ESR studies on the formation of p-benzosemiquinone anions over manganese dioxide

The reaction between a hydroquinone aqueous solution and manganese dioxide has been investigated by electron paramagnetic resonance spectroscopy. A very stable p-benzosemiquinone anion is formed when an aqueous solution of hydroquinone is passed through a column of manganese dioxide. The kinetics for the reaction between hydroquinone and manganese dioxide follow the equation where A₀ is the initial concentration of hydroquinone, C is the concentration of p-benzosemiquinone anions, W is the amount of manganese dioxide, F is the feed rate of a hydroquinone aqueous solution, and k₁⁰ and k₂⁰ are constants; k₁⁰ = 3.1 × 10^?2 (cm³/g MnO₂· min), k₂⁰ = 3.2 (cm³/g MnO₂·min). A mechanism for the reaction is proposed such that Mn(IV) in manganese dioxide is reduced to Mn (II) with hydroquinone from which the semiquinone anion is formed via a neutral semiquinone. The formation of semiquinone anions from several substituted hydroquinones is also discussed.     

Subwavelength optical imaging through a metallic nanorod array

We propose a subwavelength imaging system without a lens or a mirror but with an array of metallic nanorods. The near-field components of dipole sources were plasmonically transferred through the rod array to reproduce the source distribution in the other side. We calculated the field distribution at the different planes of imaging process using the finite-difference time-domain algorithm and found that the spatial resolution was 40 nm given by the rod size and spacing. A typical configuration is a hexagonal arrangement of silver rods of 50 nm height and 20 nm diameter. We also show that the image formation highly depends on the coherence and the polarization of the source distribution and the source-array distance.     

Direct observation of excitons and a continuum of one-dimensional Mott insulators: a reflection-type third-harmonic-generation study of Ni-halogen chain compounds

The third-harmonic-generation (THG) spectrum was measured for a NiBr-chain compound, which is a one-dimensional Mott insulator, in a reflection configuration. A sharp peak and a shoulder structure in the THG spectrum are attributed to three-photon resonance to an exciton and a continuum, respectively. The band-edge energy, the exciton binding energy, and the spectral weights for the exciton and the continuum were determined from comparative studies of linear absorption, THG, and electroreflectance spectra. The excitonic effect is more pronounced in the NiCl chain than in the NiBr chain.     

Evolution of the Hall coefficient and the peculiar electronic structure of the cuprate superconductors

Although the Hall coefficient R(H) is an informative transport property of metals and semiconductors, its meaning in the cuprate superconductors has been ambiguous because of its unusual characteristics. Here we show that a systematic study of R(H) in La2-xSrxCuO4 single crystals over a wide doping range establishes a qualitative understanding of its peculiar evolution, which turns out to reflect a two-component nature of the electronic structure caused by an unusual development of the Fermi surface recently uncovered by photoemission experiments.     

Oligocyclization of 2-(hydroxymethyl)pyrroles with electron-withdrawing groups at beta-positions: formation and structural elucidation of porphyrinogens and hexaphyrinogens

Acid-catalyzed oligomerization of 2-(hydroxymethyl)pyrroles bearing C6F5, 2,6-Cl2C6H3, CF3 and CO2Et groups at beta-positions was examined. The reaction of ethyl pyrrole-3-carboxylates gave a mixture of oligomers and type I isomers of porphyrinogens and hexaphyrinogens were isolated when the other beta-substituents were sufficiently bulky, for example, mesityl, 2,6-Cl2C6H3 and C6F5 groups. On the other hand, the pyrroles having other electron-withdrawing groups afforded porphyrinogens as the only isolable products.     

A new norsesquiterpenoid from Russula delica Fr

Russulanorol (1), a new norsesquiterpenoid with a novel carbon skeleton, was isolated from the fruiting bodies of Russula delica FR. (Russulaceae) together with three known sesquiterpenoids. The structure of 1 was elucidated on the basis of spectral data and chemical transformation. Compound 1 is an equilibrium mixture of two stereoisomers (1a, b) on the C-11 acetal carbon.     

In Vivo EPR Imaging of a Perfluoroalkyl Radical in Mouse Abdomen

Although it is thought that perfluoro-2,4-dimethyl-3-isopropyl-3-pentyl (PFR-2) is a candidate for electron paramagnetic resonance (EPR) imaging agents because of its high stability, no study has been made yet on the EPR imaging of PFR-2. In this study, EPR imaging of a phantom including PFR-2 and mice that had received PFR-2 was performed by an in vivo EPR imaging system operating at an EPR frequency of 700 MHz equipped with a bridged loop-gap resonator (inner diameter, 41 mm; axial length, 10 mm). Because PFR-2 is insoluble in water, it was dissolved in perfluorocarbon. The PFR-2 solution was put in cylindrical sample tubes with various inner diameters, and these sample tubes were placed together in a larger cylindrical sample tube filled with a physiological saline solution, which was used as a phantom. The spatial resolution was estimated to be about 3 mm on the basis of EPR imaging of the phantom. EPR images of mice that had received a PFR-2 injection via the intraperitoneal route indicated that PFR-2 remained in the peritoneal cavity even 2 days after the injection. This finding suggests that it is possible to perform EPR imaging of experimental animals using PFR-2 as an imaging agent which persists in a biological system. Authors' address: Hidekatsu Yokoyama, National Institute of Advanced Industrial Science and Technology, 2266-98 Anagahora, Shimoshidami, Moriyama-ku, Nagoya, Aichi 463-8560, Japan     

Epoxidation of phosphinoyl alkenes with hydrogen peroxide

The epoxidation of alkenylphosphorus compounds with hydrogen peroxide was systematically studied, revealing that while alkenylphosphine oxides failed to produce the corresponding epoxides, alkenylphosphonates, or phosphinates having a phenyl group at α-position reacted with H₂O₂/K₂CO₃ or alkenylphosphonic acids or phosphinic acids having an aliphatic group at α- or β-positions reacted with H₂O₂/Na₂WO₄/Et₃N to produce high yields of the corresponding epoxides.