Potentiometry and NMR studies of 1,5,9-triazacyclododecane-N,N′,N″-triacetic acid and its metal ion complexes

E. Cortes, S. Brucher, C. F G C Geraldes, A. D. Sherry

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Abstract

A new chelating macrocycle, 1,5,9-triazacyclododecane-N,N′,N″-triacetic acid (DOTRA), has been synthesized, and its complexes with Zn2+, Cd2+, Ca2+, Mg2+, and Mn2+ have been examined by potentiometry and NMR spectroscopy. The first protonation constant of the free ligand (log K1 = 12.8) was determined spectrophotometrically, while the remaining were evaluated from potentiometric data (log K2 = 7.55, log K3 = 3.65, log K4 = 2.1). DOTRA forms complexes with Mn2+, Mg2+, and Ca2+ rather slowly but reacts much more rapidly with Zn2+ and Cd2+. As reported previously for the nine-membered-ring triaza analogue NOTA, DOTRA also forms a more stable complex with Mg2+ than with Ca2+ (log Kst = 7.1 versus 6.0). High-resolution NMR spectra of the Zn2+, Cd2+, and Mg2+ complexes (log Kst = 19.0, 15.7, and 7.1, respectively) indicate the three six-membered chelate rings are symmetrical and quite rigid in aqueous solution, as evidenced by nonequivalence of all six chelate ring protons.

Original languageEnglish (US)
Pages (from-to)5-9
Number of pages5
JournalInorganic Chemistry
Volume29
Issue number1
StatePublished - 1990

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potentiometric analysis
Protonation
Chelation
Nuclear magnetic resonance spectroscopy
Metal ions
Protons
metal ions
Nuclear magnetic resonance
Ligands
chelates
nuclear magnetic resonance
acids
Acids
rings
analogs
aqueous solutions
ligands
protons
high resolution
spectroscopy

ASJC Scopus subject areas

  • Inorganic Chemistry

Cite this

Potentiometry and NMR studies of 1,5,9-triazacyclododecane-N,N′,N″-triacetic acid and its metal ion complexes. / Cortes, E.; Brucher, S.; Geraldes, C. F G C; Sherry, A. D.

In: Inorganic Chemistry, Vol. 29, No. 1, 1990, p. 5-9.

Research output: Contribution to journalArticle

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N2 - A new chelating macrocycle, 1,5,9-triazacyclododecane-N,N′,N″-triacetic acid (DOTRA), has been synthesized, and its complexes with Zn2+, Cd2+, Ca2+, Mg2+, and Mn2+ have been examined by potentiometry and NMR spectroscopy. The first protonation constant of the free ligand (log K1 = 12.8) was determined spectrophotometrically, while the remaining were evaluated from potentiometric data (log K2 = 7.55, log K3 = 3.65, log K4 = 2.1). DOTRA forms complexes with Mn2+, Mg2+, and Ca2+ rather slowly but reacts much more rapidly with Zn2+ and Cd2+. As reported previously for the nine-membered-ring triaza analogue NOTA, DOTRA also forms a more stable complex with Mg2+ than with Ca2+ (log Kst = 7.1 versus 6.0). High-resolution NMR spectra of the Zn2+, Cd2+, and Mg2+ complexes (log Kst = 19.0, 15.7, and 7.1, respectively) indicate the three six-membered chelate rings are symmetrical and quite rigid in aqueous solution, as evidenced by nonequivalence of all six chelate ring protons.

AB - A new chelating macrocycle, 1,5,9-triazacyclododecane-N,N′,N″-triacetic acid (DOTRA), has been synthesized, and its complexes with Zn2+, Cd2+, Ca2+, Mg2+, and Mn2+ have been examined by potentiometry and NMR spectroscopy. The first protonation constant of the free ligand (log K1 = 12.8) was determined spectrophotometrically, while the remaining were evaluated from potentiometric data (log K2 = 7.55, log K3 = 3.65, log K4 = 2.1). DOTRA forms complexes with Mn2+, Mg2+, and Ca2+ rather slowly but reacts much more rapidly with Zn2+ and Cd2+. As reported previously for the nine-membered-ring triaza analogue NOTA, DOTRA also forms a more stable complex with Mg2+ than with Ca2+ (log Kst = 7.1 versus 6.0). High-resolution NMR spectra of the Zn2+, Cd2+, and Mg2+ complexes (log Kst = 19.0, 15.7, and 7.1, respectively) indicate the three six-membered chelate rings are symmetrical and quite rigid in aqueous solution, as evidenced by nonequivalence of all six chelate ring protons.

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