ISSN:
0538-8066
Keywords:
Chemistry
;
Physical Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The kinetics of the complexation of Al3+ with aminoacids, IDA and NTA are investigated by the stopped flow method with conductivity detection in the range of pH 〈 4. Reaction amplitudes and pseudo-first-order rate constants are evaluated yielding equilibrium and rate constants. It is shown that Al3+ forms only complexes with the negatively charged species and that the kinetics of all investigated ligands can be explained with the same reaction scheme. For aspartic acid, IDA and NTA a stepwise complexation is observed where monodentate complexes are formed by a fast reaction (2s -1 〈 k 〈 20s1) which is base catalyzed. The rate determining step is the solvent exchange at Al3+ according to the Eigen-Wilkins mechanism. However, the ligand influences this exchange rate and a linear free energy relation is found between log k and pKa, which also describes the kinetics of other ligands. This fast reaction is followed by the much slower formation of chelates (for NTA:k = 0.27 s -1) which is controlled by the deprotonation of the nitrogen atom. The overall association constant of the Al-NTA complex is determined as log (Kass/dm3mol-1) = 13.0 ± 0.3. © 1996 John Wiley & Sons, Inc.
Additional Material:
6 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/kin.8
