Dissolution promoter

The same principle may hold for the anion accompanying the proton, when the anion replaces surface OH groups and thereby assists in the release of Fe. Cl ions have a strong dissolution promoting effect, whereas CIOJ, which has a much lower affinity with the oxide surface, does not sulphate is intermediate. These anions have a similar effect on the dissolution of both natural and synthetic goethite (Surana Warren, 1969 Cornell et al., 1976). 

Cocozza C., Tsao C. C. G., Cheah S.-F., Kraemer S. M., Raymond K. N., Miano T. M., and Sposito G. (2002) Temperature dependence of goethite dissolution promoted by trihydroxamate siderophores. Geochim. Cosmochim. Acta 66, 431-438. 

Figure 13.7 lists some of the factors that promote and inhibit dissolution. Obviously, substances that block surface functional groups or prevent the approach of dissolution promoting H, OH , ligands, and reductants to the functional groups inhibit the dissolution. A very small concentration of inhibitor can often be effective because it may suffice to block the functional groups of... 

The fact that oxoanions can effectively inhibit reductive and nonreductive dissolution with regard to a reference system supports and the concept of competition between dissolution-promoting and dissolution-inhibiting ligands. As Figure 13.20 shows with the help of MICROQL calculations (Westall, 1979 based on complex formation constants fitted to actual data by Sigg and Stumm, 1981, on one hand and by Dos Santos-Afonso and Stumm, 1992, on the other hand), the dissolution system is very sensitive to phosphate. 

Figure 11 shows the effect of some oxoanions and of complex formers on the reductive dissolution of goethite by H2S (45). These data illustrate once more the competition among various dissolution-promoting and dissolution-... 

Observations indicate that Ca-rich feldspars are more susceptible to organo-ligand promoted dissolution than are the Na-or K-feldspars in experiments, soils and lithified sediment (32.70.73). although the proton-promoted dissolution rates of albite, anorthite and K-feldspar are approximately equal (22). The rate of feldspar dissolution promoted by organo-ligands is proposed to increase when inner-sphere adsorption of organo-ligands on aluminosilicates weakens critical crystal lattice bonds at the site of adsorption (77). 

Moolenaar F, Kaufmann BG, Visser J, Meijer DKF (1986) Rectal absorption of methadone from dissolution-promoting vehicles. Int J Pharm 33 249-252... 

An interesting system consisting of a novolac matrix resin, an onium salt photoadd generator and silanol compounds that act as dissolution promoters for novolac resins in aqueous base was described recently (37, 38). Compounds such as diphenylsilanediol (DPS) are readily soluble in aqueous base and may in fact ino ase novolac solubQity in aqueous media by as much as a factor of S. Upon exposme to light followed by post-exposure bake, acid catalyzed condensation of the silanol additive results in formation of a polysiloxane. While silanols are dissolution promoters, polysiloxanes are hydrophobic, aqueous-base insoluble resins that may act as dissolution inhibitors. Suffident differential solubility is achieved between the exposed and unexposed areas of a resist film resulting in negative tone images. Polysiloxanes are dtemate dissolution inhibitors that may be used in these processes (39). 

In addition, the phenoi group, as a part of the protection group, is virtualfy a masked promoter. After the cleavage reaction, the deprotected compound, phenol fi om the phenoi group, acts as a dissolution promoter since it is very soluble in aqueous base solutions. As the result, the sensitivity of the tystem should be improved. 

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