Photonics of UO2+2 complexes with tryptophan: 3. Oxidation of tryptophan photocatalyzed by UO2+2 ions

Intraspheric oxidation of tryptophan (Trp) photocatalyzed by UO 2 2+ ions was studied by luminescence spectroscopy. The photocatalytic effect of uranyl ion is cased by stabilization of charge separation in the complex [UO 2 2+ ⋯ $$Trp^{\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\cdot}$}}{ + } } $$ ], which increases the probability of electron transfer from uranyl ion to the oxygen to form superoxide ion O 2 − . This anion reacts with $$Trp^{\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle\cdot}$}}{ + } } $$ radical cation to form N-formylkynurenine and kynurenine. The excitation and fluorescence spectra of the oxidation products of Trp showed that N-formyl-kynurenine and kynurenine are formed and then remain in the coordination sphere of the uranyl ion.