Thiolated Janus silsesquioxane tetrapod : new precursors for functional materials

Herein, we report synthetic strategies for the development of a bifunctional Janus T4 tetrapod (Janus ring), in which the orthogonal silsesquioxane and organic faces are independently functionalized. An all‐cis T4 tetrasilanolate was functionalized to introduce thiol moieties on the silsesquioxane face and naphthyl groups on the organic face to introduce luminescent and self‐or‐ ganization properties. The stepwise synthesis conditions required to prepare such perfectly defined oligomers via a suite of well‐defined intermediates and to avoid polymerization or reactions over all eight positions of the tetrapod are explored via 29Si, 13C and 1H NMR, FTIR and TOF‐ESI mass spectroscopy. To the best of our knowledge, this is one of the few reports of Janus T4 tetrapods, with different functional groups located on both faces of the molecule, thus expanding the potential range of applications for these versatile precursors

Sol-gel processing of polyhedral oligomeric silsesquioxanes : nanohybrid materials incorporating T8 and T10 cages

Polyhedral oligomeric silsesquioxanes (POSS, T8 and T10) have been incorporated in hybrid silica materials via hydrolysiscondensation of octa- and deca(triethoxysilylated)-POSS precursors, respectively. The precursors were synthesized via a thiol-ene Click reaction involving the corresponding octastyryl-T8 or decastyryl-T10 molecules and thiopropyltriethoxysilane. Following addition of water and HCl (as catalyst) to a solution of the precursors, gels were formed within a few minutes. The resulting hybrids were characterized by TEM, FTIR, N2 physisorption analyses, solid-state NMR (29Si and 13C), and TGA, which indicated that the T8 and T10 cages were incorporated and remained intact within the hybrid gel network, with no Si–C cleavage being observed via 29Si NMR. FTIR data indicated that water retained within the gels following drying and aging at ambient temperature exhibited an unusual “connective”, ice-like structure, suggesting that it is initially retained as a key component of the gel network during consolidation and aging at ambient temperature. Following aging, the water was readily removed by evacuation at 100 °C without significantly modifying the network structure, on the basis of the FTIR spectrum of the gel. To the best of our knowledge, this is the first report of the incorporation of T10 cages in such gels

Mechanism of carbon nanotube dispersion and precipitation during treatment with poly(acrylic acid)

Carbon nanotubes have been shown to be easily dispersed within an acidic aqueous solution of poly(acrylic acid) but precipitate when the pH is increased. Transmission electron microscopy showed that the nanotubes were more exfoliated under the acidic condition but highly aggregated under the basic condition. Carbon K-edge NEXAFS spectroscopy showed that the carbon nanotubes did not chemically react with poly(acrylic acid) during the dispersion or precipitation and that the dispersion mainly involved physical adsorption of poly(acrylic acid) onto the nanotubes. Together with the carbon K-edge NEXAFS spectra, the cobalt L3,2-edge NEXAFS spectra suggested that under the basic condition, the cobalt impurity within the nanotubes strongly reacted with poly(acrylic acid) resulting in complex formation. Cobalt reduces the adsorption of poly(acrylic acid) onto the nanotubes, which then reduced the nanotube dispersion and resulted in the precipitation

Large polyhedral oligomeric silsesquioxane cages : the isolation of functionalized POSS with an unprecedented Si18O27 core

The synthesis of organo-functionalized polyhedral oligomeric silsesquioxanes (POSS, (R-SiO1.5)n, Tn) is an area of significant activity. To date, T14 is the largest such cage synthesized and isolated as a single isomer. Herein, we report an unprecedented, single-isomer styryl-functionalized T18 POSS. Unambiguously identified among nine possible isomers by multinuclear solution NMR (1H, 13C, and 29Si), MALDI-MS, FTIR, and computational studies, this is the largest single-isomer functionalized Tn compound isolated to date. A ring-strain model was developed to correlate the 29Si resonances with the number of 6-, 5-, and/or 4-Si-atom rings that each non-equivalent Si atom is part of. The model successfully predicts the speciation of non-equivalent Si atoms in other families of Tn compounds, demonstrating its general applicability for assigning 29Si resonances to Si atoms in cage silsesquioxanes and providing a useful tool for predicting Si-atom environments

Functionalised polyhedral oligomeric silsesquioxane with encapsulated fluoride : first observation of fluxional Si⋯F interactions in POSS

The synthesis of a styryl functionalised POSS incorporating an encapsulated fluoride ion within a (SiO1.5)8 cage (T8-F) is reported. It was characterised by single crystal XRD, MALDI-MS, FTIR, solution (29Si, 19F, 13C, 1 H) and solid state (29Si, 19F) NMR. In the absence of 1 H decoupling, the 29Si solution NMR spectrum exhibited a triplet of doublets. In contrast, 1 H, 19F and 1 H/19F double-decoupling resulted in two, three and one signal, respectively, being consistent with a single Si site whose 29Si NMR signal is modulated by both the proximal aromatic-ring protons and fluoride. The associated Si⋯F coupling constant (2.5 Hz) is substantially lower than expected for a covalent Si–F bond and arises from a fluxional Si⋯F covalent effect in which the F− interacts equivalently with all eight Si atoms. Additional variable temperature NMR studies demonstrated a threshold at −5 °C below which no Si⋯F interactions are observed, and above which an increasing Si⋯F covalent character occurs

