Silica mesoporous carriers

An other approach was followed with a micelle-templated silica of the MCM-41 type. These mesoporous carriers were first grafted with the chlorosilane 7 and then aminated with a guanidine such as TBD 2 11 (Figure 8). 

Fig. 6 Schematic representation of the synthetic route to obtain constitutional silica mesoporous membranes is (a) filled with mesostructured silica-CTAB, (b) then calcinated, (c) reacted with hydrophobic ODS and finally filled with the hydrophobic carriers. Generation of directional ion-conduction pathways which can be morphologically tuned by alkali salts templating within dynamic hybrid materials by the hydrophobic confinement of ureido-macrocyclic receptors within silica mesopores [130]...

Those results indicate two st lges of zeolite crystallization in silica pellets formation of small zeolite ZSM-5 crystals (0.025 pm) in the silica mesopores and large zeolite crystals (1-4 pm) in the silica macropores and on the outer surface of silica pellets followed by faster crystallization in the interior of the carriers pellets. At this second stage the mesopores and small zeolite crystals inside them do not grow but the pellets structure fails forming large slabs of amorphous silica with incapsulated zeolite crystals not accessible for adsorption and catalysis. 

With the development of structurally well-defined mesoporous molecular sieves and other silica-based carriers as chiral catalyst supports, it was possible to achieve high enantioselectivity and reactivity, and some were even higher than those of the homogeneous parent systems [22,26]. The more recent developments of effective inorganic sohd or organic and inorganic hybrid-sup-ported chiral catalysts are important advancements in this area of research [4]. 

Functionalization of the mesoporous carrier by installing the drug molecule directly onto the silica surface through ester bonds is another weU-studied way for efficient dehvery of the drugs. For example, Tourne-PeteiUi et al. investigated ibuprofen linked onto the surface of MCM-41 by ester bonds (Figure 19.2) [65]. A... 

Ordered mesoporous silica have already been studied as carriers for drug delivery [1,2] recently, their use has also been proposed in bone tissue engineering [3,4], in combination with bioactive glass-ceramic scaffolds [5,6]. The kinetics of ibuprofen release in SBF [7] from MCM-41 silica with similar pore diameter has shown puzzling discontinuities [3,6,8] aim of the present work is to assess whether these anomalies may be related to structural changes in the MCM-41 mesoporous spheres under the adopted conditions. 

Relatively little attention has been paid to enzyme immobilization in connection with ionic liquids, and only one systematic study of this subject has appeared [78]. Itoh et al. studied the effects of the carrier material on PcL in [BMIm][PF6] [79]. The activity of PsL on ceramic Toyonite carriers varied by a factor of 1000 between Toyonite 200M and Toyonite 200A. PsL adsorbed on a methacryloxypropyl-modified mesoporous silica also had a relatively high activity [78]. 

A mesoporous silica nanosphere-based carrier system with chemically removable CdS nanoparticle caps for stimuli-responsive controlled release of neurotransmitters and drag molecules. 

As an intermediate between solid supported layers and the inherent dynamic and nanostructured properties of phospholipid vesicle supports, silica and especially mesoporous silica nanoparticles may provide interesting platforms for dynamic bilayers. Previous studies have shown that stable bilayers can form on both amorphous [102] or functional silica [103, 104] and mesoporous nanoparticles [105] or membranes [106]. This type of biomimetic carrier has great potential as a type of trackable stabilized membrane capable of displaying cellular targeting elements in a close to natural configuration. 

C.L. Lin et al. [71] reported deposition of silica layers (plugs) with a thickness of about 1.5 pm within the pores of commercial, mesoporous y-alumina films (pore diameter 4 nm, thickness 1-3 pm) on a-alumina supports (US filter). The deposits were obtained by reaction of TEOS-oxygen (10-20%) mixtures in He as carrier gas applied in the OSG mode to the mesoporous layer. No further details (e.g., temperature or pressure) were given. Depending on these unknown conditions, dense as well as microporous silica membranes with pores down to estimated values of 0.4-0.6 nm were obtained. These membranes have interesting combinations of permselectivity and flux values for several gas combinations (see Chapter 9 on gas transport properties). 

A second hurdle is that direct silanation of mesoporous silica using conventional solution based protocols has lead to poor levels of silane incorporation.In this respect, SCF CO2 has an important characteristic of high diffusivity and low viscosity and therefore can be used as a carrier to bring reagents into the pore stracture of the oxide. With these attributes in mind, we have used SCF CO2 to modify the surface chemistry of the synthesized mesoporous materials. Specific surface modifications applied for the detection of organophosphate pesticides have included the use of hexamethyldisilazane (CH3), octadecyldimethylchlorosilane (C-18), and trifluoropropyldimethylchlorosilane (CH2CH2CF3). The results shown in this paper are for a methylated (CH3) surface. 

Several Pd-Pt (Pd Pt=4 l) catalysts for deep hydrodesulfurization (HDS) were prepared using a commercial amorphous silica-alumina (ASA), a novel mesoporous silica (MPS) and a novel mesoporous silica-alumina (MPSA) as carriers with dispersions of > 50%. They were characterized by various techniques and their performance in deep HDS of 4-ethyl, 6-methyl-dibenzothiophene measured at 633 K and 6.0 MPa in the presence of carbazole and H2S. The Pd-Pt catalysts showed good activity as compared to typical conventional HDS catalysts. Their activity decreased with a decreasing Al content in the support (thus support acidity) ASA > MPAS > MPS. Enhanced support acidity seems to favor the stabilization of the dispersed metal particles against sintering. 

SBA-15 is a mesoporous ordered silica with promising properties as a catalyst support [1], where functionalization of the siliceous carrier with an active component can be achieved through a number of methods [2]. In this study we describe the use of the deposition-precipitation technique (DP) employed to functionalize the SBA-15 with Pt. The use of the DP method on the SBA class of materials has not been studied so far, excluding a few studies dealing with deposition of gold on titania-modified SBA-15 [3, 4]. The method... 

Recently, there has been increased interest in mesoporous silica materials for utilization as drug carrier in the field of controlled drug release, to meet the need for prolonged and better control of drug administration. Amorphous mesoporous silica materials have been investigated as drug supports due to their non-toxic nature, adjustable pore diameter, and very high specific surface area... 

The potential of zeolites and porous solids as high capacity carriers for drug molecules has also been recognised. Whereas zeolites may have applications for the controlled release of small molecules of medicinal importance, such as nitric oxide, mesoporous silica nanospheres that are sub-micron in particle size, with pore sizes of 2 10 nm, may be used for the targeted in situ delivery of larger drug molecules. 

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