Contribution of DFT computed molecular descriptors in the study of radical scavenging activity trend of natural hydroxybenzaldehydes and corresponding acids

Abstract

The present study focuses on the examination of the radical scavenging activity trend of some natural hydroxybenzaldehydes and their corresponding acids with the aid of DFT/B3LYP. Values of computed molecular descriptors (bond dissociation enthalpy, BDE; ionization potential, IP; proton affinity, PA; electron transfer energy, ETE) characterizing the hydrogen atom or electron donating efficiency of parent compounds and ions were discussed considering published experimental findings for the radical scavenging activity of the same compounds using various methods (Rancimat, crocin bleaching, trolox equivalent antioxidant capacity and 2,2-diphenyl-1-picrylhydrazyl assays). Calculations in the gas and/or liquid phase (benzene, methanol, water) were performed to approximate the activity in a lipid substrate or in solution. BDE values could predict the activity of the compounds when hydrogen atom transfer prevailed. Thus, protocatechuic (1) aldehyde, syringaldehyde (2) and their respective acids (1′, 2′) were predicted to be the most efficient hydrogen atom donors, in line with Rancimat data. In polar media, where electron donation should be favored for hydroxybenzaldehydes, experimental findings could not always be supported by molecular descriptors. Combined information from various descriptors, as shown for DPPH data, could justify the higher efficiency of 1 over that of 1′ and 2′. The results document further the use of computed molecular descriptors as a green tool that can facilitate antioxidant activity studies and selection of efficient antioxidants.