Synthesis of aminocyclohexitol via carbon-carbon bond-forming radical cyclization of oxime ether

The stannyl radical mediated-cyclization of oxime ether, derived from D-glucose, gave the aminocyclohexitol derivative. Stereoselective C-C bond forming cyclization proceeded via favorable conformers minimizing A(1,3)-strain between the oxime ether group and alpha-substituents.     

Electron-transfer mechanism in radical-scavenging reactions by a vitamin E model in a protic medium

The scavenging reaction of 2,2-diphenyl-1-picrylhydrazyl radical (DPPH.) or galvinoxyl radical (GO.) by a vitamin E model, 2,2,5,7,8-pentamethylchroman-6-ol (1H), was significantly accelerated by the presence of Mg(ClO4)2 in de-aerated methanol (MeOH). Such an acceleration indicates that the radical-scavenging reaction of 1H in MeOH proceeds via an electron transfer from 1H to the radical, followed by a proton transfer, rather than the one-step hydrogen atom transfer which has been observed in acetonitrile (MeCN). A significant negative shift of the one-electron oxidation potential of 1H in MeOH (0.63 V vs. SCE), due to strong solvation as compared to that in MeCN (0.97 V vs. SCE), may result in change of the radical-scavenging mechanisms between protic and aprotic media.     

Quantitative measurements of oxidative stress in mouse skin induced by X-ray irradiation

To find efficient methods to evaluate oxidative stress in mouse skin caused by X-ray irradiation, several markers and methodologies were examined. Hairless mice were irradiated with 50 Gy X-rays and skin homogenates or skin strips were prepared. Lipid peroxidation was measured using the skin homogenate as the level of thiobarbituric acid reactive substances. The level of lipid peroxidation increased with time after irradiation and was twice that of the control at 78 h. ESR spectra of skin strips showed a clear signal for the ascorbyl radical, which increased with time after irradiation in a manner similar to that of lipid peroxidation. To measure levels of glutathione (GSH) and its oxidized forms (GSSG) simultaneously, two HPLC methods, sample derivatization with 1-fluoro-2,4-dinitrobenzene and detection with a UV detector (method A) and no derivatization and detection with an electrochemical detector (method B), were compared and the latter was found to be better. No significant change was observed within 24 h after irradiation in the levels of GSH and GSSG measured by method B. The GSH/GSSG ratio may be a less sensitive parameter for the evaluation of acute oxidative stress caused by X-ray irradiation in the skin. Monitoring the ascorbyl radical seems to be a good way to evaluate oxidative stress in skin in vivo.     

A convenient procedure for palladium catalyzed cyanation using a unique bidentate phosphorus ligand

A palladium complex bearing 1,2-diphenyl-3,4-diphosphinidenecyclobutene ligand (DPCB) has been used to facilitate the catalytic cyanation of aryl bromides. A series of substituted benzonitriles was prepared in good to high yields by the treatment of the corresponding aryl bromides with Zn(CN)₂ in N-methyl-2-pyrrolidone in the presence of 2-4 mol % catalyst at 100 °C for 16 h.     

Solid-phase tandem radical addition-cyclization reaction: triethylborane-induced reaction of oxime ethers anchored to polymer support

Tandem radical addition-cyclization of oxime ethers anchored to polymer support was studied. The reaction of oxime ethers with stannyl radical proceeded effectively by the use of triethylborane as a radical initiator. The alkyl radical addition-cyclization reactions of oxime ether connected with alpha,beta-unsaturated carbonyl group proceeded under iodine atom-transfer reaction conditions to give the functionalized azacycles via two carbon-carbon bonds-forming process.     

Historical review on research of kinetics in thermal analysis and thermal endurance of electrical insulating materials

Thermal analysis techniques, such as thermogravimetry, differential thermal analysis and evolved gas analysis, have been applied to thermal endurance evaluation of electrical insulating materials of high polymers, which are used for a long time at a relatively high operating temperature. Various attempts have been made to estimate the life time of the materials at the operating temperature by thermal analysis and a calorimetric method. These are critically described in this review paper.     

A column gel electrophoresis-coupled genomic DNA subtractive hybridization technique

We have developed a DNA subtractive hybridization technique especially designed for mammalian genome comparison. The core of this protocol is a newly devised denaturant-containing polyacrylamide gel formed in a glass-column. In this gel system, the following DNA manipulation steps are carried out sequentially: size separation by electrophoresis, heat-denaturation, renaturation, and recovery. In the first step, a mixture of tester and driver DNA fragments are segregated according to their size whilst keeping their double-stranded forms. This reduces the complexity of the original genomic DNA fragments and also segregates DNA fragments having closely related sequences. In the second step, fractionated DNA fragments are quickly denatured and subjected to successive subtractive hybridization in situ by controlling gel temperature in a water bath. In the third step, DNA fragments are recovered by electrophoresis towards the reverse-orientation and are adsorbed onto ion-exchange beads. Two lines of experiments show that our protocol is able to highly enrich or directly extract differences among genomic DNA samples.     

Investigation of latent heat-thermal energy storage materials. I. Thermoanalytical evaluation of modified polyethylene

Differential scanning calorimetry is used to evaluate polyethylene for latent heat-thermal energy storage. Polyethylene is a suitable material from the points of view of latent heat, behavior of melting and crystallization, and material cost. The thermal stability is satisfactory when it is used in a closed system with heat transfer media, such as silicone oil, alkyldiphenyl, alkyldiphenylethane, Caloria HT and ethylene glycol, which shield polyethylene from air. Surface-crosslinking by ion bombardment prevents polyethylene from mutual adhesion and it retains its form after melting. Surface-crosslinked polyethylene with silicone oil or ethylene glycol is the most promising, while the heat transfer media, such as alkyldiphenyl, alkyldiphenylethane and Caloria HT, which dissolve polyethylene, decrease the melting point, but have little effect on the latent heat and sharp DSC peaks of melting and crystallization. Thus, the composite of polyethylene with these media can also be used at an adjusted and desirable operating temperature.     

Beta-NMR detection of beta-emitting fragment43Ti

NMR on the beta emitter⁴³Ti has been observed by use of the -NMR technique. From the observed NMR spectrum, the magnetic moment of⁴³Ti was determined to be || =0.85±0.02 µ_N. The value is significantly quenched from the single particle value –1.91 µ_N, which shows a strong effect resulting from meson-exchange currents andconfiguration mixing.