Optical and luminescent properties of vitamin B6 and its derivatives. IV. Pyridoxal and pyridoxal-5-phosphate. Absorption spectra
Morozov, I.V.; Bazhulina, N.P.; Cherkashina, L.P.; Karpeĭskiĭ, M.I.
Biofizika 12(3): 397-406
Studies were performed on the UV absorption spectra of pyridoxal-HCl (I) and pyridoxal-5'-phosphate (n) under different conditions of pH. A comparison of the spectra of the 2 compounds in the 250-450 [mu] range and at pH 3-13 showed that the phosphate group did not affect the absorbancy properties, nor did the ionization of the phosphate OH groups. However, changes in the absorption data may yield information on the ionization of the oxy group on the 3-carbon position, the nitrogen of the pyridine nucleus, and the OH group on the 4' position of the semiacetal. The formation of the semiacetals and hydrates is a nucleophilic addition reaction, catalyzed by the hydrogen ions.