Silica vesicles

Rana RK, Mastai Y, Gedanken A (2002) Acoustic cavitation leading to the morphosynthesis of mesoporous silica vesicles. Adv Mater 14(19) 1414—1418... 

Fig. 2.18 Vesicle structures with silica wall (A) mesostructured silica vesicle (B) hollow capsule composed of silica particles prepared by LbL assembly.

Zhu Y, Shen W, Dong X et al (2005) Immobilization of hemoglobin on stable mesoporous multilamellar silica vesicles and their activity and stability. J Mater Res 20 2682-2690... 

Rana [117] has recently demonstrated that ultrasound radiation can be employed for the formation of vesicular mesoporous silica. The dimension of the vesicles ranged from 50-500 nm. If the synthesis is compared with a previous work on the synthesis of MSP silica vesicles [118], the advantages of the sonochemical synthesis are as follows (1) It employs the commonly used CTAB as a surfactant, instead of Gemini surfactant, C H2 +iNH(CH2)2NH2 (2) the sonochemical reaction takes 1 h as compared with 48 h (3) the reaction is conducted at 25-35 °C instead of 100 °C and (4) a higher surface area is obtained, 940, as compared with 280-520 m g k The special role of the bubbles in the formation of the vesicle is also explained. 

Use of the LbL technique is not restricted to the preparation of planar thin films. One of the most outstanding strategy modifications of the LbL technique involves assembly on colloidal particles followed by hollow capsule formation. For example, Caruso and co-workers reported the formation of hollow silica vesicles through LbL assembly on colloidal nanoparticle templates (Fig. 14). Polyelectrolytes and smaller silica particles were initially formed on a larger colloidal core, which was subsequently selectively destroyed. Calcination of the hybrid vesicles resulted in a hollow vesicle composed of silica. Formation of controlled organic-inorganic layer structures on colloidal particles by LbL assembly also provides media appropriate for investigation of fundamental phenomena. 

Hubert DHW, Jung M, Frederick PM, Bomans PHH, Meuldijk J, German AL (2000) Vesicle-directed growth of silica. Adv Mater 12(17) 1286-1290... 

Luo, T.J.M., Soong, R., Lane, E., Dunn, B. and Montemagno, C. (2005) Photo-induced proton gradients and ATP biosynthesis produced by vesicles encapsulated in a silica matrix. Nature Materials, 4, 220-224. 

Goltner, C. G. Berton, B. Kramer, E. Antonietti, M. 1999. Nanoporous silicas by casting the aggregates of amphiphilic block copolymers The transition from cylinders to lamellae and vesicles. Adv. Mater. 11 395-398. 

Pyrene has been used to investigate the extent of water penetration into micelles and to accurately determine critical micellar concentrations (Kalyanasundaram, 1987). Polarity studies of silica or alumina surfaces have also been reported. In lipid vesicles, measurement of the ratio Ii/Iui provides a simple tool for determination of phase transition temperatures and also the effect of cholesterol addition. 

Uncoated fused-silica capillaries have similarly been applied to elec-trokinetic chromatography (EKC) analysis of solute interactions with both liposomes (33,34) and surfactant vesicles (59,60). 

Although the bulk of PDA sensors involve vesicles and Langmuir monolayers, a few examples of responsive PDA assemblies based on bolaamphiphiles and diyne silica nanocomposites have been reported (Lu et al. 2001 Song et al. 2001, 2004 Yang et al. 2003 Peng et al. 2006). Although these materials have not been broadly utilized for analyte sensing, they do exhibit the thermochromic, solvatochro-mic, and pH responsive behavior seen with monolayers and liposomes and hold promise for future development. 

The process utilizing supramolecular organization involves pore expansion in silicas. A schematic view of such micelles built from the pure surfactant and those involving in addition n-alkane is shown in Figure 4.9. Another example of pore creation provides a cross-linking polymerization of monomers within the surfactant bilayer [30]. As a result vesicle-templated hollow spheres are created. Dendrimers like that shown in Figure 4.10 exhibit some similarity to micellar structures and can host smaller molecules inside themselves [2c]. Divers functionalized dendrimers that are thought to present numerous prospective applications will be presented in Section 7.6. 

In principle the bicontinuous 3-dimensional network structure of MCM-48 would act as a good catalytic support.[7] However, its lower hydrothermal and thermal stability has led to much less application of MCM-48 in catalysis. Recently, a family of mesoporous molecular sieves (denoted as MSU-G) with vesicle-like hierarchical structure, worm-like mesoporous structure and bicontinuous nano-porous silica had been synthesized.[8-10] It was proposed that highly accessible mesoporous materials could be obtained through different synthetic procedure and composition. 

If the nanodispersed species have sizes of the order of 10 nm, diagnostic agents encapsulated in such nanoparticles could potentially cross into human cells. For example, 10 nm diameter, silica-coated, cadmium selenide crystals have been able to transfer into vesicles and be transported by them [901], These protein-sized particles fluoresce for long periods of time making them potentially useful for diagnostic labelling. 

To gain insight into the effect of physical state and/or molecular organization on lipid oxidation, a variety of model systems have been used. These include dispersions, liposomes or vesicles (37,38), monolayers adsorbed on silica (39,40,41), and red blood cell ghosts (42). In most of these studies, oxidation was conducted at relatively low temperatures, i.e., 20 - 40°C. Very little information is available on the effects of physical state on high temperature oxidative reactions or interactions of lipids. 

Fig. 14 Cryo-TEM (a), AFM- (b), and TEM images of polyelectrolyte block copolymer vesicles (PB-P2VP.MeI). The image (c) is taken from a silica-template which was obtained by a sol/gel-process of a concentrated micellar solution [47, 56, 64]...

Diatoms are unicellular, photosynthetic microalgae that are abundant in the world s oceans and fresh waters. It is estimated that several tens of thousands of different species exist sizes typically range from ca 5 to 400 pm, and most contain an outer wall of amorphous hydrated silica. These outer walls (named frustules ) are intricately shaped and fenestrated in species-specific (genetically inherited) patterns5,6. The intricacy of these structures in many cases exceeds our present capability for nanoscale structural control. In this respect, the diatoms resemble another group of armored unicellular microalgae, the coccolithophorids, that produce intricately structured shells of calcium carbonate. The silica wall of each diatom is formed in sections by polycondensation of silicic acid or as-yet unidentified derivatives (see below) within a membrane-enclosed silica deposition vesicle 1,7,8. In this vesicle, the silica is coated with specific proteins that act like a coat of varnish to protect the silica from dissolution (see below). The silica is then extruded through the cell membrane and cell wall (lipid- and polysaccharide-based boundary layers, respectively) to the periphery of the cell. 

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