Investigation of the kinetics of aquation of the 1:2 complex between CrIII and nitrilotriacetic acid

Magdalena E. Mendola, Tias Paul, Timothy J. Strathmann, Richard F. Carbonaro

Research output: Contribution to journalArticlepeer-review


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.

Original languageEnglish (US)
Pages (from-to)269-278
Number of pages10
Issue number2
StatePublished - Feb 3 2009
Externally publishedYes


  • Aquation
  • Capillary electrophoresis
  • Chromium
  • Ligand exchange
  • NTA

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry
  • Materials Chemistry


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