Valorization of Hesperidin from Citrus Residues: Evaluation of Microwave-Assisted Synthesis of Hesperidin-Mg Complex and Their Insecticidal Activity

The aim of the current study was the valorization of hesperidin, the dominant flavonoid in citrus processing waste, by microwave-assisted synthesis of hesperidin-Mg complex, improving its antioxidant activity and insecticidal potential. Here we show, for the first time, that microwave-assisted synthesis of [Mg(hesp)₂(phen)]OAc (1) (hesp: hesperidin, phen: phenanthroline) improve the reaction rate and yield. The nuclear magnetic resonance (NMR) experiments proved to be powerful tools for the identification of three isomers in metal complexes. Moreover, we explore the insecticidal potential of 1 and [Mg(phen)₂(Isov)]OAc (2) (Isov : isovanillic acid) complexes against three insects. Complex 1 killed 80% of adults whitefly at 0.14 μmol L^-1, and 2 76% at 0.36 μmol L^-1. There was a total mortality of Spodoptera frugiperda with 2 at 0.39 μmol L^-1, and 83% with 1 at 0.14 μmol L^-1. Both have similar activity, and represent a novel group of insecticide for Bemisia tabaci and S. frugiperda; nevertheless, the benefits of both as Myzus persicae repellent require further evaluation.

Keywords:
Citrus; citrus waste; hesperidin; magnesium; microwave