Benzimidazole‐based silver(I)–N‐heterocyclic carbene complexes as anti‐bacterials: synthesis, crystal structures and nucleic acids interaction studies

Abstract

A series of new benzimidazolium salts as N-heterocyclic carbene (NHC) precursors has been synthesized. Reactions of these salts with Ag 2 O with varying metal-to-salt ratio facilitate the formation of a series of new binuclear and mononuclear Ag(I)-NHC complexes. All compounds were characterized using physicochemical and spectroscopic techniques. Single-crystal X-ray diffraction study reveals a binuclear structure for one of the complexes and a mononuclear one for two others. These complexes exist as cationic Ag(I)-NHC complexes with the chelation of carbene carbons to the silver centre in an almost linear manner. The compounds were screened for their anti-bacterial activities against Staphylococcus aureus (ATCC 12600) as a Gram-positive bacterium and Escherichia coli (ATCC 25922) as a Gram-negative bacterium. The results show that both bacteria appear markedly inhibited. Furthermore, the results suggest the possibility of steric variation as a modulation of the anti-bacterial activities. The nuclease activities of the compounds were assessed using gel electrophoresis and the results indicate that these complexes can cleave or degrade DNA and RNA via a non-oxidative mechanism.

Steroid–AuI–NHC Complexes: Synthesis and Antibacterial Activity

“…[13] An analogous methodw as followed for the synthesis of [Au(MeMeOEtIm)Cl] (2)( MeMeOEtIm = 1-(2methoxyethyl)-3-methylimidazol-2-ylidene). On the other hand, 1 HNMR spectra of 5 and 6 are similart ot hose of 3 and 4,w ith the only exception that there is as ingle aromatic protoni nt he testosterone moiety at 5.71 ppm for both 5 and 6.A ll four complexes (3)(4)(5)(6) show severalm ultiplets in the region 2.50-0.90 ppm corresponding to the CH and CH 2 protons of the three rings of estradiol or testosterone. [14] Hereafter,t he resulting compound 2 was obtained as aw hite powder.…”

“…Modernv ariations of such complexes are closelyr elatedt oc utting-edge ligands in chemistry,a st hose based on N-heterocyclicc arbenes (NHCs). Thus, while Ag-NHC complexes exhibit excellent properties as antimicrobials, [4] antibacterials, [5] antibiotics, [6] or anticancer agents, [7] the antitumor activity of certain gold complexes, underpinned in many cases by the stabilityo ft heir Au I -NHC bonds, [8] has been the focus of numerousi nvestigations. The first report on antibacterial and antifungal properties of metal-NHC complexes dates from 1996, [2] and sincet hen, their use has become widespread.…”

“…To test the antimicrobial activity,t he carbene Au I precursors 1 and 2,t he four complexes bearinge strogens (3)(4)(5)(6), and the two pro-ligandse thynylestradiol (EE)a nd ethisterone (ES)w ere screened in in vitro antibacterialt ests against two bacterial strains: S. aureus (Gram positive) and E. coli (Gram negative). Activities as MIC 50 values are listed in Ta ble1,a nd are similar to those of previously reportedA u I -NHC complexes.…”

“…[3] In particular, the incorporation of NHCl igands to the bioactive silver and gold metals has opened up new possibilities for the design of novel compounds. Thus, while Ag-NHC complexes exhibit excellent properties as antimicrobials, [4] antibacterials, [5] antibiotics, [6] or anticancer agents, [7] the antitumor activity of certain gold complexes, underpinned in many cases by the stabilityo ft heir Au I -NHC bonds, [8] has been the focus of numerousi nvestigations. [7,9] Nevertheless,a lthough less common, there are an umber of NHC-based goldc ompounds that show antimicrobial activity.…”

Cobalt(II) Benzazole Derivative Complexes: Synthesis, Characterization, Antibacterial and Synergistic Activity

“…Meanwhile, Gram‐negative bacteria have a thin cell wall containing a limited number of peptidoglycan layers enclosed by the outer lipid membrane comprising lipopolysaccharides and lipoproteins. Therefore, different compounds have different susceptibility against Gram‐positive and Gram‐negative bacteria …”