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Influence of pH on spectral and photophysical properties of 9-methyl-5-deazaalloxazine and 10-ethyl-5-deaza-isoalloxazine

Paper ID Volume ID Publish Year Pages File Format Full-Text
26307 43946 2014 9 PDF Available
Title
Influence of pH on spectral and photophysical properties of 9-methyl-5-deazaalloxazine and 10-ethyl-5-deaza-isoalloxazine
Abstract

•Protonation/deprotonation equilibria for derivatives of 5-deazaflavins in the ground and in the excited state are proposed.•Prototropic equilibria for investigated compounds in the excited state reflect those achieved in the ground state.•The structures of absorptive and emissive species of investigated compounds in different pH were identified.•The excited-state tautomeric form of the monoanion of derivative of 5-deazaizoalloxazine was found.

Absorption, emission, excitation and synchronous fluorescence spectra were used to describe protonation/deprotonation equilibria for a derivative of deazaalloxazine, 9-methyl-5-deazaalloxazine (9Me-5-DAll), and its flavin derivative 10-ethyl-5-deaza-isoalloxazine (10Et-5-DIAll). In addition, spectral and photophysical properties of 9Me-5-DAll and of 10Et-5-DIAll were compared to those of methyl derivatives of alloxazine, such as lumichrome or lumiflavin (10-methyl-isoalloxazine).One species only is present in acidic and neutral solutions of 9Me-5-DAll, which absorbs and emits light, in contrast to basic solutions where three such species are present, identified as the two monoanions and one dianion. The analysis of steady-state and time-resolved spectra predict that the N(3) monoanion of 9Me-5-DAll has “alloxazinic” structure while its N(1) monoanion and N(1,3) dianion have predominantly isoalloxazinic structures. The lifetimes of these forms were determined at selected pH values. Similarly, for 10Et-5-DIAll there is one protonated species at low pH values. At higher pH, this species undergoes deprotonation forming the neutral molecule, which is present in aqueous solutions up to pH 12. At pH > 12 the monoanionic, isoalloxazinic form of 10Et-5-DIAll is predominant. Based on the analysis of the time-resolved spectra of the latter species, we conclude that its protonated form has no detectable fluorescence. Additionally, time-resolved spectra indicate that at pH > 11 there are two emitting species in solution. The first is identified as the isoalloxazinic monoanion of 10Et-5-DIAll, and the second as the tautomeric form of this monoanion, which is formed in the excited state.Based on the measurements, we also estimated pKa values of the two compounds for the equilibria between the individual species both in the ground and excited states.

Keywords
Absorbance; Fluorescence; Synchronous fluorescence spectra; 5-Deazaalloxazine; 5-Deazaflavin; Acid–base equilibria
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Influence of pH on spectral and photophysical properties of 9-methyl-5-deazaalloxazine and 10-ethyl-5-deaza-isoalloxazine
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Publisher
Database: Elsevier - ScienceDirect
Journal: Journal of Photochemistry and Photobiology A: Chemistry - Volume 275, 1 February 2014, Pages 12–20
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Bioengineering
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us