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

智能优点：随着人们认识到硅是一种高度生物的元素，它在控制硅和碳的全球生物地球化学方面的作用已经成为科学研究的前沿。尤其令人感兴趣的是了解生物矿化过程，这种过程很容易产生高活性的硅池，形成无定形水合二氧化硅，也被称为生物成因二氧化硅。海洋和陆地硅化物产生的生物成因二氧化硅的广泛的形态研究(例如。硅藻、鞭毛虫、维管束植物)表明，许多生物在矿化方法上有共同之处。这一点和来自系统发育记录的证据表明，必须存在潜在的原则来控制生物硅石的形成(和其他生物矿物)，通过“现成”的生化过程，一次又一次地引导一种特定类型的矿化跨越多个王国和门类。虽然文献中充斥着生物硅酸盐的现象学特征，但它们本身并不能产生生物硅化过程的基本规律。要取得进展，就需要了解分子水平上发生的成核和生长过程。这一研究领域的推进已经成熟，这项建议描述了一项计划，该计划利用PI在二氧化硅地球化学和生物成矿系统中矿物成核和生长的纳米模型研究方面的独特经验。目标和方法：该项目将使用新型模型生物底物来确定生物硅化环境中界面的生物化学如何控制二氧化硅成核的时间(动力学)和程度/位置(热力学)。该项目将：1)测试旨在发现生化界面如何控制成核步骤和早期生长的假说；以及2)量化断言，即与膜相关的关键官能团通过调节界面能量和附着/脱离动力学促进水合二氧化硅的形成。这也将允许直接测试Gibbs-Thomson关系，这是一个基本的热力学原理，长期以来被认为决定了矿物成核的自发开始。该项目不同于以前的研究，因为我们专注于生化界面，并通过原位纳米级方法进行分析来测量和表征产品。应用本实验室正在使用的方法，将模型膜制备成纳米级的化学模板。成核的动力学、热力学和表征研究将使用原位流体敲击原子力显微镜和共聚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确定在富含有机物质的环境中促进和延缓硅化的因素。在量化这些有机控制时，将出现对诱导成核的热力学驱动因素和动力学因素的相对重要性的理解。广泛的影响：结果将有利于许多学科的前沿研究问题1)微生物如何(被动地或主动地？)促进热泉中广泛的硅化作用？2)在什么条件下，最初的硅化步骤可以确定磷酸盐矿化的开始？3)在地球/工业系统中，对二氧化硅沉淀物/鳞片的形成有什么动力学和热力学控制？4)硅化生物如何利用环境友好的条件来启动和塑造精细的结构？矿物和生物体的世界自然是令人兴奋的外展和教育。这两个领域之间令人着迷的联系将成为第二个“生物矿物--地球与生命”活动的重点。我们将构建一个整合了矿物、无定形硅胶和硅化生物的新模块，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.