Photochemical interaction of ascorbic acid with riboflavin, nicotinamide and alpha-tocopherol in cream formulations / I. Ahmad in INTERNATIONAL JOURNAL OF COSMETIC SCIENCE, Vol. 34, N° 2 (04/2012)  

[article]  inINTERNATIONAL JOURNAL OF COSMETIC SCIENCE > Vol. 34, N° 2 (04/2012) . - p. 123-131 Titre : Photochemical interaction of ascorbic acid with riboflavin, nicotinamide and alpha-tocopherol in cream formulations Type de document : texte imprimé Auteurs : I. Ahmad, Auteur ; M. A. Sheraz, Auteur ; S. Ahmed, Auteur ; F. H. M. Vaid, Auteur Année de publication : 2012 Article en page(s) : p. 123-131 Note générale : Bibliogr. Langues : Anglais (eng) Catégories : Ascorbique, Acide Cosmétiques Dynamique moléculaire Formulation (Génie chimique) Photochimie Produits hydratants Vitamine B Vitamine B2 Vitamine E Index. décimale : 668.5 Parfums et cosmétiques Résumé : The present work is based on a study of the effect of some vitamins such as riboflavin (RF), nicotinamide (NA) and alpha-tocopherol (TP) on the photodegradation of ascorbic acid (vitamin C) (AH2) in oil-in-water cream formulations using a UV irradiation source. A UV spectrophotometric and the official iodimetric methods have been used for the assay of AH2 in cream formulations. These methods have been validated in the presence of RF, NA and TP before their application to the creams. The recoveries of AH2 in the creams are in the range of 90–95% and the reproducibility of the method is within ±5%. The apparent first-order rate constants (kobs) for the photodegradation of AH2 in the presence of RF, NA and TP, individually, in the creams have been obtained. The second-order rate constants for the photochemical interaction of AH2 and the vitamins RF, NA and TP have been determined from the plots of kobs for AH2 photolysis versus the individual vitamin concentration along with the values of k0 from the intercept on the vertical axis. The values of k0 in the presence of RF and NA are lower than those of the kobs, indicating that these vitamins act as photosensitizers for the degradation of AH2 in creams. On the contrary, the value of k0 in the presence of TP is higher than that of the kobs, suggesting a stabilizing effect of this vitamin on the degradation of AH2 in creams. The mode of interaction of the individual vitamins with AH2 on photolysis has been discussed. Note de contenu : - MATERIALS AND METHODS : Cream formulations - Preparation of cream formulations - Measurement of pH - Measurement of light intensity - Photolysis of cream formulations - Measurement of absorption spectra - Thin-layer chromatography - RF and photoproducts - RESULTS AND DISCUSSION : Absorption characteristics of photolysed creams - Photoproducts of ascorbic acid and other vitamins - Assay method - Kinetics of photodegradation of ascorbic acid - Interaction of riboflavin with ascorbic acid - Interaction of nicotinamide with ascorbic acid - Interaction of ?-tocopherol with ascorbic acid - Effect of physicochemical factors DOI : 10.1111/j.1468-2494.2011.00690.x En ligne : https://onlinelibrary.wiley.com/doi/10.1111/j.1468-2494.2011.00690.x Format de la ressource électronique : Pdf Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=14382 [article]

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Photostabilization of ascorbic acid with citric acid, tartaric acid and boric acid in cream formulations / I. Ahmad in INTERNATIONAL JOURNAL OF COSMETIC SCIENCE, Vol. 34, N° 3 (06/2012)  

[article]  inINTERNATIONAL JOURNAL OF COSMETIC SCIENCE > Vol. 34, N° 3 (06/2012) . - p. 240-245 Titre : Photostabilization of ascorbic acid with citric acid, tartaric acid and boric acid in cream formulations Type de document : texte imprimé Auteurs : I. Ahmad, Auteur ; M. Ali Sheraz, Auteur ; S. Ahmed, Auteur ; Z. Shad, Auteur ; F. H. M. Vaid, Auteur Année de publication : 2012 Article en page(s) : p. 240-245 Note générale : Bibliogr. Langues : Anglais (eng) Catégories : Cinétique chimique Cosmétiques Formulation (Génie chimique) Photodétérioration Stabilisants (chimie) Vitamine C Index. décimale : 668.5 Parfums et cosmétiques Résumé : This study involves the evaluation of the effect of certain stabilizers, that is, citric acid (CT), tartaric acid (TA) and boric acid (BA) on the degradation of ascorbic acid (AH2) in oil-in-water cream formulations exposed to the UV light and stored in the dark. The apparent first-order rate constants (0.34–0.95 × 10−3 min−1 in light, 0.38–1.24 × 10−2 day−1 in dark) for the degradation reactions in the presence of the stabilizers have been determined. These rate constants have been used to derive the second-order rate constants (0.26–1.45 × 10−2 M−1 min−1 in light, 3.75–8.50 × 10−3 M−1 day−1 in dark) for the interaction of AH2 and the individual stabilizers. These stabilizers are effective in causing the inhibition of the rate of degradation of AH2 both in the light and in the dark. The inhibitory effect of the stabilizers is in the order of CT > TA > BA. The rate of degradation of AH2 in the presence of these stabilizers in the light is about 120 times higher than that in the dark. This could be explained on the basis of the deactivation of AH2-excited triplet state by CT and TA and by the inhibition of AH2 degradation through complex formation with BA. AH2 leads to the formation of dehydroascorbic acid (A) by chemical and photooxidation in cream formulations. Note de contenu : - MATERIALS AND METHODS : Preparation of cream formulations - pH measurements - Spectral measurements - Light intensity measurements - Photolysis of cream formulations - Thin-layer chromatography (TLC) of photolysed creams - Assay of ascorbic acid in creams - RESULTS AND DISCUSSION : Products of ascorbic acid photodegradation - Spectral changes in photodegraded creams - Assay of ascorbic acid in creams - Kinetics of photodegradation - Effect of stabilizers - Statistical evaluation of stabilizers and concentration - Degradation of AH2 in presence of stabilizers in the dark - Mode of interaction DOI : 10.1111/j.1468-2494.2012.00708.x En ligne : http://onlinelibrary.wiley.com/doi/10.1111/j.1468-2494.2012.00708.x Format de la ressource électronique : Pdf Permalink : https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=15034 [article]

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