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Vibrational spectra and density functional theoretical calculations on the antitumor drug, plumbagin
Author(s) -
Sajan D.,
Laladhas K. P.,
Joe I. Hubert,
Jayakumar V. S.
Publication year - 2005
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.1398
Subject(s) - chemistry , density functional theory , raman spectroscopy , hydrogen bond , hydrogen atom , computational chemistry , molecular vibration , photochemistry , crystallography , molecule , organic chemistry , group (periodic table) , physics , optics
Plumbagin is a potential toxic antitumor drug extracted from Plumbago rosea . Vibrational spectral analysis of plumbagin is carried out using NIR‐FT Raman and FT‐IR spectra. The DFT computations are also performed at B3LYP/6‐31G (d,p) level to derive equilibrium geometry, vibrational wavenumbers, intensities and atomic charges. Optimized geometry reveals that the contraction of C 12 O 16 and C 13 C 14 bonds is due to the increase in the electron donating ability of the CH 3 group. Vibrational analysis is used to investigate the electronic effects of hyperconjugation and induction of the methyl group with the π orbital of an aromatic ring system and resulting increase of stretching mode wavenumbers and decrease of infrared intensities. The splitting of the carbonyl modes might be attributed to structural and functional asymmetry in the carbonyl groups and intermolecular association based on CO···H‐type hydrogen bonding in the molecule. In a hydrogen‐bonded carbonyl, resonance can occur, which puts a partial negative charge on the oxygen atom accepting the hydrogen bond and a positive charge on the atom donating the hydrogen. The resulting partial ‘transfer of allegiance’ of the proton enhances resonance and lowers the C 15 O 19 stretching wavenumber. It is inferred that this mechanism plays an important role in the biological activity of PLBN. Condensation of the two ring systems disturbs the benzene ring slightly, which gives rise to a shift in those modes to the lower wavenumbers. Copyright © 2005 John Wiley & Sons, Ltd.