Unusual magnetic relaxation behavior of hydrophilic colloids based on gadolinium(III) octabutoxyphthalocyaninate

The work introduces the original and efficient approach toward hydrophilization of Gd(III) complex with hydrophobic octa-2,3,9,10,16,17,23,24-n-butoxyphthalocyanine (1H2). It consists in the solvent-mediated self-assembly of the preliminary synthesized octa-2,3,9,10,16,17,23,24-n-butoxyphthalocyaninatogadolinium(III) acetate 1GdOAc into the colloid species followed by their hydrophilization through the polyelectrolyte deposition. Small-angle X-ray scattering, TEM, and DLS measurements of the aqueous colloids reveal the disk-like colloid species formation with the greatest size value about 40 nm. Deposition of polystyrene sulfonate layer onto the surface of nanocolloids does not prevent their partial aggregation in aqueous solutions. The phthalocyaninate ligand is the reason for specific electrochemical behavior of the colloids, which is affected by the nanoparticulate form of the complex. The magnetic behavior of the complex reveals it as pure paramagnetic, while magnetic relaxation behavior of the colloids points to some specificity. The r2/r1 ratio measured at 0.47 T is higher (2.6) than the ratios commonly reported for Gd(III) complexes, coming to 36.8 at 11.75 T. Thus, the synthesized colloids are more efficient as T2- than T1-contrasting agents at magnetic field strengths above 1.4 T.