The aim of the research was to examine a model system for the chemistry that is involved in the biomineralization of SiO2 in certain demosponges. In particular, the interaction of a silica protein, a silicatein, with silicon reagents was modeled. The active site of silicatein contains histidine and serine amino acid side4 chains.
Several imidazole-based silane complexes of the general form SiPh3OL were synthesized as a preliminary model. In order to model the histidine-serine sites of the silicatein, the ligands were used that are bound to the silicon via Si-O linkages and also have a potentially chelating imidazole ring. The three OL ligands were derided from the alcohols ROH: 1-hydroxydecyl-imidazole (HOL1), 4-hydroxymethyl-5-methyl-imidazole (HOL2), and 6-imidazole-1-ylmethyl-pyridine-2-ylmethanol (HOL3). Synthesis of the SiPh3OL complexes from chlorosilanes was achieved in two ways. The first one is the reaction of chlorosilanes or alkoxysilanes with the same number of equivalents of ligand and triethylamine or pyridine as a base. The second method is the reaction of chlorosilanes with two equivalents of the imidazole containing ligand, where one equivalent acts as a base for the HCl generated during the reaction. Removal of the HCl by-product from the reaction of SiPh3Cl and HOL was a problematic part of the syntheses of the three SiPh3OL compounds. The use of such bases as pyridine and Et3N yielded products that were less pure than when HOL was used as the base. Compounds with a high reactivity toward hydrolysis were obtained and characterized by a variety of techniques.
The syntheses of other complexes of the OL ligands were attempted. The oil Si(OL1)4 was prepared in low yield. Attempt to prepare the compounds SiPh2(OL1)2 and SiPh2(OL2)2 from chlorosilanes and from alkoxysilanes at best gave impure compounds or very complex mixtures.
Another project included the syntheses of proposed intermediates which could form during biomineralization. These intermediates are predicted to be high coordinate species extremely sensitive to hydrolysis reactions. To investigate the possible products, the reactions of chlorosilanes: SiPhCl3 and SiCl4 with 1,1‵-methyline imidazole and methyl imidazole and HOL1, respectively were performed. The products of this reaction were solids with specific chemical shifts of 5- and 6-coordinated silicon complexes were characterized by solid state NMR due low solubility.