Metal ion table

Where there is a danger of contamination of a hydrocarbon polymer with such ions it is common practice to use a chelating agent which forms a complex with the metal. It is, however, important to stress that a chelating agent which effectively slows down oxidation initiated by one metal ion may have a prooxidant effect with another metal ion. Table 7.5 summarises some work by... 

Note The copper in the reagent may be replaced by other metal ions. Table 1 [3] lists the colors obtainable with some cations. 

Major efforts have been undertaken in recent years for developing new CL systems. These studies extend the application of CL analysis to inorganic species. It should be noted, however, that there still exists no new CL system that exceeds the sensitivity offered by luminol for current metal ions. Table 2 lists some typical examples of inorganic analyses using different CL systems. 

The end points of precipitation titrations can be variously detected. An indicator exhibiting a pronounced colour change with the first excess of the titrant may be used. The Mohr method, involving the formation of red silver chromate with the appearance of an excess of silver ions, is an important example of this procedure, whilst the Volhard method, which uses the ferric thiocyanate colour as an indication of the presence of excess thiocyanate ions, is another. A series of indicators known as adsorption indicators have also been utilized. These consist of organic dyes such as fluorescein which are used in silver nitrate titrations. When the equivalence point is passed the excess silver ions are adsorbed on the precipitate to give a positively charged surface which attracts and adsorbs fluoresceinate ions. This adsorption is accompanied by the appearance of a red colour on the precipitate surface. Finally, the electroanalytical methods described in Chapter 6 may be used to scan the solution for metal ions. Table 5.12 includes some examples of substances determined by silver titrations and Table 5.13 some miscellaneous precipitation methods. Other examples have already been mentioned under complexometric titrations. 

By analogy with the basicity towards protons (equation 5) the basicity towards monocharged metal ions (Table 4) is defined by means of the thermodynamics of the reaction ... 

The contention that disulfides are the major products of reaction when thiols are oxidized in aqueous alkaline solution has been amply confirmed by the present investigation. Thus, in the absence and in the presence of various metal ions (Table I) and in the oxidation of various simple alkyl and aryl thiols (Table III) disulfide has always been produced quantitatively. Under these circumstances, experiments have been designed to investigate the kinetics and mechanism of the reaction as a basis for further detailed studies. 

Note that Kf for EDTA is defined in terms of the species Y4 reacting with the metal ion. The equilibrium constant could have been defined for any of the other six forms of EDTA in the solution. Equation 12-5 should not be interpreted to mean that only Y4 reacts with metal ions. Table 12-2 shows that formation constants for most EDTA complexes are quite large and tend to be larger for more positively charged cations. 

Racah parameters B and C for the given transition metal ion (Table 46) ... 

Perhaps the simplest reaction to envisage is the alkylation of a co-ordinated amine. These reactions are well-known and usually occur under strongly basic conditions. It is most likely that these reactions involve deprotonated amido intermediates, and are considered in that context. As we have seen in Chapter 2, the acidity of an amine proton should increase upon co-ordination to a metal centre, and with the charge on that metal. As a consequence, we might expect to see new types of reaction products derived from the amido ligand, particularly with high oxidation state metal complexes. The former effect is indeed the case, and dramatic reduction of the pKa of ammonia and amines is observed upon co-ordination to a metal ion (Table 5-1). 

An action potential in the presynaptic fiber propagates into the synaptic terminal and activates voltage-sensitive calcium channels in the membrane of the terminal (Figure 6-3). The calcium channels responsible for the release of transmitter are generally resistant to the calcium channelblocking agents discussed in Chapter 12 Vasodilators the Treatment of Angina Pectoris (verapamil, etc) but are sensitive to blockade by certain marine toxins and metal ions (Tables 12-4 and 21-1). Calcium flows into the terminal, and the increase in intraterminal calcium concentration promotes the fusion of synaptic vesicles with the presynaptic membrane. The transmitter contained in the vesicles is released into the synaptic cleft and diffuses to the receptors on the postsynaptic... 

