ESR study of europium ions in hydrolyzed CaF2: Eu crystals

Oxidation and reduction processes of europium ions in CaF₂ were studied by optical and ESR methods. Europium ions can be readily oxidized from the divalent to the trivalent states by heat-treatment above 600°C in a moist air atmosphere. The conversion can be well approximated by first order kinetics with an activation energy of 0.75 eV.

The reverse conversion from the trivalent to the divalent states can be accomplished by exposure to ionizing X-ray radiation. However, those reduced europium ions are thermally unstable and bleached completely by heating to 200°C. The decay process by low temperature annealing also follows first order kinetics with an activation energy of 0.60 eV. The conversions between the two states are explained by electron transfer.     

Spontaneous formation of a plasma hole in a rotating magnetized plasma: a giant burgers vortex in a compressible fluid

Spontaneous formation of a cylindrical density cavity, or "plasma hole," has been observed in a rotating magnetized plasma. Density of the plasma hole is one-tenth of that of ambient plasma and is bounded by a steep transition layer of the order of several ion Larmor radii. The flow velocity field associated with the plasma hole is experimentally determined, exhibiting a monopole vortical structure. It is found that the vorticity distribution is localized near the center of the hole and is identified as a Burgers vortex. This is the first experimental observation of a Burgers vortex in a plasma.     

The improved synthesis of OPC-29030, a platelet adhesion inhibitor via diastereoselective oxidation of chiral non-racemic sulfide

An improved synthetic route of OPC-29030, the platelet adhesion inhibitor, was established via the diastereoselective oxidation of a chiral non-racemic sulfide (R)-5 to (S(S))-6 by the catalytic oxidation using VO(acac)(2) and cumene hydroperoxide (CHP) in the presence of MS4A. Under the current condition, the diastereoselectivity was not influenced by the presence of moisture, and moderate to high selectivity (72% de) was obtained at -30 degrees C. The obtained sulfoxide, which diastereomeric excess was easily raised by the recrystallization, could successfully lead to OPC-29030.     

Base-catalyzed endo-mode cyclization of allenes: easy preparation of five- to nine-membered oxacycles

A reliable and efficient procedure for constructing five- to eight-membered oxacycles has been developed. Allenes with both a phosphoryl group and a suitable delta-hydroxyalkyl side chain at the C1-position underwent an endo mode ring-closing reaction to give five- to seven-membered oxacycles. Changing the phosphoryl group to a phosphono functionality facilitated the preparation of eight-membered congeners. Introduction of a cis double bond to the alkyl side chain of the starting allenes made possible the easy formation of medium-sized oxacycles, such as the dihydrooxocin and tetrahydrooxonin frameworks, regardless of the electron-withdrawing group (POPh2, PO(OEt)2, SOPh, and SO2Ph) at the C1-position.     

Magnetic behavior of tetrakis[4-(N-tert-butyl-N-oxylamino)pyridine]bis(isocyanato-N)cobalt(II) in frozen solution

A complex of cobalt(II)(OCN)(2) coordinated with four pyridines having a stable tert-butyl aminoxyl exhibited in frozen MTHF a slow magnetic relaxation for the reorientation of magnetization with activation barrier, Delta/k(B) = 50 K, and a hysteresis loop having a fast relaxation at 0 Oe below 2.5 K.     

Isolation of equatorial conformers of chloro- and bromocyclohexane in a pure state as inclusion complexes with a host compound

The equatorial conformers of chloro- and bromocyclohexane were isolated in a pure state as inclusion complexes with a host compound, and their structures were studied by IR spectra and X-ray analysis.     

N-substituent effect on the cis-trans geometry of nine-membered lactams

The cis-trans geometry of a nine-membered lactam significantly depends on the N-substituents; N-acyl-1-aza-2-cyclononanones (1a-c) exist as cis form; in contrast, N-Z- 1-aza-2-cyclononanone (1d) exists as trans form both in the crystal and in solution.