Browsing by Author "Maafi, Wassila"
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Item Open Access Modelling and elucidation of photoreaction kinetics - Applications and actinometry using nifedipine, nisoldipine, montelukast, fluvoxamine and riboflavin.(De Montfort University, 2016-04) Maafi, WassilaThe kinetics of drugs photodegradation have traditionally been treated using thermal kinetic analysis methods consisting most commonly in zero and first order kinetics. These treatment strategies were shown to lack specificity and present a number of limitations when applied to photoreactions kinetics. Nevertheless, these methods have widely been used due to a lack of integrated rate-laws for the majority of photoreactions types, in turn, due to the presence of a variable time-dependent factor in most photoreactions rate-laws that prevents their mathematical integration. To address these limitations, a new methodology for the development and validation of semi-empirical integrated rate-laws that faithfully describe photoreactions kinetics and photoreactions simulated cases generated by numerical integration methods (NIMs), is hereby presented. Using this methodology, a new kinetic order was ascribed to photoreactions namely the Φ-order kinetics. Semi-empirical integrated rate-laws were, thus, developed for three photoreaction types namely, unimolecular, AB(1Φ), photoreversible ,AB(2Φ), and consecutive, AB4(4Φ), photoreactions. The proposed models were further tested experimentally on drugs following these photodegradation mechanisms using; nifedipine and nisoldipine for unimolecular photoreactions; montelukast and fluvoxamine for photoreversible reactions; and riboflavin for consecutive photoreactions. The developed models not only accurately described the photoreaction kinetics of these drugs but also allowed the determination of all the kinetic parameters that characterise them. Furthermore, the above studied drugs were shown to act as precise and simple actinometers when analytically treated with the Φ-order kinetic methods, hereby presented. A universal standard method for the precise and worldwide reproducible study of drugs stability and compounds photoreactions, based on monochromatic irradiation and Φ-kinetics data analysis, is also detailed and adopted throughout the thesis. Finally, two new kinetic parameters namely, the pseudo-rate-constant and pseudo-initial velocity have been identified and shown to be more reliable and accurate in the description and universal comparison of photoreactions kinetics.Item Open Access Quantification of unimolecular photoreaction kinetics: Determination of quantum yields and development of actinometers—The photodegradation case of cardiovascular drug Nisoldipine.(Hindawi, 2015) Maafi, Mounir; Maafi, WassilaThe lack of integrated rate-laws for photoreactions has led to carry out the treatment of drugs photodegradation kinetic data using the classical zeroth-, first- and second-order kinetics that were originally developed for thermal reactions. The recent developments of –order kinetic models has opened new perspectives in the treatment of photoreaction kinetics of systems involving a photolabile molecule (A) transforming into a photochemically and thermally stable product (B), i.e. the AB(1) photoreaction systems. Within this framework, the kinetics of cardiovascular and photosensitive drug Nisoldipine (NIS) has been rationalised. Continuous and monochromatic irradiation of NIS in ethanol obeyed –order kinetics with a sigmoid–shaped quantum yield variation with irradiation wavelength (0.0041–0.35 within 235–390 nm spectral region). Both NIS initial concentration-induced self photostabilisation effect and the photostabilisation by absorption competitors were quantified (up 70 %) and related to a reduction of the photokinetic factor. Finally, the –order kinetics also served to demonstrate the actinometric potential of NIS for the 320–400 nm dynamic range.Item Open Access Quantitative assessment of photostability and photostabilisation of Fluvoxamine and its design for actinometry.(Royal Society of Chemistry, 2015-03-09) Maafi, Mounir; Maafi, WassilaDespite the numerous concerns that have been raised in relation to considering 0th, 1st and 2nd–order kinetic treatments for drugs’ photodegradation characterisation and assessments, yet they still are employed, as the only tool available for these types of studies. The recently developed –order kinetic models have opened new perspectives in the treatment of photoreaction kinetics that stands as the best known alternative to the classical approach. The –order kinetics have been applied here to Fluvoxamine (Fluvo) with the aim to set out a detailed and comprehensive procedure able to rationalise photodegradation/photostability of drugs and propose a platform for photosafety studies. Our results prove that drugs’ quantum yields (0.0016 <Φ < 0.43) should a priori be considered wavelength–dependent, their photostabilisation (up to 75% for Fluvo) by means of absorption competitors could explicitly be related to a decrease of the photokinetic factor, and photoreversible drugs can be developed into efficient actinometers (as Fluvoxamine in the 260–290 nm range). A pseudo– rate–constant factor was proposed as a descriptive parameter, circumventing the limitations of overall rateconstants and allowing comparison between drugs’ kinetic data obtained in different conditions.