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Stéphanie Girard

Publications and source records attributed to Stéphanie Girard.

5 recordsLinked to original sources
PubMed2003

Assessment of the skin photoprotective capacities of an organo-mineral broad-spectrum sunblock on two ex vivo skin models.

UV irradiation can cause cutaneous damage that may be specific according to the wavelength of UV rays. For example, damage from UVB irradiation manifests itself in the form of sunburn cells and enhancement of the expression of p53, while damage from UVA exposure results in an increase in the expression of vimentin. These reactions to UV irradiation were used in this work to evaluate the photoprotective capacities of two sunblock preparations that were applied to the surface of the skin. One sunblock preparation is a UVB absorber containing zinc oxide (ZnO) and titanium oxide (TiO2) exclusively. The other sunblock preparation is a new organo-mineral sunblock containing Tinosorb M, OCM, ZnO and TiO2. Evaluation of the photoprotective capacities of both preparations on hairless rat skin and on in vitro reconstructed human epidermis revealed that they were effective in preventing UVB-induced damage. In contrast, only the organo-mineral sunblock was effective in the prevention of UVA-specific damage such as dermal alterations characterized by the expression of vimentin. Furthermore, our data support the fact that hairless rat skin and in vitro reconstructed human epidermis are a reliable basis for the evaluation of the photoprotective capacities of various sunscreens against UVB and UVA damage.

Animals↗
PubMed2002

Novel inorganic frameworks constructed from double-four-ring (D4R) units: computational design, structures, and lattice energies of silicate, aluminophosphate, and gallophosphate candidates.

The design of new and interesting inorganic frameworks is an ongoing challenge in materials sciences. New structures containing double-four-ring (D4R) units have recently received particular attention. The present work focuses on the computational design of new three-dimensional frameworks made of D4R units exclusively. In a first step, our simulations explore the possible ways to assemble predefined D4R units in 3D space using a sophisticated cascade of simulated annealing/minimizations steps (autoassembly of secondary building units method). While the existing zeotype topologies were successfully generated, new topologies were predicted including very open frameworks containing new types of cages. In a second step, lattice energy minimizations were performed to estimate the viability of these hypothetical frameworks as silicate, aluminophosphaste, and gallophosphate candidates. When comparing the hypothetical structures to existing compounds, our results raise the challenging question of the appropriate chemical composition that should be aimed at for a given framework topology of interest.

Journal Article↗
PubMed2002

Computational design and prediction of interesting not-yet-synthesized structures of inorganic materials by using building unit concepts.

The computational design of new and interesting inorganic materials is still an ongoing challenge. The motivation of these efforts is to aid the often difficult task of crystal structure determination, to rationalize different but related structure types, or to help limit the domain of structures that are possible in a given system. Over the past decade, simulation methods have continuously evolved towards the prediction of new structures using minimal input information in terms of symmetry, cell parameters, or chemical composition. So far, this task of identifying candidate structures through an analysis of the energy landscape of chemical systems has been particularly successful for predominantly ionic systems with relatively small numbers of atoms or ions in the simulation cell. After an introductory section, the second section of this work presents the historical developments of such simulation methods in this area. The following sections of the work are dedicated to the introduction of the building unit concept in simulation methods: we present simulation approaches to structure prediction employing both primary (aggregate of atoms) and secondary (aggregate of coordination polyhedra) building units. While structure prediction with primary units is a straightforward extension of established approaches, the AASBU method (automated asssembly of secondary building units) focusses on the topology of network-based structures. This method explores the possible ways to assemble predefined inorganic building units in three-dimensional space, opening the way to the manipulation of very large building units (up to 84 atoms in this work). As illustrative examples we present the prediction of candidate structures for Li(4)CO(4), the identification of topological relationships within a family of metalphosphates, ULM-n and MIL-n, and finally the generation of new topologies by using predefined large building units such as a sodalite or a double-four-ring cage, for the prediction of new and interesting zeolite-type structures.

Journal Article↗
PubMed2002

Framework stability of nanoporous inorganic structures upon template extraction and calcination: a theoretical study of gallophosphate polymorphs.

A systematic computational study of gallophosphates was undertaken. First, lattice energy minimization calculations using a formal-charge shell model potential have been carried out on a series of hypothetical gallium phosphates derived from their metallogallophosphate, aluminophosphate, or aluminosilicate analogues through atomic substitution. The minimized structures show the typical features in terms of bond angles and distances as expected in zeolitic gallophosphates. Second, the crystal structures of several gallophosphates in their calcined forms have been predicted, using for each compound lattice energy minimization and an initial model derived from its as-synthesized templated form. All the modified structures thus have the same GaPO(4) composition. The lattice energies of all the simulated gallophosphate structures were compared to that of GaPO(4)-quartz as a reference structure. Interestingly, among all predicted calcined structures, various zeolitic topologies were found. The study of the energetics of these zeotypic structures showed a linear dependence of lattice energy upon density. Strikingly, a few simulated structures showed unrealistic structural features, such as important framework distortions, often associated with the occurrence of a hexameric unit in the original as-synthesized structures. Also, those gallophosphates with structural faults were found in the upper part of the energy/density plot. To address the validity of our force field calculations in these special cases, first principles calculations were undertaken on ULM-4, chosen as a typical representative structure. Indeed, the qualitative agreement found between our results and those obtained with the nonlocal density functional theory demonstrates the robustness of our force field. Further minimization also showed that the inclusion of polarizability is crucial for yielding results comparable with those obtained using first principles methods.

Journal Article↗