Chemical stability, in aqueous

Among the various catalysts employed in the photocatalytic processes, the most popular and used is titanium dioxide, Ti02, thanks to its strong catalytic activity, high chemical stability in aqueous media and in a large range of pH (0-14), low cost due to the abundance of Ti (0.44% of the Earth s crust) and long lifetime of electron-hole pairs. 

The majority of metals and alloys available depend for their resistance to corrosion on the properties of an oxide film or corrosion product which is formed initially by the corrosion process. In many cases the protectiveness of the oxide film is determined by its stability in aqueous solutions in a specific pH range, either chemically dissolving to form aquocations at lower pH values or complex anions (aluminate, ferroate, plumbate, zincate, etc.) at higher pH values (Fig. 2.22). An important property of the chemical is therefore the pH value that it develops when dissolved in water. For many materials and many chemicals this is the overriding factor and in many cases... 

Chemical stability. Some medicaments undergo chemical change in aqueous soluhons. If the change is due to oxidation, a reducing agent such as sodium metabisulphite is included (e.g. Adrenaline Injection BP). 

It is interesting to speculate on the chemical properties of molybdenum which make it suitable for its biological function. Obvious features in the chemistry of molybdenum are (a) a range of oxidation states which can be stabilized in aqueous solution by the common ligands of biology (b) the formation of oxo compounds and the sulfur analogue (c) the ability to participate in atom-transfer reactions and (d) the possibility of higher coordination numbers. 

Once good physical stability of an emulsion is insured, its commercialization mandates chemical stability of the incorporated drug and other essential components for at least 18 months. Key factors that affect the chemical stability of pharmaceutical emulsions include drug stability in oil, drug stability in aqueous media, drug concentration in oil and emulsion, phase volume ratio, droplet size, presence of excipients, and presence of air and/or peroxide radicals. As mentioned earlier, choice of appropriate antioxidant is important. 

A detailed knowledge of the predominant physicochemical/biochemical mechanism by which gas microbubbles are stabilized in aqueous media is of practical importance to numerous and varied fields acoustic and hydrodynamic cavitation, commercial oil recovery, hydraulic and ocean engineering, waste-water treatment, chemical oceanography, meteorology, marine biology, food technology, echocardiography, and the continual medical problem of decompression sickness. Many of these applications... 

Bischoff W.D. (1985) Magnesian calcites Physical and chemical properties and stabilities in aqueous solution of synthetic and biogenic phases. Ph.D. dissertation, Northwestern Univ.. 

In addition [103,104], a new type of composite that combines DNA with silica components via a sol-gel method was described. The DNA-silica hybrid material is advantageous with respect to its mechanical and chemical stability in both aqueous and organic solvents. Similar to the previously described hybrids, the specific functions of the DNA molecules were retained and maintained the DNA-silica hybrid materials adsorb DNA-interactive chemicals from diluted aqueous solution. In another series of reports [105-109], DNA-loaded PSf microspheres were fabricated by means of a liquid-liquid phase separation technique. The release rate of DNA from the microspheres can be controlled by manipulating the microsphere structure. Increasing the polymer concentration causes lower porosity and smaller pores on the outer surface of the microspheres, and leads to a low release rate of DNA from the microspheres. The DNA-loaded PSf microspheres could effectively accumulate harmful DNA-intercalating pollutants and endocrine disruptors, as described in previous reports. 

Kittrick, J. A. Ion exchange and mineral stability Are the reactions linked or separate Jenne, E. A., ed., "Chemical Modeling in Aqueous Systems, Speciation, Sorption, Solubility, and Kinetics," Amer. Chem. Soc., (this volume). 

One year later, Brust and Schiffrin [28,29] published a method for AuNPs synthesis which has a considerable impact on the overall field in less than a decade because it allowed the facile synthesis of thermally stable and air-stable AuNPs of reduced dispersity and controlled size for the first time. In this method, the gold colloids are sterically stabilized by organic molecules having thiol, amide or acid groups in contrast to the citrate reduction method where the gold colloids are kinetically stabilized in aqueous solutions by an electrical double layer [28,29], The main advantage of the Brust method is that the gold particles behave in a way as chemical compounds. These AuNPs can be repeatedly isolated and... 

MacCarthy, P. and Smith, G. C. (1979). Stability surface concept A quantitative model for complexation in multiligand mixtures. In Chemical Modeling in Aqueous Systems (E. A. Jenne, ed.). ACS Symp. Ser. No. 93, American Chemical Society, Washington, D.C., pp. 94-114. 

Figure 3.7 Stabilities of some class B divalent cation complexes are shown at zero ionic strength, based on published data. Ligand EN values are 1 (2.66), Br (2.96), Cl- (3.16), F- (3.98), OH" (3.1), and SH (2.33). Cation EN values all range from 1.6 to 1.7, except EN = 2.00 for Hg -. Reprinted with permission from Techniques of estimating thermodynamic properties for some aqueous complexes of geochemical interest, D. Langmuir. In Chemical modeling in aqueous systems, ed. E. A. Jenne, Am. Chem. Soc. Symp. Sen 93. Copyright 1979 American Chemical Society.

Partiele size, shape, surfaee area Density Hygroscopicity Aqueous solubility as a flmetion of pH Solubility in organie solvents Solubility in presenee of surfaetants (e.g., bile acids) Dissolution rate Wettability Partition coefficient (octanol-water) Chemical stability in solid state Photolytic stability Oxidative stability Incompatibility with formulation additives Complexation with formulation additives Systemic metabolism... 

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