Complexing of metal ions

The increased acidity of the larger polymers most likely leads to this reduction in metal ion activity through easier development of active bonding sites in siUcate polymers. Thus, it could be expected that interaction constants between metal ions and polymer sdanol sites vary as a function of time and the sihcate polymer size. The interaction of cations with a siUcate anion leads to a reduction in pH. This produces larger siUcate anions, which in turn increases the complexation of metal ions. Therefore, the metal ion distribution in an amorphous metal sihcate particle is expected to be nonhomogeneous. It is not known whether this occurs, but it is clear that metal ions and siUcates react in a complex process that is comparable to metal ion hydrolysis. The products of the reactions of soluble siUcates with metal salts in concentrated solutions at ambient temperature are considered to be complex mixtures of metal ions and/or metal hydroxides, coagulated coUoidal size siUca species, and siUca gels. 

Use of the K p for precipitation information is often complicated by a number of interfering factors including complexation of metallic ions, high ionic strength solutions, and high solids contents. This principle is applicable solely to ionic compounds, i.e., primarily inorganic compounds. 

As noted above, biouptake involves a series of elementary processes that take place in the external medium, in the interphasial region, and within the cell itself. One of the most important characteristics of the medium is the chemical speciation of the bioactive element or compound under consideration. Speci-ation not only includes complexation of metal ions by various types of ligands, but also the distribution over different oxidation states, e.g. Fe(II) and Fe(III), and protonation/deprotonation of organic and inorganic acids of intermediate strength. The relationship between speciation and the direct or indirect bioavailability1 of certain species has received a lot of recent attention. 

Beauvais, R. A., Alexandratos, S. D., polymer-supported reagents for the selective complexation of metal ions An overview. React. Funct. Polym. 36,1998,113-123. 

R. D. Hancock and A. E. Martell, Ligand design for selective complexation of metal ions in aqueous solution, Chem. Rev. 89, 1875-1914(1989). 

Humus can form stable complexes such as chelates with polyvalent cations. SOM is capable of strong polydentate binding to transition metals in a chelate [17,19,45, 65-67]. The complexation of metal ions by SOM is extremely important in affecting the retention and mobility of metal contaminants in solid phases and waters [45]. Several different types of SOM/humus-metal reactions can occur (Fig. 11), and include reactions between DOC-metal ions, complexation reactions between SOM-metal ions, and bottom sediments-metal ions. The functional groups of SOM (Fig. 10) have different affinities for metal ions as shown below ... 

Fig. 11. Complexation of metal ions by organic matter in suspended sediments, bottom sediments, colloidal and dissolved phases...

Boyle EA(1981) Cadmium, zinc, copper, and barium in foraminifera tests. Earth Planet Sci Lett 53 11-35 Brugger J, McPhail DC, Black J, Spiccia L (2001) Complexation of metal ions in brines application of electronic spectroscopy in the study of the Cu(II)-LiCl-H20 system between 25 and 90°C. Geochim Cosmochim Acta 65 2691-2708... 

Table 8.7 Comparison of Kinetic Parameters for the Formation of 1 1 Complexes of Metal Ions with NCS- at 25°C. From Ref. 98.

The first step in the preparation of dendrimer-encapsulated metal and semiconductor particles involves complexation of metal ions with the dendrimer in-... 

In our opinion, the differences in partition constants of neutral complexes of metal ions of the same charge with the same number of the same ligands, extracted to inert organic solvents, are almost entirely due to the differences in hydration of these complexes in the aqueous phase or, more precisely, to... 

In a review on the design of ligands for selective complexation of metal ions in aqueous media and a book on the principles underlying stability constants and on the design of metal complexes for various medical applications iron complexes and their solution chemistry take their appropriate place. 

The following are descriptions and examples of complexes of metal ions having coordination numbers of two to six. 

Complexation of metal ions by hydroxamic acids is the starting point of a number of analytical determinations . All hydroxamic acids, in acid solutions, react with ferric chloride to give rust brown complex salts 89 (Scheme 47). These colored complexes form the basis for the sensitive qualitative and quantitative determination of carboxylic acids and their derivatives too. 

In solvents, the complexes of metal ions with organic ligands are more soluble, which makes studies easier moreover, in anhydrous and aprotic media, it is possible to reduce the catalysts and their oxygen complexes out of reach of protons and thus to study the first steps of the catalytic cycle. It has been possible to show by studies in benzonitrile that the mixed-valence Co Co redox state of the... 

The electrochemistry of dissolved cyanide complexes of metal ions is very well documented [1] and there is no need to discuss these compounds here. However, the electrochemistry of... 

Metal ions can serve as effector molecules as well as control the DNA-binding activity of regulatory proteins. An example is the regulation of the metallothionein gene in eucaryotes (Fig. 1.23). The metallothioneins are small, cysteine rich proteins which can specifically bind metal ions like Cu or Zn The complexation of metal ions functions to sequester the ions in a form that is not damaging to the cell. 

The gene for metallothionein is induced by metal ions. The goal of the regulation is to provide enough metallothionein for the complexation of metal ions and thus to maintain the concentration of free metal ions at a tolerable level for the cell. 

The stability constants of several carbonato complexes of metal ions in solution has been compiled (3). Several recent publications have dealt with the isolation and characterization of carbonato complexes... 

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