Premium
Kinetics of the complexation of Al 3+ with aminoacids, IDA and NTA
Author(s) -
Pohlmeier Andreas,
Knoche Wilhelm
Publication year - 1996
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/(sici)1097-4601(1996)28:2<125::aid-kin8>3.0.co;2-x
Subject(s) - chemistry , deprotonation , reaction rate constant , kinetics , denticity , medicinal chemistry , ligand (biochemistry) , chelation , equilibrium constant , inorganic chemistry , metal , ion , organic chemistry , biochemistry , physics , receptor , quantum mechanics
The kinetics of the complexation of Al 3+ 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 Al 3+ 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 < 20s 1 ) which is base catalyzed. The rate determining step is the solvent exchange at Al 3+ 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 p K a , 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 ( K ass /dm 3 mol −1 ) = 13.0 ± 0.3. © 1996 John Wiley & Sons, Inc.