Substitution effect on the nonradiative decay and trans → cis photoisomerization route: a guideline to develop efficient cinnamate-based sunscreens.

Cinnamate derivatives are very useful as UV protectors in nature and as sunscreen reagents in daily life. They convert harmful UV energy to thermal energy through effective nonradiative decay (NRD) including trans → cis photoisomerization. However, the mechanism is not simple because different photoisomeirzation routes have been observed for different substituted cinnamates. Here, we theoretically examined the substitution effects at the phenyl ring of methylcinnamate (MC), a non-substituted cinnamate, on the electronic structure and the NRD route involving trans → cis isomerization based on time-dependent density functional theory. A systematic reaction pathway search using the single-component artificial force-induced reaction method shows that the very efficient photoisomerization route of MC can be essentially described as "1ππ* (trans) → 1nπ* → T1 (3ππ*) → S0 (trans or cis)". We found that for efficient 1ππ* (trans) → 1nπ* internal conversion (IC), MC should have the substituent at the appropriate position of the phenyl ring to stabilize the highest occupied π orbital. Substitution at the para position of MC slightly lowers the 1ππ* state energy and photoisomerization occurs via a slightly less efficient "1ππ* (trans) → 3nπ* → T1 (3ππ*) → S0 (trans or cis)" pathway. Substitution at the meta or ortho positions of MC significantly lowers the 1ππ* state energy so that the energy barrier of IC (1ππ* → 1nπ*) becomes very high. This substitution leads to a much longer 1ππ* state lifetime than that of MC and para-substituted MC, and a change in the dominant photoisomerization route to "1ππ* (trans) → C[double bond, length as m-dash]C bond twisting on 1ππ* → S0 (trans or cis)". As a whole, the "1ππ* → 1nπ*" IC observed in MC is the most important initial step for the rapid change of UV energy to thermal energy. We also found that the stabilization of the π orbital (i) minimizes the energy gap between 1ππ* and 1nπ* at the 1ππ* minimum and (ii) makes the 0-0 level of 1ππ* higher than 1nπ* as observed in MC. These MC-like relationships between the 1ππ* and 1nπ* energies should be ideal to maximize the "1ππ* → 1nπ*" IC rate constant according to Marcus theory.

3,4-Dimethoxycinnamic Acid as a Novel Matrix for Enhanced In Situ Detection and Imaging of Low-Molecular-Weight Compounds in Biological Tissues by MALDI-MSI.

Low-molecular-weight (low-MW) compounds have many essential functions in biological processes, and the molecular imaging of as many low-MW compounds as possible is critical for understanding complex biological processes. Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) is an emerging molecular-imaging technology that enables determination of the spatial distributions and the relative abundances of diverse endogenous compounds in tissues. New matrices suitable for the imaging of low-MW compounds by MALDI-MSI are important for the technological advancement of tissue imaging. In this study, 3,4-dimethoxycinnamic acid (DMCA) was evaluated as a new matrix for enhanced low-MW compound detection by MALDI-MSI because of its strong ultraviolet absorption, low matrix-ion related interferences below m/ z 500, and high ionization efficiency for the analysis of low-MW compounds. DMCA was successfully used for improved in situ detection of low-molecular-weight metabolites ( m/ z < 500) and lipids in rat liver, rat brain, and germinating Chinese-yew seed tissue sections. The use of DMCA led to the successful in situ detection of 303, 200, and 248 low-MW compound ion signals from these three tissues, respectively. Both MALDI-MS/MS and LC-MS/MS were used to identify these ion signals, leading to the identification of 115 low-MW compounds from rat liver (including 53 lipids, 29 oligopeptides, and 33 metabolites), 130 low-MW compounds from rat brain (including 104 lipids, 5 oligopeptides, and 21 metabolites), and 111 low-MW compounds from germinating Chinese-yew seeds (including 77 lipids, 22 oligopeptides, 8 flavonoids, and 4 alkaloids). A larger number of low-MW compounds could be detected and imaged when DMCA was used as the MALDI matrix than with other commonly used MALDI matrices such as 2,5-dihydroxybenzoic acid, α-cyano-4-hydroxycinnamic acid, 2-mercaptobenzothiazole, graphene oxide, and silver nanoparticles. Our work provides a new and powerful matrix for enhanced MALDI-MS profiling of low-MW compounds in both animal and plant tissues.

Photochemical degradation of the UV filter octyl methoxycinnamate in solution and in aggregates.

