Zinc-substituted

The redox potentials of zinc-substituted phthalocyanines are shown to be linearly dependent on the total Hammett substituent constant.837 In 1987, Stillman and co-workers used the absorption and magnetic circular dichroism spectra of the zinc phthalocyanine and its 7r-cation-radical species to assign the observed bands on the basis of theoretical calculations. The neutral and oxidized zinc phthalocyanine complexes with cyanide, imidazole, and pyridine were used with the key factor in these studies the stability of the 7r-cation-radical species.838 The structure of zinc chloro(phthalocyaninato) has been determined and conductivity investigated.839... 

Only a few attempts have been made to use Ni(PPh3)4 and Pt(PPh3)4 as catalysts in cross-coupling reactions of zinc-substituted allene 68 with phenyl iodide (cf. Eq. 14.7). In both cases the resulting coupling product 70 was formed in <5% yield [33]. 

Toxicity of cadmium increases in cases of zinc deficiency, due to the zinc substitution in biological systems, which leads to functional disorders. Cadmium reduces assimilation of vitamins C and D. However, a large amount of these vitamins in the diet will decrease the toxicity of cadmium through the reduction of its absorption from the intestinal tract (Friberg et ah, 1986 Hill, 1996 McLaughlin et ah, 1999). 

In the experiment, ZnCcP is produced by laser photolysis, then transient absorption spectroscopy follows the formation (k ) and decay (/Ceb) of ZnCcP + in wild-type and mutant crystals. Kang and Crane have studied the effects of interface mutations on electron transfer rates in single crystals using complexes between a zinc-substituted cytochrome c peroxidase (ZnCcP) and site-directed mutants of yeast cytochrome c (yCc).The mutants replaced the... 

An alternative application of flash photolysis to study myoglobin electron transfer kinetics has been employed by Hofifinan and co-workers 156). In this approach, the photoactive zinc-substituted derivative of Mb is mixed with an equivalent amoimt of ferricytochrome bs to form an electrostatically stabilized binary complex. Upon transient irradiation, the strongly reducing Zn-Mb intermediate is formed, and the kinetics of ferricytochrome reduction within the preformed complex can be monitored spectrophotometrically. The resulting kinetics represents a mixed-order process consistent with electron transfer both within the electrostatically stabilized complex and between the dissociated components of the complex. 

Fe "-OOH (ES) complex, 43 95-97 heme-bound CO, 43 115 lock-and-key model, 43 106-107 mutation in proximal heme cavity, 43 98 residue location, 43 101-102 van der Waals surfaces, 43 112-113 Velcro model, 43 107 zinc-substituted, 43 110-111 plastocyanin, cross-linked, cyclic voltammogram, 36 357-358 promoters, 36 345-346 protein-electrode complex, 36 345, 347 redox potential, 36 349 self-exchange rate constants, 36 402 stability at electrode/electrolyle interface, 36 349-350... 

The conjugate addition of bis(iodozincio)methane to -unsaturated carbonyl compound gives y-zincio substituted enolate. As shown in equation 31, bis(iodozincio)methane reacts with. v-cis a,/3-unsaturated ketone in the presence of chlorotrimethylsilane to afford the silyl enol ether carrying a C—Zn bond. These zinc-substituted silyl enolates can be used for further coupling reactions (equation 32)54. 

An analogous approach has been applied to study the electron transfer reaction between yeast cytochrome c peroxidase (CCP) and cytochrome c (cyt c) by employing the complex between zinc-substituted CCP (ZnCCP) and native cyt c [70]. The two heme planes in this complex are nearly parallel at a metal-metal distance of 25 A and an edge-to-edge distance of 17-18 A. 

Electron phototransfer in zinc-substituted cytochrome c/cytochrome 65 complex [Zn(II)cyt c /Fe(III)cyt 65] has been studied [92]. Porphyrin rings lie parallel in this complex with the distances of ca. 8 A edge-to-edge, 18 A centre-to-centre. The Zn cyt c triplet excited state is quenched by Fe(III)cyt bn with the rate constant k = 5 x 105 s 1. Neither Fe(II)cyt b5 nor Zn(II)cyt quench TZn cyt c. 

