Germain Puccetti

Design of a Photostabilizer Having Built‐in Antioxidant Functionality and Its Utility in Obtaining Broad‐spectrum Sunscreen Formulations

Abstract Di-2,2′-diethylhexyl-3,5-dimethoxy-4-hydroxy-benzylidenemalonate (INCI name diethylhexyl syringylidene malonate, DESM), the target photostabilizer, was synthesized in one step by condensation of 3,5-dimethoxy-4-hydroxy benzaldehyde (Syringaldehyde) with di-2,2′-diethylhexyl malonate. Photostability data in sunscreen formulations showed that DESM is photostable and improves the photostability of avobenzone significantly when compared to control (without a photostabilizer). Photostable broad-spectrum sunscreen formulations with high SPF (>30) have been achieved by combining avobenzone, DESM and UV-B sunscreens, such as homosalate, octisalate or other UV-B sunscreens. It seems that (a) triplet-state energy transfer from avobenzone to DESM and (b) scavenging of reactive species are responsible for the observed stabilization of avobenzone. In vitro study of the two formulations containing DESM clearly showed critical wavelength of well over 370 nm and can thus be categorized as broad-spectrum sunscreens. DESM does not have any contribution to in vivo SPF; instead it boosts SPF by about 5 units in high-SPF products. DESM was found to be an excellent singlet-oxygen quencher, thereby reducing photodegradation of avobenzone caused by singlet oxygen. In short, the multiplicity of effects and formulation benefits seen with DESM makes it an ideal choice as a unique antioxidant photostabilizer for a variety of cosmetic products targeting young and mature skin alike.

A Sunscreen-Tanning Compromise: 3D Visualization of the Actions of Titanium Dioxide Particles and Dihydroxyacetone on Human Epiderm

Abstract The self-tanning agent dihydroxyacetone (DHA) was applied to human skin samples, and its effect on light absorption was followed in time to study the DHA influence inside the different layers of skin. Application of DHA shows increased light absorption in the visible light region, as evidenced by skin tanning. The tanning effect is enhanced by UV irradiation and appears localized in the near-stratum corneum layer as revealed by depth analysis of the time signal. As a reference, application of an emulsion containing titanium dioxide particles shows clear surface stability and a screening of light penetration beyond the stratum corneum.

Pulsed photoacoustic spectroscopy applied to the diffusion of sunscreen chromophores in human skin: the weakly absorbent regime

Pulsed photoacoustic spectroscopy was used to study the penetration of sunscreen chromophores into human skin. This study focuses on basic solutions containing single typical filter molecules, as used in current sunscreens, dissolved in mineral oil. The pulsed form of the photoacoustic technique was preferred because it provides more detailed information on the filter distribution within the different layers of human skin. A new methodology provides better insight into the diffusion process through signal analysis in the time and frequency domains, allowing for global and depth-related characterization. The penetration of the chromophore influences the response signal by inducing changes in the optical and thermal properties at different depths within the medium. The light scattering effect of titanium dioxide was demonstrated by the same technique.

A comparative study on chromophore diffusion inside porous filters by pulsed photoacoustic spectroscopy

In the context of investigations on drug diffusion into human skin, first examples of using porous filters as model bio-membranes to understand the role of physical and chemical parameters on the penetration of chromophores. The diffusion of small molecules has been investigated in porous filters of different pore sizes by using pulsed photoacoustic spectroscopy. An analogy is made between the model membranes and human skin concerning the influence of the filter structure and the hydrophilic nature of the matrix support material. Finally, first data are presented on the effect of a modified surface filter structure on the diffusion pattern, thus opening the field to the potential use of these filters as model membrane of adjustable structural and chemical parameters.

Pulsed Photoacoustic Study of the Diffusion of Chromophores in Human Skin

The technique of pulsed photoacoustic spectroscopy was used to investigate the diffusion of chromophores in human skin. The kinetic of diffusion has been studied for five solutions at different concentrations in a mixture of chromophores, as used in commercial sunscreens. In addition to the classical macroscopic interpretation of the diffusion process, a new method is shown to give more detailed information on chromophore presence at different depths in skin. For the first time, results are expressed in the frequency domain by means of the Fourier transform applied to the photoacoustic signal. The spectra are discussed versus the depth in skin samples and the time of diffusion kinetics. This new method of data analysis is shown to be very useful for understanding the influence of the internal structure of a medium on the penetration rate of chromophores into skin.

Influence of thermal and optical properties on the visibility of liquid-crystal phase transitions in photoacoustic spectroscopy

The thermal, optical light absorption and light scattering properties of a liquid crystal can be distinguished and separately studied by a single technique, pulsed photoacoustic spectroscopy (PPAS), by using different excitation/detection configurations. The advantages of performing complementary thermal and optical measurements without modifying the sample environment are demonstrated in the case of a typical liquid crystal: 4-octyl-4′-cyanobiphenyl (8CB). Results show that light scattering can strongly influence the PPAS response signal through the light absorption profile, especially at phase transitions subjected to small changes in thermal properties, such as the Nematic/isotrope phase transition.

Caging interactions between a dopant chromophore and the sol-gel matrix

Abstract The successful incorporation of chromophores in a sol–gel matrix requires a careful study of their interaction with the gel environment. Photoacoustic spectroscopy is used to probe chemical changes in the direct neighborhood of dopant molecules in a silica-based sol–gel during times of evolution up to 100 times the gelation time. Studies of different chromophores such as β-carotene (β-Car.) and copper phthalocyanine (Cu-Pht.) show a size dependent steric hindrance effect as well as chromophore relaxation phenomena within the gel pores. Three main phases of evolution of the medium are distinguished. The stability of the chromophores is discussed and the results compared to FTIR spectra over time.

Visualization of Surface Gelation Processes in a Doped Sol-Gel Glass.

Pulsed photoacoustic spectroscopy has enabled depth-resolved, in situ measurements of the chemical changes that occur in a sol-gel process to be examined. By use of beta-carotene as a probe to determine the efficiency of heat transfer to the immediate molecular environment in thin and thick samples, separate surface and bulk gelation processes in a sol-gel material have been observed.

Photoacoustic Spectroscopy Applied to Biological Materials

The conventional method of analysis used to investigate properties of molecules inside a medium consists of measuring the transmission and reflection coefficients of the material in order to determine the absorption of a given chromophore in the medium. However, this classical technique only gives access to an average value over the thickness of the material being investigated. It does not allow for the establishment of a depth profile of the density of chromophores in the material, i.e. their local concentration. In addition, this technique necessitates good optical quality of the medium in the range of the optical wavelengths used which makes it less suited to amorphous biological tissues because these are often subject to strong light diffusion, diffraction or a too high absorption. In contrast to this technique, photoacoustic spectroscopy (PAS) allows for the in-depth characterization of either homogenous or heterogenous non-transparent materials.1–4 This spectroscopy has already been applied to study complex biological media like leaves (photosynthesis)5–7, eye retina (vision)8–9 or human skin (membrane permeability).10–12