Modeling and Elucidation of the Kinetics of Multiple Consecutive Photoreactions AB4 (4Φ) With Φ-order Kinetics. Application to the Photodegradation of Riboflavin.

Date

2016-10-06

Advisors

Journal Title

Journal ISSN

ISSN

Volume Title

Publisher

Elsevier

Type

Article

Peer reviewed

Yes

Abstract

New semi-empirical rate-law system of equations is proposed for the first time for consecutive photoreactions that involve up to 4 photoreaction steps, AB4(4Φ). The equation system was developed, tested, and validated against synthetic kinetic traces generated by fifth-order Runge-Kutta calculations. The model accurately fitted the kinetic traces of Riboflavin photodegradation in ethanol which decomposes via the AB2(2Φ) mechanism involving 2 consecutive photoreaction steps. A kinetic elucidation methodology useful for consecutive photoreactions was also proposed to determine all the kinetic parameters and reaction attributes defining AB2(2Φ) reactions. The quantum yields of photodegradation, determined for wavelengths in the visible region 400-480 nm, ranged from 0.005 to 0.00756 and 0.0012 to 8 10−5 for the first and second photoreaction steps, respectively. They were found to increase with wavelength in defined sigmoid functions. For this monochromatic irradiation range, riboflavin proved to be a useful actinometer. Finally, a photodegradation scale based on pseudo-rate-constant values was also proposed for drugs. This scale (including 4 groups) is thought to contribute to rationalizing photodegradation testing and might prove useful in categorizing drugs' photodegradation reactivity.

Description

The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link.

Keywords

spectrophokinetics, Φ-order kinetics, Quantum yield

Citation

Maafi, M. and Maafi, W. (2016) Modeling and Elucidation of the Kinetics of Multiple Consecutive Photoreactions AB4 (4Φ) With Φ-order Kinetics. Application to the Photodegradation of Riboflavin. Journal of pharmaceutical sciences, 105 (12), pp. 3537-3548

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Research Institute

Leicester Institute for Pharmaceutical Innovation - From Molecules to Practice (LIPI)