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

揭示生物硅化过程的复杂性：有机基质对无定形二氧化硅成核的动力学和热力学控制

• 批准号: 0545166
• 负责人: Patricia Dove
• 金额: $ 21.98万
• 依托单位: Virginia Polytechnic Institute and State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-09-15 至 2010-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0545166&HistoricalAwards=false
• 关键词: Unraveling; Complexity; Biosilicification; Processes; Kinetic

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.

知识价值：随着人们认识到硅是一种高度生物元素，它在控制硅和碳的全球生物地球化学中的作用已经成为科学研究的前沿。特别感兴趣的是了解生物矿化过程，容易产生高度反应的Si池作为无定形水合二氧化硅，也被称为生物二氧化硅。对海洋和陆生硅藻（如硅藻、鞭藻、维管植物）产生的生物硅的广泛形态学研究表明，许多生物在矿化途径上具有共性。这一点和系统发育记录的证据表明，通过“现成的”生物化学过程，一定存在着控制生物二氧化硅形成（和其他生物矿物）的基本原理，这些生物化学过程在多个王国和门之间一次又一次地指导特定类型的矿化。虽然文献大量的现象学特征的生物硅，他们不能，通过自己，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。该研究领域的发展已经成熟，该提案描述了一个利用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尺度模型研究方面的独特经验的计划。目的和方法：该项目将使用新型生物底物模型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设；2)量化与膜相关的关键官能团通过调节界面能和附着/脱离动力学促进水合二氧化硅形成的断言。这也将允许对吉布斯-汤姆逊关系进行直接测试，这是一个长期以来被认为决定矿物成核自发发生的基本热力学原理。该项目与以往的研究不同，我们专注于生物化学界面，并通过原位纳米尺度方法进行分析，以测量和表征产物。应用我们实验室使用的方法，模型膜将被制备为纳米级化学模板。动力学，热力学和表征研究的成核将使用原位流体攻丝AFM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富有机质环境中促进和阻碍硅化的因素。在量化这些有机控制时，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将会出现。更广泛的影响：结果将有利于许多学科的前沿研究问题。1)微生物是如何（被动还是主动）促进热液泉广泛的硅化作用的？2)在什么条件下可以通过初始硅化步骤确定磷酸盐矿化的开始？3)地球/工业系统中二氧化硅沉淀/水垢形成的动力学和热力学控制是什么？4)硅化生物如何利用环境良性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成为第二个“生物矿物-地球到生命”活动的重点。我们将构建一个新的模块，整合矿物质，无定形硅胶和硅化生物，开发一个针对中学生的互动活动。