Oxidatively Locked Co2L36+ Cylinders Derived from Bis(bidentate) 2-Pyridyl-123-triazole Click Ligands: Synthesis Stability and Antimicrobial Studies

摘要

A small family of [Co2(>Lpytrz)3]⁶⁺ cylinders was synthesised from bis(bidentate) 2-pyridyl-1,2,3-triazole “click” ligands (>Lpytrz) through an “assembly-followed-by-oxidation” method. The cylinders were characterised using ¹H, ¹³C, and DOSY NMR, IR, and UV-Vis spectroscopies, along with electrospray ionisation mass spectrometry (ESMS). Stability studies were conducted in dimethyl sulfoxide (DMSO) and D2O. In contrast to similar, previously studied, [Fe2(>Lpytrz)3]⁴⁺ helicates the more kinetically inert [Co2(>Lpytrz)3]⁶⁺ systems proved stable (over a period of days) when exposed to DMSO and were even more stable in D2O. The triply stranded [Co2(>Lpytrz)3]⁶⁺ systems and the corresponding “free” ligands were tested for antimicrobial activity in vitro against both Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) microorganisms. Agar-based disk diffusion and Mueller–Hinton broth micro-dilution assays showed that the [Co2(>L_pytrz)₃]⁶⁺ cylinders were not active against either strain of bacteria. It is presumed that a high charge of the [Co₂(>L_pytrz)₃]⁶⁺ cylinders is preventing them from crossing the bacterial cell membranes, rendering the compounds biologically inactive.