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The self-assembly and crystal packing of a unique series of nanocrystalline fluoride ion-encapsulated polyhedral oligomeric silsesquioxane (F-POSS) compounds, with substituted electron-withdrawing group (EWG) perfluorinated alkyl chain arms of varying lengths, were investigated. The fluorine-encapsulated T8[(CH2)n-EWG]8F−-18-crown-6-ether-M+ and T8[(CH2)n-EWG]8F−-tetrabutyl ammonium TBA+ compounds with fluorinated alkyl chain arms were synthesized and subsequently analyzed using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and simultaneous small- and wide-angle X-ray scattering (SAXS/WAXS) techniques. DSC and TGA of the compounds showed that the melting temperatures occurred below 100 °C and the compounds were thermally stable above their melting temperatures. SAXS/WAXS data probed the crystalline structure and self-assembly of the nanocrystalline compounds. At ambient temperatures, the crystalline structures of the compounds were seen to be complex with triclinic unit cells. On cooling from the melt, the self-assembly of the compounds with shorter fluorinated alkyl chain arms is dominated by the ionic attraction between the cages such that the arms form a disordered state that only reorder on standing. In contrast, the self-assembly of the compounds with longer fluorinated alkyl chain arms is dominated by the alignment of the arms into rod-like morphologies such that a fully ordered solid is formed from the melt. Electrical characterization has revealed that the POSS cages exhibited an insulating behavior. The POSS cages with or without fluoride ion encapsulation had similar AC conductivities but cages without fluoride ion encapsulation have the highest relative permittivity. The results show that due to the inorganic–organic-ionic nature of the F-POSS ion encapsulated compounds and nanocrystalline self-assembly, they have great potential as interfacial compatibilizers enhancing the miscibility of polymer composites and aiding interactions between polar and non-polar solvents as ionic liquids. [ABSTRACT FROM AUTHOR]

Reflecting the increasing interest in combinatorial approaches, peptide phage display has seen an unprecedented expansion in a wide range of research areas. Its application to the discovery and analysis of metal binding peptides has opened up new research directions and largely contributed to the nanotechnology field. The rationale behind the need to identify such peptides varies depending on the final aim of the research and its application. Therefore, the possibility to modify the selection technique according to the different requirements would allow for a more systematic approach to be adopted and would ultimately provide substantial benefits. Although the standard panning method can be virtually applied to any target, its use for the identification of metal binding peptides does not provide the characteristics and the flexibility required for an efficient and tailored selection. Here we report on the development of a new panning method that can contribute to a faster, versatile and more informative analysis. Through the use of rolling-circle amplification, polymerase reaction and wild type phage, we have converted the standard selection technique into a more dynamic process in which adjustments can be evaluated and made consistently with the need of the experiment. The successfulness of the improved method is demonstrated in a number of panning experiments with different inorganic targets. The modifications applied to each selection are described and comparisons between the results obtained are made in order to extensively assess and evaluate the impact of the new process. The importance of tailoring the screening method to the specific objectives of a study is also considered. New binder sequences for the materials included in the investigation are identified; their sequences and distinctive characteristics are reported and their ability to act as templates for the nucleation of inorganic material is demonstrated and discussed. [ABSTRACT FROM AUTHOR]

The potential for expanding the variety of enzymic methods for siloxane bond formation is explored. Three enzymes, Rhizopus oryzaelipase (ROL), lysozyme and phytase are reported to catalyse the condensation of the model compound, trimethylsilanol, formed in situfrom trimethylethoxysilane, to produce hexamethyldisiloxane in aqueous media at 25 °C and pH 7. Thermal denaturation and reactant inhibition experiments were conducted to better understand the catalytic role of these enzyme candidates. It was found that enzyme activities were significantly reduced following thermal treatment, suggesting a potential key-role of the enzyme active sites in the catalysis. Similarly, residue-specific modification of the key-amino acids believed to participate in the ROL catalysis also had a significant effect on the silicon bio-catalysis, indicating that the catalytic triad of the lipase may be involved during the enzyme-mediated formation of the silicon–oxygen bond. E. coliphytase was found to be particularly effective at catalysing the condensation of trimethylsilanol in a predominantly organic medium consisting of 95% acetonitrile and 5% water. Whereas the use of enzymes in silicon chemistry is still very much a developing and frontier activity, the results presented herein give some grounds for optimism that the variety of enzyme mediated reactions will continue to increase and may one day become a routine element in the portfolio of the synthetic silicon chemist. [ABSTRACT FROM AUTHOR]

A new pentacoordinate silicon species containing two chelating ligands has been synthesized. The structures of four independent cations of the same compound correspond to different points on the Berry pseudorotation pathway. The percentage of square planar character varies between 19% and 40%. [ABSTRACT FROM AUTHOR]

