Subgroup ions

The insolubility of AgCl in water was ascribed to the strong attraction of the subgroup ion Ag+, and this would be a plausible explanation if it were not for the fact that AgF is very soluble in water. In fact it would have been expected that this compound, containing a smaller negative ion than AgCl, would be less soluble than AgCl, itself. 

The extra field of the subgroup ions certainly plays a part in the low solubility of these compounds, but it cannot be said that this alone reduces solubility since AgF, in which the fluorine ion is particularly small, is freely soluble in contrast to AgCl and the other silver halides. It must be kept in mind that, in general, lattice energy... 

In this section we discuss the stereochemistry of B-subgroup ions with filled d shells. The most striking feature is that in addition to forming tetra-hedrally and octahedrally coordinated compounds, these ions exhibit a more or less pronounced tendency to occur in linear environments, for example, Ag+ in the linear cation [Ag(NHa)2]+, Au+ in the linearly coordinated infinite chains of Aul, and Hg++ in the discrete molecules of HgCla which exist in both the gas and crystalline phases. We believe that two influences are at work in determining these structures. One is related to the Jahn-Teller effect, and the other to covalent bonding. We shall discuss them in this order and then consider their relative importance. 

Zirconium [7440-67-7] is classified ia subgroup IVB of the periodic table with its sister metallic elements titanium and hafnium. Zirconium forms a very stable oxide. The principal valence state of zirconium is +4, its only stable valence in aqueous solutions. The naturally occurring isotopes are given in Table 1. Zirconium compounds commonly exhibit coordinations of 6, 7, and 8. The aqueous chemistry of zirconium is characterized by the high degree of hydrolysis, the formation of polymeric species, and the multitude of complex ions that can be formed. 

Metalloproteinases are a subgroup of proteinases. They are responsible for the cleavage of peptide bonds within a protein (proteolysis). Metalloproteinases contain a metal ion in the active center and are divided into four subclasses dependent on their mechanism of catalysis. 

The diazonio group in an arenediazonium salt can be replaced by one of several transition metal ions in subgroups lb (Cu), Illb (Tl), IVb (Ge, Sn, Pb), or Vb (P, As, Sb, Bi) or by certain compounds of the transition elements. There is only one report of a substitution by a main group metal, magnesium, but the primary product has not been clearly identified (Nesmeyanov and Makarova, 1959). 

Metallothionein was first discovered in 1957 as a cadmium-binding cysteine-rich protein (481). Since then the metallothionein proteins (MTs) have become a superfamily characterized as low molecular weight (6-7 kDa) and cysteine rich (20 residues) polypeptides. Mammalian MTs can be divided into three subgroups, MT-I, MT-II, and MT-III (482, 483, 491). The biological functions of MTs include the sequestration and dispersal of metal ions, primarily in zinc and copper homeostasis, and regulation of the biosynthesis and activity of zinc metalloproteins. 

Various processes separate rare earths from other metal salts. These processes also separate rare earths into specific subgroups. The methods are based on fractional precipitation, selective extraction by nonaqueous solvents, or selective ion exchange. Separation of individual rare earths is the most important step in recovery. Separation may be achieved by ion exchange and solvent extraction techniques. Also, ytterbium may be separated from a mixture of heavy rare earths by reduction with sodium amalgam. In this method, a buffered acidic solution of trivalent heavy rare earths is treated with molten sodium mercury alloy. Ybs+ is reduced and dissolved in the molten alloy. The alloy is treated with hydrochloric acid, after which ytterbium is extracted into the solution. The metal is precipitated as oxalate from solution. 

In contrast, receptors in the second group have a low affinity [micromolar range] for serotonin and have been divided into three different classes— named S-HTj, S-HTj, and 5-HT4—with specific pharmacological properties [Miquel and Hamon 1992]. The S-HTj receptor [with subgroups 5-HT2A, S-HTjb, and S-HTjc] mediates facilitatory effects of serotonin, whereas the 5-HT3 receptor is the only serotonin receptor that directly activates an ion channel and therefore provides rapid activation of target cells. 

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