Dendrimeric ß-cyclodextrin/Gd(III) chelate supramolecular host-guest adducts as high-relaxivity MRI probes.

We have synthesized a new macromolecular architecture, (PAMAM)-CD8 , which consists of eight ß-cyclodextrin units (ß-CD) attached to a generation 1 poly(amidoamine) (PAMAM) dendrimer through a disulfide bond, which can be cleaved under reducing conditions. This system shows a pronounced hosting capability towards Gd(III) chelates functionalized with hydrophobic groups, thus leading to well-defined supramolecular adducts. (1)H NMR relaxometric investigations were carried out to follow the formation of adducts with three Gd(III) chelates based on the ligand architectures of 6-amino-6-methylperhydro-1,4-diazepinetetraacetic acid (AAZTA) or 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) suitably functionalized with benzyl or adamantyl (Ad) pendant groups. In particular, the ditopic complex composed of two AAZTA chelating units connected to a central aromatic ring that bears an adamantyl group showed a strong affinity (ca. 10(6) M(-1)) for the CD units of the dendrimer, which is two orders of magnitude higher than toward human serum albumin (HSA). Remarkable relaxivity enhancements (i.e., up to 71% at 1 T and 25 °C) were observed upon the formation of the macromolecular host-guest adducts due to a decrease in the molecular tumbling rate and fast water-exchange. Reduction experiments and competition studies between the paramagnetic dendrimer and HSA were carried out by relaxometric techniques. The results show that the metal complexes are not displaced by the protein, thus suggesting that this novel macromolecular probe is potentially suitable for applications in vivo.

Colloidal assemblies of oriented maghemite nanocrystals and their NMR relaxometric properties.

An elevated-temperature polyol-based colloidal-chemistry approach allows for the development of size-tunable (50 and 86 nm) assemblies of maghemite iso-oriented nanocrystals, with enhanced magnetization. (1)H-nuclear magnetic resonance (NMR) relaxometric experiments show that the ferrimagnetic cluster-like colloidal entities exhibit a remarkable enhancement (4-5 times) in transverse relaxivity when compared to that of the superparamagnetic contrast agent Endorem®, over an extended frequency range (1-60 MHz). The marked increase in the transverse relaxivity r2 at a clinical magnetic field strength (∼1.41 T), which is 405.1 and 508.3 mM(-1) s(-1) for small and large assemblies, respectively, makes it possible to relate the observed response to the raised intra-aggregate magnetic material volume fraction. Furthermore, cell tests with a murine fibroblast culture medium confirmed cell viability in the presence of the clusters. We discuss the NMR dispersion profiles on the basis of relaxivity models to highlight the magneto-structural characteristics of the materials for improved T2-weighted magnetic resonance images.

Investigation on NMR relaxivity of nano-sized cyano-bridged coordination polymers.

We present the first comparative investigation of the Nuclear Magnetic Resonance (NMR) relaxivity of a series of nanosized cyano-bridged coordination networks stabilized in aqueous solution. These Ln(3+)/[Fe(CN)6](3-) (Ln = Gd, Tb, Y) and M(2+)/[Fe(CN)6](3-) (M = Ni, Cu, Fe) nanoparticles with sizes ranging from 1.4 to 5.5 nm are stabilized by polyethylene glycols (MW = 400 or 1000), polyethylene glycol functionalized with amine groups (MW = 1500), or by N-acetyl-D-glucosamine. The evaluation of NMR relaxivity allowed estimation of the Magnetic Resonance Imaging (MRI) contrast efficiency of our systems. The results demonstrate that Gd(3+)/[Fe(CN)6](3-) nanoparticles have r1p and r2p relaxivities about four times higher than the values observed in the same conditions for the commercial Contrast Agents (CAs) ProHance or Omniscan, regardless of the stabilizing agent used, while nanoparticles of Prussian blue and its analogues M(2+)/[Fe(CN)6](3-) (M = Ni, Cu, Fe) present relatively modest values. The influence of the chemical composition of the nanoparticles, their crystal structure, spin values of lanthanide and transition metal ions, and stabilizing agent on the relaxivity values are investigated and discussed.

Structure and dynamics of the hydration shells of citrate-coated GdF3 nanoparticles.

The 1H and 17O relaxometric behaviour in aqueous solution of GdF3 nanoparticles (<5 nm) coated with citrate molecules (Gd-NPs) was investigated as a function of magnetic field strength and temperature in order to unravel the mechanisms underlying their magnetic interaction with water molecules.