DFT based relaxed PES scan studies and SERS of anti cancer drug, Combretastatin A-4

Combretastatin A-4 (CA4) has recently evolved as a potential anti cancer drug, which selectively kills the cancer cells leaving the healthy cells unaffected. Density functional theoretical computations are performed at B3LYP/6-31G (d) level to derive the optimized geometry and vibrational spectrum of CA4. The steric interaction resulting in the twisting of phenyl ring with respect to the ethylene bridge is inferred from the optimized geometry. Also the conformations of methoxy groups attached to the phenyl ring are found out from the DFT geometry, which gives planar conformations for groups Me1, Me3 and Me4 while Me2 possesses perpendicular conformation. The potential energy surface scan studies have been performed to investigate the rotational stability of methoxy group Me2 and the effect of conjugation and steric interaction upon methoxy rotation. The optimum scaling factor for vibrational wavenumber has been found as 0.962798 using least square minimization technique. The scaled force field along with the SERS, normal Raman and FT IR spectral investigations have been performed to predict the adsorption geometry of the compound on the silver surface and the phenyl ring Ph2 is round to possess a Hat metal surface.