Combined infrared spectroscopic and computational study on simpler capsaicin derivatives and their anion intermediates in the scavenging of free radicals

Abstract Two capsaicin analogues – N-(4-hydroxy-3-methoxybenzyl)acetamide and N-(4-hydroxy-3-methoxybenzyl)benzamide, were studied by DFT methods in order to estimate their ability to act as antioxidants. A comparative study on the stability of benzylic, phenoxyl and amide radicals has outlined the most reactive site for hydrogen atom abstraction and proton transfer. The enthalpies related to the formation of those species were modeled in gas phase, benzene, DMSO and water in order to determine the most probable mechanism of antioxidant action in polar and nonpolar medium. The formation of phenoxyl anion, energetically favoured in polar medium, was investigated by infrared spectroscopy methods based on the conversion of the benzamide derivative.