Synthesis and Complexation Properties of 1,4,7-Triazacyclononane-1,4,7-tris(2-methylacetate)

E. Brcher, S. L. Stefan, D. R. Allen, A. D. Sherry

Research output: Contribution to journalArticle

6 Citations (Scopus)

Abstract

A new ligand, l,4, 7-triazacyclononane-l,4, 7-tris(2-methylacetate) (NOTMA) has been prepared and some of its thermodynamic and kinetic complexation properties determined. The highest protonation constant in NOTMA was somewhat higher than the corresponding value in the analogous acetate ligand, NOTA (logK1 = 12.2 versus 11.4). The measured metal ion NOTMA stability constants were logKML = 6.4, 8.8, 12.3, 12.8, 15.5, and 18.6 for Ca2 +, Mg2 +, Cd2 +, Gd3 +, Mn2+ and Zn2 +, respectively. These stability constants were either similar to (Mg2 +, Mn2 +, Zn2+) or smaller (Ca2 +, Cd2 +, Gd3+) than the respective complexes of NOTA, perhaps reflecting steric interactions between the ethylenediamine protons and the methyl groups in the NOTMA complexes formed with metal ions of larger ionic radii. Water proton relaxivity measurements indicate that Gd(NOTMA) has a higher water coordination number than Gd(NOTA). This was confirmed by fluorescence lifetime measurements of Eu(NOTMA) and Eu(NOTA) in H2O and D2O. The mechanism of complex formation and dissociation appears to be similar for NOTA and NOTMA. NOTMA forms complexes with Gd3 + about 2-orders of magnitude more slowly than NOTA (kOH = 5.8 × 105 M-1s-1 versus 7.1 × 107 M-1s-1) while free Gd3+ is released somewhat slower at pH 7 from Gd(NOTMA) than from Gd(NOTA) (kd' (acid catalyzed) = 9.3 × 10-3 M-1s-1 versus 2.3 × 10-2 M-1s-1, respectively).

Original languageEnglish (US)
Pages (from-to)207-212
Number of pages6
JournalRadiochimica Acta
Volume61
Issue number3-4
DOIs
StatePublished - 1993

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ethylenediamine
Complexation
Metal ions
Protons
Ligands
Water
Protonation
metal ions
synthesis
ligands
Acetates
protons
Fluorescence
Thermodynamics
coordination number
water
Kinetics
Acids
acetates
dissociation

Keywords

  • Hydration numbers
  • Kinetics
  • Metal ion complexes
  • NOTMA complexes
  • Protonation constants

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

Synthesis and Complexation Properties of 1,4,7-Triazacyclononane-1,4,7-tris(2-methylacetate). / Brcher, E.; Stefan, S. L.; Allen, D. R.; Sherry, A. D.

In: Radiochimica Acta, Vol. 61, No. 3-4, 1993, p. 207-212.

Research output: Contribution to journalArticle

Brcher, E. ; Stefan, S. L. ; Allen, D. R. ; Sherry, A. D. / Synthesis and Complexation Properties of 1,4,7-Triazacyclononane-1,4,7-tris(2-methylacetate). In: Radiochimica Acta. 1993 ; Vol. 61, No. 3-4. pp. 207-212.
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T1 - Synthesis and Complexation Properties of 1,4,7-Triazacyclononane-1,4,7-tris(2-methylacetate)

AU - Brcher, E.

AU - Stefan, S. L.

AU - Allen, D. R.

AU - Sherry, A. D.

PY - 1993

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N2 - A new ligand, l,4, 7-triazacyclononane-l,4, 7-tris(2-methylacetate) (NOTMA) has been prepared and some of its thermodynamic and kinetic complexation properties determined. The highest protonation constant in NOTMA was somewhat higher than the corresponding value in the analogous acetate ligand, NOTA (logK1 = 12.2 versus 11.4). The measured metal ion NOTMA stability constants were logKML = 6.4, 8.8, 12.3, 12.8, 15.5, and 18.6 for Ca2 +, Mg2 +, Cd2 +, Gd3 +, Mn2+ and Zn2 +, respectively. These stability constants were either similar to (Mg2 +, Mn2 +, Zn2+) or smaller (Ca2 +, Cd2 +, Gd3+) than the respective complexes of NOTA, perhaps reflecting steric interactions between the ethylenediamine protons and the methyl groups in the NOTMA complexes formed with metal ions of larger ionic radii. Water proton relaxivity measurements indicate that Gd(NOTMA) has a higher water coordination number than Gd(NOTA). This was confirmed by fluorescence lifetime measurements of Eu(NOTMA) and Eu(NOTA) in H2O and D2O. The mechanism of complex formation and dissociation appears to be similar for NOTA and NOTMA. NOTMA forms complexes with Gd3 + about 2-orders of magnitude more slowly than NOTA (kOH = 5.8 × 105 M-1s-1 versus 7.1 × 107 M-1s-1) while free Gd3+ is released somewhat slower at pH 7 from Gd(NOTMA) than from Gd(NOTA) (kd' (acid catalyzed) = 9.3 × 10-3 M-1s-1 versus 2.3 × 10-2 M-1s-1, respectively).

AB - A new ligand, l,4, 7-triazacyclononane-l,4, 7-tris(2-methylacetate) (NOTMA) has been prepared and some of its thermodynamic and kinetic complexation properties determined. The highest protonation constant in NOTMA was somewhat higher than the corresponding value in the analogous acetate ligand, NOTA (logK1 = 12.2 versus 11.4). The measured metal ion NOTMA stability constants were logKML = 6.4, 8.8, 12.3, 12.8, 15.5, and 18.6 for Ca2 +, Mg2 +, Cd2 +, Gd3 +, Mn2+ and Zn2 +, respectively. These stability constants were either similar to (Mg2 +, Mn2 +, Zn2+) or smaller (Ca2 +, Cd2 +, Gd3+) than the respective complexes of NOTA, perhaps reflecting steric interactions between the ethylenediamine protons and the methyl groups in the NOTMA complexes formed with metal ions of larger ionic radii. Water proton relaxivity measurements indicate that Gd(NOTMA) has a higher water coordination number than Gd(NOTA). This was confirmed by fluorescence lifetime measurements of Eu(NOTMA) and Eu(NOTA) in H2O and D2O. The mechanism of complex formation and dissociation appears to be similar for NOTA and NOTMA. NOTMA forms complexes with Gd3 + about 2-orders of magnitude more slowly than NOTA (kOH = 5.8 × 105 M-1s-1 versus 7.1 × 107 M-1s-1) while free Gd3+ is released somewhat slower at pH 7 from Gd(NOTMA) than from Gd(NOTA) (kd' (acid catalyzed) = 9.3 × 10-3 M-1s-1 versus 2.3 × 10-2 M-1s-1, respectively).

KW - Hydration numbers

KW - Kinetics

KW - Metal ion complexes

KW - NOTMA complexes

KW - Protonation constants

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