Dynamic aggregation of the mid-sized gadolinium complex {Ph4[Gd(DTTA)(H2O)2]−3}

• Published in: Journal of biological inorganic chemistry Vol. 19; no. 2; pp. 145 - 159
• Main Authors: Jaccard, Hugues, Miéville, Pascal, Cannizzo, Caroline, Mayer, Cédric R., Helm, Lothar
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.02.2014; Springer Verlag
• Subjects: Biochemistry; Biomedical and Life Sciences; Chemical Physics; Gadolinium - chemistry; Life Sciences; Ligands; Microbiology; Models, Molecular; Molecular Conformation; Organometallic Compounds - chemical synthesis; Organometallic Compounds - chemistry; Original Paper; Pentetic Acid - analogs & derivatives; Pentetic Acid - chemistry; Physics; Topical Issue on Metal-Based MRI Contrast Agents; Aggregation; Gadolinium; Relaxometry; Imaging agent; stacking
• ISSN: 0949-8257; 1432-1327
• DOI: 10.1007/s00775-013-1036-y

A compound binding three Gd 3+ ions, {Ph 4 [Gd(DTTA)(H 2 O) 2 ] − 3 } (where H 5 DTTA is diethylenetriaminetetraacetic acid), has been synthesized around a hydrophobic center made up of four phenyl rings. In aqueous solution the molecules start to self-aggregate at concentrations well below 1 mM as shown by the increase of rotational correlation times and by the decrease of the translational self-diffusion constant. NMR spectra recorded in aqueous solution of the diamagnetic analogue {Ph 4 [Y(DTTA)(H 2 O) 2 ] − 3 } show that the aggregation is dynamic and due to intermolecular π -stacking interactions between the hydrophobic aromatic centers. From estimations of effective radii, it can be concluded that the aggregates are composed of two to three monomers. The paramagnetic {Ph 4 [Gd(DTTA)(H 2 O) 2 ] − 3 } exhibits concentration-dependent 1 H NMR relaxivities with high values of approximately 50 mM −1  s −1 (30 MHz, 25 °C) at gadolinium concentrations above 20 mM. A combined analysis of 1 H NMR dispersion profiles measured at different concentrations of the compound and 17 O NMR data measured at various temperatures was performed using different theoretical approaches. The fitted parameters showed that the increase in relaxivity with increasing concentration of the compound is due to slower global rotational motion and an increase of the Lipari–Szabo order parameter S 2 .