Structural, Electronic, Topological and Vibrational Properties of Isomers of Thymidine ? A Study Combining Spectroscopic Data with DFT Calculations

MAXIMILIANO A. IRAMAIN; ANA E. LEDESMA; DAVIDE ROMANI; SILVIA A. BRANDÁN

International Journal of Science and Research Methodology

Human Journals

Año: 2017

2454-2008

In this work, the structural, electronic, topological and vibrational properties of six Cis and Trans isomers of Thymidine (THY) in gas and aqueous solution phases were studied combining the hybrid B3LYP/6-31G* method with the Polarized Continuum Model (PCM) model and the available experimental infrared, Raman, 1H-NMR, 13C-NMR and UV spectra. Hence, theoretical molecular structures of two Cis isomers and one Trans isomers of THY were determined in the two media for first time. The population analyses suggest the presence in solution of a Trans isomer and of two Cis isomers in accordance with the experimental structures reported by X-ray diffraction by different authors. The study of the charges show clearly the differences between the Cis and Trans isomers where the charges on the O atoms belonging to the ribose rings in all the structures, on the N atoms belonging to the glycosidic bond and on the two chiral C atoms show the higher modifications. The Molecular Electrostatic Potential (MEP) surface mapped evidence clearly that the group's acceptors of H bonds in all the isomers are the two C=O groups of the pyrimidine rings while the OH groups of the ribose rings and the NH group of the pyrimidine rings are donors of H bonds showing their surfaces colorations red and blue in those sites, respectively. Natural Bond Orbital (NBO) and Quantum Atoms in Molecules (QAIM) calculations clearly reveal the high stabilities of those three isomers of THY in both media. The frontier orbitals show that in gas phase the decreasing of the gap values are different than those in solution. The vibrational analyses show the presence of different isomers in both media and confirm that the different positions of the bands are characteristic of their different structures. Here, the 1H-NMR, 13C-NMR and UV spectra present a reasonable concordance with the corresponding experimental ones. Finally, the spectroscopic studies support the presence of more of an isomer of THY in solution.