Reaction with Water Vapor Defines Surface Reconstruction and Membranolytic Activity of Quartz Milled in Different Molecular Environments.

Industrial processing of quartz (SiO2) and quartz-containing materials produces toxic dust. Fracturing quartz crystals opens the Si‒O bond and produces highly reactive surface species which mainly react with molecules like water and oxygen. This surface-reconstruction process forms silanol (Si‒OH) on the quartz surface, which can damage biological membranes under specific configurations. To comprehend the impact of the quartz surface restructuring on membranolytic activity, the formation and reactivity of quartz radicals produced in four distinct molecular environments with electron paramagnetic resonance (EPR) spectroscopy are evaluated and their membranolytic activity is measured through in vitro hemolysis test. The four molecular environments are formulated with and without molecular water vapor and oxygen (±H2O/±O2). The absence of water favored the formation of surface radical species. In water-rich environments, diamagnetic species prevailed due to radical recombination. Quartz milled in -H2O/±O2 acquired membranolytic activity when exposed to water vapor, unlike quartz milled in +H2O/±O2. After being stabilized by reaction with water vapor, the membranolytic activity of quartz is maintained over time. It is demonstrated that the type and the reactivity of radical sites on quartz are modulated by the outer molecular environment, ultimately determining the biological activity of milled quartz dust.

Short-Range Electronic Interactions between Vanadium and Molybdenum in Bimetallic SAPO-5 Catalysts Revealed by Hyperfine Spectroscopy.

Engineering two cooperative sites into a catalyst implies the onset of synergistic effects related to the existence of short-range electronic interactions between two metal components. However, these interactions and the relative structure-property correlations are often difficult to obtain. Here we show that hyperfine spectroscopy has the potential to reveal the presence of V4+-O-Mo6+ linkages assessing the degree of spin density transfer from paramagnetic V4+ species to proximal oxo-bridged Mo6+ metal ions. The dimer species were prepared by adsorption of Mo(CO)6 in the pores of SAPO-5, followed by thermal decomposition and oxidation and subsequent grafting of anhydrous VCl4(g) followed by hydrolysis and dehydration. The metal species react with SAPO protons during the exchange process and generate new Lewis acid sites, which act as redox centers. X- and Q-band EPR and HYSCORE experiments have been employed to monitor the local environment of V4+ species obtaining direct evidence for spin delocalization over 27Al, 31P, 95Mo, and 97Mo nuclei, demonstrating the presence of bimetallic V-O-Mo well-defined structures.