Stability metal ions

A combination of P- and N- donors is another useful approach to potentially reactive (and cataly-tically active) Ni species. Similar to O- donors, N is a hard donor capable of stabilizing metal ions in higher oxidation states, whereas the soft donor P is best suited to stabilize medium or low oxidation states. A neutral bidentate P,N ligand combining a hard dimethylamino and a soft phosphine donor in /V,/V -dimethyl-2-(diphenylphosphino)aniline (241) affords the neutral trigonal bipyramidal and the... 

This kind of argument may also be invoked for some Cr(III)-azamacrocyclic complexes. In this regard, it is noted that the macrocycle effect (which is essentially an enhanced chelate effect) stabilizes metal ions entrapped in the cavity formed by macrocyclic organic ligands... 

Macrocyclic ligands often stabilize metal ions in uncommon oxidation states, and a number of Ni(I) species have been detected in solutions mainly by epr spectroscopy. However, the Ni(I) species are usually unstable, and only a few Ni(I) macrocyclic complexes have been isolated in the solid state thus far. Their electronic absorption spectra, epr spectra, and X-ray crystal structures have been measured. 

Compared to other 1,1-dithiolates, the R2DED ligands are quite unique in their properties. These ligands appear to be more effective than the dithio-carbamate ligands in stabilizing metal ions in high formal oxidation states and are characterized by a conjugated n system (Fig. 54). 

The basic premise of CMP waste treatment is to remove the target trace metals (Cu, W, Ta, etc.). The primary challenges that add complexity to the CMP waste treatment systems is the presence of the suspended solids, organics added to stabilize metal ions that may be counteractive to some of the treatment chemistries, and oxidizers in the slurry waste. 

The expected macrobicyclic ligands with a contracted cavity and high delocalizing ability can stabilize metal ions in the high oxidation states. In this case, one should expect the formation of a mixture of fac- and mer-isomers because of the initial ligand C2-nonsymmetry. 

A variety of cyclic tetraamides, e.g., (61), which stabilize metal ions in high oxidation states and are resistant to oxidation, have been synthesized for use as oxidation catalysts for peroxide bleaching.61... 

However, the cyanide ion does have the ability to stabilize metal ions in low formal oxidation states, and it presumably does this by accepting electron density into its n orbitals. The fact that cyano complexes of zerovalent metals are generally much less stable (in a practical as opposed to a well-defined thermodynamic or chemical sense) than similar metal carbonyls has often been taken to show the poor 7t-acidity of CN-, but it should be noted that the cyano compounds, e.g., [Ni(CN)4]4-, are anionic and might thus tend to be more reactive for this reason alone. In some instances cyano... 

Information about metal interactions with RNA and DNA comes from functional studies and also from structural investigations, including X-ray crystallography, NMR spectroscopy, optical spectroscopies, and measurements of thermodynamic stability. Metal ions have been localized in several X-ray crystal structures of canonical DNA duplexes. Metal sites were elucidated in early X-ray structures of tRNA which, like other RNA molecules, has a more complex folded structure. More recently, many metal sites have been revealed in X-ray crystal structures of ribozymes, RNA molecules that perform chemical reactions, and in some cases metals have been proposed to be cofactors in these reactions. Finally, from very recent X-ray crystal structures, hundreds of embedded metal ions are predicted within the RNA components of the enormous ribosomal subunits.An interesting aspect of such structures is also the use of heavy-metal coordination compounds for the purposes of X-ray phasing. 

In addition to their microporous environment, zeolites offer a range of other important chemical properties. They are highly acidic materials. One can time both the number of acid sites and the strength of these sites and thus control their overall acidity. They have high thermal stabilities. Metal ions can be readily exchanged, impregnated or added into the synthesis to open up many other types of reactions. 

Phosphatase (Stepan and Ferwerda, 1973), acid phosphatase (Campbell et al, 1973), and alkaline phosphatase (Ramadose et al, 1974) were all found to exist in three forms, and in each case only one of the isoenzymes was susceptible to neuraminidase. In the case of alkaline phosphatase neuraminidase treatment of the sialic-acid-containing isoenzyme did not alter it with respect to reaction rate, affinity for substrates, or response to activators and inhibitors. The sialic acid residues thus seemed not to be essential to the catalytic properties of the isoenzyme, although it differed from the other two nonsialo species in thermal stability, metal ion effect, and affinity toward some substrates (Rama-... 

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