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AAPS PharmSciTech. 2015 Oct;16(5):1122-8. doi: 10.1208/s12249-015-0304-2. Epub 2015 Feb 21.

Solvent Effect on the Photolysis of Riboflavin.

Author information

1
Baqai Institute of Pharmaceutical Sciences, Baqai Medical University, Toll Plaza, Super Highway, Gadap Road, Karachi, 74600, Pakistan.
2
Baqai Institute of Pharmaceutical Sciences, Baqai Medical University, Toll Plaza, Super Highway, Gadap Road, Karachi, 74600, Pakistan. ali_sheraz80@hotmail.com.
3
Department of Biochemistry, Dow International Medical College, Dow University of Health Sciences, Ojha Campus, Karachi, 74200, Pakistan.

Abstract

The kinetics of photolysis of riboflavin (RF) in water (pH 7.0) and in organic solvents (acetonitrile, methanol, ethanol, 1-propanol, 1-butanol, ethyl acetate) has been studied using a multicomponent spectrometric method for the assay of RF and its major photoproducts, formylmethylflavin and lumichrome. The apparent first-order rate constants (k obs) for the reaction range from 3.19 (ethyl acetate) to 4.61 × 10(-3) min(-1) (water). The values of k obs have been found to be a linear function of solvent dielectric constant implying the participation of a dipolar intermediate along the reaction pathway. The degradation of this intermediate is promoted by the polarity of the medium. This indicates a greater stabilization of the excited-triplet states of RF with an increase in solvent polarity to facilitate its reduction. The rate constants for the reaction show a linear relation with the solvent acceptor number indicating the degree of solute-solvent interaction in different solvents. It would depend on the electron-donating capacity of RF molecule in organic solvents. The values of k obs are inversely proportional to the viscosity of the medium as a result of diffusion-controlled processes.

KEYWORDS:

dielectric constant; kinetics; photolysis; riboflavin; solvent effect; viscosity

PMID:
25698084
PMCID:
PMC4674638
DOI:
10.1208/s12249-015-0304-2
[Indexed for MEDLINE]
Free PMC Article

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