Zinc compounds systems

Complexing of zinc and cadmium by amino acids, both natural and otherwise, and of polypeptides, has been the subject of study for many years because of the importance of zinc-protein systems and the physiological effect of cadmium compounds (see Section 56.1.14). 

II elements invariably are not used singly, but in Subgroup A-B couples. Aside from lead compounds, the elements currently used in most applications are barium, cadmium, calcium, zinc, and tin—e.g., the calcium-zinc soap systems for nontoxic (food contact) applications, the general purpose barium-cadmium soap stabilizers, and the organotin stabilizers. The objective of this paper is to consider the rheological consequences of... 

Organozinc addition reactions to unsaturated systems lead to an intermediate zinc compound which is in most cases further hydrolyzed to give the corresponding protonated organic compound. This intermediate can also be trapped by reaction with electrophiles (see Electrophile) (E+) such as aldehydes, acyl chlorides, organic halides, silyl halides, and so on. Depending on the nature of the electrophile (see... 

Organozinc compounds add to conjugated systems. The use of chiral ligands is effective for conjugate addition of diaUcylzinc compounds to a,p-unsaturated ketones, esters, and so on, including conjugated lactones." Many dialkyl-zinc compounds can be used, including vinylzinc compounds.Dialkylzinc... 

A recent paper by Cooper et al. [155] reported a fairly strong catalytic effect of an unidentified zinc compound on the reaction of an aromatic isocyanate with 3,3 -dichlorobenzidine. Axelrood et al. [184] found diethylene triamine and stannous octoate to be powerful cateilysts for the reaction of phenyl isocyanate and an aromatic diamine, whereas di-butyltin dilaurate and cobalt naphthenate had only a mild effect in their system. 

The dilution of the spin crossover system in a similar host lattice with bigger ions (e.g. an iron system in the corresponding zinc compound) will create a negative image pressure. The HS state becomes preferentially stabilised and consequently Tc decreases. Simultaneously the conversion curve xHs versus T becomes more gradual. Analogous behaviour is exhibited by [Fe M1 (2-pic)3]Cl2 EtOH systems (M = Co, Zn) and [Fe Mi (phen)2 (NCS)2] systems (M = Mn, Co, Zn). 

Zinc is one of the most mobile of the heavy metals. The zinc compounds formed with the common anions found in surface waters are soluble in neutral and acidic conditions. In reducing environments, zinc sulfide (ZnS) is a relatively insoluble and stable compound, which may oxidize in the presence of dissolved oxygen. Zinc carbonate (ZnCOj) is assumed to be less stable than zinc sulfide, though still relatively insoluble. Zinc ions are dominant up to pH values of about 9 in simple aqueous systems. In basic solutions, zinc hydroxide (Zn(OH)2) precipitates if the concentration of zinc is 10.4 M. Zinc hydroxide shows minimal solubility at pH 9.5 and dissolves at higher pH values as the zincate anion, Zn(OH) . 

Also Pdotalyzed Negishi cross-coupling reactions have been described in ionic liquids. Knochel and coworkers investigated the reaction between organometalhc zinc compounds and aryl iodide in [BMMIM][Bp4] using an ionic phosphine ligand. Scheme 5.3-30 illustrates the reaction for the formation of a 3-substituted cyclohexenone from 3-iodo-cyclohex-2-en-l-one [170]. The reaction vras carried out in an ionic liquid/toluene biphasic system, which allowed easy product recovery from the catalyst by decantation. However, attempts to recycle the ionic catalyst phase resulted in significant catalyst deactivation, after only the third recycle. 

No studies were located regarding musculoskeletal effects in humans or animals after inhalation exposure to zinc or zinc compounds. The systemic effects observed after inhalation exposure are discussed below. In most cases, the effects of zinc are discussed without separating effects caused by the individual zinc compounds. However, the respiratory effects of the individual zinc compounds are discussed separately because the nature of the respiratory toxicity differs depending on the particular compound to which one is exposed. The highest NOAEL values and all LOAEL values from each reliable study for systemic effects in each species and duration category are recorded in Table 2-1 and plotted in Figure 2-1. 

The LCTso of zinc chloride was reported as 11,800 mg-min/m (Schenker et al. 1981), but the basis for this value was not provided. Exposure to 119.3-121.7 mg zinc/m as zinc chloride smoke for 3-20 weeks decreased the survival of guinea pigs and mice (Marrs et al. 1988). Death was reported in ferrets orally exposed to 390 mg zinc/kg/day as zinc oxide (Straube et al. 1980) and mice exposed to 1,110 mg zinc/kg/day as zinc sulfate (Malta et al. 1981) following acute and intermediate oral exposures, respectively. Adverse systemic effects were observed in these animals, but the specific cause of death could not be determined. Acute oral LDso values in rats depend on the specific zinc compound and rnge from 237 mg zinc/kg as zinc acetate to 623 mg zinc/kg as zinc sulfate. In mice, the range of LDso values is 86 mg zinc/kg as zinc acetate to 605 mg zinc/kg as zinc chloride (Domingo et al. 1988a). Death from exposure to environmental levels of zinc is improbable. 

Systemic effects of acute inhalation exposure to generally unspecified levels of various zinc compounds in humans have been reported in several clinical case studies (Blanc et al. 1991 Brown 1988 Hjortso et al. 1988 Matarese and Matthews 1966 Vogelmeier et al. 1987). Case studies and experimental studies of systemic effects in humans following acute, intermediate, and chronic oral exposures are available (Anonymous 1983 Black et al. 1988 Brandao-Neto et al. 1990a Chandra 1984 Chobanian 1981 Hale et al. 1988 Hallbook and Lanner 1972 Hoffman et al. 1988 Hooper et al. 1980 Malo et al. 1990 Moore 1978 Patterson et al. 1985 Porter et al. 1977 Potter 1981 ... 

Immunotoxicity. Metal fume fever is believed to be an immune response to zinc oxide. A correlation between the concentration of airborne zinc and the number of all types of T cells (helper, inducer, suppressor, and killer) in the bronchoalveolar lavage fluid of humans, possibly related to the onset of metal fume fever, was observed in an acute-duration inhalation study (Blanc et al. 1991). Impaired immune response in humans has been reported in an intermediate- duration oral study (Chandra 1984). No immune effects were observed in mice after oral exposure to zinc (Schiffer et al. 1991). There is some limited information to suggest that the immune system is a target of zinc toxicity. A battery of immune function tests after inhalation, oral, and dermal exposure to zinc compounds would be useful in determining if zinc is immunotoxic. 

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