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A facile and low-cost method for structuring carbon-encapsulated cobalt nanoparticles (Co@C) is presented. Three samples were solvothermally prepared in one step at 220 °C and one in two steps at 200 °C. Three different polyols such as propylene glycol, triethylene glycol, and tetraethylene glycol were used as carbon sources, solvents, and reducing agents. The samples were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and Raman spectroscopy. Concerning the crystal structure of the particles, a mixture of hcp/ fcc Co phases was obtained in three of the samples, independently of the polyol used. The coexistence of cubic and hexagonal phases was revealed both from XRD and high-resolution TEM (HRTEM). The formation of the cubic fcc structure, despite the relatively low reaction temperature, is attributed to the role of the interface between carbon coating and metallic core. The presence of carbon coating was demonstrated by Raman spectrometry, exhibiting the characteristic D and G graphitic bands, and by HRTEM observations. All samples showed ferromagnetic behavior with saturation magnetization up to 158 emu/g and coercivity up to 206 Oe. From the magnetic particle hyperthermia measurements recorded at a frequency of 765 kHz, a maximum SLP value of 241 W/g was obtained. [ABSTRACT FROM AUTHOR]

Copper(i) oxide (Cu2O) nanoparticles (NPs) of 30 nm with antifungal properties have been functionalized with 9 nm nickel ferrite (NiFe2O4) magnetic nanoparticles (MNPs) to construct hetero-nanocomposites (NCs) of a submicron hydrodynamic size for magnetomechanical stress induction in the yeast, Saccharomyces cerevisiae. A post-synthetic approach involving the assembly through hydrophobic interactions of the preformed NPs of non-uniform sizes, albeit coated with the same surfactant (oleylamine), is reported. Solvents of different polarity were implemented during the synthetic procedure resulting in NCs of similar composition consisting mainly of MNPs randomly decorated onto the bigger Cu2O NPs. The antifungal properties of the building NPs and the NCs were studied in terms of fungistatic and fungicidal activity, whereas the ionic leaching was found to be negligible, highlighting the nanosize effect. Although S. cerevisiae cells were found to be resistant to individual NiFe2O4 MNPs because of their small size, their sensitivity to NCs significantly increased upon short-time exposure to a rotating low-frequency magnetic field (10 min, 30 Hz, 35 G) and this arises from the collective properties. The magnetomechanical cell stress induction was accompanied by alteration of cellular membrane integrity and programmed cell death signaling. [ABSTRACT FROM AUTHOR]

Manganese ferrite (MnFe2O4) nanoparticles of identical size (9 nm) and with different inversion degrees were synthesized under solvothermal conditions as a candidate theranostic system. In this facile approach, a long-chain amine, oleylamine, was utilized as a reducing and surface-functionalizing agent. The synthesized nanoparticles were shown to have a cubic-spinel structure as characterized by TEM and XRD patterns. Control over their inversion degree was achieved by a simple change of manganese precursor from Mn(acac)2 to Mn(acac)3. The variation in the inversion degree is ascribed to the partial oxidation of Mn2+ to Mn3+, as was evidenced by X-ray absorption near edge structure spectroscopy and extended X-ray absorption fine structure spectroscopy at both the Fe and Mn K-edges. The reduction of the inversion degree from 0.42 to 0.22 is close to the corresponding bulk value of 0.20 and led to elevated magnetization (65.7 emu gâ'1), in contrast to the Néel temperature, which was decreased owing to the weaker superexchange interactions between the tetrahedral and octahedral sites within the spinel structure. In order to evaluate the performance of these nanoprobes as a possible bifunctional targeting system, the ¹H NMR relaxation of the samples was tested together with their specific loss power under an alternating magnetic field as a function of concentration. The hydrophobic as prepared MnFe2O4 nanoparticles converted to hydrophilic nanoparticles with cetyltrimethylammonium bromide (CTAB). The MnFe2O4 nanoparticles, well-dispersed in aqueous media, were shown to have r2 relaxivity of up to 345.5 mMâ'1 sâ'1 and heat release of up to 286 W gâ'1, demonstrating their potential use for bioapplications. [ABSTRACT FROM AUTHOR]

