Transverse magnetoresistance and Hall effect in p-type tellurium in strong magnetic fields

Galvanomagnetic effects in tellurium with carrier concentrations ranges from 10¹⁴ ∽7×10¹⁵cm^-3 were measured at liquid helium temperatures in intense magnetic fields up to 90 kOe. In slightly doped crystals, whose carrier concentrations were about 3 ∽ 7 × 10¹⁵cm^-3, the magnetic field dependences of the Hall coefficient and the transverse magnetoresistance were found to be different from those in purer crystals. The results can be explained by assuming the existence of an impurity band and by taking into account the complicated structure of the Landau levels.     

Time-resolved total internal reflection fluorescence spectroscopy of polymer films

Using total internal reflection, the possibility of a subnanosecond fluorescence spectroscopy for elucidating photophysical and photochemical processes of polymer surface is demonstrated. The thickness which can be studied under the present experimental conditions is of the order of 0.01 μm.     

Molecular probe for a fluorous medium: long-lived phosphorescence of alpha-diketones in perfluoromethylcyclohexane at room temperature.

We found that alpha-diketones (2,3-butanedione (BD) and 1-phenyl-1,2-propanedione (PPD)) were very suitable luminescence probes for studying the properties of a perfluorinated solvent (i.e., fluorous solvent; perfluoromethylcyclohexane (PFMC)), since these compounds were soluble in PFMC and showed long-lived phosphorescence even at room temperature. The phosphorescence lifetime (tau(p)) of BD in PFMC (650 micros) was much longer than that in cyclohexane (CH, 270 micros). The longer tau(p) value of BD in PFMC was ascribed to the variation of the intersystem crossing rate constant (k(isc)) from the excited triplet state (T1) to the ground state (S0) with the solvent. Some possible reasons for the change in k(isc) were discussed in terms of solute-solvent interactions. Furthermore, by utilizing phosphorescence quenching of BD by pyrene, we, determined a rate constant of the diffusion-controlled reaction in PFMC. Characteristic behaviors of mixing/separation processes between PFMC and a common organic solvent observed by Schlieren photographs were also reported.     

A new synthesis of 7-substituted 2,3-bis(alkylthio)naphth[1,8-bc]-azepines using the tris(alkylthio)cyclopropenyl cation

7-Substituted 2,3-bis(isopropylthio)naphth[1,8-bc]azepines 3a-c were synthesized in good yields by the reactions of 5-substituted 1-naphthylamines 2a-c with tris(isopropylthio)cyclopropenylium perchlorate ( 1 ) in acetonitrile under reflux. This reaction proceeds through the facile ring opening of 1 , followed by the intermediary formation of iminium salts 5a-c and then intramolecular cyclization.     

Quantitative analysis of original and powdered rocks and mineral inclusions by laser ablation inductively coupled plasma mass spectrometry

Direct analysis of rocks by laser ablation inductively coupled plasma mass spectrometry is described. Both powdered standard rocks and the original rocks were analysed and the results agreed with each other in spite of the difference in the surface states. Microprobe analysis of biotite in granite JG1 was also done directly with a focused laser beam and the results obtained were very close to the solution values given by the conventional aqueous method using biotite separated from an original rock. For quantitative analysis, the measured signal intensity was normalized either by the ablated weight or the barium signal intensity. Forty-two major and minor elements (two of them being used as internal standards) in twelve standard rocks fromt the igneous rock series of the Geological Survey of Japan were determined successfully.     

Novel enhancement of the reducing ability of ytterbium diiodide by irradiation with near-UV light

Irradiation with near-UV light, dramatically enhances the reducing ability of ytterbium diiodide (YbI₂). Organic bromides, iodides, tosylates, and tellurides are reduced efficiently by a YbI₂-hv system, while these can not be reduced with YbI₂ in the dark.     

Exciton and magneto-absorption in tellurium

Infrared magneto-absorption has been investigated in tellurium crystals in magnetic fields up to 45 koe at liquid helium temperatures. When the magnetic field was applied parallel or perpendicular to the c-axis, oscillatory absorptions with many transmission minima involving the exciton absorption were observed. The results were analysed taking into account the complicated structure of the valence band.     

Stereospecific synthesis of chiral precursors of thienamycin from L-Threonine

L-Threonine was transformed, stereospecifically, to a versatile β-lactam (5a) in 3 steps. This β-lactam was further converted to a key intermediate (25) for the synthesis of thienamycin and its biologically active analogues. Furthermore, the compound 5a was changed to iodides (18 and 23), cyanides (19 and 24), chloromethylketone (26) and aldehydes (30 and 31) which appear to have a latent potential as precursors for the syntheses of the carbapenems.