Normal coordinate analysis and vibrational spectroscopy (FT-IR and FT-Raman) studies of (2S)-2-amino-3-(3,4-dihydroxyphenyl)-2-methylpropanoic acid using ab initio HF and DFT method

The FT-IR and FT-Raman spectra of (2S)-2-amino-3-(3,4-dihydroxyphenyl)-2-methylpropanoic acid (2ADMA) were recorded in the region 4000–400 cm−1 and 4000–100 cm−1, respectively. The geometrical structure, harmonic vibrational frequency, infrared intensity, Raman activities and bonding features of this compound was carried out by ab initio HF and DFT methods with 6-31G (d,p) basis set. The complete vibrational frequency assignments were made by normal coordinate analysis (NCA) following the scaled quantum mechanical force field methodology (SQMF). The electric dipole moment (μ) and the first-order hyperpolarizability (β0) values have been the computed quantum mechanically. The calculated HOMO and LUMO energies show that, the charge transfer occurs within the molecule. The charge delocalizations of these molecules have been analyzed using NBO analysis. The solvent effects have been calculated using TD-DFT in combination with the polarized continuum model (PCM), and the results are in good agreement with experimental measurements. The other molecular properties like Mulliken population analysis, electrostatic potential (ESP) and thermodynamic properties of the title compound at the different temperatures have been calculated. Finally, the calculation results were applied to simulate infrared and Raman spectra of the title compound which shows good agreement with observed spectra.

In this work, the complete vibrational assignments with PED were calculated using NCA calculation. NLO and NBO properties of 2ADMA were performed by DFT with 6-31G (d,p) basis set. Electronic transition within molecule and HOMO and LUMO energy of 2ADMA were studied. MEP map shows that the negative potential sites (red and yellow) are electronegative oxygen atoms, while the positive potential sites (blue) are around the hydrogen atoms. Thermodynamics properties of the title compound were calculated at the different temperatures.Figure optionsDownload as PowerPoint slideHighlights
► Vibrational assignments with PED of 2ADMA were calculated.
► A thermodynamics property of the title compound was calculated at the different temperatures.
► MEP, NLO, NBO and HOMO and LUMO energies of 2ADMA were studied.