Cobalt complexes agents

In the absence of complexing agents and in acidic solution the cobalt(II) hexaaquo ion [15276-47-8] oxidizes with difficulty. 

Indeed the cobalt(III) ion is sufficientiy unstable in water to result in release of oxygen and formation of cobalt(II) ion. Under alkaline conditions the oxidation is much more facile and in the presence of complexing agents, eg, ammonia or cyanide, the oxidation may occur with ease or even spontaneously. 

Enikolopyan et al.til found that certain Co11 porphyrin complexes (eg. 87) function as catalytic chain transfer agents. Later work has established that various square planar cobalt complexes (e.g. the cobaloximes 88-92) are effective transfer agents.Ij2 m The scope and utility of the process has been reviewed several times,1 lt>JM ns most recently by Hcuts et al,137 Gridnev,1 3X and Gridnev and Ittel."0 The latter two references1provide a historical perspective of the development of the technique. 

Wu JH, Winn PJ, Ferenczy GG, Reynolds CA (1999) Solute polarization and the design of cobalt complexes as redox-active therapeutic agents. Int J Quant Chem 73(2) 229-236... 

Perez-Pina et al. [805] studied the use of triethanolamine and dimethyl-glyoxime complexing agents in absorptive cathodic stripping voltammetry of cobalt and nickel in seawater. Nickel and cobalt could be determined at levels down to 2 nM and 50 pM, respectively. 

In these procedures 1 litre of seawater was shaken with 60 mg charcoal for 15 min. Complexing agents were added in amounts of 1 mg, dissolved in 1 ml of acetone. The pH was 5.5, or it was adjusted to 8.5 by addition of 0.1 M ammonia. The charcoal was filtered off and irradiated. Results of three sets of experiments with charcoal alone, charcoal in the presence of dithizone, and charcoal in the presence of sodium diethyldithiocarbamate are compared. The following elements are adsorbed to an extent from 75 to 100% silver, gold, cerium, cadmium, cobalt, chromium, europium, iron, mercury, lanthanum, scandium, uranium, and zinc. The amount of sodium is reduced to about 10 6, bromine to about 10 5, and calcium to about 10 2. 

Effect of Complexing Agents on Potentials for the Cobalt(II)-Cobalt(0)... 

Cobalt(III) is a potent oxidant in an aqueous solution and, in the absence of a complexing agent that can stabilize cobalt(III), it is rapidly reduced to cobalt(II) with the concomitant oxidation of water to dioxygen ... 

In zinc metalloenzymes. zinc is a selective stoichiometric constituent and is essential for catalytic activity. It is frequently present in numerical correspondence with the number of active enzymatic sites, coenzyme binding sites, or enzyme subunits Removal of zinc results in loss of activity. Inhibition by metal complexing agents is a characteristic feature of zinc metalloenzymes. However, no direct relationship holds between the inhibitory effectiveness of these agents and their affinity for ionic zinc. Although zinc is the only constituent of zinc metalloenzymes in vivo, it can be replaced by other metals m vitro, such as cobalt, nickel, iron, manganese, cadmium, mercury, and lead, as m the case of carboxy-peprida.ses. 

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