Rui F. P. Pereira

Novel Highly Luminescent Amine-Functionalized Bridged Silsesquioxanes

Amine-functionalized bridged silsesquioxanes (BSs) were synthesized from bis[(3-trimethoxysilyl)propyl] amine via a solvent-mediated route. BS-1 and BS-2 were obtained at neutral pH with sub- and stoichiometric amounts of water, respectively, and high tetrahydrofuran content. BS-3 was prepared with hyperstoichiometric water concentration, high tetrahydrofuran content, and hydrochloric acid. BS-4 was synthesized with hyperstoichiometric water concentration, high ethanol content, and sodium hydroxide. BS-1 and BS-2 were produced as transparent films, whereas BS-3 and BS-4 formed white powders. Face-to-face stacking of flat or folded lamellae yielded quasi-hydrophobic platelets with emission quantum yields of 0.05 ± 0.01 (BS-1 and BS-2) or superhydrophilic onion-like nanoparticles with exciting emission quantum yields of 0.38 ± 0.03 (BS-3) and 0.33 ± 0.04 (BS-4), respectively. The latter two values are the largest ever reported for amine-functionalized siloxane-based hybrids lacking aromatic groups. Fast Grotthus proton hopping between = NH2+/ = NH groups (BS-3) and = N−/ = NH groups (BS-4), promoted by H+ and OH− ions, respectively, and aided by short amine-amine contacts provided by the onion-like morphology, account for this unique optical behavior.

Structuring of di-alkyl-urethanesils

AbstractA novel organized di-urethane crossed-linked dodecyl/siloxane (di-alkyl-urethanesil) was synthesized by the sol–gel process and self-directed assembly, from the organosilane precursor (CH3CH2O)3-Si-(CH2)3-NHC( = O)O-(CH2)12-O(O = C)NH-(CH2)3-Si-(OCH2CH3)3, through a fine control of the reaction conditions (hyper-stoichiometric amount of water, minor amount of tetrahydrofuran, and acid catalysis; molar ratio Si:H2O:HCl:THF = 1:300:0.1:12.5). The new bridged silsesquioxane was identified by the notation d-Ut(CY)AC, where Y = 12 is the number of carbon atoms C of the bridging alkyl chains and AC represents acid catalysis. The d-Ut(C12)AC material exhibits a structured lamellar organization with medium long-range order, a texture composed of homogeneous lamellae immersed in a sponge-like matrix made of randomly distributed thin plates, and is thermally stable up to ca. 350 °C. Despite the hydrophobic nature of the dodecane chains, the weakness of the urethane–urethane hydrogen-bonded array formed led to the growth of moderately ordered assemblies of amphiphilic organo(bis-silanetriol) substructures comprising mainly all-trans conformers. A lamellar di-urethane cross-linked dodecyl/siloxane (di-alkyl-urethanesil) with medium long-range order, a texture composed of homogeneous lamellae immersed in a sponge-like matrix made of randomly distributed thin plates, and an average water contact angle of 94.17 ± 17.10°, was synthesized by the sol–gel process and self-directed assembly.HighlightsA di-urethane crossed-linked dodecyl/siloxane was produced using a controlled hydrolytic sol–gel route.The material exhibits a structured lamellar organization with medium long-range order.The morphology of the material includes homogeneous lamellae immersed in a sponge-like matrix.The material is thermally stable up to ca. 350 °C.

Ionic Liquid-Assisted Synthesis of Mesoporous Silk Fibroin/Silica Hybrids for Biomedical Applications

New mesoporous silk fibroin (SF)/silica hybrids were processed via a one-pot soft and energy-efficient sol–gel chemistry and self-assembly from a silica precursor, an acidic or basic catalyst, and the ionic liquid 1-butyl-3-methylimidazolium chloride, acting as both solvent and mesoporosity-inducer. The as-prepared materials were obtained as slightly transparent-opaque, amorphous monoliths, easily transformed into powders, and stable up to ca. 300 °C. Structural data suggest the formation of a hexagonal mesostructure with low range order and apparent surface areas, pore volumes, and pore radii of 205–263 m2 g–1, 0.16–0.19 cm3 g–1, and 1.2–1.6 nm, respectively. In all samples, the dominating conformation of the SF chains is the β-sheet. Cytotoxicity/bioactivity resazurin assays and fluorescence microscopy demonstrate the high viability of MC3T3 pre-osteoblasts to indirect (≥99 ± 9%) and direct (78 ± 2 to 99 ± 13%) contact with the SF/silica materials. Considering their properties and further improvements, these systems are promising candidates to be explored in bone tissue engineering. They also offer excellent prospects as electrolytes for solid-state electrochemical devices, in particular for fuel cells.