Abstract
This report highlights the synthesis and characterization of ten new bis(N‐picolinamido)cobalt(II) complexes of the type [(L)2CoX2]0/2+, whereby L=N‐picolinamide ligand and X=diisothiocyanato (−NCS), dichlorido (−Cl) or diaqua (−OH2) ligands. Single crystal X‐ray (SC‐XRD) analysis for nine of the structures are reported and confirm the picolinamide ligand is bound to the Co(II) center through a neutral N,O binding mode. With the addition of powder X‐ray diffraction (PXRD), we have confirmed the cis and trans ligand arrangements of each complex. All complexes were screened against several fungal species and show increased antifungal activity. Notably, these complexes had significant activity against strains of Candida albicans and Aspergillus fumigatus, with several compounds exhibiting growth inhibition of >80 %, and onecompound inhibiting Aspergillus fumigatus hyphal growth by >90 %. Conversely, no antifungal activity was exhibited toward Cryptococcus neoformans and no cytotoxicity towards mammalian cell lines.
Highlights
It is estimated that > 1.5 million deaths can be attributed to fungal infections annually.[1]
Synthesis of Co(II) complexes: The N-picolinamide ligands were synthesized via a known literature procedure from the condensation of picolinic acid with a functionalized aniline.[41]
The synthesis of the dichlorido analogue was only successful when no electron withdrawing groups were present on the aryl ring of the ligand, and this may be explained by the increased acidity of the amide proton when electron withdrawing groups are present
Summary
This article belongs to the joint Special Collection with the European Journal of Inorganic Chemistry, “Metals in Medicine”. G. Figure 1E),[31] have shown promising activity against a range of fungal species, with the majority of this research being conducted by Chohan and co-workers.[23,24,30,32,33,34] Other ligands which have been investigated, include; azoles,[32] cephalexins,[23] sulfonamides,[33] dithiones,[34] and thiolenes,[24] with complexes exhibiting a wide range of antimicrobial activities when bound to other transition metals. In 2012, Sathyadevi and co-workers studied two Co(II)hydrazone complexes (Figure 1F, R = phenyl (1F-a) or thiophenyl (1F-b)),[25] and reported that both complexes interact with Bovine Serum Albumin (BSA), with binding constants of 6.5 × MÀ 1 (1F-a) and 3.4 × MÀ 1 (1F-b), and the complexes display the ability to scavenge hydroxyl radicals These complexes were able to scavenge nitric oxide radicals, with antioxidant activity of the complexes ~ 5.8 × higher than the free ligand. The cytotoxicity of all complexes has been determined through screening against a range of human cell lines, bacterial species and fungal species
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