Experimental and theoretical investigations on the antioxidant activity of isoorientin from Crotalaria globosa

• Quantification of ethanol extract of leaves shows high TPC and TFC than root.
• DPPH, FRAP and NOS assays are analyzed and compared.
• Presence of isoorientin is confirmed by isolation and spectroscopic techniques.
• BDE, IP, MSD, FMOs and MEP analysis are carried out by DFT method and compared.
• Reverse behavior of MSD due to presence of C6 glycoside in isoorientin.

The increasing interests in naturally occurring flavonoids are well known for their bioactivity as antioxidants. The present investigations with combined experimental and theoretical methods are employed to determine the radical scavenging activity and phytochemicals present in Crotalaria globosa, a novel plant source. Preliminary quantification of ethanolic extract of leaves shows high phenolic and flavonoid content than root extract; also it is validated through DPPH assay. Further analysis is carried out with successive extracts of leaves of varying polarity of solvents. In DPPH and FRAP assays, ethyl acetate fraction (EtOAc) exhibit higher scavenging activity followed by ethanol fraction (EtOH) whereas in NOS assay ethanol fraction is slightly predominant over the EtOAc fraction. The LC–MS analysis provides tentative information about the presence of flavonoid C-glycoside in EtOAc fraction (yellow solid). Presence of flavonoid isorientin has been confirmed through isolation (PTLC) and detected by spectroscopy methods (UV–visible and 1H NMR). Utilizing B3LYP/6-311G (d,p) level of theory the structure and reactivity of flavonoid isoorientin theoretically have been explored. The analysis of the theoretical Bond dissociation energy values, for all OH sites of isoorientin reveals that minimum energy is required to dissociate H-atom from B-ring than A and C-rings. In order to validate the antioxidant characteristics of isoorientin the relevant molecular descriptors IP, HOMO–LUMO, Mulliken spin density analysis and molecular electrostatic potential surfaces have been computed and interpreted. From experimental and theoretical results, it is proved that isoorientin can act as potent antiradical scavenger in oxidative system.

The present study is employed to demonstrate the antioxidant activity of isoorientin present in C. globosa, a novel plant source. Enrichment of polyphenolics and flavonoid in leaves extract can be validated through quantification. Comparison of DPPH, FRAP and NOS assay are carried out for different fractions of leaves extract. Presence of a C-glycoside flavone (isoorientin) in EtOAc fraction has been confirmed by isolation (PTLC) and spectroscopic (UV–visible and 1H NMR) techniques. To emphasize, the radical scavenging activity of isoorientin has been computed with aid of DFT model chemistry. BDE, IP values and other relevant molecular descriptor FMOs (frontier molecular orbital), Mulliken spin density distribution (MSD) and molecular electrostatic potential maps for neutral and radical species are compared and analyzed respectively.Figure optionsDownload as PowerPoint slide