AAPS PharmSciTech

, Volume 16, Issue 5, pp 1122–1128 | Cite as

Solvent Effect on the Photolysis of Riboflavin

  • Iqbal Ahmad
  • Zubair Anwar
  • Sofia Ahmed
  • Muhammad Ali SherazEmail author
  • Raheela Bano
  • Ambreen Hafeez
Research Article


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.


dielectric constant kinetics photolysis riboflavin solvent effect viscosity 


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Copyright information

© American Association of Pharmaceutical Scientists 2015

Authors and Affiliations

  • Iqbal Ahmad
    • 1
  • Zubair Anwar
    • 1
  • Sofia Ahmed
    • 1
  • Muhammad Ali Sheraz
    • 1
    Email author
  • Raheela Bano
    • 1
  • Ambreen Hafeez
    • 2
  1. 1.Baqai Institute of Pharmaceutical SciencesBaqai Medical UniversityKarachiPakistan
  2. 2.Department of Biochemistry, Dow International Medical CollegeDow University of Health SciencesKarachiPakistan

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