Transport Complexing Agents

In the examples given above to illustrate coupled transport, various oxime carriers for copper and other cations and tertiary amines as carriers for uranyl anions were used. However, a large number of complexing agents have been described in the literature some of them are listed in Table 9.1. 

Trade Name and Manufacturers Chemical Formula Complexed Ion References Supported Membranes Emulsion Membranes 

LIX 70 a mixture of LIX 63 Sbnd this oxime Henkel Corp. It P Cu2+ 64 

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Neutral carriers are organic complexing agents which are capable of sequestering and transporting ionic species in a hydrophobic organic phase. The antibiotics, valino-mycin and nonactin were the first neutral carriers to be incorporated in an ISE These macrocyclic neutral carriers contain a polar internal cavity and an outer hydro-phobic shell. The excellent selectivity exhibited by valinomycin for potassium ions is... 

Villamo, O., Barboiu, C., Barboiu, M., Yau-Chun-Wan, W. and Hovnanian, N. (2002) Hybrid organic-inorganic membranes containing a fixed thioether complexing agent for the facilitated transport of silver ions. Journal of Membrane Science, 204, 97-110. 

As yet there have been no reports that the actinides in the biosphere become complexed in a chemical form which would facilitate their transport through the food chain to man. All the available evidence indicates that solutions of the actinides hydrolyze to give polymeric forms which exhibit limited mobility in cellular systems. There are, however, many complexing agents in the biosphere which could form stable complexes with the actinides, such complexes could alter the transport of the actinides in microenvironments but these microenvironments have yet to be identified. 

It is significant that oat plants, which are known to contain the Fe3+ complexor, 2,4-dihydroxy-7-methoxy-l,4-benzoxazin-3-one (128), do not show any significant accumulation of plutonium, or the other actinides. It is possible that this complexing agent is located within plant cells which do not come into contact with the cation transporting mechanisms. Although there is evidence of the existence of microbial hy-droxamates in soil and that hydroxamates do become concentrated in plants (129), there has been no evidence presented yet that hydroxamates are the agents responsible for plutonium uptake into plants. On the other hand there is evidence that EDTA and DTPA can stimulate actinide concentration in plants (See Table 6). 

As a consequence of the conjecture that sewage could contain plutonium complexing agents which might make the element more available to vegetation Myers et al. (139) evaluated this potential transport mechanism and concluded that no such chemicals were present. 

Within the organism a variety of complexing agents are used to transport the iron. 

However, a large number of complexing agents of all kinds with chemistries designed for specific metal ions have been reported in the literature. The tertiary amine Alamine 336 is widely used to transport anions such as U02(S04)4- and CfiOj [44-46], The macrocyclic crown ether family has also been used to transport alkali and rare earth metals [47,48] ... 

Figure 11.13 The effect of replenishing a hollow fiber coupled transport module with fresh complexing agent. Membrane, polysulfone, hollow fiber/Kelex 100 feed, 0.2 % copper, pH 2.5 product, 2% copper, 100 g/L H2S04 [49]...

Water is almost exclusively the liquid phase which transports the dye in textile dyeing. For most dyeing processes demineralized water should be used if not available, complexing agents must be added, where necessary, to avoid negative interference of metal ions. 

Kent, D.B. et al., Transport of Zinc in the Presence of a Strong Complexing Agent in a Shallow Aquifer on Cape Cod, Massachusetts, U.S. Geological Survey Water-Resources Investigations, Rep. 91-4034, 1991, p. 78. 

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