Role of Silicon-Organic Interactions in Silica Biomineralization

人们越来越认识到需要在分子水平上理解有机-无机相互作用，以生物地球化学为例，如二氧化硅生物矿化，以及材料科学，如仿生介孔二氧化硅的受控合成。我建议结合理论和实验方法来研究水相中二氧化硅与碳水化合物和胺相互作用的本质。我们将(i)确定假设的超配硅-碳水化合物复合物是否可以在生物硅摄取中发挥作用，以及（ii）确定胺在催化溶解硅物种的生物聚合中的作用。检查的碳水化合物包括多元醇、糖酸和多糖。这些胺将被检查最可能的生物硅成核和聚合途径。具体来说，我们将尝试确定胺是否通过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使无机形成的二氧化硅团簇聚集。对于前一种机制，我们将研究不同亲核性的胺，包括甲胺、二甲胺、吡啶、胍、咪唑、赖氨酸、精氨酸和组氨酸。将以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类似的丁烷主链上的三胺作为模型多胺来研究替代机理。通过比较1,3-二氨基戊烷和咪唑来确定氮杂化的效果。此外，1,6-二氨基己烷对1,4-二氨基苯的影响将允许检查碳杂化效应。实验核磁共振和衰减全反射傅立叶变换红外光谱（ATR FTIR）将提供独立的测量。温度依赖核磁共振将提供活化焓。计算方法将采用从头计算MO理论来计算结构、能量、振动频率和29Si核磁共振（NMR）位移，以解释实验光谱，并确定电子对胺的总体亲核性的贡献。

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.