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Communication

Optimized Relaxivity and Stability of [Gd(H(2,2)-1,2-HOPO)(H₂O)]^- for Use as an MRI Contrast Agent¹

Supporting Info

Christoph J. Jocher,^† Mauro Botta,^‡ Stefano Avedano,^‡ Evan G. Moore,^† Jide Xu,^† Silvio Aime,^§ and Kenneth N. Raymond*^†

Department of Chemistry, University of California, Berkeley, California 94720-1460, Dipartimento di Scienze dell'Ambiente e della Vita, Universit del Piemonte Orientale A. Avogadro, Via Bellini 25/G, I-15100 Alessandria, Italy, and Dipartimento di Chimica I.F.M., Universit di Torino, Via P. Giuria 7, I-10125 Torino, Italy

Inorg. Chem., 2007, 46 (12), pp 4796–4798

DOI: 10.1021/ic700399p

Publication Date (Web): May 11, 2007

†

University of California, Berkeley.

‡

Università del Piemonte Orientale “A. Avogadro”.

Università di Torino.

To whom correspondence should be addressed. E-mail: raymond@ socrates.berkeley.edu. Fax: +1 510 486 5283. Phone: +1 510 642 7219.

Abstract

Relaxometry and solution thermodynamic measurements show that Gd(H(2,2)-1,2-HOPO) is a good candidate as a contrast agent for magnetic resonance imaging (MRI-CA). Acidic, octadentate H(2,2)-1,2-HOPO forms a very stable Gd(III) complex [pGd = 21.2(2)]. The coordination sphere at the Gd(III) center is completed by one water molecule that is not replaced by common physiological anions. In addition, this ligand is highly selective for Gd(III) binding in the presence of Zn(II) or Ca(II). The symmetric charge distribution of the 1,2-HOPO chelates is associated with favorably long electronic relaxation time T_1,2e comparable to those of GdDOTA. This, in addition to the fast water exchange rate typical of HOPO chelates, improves the relaxivity to r_1p = 8.2 mM^-1 s^-1 (0.47 T). This remarkably high value is unprecedented for small-molecule, q = 1 MRI-CA.

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Published In Issue June 11, 2007
Received March 1, 2007

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Communication

Optimized Relaxivity and Stability of [Gd(H(2,2)-1,2-HOPO)(H₂O)]^- for Use as an MRI Contrast Agent¹