Investigations of vibrational frequencies and modes of pyridoxine and trimethoprim molecules and conformational analysis by ab-initio HF and density functional theory (DFT) methods

Pyridoxine is one of the naturally occurring forms of vitamin B6. Pyridoxine is essential for the absorption and metabolism of amino acids. It is a coenzyme that acts with other enzymes, in a lot of chemical processes in the body. It is necessary for proteins metabolism, for the body to convert fats to energy, to improve circulation by lowering the levels of homocysteine. Lack of pyridoxine may cause anemia, nerve damage, seizures, skin problems, and sores in the mouth. Trimethoprim eliminates bacteria that cause urinary tract infections. It is used to treat bacterial infections and diarrhea. In this thesis, the possible stable conformers of free molecule were searched by means of potential energy surfaces scan studies through four dihedral angles for pyridoxine and five dihedral angles for trimethoprim. The lowest energy geometry, vibrational frequencies and modes of pyridoxine and trimethoprim were calculated by using Gaussian 09 software with Ab-Initio HF/6-311++G(d,p) and DFT/B3LYP/6-311++G(d,p) level of theory. The harmonic and anharmonic vibrational wavenumbers and IR intensities were calculated at the same theory levels used in geometry optimizations. In order to investigate the hydrogen bonding interaction of pyridoxine and trimethopim, hydrogen bonded complexes of the molecules were studied by DFT/B3LYP/6-311G++(d,p) level of theory. In the experimental part of this study, Bruker Tensor FT-IR spectrometer and Bruker MultiRam FT-Raman spectrometer were used to determine the experimental vibrational spectra of the molecules. The experimental wavenumbers were compared with those of calculated.