The photodegradation of the ultraviolet (UV) filter octyl methoxycinnamate (OMC) is investigated in both dilute solution and in aggregated form. In dilute solution, the ratio of trans and cis isomers achieved at the photostationary state is solvent-dependent because of variations in the isomerization quantum yield. The two isomeric forms at the photostationary state are highly resistant to further photodegradation and no other UVA-absorbing species are formed. Aggregation of OMC, either in a neat film or in aqueous colloidal suspensions, leads to irreversible photodegradation of the molecule and the formation of multiple photoproducts. In addition to previously identified photoproducts like the UVB-absorbing cis and trans isomers and photodimers, we find photoproduct species whose absorption extends into the UVA. Characterization of the photophysical properties of these species indicates that they have long-lived excited-states (τf > 1 ns, 400 nm), unlike the isomeric forms of OMC (τf < 30 ps, 266 nm), and that excitation at 405 nm can sensitize the formation of singlet oxygen. These results show that the environment of OMC affects the photochemistry of the molecule and that the environmental conditions must be taken into account when considering the molecule's stability. In particular, aggregation of OMC molecules results in complex photochemistry that can produce species whose absorption extends into UVA and are capable of generating reactive oxygen species.

Photoexcited triplet states of new UV absorbers, cinnamic acid 2-methylphenyl esters.

Phosphorescence spectra of nonphosphorescent or very weakly phosphorescent new UV absorbers, 2-methylphenyl cinnamate (MePC), 2-methylphenyl 4-methoxycinnamate (MePMC) and 2-methylphenyl 4-ethoxycinnamate (MePEC) have been observed by using external heavy atom effects of ethyl iodide in ethanol at 77 K. The lowest excited triplet (T(1)) energies of these new UV absorbers are lower than those of a widely used UV-A absorber, 4-tert-butyl-4'-methoxydibenzoylmethane (BM-DBM), in both keto and enol forms. The intermolecular triplet-triplet energy transfer from photolabile BM-DBM to MePMC was observed by measuring the time-resolved phosphorescence spectra. Electron paramagnetic resonance spectra have been observed for the T(1) states of these new UV absorbers in ethanol at 77 K by using benzophenone as a triplet sensitizer. The observed T(1) lifetimes, zero-field splitting (ZFS) parameters and molecular orbital calculations of the ZFS parameters suggest that T(1) states of these new UV absorbers posses mainly (3)ππ* character. The deactivation processes of the lowest excited singlet (S(1)) states are predominantly fluorescence and internal conversion to the ground (G) states in MePMC and MePEC, while the main deactivation process of the S(1) state of MePC is internal conversion to the G state. The molar absorption coefficients of MePMC and MePEC in the UV-A and UV-B regions are larger than that of most widely used UV-B absorber, octyl methoxycinnamate.

Interfacial Photo-Cross-Linking: Simple but Powerful Approach for Fabricating Capsule Polymer Particles with Tunable pH-Responsive Controlled Release Capability.

Herein, we describe capsule polymer particles with precisely controlled pH-responsive release properties prepared directly via the interfacial photo-cross-linking of spherical poly(2-diethylaminoethyl methacrylate-co-2-cinnamoylethyl methacrylate) (P(DEAEMA-CEMA)) particles. In the interfacial photo-cross-linking, photoreactive cinnamoyl groups in the polymer particles were cross-linked via [2π + 2π] cycloaddition reactions at the polymer/water interface, showing that the shell-cross-linked hollow polymer particles can be directly prepared from spherical polymer particles. The approach has fascinating advantages such as using minimal components, simplicity, and not requiring sacrificial template particles and toxic solvents. The following important observations are made: (I) encapsulated materials were stably retained in the capsule particles under neutral pH conditions; (II) encapsulated materials were released from the capsule particles under acidic pH conditions; (III) the release kinetics of encapsulated materials were controlled by the pH conditions; i.e., immediate and sustained release was achieved by varying the acidity of the aqueous media; (IV) the photoirradiation time did not significantly affect the release kinetics under different pH conditions; and (V) the pH-responsive release properties were regulated by changing the polymer composition in P(DEAEMA-CEMA). Furthermore, by exploiting the pH-responsiveness, capsule particles are successfully obtained via an all-aqueous process from spherical polymer particles. The advantages of the all-aqueous encapsulation process allowed the water-soluble biomacromolecules such as DNA and saccharides to be successfully encapsulated in the P(DEAEMA-CEMA) hollow particles. With this simple interfacial photo-cross-linking strategy, we envision the ready synthesis of sophisticated particulate materials for broad application in advanced research fields.

