Silica redox-active

Poly(propylene amine) dendrimers containing 4, 8, and 64 amidoferrocene peripheral units have also been incorporated in the highly ordered channels of mesoporous silica obtaining a novel type of redox-active materials. One significant feature of these new composite materials is that the ferrocene units of the guest dendrimers are easily accessible to electrochemical oxidation, as revealed by studies carried out in MeCN solutions by using Pt electrodes derivatized with films of such dendrimer-matrix complexes.33... 

Some accessory minerals that accompany the inhaled dose of particles may themselves be reactive (such as pyrite, an iron sulfide) and may be able to modify fluid chemistry sufficiently to enhance or diminish particle solubility, or to release redox-active species such as iron. For example, the well-documented decrease in crystalline silica toxicity when combined with other, nonsilica mineral particles (SSDC, 1988) implies that the other mineral particles are reacting chemically with the body fluids and the silica to modify the surface chemistry of the silica that induces ROS generation and cytotoxicity. 

Recently, we (82) and others (82-84) have shown that similar hetero-structures can be prepared by using two-dimensional inorganic sheets (made by exfoliation of various lamellar solids) in place of the organic polyanion. This technique offers a potentially powerful alternative to the construction of multi-component electron transfer systems, because it can, in principle, be used to stack up an arbitrary number of redox-active polymers without interpenetration (85). This chapter describes the preparation and photochemistry of simple multilayer composites on high-surface-area silica. Specifically, the synthesis and electron transfer kinetics of systems containing a polycationic sensitizer, poly-[Ru(bpy)2(vbpy)(Cl)2] (1), (abbreviated [Ru(bpy)3 ]n bpy = 2,2 -bipytidine and vbpy = 4-vinyl-4 -methyl-2,2 -bipyridine), and an electron-acceptor polycation poly[(styrene-co-]V-vinylbenzyl-N -methyl-4,4 -bipyridine)(Cl)2] (2), (PS-MV ) are presented. Using a solution-phase electron donor, 3, as the third electroactive component, it was possible to prepare and study the photoinduced electron transfer reactions of several different diad and triad combinations. 

Deposition of the redox-active polymers onto high-surface-area silica was monitored using diffuse reflectance UV-visible spectroscopy. Shown in Figure 4a are the spectra for the PS-MV /Cab-O-Sil composites, both coiled and... 

The aptamer described above was attached to the surface of the silica colloidal crystal comprising 290 nm silica spheres (resulting in 22.5 nm radius nanopores) via maleimide-activated support. The transport rate of a redox-active probe molecule (ferrocene dimethanol) through the resulting nanoporous films was measured as a function of cocaine concentration using cyclic voltammetry. A neutral redox probe, Fc(CH20H)2, was used to exclude the possibility that the observed changes in the molecular transport would result from electrostatic effects [26,27]. 

In the case of ceria as an abrasive in contact with silica as the layer to be polished, its redox-active behaviour additionally influences the RR. This effect is called the chemical tooth . 

The chemical composition of sol-gels is typically a basic inorganic oxide. A common example of a sol-gel is silica gel, which has particular utility as stationary phase supports in chromatographic columns. The sol-gel materials used for electrode modification are typically created from two different classes of material inert and redox active. Many different types of sol-gels are derived from these classes, as outlined in Table 8.7 (113). 

The first class, inert inorganic sol-gels, are not redox active (e.g., silica, alumina, and zirconia) (113). In the gel form these materials have a large surface area, high ion-exchange capacity (due to surface hydroxyls), and exhibit good adhesion to metal oxide and ceramic supports. 

Inert, inorganic materials (2) Redox-active metal oxides Electroinactive (silica, alumina, and zirconia) Electroactive (vanadium pentoxide, manganese oxide, tungsten oxide, etc.)... 

Microporous crystalline solids in which transition metals are tetrahedrally substituted via template-mediated hydrothermal synthesis have remarkable properties in selective oxidation reactions [66]. Unfortunately, the microporous structure and the rigidity of the crystalline frameworks limit the substitution degree, variety of substituted metal, and their general applicability. For this reason, the amorphous microporous mixed oxides (AMMs) with uniform microporosity and wide compositional variability are devoid of Bronsted acidity, but are not associated with the redox-active elements. However, metals such as Ti, V, and Mo incorporated in amorphous silica were good catalysts in allylic oxidation or epoxidation of olefins [67]. 

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