No abstract

Co3O4 nanoparticles of 35 nm with a cauliflower-like morphology were obtained when a monolayer colloidal dispersion of dodecyl sulfate intercalated alpha-cobalt hydroxide in butanol was subjected to solvothermal hydrolytic decomposition. The nanogranular particles exhibit weakly ferromagnetic properties in contrast with both bulk and dispersed nanoparticulate Co3O4.

Nano-objects composed of metals or semiconductors are known to display interesting electronic and optical properties. To a major extent, these properties are controlled by their size, due to specific confinement effects. Equally important, as far as confinement is concerned, is the dimensionality or shape of the nano-object. Quantum dots, wires, and films are characterized by extremely different densities of electronic states and, thus, by very different optoelectronic properties unique to each shape. [1,2] Further examples of these effects include the plasmonic properties, that is, absorption and scattering properties, of nano-objects composed of noble metals such as gold. Both the size and shape control the number of plasmonic resonance bands and their location on the frequency scale. [3,4] This paper is concerned with nano-objects composed of materials which display ferromagnetism in the bulk state, such as cobalt or iron. It is well known that such materials display superparamagnetism rather than ferromagnetism if prepared as nanoparticles, [5] the relaxation time and the blocking temperature being strongly dependent on the size. Such superparamagnetic systems are of interest for a broad range of applications, for example, in drug delivery or ferrofluids. [6,7] Thus, it is not surprising that the number of papers focusing on superparamagnetic particles is very high. There are also a smaller, but increasing, number of papers that consider the ferrimagnetic and ferromagnetic properties of nanorods. One of the motivations for these studies is that they are of interest for use in high-density storage systems, in particular for perpendicular magnetic recording and also for use as sensors and spintronic devices. [8][9][10][11] Experimental findings show characteristic magnetization features such as coercive force, remanence, and a hysteresis shape that becomes anisotropic. The hysteresis properties depend on the composition of the nanorods and the presence of imperfections. [12,13] Typical investigations considered rods characterized by axial ratios of up to 10 and diameters in the 10 to 100 nm range. These systems are predicted to exhibit spontaneous spin-polarized transport of charges.[14]To prepare these rod-shaped objects a variety of methods were employed including microlithography, vapor-liquid-solid growth, and template deposition based on electrodeposition or vapor deposition. [12,15] The axial ratio is in all cases limited, and the amount of materials that can be produced is often restricted, for instance in the case of the template approaches. Also, rod handling may pose a problem due to the strong aggregation effects that are known to take place with nanorods. This aggregation, in turn, will introduce magnetic interactions between the rods, affecting the magnetization behavior considerably. The preparation of nanofibers by electrospinning offers a promising alternative.[16]During electrospinning, a strong electrical field is applied to a droplet formed by a polymer solution or polymer melt at the tip of ...

The 3d-metal mediated nitrene transfer is under intense scrutiny due to its potential as an atom economic and ecologically benign way for the directed amination of (un)functionalised CÀH bonds. Here we present the isolation and characterisation of a rare, trigonal imido cobalt(III) complex, which bears a rather long cobalt-imido bond. It can cleanly cleave strong C À H bonds with a bond dissociation energy of up to 92 kcal mol À1 in an intermolecular fashion, unprecedented for imido cobalt complexes. This resulted in the amido cobalt(II) complex [Co(hmds) 2 (NH t Bu)] À . Kinetic studies on this reaction revealed an H atom transfer mechanism. Remarkably, the cobalt(II) amide itself is capable of mediating H atom abstraction or stepwise proton/electron transfer depending on the substrate. A cobalt-mediated catalytic application for substrate dehydrogenation using an organo azide is presented.

No abstract

Superparamagnetic polymer nanofibers intended for drug delivery and therapy are considered here. Magnetite (Fe3O4) nanoparticles in the diameter range of 5-10 nm were synthesized in aqueous solution. Polymer nanofibers containing magnetite nanoparticles were prepared from commercially available poly(hydroxyethyl methacrylate), PHEMA, and poly-L-lactide (PLLA) by the electrospinning technique. Nanofibers with diameters ranging from 50 to 300 nm were obtained. Nanofibers containing up to 35 wt % magnetite nanoparticles displayed superparamagnetism at room temperature. The blocking temperature was about 50 K for an applied field of 500 Oe, and the saturation magnetization was 3.5 emu g(-1) and 1.1 emu g(-1) for Fe3O4/PHEMA and Fe3O4/PLLA nanofibers, respectively, and depended on the amount of Fe3O4 nanoparticles in the nanocomposites. To test such magnetic nano-objects for applications as drug carriers and drug-release systems we incorporated a fluorescent albumin with dog fluorescein isothiocyanate (ADFI).

No abstract

This is an electronic reprint of the original article. This reprint may differ from the original in pagination and typographic detail.