Browsing by Author "Maafi, Mounir"

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    Actinometric and Φ-order photodegradation properties of anti-cancer Sunitinib.
    (Elsevier, 2015-02-24) Maafi, Mounir; Lee, Lok Yan
    The photodegradation reaction of Sunitinib (SUT), occurring via Z–E photoisomerization, has been evaluated in this study using the recently developed –order kinetics. In ethanol, the forward (Z E) photoreaction of SUT was invariant with irradiation (its quantum yield, 0.019) in contrast to the E Z isomerisation whose undergoes a 30‐fold, sigmoid–shaped, increase with increasing irradiation wavelength. This situation limited usefully the extent of Z– SUT photodegradation at the photostationary state to a maximum of c.a. 30 % of the initial concentration. Nevertheless, these results support a strong recommendation for a complete protection of SUT from light at all stages. Furthermore, a SUT‐actinometer was developed and was proven to be useful for the 320–480 nm spectral range. The latter wavelength interval defined as well SUT photodegradation causative range. The formalism of –order kinetics, proves to be a useful investigative tool for drugs’ photodegradation studies.
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    Determination of Dacarbazine Φ‐Order Photokinetics, Quantum Yields, and Potential for Actinometry.
    (Elsevier, 2016-01-08) Maafi, Mounir; Lee, Lok Yan
    The characterization of drugs’ Photodegradation kinetics is more accurately achieved by means of the recently developed –order kinetics than by the 0th–, 1st– and/or 2nd–order classical treatments. The photodegradation of anti–cancer Dacarbazine (DBZ) in ethanol has been investigated and found to obey –order kinetics when subjected to continuous and monochromatic irradiation of various wavelengths. Its photochemical efficiency was proven to be wavelength–dependent in the 220‐350 nm range, undergoing a 50–fold increase. Albeit this variation was well defined by a sigmoid pattern, the overall photoreactivity of DBZ was proven to depend also on the contributions of reactants’ and experimental attributes. The usefulness of DBZ to serve as a drug–actinometer has been investigated using the mathematical framework of –order kinetics. It has been shown that DBZ in ethanol can represent a good candidate for reliable actinometry in the range 270–350 nm. A detailed and easy–to–implement procedure has been proposed for DBZ–actinometry. This procedure could advantageously be implemented prior to the determination of the photodegradation quantum yields. This approach might be found useful for the development of many drug–actinometers as alternatives to quinine hydrochloride.
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    Editorial: Recent advances in photokinetics
    (Frontiers in Chemistry, 2024-08-23) Maafi, Mounir
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    Excitation Wavelength-Dependent Photochemistry
    (MDPI, 2024-06-07) Maafi, Mounir
    The dependence of photochemistry on excitation wavelength is not a recently observed phenomenon; nonetheless, it has, surprisingly enough, been largely ignored in the field. The reasons for this situation are not fully understood but might be related to a provisional extension of Kasha’s rule to photochemistry, or perhaps to a difficulty to justify the kind of short time-scales implied in such photochemistry, that challenges the usually held view giving predominance to fast internal conversion and vibrational relaxation. Regardless of the reasons, it is still a matter of fact that a complete and satisfactory interpretation for experimentally proven wavelength-dependent photochemistry is not yet available and the community endeavor to build a holistic understanding and a comprehensive view of the phenomenon. The present review is a non-exhaustive overview of the published data in the field, reporting on some of the most prominent features, issues, and interpretations.
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    Modeling and Elucidation of the Kinetics of Multiple Consecutive Photoreactions AB4 (4Φ) With Φ-order Kinetics. Application to the Photodegradation of Riboflavin.
    (Elsevier, 2016-10-06) Maafi, W.; Maafi, Mounir
    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.
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    Modelling nifedipine photodegradation, photostability and actinometric properties.
