Relaxivity Enhancement of Ditopic Bishydrated Gadolinium(III) Complexes Conjugated to Mesoporous Silica Nanoparticles

Abstract

Dinuclear Gd 3+ complexes containing thermodynamically stable and bishydrated GdAAZTA (AAZTA = 6-amino-6methylperhydro-1,4-diazepinetetraacetic acid) chelates were covalently linked to the surfaces of mesoporous silica nanoparticles and decorated with poly(ethylene glycol) (PEG 5000 ) molecules. The surface and textural properties of the samples were analyzed. A detailed 1 H NMR relaxometric characterization as a function of the applied magnetic-field strength was performed for the conjugated systems in aqueous solutions to evaluate their efficacy as potential magnetic resonance imaging (MRI) diagnostic probes. The samples showed enhanced longi- [a]

Derivatives of GdAAZTA Conjugated to Amino Acids: A Multinuclear and Multifrequency NMR Study

“…In principle, the presence of multiple isomers in solution featuring different water exchange rates could also account for such an unusual trend of the 17 O-R 2 profiles, as already observed for other Gd(III) chelates. 37,38 However, such hypothesis is ruled out by the presence of a single set of signals in the variable temperature NMR spectra of the EuAAZTA-aa complexes (Figure S13).…”

“…8 Such behavior is attributable to the presence of two Gdbound water molecules occupying different positions of the coordination polyhedron with different bond lengths and therefore characterized by different rates of exchange. The hydration water closer to the metal center is in an intermediate exchange regime with the bulk and generates a 17 O-R 2 maximum at ∼300 K. The more labile and distant from Gd(III) water ligand has a faster rate of exchange (k ex = 1/τ M ), and is responsible for the 17 O-R 2 increase observed below 285 K. 8 As an example, the distinct contribution of the two water molecules to the 17 O-R 2 profile of GdAAZTA-Glu is emphasized in Figure S19.…”

Drawing on biology to inspire molecular design: a redox-responsive MRI probe based on Gd(iii)-nicotinamide

“…Commun., 2018, 54, 12986--12989 | 12989 slow tumbling system, and the slow tumbling implies that aggregation has occurred. However, the relaxivity is much lower than expected for a slow tumbling Gd-complex with inner-sphere water ligand(s), [36][37][38][39] and this low relaxivity implies that the hydration number is decreased and likely q is close to 0. We then investigated the effects of pH on relaxivity.…”

Gd‐Based Mesoporous Silica Nanoparticles as MRI Probes

“…The resulting Gd 3+ ‐bis‐phosphonate complex was shown to contain two coordinated water molecules, hence a quite good relaxivity value was measured for this nanosized system. Finally, we have recently reported the attachment to MSNs of binuclear Gd 3+ complexes containing the thermodynamically stable and bishydrated [GdAAZTA] – chelating units (AAZTA = 6‐amino‐6‐methylperhydro‐1,4‐diazepinetetraacetic acid; 9 in Scheme ) . [GdAAZTA] – is a q = 2 complex featuring a fast rate of water exchange, high thermodynamic stability and improved kinetic inertness .…”