Relaxivity enhancement of aquated Tris(β-diketonate)gadolinium(III) chelates by confinement within ultrashort single-walled carbon nanotubes

Abstract

Ultrashort single-walled carbon nanotubes loaded with gadolinium ions (gadonanotubes) have been previously shown to exhibit extremely high T1-weighted relaxivities (>100 mm-1 s-1). To further examine the effect of nanoconfinement on the relaxivity of gadolinium-based contrast agents for magnetic resonance imaging, a series of ultrashort single-walled carbon nanotube (US-tube) materials internally loaded with gadolinium chelates have been prepared and studied. US-tubes were loaded with Gd(acac)3·2H2O, Gd(hfac)3·2H2O, and Gd(thd)3 (acac=acetylacetone, hfac=hexafluoroacetylacetone, thd=tetramethylheptanedione). The longitudinal relaxivities of the prepared materials determined at 25°C in a 1.5 T field were 103 mm-1 s-1 for Gd(acac)3·2H2O@US-tubes, 105 mm-1 s-1 for Gd(hfac)3·2H2O@US-tubes and 26 mm-1 s-1 for Gd(thd)3@US-tubes. Compared with the relaxivities obtained for the unloaded chelates (<10 mm-1 s-1) as well as accounting for the T1 reduction observed for the empty US-tubes, the boost in relaxivity for chelate-loaded US-tubes is attributed to confinement within the nanotube and depends on the number of coordinated water molecules. Copyright © 2014 John Wiley & Sons, Ltd. Gadolinium ions trapped within single walled carbon nanotubes have been shown to exhibit remarkably high r1 relaxivities. This work explores the role of the local coordination environment in modulating the order-of-magnitude increases in relaxivities of gadoliniums ions which are encapsulated. Relaxivities within the nanotube on number of coordinated water molecules. © 2014 John Wiley & Sons, Ltd.