Role of Silicon-Organic Interactions in Silica Biomineralization

SahaiEAR-0208036人们越来越认识到需要在分子水平上了解有机-无机相互作用，以二氧化硅生物矿化为例的与生物地球化学相关的过程，以及如在仿生介孔二氧化硅的受控合成中的材料科学。我建议采用理论和实验相结合的方法来研究二氧化硅与水相中碳水化合物和胺的相互作用的性质。我们将(I)确定假定的高配位硅-碳水化合物络合物是否在生物硅吸收中发挥作用，以及(Ii)确定胺在催化溶解硅物种的生物聚合中的作用。检查的碳水化合物将包括多元醇、糖酸和多糖。将对这些胺进行检查，以寻找最有可能的生物硅成核和聚合途径。具体地说，我们将试图确定胺是否通过SN2机制催化起始硅有机化合物的水解，或者多胺是否通过硅酸起始化合物导致无机形成的二氧化硅簇合物的聚集。对于前者，我们将检测不同亲核性的胺，包括甲胺、二甲胺、吡啶、胍、咪唑、赖氨酸、精氨酸和组氨酸。以1，2-二氨基乙烷、1，2-二氨基丙烷、1，3-二氨基丙烷、1，2，3-三氨基丙烷和丁烷骨架上的类似三胺为模型多胺，研究其替代机理。氮杂化的效果将通过比较1，3-二氨基戊烷和咪唑来确定。此外，1，6-二氨基己烷与1，4-二氨基苯的作用将允许检查碳杂交效应。实验核磁共振和衰减全反射傅里叶变换红外(ATR FTIR)光谱将提供独立的测量。依赖温度的核磁共振将提供活化热。计算方法将采用从头算分子轨道理论来计算结构、能量、振动频率和29Si核磁共振位移，以解释实验光谱，并确定电子对胺的整体亲核性的贡献。

SahaiEAR-0208036There is a growing appreciation of the need to understand organic-inorganic interactions at the molecular-level for processes relevant to biogeochemistry as exemplified by silica biomineralization, and to materials science as in the controlled synthesis of biomimetic mesoporous silica. I propose to investigate the nature of silica interactions with carbohydrates and amines in the aqueous phase combining theoretical and experimental approaches. We will (i) determine whether putative hypercoordinated Si-carbohydrate complexes can play a role in biological silicon uptake, and (ii) identify the role of amines in catalyzing the biopolymerization of dissolved silicon species. The carbohydrates examined will include polyalcohols, sugar-acids and polysaccharides. The amines will be examined for the most likely pathway of biogenic silica nucleation and polymerization. Specifically, we will attempt to determine whether the amines act to catalyze hydrolysis of a starting Si-organic compound via a SN2 mechanism or whether polyamines act to bring about aggregation of inorganically formed silica clusters from a starting compound of silicic acid. For the former mechanism, we will examine amines of different nucleophilicities including methylamine, dimethylamine, pyridine, guanidine, imidazole, lysine, arginine and histidine. The alternative mechanism will be studied using 1,2-diaminoethane, 1,2-diaminopropane, 1,3-diaminopropane, 1,2,3-triaminopropane, and analogous triamines on a butane backbone as the model polyamines. The effect of nitrogen hybridization will be determined by comparing 1,3-diaminopentane to imidazole. Further, the effect of 1,6-diaminohexane versus 1,4-diaminobenzene will permit examination of carbon hybridization effects. Experimental NMR and Attenuated Total Reflectance Fourier Transform Infra-Red (ATR FTIR) spectroscopy will provide independent measurements. Temperature dependence NMR will provide activation enthalpies. The computational method used will be ab initio MO theory to calculate the structure, energy, vibrational frequencies and 29Si Nuclear Magnetic Resonance (NMR) shifts to explain the experimental spectra, and to determine the electronic contributions to the overall nucleophilicities of the amines.