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Spectroscopic and Theoretical Study on Electronically Modified Chromophores in LOV Domains: 8‐Bromo‐ and 8‐Trifluoromethyl‐Substituted Flavins
Author(s) -
Mansurova Madina,
Simon Julian,
Salzmann Susanne,
Marian Christel M.,
Gärtner Wolfgang
Publication year - 2013
Publication title -
chembiochem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.05
H-Index - 126
eISSN - 1439-7633
pISSN - 1439-4227
DOI - 10.1002/cbic.201200670
Subject(s) - quantum yield , intersystem crossing , chemistry , photochemistry , chromophore , trifluoromethyl , flavin group , triplet state , pyrazine , yield (engineering) , fluorescence , excited state , stereochemistry , alkyl , materials science , singlet state , organic chemistry , molecule , physics , enzyme , quantum mechanics , metallurgy , nuclear physics
Two chemically synthesized flavin derivatives, 8‐trifluoromethyl‐ and 8‐bromoriboflavin (8‐CF 3 RF and 8‐BrRF), were photochemically characterized in H 2 O and studied spectroscopically after incorporation into the LOV domain of the blue light photoreceptor YtvA from Bacillus subtilis . The spectroscopic studies were paralleled by high‐level quantum chemical calculations. In solution, 8‐BrRF showed a remarkably high triplet quantum yield (0.97, parent compound riboflavin, RF: 0.6) and a small fluorescence quantum yield (0.07, RF: 0.27). For 8‐CF 3 RF, the triplet yield was 0.12, and the fluorescence quantum yield was 0.7. The high triplet yield of 8‐BrRF is due to the bromine heavy atom effect causing a stronger spin–orbit coupling. Theoretical calculations reveal that the decreased triplet yield of 8‐CF 3 RF is due to a smaller charge transfer and a less favorable energetic position of T 2 , required for intersystem crossing from S 1 to T 1 , as an effect of the electron‐withdrawing CF 3 group. The reconstitution of the LOV domain with the new flavins resulted in the typical LOV photochemistry, consisting of triplet state formation and covalent binding of the chromophore, followed by a thermal recovery of the parent state, albeit with different kinetics and photophysical properties.