Covalent Hydrates of Alloxazines
نویسنده
چکیده
In the course of a study on spectral behaviour of alloxazine and its methylated derivatives light absorption spectra and apparent pKa values of individual ionic species have been evaluated *. Alloxazine, lumichrome and 3-methyllumichrome in aqueous alkaline solutions undergo a slow base-catalysed reaction which manifests by evident changes in the light absorption spectra (Fig. 1), while 1-methyllumichrome is stable towards alkaline solutions. The pKa are 8.1 and 12.6 for alloxazine, 8.23 and 12.82 for lumichrome (7,8-dimethylalloxazine), 8.66 for 1-methyllumichrome and 8.71 for 3-methyllumichrome. The latter pK values are in good agreement with data obtained independently by MÜLLER and DUDLEY 1 . The reaction does not proceed in methanolic KOH or sodium methoxide. The position of equilibrium between alloxazine or lumichrome and their products depends on the base concentration. However, the equilibrium between 3-methyllumichrome and its product does not depend on the base concentration. The reactions are not reversed upon acidification of the reaction mixture. The reaction products have been isolated by means of preparative TLC on silicagel (they are more polar than the starting compounds) or continuous extraction of the starting materials with chloroform from the neutralised reaction mixtures.
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