Structural and conformational studies on citreoviridinol and isocitreoviridinol: syntheses of some 2,6-dioxabicyclo[3.2.1]octanes

Isocitreoviridinol has been newly isolated from the mycelium of $\text{Penicillium citreo-viride}$ B. (IFO 6050) together with citreoviridinol, and their stereostructures have also been elucidated by means of chemical method: the 2,6-dioxabicyclo[3.2.1]octanes have been made, one of which is regarded as a promising synthetic intermediate of citreoviridinol. In addition, isocitreoviridinol diacetate has been derived from citreoviridin in 3 steps.     

Determination of peptide φ angles in solids by relayed anisotropy correlation NMR

A solid state NMR method is presented for determination of a backbone dihedral angle φ in peptides, being based on the previously reported method, relayed anisotropy correlation (RACO) NMR [Y. Ishii et al., Chem. Phys. Lett. 256 (1996) 133]. In the present method, the and the dipolar tensors in the system are two-dimensionally (2D) correlated via polarization transfer from to under magic angle spinning (MAS). This method was applied to N-acetyl , -valine, and the H–C–N–H dihedral angle was determined to be 154.0±1.4° or 206.0±1.4°, the former agreeing with the X-ray value of 154±5°.     

The stereochemistry of 4-methyl-6-phenyl-5,6,7,8-tetrahydro-4H-1,3,2,6-dioxathiazocine 2-oxides using NMR

Two isomeric 4-methyl-6-phenyl-5,6,7,8-tetrahydro-4H-1,3,2,6-dioxathiazocine 2-oxides were prepared, and their pmr and cmr spectra were examined. From the aromatic solvent shielding values and the magnitudes of the γ shifts, the title compounds are found to exist in the trans and cis forms in solution.     

Magnetic moments of isomeric levels in the Br-isotopes measured with in-beam NMR-PAC

The γ-ray angular correlation of the 9/2⁺, 37 μs state in⁸¹Br and of the 181 keV, 120 μs state in⁷⁸Br was disturbed by nuclear magnetic resonance. Theg-factors were determined to be ¦g¦=1.297±0.015 for the 37 μs level in⁸¹Br and ¦g¦=1.025±0.003 for the 120 μs state in⁷⁸Br.     

NMR studies on polarized12B implanted in highly oriented pyrolytic graphite

NMR measurements on¹²B nuclei implanted in a thin sheet of highly oriented pyrolytic graphite (Grafoil) have been made to study the magnitude of the polarization of¹²B and its electric quadrupole coupling. The magnitude of the residual polarization of¹²B held in carbon material is of crucial importance to the experiment measuring the average polarization of¹²B produced in the muon capture by¹²C. It was found that the polarization of¹²B can be maintained at 101.0±2.2% in Grafoil under a magnetic field of 3 kG. The electric quadrupole coupling was determined to bee ² qQ/h=+1207.3±8.2 kHz. From the magnitude and the sign of the electric field gradienteq, the location of¹²B was found to be a substitutional site in the carbon lattice. The anomalous B-C bond involving thesp ₂ hybrid orbitals with partially filledp _z electrons is also discussed.     

Air-assisted addition of grignard reagents to olefins. A simple protocol for a three-component coupling process yielding alcohols

Silylmethyl, tertiary-alkyl, alkenyl, and aryl Grignard reagents underwent intermolecular addition to olefins, such as styrenes, conjugated dienes, and enynes under an air atmosphere to give homologated alcohols. For example, (trimethylsilyl)methylmagnesium chloride and alpha-methylstyrene in ether at room temperature under dry air directly furnished 2-phenyl-4-(trimethylsilyl)-2-butanol in good yield. As the Grignard addition to olefins under argon with rigorous exclusion of O2 did not proceed at all, the above reaction should involve a radical mechanism: an alkyl radical generated by the aerial oxidation of the Grignard reagent adds to olefin, which is followed by oxygenation. Representative examples of this transformation, where products were obtained in good to excellent diastereo- or regioselectivity, are also disclosed.     

Thermal neutron calibration method using an intense neutron beam from JRR-3M

We have developed a thermal neutron calibration method using a reactor produced neutron beam in JRR-3M of the Japan Atomic Energy Agency. Neutron-induced prompt gamma ray analysis has usually been performed in this beam line. Neutron energy distributions with negligible contributions from epithermal neutrons were measured by a time-of-flight method with a chopper made of ⁶LiF powder. The thermal neutron flux was determined by a gold foil activation method. We found that the thermal neutron beam in JRR-3M was well suited for calibration, neutron detector development or neutron dosimetry.     

Pulse laser ablation at water–air interface

We studied a new pulse laser ablation phenomenon on a liquid surface layer, which is caused by the difference between the refractive indices of the two materials involved. The present study was motivated by our previous study, which showed that laser ablation can occur at the interface between a transparent material and a gas or liquid medium when the laser pulse is focused through the transparent material. In this case, the ablation threshold fluence is reduced remarkably. In the present study, experiments were conducted in water and air in order to confirm this phenomenon for a combination of two fluid media with different refractive indices. This phenomenon was observed in detail by pulse laser shadowgraphy. A high-resolution film was used to record the phenomenon with a Nd:YAG pulse laser with 10-ns duration as a light source. The laser ablation phenomenon on the liquid surface layer caused by a focused Nd:YAG laser pulse with 1064-nm wavelength was found to be followed by the splashing of the liquid surface, inducing a liquid jet with many ligaments. The liquid jet extension velocity was around 1000 m/s in a typical case. The liquid jet decelerated drastically due to rapid atomization at the tips of the ligaments. The liquid jet phenomenon was found to depend on the pulse laser parameters such as the laser fluence on the liquid surface, laser energy, and laser beam pattern. The threshold laser fluence for the generation of a liquid jet was 20 J/cm². By increasing the incident laser energy with a fixed laser fluence, the laser focused area increased, which eventually led to an increase in the size of the plasma column. The larger the laser energy, the larger the jet size and the longer the temporal behavior. The laser beam pattern was found to have significant effects on the liquid jet’s velocity, shape, and history.