Intellectual Merit: With the recognition that silicon is a highly biological element, its roles in controlling the global biogeochemistry of both silicon and carbon have emerged as a forefront of scientific investigation. Of particular interest is to learn the biomineralization processes that readily produce the highly reactive pool of Si as amorphous hydrated silicas, also referred to as biogenic silica. Extensive morphological studies of biogenic silicas produced by marine and terrestrial silicifiers (ex. diatoms, choanoflagellates, vascular plants) show that many organisms share commonalities in their approaches to mineralization. This and evidence from the phylogenetic record have led to suggestions that underlying principles must exist to control biosilica formation (and other biominerals) by 'off the shelf' biochemical processes that direct a given type of mineralization again and again across multiple kingdoms and phyla. While the literature abounds in phenomenological characterizations of biological silicas, they cannot, by themselves, yield fundamental laws of biosilicification processes. Advances will require understanding the nucleation and growth processes taking place at the molecular level. This research area is ripe for advancement and this proposal describes a plan that takes advantage of the PI's unique experience in silica geochemistry and nanoscale model studies of mineral nucleation and growth in biomineralizing systems. Objectives, Methods: The project will use novel model biosubstrates to determine how the biochemistry of interfaces in biosilicification environments control the timing (kinetics) and extent/location (thermodynamics) of silica nucleation. The project will: 1) test hypotheses aimed at discovering how biochemical interfaces govern the nucleation step and early growth; and 2) quantify assertions that key functional groups associated with membranes promote the formation of hydrated silicas by modulating interfacial energy and attachment/detachment kinetics. This will also allow a direct test of the Gibbs-Thomson relation, a fundamental thermodynamic principle long believed to determine the spontaneous onset of mineral nucleation. This project is unique from previous studies by our focus on biochemical interfaces and our analysis by in situ nanoscale methods to measure and characterize the products. Applying methods in use in our laboratory, model membranes will be prepared as nanoscale chemical templates. The kinetic, thermodynamic, and characterization studies of nucleation will use insitu fluid tapping AFM and confocal Surface Enhanced Raman spectroscopy. Results will be analyzed within the framework of classical nucleation and growth theories. This basic science study will establish factors that promote and retard silicification in organic-rich environments. In quantifying these organic controls, an understanding of the relative importance of thermodynamic drivers and kinetic factors in inducing nucleation will emerge. Broader Impacts: The outcomes will benefit forefront research questions in many disciplines.1) How do microbes (passively or actively?) promote extensive silicification in hydrothermal springs? 2) Under what conditions could the onset of phosphate-based mineralization be determined by an initial silicification step? 3) What are the kinetic and thermodynamic controls on the formation of silica precipitates/scales in earth/industrial systems? 4) How do silicifying organisms utilize environmentally benign conditions to initiate and mold elaborate structures? The world of minerals and organisms is naturally exciting for outreach and education. The fascinating linkages between these two areas will be the focus of a second 'Biominerals- Earth to Life' activity. We will build a new module that integrates minerals, amorphous silica gels, and silicifying organisms to develop an interactive activity targeted to middle school students.
