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Antioxidant and Free Radicals Scavenging Activity of Biomolecules: Hydroxamic Acids

Oxidative stress is initiated by free radicals which seek stability through electron pairing with biological macromolecules such as proteins, lipids and DNA in healthy human cells and cause protein and DNA damage along with lipid peroxidation. Although human cells protect themselves against free radical damage but sometimes antioxidant supplements are required to combat this damage. Therefore, in the present study attention is focused towards the investigation of antioxidant agents.
N-arylhydroxamic acids are neutral polyfunctional molecules, with pharmacophoric functionality, -NOH.C=O in their structure. The antioxidant effect is due to the presence of hydroxyl group in their chemical moiety. The radical scavenging of five derivatives of hydroxamic acids is estimated following the DPPH (1, 1-diphenyl-2-picryl-hydrazyl) method. The method is based on the reduction of alcoholic DPPH solutions in presence of a hydrogen donating antioxidant, hydroxamic acids. DPPH solution shows a strong absorption band at 517 nm appearing a deep violet colour. The absorption vanishes and the resulting decolourisation is stoichiometric with respect to degree of reduction. The remaining DPPH, measured after a certain time, corresponds inversely to the radicals scavenging activity of the antioxidant. All experiments were performed at 517 nm using initial DPPH concentration, C0 =1.0 μM in ethanol. Molar absorptivity of DPPH free radicals εv = 86000 M-1 cm-1 was estimated from Lambert-Beer relation.
The results suggest that all the molecules posses potent antioxidant activity in the order, N-m-chloro-2-methoxybenzo-, (82.55%) > N-m- chloro-4-methoxybenzo-, (66.27%) > N-phenyl-4- ethoxybenzo-, (65.38%) > N-p-tolyl-4-ethoxybenzo-, (61.62 %) > N-o- tolyl-4-ethoxybenzo-, (29.06 %) hydroxamic acids. The antioxidant effect is concentration dependent and effective concentration, EC50 range is from 14 to 85.99 mM.