Astaxanthin diferulate as a bifunctional antioxidant

Abstract

Astaxanthin when esterified with ferulic acid is better singlet oxygen quencher with k2 = (1.58 ± 0.1) 1010 L mol− 1s− 1 in ethanol at 25°C compared with astaxanthin with k2 = (1.12 ± 0.01) 109 L mol− 1s− 1. The ferulate moiety in the astaxanthin diester is a better radical scavenger than free ferulic acid as seen from the rate constant of scavenging of 1-hydroxyethyl radicals in ethanol at 25°C with a second-order rate constant of (1.68 ± 0.1) 108 L mol− 1s− 1 compared with (1.60 ± 0.03) 107 L mol− 1s− 1 for the astaxanthin:ferulic acid mixture, 1:2 equivalents. The mutual enhancement of antioxidant activity for the newly synthetized astaxanthin diferulate becoming a bifunctional antioxidant is rationalized according to a two-dimensional classification plot for electron donation and electron acceptance capability.