Kinetics of DPPH • scavenging by bacterioruberin from Haloferax alexandrinus GUSF-1 (KF796625)

This is the first account of the kinetics of free radical scavenging by bacterioruberin obtained from cells of Haloferax alexandrinus GUSF-1(KF796625), grown at optimum conditions of 25% NaCl, pH 7, 42 °C, 150 rpm in NaCl Tryptone yeast extract medium and light. Bacterioruberin separated from methanolic extract displayed characteristics absorption peaks at 368, 386, 463, 492 and 525 nm and gave an m / z value of 740.4 (C 50 H 76 O 4 ) in Liquid Chromatography-Mass Spectroscopy validating its purity. Bacterioruberin (13 µM) decolorized and decayed 0.2 mM 1,1-diphenyl-2-picrylhydrazyl radicals (DPPH • ) monitored at 517 nm and reached a steady state within 30 min. An EC 50 of 6.50 µM ± 0.27 (4.81 µg/mL ± 0.2) was deduced for the 0.2 mM DPPH • -bacterioruberin reaction using the GraphPad Prism 9 statistical software and employing the right-angled triangle technique. The study also revealed a comprehensive information of the total kinetic activity of bacterioruberin with DPPH • : the antioxidant activity index was 16.38 ± 0.67; time needed to reach the steady state with the added EC 50 —30 min; the antiradical power 30.77 ± 1.27 and the antiradical efficiency of 54.7 × 10 –3 ± 2.24, thus reflecting the strong antioxidant nature of bacterioruberin. Scavenging of DPPH • by bacterioruberin was a pseudo-first-order reaction with a rate constant k 2 of 2.76 × 10 –5 ± 0.001 µM −1 s −1 calculated at t = 0 or initial time and t = 30 min. The knowledge of the kinetics of bacterioruberin to scavenge DPPH • adds to its effective application as an antioxidant in medicinal use, pharmaceutical products and others. Additionally, the use of simple conventional method of DPPH • free radical scavenging, monitored using an easily available laboratory spectrophotometer, will certainly help in the effective use of any antioxidant compound.