Exploring Zinc(II) Coordination Chemistry with Picolinate and Amino Alcohols: Toward New Antibacterial Agents.

Zinc-(II) coordination chemistry with picolinate (abbreviated as pic-, an anion of pyridine-2-carboxylic acid) and a series of β-amino alcohols (2-aminoethanol, 2-methylaminoethanol, 2-ethylaminoethanol, 2-dimethylaminoethanol, 2-amino-1-propanol, 1-amino-2-butanol, and 1-amino-2-methyl-2-propanol) was systematically investigated. Reaction systems typically yielded complexes with the general composition [Zn-(pic)2(amino alcohol)] via a straightforward synthetic route. Zinc-(II) adopts an octahedral coordination environment consisting of two N,O-bidentate chelating picolinates and one amino alcohol, likewise coordinated in a chelating manner through amino and hydroxyl groups. As no fac isomers were isolated, the relative stability of mer and fac isomers of the 2-methylaminoethanol complex was evaluated by DFT calculations, which supported a preference for the mer geometry. Interestingly, the 1-amino-2-methyl-2-propanol system also produced an ionic species, [Zn-(pic)3]-, which crystallized as a salt with protonated amino alcohol. All novel compounds were characterized using infrared and 1H NMR spectroscopy, elemental analysis, mass spectrometry, and single-crystal X-ray diffraction. Selected tris-chelates displayed moderate antibacterial activity against S. epidermidis, with MIC values ranging from 32 to 64 μg/mL, whereas picolinic acid alone was inactive.