Ligand-exchange kinetics

The ligand exchange kinetics between free and coordinated ligands were studied more thoroughly for the ligands trimethylphosphite and triphenylphosphine. The kinetics were analyzed using conventional NMR line shape technique 140). 

Ultimately, for Pt(IV) anticancer drugs, a combination of incorporation of bioactive ligands that specifically target cancer cells, control over ligand-exchange kinetics, and selective activation by light would allow for temporal and spatial control of drug delivery and activation. 

If the metals bound in complexes exchange with biological ligands, the dissociation kinetics of these complexes, the ligand-exchange kinetics and the association kinetics with the biological ligands must be considered. Simple dissociation kinetics of complexes are related to their thermodynamic stability constants by the relationship ... 

A kinetic cis effect has been investigated by Eaton and Eaton (131 — see Table 16). The ligand exchange kinetics of reaction (9) involving various carbonylrutheni-um(II)porphyrin species [36a-36h] were derived from a H-NMRline shape analysis at various temperatures for the t-butyl protons of coordinated and uncoordinated 4-t-butylpyridine. 

A comparison with cross-linker 4a proves the underlying dynamics are controlled by metal-ligand dissociation. Ligand exchange kinetics for 4a are substantially faster than for 4b but the association thermodynamics are very similar, and the effect of those kinetics is dramatic. At 5% cross-linker, the dynamic viscosity of lOOmgmL 4a-PVP is only 6.7 Pa s, a factor of 80 less than that of the isostmctural network 4b PVP. Although the association constants are not identical, the effect of the thermodynamics would be to increase the viscosity of 4a PVP relative to 4b PVP, the opposite direction of that observed. The kinetics dominate even the extent of cross-linking 5% 4a PVP is less viscous by a factor of 5 than is 2% 4b PVP. 

The more selective kind of ion exchange, the chelating ion exchange [22], suffers often from kinetic limitations, which limit the application range to cationic compounds with fast ligand exchange kinetic for the inner coordination sphere. Ion exchange is well suitable for preconcentration as well as for separation of chemically similar compounds. 

Techniques for demonstrating channeling behavior include enzyme buffering, ligand exchange kinetics, isotope dilution, and estimation of the transition time. One of the most... 

Both dipolar and contact contributions are important in glycinate complexes. (166) U(iv) complexes with a-alanine, (167) various amino-acids, (168) ethyl trifluoroacetoacetate, (169) tetrakis-(tetra-ethylammonium)octathiocyanatouranate U(NCS)g(NEt4)4, (170) and -diketones (171, 172) have been examined. In studying the ligand exchange kinetics of the latter complexes (172) the mechanism is considered to involve a ninth coordination site in the U(iv) chelate. 

The author thanks Dr. Wesley R. Harris for helpful discussions on A1 ligand exchange kinetics, and Maggie Johnson for extensive, helpful literature searches. 

Garrison JM and Crumbliss AL (1987) Hydrox-amic acid ligand-exchange kinetics at hexa-aquoaluminum ion. Inorg Chem 26 3660-3664. 

Survival of metal complex architectures during sol-gel immobilization requires either (1) that there are no thermodynamically favorable interactions between the metal centers and any components of the sol-gel medium that will disrupt the desired coordination structure, or (2) that the ligand exchange kinetics at the metal centers are sufficiently slow that the stmcture will not... 

Solvent and ligand exchange kinetics 348 3.10. Oxidation of peroxocompounds ... 

Iron uptake rates for most phytoplankton species appear to be limited by the rate of cross-membrane transport, itself a function of ligand exchange kinetics and the amount of space available on the outer cell membrane for transporter proteins... 

Frankel has given a preliminary account of studies, involving nickel(ii) and cobalt(ii) in mixed solvents, which might prove to have far-reaching mechanistic consequences. He found that the ligand exchange kinetics for (where L is DMSO) in pure DMSO, DMSO-nitro-... 

From other experiments in which the effects of mass transfer have been analyzed, it appears that the following systems are mass transfer limited uranyl nitrate extraction by TBP." copi extraction by sodium-loaded DEHPA, and extraction of zinc and copperfU) chlorides by TIOA. Zinc extractioa by dithizone in carbon tetrachloride is mass transfer limited at high zinc concentrations but kinetically comrolled at low zinc levels. Ferric ion extractions are reputed to be slow because of its sluggish ligand-exchange kinetics. Extraction of ferric chloride by TIOA, for example, is controlled by a slow heterogeneous reaction. ... 

Lead.— Exchange reactions involving polyamine-A-polyacetate complexes of lead(ii) continue to be studied. An investigation of the substitution of lead(ii) by cobalt(n) has been reported, and there has been a re-interpretation of earlier data on ligand-exchange kinetics between [Pb (edta)] and R-(—)-pdta. Rates... 

---