Zinc complexation

Porphyrin, octaethyl-, zinc complex cyclic voltammetry, 4, 399 <73JA5140)... 

Simultaneous detenuination of Cu and Zn in the form of coloured PAR complexes is performed at pH 10 in the presence of pyrophosphate which binds the admixtures of Al, Fe and Mn into the inactive complexes. The measurements of the change in the optical density are made at 520 and 550 nm before and after the destmction of the complexes by EDTA, or at 530 nm before and after the destruction of the copper complexes by the thioglycolic acid and the destmction of the zinc complexes by EDTA. The detection limit for Cu is 2-5, for Zn - 3 p.g/diW. The application of these methodics at pH 8 enables one to determine simultaneously Cu and Zn at high excess of the latter. 

The Auger depth profile obtained from a plasma polymerized acetylene film that was reacted with the same model rubber compound referred to earlier for 65 min is shown in Fig. 39 [45]. The sulfur profile is especially interesting, demonstrating a peak very near the surface, another peak just below the surface, and a third peak near the interface between the primer film and the substrate. Interestingly, the peak at the surface seems to be related to a peak in the zinc concentration while the peak just below the surface seems to be related to a peak in the cobalt concentration. These observations probably indicate the formation of zinc and cobalt complexes that are responsible for the insertion of polysulfidic pendant groups into the model rubber compound and the plasma polymer. Since zinc is located on the surface while cobalt is somewhat below the surface, it is likely that the cobalt complexes were formed first and zinc complexes were mostly formed in the later stages of the reaction, after the cobalt had been consumed. 

Other flame retardants and/or smoke suppressants can also be used such as magnesium hydroxide, magnesium carbonate, magnesium-zinc complexes and some tin-zinc compositions. Zinc oxide is a common ingredient in many rubber base formulations used as part of the curing system. At the same time, the action of zinc oxide is similar to that of antimony trioxide, but less effective. 

The reaction of CF3I and CgFjI with dialkylzmc in the presence of a Lewis base, such as diglyme or pyridine, quantitatively gives the corresponding fluori-nated organozinc complexes [32] (equation 23) When Rf is C2F5 or iso CjF-j, the pure zinc complexes are not isolated... 

Thiophene is also metal ated by a benzene-soluble ethyl sodium-diethyl zinc complex. Upon carbonation, 65% of 2-thiophenecar-boxylic acid was obtained. ... 

Fig. 3.24 X-ray crystal structure of the 131b-bipy zinc complex. [Denmark, S.E. O Connor, S.O. Wilson, S.R. Angew. Chem., int. Ed. Eng. 1998, 37, 1149. Reprinted with permission from Wiley-VCH ...

The zinc complex of oxine fluoresces in ultraviolet light, and this forms the basis of the following method. 

It is interesting to note that the magnesium or zinc complexes of methyl pheophorbide a (11, M = Mg, Zn R = C02Me) or methyl pyropheophorbide a (11, M = Mg, Zn R = H) are cleaved between positions 20 and 1 by singlet oxygen, whereas in contrast nature cleaves the chlorin at the 4,5-C —C double bond.44-45a h46 The ring fission at the 4.5-C —C double bond can be achieved with the cadmium(II) complex of methyl pheophorbide (11, M = Cd R = C02Me) to produce 12.43i... 

In contrast, with the corresponding zinc complexes isobacteriochlorins are formed. 5,10,15,20-Tetraphcnylbactcriochlorin (1, R = H) Typical Procedure 3 ... 

An alternative method for generating enriched 1,2-diols from meso-epoxides consists of asymmetric copolymerization with carbon dioxide. Nozaki demonstrated that a zinc complex formed in situ from diethylzinc and diphenylprolinol catalyzed the copolymerization with cyclohexene oxide in high yield. Alkaline hydrolysis of the isotactic polymer then liberated the trans diol in 94% yield and 70% ee (Scheme 7.20) [40]. Coates later found that other zinc complexes such as 12 are also effective in forming isotactic polymers [41-42]. 

The stereocontrol observed in these reactions is rationalized on the basis of zinc complexes formed with the Schiff bases, as described in Section 1.4.4.2.2. The isocyanide, being a free and potent nucleophile, attacks this complex from the sterically less-hindered side, that is. from the side of the ring oxygen. 

Tacticity of VIA A is influenced by solvent,90 9 the presence of amines (Table 8.3)90 and complcxation. PYIAA appears more isotactic when formed in a nonhydrogen-bonding solvent,90 95 Polymerization of MAA in CHCh in the presence of 14 or 15 also yields a more isotactic polymer90 Polymerization of zinc complexes of MAA also yields more isotaclic polymers,9 >... 

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