Pixel-isolation liquid crystals formed by polarization-selective UV-curing of a prepolymer containing cinnamate oligomer.

A pixel isolated liquid crystal display was fabricated by polarization-selective anisotropic photoreaction of a prepolymer containing a cinnamate oligomer. The cinnamate oligomer was mainly distributed on the surface region of a UV-cured polymer wall. Anisotropic photo-dimerization of cinnamate moiety was achieved by polarized UV exposure. It was found that the polymer walls containing cinnamate dimers formed by polarized UV exposure showed ordered orientation of LC molecules at the boundary of the polymer walls resulting in electro-optic performance improvement.

The photocatalytic destruction of cinnamic acid and cinnamyl alcohol: Mechanism and the effect of aqueous ions.

Cinnamic acid was chosen as an exemplar molecule to study the effect of potential contaminants on the kinetics and mechanism of the photocatalytic destruction of hydrocarbons in aqueous solutions. We identify the principal intermediates in the photocatalytic reaction of the acid and corresponding alcohol, and propose a mechanism that explains the presence of these species. The impact of two likely contaminants of aqueous systems, sulfate and chloride ions were also studied. Whereas sulfate ions inhibit the degradation reaction at all concentrations, chloride ions, up to a concentration of 0.5 M, accelerate the removal of cinnamic acid from solution by a factor of 1.6. However, although cinnamic acid is removed, the pathway to complete oxidation is blocked by the chloride, with the acid being converted (in the presence of oxygen) into new products including acetophenone, 2-chloroacetophenone, 1-(2-chlorophenyl)ethenone and 1,2-dibenzoylethane. We speculate that the formation of these products involves chlorine radicals formed from the reaction of chloride ions with the photoinduced holes at the catalyst surface. Interestingly, we have shown that the 1-(2-chlorophenyl)ethenone and 1,2-dibenzoylethane products form from 2-chloroacetophenone when irradiated with 365 nm light in the absence of the catalyst. The formation of potentially dangerous side products in this reaction suggest that the practical implementation of the photocatalytic purification of contaminated water needs to considered very carefully if chlorides are likely to be present.

Generation of pretilt angles of liquid crystals on cinnamate-based photoalignment layer by a simple directional peel-off process.

As an alternative to the rubbing method, the photoalignment method has been extensively developed for liquid crystal displays owing to its various advantages including the absence of any contamination problems, feasibility of multi-domain structure formation, and low temperature processing capability. However, cinnamate-based photo-reactive materials that are widely used in photoalignment suffer from several limitations including low pretilt angle and limited control of tilted-up direction of the liquid crystals compared to that of the rubbing process. In this work, we demonstrate a simple and convenient method to generate the pretilt angle, compared to that achieved via the rubbing method, by means of a simple directional peel-off process using a photo-reactive cinnamate oligomer having flexible molecular chain.

Trans-cinnamic acid and coumarin-3-carboxylic acid: experimental charge-density studies to shed light on [2 + 2] cycloaddition reactions.

As part of an ongoing series of experimental charge-density investigations into the intra- and intermolecular interactions present in compounds which undergo solid-state [2 + 2] cycloaddition reactions, the charge-density analyses of trans-cinnamic acid and coumarin-3-carboxylic acid are reported. Thus, high-resolution single-crystal X-ray diffraction data were recorded at 100 K for trans-cinnamic acid (sin theta/lambda(max) = 1.03 A(-1)) and coumarin-3-carboxylic acid (sin theta/lambda(max) = 1.19 A(-1)). In addition to the anticipated O-H...O hydrogen bonds weak C-H...O interactions were identified in both structures along with very weak intermolecular interactions between pairs of molecules that undergo solid-state [2 + 2] cycloaddition reactions upon irradiation.

The enhancement and scale up of the extraction of anti-oxidants from Rosmarinus officinalis using ultrasound.

The aim of this study was to examine the effect of ultrasound on the solvent extraction of anti-oxidants from the rosemary herb and to scale up the ultrasonic extraction process. The anti-oxidants of interest were identified using HPLC. Results indicated that, compared with conventional solvent extraction, the use of ultrasound gives a more effective extraction at lower temperatures with less dependence on the extraction solvent employed and that scale up of the process is possible.

Poly(D,L-lactide) nanoencapsulation to reduce photoinactivation of a sunscreen agent.