Reflecting the increasing interest in combinatorial approaches, peptide phage display has seen an unprecedented expansion in a wide range of research areas. Its application to the discovery and analysis of metal binding peptides has opened up new research directions and largely contributed to the nanotechnology field. The rationale behind the need to identify such peptides varies depending on the final aim of the research and its application. Therefore, the possibility to modify the selection technique according to the different requirements would allow for a more systematic approach to be adopted and would ultimately provide substantial benefits. Although the standard panning method can be virtually applied to any target, its use for the identification of metal binding peptides does not provide the characteristics and the flexibility required for an efficient and tailored selection. Here we report on the development of a new panning method that can contribute to a faster, versatile and more informative analysis. Through the use of rolling-circle amplification, polymerase reaction and wild type phage, we have converted the standard selection technique into a more dynamic process in which adjustments can be evaluated and made consistently with the need of the experiment. The successfulness of the improved method is demonstrated in a number of panning experiments with different inorganic targets. The modifications applied to each selection are described and comparisons between the results obtained are made in order to extensively assess and evaluate the impact of the new process. The importance of tailoring the screening method to the specific objectives of a study is also considered. New binder sequences for the materials included in the investigation are identified; their sequences and distinctive characteristics are reported and their ability to act as templates for the nucleation of inorganic material is demonstrated and discussed.

Polyhedral oligomeric silsesquioxane (POSS) cubic cage systems (octa-n-octadecyloctasilsesquioxane, (T8C18) and octakis(n-octadecyldimethylsiloxy)octasilsesquioxane, (Q8C18)) were synthesised with eight long n-alkyl chain (R = C18H37) substituent arms, as model nano-functionalized compounds. The crystalline packing morphology of the cages was studied using time-resolved Small- and Wide-angle X-ray scattering (SAXS/WAXS), thermal and optical techniques. From thermal analysis the melting and crystallization temperatures of the Q8 cage were significantly less than those for the T8 cage. X-ray scattering showed that both cage systems have long-range crystalline ordering where the alkyl chains align in a parallel axial disposition from the POSS core giving a 'rod-like' self-assembled packing morphology. The packing length-scale can be directly related to the overall dimensions of the POSS molecules. Compared to the T8 cages, the Q8 cages pack more efficiently allowing the interdigitation of the alkyl chain arms. Different packing modes and thermal behaviour observed for the T8 and Q8 cages is directly attributed to their structural chemistry. For the Q8 cage, the presence of the OSiMe2 spacer groups which tether the alkyl chain arms to the cage (absent in the T8 cages) allows greater flexibility of the arms letting them interdigitate with each other when packing which is not observed for the analogous T8 cages.

Synthesis and X-ray diffraction study of cationic bischelates MeSi(SCH(2)CONMe(2))(2)(+)Cl(-) and MeGe(SCH(2)CONMe(2))(2)(+)Br(-) are reported. According to X-ray data, the Si and Ge atoms in these compounds have distorted TBP environments with two coordinating oxygen atoms in axial positions.

A range of fluoride-encapsulated octasilsesquioxane cage compounds have been prepared using the TBAF route. Our studies suggest that whilst it is relatively straightforward to prepare fluoride-encapsulated octasilsesquioxane cage compounds with adjacent sp(2) carbons, leading to a range of aryl and vinyl substituted compounds, the corresponding sp(3) carbon derivatives are more capricious, requiring an electron withdrawing group that can stabilize the cage whilst not acting as a leaving group. Analysis by X-ray crystallography and solution (19)F/(29)Si NMR spectroscopy of R(8)T(8)@F(-) reveal very similar environments for the encapsulated fluoride octasilsesquioxane cages. Migration of a fluoride ion from inside the cage to outside the cage without breaking the T(8) framework and the possibility of encapsulating other anions within silsesquioxane cages have been also investigated.

The potential for expanding the variety of enzymic methods for siloxane bond formation is explored. Three enzymes, Rhizopus oryzae lipase (ROL), lysozyme and phytase are reported to catalyse the condensation of the model compound, trimethylsilanol, formed in situ from trimethylethoxysilane, to produce hexamethyldisiloxane in aqueous media at 25 °C and pH 7. Thermal denaturation and reactant inhibition experiments were conducted to better understand the catalytic role of these enzyme candidates. It was found that enzyme activities were significantly reduced following thermal treatment, suggesting a potential key-role of the enzyme active sites in the catalysis. Similarly, residue-specific modification of the key-amino acids believed to participate in the ROL catalysis also had a significant effect on the silicon bio-catalysis, indicating that the catalytic triad of the lipase may be involved during the enzyme-mediated formation of the silicon-oxygen bond. E. coli phytase was found to be particularly effective at catalysing the condensation of trimethylsilanol in a predominantly organic medium consisting of 95% acetonitrile and 5% water. Whereas the use of enzymes in silicon chemistry is still very much a developing and frontier activity, the results presented herein give some grounds for optimism that the variety of enzyme mediated reactions will continue to increase and may one day become a routine element in the portfolio of the synthetic silicon chemist.

The synthesis, characterisation and crystal structure of D(8) and D(6) cages from the corresponding bis(dialkoxy)methane is reported.

The use of rolling circle amplification together with the addition of a wild-type control significantly improves the usefulness of phage display methodology as exemplified by the production of silver and platinum nanoparticles.

Hexasilsesquioxane cages (T6) have been prepared from a range of alkyl and aryl trichlorosilanes using a "non aqueous" hydrolysis with dimethyl sulfoxide.