NER: Catalytic formation of nanostructured ceramics by a bio-mimetic and environmentally friendly approach

美国国家科学基金会-活性纳米结构和纳米系统(ANN)(NSF 06-595)纳米探索性研究(NER)建议编号：CBET-0708054主要研究员：道格拉斯附属机构：普林斯顿大学提案标题：NER：通过模拟生物和环境友好的方法催化形成纳米结构陶瓷NER：通过模拟生物和环境友好的方法催化形成纳米结构陶瓷数百万年来，大自然一直能够在纳米尺度上制造具有精确细节和控制的陶瓷结构。鲍鱼壳的强度和硅藻中复杂的设计是在常温近中性pH条件下产生高度有序陶瓷材料的两个生物例子。对于人造材料，不仅缺乏精确的纳米结构，形成陶瓷所需的条件还涉及极端的pH和/或高温。这些条件在成本和环境影响方面是有害的，可能会阻碍许多有机结构导向剂的使用，以及可能包含在多孔陶瓷基质中的催化剂的加入。一种可以模仿自然在温和的条件下生产纳米级有序陶瓷的合成系统将在结构材料、催化和过滤技术中得到广泛的应用。我们所关注的自然系统是蛋白质硅酸盐，它存在于海洋海绵特提亚奥兰提亚中。这种海绵产生硅质针状体，由含有75%针状体重量的二氧化硅外壳和含有混合蛋白质的核心组成。在核心中发现的蛋白质中，70%是硅酸盐。我们之所以关注该蛋白，有两个原因：一是确定了该蛋白的结构，二是阐明了它的催化机制。这些研究表明，硅酸盐具有催化正硅氧基硅烷(TEOS)水解的能力。水解后的硅烷随后迅速缩合，形成硅灰石。利用这一机制，在室温和近中性的pH条件下，相对稳定的TEOS可以快速转化为Silca。我们最近开发了一种模拟蛋白质硅酸盐的催化功能的人工合成的非肽基聚合物。通过将在蛋白质催化活性中起关键作用的官能团的类似物加入到纯合成聚合物中，我们已经在非肽嵌段共聚物中展示了催化功能。这项工作已经在《美国化学学会杂志》目前正在审议的一份手稿中进行了描述。我们已经通过许多分析和化学方法证明了我们的聚合物在TEOS缩合方面的催化性质。在我们成功演示催化的基础上，我们将利用嵌段共聚催化剂的两亲性，在近中性的pH和常温下形成纳米结构陶瓷。这项工作的高风险因素是使用这种聚合物来制作具有纳米级特征的陶瓷模板，以及加入除二氧化硅以外的其他陶瓷，这两种方法以前都没有得到证明。因此，我们将创建一个模拟自然系统的合成系统，在该系统中，纳米级模板试剂也是催化剂。这笔赠款的更广泛影响包括创造新材料，提高催化效率，生产新的纳米结构陶瓷，并在环境友好的条件下创造新的结构材料。它还将允许将温度或pH敏感材料合并到多孔陶瓷基质中。此外，这笔赠款将支持PI参与的外联计划，包括本科生研究经验(REU)计划、普林斯顿大学材料学院(PUMA)针对未被充分代表的少数族裔高中生的计划，以及自由科学中心的常驻科学家计划。这笔助学金还包括本科生的研究活动。将尽一切努力吸引一名女性或少数族裔学生，并向他们介绍尖端研究。这项工作的智力影响是双重的。能够模拟生物过程是真正理解它的最好方法之一。因此，我们努力在一个完全合成的系统中重现自然所做的事情，将导致对自然过程的更深层次的理解。其次，在合成纳米级有序陶瓷的过程中，我们将增加对自组装两亲性体系的理解，以及如何将形成的结构固定和利用。

National Science Foundation - Active Nanostructure and Nanosystems (ANN) (NSF 06-595)Nanoscale Exploratory Research (NER)Proposal Number: CBET-0708054Principal Investigator: Adamson, DouglasAffiliation: Princeton UniversityProposal Title: NER: Catalytic formation of nanostructured ceramics by a bio-mimetic and environmentally friendly approachNER:Catalytic formation of nanostructured ceramics by a bio-mimetic andenvironmentally friendly approachFor millions of years nature has been able to make ceramic structures with precise detail and control at the nanoscale. The strength of the abalone shell and the intricate designs found in diatoms are two examples of organisms producing highly ordered ceramic materials under conditions of near-neutral pH at ambient temperatures. In the case of man-made materials, not only is the precise nano-structure lacking, the conditions required to form ceramics involve extremes of pH and/or high temperatures. These conditions are detrimental in terms of cost and environmental impact, and may preclude the use of many organic structure-directing agents as well as the incorporation of catalysts that could be included in a porous ceramic matrix. A synthetic system that can mimic the ability of nature to produce well ordered ceramics at the nano-scale under mild conditions would find applications ranging in structural materials, catalysis, and filtration technologies. The natural system on which we have focused our efforts is the protein Silicatein, found in the marine sponge Tethya aurantia. This sponge creates silica spicules that are composed of a silica outer casing comprising 75% of the spicule weight and a core containing a mixture of proteins. Of the protein found in the core, 70% is Silicatein. We focused on this protein for two reasons: first, the structure of the protein had been determined and second, the mechanism of its catalysis had been elucidated. These studies revealed that Silicatein has the ability to catalyze the hydrolysis of tetraethoxysilane (TEOS). The subsequent condensation of the hydrolyzed silane is rapid and results in the formation of silca. Exploiting this mechanism, the relatively stable TEOS can be quickly converted to silca at room temperature and under near neutral pH. We have recently developed a synthetic, non-peptide based polymer that mimics the catalytic function of the protein Silicatein. By incorporating analogs of the functional groups shown to be critical in the catalytic activity of the protein into a purely synthetic polymer, we have demonstrated catalytic function in a non-peptide block copolymer. This work has been described in a manuscript currently under consideration by the Journal of the American Chemical Society. We have demonstrated by numerous analytical and chemical methods the catalytic nature of our polymer with respect to TEOS condensation. Building on our successful demonstration of catalysis, we will exploit the amphiphilic nature of our block copolymer catalyst to form nano-structured ceramics under near-neutral pH and ambient temperatures. The high-risk element of this work is the use of this polymer to template ceramics with nanoscale features and the incorporation of ceramics other than silica, neither of which has been previously demonstrated. We thus will create a synthetic system that mimics the natural system in which a nanoscale templating agent is also a catalyst. The broader impacts of this grant include the creation of new materials that increase the efficiency of catalysis, produce new nanostructured ceramics, and create new structural materials, under environmentally benign conditions. It will also allow for the incorporation of temperature or pH sensitive materials into a porous ceramic matrix. Additionally, this grant will support the PI's involvement in outreach programs that include a Research Experience for Undergraduates (REU) program, Princeton University Materials Academy (PUMA) targeted at underrepresented minority high school students, and the Scientist in Residence program at the Liberty Science Center. This grant also includes research activities for an undergraduate student. Every effort will be made to attract a female or minority student and introduce them to cutting edge research. The intellectual impact of this work is two-fold. Being able to mimic a biological process is one of the best ways to truly understand it. Thus our efforts to reproduce what nature does in a completely synthetic system will lead to a deeper understanding of the natural process. Secondly, in synthesizing a ceramic ordered at the nano-scale, we will increase our understanding of self-assembled amphiphilic systems and how the structures formed can be immobilized and exploited.