The use of sunscreens is the 'gold standard' for protecting the skin from ultraviolet light. Octyl methoxycinnamate (OMC) is one of the most widely used UVB filter but it can act as a sensitizer or photoallergen. When exposed to sunlight, OMC can change from the primary trans-form to cis-form and the isomerization, not reversible, conducts to a reduction of the UVB filtering efficiency because the trans-form has a higher extinction coefficient. Photostability is the most important characteristic of effective sunscreens and it can be influenced by formulation ingredients and by applying technological strategies. In this work, photostability experiments, performed on emulsion-gels containing different percentages of OMC free or loaded in poly(D,L-lactide) nanoparticles, were carried out. The presence of a polymeric envelop may act to protect the active ingredient. In this study, the influence of poly(D,L-lactide) matrices on the photochemical stability of the sunscreen agent was investigated. As highlighted in this study, free OMC in different formulations has different photoisomerization degree. Moreover, a dissimilar behaviour was observed by studying different sunscreen concentrations in the same cosmetic formulation. Photostability results show a significant reduction in photoisomerization degree for formulations containing sunscreen loaded in nanoparticles, highlighting that the encapsulation is a suitable strategy to improve OMC photostability. Moreover, sun protection factor (SPF) results show that the UVB filter protective power is also maintained after encapsulation.

Microsphere based improved sunscreen formulation of ethylhexyl methoxycinnamate.

Polymethylmethacrylate (PMMA) microspheres of ethylhexyl methoxycinnamate (EHM) were prepared by emulsion solvent evaporation method to improve its photostability and effectiveness as sunscreening agent. Process parameters like stirring speed and aqueous polyvinyl alcohol (PVA) concentration were analyzed in order to optimize the formulations. Shape and surface morphology of the microspheres were examined using scanning electron microscopy. Particle size of the microspheres was determined using laser diffraction particle size analyzer. The PMMA microspheres of EHM were incorporated in water-removable cream base. The in vitro drug release of EHM in pH 7.4 was performed using dialysis membrane. Thin layer chromatography was performed to determine photostability of EHM inside the microspheres. The formulations were evaluated for sun protection factor (SPF) and minimum erythema dose (MED) in albino rats. Cream base formulation containing microspheres prepared using EHM:PMMA in ratio of 1:3 (C(3)) showed slowest drug (EHM) release and those prepared with EHM: PMMA in ratio of 1:1 showed fastest release. The cream base formulations containing EHM loaded microspheres had shown better SPF (more than 16.0) as compared to formulation C(d) that contained 3% free EHM as sunscreen agent and showed SPF 4.66. These studies revealed that the incorporation of EHM loaded PMMA microspheres into cream base had greatly increased the efficacy of sunscreen formulation approximately four times. Further, photostability was also shown to be improved in PMMA microspheres.

Photolysis and cellular toxicities of the organic ultraviolet filter chemical octyl methoxycinnamate and its photoproducts.

Organic ultraviolet filter chemicals (UVFCs) are the active ingredients used in many sunscreens to protect the skin from UV light; these chemicals have been detected in numerous aquatic environments leading to concerns about how they might affect aquatic organisms and humans. One commonly used organic UVFC is octyl methoxycinnamate (OMC), better known by its commercial name, octinoxate. Upon exposure to UV light, OMC degrades rapidly, forming numerous photoproducts, some of which have been previously identified. In this study, we isolated and completely characterized the major products of OMC photolysis, including the two major stable OMC cyclodimers. One of these cyclodimers is a δ-truxinate, resulting from a head-to-head dimerization of two OMC molecules, and the other cyclodimer is an α-truxillate, resulting from a head-to-tail dimerization of two OMC molecules. Additionally, the cellular toxicities of the individual photoproducts were determined; it was found that the parent UVFC, OMC, 4-methoxybenzaldehyde, and two cyclodimers are significantly toxic to cells. The photoproduct 2-ethylhexanol is not cytotoxic, demonstrating that different components of OMC photolysate contribute differently to its cellular toxicity. This study thus provides an enhanced understanding of OMC photolysis and gives toxicity data that can be used to better evaluate OMC as a sunscreen agent.

Evaluation of the photostability of different UV filter combinations in a sunscreen.

