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Structural Study of Vitamin B1, B2 and B6 by NMR Spectroscopy and ab-initio Methods

Aghaee, Zahra | 2015

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 47113 (03)
  4. University: Sharif University of Technology
  5. Department: Chemistry
  6. Advisor(s): Tafazzoli, Mohsen
  7. Abstract:
  8. The structure and energy of vitamin B1 (Thiamine), vitamin B2 (Riboflavin) and vitamin B6 (Pyridoxine) have been studied employing quantum mechanical calculation, DFT methods at B3LYP level using 6-311+G* basis set. Values of the coupling constants involving carbon-hydrogen and hydrogen-hydrogen on the torsion angle α and β were theoretically calculated. All Karplus equations which represent the correlation between coupling constants 1JCH, 2JHH, 2JCH, 3JHH, 3JCH and proper dihedral angle have been yielded. The effect of three solvents, water, ethanol and carbon¬ tetrachloride with different polarity on coupling constants, energy and structural parameters were calculated employing PCM model. The simulation of the aqueous environment leads to the conclusion that solvent effects are substantial for the single bond coupling constants but negligible for three bond coupling constants. Increasing the polarity of the solvent, reduces the energy level and the maximum increment about 0.05 Hartree (30kcal/mol) in water have been observed. Solvent environment made changes about 0.01Å in bond length and maximum changes about one degree in bond angles. In experimental section, H-H and H-C coupling constants including 1JCH, 2JHH and 3JHH have been measured by two-dimensional NMR spectroscopy H-H COSY and HMQC spectra at 298K in DMSO for Riboflavin and the values 1JC27 H30 = 141.5 Hz, 2JH29 H30 =13.8 Hz and 3JH30 H32=3.9 Hz have been obtained. Maximum difference about 1 Hz have been observed comparing theoretical coupling constants 1JC27 H30 = 140.6 Hz, 2JH29 H30 =14.1 Hz and 3JH30 H32=4.7 Hz with experimental values. Good agreement between calculated and experimental coupling constants with maximum difference about 1.0 Hz revealed that DFT method was able to predict J-coupling in aqueous solution
  9. Keywords:
  10. Karplus Equation ; Spin-Spin Coupling ; Coupling Constant ; Nuclear Magnetic Resonance Spectroscopy ; B1 Vitamin ; B2 Vitamin ; B6 Vitamin

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