TY - JOUR
T1 - Investigation of the kinetics of aquation of the 1:2 complex between CrIII and nitrilotriacetic acid
AU - Mendola, Magdalena E.
AU - Paul, Tias
AU - Strathmann, Timothy J.
AU - Carbonaro, Richard F.
N1 - Funding Information:
This research was funded by the National Institute of Environmental Health Sciences through a Superfund Basic Research Program Grant (P42ES10344). Support for Tias Paul was provided by a US Environmental Protection Agency STAR Graduate Fellowship (Agreement No. 91683701-01) and WaterCAMPWS, a Science and Technology Center of Advanced Materials for the Purification of Water with Systems under the National Science Foundation Agreement number CTS-0120978. The authors wish to also thank Christina Manthos, Conor Shea, and Christopher Groth.
PY - 2009/2/3
Y1 - 2009/2/3
N2 - Aquation of the 1:2 complex between CrIII and nitrilotriacetic acid (NTA) was monitored using a combination of capillary electrophoresis (CE), ultraviolet-visible (UV-vis) spectrophotometry, and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. To our knowledge, this is the first published report of the use of either CE or ATR-FTIR to monitor the kinetics of ligand exchange reactions of CrIII-aminocarboxylate complexes. The aquation products were identified as the 1:1 CrIII complex with NTA and "free" NTA. The 1:1 complex dimerized to form a 2:2 complex in a slower subsequent reaction step. Rates of disappearance of the 1:2 complex were first-order under all experimental conditions. First-order rate constants for aquation, kobs (h-1), measured using all three techniques were similar at equivalent pH conditions, and with values reported previously in the literature. Measured kobs values exhibited a complicated pH dependence with three distinct regions: (i) at pH < 6.5, kobs values increased with decreasing pH, (ii) between pH 6.5 and 8.0, kobs values were relatively constant, and (iii) at 8.0 < pH < 10.0, kobs increased with increasing pH and then leveled off. A kinetic model incorporating five distinct aquation pathways was successfully employed to model the pH dependence of kobs from 0.0 < pH < 10.0. These results show that CE and ATR-FTIR can be used as tools for better understanding ligand exchange processes occurring in aqueous solution.
AB - Aquation of the 1:2 complex between CrIII and nitrilotriacetic acid (NTA) was monitored using a combination of capillary electrophoresis (CE), ultraviolet-visible (UV-vis) spectrophotometry, and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. To our knowledge, this is the first published report of the use of either CE or ATR-FTIR to monitor the kinetics of ligand exchange reactions of CrIII-aminocarboxylate complexes. The aquation products were identified as the 1:1 CrIII complex with NTA and "free" NTA. The 1:1 complex dimerized to form a 2:2 complex in a slower subsequent reaction step. Rates of disappearance of the 1:2 complex were first-order under all experimental conditions. First-order rate constants for aquation, kobs (h-1), measured using all three techniques were similar at equivalent pH conditions, and with values reported previously in the literature. Measured kobs values exhibited a complicated pH dependence with three distinct regions: (i) at pH < 6.5, kobs values increased with decreasing pH, (ii) between pH 6.5 and 8.0, kobs values were relatively constant, and (iii) at 8.0 < pH < 10.0, kobs increased with increasing pH and then leveled off. A kinetic model incorporating five distinct aquation pathways was successfully employed to model the pH dependence of kobs from 0.0 < pH < 10.0. These results show that CE and ATR-FTIR can be used as tools for better understanding ligand exchange processes occurring in aqueous solution.
KW - ATR-FTIR
KW - Aquation
KW - Capillary electrophoresis
KW - Chromium
KW - Ligand exchange
KW - NTA
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U2 - 10.1016/j.poly.2008.11.018
DO - 10.1016/j.poly.2008.11.018
M3 - Article
AN - SCOPUS:58149330105
SN - 0277-5387
VL - 28
SP - 269
EP - 278
JO - Polyhedron
JF - Polyhedron
IS - 2
ER -