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Reduction–Oxidation Photocycle Dynamics of Flavins in Starch Films
Faculty of Physics, University of Regensburg, Universitaetsstrasse 31, D-93053 Regensburg, Germany
Received: 10 May 2012; in revised form: 2 July 2012 / Accepted: 11 July 2012 / Published: 23 July 2012
(This article belongs to the Special Issue Flavins
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.
Keywords: riboflavin; lumiflavin; starch; oxystarch; flavin photo-reduction cycle; starch photo-oxidation cycle; static fluorescence quenching; photo-induced starch restructuring; phosphorescence; delayed fluorescence
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Penzkofer, A. Reduction–Oxidation Photocycle Dynamics of Flavins in Starch Films. Int. J. Mol. Sci. 2012, 13, 9157-9183.
Penzkofer A. Reduction–Oxidation Photocycle Dynamics of Flavins in Starch Films. International Journal of Molecular Sciences. 2012; 13(7):9157-9183.
Penzkofer, Alfons. 2012. "Reduction–Oxidation Photocycle Dynamics of Flavins in Starch Films." Int. J. Mol. Sci. 13, no. 7: 9157-9183.