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pH dependence of the absorption and emission behaviour of lumiflavin in aqueous solution

Paper ID Volume ID Publish Year Pages File Format Full-Text
27808 44043 2010 10 PDF Available
Title
pH dependence of the absorption and emission behaviour of lumiflavin in aqueous solution
Abstract

The spectroscopic behaviour of lumiflavin (7,8,10-trimethyl-isoalloxazine, oxidized form LFox) in aqueous solutions of pH range −1.08 to 14.6 is studied. Absorption spectra, fluorescence quantum distributions, quantum yields and lifetimes are determined. The ionization stage of ground-state LFox changes from cationic (LFoxH2+) at low pH (pKc ≈ 0.38) via neutral (LFoxH) to anionic (LFox−) at high pH (pKa ≈ 10.8). The cationic, neutral, and anionic forms are identified by their different absorption spectra. LFoxH in neutral aqueous solution is reasonably fluorescent (fluorescence quantum yield ϕF ≈ 0.29, fluorescence lifetime τF ≈ 5.2 ns), while LFox− is weakly fluorescent (ϕF ≈ 0.0042, τF ≈ 90 ps), and LFoxH2+ is nearly non-fluorescent (ϕF ≈ 3.6 × 10−5, τF ≈ 0.4 ps).A theory of the pH dependent equilibration of cationic, neutral and anionic molecules in the ground state and their dynamics in the excited state is developed. For lumiflavin in aqueous solution in the excited state no equilibrium distributions are reached between the cationic, neutral, and anionic forms. Some neutral excited lumiflavin transforms to the cationic ground-state form at low pH by intermolecular photo-induced proton transfer from H3O+ to LFoxH*. At high pH no photo-induced intermolecular proton transfer takes place.

Keywords
Lumiflavin; pH dependent absorption; pH dependent fluorescence; Fluorescence quantum yields; Fluorescence lifetimes; Ground-state ionization equilibrium constants; Relaxation dynamics
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pH dependence of the absorption and emission behaviour of lumiflavin in aqueous solution
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Publisher
Database: Elsevier - ScienceDirect
Journal: Journal of Photochemistry and Photobiology A: Chemistry - Volume 215, Issue 1, 5 September 2010, Pages 108–117
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Bioengineering
Get Full-Text Now
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Price was $35.95
You save - $31
Price after discount Only $4.95
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