Evaluation of Free Radical Scavenging Ability of Triazole-3-Thiol: A Combination of Experimental and Theoretical Approaches

Abstract

An assessment of the free radical scavenging potential of 4-amino-5-phenyl-4H-1,2,4-triazole-3-thiol (AT) and 4-amino-5-(4-pyridyl)-4H-1,2,4-triazole-3-thiol (AP) involved a combination of experimental methodologies and theoretical calculations. In the 2,2-diphenyl-1-picrylhydrazyl (DPPH•) assay, AT exhibited an heightened efficacy in scavenging DPPH• radicals compared to AP. This was evidenced by the notably lower IC50DPPH value observed for AT (1.3 × 10–3 ± 0.2 × 10–3 M) in comparison to AP (2.2 × 10–3 ± 0.1 × 10–3 M). Similarly, in the 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonate) (ABTS• +) test, AT exhibited superior ability in neutralizing ABTS•+ free radical cations compared to AP, with the computed IC50ABTS values of 4.7 × 10–5 ± 0.1 × 10–5 M for AT and 5.5 × 10–5 ± 0.2 × 10–5 M for AP. Density functional theory served as the tool for evaluating the correlation between structural attributes and the antioxidant efficacy of the studied molecules. The findings highlighted the flexibility of hydrogen atoms within NH and NH2 groups to nucleophilic attacks, indicative of their pivotal role in the scavenging mechanism. Furthermore, investigations into the interactions between AT and AP with the free radical HOO• revealed predominantly the reaction via the hydrogen atom transfer mechanism. Both experimental observations and theoretical deductions collectively affirmed AT’s superior free radical scavenging ability over AP in the gas phase and ethanol.