A Potentiometric Study of Metal Chelates With Tetraethylenepentaaminehepta-Acetic Acid

Abstract

The protonation constants of tetraethylenepentaamineheptaacetic acid, TPHA, were determined by potentiometric titration in aqueous solution at an ionic strength of 0.10 M KNO3 and at 25°C. The formation constants of various metal-TPHA complexes were also obtained by titrating mixtures of metal to ligand in molar ratios of 1 : 1 and 2 : 1. Calculations were performed with the computer program BEST. Individual stability constants are reported for Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Hg(I1) and Pb(I1) with TPHA as well as their related protonated species. The stabilities of the 1 : 1 complexes parallel to those of similar complexes with DTPA and TTHA. However the 2 : 1 complexes have significantly larger log KML's than their TTHA counterparts. The extra stability of the 2 : 1 metal-TPHA complexes is explained in terms of ligand denticity and steric effects. Mercury(I1)-TPHA complexes exhibited the highest formation constants and the copper-TPHA complexes had slightly higher log KML's than those for Co(II), Ni(II), Zn(II), Cd(I1) and Pb(I1).

Iron(III) Chelation: Tuning of the pH Dependence by Mixed Ligands

“…The values of the lowest protonation constants (1.8 and 2.89 for L 1 ; 2.34 for L 2 ) correspond to the pyridine nitrogen of the sulfohydroxyquinoline moieties. Compared to 8‐hydroxyquinoline‐5‐sulfonic acid (log K H = 3.93),10 the protonation constants determined for L 1 and L 2 are two orders of magnitude lower. This could be explained by the electron‐withdrawing effect of the carbonyl linker in position 7, which is similar to that of the nitro group in 7‐nitro‐8‐hydroxyquinoline‐5‐sulfonic acid (log K H = 2.01) 11.…”

“…This could be explained by the electron‐withdrawing effect of the carbonyl linker in position 7, which is similar to that of the nitro group in 7‐nitro‐8‐hydroxyquinoline‐5‐sulfonic acid (log K H = 2.01) 11. The hydroxyl protonation constant of 8‐hydroxyquinoline‐5‐sulfonic acid10 is equal to 8.42 and those of L 0 vary between 7.44 and 8.62 2. We attribute the values 8.78 and 7.85 for L 1 and 7.93 for L 2 to the protonation of the 8‐hydroxyquinoline OH groups.…”

In Vivo Uranium Sequestration using a Nanoscale Metal–Organic Framework

“…An effect that is likely ascribed to its poor uranium-specific binding affinity. For instance, the stability constant logb 110 (13. [20] Therefore, DTPA type decorporation agents are commonly used in the form of CaNa 3 -DTPA or ZnNa 3 -DTPA to avoid hypocalcemia or even death due to Zn II or Ca II depletion. [21,22] This issue is complicated further by the competitive binding of uranyl by molecular chelators with siderophores that also significantly affects the binding kinetics and removal efficacy of uranium.…”