Kinetic lanthanide complexes

Assays based on luminescent lanthanide ions were developed initially in the 1970s, when instrumentation became available which could distinguish long-lived luminescence from a shortlived background. Leif and co-workers reported the first attempts to use lanthanide complexes (in this case europium complexes with 1,10-phenanthroline and 7-diketonates, i.e., [Eu(phen)(diketo-nate)3]) as tags for antibodies.107 These proved kinetically unstable in the pH regime required... 

In this reaction, a rhodium atom complexed to a chiral diphosphine ligand ( P—P ) catalyzes the hydrogenation of a prochiral enamide, with essentially complete enan-tioselectivity and limiting kinetic rates exceeding hundreds of catalyst turnovers per second. While precious metals such as Ru, Rh, and Ir are notably effective for catalysis of hydrogenation reactions, many other transition-metal and lanthanide complexes exhibit similar potency. 

For the application of lanthanide complexes in medical diagnosis and therapy, a general requirement is that the ion Ln3+ and the ligand should remain associated while the complex is in the body, i. e. their dissociation should be minimal, since the free ligand and Ln3+ are toxic. For the dissociation to be negligible, the complexes must be kinetically inert under physiological conditions. Since the complexation properties of the lanthanide ions and Y3+ are quite similar, it is of interest to compare the results obtained as concerns the kinetic behavior of Gd3+ complexes with those known for the complexes of other lanthanides and Y3+. 

The use of aqueous chiral lanthanide complexes in the determination of the enantiomeric purity of chiral a-hydroxy acids has also been assessed by H NMR [21], Large lanthanide induced shifts, chemical shift non-equivalence and an apparent absence of kinetic resolution in complex formation is observed upon addition of racemic lactate to [Yb.3a]3+ (Figure 1). The lactate CH3 resonances are clearly resolved for the... 

By redesigning the above acyclic podand-type ligand 3 into a cyclic cryptate, the issue of stability can be resolved resulting in kinetically stable complexes (Scheme 4) [102]. The Tb(III) and Eu(III) complexes of cryptate 5 show an increase in lanthanide emission lifetimes of 0.72 ms and 0.41 ms, respectively, upon excitation at 310 nm. Similar results are found with the phenanthroline analogue 6 with Eu(III). A large number of modifications of these cryptates have been reported, all showing enhancements in the lanthanide ion emission [103-106]. 

K.L. Nash and J.C. Sullivan, Kinetics of complexation and redox reactions of the lanthanides in aqueous solutions 347... 

Lanthanide aryloxides have proved to be excellent precursors to homoleptic lanthanide alkyls (B, Eq. 13) [140], The reaction can be conducted in non-polar solvents because of the good solubility of the starting compounds. The formation of insoluble alkali metal aryloxides is the driving force (kinetic control). Complexes derived from aliphatic alcohols [141] and acetylacetonates [131] are... 

The most thermodynamically stable and kinetically inert complexes of the trivalent lanthanides are those of the ligand DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate) (42, 43). Our search for lanthanide macrocyclic complexes that would remain intact for longer time periods led us to examine derivatives of DOTA. There are two potential difficulties with the use of DOTA complexes of the trivalent lanthanides for RNA cleavage. First, the overall negative charge on the complex is not conducive to anion binding for example, Gd(DOTA)-does not bind hydroxide well (44). Second, DOTA complexes of the middle lanthanides Eu(III) and Gd(III) have only one available coordination site for catalysis. The previous lanthanide complexes that we used, e.g., Eu(L1)3+, were good catalysts and had at least two available coordination sites. 

The dissociation kinetics of lanthanide complexes with the macrocycle, 1,7-diaza-4,10,13-trioxacyclopentadecane-A, A -diacetic acid (K21DA) were studied in acetic acid-acetate buffer with Cu2+ as the scavenger of the ligand [73]. The dissociation rates were... 

Kinetics of formation and dissociation of lanthanide complexes [La(III) = Pr, Eu, Tb, Ho, and Yb] with l-phenyl-3-methyl-4-benzoyl-5-pyrazolone (HPMBP) in toluene-water phase were studied by monitoring the fate of La3+— arsenazo III (AZ) complex (MAZ) in the aqueous phase with the hydrophilic separator. The structures of the ligands and AZ are given below ... 

The structural characteristics of cyclen and cyclam and their carboxylic and amidic derivatives in variously protonated states as well as their metal complexes were excellently reviewed by Guilard and co-workers <1998CCR1313>. As those derivatives are frequently used in the complexation of transition metal or lanthanide ions, the space arrangement, exact protonation sites, and presence of intramolecular hydrogen bonds are of interest from the point of view of kinetics of complex formation/dissociation. Since the number of related structures is very high, but no new remarkable information appeared since Guilard s review, derivatives of these macrocycles are not discussed in detail. 

Poole, R.A., Bobba, G, Cann, M.J., et al. (2005) Synthesis and characterisation of highly emissive and kinetically stable lanthanide complexes suitable for usage in cellulo . Organic and Biomolecular Chemistry, 3, 1013-1024. 

The lanthanide complexes lack distinct ultraviolet-visible spectra and, hence, kinetic information on their complex formation and dissociation reactions was obtained indirectly by the metallochromic indicator method [9]. These studies indicate that in the case of the Cyanex 272 complexes, the CPC efficiencies are mainly limited by the slow dissociation of the M(HL2)HL+ complex at the heptane-H20 interface. 

Edta-related lanthanide complexes are of course coordinatively unsaturated in the absence of other ligands. In water, they are hydrated and the water of hydration may be displaced by other species. The kinetics of such a process, the reaction of europium 1,2-diaminocyclohexane-tetraacetate, [Eu(dcta)aq] with iminodiacetate ion, ida , to give [Eu(dcta)(ida)] ", have been studied by the elegant method of selective tunable laser excitation of the transition in... 

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