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 Ln3+/[Fe­(CN)6]3‑ (Ln = Gd, Tb, Y) and M2+/[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 Gd3+/[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 M2+/[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.