on request.