    (Elsevier, 2013-08-14) Maafi, W.; Maafi, Mounir
    Background The photodegradation of drugs obeying unimolecular mechanisms such as that of Nifedipine (NIF) were usually characterized in the literature by zero-, first- and second-order kinetics. This approach has been met with varying success. This paper addresses this issue and proposes a novel approach for unimolecular photodegradation kinetics. The photodegradation of the cardiovascular drug Nifedipine is investigated within this framework. Methods Experimental kinetic data of Nifedipine photodegradation were obtained by continuous monochromatic irradiation and DAD analysis. Fourth-order Runge-Kutta calculated kinetic data served for the validation of the new semi-empirical integrated rate-law model proposed in this study. Results A new model equation has been developed and proposed which faithfully describes the kinetic behaviour of NIF in solution for non-isosbestic irradiations at wavelengths where both NIF and its photoproduct absorb. NIF absolute quantum yield values were determined and found to increase with irradiation wavelength according to a defined sigmoid relationship. The effects of increasing NIF or excipients’ concentrations on NIF kinetics were successfully modelled and found to improve NIF photostability. The potential of NIF for actinometry has been explored and evaluated. A new reaction order (the so-called -order) has been identified and specifically proposed for unimolecular photodegradation reactions. Conclusion The semi-empirical and integrated rate-law models facilitated reliable kinetic studies of NIF photodegradation as an example of AB(1) unimolecular reactions. It allowed filling a gap in kinetic studies of drugs since, thus far, thermal first-order or a combination of first- and zero order kinetic equations were generally applied for drug photoreactions in the literature. Also, a new reaction order, the “-order”, has been evidenced and proposed as a specific alternative for photodegradation kinetics.
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    Mono- and polychromatic light diarylethene-actinometer for the visible range
    (Elsevier, 2022) Maafi, Mounir; Al-Qarni, Mohammed Ahmed
    Photochromes have proven to be attractive molecules for potential applications not necessary based on their spectacular colour change (such as biomimetic chemistry and photoswitchable nucleosides). Their development was incited by the versatility of compounds that could be prepared, but their applications also depended on their photobehaviour. The latter, conceptually requires a comprehensive description of their kinetics. A field which is somewhat still to be developed since, thus far, a single integrated rate-law (c = f (t), expressing the variation of the concentration with irradiation time) has been analytically established for samples exposed to monochromatic light. Similar integrated rate-law equations have yet to be analytically developed for polychromatic light irradiation. The present paper investigates the facets of photokinetics of a photochromic closed-form diarylethene de- rivative (c-DAE) and its variability with the light type impinging on the sample. An integrated rate-law equation has been derived, to describe kinetics under polychromatic light. The findings have then been applied to establish robust methodologies for both monochromatic and polychromatic light actinometries for the visible range. c- DAE is been shown to be a reliable, easily manipulated, actinometer for the 400–600 nm range for both light types. It is an exemplar of a new generation of actinometers that are easy-to-handle, regenerated, reliable, do not require to have a wavelength-invariant quantum yield, useful for both monochromatic and polychromatic light set-ups, and their procedures are based on integrated rate-law equations.
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    Montelukast photodegradation: Elucidation of Ф-order kinetics, determination of quantum yields and application to actinometry.
    (Elsevier, 2014-05-15) Maafi, W.; Maafi, Mounir
    A recently developed F–order semi–emperical integrated rate–law for photoreversible AB(2F) photoreversible reactions has been successfully applied to investigate Montelukast sodium (Monte) photodegradation kinetics in ethanol. The model equations also served to propose a new stepwise kinetic elucidation method valid for any AB(2F) system and its application to the determination of Monte forward (ΦA→Blirr) and reverse (ΦB→Alirr ) quantum yields at various irradiation wavelengths. It has been found that ΦA→Blirr undergoes a 15–fold increase with wavelength between 220 and 360 nm, with the spectral section 250 – 360 nm representing Monte effective photodegradation causative range. The reverse quantum yield values were generally between 12 and 54 % lower than those recorded for ΦA→Blirr, with the trans–isomer (Monte) converts almost completely to its cis–counterpart at high irradiation wavelengths. Furthermore, the potential use of Monte as an actinometer has been investigated and an actinometric method was proposed. This study demonstrated the usefulness of Monte for monochromatic light actinometry for the dynamic range 258 – 380nm.
