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.Quartz surface reconstruction during and after milling depends on the molecular environment. Water vapor and molecular oxygen influence radical species formation. Presence of water vapor results in few radicals and negligible membranolytic activity. Absence of water vapor leads to highly reactive surfaces that rapidly reconstruct and confer membranolytic activity to quartz.image