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Updated: Jun 10, 2025

Monitoring the Reductive and Oxidative Half-Reactions of a Flavin-Dependent Monooxygenase using Stopped-Flow Spectrophotometry
Published on: March 18, 2012
Fast singlet excited-state deactivation pathway of flavin with a trimethoxyphenyl derivative
Stanisław Niziński1,2, Naisargi Varma3, Marek Sikorski4
1Department of Biomolecular Mechanisms, Max Planck Institute for Medical Research, Jahnstrasse 29, 69120, Heidelberg, Germany.
Abstract:
Incorporation of the trimethoxyphenyl group at position 7 of flavin can drastically change the photophysical properties of flavin. We show unique fast singlet 1(π,π*) excited state deactivation pathway through nonadiabatic transition to the 1(n,π*) excited- state, and subsequent deactivation to the ground electronic state (S0), closing the photocycle. This mechanism explains the exceptionally weak fluorescence and the short excited-state lifetime for the flavin trimethoxyphenyl derivative and the lack of excited triplet T1 state formation. Full recovery of flavin in its ground state takes place within a 15 ps time window after photoexcitation in a polar solvent such as acetonitrile. According to quantum chemical calculations, the C(2)-O distance elongates by 0.16 Å in the 1(n,π*) state, with respect to the ground state. Intermediate-state structures are predicted by theoretical ab initio calculations and their dynamics are investigated using broadband vis-NIR time-resolved transient absorption and fluorescence up-conversion techniques.
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