Experimental Raman, FTIR and UV-Vis Spectra, DFT Studies of Molecular Structures and Conformations, Barrier Heights Against Internal Rotations, Thermodynamic Functions and Bioactivity of Biologically Active Compound - Isorhamnetin

Abstract

Molecular structural, conformational and spectroscopic investigations on the isorhamnetin molecule have been carried out at the B3LYP/6-311++G(d,p) level. Experimental FTIR, Raman and UV–vis spectra have been recorded and analyzed in light of the computed quantities and potential energy distributions (PEDs). In addition, MEP, Iso-surface plot of ESP and HOMO-LUMO energies, the barrier heights for the internal rotations about different axes and different thermodynamic functions were computed. Moreover, the wavefunction properties like reduced density gradient and electron localization function were computed. To investigate the biological properties, the bioactivity scores were computed and the molecular docking was also performed. The planarity of the flavone skeleton was stabilized by intramolecular interactions of O₁₆.H₂₄, and O₂₆…H₂₂. The barrier heights for bound OH tops were three times than the free OH tops. The bond length of the C-C linkage was found to be the longest among all the C-C bonds. Out of 99 normal modes, only 66 normal modes were seen to be conformer dependent. The sites near the H and O-atoms of free OH groups are more effective for nucleophilic and electrophilic attacks. The HOMO-LUMO analysis suggests that the molecule is chemically soft. From the observed UV-Vis spectral analysis bathochromic shift was noticed. Thermodynamic functions varied non-linearly with temperature. The bioactivity scores and molecular docking suggest that the molecule is a bioactive molecule. The results of the present investigations made on the isorhamnetin molecule are reported for the first time.

Keywords:

• Vibrational spectra
• DFT
• conformers
• thermodynamics and barrier height

Acknowledgements

The author(s) are grateful to Dr. V. G. Sathe, the in-charge of the Raman Spectrometer the facility, UGC-DAE Consortium for Scientific Research Centre, Indore (India) to allow us to use the Raman Spectrometer for the measurements of the Raman spectrum. The authors are also thankful to the Head, Department of Physics, I. Sc., Banaras Hindu University for permission to use Raman and FTIR facilities.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

RKY is grateful to the UGC, India for the financial support in the form of fellowships. BY is grateful to the BHU-UGC Non-NET fellowship and IoE (R/Dev/D/IoE/2022-23/Incentive to Res. Scholar/51476) BHU for the financial support.