Étude de la complexation des lanthanides trivalents par les six isomères de l'acide diaminocyclohexane-tétraacétique : Partie 3. Relation entre les Constantes d'Acidité et la Structure Moleculaire des Chélatants

(Study of the complexation of trivalent lanthanides by the six isomers of diaminocyclohexanetetraacetic acid. Part 3. Relationship between the acidity constants and the molecular structure of the ligands.)Potentiometric measurements of the acidity constants of the six isomers of diaminocyclohexane-N,N,N′,N′-tetraacetic acid (DCTA) are reported for an ionic strength of 1 mol l^?1 (KCl) at 25°C. The values of the two constants K_a3 and K_a4 are correlated with the maximum N—N distance for each ligand. Ethylenediamine-N,N,N′,N′-tetraacetic acid (EDTA) and some homologous ligands, including specially synthesized, 1,8-diaminooctane-N,N,N′,N′-tetraacetic acid and 1,10-diaminodecane-N,N,N′,N′-tetraacetic acid, are studied under the same conditions. It is proved that there is a relationship between the molecular structure and the affinity for protons.