Complexation agents, effect system

Fig. 15-11 Effects of strong complexation on metal ion toxicity, (a) Increasing concentration of NTA, a strong multi-dentate complexing agent, decreases the toxicity of Cd to grass shrimp. All systems have equal concentrations of total Cd. (b) When the results are replotted showing survival as a function of Cd concentration, the data for all concentrations of NTA collapse to a single curve. (Reprinted with permission from W. G. Sunda et al. (1978). Effect of chemical speciation on toxicity of cadmium to grass shrimp, Palaemonetes pugio importance of free cadmium ions. Environ. Sci. Technol. 12,409-413, American Chemical Society.)...

In practical systems, no solvent is as universally effective as sodium thiosulfate, Na2S203. Itis inexpensive, stable and produces few undesirable side effects such as stains, odors or toxicity. It rapidly forms stable, soluble complex ions with silver halide (for example [Ag(S203)2]3 ), which are rapidly diffusible. Several other silver complexing agents are proposed as being useful in diffusion transfer processes, however, and some of these are used either singly or in combination with other, more common solvents. Some are used with certain developers. 

A modified procedure illustrated by the synthesis of a diynediol (Expt 5.27) from the acetylenic alcohol, 2-methylbut-3-yn-2-ol, uses methanol and pyridine as the solvent, the latter acting also as a complexing agent for the copper(i) ions. An alternative effective coupling system involves the use of copper(n) acetate in pyridine which does not require the use of air or oxygen. 

Before leaving the matter of amines, we should examine some of the known simpler ones for their effects upon the circulation, especially as to cardiac action and duration of pressor response. The former is noteworthy, as its absence is a necessary prerequisite of the Hochdruckstoff. Presumably an extended vasospastic action should also be a prerequisite. Prolonged action can be produced in at least four ways (1) by some property inherent in the structure of the molecule of the pressor agent which prevents its rapid destruction in situ or in blood (2) by slow liberation of an effector substance from a larger, more complex molecule or system (3) by inhibition of the action of an enzyme system which inactivates some naturally occurring pressor agent and (4) by continuous production from parent sources. Clear-cut examples are not evident at present, although... 

In common with other sequential extraction procedures, the BCR scheme suffers from a degree of non-specificity (Whalley and Grant, 1994 Coetzee et d., 1995) and redistribution of analytes during extraction (Raksasataya et d., 1996). Some success in limiting lead redistribution by addition of cryptand 2.2.2 or nitriloacetic acid to the acetic acid in Step 1 has been reported, but the effectiveness of the complexing agent was found to be strongly dependent on the bulk composition of the model soil system studied (Raksasataya et d., 1997). 

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