NMR Relaxation in Solution of Paramagnetic Complexes: Recent Theoretical Progress for S≥1

Synthesis, complexation and NMR relaxation properties of Gd3+ complexes of Mes(DO3A)3

“…After restoring the pH to 5.8, the two acetates of the uncomplexed DO3A, instead of staying deprotonated and free, are suspected to bind immediately to the two chelated Gd 3+ ions by replacing one water molecule from the first coordination sphere of each of the two paramagnetic centers (Scheme 3). 25- 26 We therefore conclude that we synthesized the compound [Gd 2 (6)] -, which we named bis-Gd as opposed to [Gd 3 (6)] which we named tris-Gd. A preparation of the tris-Gd complex by starting the reaction at much higher pH is not possible due to the formation of gadolinium hydroxide at pH >5.9.…”

“…The classical complexation method consists in mixing a ligand solution with stoichiometric quantities of Gd 3+ calculated for Gd 3 (6)(H 2 O) 6 (see Experimental). In the case of our ligand 6 this leads to a surprising result.…”

“…A preparation of the tris-Gd complex by starting the reaction at much higher pH is not possible due to the formation of gadolinium hydroxide at pH >5.9. We therefore decided to prepare [Gd 3 (6)] in two steps. In a first step we complex the ligand 6 with a metal ion forming much weaker complexes than Gd 3+ .…”

“…6 If we are not interested in detailed information about the electron spin relaxation and if we restrict the data analysis to medium to high magnetic fields the SBM approach gives reliable information on dynamic processes like water exchange rate constants and rotational correlation times for small to midsize complexes. 32 In a first step we fitted the 17 O relaxation rates and chemical shift data of both compounds together.…”

“…The tris-Gd complex Gd 3 (6)(H 2 O) 6 was prepared by complexing 6 in a first step with Mg 2+ followed by transmetallation with Gd 3+ . 11.8 mg of MgCl 2 ·2H 2 O (58 mmol, 3 eq.)…”