Unraveling the Complexity of Biosilicification Processes: Kinetic and Thermodynamic Controls of Organic Substrates on the Nucleation of Amorphous Silica

DOVE-0545166知识专长：随着人们认识到硅是一种高度生物化的元素，它在控制硅和碳的全球地球化学中的作用已经成为科学研究的前沿。特别感兴趣的是学习生物矿化过程，容易产生高活性池的硅作为无定形水合二氧化硅，也被称为生物硅。对海洋和陆地硅化作用产生的生物硅进行了广泛的形态学研究。硅藻、领鞭毛虫、维管植物）表明，许多生物体在矿化途径上具有共性。这一点和来自系统发育记录的证据表明，通过“现成的”生物化学过程控制生物硅形成（和其他生物矿物）的基本原则必须存在，这些生物化学过程一次又一次地指导给定类型的矿化作用。虽然文献中充满了生物硅的现象学特征，但它们本身不能产生生物硅化过程的基本规律。要取得进展，就需要了解在分子水平上发生的成核和生长过程。该研究领域的发展时机已经成熟，该提案描述了一项计划，该计划利用PI在二氧化硅地球化学和生物矿化系统中矿物成核和生长的纳米级模型研究方面的独特经验。该项目将使用新的生物基质模型来确定生物硅化环境中界面的生物化学如何控制时间（动力学）和二氧化硅成核的程度/位置（热力学）。该项目将：1）测试假设，旨在发现生物化学界面如何控制成核步骤和早期生长;和2）量化断言，即与膜相关的关键官能团通过调节界面能和附着/分离动力学促进水合二氧化硅的形成。这也将允许直接测试吉布斯-汤姆逊关系，一个基本的热力学原理长期以来被认为是确定矿物成核的自发发生。这个项目是独特的，从以前的研究，我们专注于生物化学界面和我们的分析，通过原位纳米方法来测量和表征产品。应用我们实验室中使用的方法，将模型膜制备为纳米级化学模板。成核的动力学、热力学和表征研究将使用原位流体轻敲AFM和共焦表面增强拉曼光谱。结果将在经典成核和生长理论的框架内进行分析。这项基础科学研究将建立在有机物丰富的环境中促进和延缓硅化的因素。在量化这些有机控制，理解的相对重要性的热力学驱动程序和动力学因素在诱导成核将emerging.Broader影响：结果将有利于前沿研究问题在许多学科。1）如何做微生物（被动或主动？）促进了热泉中广泛的硅化作用2)在什么条件下，磷酸盐矿化的开始可以由初始硅化步骤来确定？3)在地球/工业系统中，二氧化硅沉淀物/水垢的形成有哪些动力学和热力学控制？4)硅化有机体如何利用环境友好的条件来启动和塑造复杂的结构？矿物和生物的世界自然是令人兴奋的推广和教育。这两个领域之间的迷人联系将是第二个“生物矿物-地球生命”活动的重点。我们将建立一个新的模块，整合矿物质，无定形硅胶和硅化生物，以开发针对中学生的互动活动。

EAR-0545166DOVEIntellectual 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.