Antioxidant behavior of mearnsetin and myricetin flavonoid compounds — A DFT study

The molecular characteristics of two naturally occurring flavonoid compounds mearnsetin and myricetin have been computed using density functional theory (DFT) approach with B3LYP/6-311G(d,p) level of theory. The computation and analysis of bond dissociation enthalpy magnitudes for all the OH sites for both the compounds clearly denotes the contribution of the B-ring for the antioxidant activity. The analysis has also indicated the higher values of BDE on the C5-OH radical species in both the compounds. The computed vibrational frequency analysis indicates the absence of imaginary frequency in the neutral as well as radical species of both the flavonoid compounds. The ionisation potential (IP) analysis was found to be within the range of the IP of synthetic food additives. In addition, various molecular descriptors such as electron affinity, hardness, softness, electronegativity, electrophilic index have also been calculated and the validity of Koopman's theorem is verified. The plot of frontier molecular orbital and spin density distribution analysis for neutral and the corresponding radical species for both the compounds have been computed and interpreted. The polar nature and their polarizing capacity are well established through the analysis of dipole moment and polarisability magnitudes.

Graphical abstractThe present investigation aims to compute the relevant electronic properties through DFT model chemistry with the purpose of generating accurate information which enables to have a better understanding of the antioxidant behavior exhibited by mearnsetin and myricetin flavonoid compounds. To enlighten the competence of their antioxidant activity, the OH BDE and other electronic properties together with HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) energies, ionization potential (IP), electron affinity (EA), hardness, softness, electronegativity and electrophilicity index have been elucidated and the validity of Koopman's theorem is also verified. Electronic structures along with spin density distribution of neutral and radical species have also been presented. The computed molecular descriptor values are compared and analyzed with reference to quercetin flavonoid compound.Mearnsetin neutral HOMO/LUMO compositions.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The reactivity of the B-ring is high for both mearnsetin and myricetin flavonoid compounds. ► The BDE values are found to be low for C3′-OH and C4′-OH radical species of both the flavonoid compounds. ► The BDE values of C5-OH radical species are found to be high for both the cases. ► The IP values are almost similar with that of synthetic food additives.