Chelate-forming resins, complex

VII. COMPLEX FORMATION OF METAL IONS IN CHELATE-FORMING RESINS... 

Due to the limited solubility of NTA and EDTA in their acid forms it is somewhat difficult to carry out elutions on H+ form resins. Speeding et al. [112] suggested the use of a retaining ion, which formed stable, soluble complexes with the eluant, to impregnate the resin column. They proposed Fe3+, Cu2+ and Ni2+ as retaining ions of these Cu2+ has been most widely used [115—117, 119]. Wolf and Massonne [108] used Zn2+ for the elution with NTA because the Zn(NTA) complex is more soluble than the Cu(NTA) complex. Recently Fuger [120] proposed the use of the EDTA chelate of the same ion with which the ion exchange resin is pretreated as eluant. This has been very useful in the case of radioactive tracers. 

Poly(ethyleneimine) cross-linked (CPEI) with ethylenedichloride forms stable complexes with copper (II) as well as with cobalt (II). The RC1 type of cross-linked poly(ethyleneimine) having an anion-exchange capacity of 6.8 meq g 1 retains copper from CuS04 and cobalt from 1 M aq. CoCl2 solutions [55], PEI is by itself a weak basic anion-exchange resin and forms stable complexes with anions and cations. The process is probably accompanied with chelate ring formation ... 

The adsorption properties of Amberlite XAD4 resins as adsorbents suitable for multielement preconcentration of complexes of 15 elements with different chelate-forming reagents from aqueous solutions have been extensively investigated by Yang and Jackwerth [129,130]. Adsorbed trace compounds can easily be eluted from the resin by use of 1 M HNOj in acetone and subsequently determined by atomic absorption spectrophotometry (AAS). Besides multielement preconcentration, selective trace separation procedures are possible by suitable selection of the complexing reagents and pH adjustment of the sample solution. 

Several chelating or metal-complexing polymers were reported in Volume 1 of the series (p. 362). There is still considerable activity in this area and polystyrene remains one of the most widely-used supports. Selective chelate-forming ion-exchange resins were prepared from polystyrene by nitration followed by reduction, diazotization then coupling with aromatic amines and derivatives of phenol. Poly(styryl-l,8-naphthyridine) (7) also functions as a chelating agent with Cu ,... 

Chelated resin that can form a complex (see Fig. 4) and amphoteric ion exchange resins that have both positive and negative changes (see Fig. 5) are both similar to ion exchange resins. Other polymers possess reactivity characteristics as affinity substrates. 

Platinum-group metals (qv) form complexes with chelating polymers with various 8-mercaptoquinoline [491-33-8] derivatives (83) (see Chelating agents). Hydroxy-substituted quinolines have been incorporated in phenol—formaldehyde resins (84). Stannic chloride catalyzes the condensation of bis(chloromethyl)benzene with quinoline (85). 

Amphiphilic resin supported ruthenium(II) complexes similar to those displayed in structure 1 were employed as recyclable catalysts for dimethylformamide production from supercritical C02 itself [96]. Tertiary phosphines were attached to crosslinked polystyrene-poly(ethyleneglycol) graft copolymers (PS-PEG resin) with amino groups to form an immobilized chelating phosphine. In this case recycling was not particularly effective as catalytic activity declined with each subsequent cycle, probably due to oxidation of the phosphines and metal leaching. 

In 1970s, first application of metal-chelate affinity chromatography which is later named as "immobilized-metal (ion) affinity chromatography (IMAC) was perfomed. Metal-chelate chromatography technique exploits selective interactions and affinity between transition metal immobilized on a solid support (resin) via a metal chelator and amino acid residues which act as electron donors in the protein of interest [25-26]. As well as aromatic and heterocyclic compounds, proteins such as histidine, tyrosine, tyriptophane and phenylalanine posses affinity to transition metals which form complexes with compounds rich in electrons [25,27]. 

Based on preliminary results from Helfferich130, further developments by Davankov and co-workers5 131 133 turned the principle of chelation into a powerful chiral chromatographic method by the introduction of chiral-complex-forming synlhetie resins. The technique is based on the reversible chelate complex formation of the chiral selector and the selectand (analyte) molecules with transient metal cations. The technical term is chiral ligand exchange chromatography (CLEC) reliable and complete LC separation of enantiomers of free a-amino acids and other classes of chiral compounds was made as early as 1968 131. 

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