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Scientia Pharmaceutica is published by MDPI from Volume 84 Issue 3 (2016). Articles in this Issue were published by another publisher in Open Access under a CC-BY (or CC-BY-NC-ND) licence. Articles are hosted by MDPI on as a courtesy and upon agreement with Austrian Pharmaceutical Society (Österreichische Pharmazeutische Gesellschaft, ÖPhG).
Open AccessArticle

Effect of Nicotinamide on the Photolysis of Riboflavin in Aqueous Solution

Baqai Institute of Pharmaceutical Sciences, Baqai Medical University, Toll Plaza, Super Highway, Gadap Road, Karachi 74600, Pakistan
Department of Pharmaceutical Chemistry, Faculty of Pharmacy, University of Karachi, Karachi 75270, Pakistan
Department of Physics, Sevastopol State University, Universitetskaya str. 33, Sevastopol 299053, Russia
Department of Biological and Chemical Sciences, Belgorod National Research University, Pobeda str. 85, Belgorod 308015, Russia
Author to whom correspondence should be addressed.
Sci. Pharm. 2016, 84(2), 289-303;
Received: 4 July 2015 / Accepted: 16 August 2015 / Published: 16 August 2015
The photolysis of riboflavin (RF) in aqueous solution in the presence of nicotinamide (NA) by visible light has been studied in the pH range 1.0-12.0 and the various photoproducts have been identified as known compounds. RF has been determined in degraded solutions by a specific multicomponent spectrometric method in the presence of its photoproducts and NA. The second-order rate constants (k2) for the bimolecular interaction of RF and NA range from 0.54 (pH 1.0) to 9.66 M-1 min-1 (pH 12.0). The log k2-pH profile for the photolysis reaction follows a sigmoid curve showing a gradual increase in the rate of pH due to a change in the ionization behavior of the molecule. The lower rate in the acid region is probably due to protonation of the molecule since the cationic form of RF is less susceptible to photolysis than the neutral form. Similarly, a slowing of the rate in the alkaline region is due to anion formation of the molecule. NA is involved as an electron acceptor during the sequence of reactions and thus enhances the rate of photolysis of RF. Absorption and fluorescence measurements did not provide evidence for the complex formation between the two compounds under the present conditions.
Keywords: Riboflavin; Nicotinamide; Photolysis; Kinetics; Rate-pH profile Riboflavin; Nicotinamide; Photolysis; Kinetics; Rate-pH profile
MDPI and ACS Style

AHMAD, I.; AHMED, S.; SHERAZ, M.A.; ANWAR, Z.; QADEER, K.; NOOR, A.; EVSTIGNEEV, M.P. Effect of Nicotinamide on the Photolysis of Riboflavin in Aqueous Solution. Sci. Pharm. 2016, 84, 289-303.

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