Ionisation spectroscopic effects

Spectroscopic studies have shown that the chromophoric system of the coenzyme absorbs at 390 nm, in a region clearly separated from the 280 nm peak of the protein moiety. This feature has been exploited for a variety of structural and kinetic studies (31,34,90]. Pyridoxal phosphate, whether in its free form or when bound in the binary or ternary complexes, can exist, depending upon the pH, in a number of ionised states dictated by the pAT values for the various ionisable groups within the molecule. Metzler and coworkers [91] have ascertained spectrophotometrically the pA gS for 3-hydroxypyridine (pAT 5.1, 8.6) and lV-methyl-3-hydroxypyridine (pAT 4.96) and concluded the pAT, of the 3-hydroxy function to be 5.1 and the pyridinium nitrogen to be 8.6 (Fig. 40). This information allows one to interpret the pAT values of 3.1 and 8.3 obtained by Morozov et al. [92] for pyridoxal, as those corresponding to the 3-hydroxy and N-1 groups respectively (Fig. 41). It was noted [92] that the presence of a 5 -phosphate group on pyridoxal had practically no effect on the shape, half-width, or position of the absorption bands and hence pAf s as noted above. 

Polymer Science Series A 35, No.3, March 1993, p.311-4 IR SPECTROSCOPIC STUDY OF THE EFFECT OF IONISING IRRADIATION ON THE STRUCTURE OF POLYACRYLONITRILE Platonova N V Klimenko I B Maiburov S P St.Petersburg,Textile Light Industry Institute... 

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