SYNTHESIS AND COMPLEXATION PROPERTIES OF ,4,7-TRIAZACYCLONONANE-1,4,7-TRIS(2-METHYLACETATE)

A new ligand, ,4,7-triazacyclononane-1,4,7-tris(2-methylacetate) (NOTM A) has been prepared and some of its thermodynamic and kinetic complex ation properties determined. The highest protonation constant in NOTMA was somewhat higher than the corresponding value in the analogous ace tate ligand, NOTA (logK1 = 12.2 versus 11.4). The measured metal ion-N OTMA stability constants were logK(ML) = 6.4, 8.8, 12.3, 12.8, 15.5, a nd 18.6 for Ca2+, Mg2+, Cd2+, Gd3+, Mn2+ and Zn2+, respectively. These stability constants were either similar to (Mg2+, Mn2+, Zn2+) or smal ler (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 la rger ionic radii. Water proton relaxivity measurements indicate that G d(NOTMA) has a higher water coordination number than Gd(NOTA). This wa s confirmed by fluorescence lifetime measurements of Eu(NOTMA) and Eu( NOTA) in H2O and D20. The mechanism of complex formation and dissociat ion appears to be similar for NOTA and NOTMA. NOTMA forms complexes wi th Gd3+ about 2-orders of magnitude more slowly than NOTA (k(OH) = 5.8 x 10(5) M-1 s-1 versus 7.1 x 10(7) M-1 s-1) while free Gd3+ is releas ed somewhat slower at pH 7 from Gd(NOTMA) than from Gd(NOTA) (kd (acid catalyzed) = 9.3 x 10(-3) M-1 s-1 versus 2.3 X 10(-2) M-1 s-1, respec tively).