title: Analysis of vibrational spectra of L-alanylglycine based on density functional theory calculations.
abstract: FT Raman and IR spectra of the crystallized biologically active molecule, L-alanylglycine (L-Ala-Gly) have been recorded and analyzed. The equilibrium geometry, bonding features and harmonic vibrational frequencies of L-Ala-Gly have been investigated with the help of B3LYP density functional theory (DFT) method. The calculated molecular geometry has been compared with the experimental data. The assignments of the vibrational spectra have been carried out with the help of normal coordinate analysis (NCA) following the scaled quantum mechanical force field methodology (SQMFF). The optimized geometry shows the non-planarity of the peptide group of the molecule. Potential energy surface (PES) scan studies has also been carried out by ab initio calculations with B3LYP/6-311+G** basis set. The red shifting of NH3+ stretching wavenumber indicates the formation of N-H...O hydrogen bonding. The change in electron density (ED) in the sigma* antibonding orbitals and E2 energies have been calculated by natural bond orbital analysis (NBO) using DFT method. The NBO analysis confirms the occurrence of strong intermolecular hydrogen bonding in the molecule.
authors.affiliation: Centre for Molecular and Biophysics Research, Department of Physics, Mar Ivanios College, Thiruvananthapuram 695 015, Kerala, India.
authors.forename: L
authors.initials: L
authors.lastname: Padmaja
authors.forename: C
authors.initials: C
authors.lastname: Ravikumar
authors.forename: C
authors.initials: C
authors.lastname: James
authors.forename: V S
authors.initials: VS
authors.lastname: Jayakumar
authors.forename: I
authors.initials: I
authors.lastname: Hubert Joe
mesh_terms: D002264:Carboxylic Acids / Q000737:chemistry; D019281:Dimerization; D004151:Dipeptides / Q000737:chemistry*; D004583:Electrons; D006860:Hydrogen Bonding; D008958:Models, Molecular; D008968:Molecular Conformation; D016011:Normal Distribution; D012984:Software; D013053:Spectrophotometry / Q000379:methods; D017550:Spectroscopy, Fourier Transform Infrared; D013059:Spectrum Analysis, Raman / Q000379:methods; D014732:Vibration
chemical_list: D002264:Carboxylic Acids; D004151:Dipeptides; C028872:alanylglycine