Methyl-substituted 2-aminothiazole--based cobalt(II) and silver(I) complexes: synthesis, X-ray structures, and biological activities

Abstract

2-Aminothiazole derivatives bear three nucleophilic centers, i.e. endocyclic N, exocyclic NH$_{2}$, and S atom in the ring system. In addition to these centers there are $\pi$-electrons in the ring system which can also expectedly be involved in some sort of coordination. To the best of our knowledge the solid state coordination chemistry of such ligands has not been fully presented in the literature. These ligands (2-amino-4-methylthiazole and 2-amino-5-methylthiazole) were coupled with CoCl$_{2}$ under aerobic conditions to form tetrahedral complexes, bis(2-amino-4-methylthiazole)dichlorocobalt(II) (1) and bis(2-amino-5-methylthiazole)dichlorocobalt(II) (2). Reaction of 2-amino-5-methylthiazole with AgNO$_{3}$ led to an expected two-coordinated, bis(2-amino-5-methylthiazole)silver(I) nitrate (3) as crystalline material. In all complexes the coordination behavior of the aminothiazole derivatives was identical, coordinating to the metal center through endocyclic N atom. The structures of these complexes were confirmed by single-crystal X-ray analysis. Compounds (1-3) were screened for their antimicrobial potency against gram-negative (E. sakazkii, E. coli, K. pneumoniae) and a gram-positive bacteria (S. aurus). Additionally, their role as enzyme inhibitors (acetylcholinesterase, AChE, and butyrylcholinesterase, BChE) and their free radical scavenging ability (2,2-Diphenyl-1-picrylhydrazyl, DPPH, and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid, ABTS) were studied. These ligands bear additional nucleophilic centers (S and NH$_{2})$ and can be involved in secondary interactions as confirmed by their solid-state structures. These interactions make the molecules biologically important and thus play a pivotal role in establishing the supramolecular network. We report here the coordination chemistry and selected biological applications of complexes 1-3.