A Bishydrated, Eight–Coordinate Gd(III) Complex with Very Fast Water Exchange: Synthesis, Characterization, and Phantom MR Imaging. Issue 27 (16th July 2018)

• Record Type: Journal Article
• Authors: Phukan, Bedika; Malikidogo, Kyangwi P.; Bonnet, Célia S.; Tóth, Éva; Mondal, Samsuzzoha; Mukherjee, Chandan
• Is Part Of: ChemistrySelect. Volume 3:Issue 27(2018)
• Page Start: 7668
• Page End: 7673
• Publication Date: 2018-07-16
• Subjects: contrast agent -- fast water exchange -- gadolinium -- high field -- magnetic resonance imaging; Chemistry -- Periodicals; 540.5
• DOI: 10.1002/slct.201801629
• Languages: English
• ISSNs: 2365-6549

Abstract

Abstract: We report here the physical‐chemical characterization of a highly water‐soluble Gd(III) complex (complex 1 ) formed with the asymmetric hexadentate ligand H4 bedik (2, 2′‐((2‐(bis (carboxymethyl)amino)benzyl)azanediyl)diacetic acid). The number of water molecules directly coordinated to the metal, q =2.2, was assessed by measuring luminescence lifetimes of the Tb(III) analogue (complex 2 ) in H2 O and D2 O and it further was confirmed by 17 O chemical shift measurements on the Gd(III) complex. The complex has moderate thermodynamic stability and remains insensitive to physiological anions [biphosphate (HPO4 2− ), bicarbonate (HCO3 − )] and pH variation (in the range 5–10) of the medium as evidenced by negligible changes in longitudinal relaxivity ( r 1 ) at 1.41 T, 25 °C. The Gd(III) complex exhibits very fast water exchange, among the fastest reported for Gd(III) chelates, and high relaxivity at high magnetic fields ( r 1 =7.47 mM –1 s –1 at 9.4 T, pH ∼ 7 and 25 °C). Interestingly, the very high positive value of the activation entropy indicates a dissociatively activated water exchange for this eight‐coordinate complex. Abstract : A highly water‐soluble and bishydrated Gd(III) complex with very fast water exchange and high relaxivity at high magnetic fields ( r 1 =7.47 mM –1 s –1 at 9.4 T, pH ∼ 7 and 25 °C) was synthesized. Interestingly, a dissociative water exchange mechanism was indicated for the bishydrated octacoordinate chelate.