DFT studies on antioxidant mechanisms, electronic properties, spectroscopic (FT-IR and UV) and NBO analysis of C-glycosyl flavone, an isoorientin

• The order of reactivity of BDEs of OH groups is similar in all phases.
• High reactivity of B-ring in isoorientin is verified by three mechanisms.
• Theoretical vibrational assignments are good accordance with recorded spectrum.
• In NBO analysis, π∗–π∗ interaction afford more stabilization energy to molecule.

The relationship between structure and electronic properties of isoorientin, a C-glycoside flavone is investigated to relate its radical scavenging activity using molecular descriptors. To elucidate the antioxidant activity of polyphenolics, three mechanisms namely hydrogen atom transfer (HAT), single electron transfer–proton transfer (SET–PT) and sequential proton-loss electron-transfer (SPLET) are employed. In gas-phase, OH bond dissociation enthalpies (BDE), ionization potential (IP), proton dissociation enthalpies (PDE), proton affinity (PA) and electron transfer enthalpy (ETE) are computed and correlated relevant to antioxidant potency of the title compound employing DFT/6-311G(d,p) protocol. The theoretically simulated FT-IR and the UV–visible absorption spectra have been compared with the experimental data. Based on the absorbed UV spectra and TD-DFT calculations, assignment of the absorption bands are carried out. In addition, formation of intramolecular hydrogen bond and most possible interaction sites are explained by using natural bond orbital (NBO) analysis.

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