Iron chelators polymeric

Use Pigments, reagent, etching aluminum, disinfectant, textiles (dyeing and calico printing), flocculant in water and sewage purification, soil conditioner, polymerization catalyst, metal pickling, chelated iron products, intermediate. 

In cold polymerization, the most widely used initiator system is the redox reaction between chelated iron and organic peroxide using sodium formaldehyde sulfoxide (SFS) as a reducing agent [see Eqs. (1) and 2]. In hot polymerization, potassium persulfate is used as an initiator. 

This is the second most important type of phosphate anticorrosive pigment. Passivation is normally accomplished through the ability of triphosphate ions to chelate iron ions. Additional passivation is through phosphate ions produced by de-polymerization of triphosphate ions. These pigments are also modified with silicates to control their solubility. 

Interestingly, 5-allyl-2-methoxyphenol is not polymerized during friction, but undergoes transformation into 2-methoxyphenol-5-(methylcarboxylate) under the action of triboemission (Molenda et al. 2003). Seemingly, the carboxylate then forms chelate compounds with the steel surface iron. 

Hydrol5dic polymerization in the ferric citrate system can be prevented if sufficient excess citrate is present in solution 66). Approximately 20 millimolar excess citrate is sufficient to supress pol3mier-ization of 1 millimolar iron, as indicated by dialysis and spectrophotomet-ric measurements. From pH titration in high citrate solutions, it was concluded 66) that a dicitrate complex of iron is formed at high pH. Presumably formation of the dicitrate chelate is competitive with hydrolytic polymerization. The fraction of polymer formed in ferric citrate solutions was found to decrease smoothly as the citrate content was increased up to 20 millimolar. The nuclear relaxation rate of the water protons in ferric citrate solutions increases with the citrate concentration. 

The reaction of hexacyanometalates with metal complexes chelated by penta-dentate ligands may afford polynuclear complexes. The presence of the penta-dentate ligand precludes the polymerization that leads to extended systems. The preparation of a representative heptanuclear, mixed-valance iron complex, [Fe (CNFe° (salmeten))6]Cl2 6H20, is detailed herein. 

The very great stability of the iron (II) — N=C—C=N— chelate ring provides the driving force for the reaction. This is further illustrated by the formation of monomeric Schiff bases between Qj-diketones and methylamine (Equation 21), for in the absence of the metal ion (Fe+2, Co+2, Ni+2) polymeric condensation products are formed (30, 49). 

In cases where metals or metal ions can contaminate the products, reaction vessels fabricated from inert polymeric materials restrict that possibility. A significant example involved the reaction of maltol with aqueous methylamine to give l,2-dimethyl-3-hydroxypyrid-4-one. The product is a metal chelator employed for the oral treatment of iron overload. Consequently, it is an excellent metal scavenger but must be produced under stringent conditions that preclude metal complexation. Literature conditions involved heating maltol in aqueous methylamine at reflux for 6 h, the product was obtained in 50% yield, but required decolourisation with charcoal135. With the CMR, the optimal reaction time was 1.3 min, and the effluent was immediately diluted with acetone and the near colourless product crystallised from this solvent in 65% yield (Scheme 9.18). A microwave-based batch-wise preparation of 3-hydroxy-2-methylpyrid-4-one from maltol and aqueous ammonia was also developed. 

The obvious method of choice is to model novel structures on natural hydroxamate and catechol siderophores which possess extremely high affinities for iron(III) [35], Hydroxamates possess many advantages for iron(III) chelation, as was outlined in the section on bidentate ligands. However, they tend to possess a low oral activity. Nevertheless, a number have been investigated, including rhodotorulic acid [36], synthetic hexadentate [37] and polymeric hydroxamates [38]. None has proved superior to DFO (Structure 2, Scheme IB). 

The function of the chelator is to complex the ferrous ion and thus limit the concentration of free iron. Redox systems appear very versatile, permitting polymerization at ambient temperatures and the possibility of control of the rate of radical initiation versus polymerization time. This would thus permit control of heal generation and the minimization of reaction time. The use of the redox system ammonium persulfate (2 mmol) together with sodium pyrosulfite (Na S Oj 2.5 mmol) together with copper sulfate (0.002 mmol) buffered with sodium bicarbonate in I liter of water form an effective redox system for vinyl acetate emulsion polymerization. The reaction was started at 25 C and run nonisothermally to 70 C. The time to almost complete conversion was 30 min (Warson, 1976 and Edelhauser, 1975). 

As the iron is released from food in the acidic environment of the stomach, ligands released in the digestion process combine with the iron to form chelates. These chelates should inhibit polymerization and precipitation of iron as the stomach contents are neutralized in the duodenum provided that localized regions of high pH caused by too rapid addition of concentrated base are avoided. This suggests that pH adjustment in an in vitro simulation is a critical step. 

Polymerized iron, even when soluble, is probably not readily available. Bates et al. (20), in studies designed to measure iron exchange rates between chelates and transferrin, showed that polymerized iron was transferred to transferrin... 

Design of Polymeric Iron Chelators for Treating Iron Overload in Cooley s Anemia... 

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