Polyaminopolycarboxylic acids

Table 4. Stability constants of transplutonium elements with polyaminopolycarboxylic acids...

Two other polyaminopolycarboxylic acids, i,2-6is-[2-di(carboxy-methyl)-aminoethoxy]-ethane (EGTA) and 2,2,- s-[di(carboxymethyl)-amino] - diethyl ether (EEDTA) also known as ethyleneglycol-6is(2-aminoethyl)ethertetraacetic acid and bis-(2-amino ethyl)ethertetraacetic acid respectively (see the structural formula below) have also been investigated. The stability constants (ju = 0.1 at 20° C) of both the EGTA and EEDTA complexes were measured [463] by polarographic... 

In recent years the organic chemistry of the polyaminopolycarboxylic acids has been studied extensively. In passing, it should be noted that the polyaminopolycarboxylic acids were mistakenly believed to be devoid of any organic chemistry. The chemistry of derivatization is discussed in Sect. 3.1.2. 

The general interests in chelation of metals have continued to lead to new forms of polyaminopolycarboxylic acids. Examination of the acid dissociation constant of ethyl-ene-bis-N,N -(2,6-dicarboxy)piperidine (9) showed that they were nearly identical with those of EDTA. However, the formation constants for metal chelates of (9) are lower by 0.5 to 3.7 log 3 units. 

Interest in the coupling of polyaminopolycarboxylic acids to macromolecules for use in nuclear medicine resulted in the synthesis of l-(p-aminophenyl)-ethylenediaminetet-raacetic acid (10, n = 0, R=NH2, pAPhEDTA). Since its first synthesis there have been improvements in its synthesis105 as well as the synthesis of related chelating agents (10, n = 2)106, (ll)107 and (12)108. In a search for a lipophilic chelator which could be incorporated into the lipid phase of liposomes, Bard et al.109 synthesized 3-cholesteryl 6-[N -iminobis(ethylenenitrilo)-tetraacetic acidjhexylether (13). 

Bisdioxopiperazines, Antitumour Agents Derived from Polyaminopolycarboxylic Acids... 

As fatty acids are taken up into the myocardium, Karesh et al.134) incorporated similar structures into polyaminopolycarboxylic acids, radiolabelled them with "mTc and 57Co and examined them for myocardial imaging. These chelators, which possessed chelating moieties similar to DTPA, had a low uptake into the heart (<0.94%) but showed an uptake into the liver of 16%. 

Rare Earth Complexes with Carboxylic Acids, Polyaminopolycarboxylic Acids, and Amino Acids ... 

This chapter will cover the synthetic, structural, and solution chemistry of rare earth complexes with carboxylic acids, polyaminopolycarboxylic acids, and amino acids, with an emphasis on their structural chemistry. As the carboxylate groups play the key roles in the metal-ligand coordination bonding in these complexes, we will start the chapter with the coordination chemistry of rare earth-carboxylic acid complexes, followed by rare earth-polyaminopolycarboxylic acid and rare earth-amino acid coordination chemistry. Owing to length limitations, an exhaustive citation of the large amount of research activities on the subjects is not possible. Instead, only selected examples are detailed to highlight the key features of this chemistry. 

Compared with their polyaminopolycarboxylic acid analogs, the solution chemistry of RE(III)-carboxylic acid complexes have received much less attention. However, from the data reported so far, we can already see some of the general aspects of the complexes in solution, the species formed, their stability, and the thermodynamic properties, as well as their evolution with the change of the central atoms. 

The synthesis is normally carried out by refluxing an aqueous mixture of polyaminopolycarboxylic acid and a selected rare earth oxide in a molar ratio of RE L = 1 1. The resulting solution can be neutralized to pH 5-6 by adding a dilute solution of NaOH, KOH, NH3 H2O, NaHCOs, or NaHC03. After filtration, the complex can be crystallized by evaporation or with the addition of EtOH. The rare earth oxide can be replaced by a rare earth carbonate or other soluble salts, such as chlorides, nitrates, perchlorates, or acetates [104], The synthesis can also be done under hydrothermal conditions [105], which leads to complexes of polymeric structure, while most of the complexes obtained under ambient conditions are monomeric (see Section 3.3.2 for examples). 

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