Polarographic AC and pulse polarographic techniques as well as stripping analysis are effective tools for the determination of trace levels of metal ions. Table 3.1 provides a comparison of the sensitivity and usefulness of the various methods.12,21 23 For metal ions, stripping voltammetry usually is the method... 

In the late 1950s and 1960s, as UV-vis spectrophotometers became available, tdt was superseded by 2,3-quinoxalinedithiol (qdt) for the quantification of metal ions (Table I) (3, 5-8, 11). Using qdt, metal ion concentration in the 0.1-10 ppm range can be determined with errors of <5%. However, metal mixtures require separation prior to analysis except in those cases where simultaneous Beer s law equations can be solved (5, 8-9, 12). 

The basic polyhedron adopted by these structures is the tricapped trigonal prism (D3h). The coordination polyhedron of oxygen atoms around the neodymium atom in Nd(C204>3 IO.5H2O is shown in Fig. 5.25. The stability of the tricapped trigonal prism is confirmed by the large variety of ligand combinations around 9-coordinate metal ions (Table 5.9) which are best described by this polyhedron. 

Finally, the electroanalytical methods described in chapter 6 may be used to scan the solution for metal ions. Table S.I2 includes some examples of substances determined by silver titrations and table S.I3 some miscellaneous precipitation methods. Other examples have already been mentioned under cornplexometric titrations. 

Cydo-(Pro-Gly)3 selectively binds Li of alkali-metal ions and of alkali-earth-metal ions (Table 13). Cyclo Pro-Gly)3 binds alkali-earth-metal ions more... 

Three types of pentanuclear cyanide-bridged complexes were described, namely, TBPs, cross-shaped clusters, and open chains. As shown by the Dunbar group (173-177), the TBP architecture is amenable to a wide variety of transition metal ions. In fact, neutral complexes of the general formula [M tmphen)2]3[M CN)6]2 were prepared with 22 different combinations of metal ions (Table V). In these structures (Fig. 34), two [M (CN)6] anions occupy the axial positions of the TBP core. Three cyanide ligands of each hexacyanometalate unit act as bridges, whereas... 

A metal atom is essential to the catalytic activity of carboxypeptidase A (53). The enzyme, as isolated, contains one gram atom of zinc per molecular weight of 34,600. Removal of the metal atom, either by dialysis at low pH or by treatment with chelating agents, gives a totally inactive apoenzyme. Activity can be restored by readdition of zinc or a number of other divalent metal ions (Table VII). The dual activity of carboxypeptidase towards peptides and esters is quite sensitive to the particular activating metal ion. Thus, the cobalt enzyme has twice the activity of the native zinc enzyme toward peptides but the same activity toward esters. Characteristic peptidase and esterase activities are also observed for the and Mn enzymes as well while the Cd ", Rh ", and Pb " en-... 

Imprinting polymerisation for recognition and separation of metal ions TABLE 9.2... 

Foremost, metal ions that catalyze hydrolysis reactions must be strong Lewis acids (electron acceptors). This property enables metal ions to facilitate hydrolytic reactions by enhancing the electrophilicity of the organic substrate and/or nucleophilicity of the water molecule, and allows hydrolysis reactions to proceed at, or around, neutral pH. Lewis acidity can be observed as a lowering of the pA/ values of bound ligands, such as a bound water molecule in hydrolysis reactions. The pA), of a water molecule decreases substantially upon coordination by a metal ion (Table 1), allowing the water molecule to become deprotonated near neutral pH. Coordination of more than one metal ion to a protic ligand, such as the case with binuclear metallohydrolases. 

Similarly, if we compare the conductivity of the alkali metal ions (Table 31.5), in the light of Eq. (31.45) we would be forced to conclude that the radius of the lithium ion is larger than that of the cesium ion. Since the crystallographic radius of lithium ion is much smaller than that of cesium ion, this indicates a difficulty with the Stokes s law interpretation ofXi. 

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