SYNTHESIS, THERMODYNAMICS AND RELAXIVITY STUDIES FOR THE COMPLEXATIONOF GD3-BIS(AMIDE) DERIVATIVES OF DIETHYLENETRIAMINEPENTAACETIC ACID(,CA2+, CU2+ AND ZN2+ BY N,N'')

Three bis(amide) derivatives of H(5)dtpa carboxymethyl)iminobis(ethyle nenitrilo)tetraacetic acid], H3L1 = bis(adamantanamide), H3L2 = bis (2 -methoxybenzylamide), and H3L3 = bis (2-methoxyphenethylamide) were sy nthesized. Their protonation constants were determined by potentiometr ic titration in 0.10 mol dm(-3) KCl and by NMR pH titration at 25.0 +/ - 0.1 degrees C. Stability and selectivity constants are measured to e valuate the possibility of using the corresponding gadolinium(III) com plexes for magnetic resonance imaging contrast agents. Low stability o r selectivity constants indicate higher possibility for releasing free Gd3+ ion and free ligand as well from gadolinium(III) complexes. The formations of gadolinium(III), copper(II), zinc(II), and calcium(II) c omplexes were investigated quantitatively by the potentiometry. The st ability constant for gadolinium(II) complex is larger than those for C a(II), Zn(II), and Cu(II) complexes for these three octadentate ligand s. The selectivity constants and modified selectivity constants of the amides for Gd3+ over endogenously available metal ions were calculate d. Effectiveness of all three ligands in binding divalent and trivalen t metal ions in biological media is assessed by comparing pM values at physiological pH 7.4. Spin-lattice relaxivity R-1 for Gd(III) complex es was also determined. The observed relaxivity were found to decrease with increasing pH in the acid range below pK 3 and relaxivity values were become invariant with respect to pH changes over the range of 3- 10. (C) 1998 Elsevier Science Ltd. All rights reserved.