Chelate complexes, ternary

Dagnall and West8 have described the formation and extraction of a blue ternary complex, Ag(I)-l,10-phenanthroline-bromopyrogallol red (BPR), as the basis of a highly sensitive spectrophotometric procedure for the determination of traces of silver (Section 6.16). The reaction mechanism for the formation of the blue complex in aqueous solution was investigated by photometric and potentiometric methods and these studies led to the conclusion that the complex is an ion association system, (Ag(phen)2)2BPR2, i.e. involving a cationic chelate complex of a metal ion (Ag + ) associated with an anionic counter ion derived from the dyestuff (BPR). Ternary complexes have been reviewed by Babko.9... 

In vivo uptake of iron by transferrins usually involves its addition as a ferric-chelate complex, to prevent hydrolytic attack on the ferric ion (211). Complexes such as ferric citrate and ferric nitrilotriacetate are commonly used. Under these conditions, kinetic schemes for the uptake of iron by transferrins have identified five steps in the formation of the specific metal-anion-transferrin ternary complex (120). These may be summarized as follows. 

Chiral ligand-exchange chromatography is based on the formation of diastereomeric ternary complexes that involve a transition metal ion (M), usually copper II a single enantiomer of a chiral molecule (L), usually an amino acid and the eitantiomers of the racemic solute R and S). The diastereomeric mixed chelate complexes formed in this system are represented by the formulas L-M-R and L-M-S. When these complexes have different stabilities, the less stable complex is eluted first, and the enantiomeric solutes are separated. 

Ability of WSP to interact with enzymes, drugs, selective and chelating properties of many polyelectrolytes make them very perspective in the development of liquid membrane bioreactors. It is known [103] that formation of a ternary metal ion-carrier-chelator complex at the inner vesicle waU can enhance the overaU selectivity in accordance with a multiplicative, rather than additive, function of equihbrium metal-hgand binding constants. Enzyme-containing lipid vesicles (liposomes), which are hpid dispersions that contain water-soluble enzymes in the trapped aqueous space, may be named as hquid membrane micro- or nanobioreactors with intraped WSP. Preparation and properties of hpid vesicles are described in [104] review. 

Ormosil spin-coated thin films obtained from vinyltriethoxysilane and doped with y9-di-ketonates have been recently investigated by H. Wang and collaborators. Both hydrated chelates and ternary complexes with phen and tppo were doped at a concentration of 5 mol% (relative to Si) by a multi step sol-gel method. Out of the 12 compounds tested, psid(tta)3(tppo)2] yielded the best results but no quantitative luminescence data are given, preventing comparison with materials of known properties (Wang et al., 2005). 

The mechanism of picolinic acid (PA)-catalysed oxidation of formic acid by chro-mium(VI) involves the formation of a Cr(VI)-PA chelate complex in a pre-equilibrium step followed by attack at the Cr(VI) centre by the substrate, leading to a ternary complex within which electron transfer occurs giving a Cr(IV)-PA complex and CO2. The Cr(IV)-PA complex reacts faster with the substrate, ultimately giving rise to a Cr(III)-PA complex. The reaction is catalysed by anionic surfactants and inhibited by cationic surfactants. The oxidation of alcohols by modified oxochromium(VI)-amine reagents has been reviewed. ... 

Spec determination of the chelate complex after chloroform extraction (pH = 6) Spec A = 520 nm after indium extraction from the aqueous phase (pH 5.0 to 5.5) into chloroform with Af-/)-chlorophenyl-2-furohydroxamic acid and formation of the 4-(2-pyridylazo)resorcinol red chelate Spec determination of the binary complex Spec determination of the ternary complex... 

Spectrophotometric determination of the binary complex Spec determination of the violet complex in acidic medium Extraction-spectrophotometric determination of the system V(V)-3,5-dinitrocatechol (DNC)-brilliant green chelate complex Extraction with H-butanol and spec X = 390 nm of a ternary complex (vanadium oxine H-butanol = 1 2 2)... 

As mentioned previously, in many siderophore complexes, a decrease in pH will result in protonation and dissociation of a donor group. This decrease in effective denticity of the chelator will lead to a corresponding decrease in complex stability and the opening of available coordination sites for the formation of ternary complexes, and/or exchange with other chelators. However, in the case of catecholamide donor group siderophores, such... 

Fig. 26. Cartoon illustrating the exchange of Fe(III) between two hexadentate chelators through a ternary complex intermediate.

BLM transport systems for ferrioxamine B were also devised based on first coordination shell recognition via ternary complex formation utilizing vacant coordination sites on the Fe(III) center (Fig. 29) (199). The tetra-coordinated substrate complex selectively transported was partially dechelated diaqua-ferrioxamine B and coordinately unsaturated di-hydroxamato iron(III) complexes, which utilized a hydrophobic membrane bound bidentate chelator as a carrier for selective transport. Active transport for these systems was accomplished using a pH gradient (199). 

A route for designing Gd(HI) complexes whose relaxivity depends on the presence of lactate, is provided by the ability shown by some hexa- or hepta-coordinate chelates to form ternary complexes with a wide array of anionic species (154-161). The interaction between the coordinatively unsatured metal complex and lactate involves the displacement of two water molecules coordinated to Gd(III) ion with the two donor atoms of the substrate, thus leading to a marked decrease in the relaxivity. Lactate is a good ligand for Gd(IH) ion because it can form a stable 5-membered ring by using the hydroxo and carboxylic oxygen donor atoms (Fig. 19). 

Fig. 8. Mechanism proposed for the transfer of iron from low molecular weight chelates to apotransferrin involving the intermediate ternary complex of protein-iron-chelate. The polynuclear iron must be depolymerized prior to its binding by the protein. The presence of excess chelating agents, particularly citrate, leads to the formation of the bis complex which reacts rapidly...

In analogy to the carboxylate binding by zinc-containing cyclodextrin 10 (see Sect. 2), Lewis acidic centers such as a copper(II) histamine unit may also serve for the chelation of the (deprotonated) 2-aminoacetate substructure of a-amino acids [51], Rizzarelli, Marchelli et al. used a respective j8-cyclodextrin derivative for the formation of the ternary complexes 36 and 37 with racemic... 

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