Search

This article shows that hydroxyl radicals adsorbed on the surface of TiO2 (Ti-•OH groups) account for about 70–100% of the photocatalytic peroxidation of linoleic acid under UVB irradiation, which results into malondialdehyde production. The experimental data are silent concerning the involvement of 1O2 in the process, although an upper limit of 30% can be hypothesized, while an involvement of surface-bound holes into the lipoperoxidation process can be excluded. [ABSTRACT FROM AUTHOR]

This article studies the peroxidation of linoleic acid and of porcine skin lipids on ultraviolet B (UVB) irradiation, in the presence of various TiO2 specimens used as inorganic sunscreen pigments in different emulsion systems. It was found that different TiO2 specimens induce quite variable lipid peroxidation in the same emulsion system, which suggests that the different coatings widely differ in their effectiveness to lower the photocatalytic activity of TiO2. However, it was also found that the extent of lipid peroxidation caused by the same TiO2 pigment in different emulsions was even more variable than the effects of different pigments in the same system. This finding might imply that the choice of the formulation components different from TiO2 could be of paramount importance as far as the potential skin damage induced by the photocatalytic activity of TiO2 is concerned. [ABSTRACT FROM AUTHOR]

Titanium dioxide is a sunscreen pigment with photocatalytic activity. We studied the behavior of different TiO2 specimens used in cosmetic products on the UVB-induced peroxidation of linoleic acid as model substrate and of porcine skin, at different pH values. Lipoperoxidation of linoleic acid occurred to a lower extent with the coated compared to the uncoated TiO2, and it decreased at pH 7.0 compared to 4.0. The addition of organic additives such as propylene glycol and ethanol induced a significant reduction of the lipoperoxidation activity, particularly with the most reactive TiO2 specimens. Similar results were obtained with the porcine skin. [ABSTRACT FROM AUTHOR]

Ferulic acid (4-hydroxy-3-methoxycinnamic acid), a phenyl-propenoid derivative of cinnamic acid, can undergo photolysis upon UV irradiation. The photodegradation kinetics of ferulic acid were thus investigated in different systems. The micellar solutions did not protect the acid from photodegradation. On the contrary, they catalyzed its degradation at a variable extent depending on the surfactant structure. The photodegradation of ferulic acid in microemulsions was slower than in micelles and near to that in water. TiO2, habitually employed as a physical sunscreen, showed photocatalytic action toward ferulic acid degradation especially at higher initial concentration of ferulic acid. The action of ferulic acid on the peroxidation of linoleic acid in micelles and microemulsions also was evaluated. When the ferulic acid is absent the peroxidation is continuous while when it is present an induction time of 40 minutes or higher was observed. Accordingly, it is likely that linoleic acid acts as photosensitizer for ferulic acid, and that in turn ferulic acid acts as an antioxidant for linoleic acid, reducing the rate of peroxidation. [ABSTRACT FROM AUTHOR]

The photodegradation of cinnamic acid under UVB irradiation was evaluated in different vehicles, such as water solutions at different pH values, Tween-20 micelles, liposomes, and O/W emulsions prepared with Xalifin 15 or Montanov 68 as emulsifiers. The increase of pH decreases the photodegradation of cinnamic acid in all the vehicles studied. Micellar solutions showed a protective effect against cinnamic acid photodegradation; this property increases according to the surfactant percentage. Emulsions appeared to be the most efficient protective systems while liposomes had lower ability to protect cinnamic acid against UVB photodegradation. [ABSTRACT FROM AUTHOR]

In this work, the direct photolysis of salicylic acid, generally used as keratolytic agent in many dermatological products and as preservative in cosmetics, was investigated. The photodegradation of the acid under UVB irradiation was evaluated in different vehicles, such as water solutions at different pH, propylene glycol/water, and ethanol/water mixtures, sodium dodecyl sulphate solutions, and O/W emulsions prepared with Montanov 68 and Amphysol K as emulsifiers. The increase of pH enhanced the photodegradation of salicylic acid while the different vehicles protected the acid from the action of UVB radiations. However, the best protection was observed dissolving the acid in the lipid core of O/W emulsions, which probably removes the active from the polar environment that can promote the photolysis. The photocatalytic activity of TiO2 on the degradation of salicylic acid also was evaluated. TiO2 frequently is used as sunscreen in many cosmetic preparations. Salicylic acid and the pigment can be contained in the same solar formulation; hence, it can be interesting to study their interaction under UVB. TiO2 enhanced the photodegradation of salicylic acid in all the media previously reported and its photocatalytic activity was influenced by the pH and by the components of the vehicles. [ABSTRACT FROM AUTHOR]

The aim of this study was to prepare solid lipid nanoparticles (SLNs) of octyl‐p‐methoxycinnamate (OMC) to improve the photostability of this UV adsorber. It was found that the rate of photodegradation is significantly dependent upon the initial concentration of the active substance and could be halved in SLN form. When different concentration of nonionic surfactant solutions were compared, it was found that OMC photodegraded more quickly from a medium containing fewer surfactant micelles. Photodegradation rate of OMC was investigated spectrophotometrically while nanoparticles were characterized by particle size examination, zeta potential determination, and thermal analysis. [ABSTRACT FROM AUTHOR]

Solid lipid nanoparticles (SLN5) have been introduced as a novel carrier system for drugs and cosmetics. It has been found that SLNs themselves show physical UV-blocking action. Cetyl palmitate, glyceryl behenate, and palmitic acid SLNs, all loaded with retinyl (vitamin A) palmitate, were prepared and introduced in an O/W emulsion. SLNs in O/W emulsion protect retinyl palmitate from the photo degradation induced by UVA and UVB radiation. This effect is probably due to the light-scattering properties of SLN. Nanoparticles also protect vitamin A palmitate from thermal degradation. DSC thermal analytical examination, Z potential determination, and particle size measurement confirmed the solid character of the nanoparticies and the encapsulation of retinyl palmitate, their easy dispersion due to their negative charge on the surface, and their mean diameters in the nanometer range. [ABSTRACT FROM AUTHOR]