O. Kaman

Magnetic heating by cobalt ferrite nanoparticles

In the quest for suitable materials for hyperthermia we explored the preparation and properties of nanoparticles of Co ferrite. The material was produced by coprecipitation from water solution of Co and Fe chlorides and afterwards annealed at 400, 600 and 800 °C. The resulting particles were characterized by XRD, TEM, Mossbauer spectroscopy, and dc and ac magnetometry. The heating experiments in ac magnetic fields of various amplitudes were performed with diluted systems of particles suspended in agarose gel and the results were interpreted on the basis of the ac magnetic losses measured at various temperatures. The increase of magnetic losses and consequently of the heating efficiency with increasing temperature is explained by the strong dependence of the constant of magnetocrystalline anisotropy of Co ferrite on temperature.

Silica encapsulated manganese perovskite nanoparticles for magnetically induced hyperthermia without the risk of overheating

Nanoparticles of manganese perovskite of the composition La(0.75)Sr(0.25)MnO(3) uniformly coated with silica were prepared by encapsulation of the magnetic cores (mean crystallite size 24 nm) using tetraethoxysilane followed by fractionation. The resulting hybrid particles form a stable suspension in an aqueous environment at physiological pH and possess a narrow hydrodynamic size distribution. Both calorimetric heating experiments and direct measurements of hysteresis loops in the alternating field revealed high specific power losses, further enhanced by the encapsulation procedure in the case of the coated particles. The corresponding results are discussed on the basis of complex characterization of the particles and especially detailed magnetic measurements. Moreover, the Curie temperature (335 K) of the selected magnetic cores resolves the risk of local overheating during hyperthermia treatment.

Magnetic heating by silica-coated Co–Zn ferrite particles

This study is aimed at the preparation of silica-coated nanoparticles of cobalt–zinc ferrite and their heating properties with respect to potential application in magnetic fluid hyperthermia. The magnetic cores of Co0.4Zn0.6Fe2O4+γ possessing two different sizes were prepared by the coprecipitation method followed by annealing and mechanical treatment. The subsequent encapsulation of the samples by silica led to colloidally stable suspensions in water. The single phase character of the cores was confirmed by x-ray powder diffraction while detailed studies of the coated products by transmission electron microscopy and x-ray photoelectron spectroscopy showed that the silica shell had a thickness of at least 5xa0nm. The dc magnetic measurements were employed in order to determine the concentrations of magnetic particles in suspensions and to analyse the distribution of blocking temperatures. The heating efficiency of the nanoparticles was studied simultaneously by means of magnetic and calorimetric measurements in various ac fields. Specifically, the magnetic losses were calculated from the ac hysteresis loops while the heating effect of the nanoparticles was determined by measuring the time dependence of the temperature of their suspensions. The evaluation of the heating power from the latter experiments was supplemented by deriving the corrections for non-adiabatic properties of the calorimeter. More accurate results enabled detailed analysis and comparison with data published for other heating agents.

Distribution of cations in nanosize and bulk Co–Zn ferrites

The structural and magnetic properties of Co(1-x)Zn(x)Fe2O4 ferrites (Co-Zn ferrites) are investigated in a narrow compositional range around x = 0.6, which is of interest because of applications in magnetic fluid hyperthermia. The study by x-ray and neutron diffraction, Mössbauer spectroscopy and magnetization measurements is done on nanoparticles prepared by the coprecipitation method and bulk samples sintered at high temperatures. In spite of the known preference of Zn2+ for tetrahedral (A) sites and Co2+ for octahedral [B] sites, the cations are distributed nearly evenly over the two sites of spinel structure and there is also a variable number of [B] site vacancies (see text), making cobalt ions trivalent. In particular for x = 0.6, the cationic distribution is refined to [Formula: see text] and [Formula: see text] for the 13 nm particles (T(C) = 335 K) and bulk sample (T(C) = 351 K), respectively.

Fluorescent magnetic nanoparticles for cell labeling: Flux synthesis of manganite particles and novel functionalization of silica shell

Novel synthetic approaches for the development of multimodal imaging agents with high chemical stability are demonstrated. The magnetic cores are based on La0.63Sr0.37MnO3 manganite prepared as individual grains using a flux method followed by additional thermal treatment in a protective silica shell allowing to enhance their magnetic properties. The cores are then isolated and covered de novo with a hybrid silica layer formed through the hydrolysis and polycondensation of tetraethoxysilane and a fluorescent silane synthesized from rhodamine, piperazine spacer, and 3-iodopropyltrimethoxysilane. The aminoalkyltrialkoxysilanes are strictly avoided and the resulting particles are hydrolytically stable and do not release dye. The high colloidal stability of the material and the long durability of the fluorescence are reinforced by an additional silica layer on the surface of the particles. Structural and magnetic studies of the products using XRD, TEM, and SQUID magnetometry confirm the importance of the thermal treatment and demonstrate that no mechanical treatment is required for the flux-synthesized manganite. Detailed cell viability tests show negligible or very low toxicity at concentrations at which excellent labeling is achieved. Predominant localization of nanoparticles in lysosomes is confirmed by immunofluorescence staining. Relaxometric and biological studies suggest that the functionalized nanoparticles are suitable for imaging applications.

Magnetic La1−xSrxMnO3 nanoparticles as contrast agents for MRI: the parameters affecting 1H transverse relaxation

Magnetic nanoparticles of the La1−xSrxMnO3 perovskite phase (xxa0=xa00.20–0.45) were synthesized by a sol–gel method followed by thermal and mechanical treatments. The particles were coated with a uniform silica shell, and differential centrifugation yielded a product with high colloidal stability in water. X-ray powder diffraction (XRD) data showed that the mechanical processing did not affect the lattice parameters of the magnetic cores but only reduced their mean size dXRD. The magnetic properties of the bare particles were mainly controlled by the chemical composition and were also affected by the size of the particles. Subsequent silica coating led to an effective decrease in magnetization. Relaxometry measurements were focused primarily on colloids using magnetic cores of the same size (dXRDxa0≈xa020xa0nm) and different compositions, and coated with a shell measuring approximately 20xa0nm in thickness. The exceedingly high transverse relaxivities [r2(20xa0°C)xa0=xa0290–430xa0s−1xa0mmol−1xa0L at B0xa0=xa00.5xa0T] of the samples exhibited pronounced temperature dependence and correlated very well with the magnetic data. Additional samples differing in the size of the cores and silica shell thickness were prepared as well to analyze the effect of the particles on 1H transverse relaxation. The results suggest that the dominant regime of transverse relaxation is the static dephasing regime.

Anilinium dihydrogen phosphate

The triclinic structure of the title compound, C(6)H(8)N(+)·H(2)PO(4)(-), with three symmetry-independent structural units (Z = 3), is formed of separate organic and inorganic layers alternating along the b axis. The building blocks of the inorganic layer are deformed H(2)PO(4) tetrahedra assembled into infinite ladders by short and hence strong hydrogen bonds. The anilinium cations forming the organic layer are not hydrogen bonded to one another, but they are anchored by four N-H···O crosslinks between the dihydrogen phosphate chains of adjacent ladders. Two H atoms of each -NH(3) group then form one normal and one bifurcated N-H···O hydrogen bond to the P=O oxygens of two tetrahedra of one chain, while the third H atom is hydrogen bonded to the nearest O atom of an adjacent chain belonging to another dihydrogen phosphate ladder.