Development of photostable sunscreens is extremely important to preserve the UV protective capacity and to prevent the reactive intermediates of photounstable filter substances behaving as photo-oxidants when coming into direct contact with the skin. Thus, the objective of this study was to evaluate the photostability of four different UV filter combinations in a sunscreen by using HPLC analysis and spectrophotometry. The formulations that were investigated included four different UV filter combinations often used in SPF 15 sunscreens. The UV filter combinations were: octyl methoxycinnamate (OMC), benzophenone-3 (BP-3) and octyl salicylate (OS) (formulation 1); OMC, avobenzone (AVB) and 4-methylbenzilidene camphor (MBC) (formulation 2); OMC, BP-3 and octocrylene (OC) (formulation 3); OMC, AVB and OC (formulation 4). In the photostability studies, 40 mg of each formulation were spread onto a glass plate and left to dry before exposure to different UVA/UVB irradiation. Exposed samples were then immersed in isopropanol and the dried film dissolved ultrasonically. The filter components in the resulting solution were quantified by HPLC analysis with detection at 325 nm and by spectrophotometry. In this study, the four UV filter combinations showed different photostability profiles and the best one was formulation 3 (OMC, BP-3 and OC), followed by formulations 4, 1 and 2. In addition, OC improved the photostability of OMC, AVB and BP-3.

Photomediated crosslinking of C6-cinnamate derivatized type I collagen.

Synthesis and characterization of cinnamated Type I collagen and its related mechanical properties after photomediated crosslinking were investigated in detail. Using an EDC/NHS conjugation method, collagen was chemically modified to incorporate a photosensitive cinnamate moiety. The cinnamated collagen was fully characterized by 1H NMR, UV-vis, and circular dichroism (CD) spectroscopy, as well as by rheological and mechanical analyses. Cinnamated collagens with varying degrees of derivatization retained collagen triple helical structure. The rheological spectra of collagen solutions demonstrate that the storage modulus decreases with increasing cinnamate content, owing to a decrease in physical crosslinking. The kinetics of the crosslinking process in both hydrated gels and dry films were monitored by UV-vis spectroscopy and confirmed that crosslinking was complete within 60 min of irradiation. The uniaxial stress-strain behavior of crosslinked collagen films, including Young's modulus and ultimate tensile strength, was comparable to values reported for glutaraldehyde-crosslinked monomeric collagen films. These data demonstrate that derivatization of collagen with photosensitive cinnamate moieties provides a facile route for solid-state crosslinking, thereby improving the mechanical properties of collagen and enhancing the potential applicability of collagen-based materials in tissue engineering and drug delivery.

Unexpected photolysis of the sunscreen octinoxate in the presence of the sunscreen avobenzone.

A major concern raised about photostability studies of sunscreen products is that the photodegradation of sunscreens does not readily translate into changes in product performance. This study examines the correlation between photochemical degradation of sunscreen agents and changes in protection provided by sunscreen films. Films of a commercial sunscreen product containing avobenzone, oxybenzone and octinoxate were irradiated using a fluorescent UV-A phototherapy lamp with additional UV-B blocking filter. Periodically, during irradiation the transmittances of the films were measured and samples collected for chemical analysis of the sunscreen agents using high-performance liquid chromatography techniques. The results show that UV-induced changes in UV transmittance of sunscreen films correlate with changes in concentration of sunscreen agents. In a parallel experiment, we also irradiated a thin film of the same product in the cavity of an electron spin resonance (ESR) spectrometer. We report the concomitant photolysis of avobenzone and octinoxate that predominates over expected E/Z photoisomerization and that irradiation of a film of this product produced free radicals detected by ESR spectroscopy that persisted even after exposure had ended.

Photostability evaluation of five UV-filters, trans-resveratrol and beta-carotene in sunscreens.

Trans-resveratrol (RES) is used in cosmetic formulations and beta-carotene (BTC) is a classical sunscreen antioxidant, but their photostability in sunscreens, a property directly correlated to performance and safety has not been addressed in the literature. This paper reports the assessment of RES and/or BTC influence on the photostability of five UV-filters (octyl methoxycinnamate - OMC, avobenzone -AVO, octocrylene - OCT, bemotrizinole - BMZ, octyltriazone - OTZ) in three different combinations after UVA exposure followed by the identification of degradation products and the assessment of photoreactivity. The evaluation of sunscreen photostability was performed by HPLC and spectrophotometric analysis, and degradation products were identified by GC-MS analysis. Components RES, BTC, OMC and AVO were significantly degraded after UV exposure (reduction of around 16% in recovery). According to HPLC analysis, all formulations presented similar photostability profiles. Eleven degradation products were identified in GC-MS analysis, among them products of RES, BTC, OMC and AVO photodegradation. All evaluated formulations were considered photoreactive, as well as the isolated compounds RES and AVO. Considering HPLC, spectrophotometric and GC-MS results, it is suggested that formulations containing BMZ were considered the most photostable. The combination RES+BTC in a sunscreen improved the photostability of AVO. The benefits of using a combination of antioxidants in sunscreens was demonstrated by showing that using RES+BTC+studied UV-filters led to more photostable formulations, which in turn implies in better safety and efficacy.

