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.

Core-shell La(1-x)Sr(x)MnO3 nanoparticles as colloidal mediators for magnetic fluid hyperthermia.

Core-shell nanoparticles consisting of La(0.75)Sr(0.25)MnO(3) cores covered by silica were synthesized by a procedure consisting of several steps, including the sol-gel method in the presence of citric acid and ethylene glycol, thermal and mechanical treatment, encapsulation employing tetraethoxysilane and final separation by centrifugation in order to get the required size fraction. Morphological studies revealed well-separated particles that form a stable water suspension. Magnetic studies include magnetization measurements and investigation of the ferromagnetic-superparamagnetic-paramagnetic transition. Magnetic heating experiments in 'calorimetric mode' were used to determine the heating efficiency of the particles in water suspension and further employed for biological studies of extracellular and intracellular effects analysed by tests of viability.

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.

Sr-hexaferrite/maghemite composite nanoparticles-possible new mediators for magnetic hyperthermia.

Composite nanoparticles with variable ratios of M-type Sr-hexaferrite and maghemite phases were prepared via the sol-gel method employing polyvinylalcohol as the stabilizing agent, followed by thermal treatment at 600 °C for 32-190 min. The measurements in static magnetic field revealed considerable variation of the coercivity and remanence depending on the relative content of the highly magnetically anisotropic Sr-hexaferrite phase. Calorimetric heating experiments were carried out on aqueous gel suspensions under an alternating magnetic field of maximum amplitude H(max) = 15.1-68.4 kA m(-1) and frequency ν = 108 kHz. They showed a strong dependence of the heating efficiency on the coercivity and remanence of the composites, with a specific absorption rate (SAR) value ranging from units to tens of W/g(Fe(ferrimagnetic)).

Can ACG serve as an initiation codon for protein synthesis in eucaryotic cells?

An ACG codon, which replaces the AUG codon used to initiate the synthesis of bacteriophage T7 gene 0.3 protein, was shown to function as a low-efficiency initiation codon in a wheat germ cell-free protein-synthesizing system.

Mutations of bacteriophage T7 that affect initiation of synthesis of the gene 0.3 protein.

Two different mutations that greatly diminish the rate of synthesis of the gene 0.3 protein of bacteriophage T7 have been characterized. One is in the initiator triplet for the 0.3 protein, changing it from AUG to ACG. This mutation was found to have little effect on binding of ribosomes to the 0.3 mRNA in vitro, although 0.3 protein synthesis was greatly depressed in vitro as well as in vivo. A suppressor mutation that partially restores the wild-type rate of synthesis was found to lie within the 0.3 RNA but not close to the mutant ACG (more than 64 nucleotides away). The second mutation is a G-to-A transition located 11 bases to the 5' side of the initiator AUG. This change eliminates a possible five-base pairing with a sequence near the 3' end of 16S ribosomal RNA, an interaction previous workers have proposed to be important for initiation of protein synthesis. This mutation causes the site of ribosome binding to shift about 15 bases to the 3' side, centering on an internal AUG, but this new site has only a poor potential interaction with 16S RNA. A suppressor mutation that restores the rate of 0.3 protein synthesis to essentially wild-type levels and also restores wild-type ribosome-binding behavior was found to lie adjacent to the original mutation, creating a new four-base complementarity with 16S RNA. These results provide strong support for the idea that a pairing interaction between mRNA and 16S RNA is involved in specific initiation of protein synthesis in Escherichia coli and indicate that this interaction may be important in selecting the site in mRNA at which the ribosomes bind.