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    Novel methods for the characterisation of nanosponges/drug complexes with fluorimetry. Detection and Quantification in human serum
    (Planta Medica, 2016) Benson, G.; Maafi, Mounir; Grootveld, Martin
    Cyclodextrins are oligosaccharides formed from a cyclic structure of 1,4-linked α-D-glucopyranose units, hydrophilic on the outside, and hydrophobic within they are able to form hydrogen bonds, van der Waals forces and hydrophobic interactions with non-polar guest molecules, including pharmaceuticals, altering their solubility and spectral properties, they are able to overcome biological barriers and be absorbed [1]. Cross-linking β-cyclodextrin with epichlorohydrin can create polymers, with modifiable properties, and greater solubility, which can form stronger inclusion complexes through both encapsulation, and adsorbing guest molecules to their exterior. Although this complexation has been investigated with some pharmaceuticals, enhancing their solubility [2], and yielding higher percentage recoveries than when monomeric β-cyclodextrin was used [3], it has also been found that an increase in the intensity of fluorimetric analytical signal also occurs as a result of this interaction, along with a shift in the maximum wavelength peak [4]. The inclusion complex doesn't appear to have been utilised for analytical chemistry purposes, therefore the drug-β-cyclodextrin polymer-complex was explored through fluorimetry, as it is anticipated that this will allow for lower pharmaceutical detection limits; this technique was then applied for the determination of drugs in human serum and canal water. This poster will illustrate how β-cyclodextrin polymer can be utilised to enhance the fluorimetric signal of drugs, and be applied for the detection of pharmaceuticals in human serum and canal water.
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    On photokinetics under monochromatic light
    (Frontiers, 2023-09-14) Maafi, Mounir
    The properties of photokinetics under monochromatic light have not yet been fully described in the literature. In addition, for the last 120 years or so, explicit, handy model equations that can map out the kinetic behaviour of photoreactions have been lacking. These gaps in the knowledge are addressed in the present paper. Several general features of such photokinetics were investigated, including the effects of initial reactant concentration, the presence of spectator molecules, and radiation intensity. A unique equation, standing for a pseudo-integrated rate law, capable of outlining the kinetic behaviour of any photoreaction is proposed. In addition, a method that solves for quantum yields and absorption coefficients of all species of a given photoreaction is detailed. A metric (the initial velocity) has been adopted, and its reliability for the quantification of several effects was proven by theoretical derivation, Runge–Kutta numerical integration calculations and through the model equation proposed. Overall, this study shows that, under monochromatic light, photoreaction kinetics is well described by Φ-order kinetics, which is embodied by a unifying model equation. This paper is aimed at contributing to rationalising photokinetics via reliable, easy-to-use mathematical tools.
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    On photokinetics under polychromatic light
    (Frontiers in Chemistry, 2024-04-22) Maafi, Mounir
    Since the dawn of photochemistry 150 years ago, photoreactions have been conducted under polychromatic light. However, despite the pivotal role that photokinetics should naturally play for such reactive photosystems, the literature lacks a comprehensive description of that area. Indeed, one fails to identify explicit model integrated rate laws for these reactions, a characteristic type for their kinetic behavior, or their kinetic order. In addition, there is no consensus in the community on standardized investigative tools to evaluate the reactivity of these photosystems, nor are there venues for the discussion of such photokinetic issues. The present work is a contribution addressing some of these knowledge gaps. It proposes an unprecedented general formula capable of mapping out the kinetic traces of photoreactions under polychromatic light irradiation. This article quantitatively discusses several reaction situations, including the effects of initial reactant concentration and the presence of spectator molecules. It also develops a methodology for standardizing actinometers and defines and describes both the spectral range of highest reactivity and the photonic yield. The validity of the model equation has been proven by comparing its results to both theoretical counterparts and those generated by fourth-order Runge–Kutta numerical calculations. For the first time, a confirmation of the Φ-order character of the kinetics under polychromatic light was established.
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    Photokinetics of Dacarbazine and Nifedipine under polychromatic light irradiation and their application as new reliable actinometers for the ultraviolet range
    (Springer Nature, 2022-05-10) Maafi, Mounir; Al-Qarni, Mohammed Ahmed
    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(1Φ)εB≠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.