Dual-mode MRI contrast agents consisting of superparamagnetic iron oxide nanoparticle (SPION) cores and gadolinium ions associated with the ionic chitosan protecting layer were synthesized and studied. Gadolinium ions were introduced into the coating layer via direct complex formation on the nanoparticles surface, covalent attachment or electrostatically driven deposition of the preformed Gd complex. The modified SPIONs having hydrodynamic diameters ca. 100 nm form stable, well-defined dispersions in water and have excellent magnetic properties. Physiochemical properties of those new materials were characterized using e.g., FTIR spectroscopy, dynamic light scattering, X-ray fluorescence, TEM, and vibrating sample magnetometry. They behave as superparamagnetics and shorten both T1 and T2 proton relaxation times, thus influencing both r1 and r2 relaxivity values that reach 53.7 and 375.5 mM−1 s−1, respectively, at 15 MHz. The obtained materials can be considered as highly effective contrast agents for low-field MRI, particularly useful at permanent magnet-based scanners.
Single-phase multicomponent
perovskite-type cobalt oxide containing
five cations in equiatomic amounts on the A-site, namely, (Gd0.2Nd0.2La0.2Sm0.2Y0.2)CoO3, has been synthesized via the modified coprecipitation
hydrothermal method. Using an original approach for heat treatment,
which comprises quenching utilizing liquid nitrogen as a cooling medium,
a single-phase ceramic with high configuration entropy, crystallizing
in an orthorhombic distorted structure was obtained. It reveals the
anomalous temperature dependence of the lattice expansion with two
weak transitions at approx. 80 and 240 K that are assigned to gradual
crossover from the low- via intermediate- to high-spin state of Co3+. The compound exhibits weak ferromagnetism at T ≤ 10 K and signatures of antiferromagnetic correlations in
the paramagnetic phase. Ab initio calculations predict a band gap
Δ = 1.18 eV in the ground-state electronic structure with the
dominant contribution of O_p and Co_d orbitals in the valence and
conduction bands, respectively. Electronic transport measurements
confirm the negative temperature coefficient of resistivity characteristic
to a semiconducting material and reveal a sudden drop in activation
energy at T ∼ 240 K from E
a ∼ 1 eV in the low-temperature phase to E
a ∼ 0.3 eV at room temperature. The possibility
of fine tuning of the semiconducting band gap via a subtle change
in A-site stoichiometry is discussed.
Polymer core−shell nanocapsules with magnetic nanoparticles embedded in their oil cores were fabricated and applied as nano(photo)reactors. Superparamagnetic iron oxide nanoparticles (SPIONs) coated with oleic acid were first synthesized and characterized structurally, and their magnetic properties were determined. The capsules with chitosan-based shells were then formed in a one-step process by sonicationassisted mixing of (1) an aqueous solution of the hydrophobically derived chitosan and (2) oleic acid containing the dispersed SPIONs. In this way, magnetic capsules with a diameter of approximately 500−600 nm containing encapsulated SPIONs with an average diameter of approximately 20−30 nm were formed as revealed by dynamic light scattering and scanning transmission electron microscopy measurements. The composition and magnetic properties of the formed capsules were also followed using dynamic light scattering, electron microscopies, and magnetic force microscopy. The water-dispersible capsules, thanks to their magnetic properties, were then navigated in a static magnetic field gradient and transferred between the water and oil phases, as evidenced by fluorescence microscopy. In this way, the capsules could be loaded in a controlled way with a hydrophobic reactant, perylene, which was later photooxidized upon transferring the capsules to the aqueous phase. The capsules were shown to serve as robust reloadable nanoreactors/ nanocontainers that via magnetic navigation can be transferred between immiscible phases without disruption. These features make them promising reusable systems not only for loading and carrying lipophilic actives, conducting useful reactions in the confined environment of the capsules, but also for magnetically separating and guiding the encapsulated active molecules to the site of action.
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