Vibrational spectral analysis of anti-neurodegenerative drug Levodopa: A DFT study

► DFT calculations have been performed on the anti-neurodegenerative drug Levodopa. ► The IR and Raman spectra of the compound were recorded. ► Spectral assignments have been carried out with normal co-ordinate analysis. ► Red-shift of OH stretching band confirms OH⋯O intermolecular hydrogen bonding. ► NBO, Mulliken analyses and HOMO–LUMO plot suggests bioactivity. The Fourier transform Raman and infrared spectra of anti-neurodegenerative drug Levodopa (L-3,4-dihydroxy phenyl alanine) in crystalline form have been recorded and analyzed. The optimized geometry, intermolecular hydrogen bonding, and harmonic vibrational wavenumbers of Levodopa have been investigated with the help of B3LYP density functional theory method. The calculated molecular geometry has been compared with the experimental data. The assignments of the vibrational spectra have been carried out with the aid of normal co-ordinate analysis following the scaled quantum mechanical force field methodology. The strong doubly hydrogen bonded interface of the dimerized system is well demonstrated by the natural bond orbital analysis. The biological activity of substituents like carboxylic acid, hydroxyl groups of the catechol ring and amino group are evident from the hydrogen bonds through which the target amino acids are linked to the drug as evidenced from molecular docking.