Theoretical and experimental characterization of a novel pyridine benzimidazole: suitability for fluorescence staining in cells and antimicrobial properties

Abstract

Benzimidazoles presenting intramolecular hydrogen bonding interactions have been normally used to better understand the role of H-bonding in biological processes. Here, we present an experimental and theoretical study of a new compound [2,4-di-tert-butyl-6-(3H-imidazo[4,5-c]pyridine-2-yl)phenol]; (B2), a benzimidazole derivate, exhibiting an intramolecular hydrogen bond. B2 was synthesized and characterized by its ¹H, HHCOSY, FT-IR and mass spectra (EI-MS 323 M⁺). The electronic and optical properties of B2 were studied with theoretical calculations using density functional theory (DFT) and time-dependent DFT (TDDFT). B2 showed luminescent emission at room temperature in different solvents, with a large Stokes shift (e.g.; λ_ex = 335 nm; λ_em = 510 nm in acetonitrile). Also, the quantum yield (φ = 0.21) and theoretical band emission are reported. We found that B2 exhibited a fluorescence emission at around 500 nm in ethanol and in acetonitrile that could be quenched by aqueous solutions of Hg(NO₃)₂ in the range of micro molar concentrations. Cyclic voltammetry in acetonitrile showed a strong anodic response due to a quasireversible process, with reduction and oxidation waves at −1.28 and −0.47 V vs. SCE. Regarding the biological properties, we assessed the antimicrobial activity of B2 in Salmonella enterica (bacteria), Cryptococcus spp. (yeast), Candida albicans (yeast), Candida tropicalis (yeast) and Botrytis cinerea (mold). To this end, we determined the minimal inhibitory concentration (MIC) (for bacteria and yeasts), the growth inhibition halos (for yeasts), and the inhibition of mycelial growth (for the mold). We observed that B2 exerted an antifungal effect against Cryptococcus spp. and Botrytis cinerea. In addition, due to its fluorescence properties, B2 has proven to be a suitable marker to observe bacteria (Salmonella enterica and an Escherichia coli derivative), yeasts (Candida albicans), and even human cells (SKOV-3 and HEK-293) by confocal microscopy.