Uses for Chelates

Table 5.17. Miscellaneous supported chelators used for pre-concentrations in seawater... 

Figure 2 Chemistry of the polymeric chelates used for loading liposomes and micelles with multiple reporter metal atoms, (a) Synthesis of a single terminus-PDP-activated chelating polymer (DTPA-polylysine) starting from CBZ-protected polylysine and SPDR...

Fig. 14. Structures of some common chelators useful for GFR measurement EDTA, ethylene-diaminetetraacetic acid DTPA, diethylenetriaminepentaacetic acid DOTA, cyclododecane-1,4,7,10-tetraazaacetic acid...

Investigations have shown that iron may contribute to endothelial cell function and increase the risk of cardiovascular disease. It is believed that strong metal chelators such as deferoxamine (DFO) can counteract iron cation formation. The primary targets of iron chelators used for treating iron overload are prevention of iron ingress into tissues and its intracellular scavenging. 

Table 13.1 Metal chelates used for different toxic metals in GC-MS ...

Figure 6.2 Some common metal chelates used for solvent extraction. Note that in all cases, the hydrogen ion of the parent chelating agent has been replaced by a metal.

The structures of fluorescent lanthanide chelates used for separation and homogeneous time resolved fluorometric assays. 

Deferasirox is an iron chelator used for the treatment of myelodysplastic syndromes, including thalassaemia. It was the first orally bioavailable drug in its class in the United States, although in Europe, deferiprone was approved first. Deferasirox chelates iron, forming a dimer that is then excreted in the faeces. Chelated iron is less able to induce oxidative stress through the formation of reactive oxygen species. It is also reported to be a potent inhibitor of NF-kB in vivo and in acute myeloid leukaemia and myelodysplastic syndrome cell lines [11 ]. 

Usually, iodides and bromides are used for the carbonylation, and chlorides are inert. I lowever, oxidative addition of aryl chlorides can be facilitated by use of bidcntatc phosphine, which forms a six-membered chelate structure and increa.scs (he electron density of Pd. For example, benzoate is prepared by the carbonylation of chlorobenzene using bis(diisopropylphosphino)propane (dippp) (456) as a ligand at 150 [308]. The use of tricyclohexylphosphine for the carbonylation of neat aryl chlorides in aqueous KOH under biphasic conditions is also recommended[309,310]. 

The benzoic acid derivative 457 is formed by the carbonylation of iodoben-zene in aqueous DMF (1 1) without using a phosphine ligand at room temperature and 1 atm[311]. As optimum conditions for the technical synthesis of the anthranilic acid derivative 458, it has been found that A-acetyl protection, which has a chelating effect, is important[312]. Phase-transfer catalysis is combined with the Pd-catalyzed carbonylation of halides[3l3]. Carbonylation of 1,1-dibromoalkenes in the presence of a phase-transfer catalyst gives the gem-inal dicarboxylic acid 459. Use of a polar solvent is important[314]. Interestingly, addition of trimethylsilyl chloride (2 equiv.) increased yield of the lactone 460 remarkabiy[3l5]. Formate esters as a CO source and NaOR are used for the carbonylation of aryl iodides under a nitrogen atmosphere without using CO[316]. Chlorobenzene coordinated by Cr(CO)j is carbonylated with ethyl formate[3l7]. 

Recent patent activity suggests that DuPont is developing a new generation of chelating diphosphite—nickel catalysts for this technology which are significantly more active than the monodentate phosphite based catalyst system used for the last two decades (61—64). 

The bonding properties of (Ti02) have been used for size-reinforcing of glass fibers so that they adhere to asphalt or to a PTEE—polysulfide mixture to impart enhanced flex endurance (434—436). Poly(vinyl alcohol) (PVA) solutions mixed with sucrose can be cross-linked with the lactic acid chelate and used generally for glass-fiber sizing (437). 

Experimentally deterrnined equiUbrium constants are usually calculated from concentrations rather than from the activities of the species involved. Thermodynamic constants, based on ion activities, require activity coefficients. Because of the inadequacy of present theory for either calculating or determining activity coefficients for the compHcated ionic stmctures involved, the relatively few known thermodynamic constants have usually been obtained by extrapolation of results to infinite dilution. The constants based on concentration have usually been deterrnined in dilute solution in the presence of excess inert ions to maintain constant ionic strength. Thus concentration constants are accurate only under conditions reasonably close to those used for their deterrnination. Beyond these conditions, concentration constants may be useful in estimating probable effects and relative behaviors, and chelation process designers need to make allowances for these differences in conditions. 

A clear solution of aluminum citrate neutralized to pH 7 is used for in situ gelling of polymers in polymer flooding and well stimulation in enhanced oil recovery techniques (128—132). The citrate chelate maintains aluminum ion solubiUty and controls the rate of release of the aluminum cross-linker. 

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