Magnetic and resonance properties of ferrihydrite nanoparticles doped with cobalt

Powders of undoped ferrihydrite nanoparticles and ferrihydrite nanoparticles doped with cobalt in the ratio of 5: 1 have been prepared by hydrolysis of 3d-metal salts. It has been shown using Mössbauer spectroscopy that cobalt is uniformly distributed over characteristic crystal-chemical positions of iron ions. The blocking temperatures of ferrihydrite nanoparticles have been determined. The nanoparticle sizes, magnetizations, surface anisotropy constants, and bulk anisotropy constants have been estimated. The doping of ferrihydrite nanoparticles with cobalt leads to a significant increase in the anisotropy constant of a nanoparticle and to the formation of surface rotational anisotropy with the surface anisotropy constant K _u = 1.6 × 10^–3 erg/cm².     

Crystal structure and electronic spectrum of SnS2

It is shown that layered metal dichalcogenides are quasi-one-dimensional molecular crystals and form a new class of crystal structures — molecular close packed. Since the minimum structural unit in these crystals is a monomolecular layer, using the symbols employed in atomic close packing to describe them gives a mistaken representation of their structure and symmetry. A new system of notation is proposed which provides complete and exact information about the ordering of the atomic layers in different polytype modifications and about their symmetries. It is found that in molecular close packing and, especially, in tin disulfide, there is not one (as in atomic close packing), but two, simplest structures, 1T and 1H, containing one molecule each in a unit cell and, therefore, two series of superlattices constructed on their basis. An energy model is constructed for the natural superlattice in tin disulfide crystals and the electronic spectra of the 2H, 4H, and 9R polytype modifications are calculated in the Kronig-Penney approximation with rectangular potential barriers as superstructure perturbations of the simplest structures. These results make it possible to explain the observed complicated dependence of the band gaps of these crystals on polytype structure. Fiz. Tverd. Tela (St. Petersburg) 40, 1712–1718 (September 1998)     

Synthesis of oligosaccharides related to the HNK-1 antigen. 5. Synthesis of a sulfo-mimetic of the HNK-1 antigenic trisaccharide

2-Aminoethyl 3,6-di-O-sulfo-β-D-glucopyranosyl-(1→3)-β-D-galactopyranosyl-(1→4)-2-acetamido-2-deoxy-β-D-glucopyranoside, which is the sulfo-mimetic of the antigenic trisaccharide HNK-1, and the corresponding monosulfates, viz., 2-aminoethyl 3-O-sulfo-and 2-aminoethyl 6-O-sulfo-β-D-glucopyranosyl-(1→3)-β-D-galactopyranosyl-(1→ 4)-2-acetamido-2-deoxy-β-D-glucopyranosides, were synthesized. 2-Azidoethyl 2,4-di-O-benzoyl-β-D-glucopyranosyl-(1→3)-2,4,6-tri-O-benzoyl-β-D-galactopyranosyl-(1→ 4)-2-acetamido-3,6-di-O-benzyl-2-deoxy-β-D-glucopyranoside served as the common precursor for the sulfated trisaccharides. This compound was synthesized according to the [2+1] pattern from monosaccharidic precursors: 3,6-di-O-acetyl-2,4-di-O-benzoyl-D-glucopyranosyl trichloroacetimidate, allyl 2-O-benzoyl-4,6-O-benzylidene-β-D-galactopyranoside, and 2-azidoethyl 2-acetamido-3,6-di-O-benzyl-2-deoxy-β-D-glucopyranoside. The structures of the glycosyl donors and glycosylation conditions were optimized for the efficient synthesis of the glucosyl-β-(1→3)-galactose disaccharide block and its subsequent transformation into the target trisaccharide sequence. Dedicated to Academician V. A. Tartakovsky on the occasion of his 75th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1593–1607, August, 2007.     

Features of the oxidative polymerization of aminothiazole in the presence of iron(III) chloride

A new conjugated polymer with semiconducting characteristics-polyaminothiazole-was obtained by oxidative polymerization of 2-aminothiazole in the presence of iron(III) chloride. A reaction scheme is proposed on the basis of the data from IR, ESR, and electronic spectroscopy. It involves the formation of an intermediate aminothiazole-FeCl₃ complex with coordination of the initiator at the nitrogen atom and subsequent oxidation of another molecule of aminothiazole by this complex with the formation of a radical-cation, leading to polymerization. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 2, pp. 91–95, March–April, 2007.     

Influence of antimony on the morphology and properties of an array of Ge/Si(100) quantum dots

The morphological features of the quantum-dot formation in the (Ge,Sb)/Si system during molecular-beam epitaxy are studied using reflection high-energy electron diffraction and atomic-force microscopy. It is found that islands obtained by simultaneous sputtering of Ge and Sb have a higher density and are more homogeneous than in the case of sputtering of pure Ge. The regularities in the island formation are discussed in terms of the theory of island formation in systems with lattice mismatch. The field-emission properties of the grown structures are studied using a scanning electron microscope. The reduced brightness of (Ge,Sb)/Si nanostructures is estimated to be B ～ 10⁵ A/(cm² sr V), which is an order of magnitude higher than the brightness of Schottky cathodes.     

Synthesis,crystal structure,and conducting properties of a new molecular metal, (<Emphasis Type="Italic">BEDO</Emphasis>)<Subscript>4</Subscript>Ni(CN)<Subscript>4</Subscript> · 4CH<Subscript>3</Subscript>CN

A new radical cation salt based on bis(ethylenedioxy)tetrathiafulvalene (BEDO) with the planesquare anion Ni(CN) ₄ ^2? is synthesized. The molecular and crystal structures of the radical cation salt are determined, and the conducting properties are investigated. In the structure, the BEDO radical cations have a β″-type packing. It is shown that the temperature dependence of the conductivity of (BEDO)₄Ni(CN)₄ · 4CH₃CN crystals exhibits metallic behavior.     

Features of the Pulsed Magnetization Switching in a High-Coercivity Material Based on ε-Fe2O3 Nanoparticles

Physics of the Solid State - The magnetic structure of the ε-Fe2O3 iron oxide polymorphic modification is collinear ferrimagnetic in the range from room temperature to ~150 K. As the...