Role of Silicon-Organic Interactions in Silica Biomineralization

越来越多的人认识到，需要在分子水平上理解有机-无机相互作用，以用于与生物地球化学相关的过程，如二氧化硅生物矿化，以及材料科学，如仿生中孔二氧化硅的受控合成。我建议调查的性质，二氧化硅与碳水化合物和胺在水相结合的理论和实验方法的相互作用。我们将（i）确定是否假定的超配位硅-碳水化合物复合物可以发挥作用，在生物硅的吸收，和（ii）确定的作用，胺在催化溶解的硅物种的生物聚合。检查的碳水化合物包括多元醇、糖酸和多糖。将检查胺的生物二氧化硅成核和聚合的最可能的途径。具体地，我们将试图确定胺是否通过SN 2机制催化起始Si-有机化合物的水解，或者多胺是否用于引起无机形成的二氧化硅簇从起始化合物的柠檬酸聚集。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。将使用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主链上的类似三胺作为模型多胺来研究替代机理。将通过比较1，3-二氨基戊烷与咪唑来确定氮杂化的影响。此外，1，6-二氨基己烷对1，4-二氨基苯的作用将允许检查碳杂化作用。实验NMR和衰减全反射傅里叶变换红外光谱（ATR FTIR）将提供独立的测量。温度依赖性NMR将提供活化谱。所使用的计算方法将是从头计算MO理论来计算结构、能量、振动频率和29 Si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.