Nickel ferrite nanoparticles were synthesized via a facile solvothermal approach. Oleylamine (OAm) was used in all synthetic procedures as a stabilizing agent and solvent. By varying the polarity of the solvents, hydrophobic NiFe2O4 nanoparticles coated with OAm of relatively similar sizes (9-11.7 nm) and in a range of magnetization values (32.0-53.5 emu g-1) were obtained. The as-prepared hydrophobic nanoparticles were characterized by XRD, TEM, SEM, TGA and VSM and converted to hydrophilic by two different approaches. The addition of a positively charged ligand (cetyltrimethyl ammonium bromide, CTAB) and the ligand exchange procedure (2,3-dimercaptosuccinic acid, DMSA) have been successfully applied. The aqueous suspensions of NiFe2O4@CTAB and NiFe2O4@DMSA showed good colloidal stability after a long period of time. The different surface modification affected both the NMR relaxometric measurements and the hyperthermia effects. In both techniques CTAB modification demonstrated higher r2 relaxivity (278.9 s-1 mM-1 in an NMR spectrometer at 11.7 T) and SAR values (423.4 W g-1 at an applied AC field with a particle concentration of 0.5 mg mL-1). The results indicate that a coating with a larger molecule as CTAB under the same size, shape and magnetization of NiFe2O4 NPs gave rise to NMR relaxometric properties and heating efficacy. [ABSTRACT FROM AUTHOR]

The linear trinuclear Cu(ii) complexes [Cu3(L1)4(H2tea)2] (1), [Cu3(L2)4(H2tea)2]·2CH3CN (2), [Cu3(L2)4(H2tea)2] (3), [Cu3(L1)2(H2tea)2(NO3)2] (4) and the dinuclear complex [Cu2(L1)2(H2tea)2] (5), where L1= 2-thiophene carboxylate, L2= 2-(thiophen-2-yl)-acetate and H2tea = the single deprotonated form of triethanolamine have been prepared and characterised while the crystal structures of 1–4have been determined. The variable-temperature magnetic susceptibilities of complexes 1–5have been measured in the range 2–300 K under various external fields in the range 0.02–1.0 T. X-band EPR spectra of 1–5compounds were recorded at 4–100 K. Complexes 1, 2and 3found to have the same J= 33 cm−1and gvalues 2.16(1), 2.20(1) and 2.16(1) respectively while for 5J= 15 cm−1and g= 2.06(1) revealing a clear ferromagnetic exchange between Cu(ii) ions. Complex 4was found to be antiferromagnetic with J= −28 cm−1and g= 2.21(1). The polycrystalline powder X-band EPR spectrum of complexes 1, 2, and 3at 4 K are dominated by a transition at 1600 G (g= 4.3) which unambiguously identifies the spin of the ground multiplet (S= 3/2) while the antiferromagnetic complex 4has a derivative centered at g= 2.1 indicative of a ground doublet (S= 1/2). Concerning complex 5a spectrum of a dominant derivative centered at g= 2.06(1) is observed with a very weak half field transition (ca.1500 G) indicative of the ferromagnetic nature of the system. Furthermore, for complexes 2and 3a strong temperature dependence of this spectroscopic g-factor is revealed and change of the gefffrom the liquid helium temperature to the room temperature is almost 2 units. [ABSTRACT FROM AUTHOR]

The natural oxidation process is studied in the case of 15 nm iron nanoparticles produced by the thermal decomposition of Fe(CO)5. X-ray diffraction spectra of the nanoparticles at different timescales after exposure to air revealed the instant oxidation of iron and the formation of wüstite and magnetite. Wüstite mainly occupies the interior of nanoparticles, as evidenced by microscopy, but is slowly transformed to a spinel structure. The shape, the dispersion and the role of surfactant were investigated by conventional microscopy and Fourier Transformed-Infrared (FT-IR) spectroscopy. Magnetic hysteresis loops confirmed the expected variation of magnetic properties till the steady state. [ABSTRACT FROM AUTHOR]

Co-based nanostructures ranging from core/shell to hollow nanoparticles were prepared by varying the reaction time and the chemical environment during the thermal decomposition of Co2(CO)8. Both structural characterization and kinetic model simulation illustrate that the diffusivities of cobalt and oxygen determine the growth ratio and the final morphology of the nanoparticles. Exchange coupling between Co and Co-oxide in core/shell nanoparticles induced a shift of field-cooled hysteresis loops that is proportional to the shell thickness, as verified by numerical studies. The increasing nanocomplexity, when passing from core/shell to hollow particles, also leads to the appearance of hysteresis above 300 K due to an enhancement of the surface anisotropy resulting from the additional spin-disordered surfaces. [ABSTRACT FROM AUTHOR]

Abstract: Co x Pt1− x nanostructures with varying composition and controllable morphologies have been synthesized through the thermal decomposition of appropriate platinum and cobalt precursors in organic solvents. The employment of several different surfactants facilitated the production of nanostructures with various sizes and shapes including nanowires, flower-like structures and spherical particles. The composition of the as-prepared nanomaterials ranged between Pt-rich and stoichiometric CoPt alloy, mainly depending on the starting ratio of the precursors. Three-dimensional structures such as the ‘flower-like’ ones showed a net ferromagnetic behavior, even at room temperature. In certain cases, the alloy nanostructures were annealed in order to obtain the ‘hard’ fct-CoPt phase, which displayed high coercivity values. [Copyright &y& Elsevier]