57Fe mössbauer study of high-T c Y−Ba−Cu oxide superconductors

⁵⁷Fe Mössbauer measurements have been performed for Fe-doped YBa₂ (Cu_1-x Fe_x)₃O_7-v (x=0.005–0.10) superconducting oxides. Fe atoms mainly substitute at Cul chain sites and the fraction of Fe at Cu2 plane sites is discussed thermodynamically. The spin direction of Fe at Cu2 was determined to be normal to thec-axis using an oxygen deficient specimen having a strong texture along thec-axis. A magnetically broadened spectrum at 4.2 K for Fe at Cul is compared with a simulated one which takes the distribution of hyperfine fields into account.     

Immobilization of enzymes by radiation-induced polymerization of glass-forming monomers. double entrapping of enzymes in the presence of various additives

Immobilization of enzymes by a double entrapping method was investigated, α-Amylase was trapped by radiation-induced low temperature polymerization of 2-hydroxyethyl methacrylate after being absorbed by various inorganic additives. Drierite showed the most remarkable effect by increased enzymatic activity and decreased activity loss in batch enzyme reactions. Double entrapping of cellulase was tried by preparing an entangled mixture of enzyme and various natural polymers as additives and then polymerizing with the monomeric system at low temperatures. The composite, including enzyme-additive mixture prepared by coprecipitating and coevaporating methods, showed a considerable enhancing effect on enzymatic activity and durability in batch enzyme reactions.     

EFFECT OF CONTINUOUS FAR-RED PREIRRADIATION ON THE LAG PHASE OF CHLOROPHYLL A ACCUMULATION IN PHARBITIS NIL COTYLEDONS

In Pharbitis nil cotyledons, the lag phase of chlorophyll a (Chi a) accumulation which continues for about 2 h after the onset of continuous white light is eliminated by preirradiation with far-red light (FR) for 24 or 48 h. When the period of FR preirradiation is prolonged to 72 h or more, however, the lag phase is observed again (FR-induced lag phase) and the rate of Chi a accumulation during the rapid accumulation phase is lowered below the dark control level.
The application of exogenous 5-aminolevulinate (J-ALA) completely eliminates the FR-induced lag phase, but this treatment eliminates the normal lag phase in dark-grown cotyledons only partially (i.e. Chi a is accumulated but only slowly during the first few h). Application of a 5-ALA precursor, such as glycin + succinate. 2-ketoglutarate or glutamate, eliminates neither the FR-induced lag phase nor the normal lag phase.
A 24- or 48-h FR irradiation seems not only to enable the synthesis of 5-ALA but also to make the other regulatory factors favourable for Chi accumulation. When the period of FR irradiation is prolonged to 72 h or more, the ability to synthesize 5-ALA may be lost.     

Organofluorosilicates in organic synthesis: XV. Reaction of exo- and endo-5-norbornen-2-ylsilyl derivatives with n-bromosuccinimide. Difference in reactivity between hexacoordinate and tetracoordinate silicon compounds

The reactions of potassium 5-norbornen-2-ylpentafluorosilicate (I) and 5-norbornen-2-yltrimethylsilane (II) with NBS were examined. The former reaction gave 3-nortricyclyl bromide (IV) as the only detectable product, arising from the carbon—silicon bond cleavage. The latter reaction, however, gave 3-bromo-1-nortricyclyltrimethylsilane (V) as the major product, resulting from cleavage of the carbon—hydrogen bond α to silicon, together with IV and an unidentified product. GLC-monitoring of the reactions showed the higher reactivity of the norbornenyl derivative having the leaving group in theendo position irrespective of whether the leaving group is SiF₅ or H. Since no inhibition was observed by the addition of hydroquinone in the dark, the reactions have been regarded as homoallylic electrophilic substitutions. A concerted mechanism seems to be consistent with the experimental data. Cleavage of 1-nortricyclyltrimethylsilane by iodine monochloride to give 1-iodonortricyclene has also been studied.     

Self-diffusion of the counterion in a salt-free solution of cylindrical polyelectrolytes with low charge density

A limiting law is derived for the self-diffusion coefficient of the counterion in a salt-free solution of cylindrical polyelectrolytes with low charge density. The limiting law generally predicts somewhat stronger counterion—polyion interactions than that of Manning.     

Long-lived muonium in water revealed by pulsed muons

The relaxation rate of muonium in pure water has been found to be smaller than 0.05 × 10⁶ s^?1. With the aid of pulsed muong. μSR and MuSR measurements have been carried out over a longer time range than ever achieved. The results indicate a stability of thermal muonium in water from 3 to 29°C.