pH-Responsive Bridged Silsesquioxane

Abstract

In recent years, significant effort has been focused toward the synthesis of porous materials with potential applications such as for drug-delivery carriers 1À3 and for catalysis. 4 These materials consist of either organic or inorganic polymers, 5,6 among which silica meets most of the requirements as a good support: chemical inertness, thermal and mechanical stability, and also the possibility of tailoring the size and the shape of the pores and cavities inside the materials. 7À9 Mesoporous materials were obtained using surfactants as structuring agents and from this surfactant-mediated route, organic groups may be covalently anchored in two ways: (1) grafting a functional alkoxysilane on a preformed mesoporous silica (MCM-or SBA-type); and (2) co-condensation of the functional alkoxysilane with TEOS in the presence of a suitable surfactant. 10À12 Following these two methods, many forms of functional mesoporous hybrids have been synthesized and exploited for many applications. 13 For example, mechanized nanomachines have been prepared for on-demand release of cargo molecules (including drugs, dyes, biomolecules, etc.) 14 as well as easily recoverable and recyclable homogeneous catalysts supported on hybrid porous silicates which have applications in a variety of chemical processes. 15 Hybrid mesoporous silica can also be prepared via the self-assembly of organopolysilane precursors bearing a long alkylene chain. In this case, self-structuring occurs to form a purely hybrid silica without added TEOS and without any surfactant. 16,17 Complementary to these are the periodic mesoporous organosilicates (PMO) obtained from bridged silsesquioxane precursors, which are prepared with surfactants. 18,19 In the series of bridged silsesquioxanes, labile SiÀC covalently bonded ethynyl units were softly cleaved by a chemical route to afford mesoporous silica. 20 The pore sizes and distribution were dependent on both the structure of the sacrificial ethynyl templates and the reaction conditions employed. 21 Porous materials can also be obtained by molecular imprinting techniques which are used to create solid materials containing chemical functionalities that are spatially localized and fixed by interactions with the imprint molecules during the synthesis process. Subsequent removal of these template molecules leaves preformed sites for the recognition of small molecules, hence affording materials which may be suitable for applications in separation chemistry. 22 Indeed, protein-imprinted silica prepared via covalent imino group bonding showed enhanced affinity for the template protein compared to the corresponding imprinted silica obtained by entrapment of the protein with no interaction of the latter with the silica surface. 23 Using a chiral cationic surfactant in conjunction with solÀgel processing, chiral imprinted silicabased thin films were obtained, which exhibited good selectivity toward chiral alcohols. 24 Imprinted polysilsesquioxanes have also been obtained by the co-condensation of a bridged organosilane (BTSE) p...

Molecular imprinting: perspectives and applications

“…The molecularly imprinted pH-sensitive nanospheres prepared by precipitation polymerization using dexamethasone-21 phosphate disodium (DXP) as the template molecule exhibited a faster DXP release rate at a lower pH value within the pH range tested (6.0-7.4). Fertier et al 282 reported a pH-responsive imprinted bridged silsesquioxane obtained from a bis-silylated triazine derivative by the sol-gel hydrolysis condensation of the precursor in the presence of cyanuric acid H-bonded through the three DAD (donor-acceptor-donor) faces. Mangeney's group 283 proposed a strategy for the development of BPA optical sensors by the combination of molecularly imprinted hydrogels and photonic crystals.…”

Hybrid Mesoporous Silica Nanoparticles with pH‐Operated and Complementary H‐Bonding Caps as an Autonomous Drug‐Delivery System

“…The syntheses of these organosilane precursors Stalk 1 and Stalk 2 are given in Figure 3. Precursor Stalk 1 was prepared according to literature25a and Stalk 2 was synthesized by reacting 5‐aminouracil with 3‐isocyanatopropyltriethoxysilane with a yield of 78 %.…”

“…Stalk 1 and 2 : Stalk 1 was prepared according to a reported procedure 25a. In a Schlenk under inert atmosphere, 5‐aminouracil (0.5 g, 3.93 mmol) was dissolved in anhydrous DMSO (25 mL).…”

Enzymatically degradable hybrid organic–inorganic bridged silsesquioxane nanoparticles for in vitro imaging

“…30 Ester-bridged silsesquioxanecoated liposomes were applied for drug delivery. 37 Only one study has been reported on biodegradable BS NPs which consisted of gadolinium-complexed bridges with disulfide linkages which can be cleaved by glutathione for MRI imaging.…”