title: Reduction-oxidation photocycle dynamics of flavins in starch films.
abstract: The blue-light photo-reduction (conversion of oxidized flavin quinone via flavin semiquinone to fully reduced flavin hydroquinone) and dark re-oxidation of the flavins riboflavin and lumiflavin in starch (α-amylose) films was studied by absorption and luminescence spectroscopy. Blue-light photo-excitation caused an absorption, fluorescence, and phosphorescence decrease which recovered in the dark. The photo-reduction dark-oxidation cycle could be repeated. The efficiency of photo-reduction decreased with exposed excitation energy, and the speed of re-oxidation in the dark slowed down with time after excitation. The absorption did not fully recover. The fluorescence efficiency after a long time of storage in the dark increased beyond the initial flavin quinone fluorescence efficiency. Flavin photo-excitation is thought to cause starch-flavin restructuring (static fluorescence quenching center formation), enabling enhanced photo-induced starch to flavin electron transfer with subsequent flavin reduction and starch oxidation. In the dark, after light switch-off, thermal reversion of flavin reduction and starch oxidation occurred.
authors.affiliation: Faculty of Physics, University of Regensburg, Universitaetsstrasse 31, D-93053 Regensburg, Germany.
authors.forename: Alfons
authors.initials: A
authors.lastname: Penzkofer
mesh_terms: D005415:Flavins / Q000737:chemistry*; D008567:Membranes, Artificial; D010084:Oxidation-Reduction; D055668:Photochemical Processes; D012256:Riboflavin / Q000737:chemistry*; D013213:Starch / Q000737:chemistry*
chemical_list: D005415:Flavins; D008567:Membranes, Artificial; C001922:lumiflavin; D013213:Starch; D012256:Riboflavin