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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.

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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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Thermally induced dehydroxylation and oxidative dehydrogenation drive the thermal decomposition of all Fe2+-containing phyllosilicates. Whereas the former produces H2O gas, the latter results in H2 evolution. Six chlorites representing the Mg-Fe2+ series from clinochlore to chamosite and biotite (as an analog of the 2:1 layer in chlorite) were investigated using thermogravimetry coupled to quadrupole mass spectrometry (TG-MS). A fast-ramp heating protocol was applied to identify if and how hydrogen gas was released from the crystal structure and whether it was quantitatively related to structural Fe2+ content. Dehydroxylation and oxidative dehydrogenation were tested under inert and oxidizing conditions. H2 liberation confirmed the H2 gas production by oxidative dehydrogenation, as shown by an evolution of the m/z = 2 signal for chamosites, Fe-rich clinochlores, and biotite heated under nitrogen gas atmosphere. Along with H2 evolution, H2O (m/z = 18) was released, suggesting that dehydroxylation is a trigger for dehydrogenation. The higher the Fe2+ content in the studied chlorites, the more intense the H2 evolution, thus the higher the H2/H2O ratios. The products of ramp-heating to 1000 °C resulted in varying amounts of newly formed Fe3+ (from 7 to 22%), however, biotite that converted into oxybiotite underwent almost complete oxidation, indicating a stronger tendency of 2:1 layer to dehydrogenation. The observed concurrent, but independent mechanisms of H2 and H2O evolution produced a feasible model of the thermal decomposition of chlorites. Despite O2 availability under oxidizing condition, the Fe2+ oxidation was not driven by attaching oxygen anions to the phyllosilicate structure, but also by dehydrogenation. Hydrogen was not detected using MS for any tested sample heated in synthetic air because any H2 if released was instantaneously combined with external O2, which resulted in an excess H2O MS signal not matched by mass loss on the TG profiles of chamosite and biotite. Without coupling of the evolved gas analysis with TG, the excess H2O produced by dehydrogenation in the O2-bearing carrier gas would result in misleading interpretations of dehydroxylation. Methodological and geological implications of the TG-MS experiments are discussed. The oxidation of Fe2+ in all Fe2+-containing phyllosilicates proceeds with simultaneous H2 gas release that is not dependent on oxygen fugacity nor temperature during the mineral formation. Therefore, the correlation between Fe3+/Fe2+ and remaining hydrogen in the structure must be considered during modeling the conditions that involve chlorite as geothermobarometer. H2 release during heating is proposed as an indicator of oxidative dehydrogenation of Fe2+-bearing minerals on Mars.