Cryptate applications

Dietrich, Lehn and Sauvage recognized not only the possibility of enclosing a cation completely in a lipophilic shell, but they also recognized the potential for using such systems for activating associated anions. This is made particularly clear in a paper which appeared some years later One of the original motivations for our work on cryptates rested on their potential use for salt solubilization, anion activation and phase transfer catalysis . This particular application is discussed below in Sect. 8.3. 

Cryptands, 42 122-124, 46 175 nomenclature, 27 2-3 topological requirements, 27 3-4 Cryptate, see also Macrobicyclic cryptate 12.2.2], 27 7-10 applications of, 27 19-22 cylindrical dinuclear, 27 18-19 kinetics of formation in water, 27 14, 15 nomenclature, 27 2-3 spherical, 27 18 stability constants, 27 16, 17 Crystal faces, effect, ionic crystals, in water, 39 416... 

Sodium or potassium ions can also participate in the phase-transfer process when they are converted to lipophilic cations by complexation or by strong specific solvation. A variety of neutral organic compounds are able to form reasonably stable complexes with K+ or Na + and can act as catalysts in typical phase-transfer processes. Such compounds include monocyclic polyethers, or crown ethers (1), and bicyclic aminopolyethers (cryptates) (2). They can solubilize inorganic salts in nonpolar solvents and are particularly recommended for reactions of naked anions. Applications of these compounds have been studied.12,21-31... 

Chemical applications. The formation of AC and AEC crown ether complexes and cryptates promotes the solubilization of salts in organic media and has three major effects, decreased cation/anion interaction, cation protection and anion activation. These are usually more pronounced for the cryptates and have numerous uses in pure and applied chemistry. 

Mathis, G., 1998. Biological applications of rare earth cryptates. In Saez Puche, R., Caro, P. (Eds.), Rare Earths. Editorial Complutense, Madrid, pp. 285-297. Matsumoto, K., Yuan, J.G., 2003. Lanthanide chelates as fluorescent labels for diagnostics and biotechnology. In Sigel, A., Sigel, H. (Eds.), Metal Ions in Biological Systems, vol. 40. Marcel Dekker, New York, pp. 191-232 (chapter 6). 

Extensive progress has been attained in determination techniques. Noteworthy is the broad applicability of a homogenic method known as the TRACE method (time-resolved amplified cryptate emission). Another interesting solution, TSA (tyramide signal amplification), employs a technique which amplifies the tyramide signal (Bednarski and Reps, 2003). 

G. Mathis, Biological applications of rare earth cryptates, in Rare Earths, eds R. Saez Puche, P. Caro, pp. 285-315, Editorial Complutense, Madrid, 1998. 

The control of the Eu redox stability is certainly a key issue for an eventual MRI contrast agent application. With the exception of cryptate complexes of Eu such as Eu (2.2.2) + and Eu (2.2.1) +, the complexation with poly(amino carboxylates) diminishes the redox stability of the Eu state, as compared to the aqua ion (some representative redox potentials are -0.63 V (Eu(H20) ) -0.21 V (Eu(2.2.2)2+) -0.82 V (EuODDA) -1.00 V (EuTETA -) -1.18 V (EuDO-TA ) -1.35 V (EuDTPA )) [111, 112]. Macrocyclic ligands that match in size with the larger Eu ion have a stabilizing effect of the reduced state, whereas carboxylate coordinating groups seem to be unfavorable in this respect. 

Cryptate complexes with macrobicychc hgands containing three bipy units, in which the Ln + ion is contained within a hgand cavity, have been synthesized. Such hgands will complex Ln + ions, such as Eu + and Sm +, under conditions where Ln + ions are not. An application has been using lanthanide cryptates of the early lanthanides (La, Ce, Eu) as catalysts in the hydrolysis of phosphate monoesters, diesters, and triesters. Schiff base complexes can be synthesized by the reaction of a lanthanide salt with a diamine and a suitable carbonyl derivative such as 2,6-diacetylpyridine. 

Reviews. Gokel and Weber have reviewed the principles involved in phase-transfer catalysis and the applications to synthesis (128 references). The review includes crown ethers and cryptates as well as quaternary ammonium and phos-phonium salts. 

A recent example of this consideration is the success of [Eu C bpy.bpy.bpy] cryptate in luminescence immunoassay (104). This cryptate is used as a label to an antibody that is coupled in a specific way to a biomolecule, the presence of which has to be proved. TTie structure of the molecule is shown in Fig. 47. Excitation is into the bpy molecule, which shows a very high absorption strength in the ultraviolet part of the spectrum (cmax 10 M cm ). From the bpy triplet state the energy is transferred to the Eu ion, which finally emits (104,107). Although the quantum efficiency is only 1% (104), the high bpy absorption strength makes application feasible. 

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