title: Investigation of solvent polarity effect on molecular structure and vibrational spectrum of xanthine with the aid of quantum chemical computations.
abstract: The main scope of this study is to determine the effects of 8 solvents on the geometric structure and vibrational spectra of the title compound, xanthine, by means of the DFT/B3LYP level of theory in the combination with the polarizable conductor continuum model (CPCM) for the first time. After determination of the most-steady state (favored structure) of the xanthine molecule, the role of the solvent polarity on the SCF energy (for the molecule stability), atomic charges (for charge distribution) and dipole moments (for molecular charge transfer) belonging to tautomer is discussed in detail. The results obtained indicate not only the presence of the hydrogen bonding and strong intra-molecular charge transfer (ICT) in the compound but the increment of the molecule stability with the solvent polarity, as well. Moreover, it is noted that the optimized geometric parameters and the theoretical vibrational frequencies are in good agreement with the available experimental results found in the literature. In fact, the correlations between the experimental and theoretical findings for the molecular structures improve with the enhancement of the solvent polarity. At the same time, the dimer forms of the xanthine compound are simulated to describe the effect of intermolecular hydrogen bonding on the molecular geometry and vibrational frequencies. It is found that the CO and NH stretching vibrations shift regularly to lower frequency value with higher IR intensity as the dielectric medium enhances systematically due to the intermolecular NH⋯O hydrogen bonds. Theoretical vibrational spectra are also assigned based on the potential energy distribution (PED) using the VEDA 4 program.
authors.affiliation: Kastamonu University, Department of Physics, Kastamonu 37100, Turkey. Electronic address: tpolat@kastamonu.edu.tr.
authors.forename: Turgay
authors.initials: T
authors.lastname: Polat
authors.affiliation: Abant Izzet Baysal University, Department of Mechanical Engineering, Bolu 14280, Turkey.
authors.forename: Gurcan
authors.initials: G
authors.lastname: Yıldırım
mesh_terms: D006860:Hydrogen Bonding; D008958:Models, Molecular; D011789:Quantum Theory; D017550:Spectroscopy, Fourier Transform Infrared; D013237:Stereoisomerism; D019820:Xanthine / Q000737:chemistry*
chemical_list: D019820:Xanthine
keywords: Density functional theory; Hydrogen bonding; Infrared spectroscopy; Solvent effect; Tautomerism; Xanthine