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Two linear bis(amide) derivaties of DTPA-(diethylenetriamine-
N,N,N',N",N"- pentaacetic acid),DTPA-BMOBA(diethylenetriamine-N,
N',N"-triacetic-N,N"-bis(N-2-methoxybenzylamide)) and DTPA-
BMOPEA(diethylenetriamine-N,N',N"-triacetic-N,N"-bis(N-2-
methoxyphenethylamide)) and two linear bis(amide) derivaties of
EDTA(ethylenediamine-N,N'-diacetic acid), EDTA-BMOBA(
ethylenediamine-N,N'-diacetic-N,N'-bis(N-2-methoxybenzylamide))
and EDTA-BTBA(ethylenediamine-N,N'-diacetic-N,N'-bis(tert-
butylamide)) were synthesized. Their protonation constants
weredetermined by potentiometric titration with 0.10 mol dm-3
KCl andby NMR pH titration at 25.0+0.1. The stability constants
of the complexes of calcium(II), zinc(II), copper(II) and
gadolinium(III) with DTPA-BMOBA, DTPA-BMOPEA, EDTA-BMOBA and
EDTA-BTBA were also quantitatively investigated bypotentiometic
technique. The stability constants determined for Gd(III)
islarger than those for Ca(II), Zn(II) and Cu(II) with DTPA-
BMOBA and DTPA-BMOPEA. The selectivity constants and modified
selectivity constants for Gd(III) with the ligands over
endogenously available metal ions were calculated and discussed.
Spin-lattice relaxivities(R1, 20MHz) of the complexes of Gd(III)
with DTPA-BMOBA and DTPA-BMOPEA as a function of pH were
determined. The similar rela-xivity R1 of the complexes of [Gd(
DTPA-BMOBA)] and [Gd(DTPA-BMOPEA)] suggestthat they contain
similar inner-sphere water and coordination numbers. Theobserved
relaxivity R1 decreased with the increasing pH in the acid
region below pH 3. Once a Gd(III) complex were fully formed, the
relaxivity became a constant, and the limiting value correlated
well with the number of inner-sphere-coordinated water
molecules.
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