Silica, physicochemical properties

Malkia, A., Murtomaki, L, Urtti, A., Kontturi, K. Drug permeation in biomembranes in vitro and in silica prediction and influence of physicochemical properties. Eur. J. Pharm. Sci. 2004, 23,13-47. 

Albert, K. 1988. Correlation between chromatographic and physicochemical properties of stationary phases in HPLC C30 bonded reversed-phase silica. Trends Anal. Chem. 17 648-658. 

The qualitative analysis of retention behaviour in liquid chromatography has now become possible. Quantitative retention-prediction is, however, still difficult the prediction of retention time and the optimization of separation conditions based on physicochemical properties have not yet been completely successful. One reason is the lack of an ideal stationary phase material. The stationary phase material has to be stable as part of an instrument, and this is very difficult to achieve in normal-phase liquid chromatography because the moisture in organic solvents ages the silica gel. 

The most commonly employed crystalline materials for liquid adsorptive separations are zeolite-based structured materials. Depending on the specific components and their structural framework, crystalline materials can be zeoUtes (silica, alumina), silicalite (silica) or AlPO-based molecular sieves (alumina, phosphoms oxide). Faujasites (X, Y) and other zeolites (A, ZSM-5, beta, mordenite, etc.) are the most popular materials. This is due to their narrow pore size distribution and the ability to tune or adjust their physicochemical properties, particularly their acidic-basic properties, by the ion exchange of cations, changing the Si02/Al203 ratio and varying the water content. These techniques are described and discussed in Chapter 2. By adjusting the properties almost an infinite number of zeolite materials and desorbent combinations can be studied. 

Physicochemical Properties of High Silica L and Clinoptilolite Zeolites... 

TTigh silica zeolites attract great attention since they are characterized by relatively high thermal stability and considerable acid resistance. Physicochemical properties of high silica zeolites, despite a number of investigations, have not been sufficiently studied. The same is true for L- and clinoptilolite zeolite. The data on synthesis, structure, adsorption properties, decationization, dealuminization, adsorption heats, and other properties of the above-mentioned zeolites have been given (1-15). Results of studies of physicochemical properties of L zeolites and of natural and modified clinoptilolite are given here. 

Inorganic materials such as silica can constitute excellent scaffolds for a variety of chemical and biochemical processes to occur, not only because of their mechanical stability or physicochemical properties, but also because of their exquisite structural... 

Hamieh T, Schultz J. 2002. New approach to characterise physicochemical properties of solid substrates by inverse gas chromatography at infinite dilution II. Study of the transition temperatures of poly (methyl methacrylate) at various tacticities and of poly (methyl methacrylate) adsorbed on alumina and silica. J. Chromatogr. A 969 27-36. 

The aim of this contribution is to present experimental data concerning the synthesis, physicochemical properties and bio-activity of several nanosilica-based composites tested by interaction with native red blood cells (RBCs). The investigations include (i) synthesis of nanocomposites by adsorption of BSA, fructose and glucose on a fumed silica surface, and (ii) analysis of the adsorption properties of composites and their bio-activity. It is known that both glucose and fructose do not individually adsorb on fumed silica therefore, bovine serum albumin was used as a mediator to bind the monosaccharides to the fumed silica surface. 

Ceramic membranes were first developed in the 1940s for uranium isotope enrichment processes. Important progress has been made since that time, mainly due to the improved knowledge of the physicochemical properties of the membrane precursors. Most CMR studies concern alumina membranes other oxides such as silica, titania, or zirconia are much less frequently mentioned. 

Stationary phases. Five stationary phases from Shandon (Runcorn, Cheslvie, GB) were used they were spherical microparticules of 5 pm mean diameter. The four bonded silicas were manufactured from the same parent silica (Hypersil) and possess a monolayer coverage of trimethylsilyl (SAS Hypersil), dimethyloctylsilyl (MOS Hypersil), octadecylsilyl (ODS Hypersil) and cyanopropylsllyl (CPS Hypersil) groups. Their physicochemical properties are listed in Table II. The elemental analysis of carbon (SIC), corrected for the SIC value of naked silica, enables to estimate the surface concentration of the substituent (r ) with ... 

Table II. Physicochemical properties of the studied silica. S-specific surface area, %C-carbon percentage,...

Calcium hydrosilicates compose a wide range of different compounds [26], One of them is tobermorite, Cas(0H)2Si60i5-4H20. It is an important material, since it has brilliant physicochemical properties, for example low density 0.5 g/cm, good ion exchange characteristics. In [27], tobermorite was synthesized by mechanical activation of a mixture of calcium hydroxide and silica in the presence of water at room temperature ... 

Materials with carbon on the surface used as column packings for chromatography include carbosils, which are prepared mainly by pyrolysis of aliphatic alcohols [92], aromatic hydrocarbons [93], chloroalkanes [94], and other organic compounds on the surface of silica gel. The carbon deposit obtained under the standard pyrolysis conditions is amorphous and possesses different physicochemical properties than graphitized carbon blacks. The transformation of such amorphous carbon deposit to graphitized carbon black on a silica gel surface is not possible because of the high temperature of the graphitization process (ca.3000 K). 

Malkia A, Murtomaki L, Urtti A, and Kontturi K Drug Permeation in Biomembranes. In vitro and in silica Prediction and Influence of Physicochemical Properties. Eur J Pharm Set 2004 23 13-47. 

Physicochemical properties, that is the hardness and polarity of silica gel, are related to particle size (pm), surface area (m /g), pore size (A), and presence or absence of additives. The surface area of silica gel adsorbent for TLC is typically 300-400 mVg. and pore sizes range from 20 to 150 A. Adsorbent with larger surface area (smaller particle size) will generally give better resolution, but a slower... 

We demonstrated that a naturally derived polysaccharide, chitosan, is capable of forming composite nanoparticles with silica. For encapsulated particles, we used silicification and biosilicification to encapsulate curcumin and analyzed the physicochemical properties of curcumin nanoparticles. It proved that encapsulated curcumin nanoparticles enhanced stability toward ultraviolet (UV) irradiation, antioxidation and antitumor activity, enhanced/added function, solubility, bioactivities/ bioavailability, and control release and overcame the immunobarrier. We present an in vitro study that examined the cytotoxicity of amorphous and composite silica nanoparticles to different cell lines. These bioactives include curcumin mdAntrodia cinnamomea. It is hoped that by examining the response of multiple cell lines to silica nanoparticles more basic information regarding the cytotoxicity as well as potential functions of silica in future oncological applications could become available. 

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