| Popis: |
The photohydration of N5− and N10− substituted alloxazinium cations is described. In dilute buffer the photoreaction of 1,3,5,7,8-pentamethyl-alloxazinium (5-PMA+) perchlorate appears to be much faster than the competing dark reaction, i.e. the N5 demethylation of 5-PMA+. Photohydration of 5-PMA+ in 1.0 mM phosphate buffer at pH 7 occurs at C9, whereas the yield of the C6OH isomer increases upon decreasing the pH. Irradiation of the N5−demethylated product of 5-PMA+, i.e. 1,3-dimethyllumichrome, in acidic aqueous solution yields both isomers in almost equal amounts. These findings are in contrast with the exclusive character of the photoaddition site observed in most of the (iso)alloxazines which have been investigated. The results of a flash photolysis study of 1,3,10-trimethylalloxazinium perchlorate are compared with those of previous work on lumichrome. |
