A new and coherent view of the local environment of Fe2+ in silicate glasses is derived from a combined study by EXAFS and Molecular Dynamics simulation. Iron is located in distorted sites, whose geometry varies continuously from a tetrahedron to a triangular bipyramid. Iron polyhedra are apex-connected to the silicate network, while edge-linked to each other, matching with a random distribution of iron in the glass. Fe2+ does not have the significance of a network-forming element. Its local structure results from the freezing of dynamical exchange processes occurring in the liquid.
Given the growing concern over antibiotic resistance, there is an urgent need to explore alternative antibacterial strategies. Metal oxide nanostructures have emerged as a promising option, and in particular, zinc oxide (ZnO) nanostructures have demonstrated strong antifungal and antibacterial properties. This study focuses on ZnO nanowires (ZnO NWs) and their potential as antibacterial agents against Pseudomonas putida, a Gram-negative bacterium. The objective is to investigate the antibacterial mechanisms and assess their efficiency. The unique shape of ZnO NWs, obtained through hydrothermal growth, may rupture bacterial cells and inhibit bacterial growth. In addition to their morphology, the release of Zn2+ ions from ZnO NWs may contribute to their antibacterial properties. These ions have the potential to disrupt the bacterial cell membrane, further impeding bacterial growth. Moreover, ZnO nanostructures exhibit excellent photocatalytic properties under UV light, enhancing their antibacterial effects. Overall, this study highlights the potential of hydrothermally synthesized ZnO NWs in inhibiting P. putida growth and provides valuable insights into their antibacterial mechanisms. The findings suggest that ZnO nanostructures have the potential to be effective antibacterial agents and could be utilized in various settings to fight microbial infections and maintain hygiene.
Experimental Mg K‐edge XANES spectra were obtained for crystals and synthetic glasses. To interpret the experiments, two different ab initio XANES calculation methods were employed. The first one is based on multiple‐scattering calculations and muffin‐tin potentials (FEFF package). The second uses a plane‐wave basis set, norm‐conserving pseudo‐potentials, periodic boundary conditions. The resulting calculations for reference models with three different Mg coordinations are used to derive the best way to analyze the experimental XANES spectra for the glasses.
Impurete dans les materiaux synthetiques et traceur des conditions de formation (redox) dans les composes naturels, le fer est un constituant majeur dont l'environnement local dans les verres varie avec le mode de formation. Ainsi, la spectroscopie d'absorption optique du fer dans les verres met en evidence l'existence de familles. Si la position des bandes d'absorption peut etre modelisee, l'interpretation des variations d'intensite liees aux phenomenes de diffusion, et d'absorption reste qualitative, limitant l'extraction d'informations structurales. Le calcul de la diffusion de la lumiere par une sphere dielectrique, presente dans ce travail, se situe tres en amont du calcul des spectres d'absorption mais constitue une etape indispensable a l'elaboration des modeles. En ce qui concerne l'absorption par un ion de transition, l'analyse systematique des hypotheses de la litterature permet de jeter les bases de la demarche a mener pour acceder aux intensites des transitions. La mise en application de ces considerations depasse largement le cadre de cette these et ces resultats n'ont pu etre appliques au fer dans les verres. La seconde partie du manuscript traite de l'environnement de l'ion fe 2 + dans un verre synthetique (cao-feo-2sio 2) et dans des tectites, verres naturels dont le mode de formation reste mal connu. L'utilisation conjointe de l'effet mossbauer, de la spectroscopie d'absorption x et des simulations de dynamique moleculaire met en evidence le caractere continu de la distribution des environnements du fer dans ces deux systemes, entre deux coordinences preponderantes (4 et 5). A moyenne distance, les distances cation-cation courtes signent la presence de domaines enrichis en cations. Malgre ces similitudes, le role du fer differe entre les deux systemes. Essentiellement modificateur de reseau dans cao-feo-2sio 2, le fer a une couche de coordination plus ordonnee que dans les tectites, ou il compense la charge induite par la presence de l'aluminium.