Combination of retinyl palmitate and UV-filters: phototoxic risk assessment based on photostability and in vitro and in vivo phototoxicity assays.

This study aimed to assess the phototoxic potential of combined UV-filters and retinyl palmitate (RP) in the presence or not of bemotrizinol (BMTZ), employing photostability and in vitro and in vivo phototoxicity assays. The formulations tested contained octocrylene (OCT), octyl methoxycinnamate (OMC), benzophenone-3 (BZP-3) and RP (photostable) or octocrylene (OCT), octyl methoxycinnamate (OMC), avobenzone (AVO) and RP (less photostable). Both formulations were supplemented with bemotrizinol. Photostability was evaluated by exposing, or not, formulations spread on a glass plate to UVA/UVB irradiation. The resulting products were quantified by HPLC analysis. In vitro phototoxicity of UV-filters and combinations were evaluated using 3T3 viable monolayer fibroblast cultures submitted, or not, to irradiation according to OECD TG 432. In vivo photoallergy and photoxicity were assessed by clinical studies (photopatch test). Photostability assays showed that UV-filter bemotrizinol was a better photostabilizer for RP/benzophenone-3 than for RP/avobenzone. The in vitro phototoxicity of the combination RP/avobenzone was reduced by bemotrizinol. Clinical studies did not indicate phototoxic or photoallergenic potentials in all formulations tested. It is concluded that the 3T3 NRU phototoxicity test may be considered a supplementary assay in formulation developments, since it can detect chemically unstable and potentially phototoxic combinations. However, extrapolation of in vitro positive results to human photopatch tests may be performed only to a limited extent.

Photostabilization of butyl methoxydibenzoylmethane (Avobenzone) and ethylhexyl methoxycinnamate by bis-ethylhexyloxyphenol methoxyphenyl triazine (Tinosorb S), a new UV broadband filter.

It is now well documented that chronic UVA exposure induces damage to human skin. Therefore, modern sunscreens should not only provide protection from both UVB and UVA radiation but also maintain this protection during the entire period of exposure to the sun. UVA filters, however, are rare and not sufficiently photostable. We investigated the effect of the introduction of a new UV filter, bis-ethylhexyloxyphenol methoxyphenyl triazine (Tinosorb S), in oil in water sunscreen formulations on the photostability of butyl methoxydibenzoylmethane (Avobenzone [AVB]) after irradiation with an optically filtered Xenon arc source (UV irradiance adjusted at 1 mean effective dose [MED]/min). With spectrophotometrical methods to assess the sun protection factor (SPF) and UVA ratio and chromatographical methods to determine the amount of UV filters recovered after irradiation we showed that Tinosorb S prevented the photodegradation of AVB in a concentration-dependent way, leading to a sustained SPF and UVA ratio even after irradiation with doses of up to 30 MED. Since AVB was shown to destabilize ethylhexyl methoxycinnamate (EHM) we tested the effect of Tinosorb S in sunscreens containing this UV filter combination. Here too Tinosorb S showed photoprotective properties toward both UV filters. Thus, Tinosorb S can be used successfully to improve the photostability and efficiency of sunscreens containing AVB and EHM.

Effect of nanoparticle encapsulation on the photostability of the sunscreen agent, 2-ethylhexyl-p-methoxycinnamate.

The aim of this study was to investigate the influence of nanoparticle-based systems on the light-induced decomposition of the sunscreen agent, trans-2-ethylhexyl-p-methoxycinnamate (trans-EHMC). Ethylcellulose (EC) and poly-D,L-lactide-co-glycolide (PLGA) were used as biocompatible polymers for the preparation of the particulate systems. The "salting out" method was used for nanoparticle preparation and several variables were evaluated in order to optimize product characteristics. The photodegradation of the sunscreen agent in emulsion vehicles was reduced by encapsulation into the PLGA nanoparticles (the extent of degradation was 35.3% for the sunscreen-loaded nanoparticles compared to 52.3% for free trans-EHMC) whereas the EC nanoparticle system had no significant effect. Therefore, PLGA nanoparticles loaded with trans-EHMC improve the photostability of the sunscreen agent.