Ionization of vitamin B6 in the gas phase and water: Theoretical study

Abstract

Abstract In the present work, the ionization energies and photoelectron spectra of conformers of vitamin B6 in pyridoxine and pyridoxal phosphate forms were calculated in both gas phase and water, separately. To investigate the effect of water on the ionization of B6 molecule, the solvent was modeled in two different ways, separately, as ( a ) only the electrostatic field of solvent was considered on the B6 molecule ( b ) considering the explicit effects of solvent molecules as well as their electrostatic field. The ionization bands were calculated using general-R symmetry adapted cluster-configuration interaction (general-R-SAC-CI) methodology and D95 (df,pd) basis set. The photoelectron spectrum of each conformer, calculated in water, was compared with its gas phase photoelectron spectrum to explore the effect of solvent on the ionization of conformer. The effect of the solvent on the assignment of the ionization bands of each conformer was also studied. It was found that the direct interaction of water molecules with each conformer created considerable changes in its ionization energies, photoelectron spectrum and the assignment of its ionization bands compared to the gas phase and when the electrostatic field of solvent was only considered. The effect of the presence of phosphate group on the ionization of vitamin B6 was also discussed.