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Effect of borate buffer on the photolysis of riboflavin in aqueous solution

Paper ID Volume ID Publish Year Pages File Format Full-Text
31123 44549 2008 6 PDF Available
Title
Effect of borate buffer on the photolysis of riboflavin in aqueous solution
Abstract

The photolysis of riboflavin (RF) in the presence of borate buffer (0.1–0.5 M) at pH 8.0–10.5 has been studied using a specific multicomponent spectrophotometric method for the determination of RF and photoproducts, formylmethylflavin (FMF), lumichrome (LC) and lumiflavin (LF). The overall first-order rate constants for the photolysis of RF (1.55–4.36 × 10−2 min−1) and the rate constants for the formation of FMF (1.16–3.52 × 10−2 min−1) and LC (0.24–0.84 × 10−2 min−1) have been determined. The values of all these rate constants decrease with an increase in buffer concentration suggesting the inhibition of photolysis reaction by borate species. The kinetic data support the formation of a RF-borate complex involving the ribityl side chain to cause the inhibition of photolysis. The second-order rate constants for the borate inhibited reaction range from 1.17–3.94 × 10−2 M−1 min−1. The log k-pH profiles for the reaction at various buffer concentrations indicate a gradual increase in rate, with pH, up to 10 followed by a decrease in rate at pH 10.5 probably due to ionization of RF and quenching of fluorescence by borate species. A graph of second-order rate constants against pH is a sigmoid curve showing that the rate of photolysis increases with an increase in pH. The results suggest the involvement of excited singlet state, in addition to excited triplet state, in the formation of LC.

Keywords
Riboflavin; Borate buffer; Photolysis; Kinetics; Spectrophotometric assay
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Effect of borate buffer on the photolysis of riboflavin in aqueous solution
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Publisher
Database: Elsevier - ScienceDirect
Journal: Journal of Photochemistry and Photobiology B: Biology - Volume 93, Issue 2, 13 November 2008, Pages 82–87
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Bioengineering
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Price was $35.95
You save - $31
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