Spectral characterization, antibacterial and antioxidant activity of 2-(5-bromo-1H-benzimidazol-2-yl)-(3’/4’/5’-substituted)phenols and some transition metal complexes

Abstract

2-(5-Bromo-1H-benzimidazol-2-yl)-3'/4'/5'-substituted-phenols (HL1 – HL25) were synthesized and characterized using various spectroscopic techniques. Then, Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Ru(III) complexes of 2-(5-bromo-1H-benzimidazol-2-yl)phenol (HL1) were prepared and the methods such as elemental analysis, thermogravimetric analysis (TGA), molar conductivity and magnetic moment measurements, FT-IR, fluorescence and NMR spectroscopy were used to make suggestions about structures of the complexes. It is interesting that the compounds HL12 and HL22 showed stronger fluorescence effects than the others. The common feature of these two compounds is that they have a fluorine substituent at the 4'-position on the phenol ring. In addition, antioxidant and antibacterial activity of the compounds were investigated. The first three compounds showing the best antioxidant activity are HL25 (trihydroxy derivative: 4-(5-bromo-1H-benzimidazol-2-yl)benzene-1,2,3-triol), HL8 (2,5-dihydroxy derivative) and HL6 (2,3-dihydroxy derivative). It was observed that HL25 showed higher antioxidant activity than the reference substances 3,5-di-tert-4-butylhydroxytoluene (BHT) and Trolox both in terms of 1,1-diphenyl-2-picrylhydrazyl radical (DPPH•) scavenging (0.0018 mg/mL) and ferric reducing / antioxidant power (FRAP) methods {trolox equivalent antioxidant capacity (TEAC) value: 1564.44±1.92}. The second and third hydroxy groups added to HL1 appear to significantly increase the antioxidant activity. It was determined that complexes of HL1 showed much better antioxidant effect with respect to HL1. The derivatives with the highest antibacterial effect were found to be HL14 (nitro derivative), HL8, HL6 and HL25 having moderate activity. The high levels of both antioxidant and antibacterial activities of HL6, HL8 and HL25 indicate a correlation between their antibacterial and antioxidant effects. It was observed that the Ru(III) and Co(II) complexes showed moderate antibacterial activity whereas the ligand was inactive.