Critical current density of polycrystalline YBa2Cu3O7−δ consisting of tin-coated grains

Tin and its oxides have been introduced into the intergrain areas of polycrystalline YBa₂Cu₃O_7−δ by coating the crystalline grains with a thin layer of tin and sintering the ceramics in flowing oxygen and argon. The transport critical current density J_c at 77 K in a magnetic field of 0−1.5 T is enhanced as a result of the coating. A probable improvement of the intergrain weak links is suggested.     

A possible correlation between a Jahn-Teller coupling and a Raman scattering

It has been shown how the Raman line of a degenerate vibration can be caused by a vibronic coupling in a degenerate electronic excited state. Such a vibronic coupling is known to cause a distortion in the equilibrium conformation of the molecule (Jahn-Teller distortion) from the symmetrical conformation, and the Raman scattering tensor is found to be calculated by the use of the amount (δ) of this distortion as an empirical parameter. It has been suggested that some of the Raman lines for the degenerate stretching vibrations, which become stronger with the exciting frequency, in some molecules, are caused by such Jahn-Teller couplings. For the intensity of the Raman line at 887 cm^?1 of the degenerate stretching vibration of chromate anion, a slightly more detailed examination has been made, and the amount of the Jahn-Teller distortion in a $\text{B}\text{?}$ (T₂) electronic state has been estimated to be 0.2₀ Å amu^1/2 along the normal coordinate of this vibration.     

Fluorometry of singlet oxygen generated via a photosensitized reaction using folic acid and methotrexate

A method for the fluorometry of singlet oxygen (¹O₂) using less fluorescent folic acid and its analogue, methotrexate (MTX), was examined. Folic acid and MTX were decomposed into a strongly fluorescent pteridine compound via a photosensitized reaction by ¹O₂-generating photosensitizers in a deuterium oxide solution. The fluorescence intensity increased in proportion to the irradiation time or the number of photons absorbed by the photosensitizer. This method using the fluorescence enhancement of these folic acid analogues can be applied to determine the quantum yield of ¹O₂ generated through a photosensitized reaction in deuterium oxide. The background fluorescence of MTX is quite smaller than that of folic acid, indicating that MTX can be used for the more sensitive detection of ¹O₂. Figure (DOC 37.0 KB)     

Polarized fluorescence excitation spectra of adenines

Polarized fluorescence excitation spectra of adenine and N⁶,N⁶-dimethyladenosine, in glassy ethanol solution at 77 K, reveal the existence of the third weak ππ^* transition at about 220 nm, which has been expccted theoretically, but not so far confirmed experimentally. Relative directions between ππ^* transition moments are discussed.     

Chaotic behavior in the Onchidium giant neuron under sinusoidal stimulation

The nonperiodic firing of the Onchidium giant neuron under sinusoidal stimulation is investigated. Attractors obtained stroboscopically show that state points on the attractor are mixed by the baker's transformation. The transition function with period three suggests that the nonperiodic oscillation is chaotic.     

Immobilization of a Bacterial Cytochrome P450 Monooxygenase System on a Solid Support

Bacterial cytochrome P450s (P450s), which catalyze regio‐ and stereoselective oxidations of hydrocarbons with high turnover rates, are attractive biocatalysts for fine chemical production. Enzyme immobilization is needed for cost‐effective industrial manufacturing. However, immobilization of P450s is difficult because electron‐transfer proteins are involved in catalysis and anchoring these can prevent them from functioning as shuttle molecules for carrying electrons. We studied a heterotrimeric protein‐mediated co‐immobilization of a bacterial P450, and its electron‐transfer protein and reductase. Fusion with subunits of a heterotrimeric Sulfolobus solfataricus proliferating cell nuclear antigen (PCNA) enabled immobilization of the three proteins on a solid support. The co‐immobilized enzymes catalyzed monooxygenation because the electron‐transfer protein fused to PCNA via a single peptide linker retained its electron‐transport function.     

Site-selective and stepwise complexation of two M(cod)+ (M = Rh,Ir) fragments with calix[4]arene

The reaction of [(cod)M(mu-OMe)]2 (M = Rh, Ir; cod = cycloocta-1,5-diene) with calix[4]arenes (LH4) in the molar ratio of 0.5-0.6:1 gave the rhodium and iridium pi-arene complexes [(cod)M(eta 6-LH3)], while that in the molar ratio of 1.1-1.5:1 (M = Rh) led to the selective formation of the dinuclear complexes [((cod)Rh)2(eta 6:eta 2-LH2)] in which one of the Rh(cod)+ fragments is coordinated by an eta 6-aryl group and the other by two phenolic oxygen atoms; the stepwise synthesis of the Rh-Ir heterobimetallic analogue of the latter complex was further achieved.     

Continuous flow system for the determination of trace boron in iron and steel utilizing in-line preconcentration/separation by Sephadex column coupled with fluorimetric detection

A simple, rapid and sensitive system for the determination of trace boron in iron and steels is presented, in which in-line separation/preconcentration of boron from iron matrix is directly coupled with fluorimetric detection in a continuous flow system. Boron was adsorbed on a small column packed with Sephadex G-25 gel, followed by elution with a small volume of dilute hydrochloric acid. The formation of boron complex with 1,8-dihydroxy-3,6-naphthalenedisulphonic acid in a continuous flow system was used for the sensitive determination of boron by fluorescence detection(lambda(ex)=314 nm and lambda(em)=355 nm). The present FIA system offers many advantages over existing methods, especially with respect to simplicity and sensitivity, permitting semi-automated determination of boron with a short analysis time (about 10 min), low limit of determination (0.1 ppm in steels) and good reproducibility (rsd<3% for 1-18 mug g(-1) boron in steels).The present FIA system can be readily applied to the steel samples.