Styryl-functionalized cage silsesquioxanes as nanoblocks for 3-D assembly

Herein we report the synthesis of a new family of styryl-functionalized polyhedral oligomeric silsesquioxanes (Tn, where n = 8, 10, and 12), in which the organic moiety is linked to all n vertices of the Tn cages via the phenyl ring rather than the vinyl group. In contrast to earlier studies in which the styryl group is linked to the cage via the vinyl moiety, our approach ensures that the vinyl moiety is less sterically hindered and available for postfunctionalization. The functional Tn cages have been characterized by a range of techniques, including single crystal X-ray diffraction, multinuclear solution NMR (1H, 13C, and 29Si), MALDI-MS, and FTIR. The solid-state structure of the T8 compound exhibited two nonequivalent Si8O12 cage atoms, which has not been previously reported in the functionalized T8 system, although all cage atoms in the corresponding T10 and T12 systems were equivalent. In contrast, multinuclear solution NMR data indicated that all cages in the T8 system were equivalent in solution, suggesting that the nonequivalent cage geometries arise in the solid state to optimize the packing of the functionalized cages. These compounds have significant potential for future use in the production of 3D cross-linked polymer networks

Photoemission and absorption spectroscopy of carbon nanotube interfacial interaction

Element-specific techniques including near edge X-ray absorption fine structure, extended X-ray absorption fine structure and X-ray photoemission spectroscopy for the characterization of the carbon nanotube interfacial interactions are reviewed. These techniques involve soft and hard X-rays from the laboratory-based and synchrotron radiation facilities. The results provided information of how the nano-particles of catalysts are involved in the initial stage of nanotube growth, the nanotube chemical properties after purification, functionalization, doping and composite formation

Luminescent coatings from bipyridine-based bridged silsesquioxanes containing Eu³⁺and Tb³⁺ salts

The sol-gel fabrication of bridged silsesquioxane thin films containing trivalent lanthanide ions (Ln³⁺) has been achieved from a 4,4'-diureido-2,2'-bipyridine bridged organosilane (P4) in the presence of Eu³⁺or Tb³⁺salts. Crack- and defect-free thin films (~50 nm) of optical quality were successfully deposited on glass substrates by spin-coating after optimizing the spinning rate and solvent system. Ellipsometry investigations revealed a significant decrease in the refractive index of the films with ageing of the corresponding precursor sols. In contrast, the photoluminescence properties of the films are independent of precursor ageing time, although significant differences are observed with respect to the corresponding bulk materials. Compared to the bulk materials, the films exhibit a significant blue-shift of the excitation spectra and an increase of the excited state lifetime. The optical conversion efficiencies (ɲopt) of the F4-Eu and F4-Tb-based collectors were also determined and potential applications of the coatings in such areas as luminescent solar concentrators are discussed

Sequential delivery of synergistic drugs by silica nanocarriers for enhanced tumour treatment

Herein hybrid silica nanoparticles have been engineered to direct the sequential delivery of multiple chemotherapeutic drugs in response to external stimuli such as variations in pH. The nanocarriers consist of conventional MCM-41-type nanoparticles, which have been functionalised with an organic ligand (or stalk) grafted onto the external surface. The stalk is designed to “recognise” a complementary molecule, which serves as a “cap” to block the pores of the nanoparticles. First, camptothecin is introduced into the pores by diffusion prior to capping the pore apertures via molecular recognition. The cap, which is a derivative of 5-fluorouracil, serves as a second cytotoxic drug for synergistic chemotherapy. In vitro tests revealed that negligible release of the drugs occurred at pH 7.4, thus avoiding toxic side effects in the blood stream. In contrast, the stalk/cap complex is destabilised within the endolysosomal compartment (pH 5.5) of cancer cells, where release of the drugs was demonstrated. Furthermore, this environmentally responsive system exhibited a synergistic effect of the two drugs, where the pH-triggered release of the cytotoxic cap followed by diffusion-controlled release of the drug cargo within the pores led to essentially complete elimination of breast cancer cells

Anti-proliferative activities of selected Chinese medicinal herbs against human cancer cell lines

The main objective of this study was to investigate the anti-proliferative properties of selected traditional Chinese medicinal herbs with a view to discover potential candidates for the isolation of anti-cancer compounds and also for designing new anti-cancer herbal formulations. The plants selected for this study have ethno pharmacological importance and currently used in Chinese medicine. The Methylthiazolyldiphenyltetrazolium bromide (MTT) assay was conducted to determine the anti-proliferative properties of the aqueous and ethanol extracts of the selected herbs against one control cell line and 5 human carcinoma cell lines. The key herbs found in this study that are expected to have excellent future potential are: Ligustrum lucidum, Paeonia suffuticosa, Sarcandra glabra, Scutellaria baicalensis, and Sanguisora officinalis. The study also indicated that the ethanol extracts of the selected herbs were generally more effective than the aqueous extracts. The findings of this study provide strong evidence that some of the medicinal plants examined are potential candidates for the isolation of anti-cancer compounds and also for designning new anti-cancer herbal formulations