Photokinetics of Dacarbazine and Nifedipine under polychromatic light irradiation and their application as new reliable actinometers for the ultraviolet range

Abstract

The photokinetic behaviour of drugs driven by polychromatic light is an area of pharmaceutics that has not received a lot of attention. Most often, such photokinetic data is treated by thermal kinetic models (i.e., the classical 0th-, 1st- or 2nd-order equations). Such models were not analytically derived from the rate-laws of the photodegradation reactions. Polychromatic light kinetic modelling is hence of importance, as a means to providing adequate toolkits and metrics. This paper aims at proposing two reliable drug-actinometers useful for polychromatic UVA range. The general actinometric methodology offered here is also useful for any drugs/materials obeying a primary photoprocess where both reactant and photoproduct absorb the incident light, of the $$AB{(1\Phi )}_{{\varepsilon }_{B}\ne 0}$$ A B ( 1 Φ ) ε B ≠ 0 type. The present method has been consolidated by the η-order kinetics. This framework further demonstrated the lamp-specificity of actinometers. Overall, Dacarbazine and Nifedipine photodegradations obeyed η-order kinetics, and stand as effective actinometers that can be recommended for the ICH Q1b photostability testing.

On photokinetics under polychromatic light

“…As a general statement, the shape of the kinetic trace of a reaction is lamp-dependent, and the trace of its total absorbance is dependent on the observation wavelength. This corroborates a similar conclusion reached in experiments with diarylethene, dacarbazine, and nifedipine ( Maafi and Al Qarni, 2022a ; Maafi and Al Qarni, 2022b ).…”

“…(1) ). However, a qualitative observation of the overall shape of experimental and RK-calculated traces of such photoreactions indicates that they do not seem to substantially differ from those recorded for reactions subjected to monochromatic light ( Lente and Espenson, 2004 ; Fabian and Lente, 2010 ; Roibu et al, 2018 ; Volfova et al, 2019 ; Yutani et al, 2019 ; Maafi and Al Qarni, 2022a ; Maafi and Al Qarni, 2022b ; Weingartz et al, 2023 ). This observation allows one to conjecture that the kinetics under polychromatic light may well be of -order character, similar to that previously established for the photokinetics of systems exposed to monochromatic light ( Maafi, 2023 ).…”

“…One approach introduces a simplifying hypothesis to derive an explicit formula to fit the experimental data. The applicability of such an equation is, however, limited to the specific reactive system and experimental conditions it was developed for ( Lehóczki et al, 2013 ; Józsa et al, 2018 ; Frigoli et al, 2020 ; Maafi and Al Qarni, 2022a ; Maafi and Al Qarni, 2022b ). A relatively popular method promotes the use of a high enough initial reactant concentration to ensure that the impinging polychromatic light is fully absorbed by the reactive medium (where the absorbance value of the reactive medium ought to be no less than 2) ( Amouroux et al, 2019 ).…”