Macrocyclic chelate

The Friedlander reaction makes available a wide variety of 1,10-phenanthrolines and other macrocyclic chelators (e.g. 33, 34 and 35). These polyaza-aromatic rings can bind a variety of metals or organic substrates. 

Thus, in the presence of macrocycles, trialkylaluminum and even diorganozinc compounds have been used as alkide and halide abstractors to generate macrocycle-chelated organozinc cations (Scheme 45).108,109... 

In conclusion, Gdm complexes currently used as MRI contrast agents can be considered as safe drugs, due to their high thermodynamic stability, kinetic inertness as well as to an efficient excretion from the body. Nevertheless, in case of renal impairment, the stability issues become much more important and macrocyclic chelates, which have considerably higher kinetic inertness, should be used instead of linear complexes. We should... 

Figure 7.24 Macrocyclic chelates with multiple Gd(III) ions and large relaxivities. (Adapted with permission from Chart 17 of Caravan, P. Ellison, J. J. McMurry, T. J. Lauffer, R. B. Chem. Rev., 1999, 99(9), 2293-2352. Copyright 1999, American Chemical Society.)...

Cdbbiness and Margerum (35) suggest the term "macrocydic effect to describe the enhanced stability of a Mn+-macrocyclic chelate complex over that of the corresponding M +-non-macrocyclic chelate complex. Their data showing enhanced stability by a macrocydic complex are given in Table 10. 

Zucchi, G. Ferrand, A.-C. Scopelliti, R. Btinzli, J.-C. G. Highly luminescent, visible-emitting lanthanide macrocyclic chelates stable in water and derived from the cyclen framework. Inorg. Chem. 2002, 41, 2459-2465. 

Current interest in c lath rate structures focuses on molecular recognition, a broad topic that includes resolution of enantiomers (Chapter 12). macrocyclic chelates ... 

The most important reaction of this type is the formation of imine bonds and Schiff bases. For example, salicylaldehyde and a variety of primary amines undergo reaction to yield the related imines, which can be used as ligands in the formation of metal complexes. However, it is often more desirable to prepare such metal complexes directly by reaction of the amine and the aldehyde in the presence of the metal ion, rather than preform the imine.113 As shown in Scheme 31, imine formation is a reversible process and isolation of the metal complex results from its stability, which in turn controls the equilibrium. It is possible, and quite likely, that prior coordination of the salicylaldehyde to the metal ion results in activation of the carbonyl carbon to amine nucleophilic attack. But it would be impossible for a precoordinated amine to act as a nucleophile and consequently no kinetic template effect could be involved. Numerous macrocyclic chelate systems have been prepared by means of imine bond formation (see Section 61.1.2.1). In mechanistic terms, the whole multistep process could occur without any geometrical influence on the part of the metal ion, which could merely act to stabilize the macrocycle in complex formation. On the other hand,... 

Ligands - [COORDINATIONCOMPOUNDS] (Vol7) -macrocyclic [CHELATING AGENTS] (Vol 5)... 

Figure 2.22. Strategies for the transition metal-templated synthesis of catenanes. The metal (in) predisposes two fragments as open chelates (A) (strategy I) or as a macrocyclic chelate (E) and an open chelate (strategy II) in intermediates (B) and (F), respectively. Cyclization of these intermediate complexes with the chain fragments (C) provides the [2]-catenate complex (D).

Figure 2.22. The equilibria shown here involve a mixture of macrocyclic chelate (E), open chelate (A), and metal cation (black disk), on the one hand, and different complexed species, on the other hand The threaded complex (F) or a mixture of homoleptic complex (B), metal-complexed macrocycle (G), and free-macrocycle (E).

Figure 2.24. Schematic representation of the principle of transition-metal-templated synthesis of [2]-rotaxanes from macrocyclic chelate (A), metal cation (black disk) and open chelate (B). The latter bears functions X at its extremities, which will be used for anchoring or constructing the stoppers (represented as diamonds). (/) Threading step (//) stoppering step (in) removal of the metal template.

While acychc polyaminocarboxylate (DTPA, ethylenedi-aminetetraacetic acid (EDTA)) complexes of copper(n) have high thermodynamic stabihty, these complexes are kinetically labile to ligand exchange. Cu(ll) has been found to have much greater kinetic stability (and consequently greater serum stability) with macrocyclic chelates, such as TETA and DOTA,... 

Current interest in c lath rate structures focuses on molecular recognition, a broad topic that includes resohition of enantiomers (Chapter 12). macrocyclic chelates (Chapter 2), and key-and-iock enzyme activity (Chapter 19). In terms of clathrates, the challenge is to structure die vacancy in such a way that particular molecules will be incorporated as guests. ... 

The great stability of these ring systems was known, and possible biological implications of compounds having similar structures were postulated. As a result extensive research in macrocyclic chelating agents developed (13). 

PRRT) is "Y-DC)TA"- l yr -()ctrc()tide. Its suitable radionuclidic decay characteristics, availability in a no-carrier added (NCA) form and high affinity for complexation with macrocyclic chelators such as DOTA are important attributes that support the choice of as the radioisotope. Recently, Lu (half-hfe 6.7 d 0.497 MeV low energy, low abundance gamma... 

The current study was undertaken to develop laboratory techniques and protocols for the preparation and evaluation of therapeutic radiopharmaceuticals and the selection of targeted radiotherapeutic compounds with potential use in cancer treatment. For the study, DOTA-[Tyr ]-octreotate (DOTATATE), a somatostatin cyclic peptide hormone analogue (TATE coupled) with a macrocyclic chelator (DOTA), was used because it has been... 

DOTATATE, the somatostatin (cyclic peptide hormone) analogue TATE coupled with the macrocyclic chelator DOTA, is currently being studied for use for internal peptide receptor radionuclide therapy (PRRT). Two radionuclides, carrier-free and Lu obtained from enriched 1. ii. were used for labelling the peptide. 

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