Long range electron-transfer has also been demonstrated within the complex between zinc-substituted cytochrome c peroxidase and cyt c 59). The kinetics of intramolecular electron-transfer from Ru(II) to Fe(III) in ruthenium modified cyt c has also been investigated 58). 

Luminescence quenching of the zinc-substituted cytochrome c (Zn-cyt c) excited state by cytochrome b5 (cyt b5) has been investigated97. The most striking result of the quenching study is that the triplet emission decay rate of Zn-cyt c (3k = 102 s ) is remarkably accelerated in Zn-cyt c/cyt b5 (3k = 5 x 105 s-1) by about a factor of... 

One of the striking successes of the N< el model was its ability to account for the magnetization curves of the zinc-substituted ferro-spinels shown in Figure 23, where nB = Mq/N hb is the number of Bohr magnetons per molecule. From the intercept at x = 0, it is theoretically possible to obtain the spectroscopic splitting factor, as defined by equation 81. However, the discrepancies shown in Table IX between the original measurements by Guillaud et al. (243) and... 

Cationic organozinc compounds are expected to be good catalysts for ring opening polymerization reactions of epoxides and lactones because the enhanced Lewis acidity (see Lewis Acids Bases) of the zinc center favors its coordination to the monomer. For example, Walker and coworkers have found that the cationic zinc substituted cyclopentadienyl complex [3,5-Me2C6H3CH2CMe2C5H4Zn(TMEDA)]+ [EtB(C6F5)3] is an active initiator species for the polymerization of cyclohexene oxide and e-caprolactone. ... 

Vitamin A Both vitamin A (= retinol) and A2 (= 3-dehydroreti-nol) occur in nature. Like their derivatives, they are classed under the umbrella term axerophtol. The major provitamin is p-carotin. Vitamin A is stored as a lipoglycoprotein complex in the fat-storing cells of the liver. It is released when necessary by being coupled with a retinol-binding protein (RBP) and is then transported to the cells which require vitamin A. In the case of zinc deficiency the rate of RBP synthesis is markedly increased, and as a result serum retinol concentration is reduced. Retinol deficiency can be compensated by zinc substitution. The daily requirement is approx. 1 mg. (7, 36)... 

Balancing of electrolytes, acid-base equilibrium and, if necessary, zinc substitution. 

This net negative effect of zinc substitution on quantum yield in spite of an overall increase in driving force for charge separation is an excellent example of the subtle interplay of competing and sequential electron transfer steps which make these complex molecular devices both interesting and challenging to study. 

In the present paper XANES and EXAFS techniques were applied to characterize zinc species with respect to their coordination in zinc substituted MFI type zeolite (H-[Zn]MFI) and zinc exchanged H-ZSM-S (ZnH-[Al]MFI). Octahedral coordination of zinc at cationic positions in hydrated ZnH-[Al]MFI was determined. In H-[Zn]MFI, zinc should be surrounded by four lattice oxygen and two other species in a further distance. Average Zn-0 distances mcrease in the order H-[Zn]MFI < ZnO < ZnH-[Al]MFI. Upon heating to 775 K a change of the anc coordination due to dehydration can be clearly observed on ZnH-[Al]MFI but not on H-[Zn]MFI. 

Extensive studies on nonphysiological electron transfer using zinc-substituted CCP (118) or cyt c (119) have also been reported. The reaction scheme using ZnCCP is the following ... 

Zinc Substitution. Although the solid solution limit for the substitution of zinc for copper has not been determined, it has been found that even at low concentrations (37 i.e. Cu Zn 2.9 0.1) high temperature superconductivity (Tc>77K) is quenched, although the electrical conductivity remains quite high. 

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