Silica systems, interest

Although the NBS-silica system has useful potential for bromination of electron rich heterocycles, it has limited application to non-acdvated aromatics and sometimes meets problems with polybromination even for the activated heterocycles. Thus, it was of interest to investigate the potential of different brominating agents and different solids. Bromination of anisole with... 

Changes in mobile-phase components such as pH, ionic strength, and water content have been systematically studied [3,310,316,317]. These studies indicate that retention of basic analytes is mediated primarily by the cation-exchange properties of the silica [2]. Interestingly, it has been suggested from retention data of various pharmaceuticals that the retention mechanisms of silica with aqueous eluents and reversed-phase systems are similar [317,318]. Due to the ion-exchange properties of silica, mobile-phase pH adjustments are useful in changing the retention of ionic compounds. 

Silver nanoparticles obtained by thermal decomposition of AgN03 within mesoporous silica pores show interesting optical properties [26]. Ag doping results in a large red shift of the adsorption edge which is attributed to the interband absorption of Ag in the Ag-silica system and dipole interaction between Ag particles. The lack of a plasmon band typical for Ag nanoparticles is attributed to a small particle size (2.4-3.6 nm) and interaction at the interfaces between... 

In recent years there has been renewed interest in silica systems. Some examples are taken from articles by Yamaguchi et al. [4], Righetto et al. [5], Chen et al. [6], and Philipse et al. [7]. These studies cover subjects such as kinetics of particle formation and growth, characterization, and application of colloidal silica. Work involving silica is not localized, but occurs in laboratories throughout the world. Reports issue routinely from countries such as the Netherlands, the United States, Great Britain, Japan, Australia, China, and Russia. Recent interest in sihca formation and growth has focused on the area of... 

Today the rheology of many liquid systems is controlled by hydrophilic or hydrophobic fumed silicas. An interesting example are 2P-epoxy resins. The resin can be thickened effectively with a hydrophilic fumed silica, but when the polyamine hardener is added, the viscosity raises and after a short time it drops tremendously and the application is impaired or even impossible. To overcome this problem surface treated silicas have been developed, which do not show detrimental interactions with the polyamine and which have a good rheological effect [75] (Figure 43.13). 

Multi-phase Systems.—Interest in the attachment of reagents to polymeric or other insoluble supports has continued, with a view to easing reaction processes. Reagents have included borohydride (Amberlite resin), permanganate and cyanide (inorganic support), metallocenes as hydrogenation catalysts (20% divinylben-zene-styrene copolymer), and chelated transition metals (modified 2% divinyl-benzene-styrene copolymer). New supports have been silica (for the Nef reaction ... 

Lipid bilayer membrane systems, having gel (solvated crystalline state)-to-liquid crystalline phase transitions are attractive as specific organic media for separation chemistry. The first approach in HPLC was direct immobilization of a phosphatidylcholine lipid onto silica. This modified silica shows interesting selectivity against amino acids, but the separation mode is too complicated, due to the zwitter-ionic property of the immobilized molecule. In addition, no lipid membrane function is realized on the silica because of the direct immobilization with covalent bonding, which prohibits lateral diffusion of lipids from forming highly-ordered structures that lead to supramolecular functions of lipid membrane systems. 

Of particular interest in this work is the use of ab initio data sets to fit empirical potential parameters to be used in molecular dynamics (MD) simulations. ReaxFF is a transferable reactive force field designed by van Duin et al. [6] to cover a wide range of elements in the periodic table including very successful predictions of a variety of hydrocarbon molecular structures. ReaxFF was also developed for boron/ nitrogen/hydrogen [7], silicon/silica systems [8], and transition metal complexes [9]... 

The elution behavior of various polymers near their critical adsorption point with silica gel packings and various eluents has been studied (12). It was of interest to apply hybrid column systems composed of active ( critical ) packings (silica gels) in combination with nonactive (nonadsorptive) PS/DVB and DVB-based gels. Some PS/DVB and DVB gels exhibited rather strong... 

Scott s results for the silica-alumina. system (Figure 8-3) are of particular interest because they show marked absorption and enhance-... 

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