Effect of compositional variation on the properties of Y-Ba-Cu-O compounds

Single phase YBa₂Cu₃O_7– as well as multi-phase compositions of the Y-Ba-Cu-O system have been prepared by ceramic techniques. The effects of the additional phases on the superconducting transition and normal state properties have been investigated. Measurements show that while the transition temperature is not effected, grain growth, resistivity and unit cell volume of the 123 phase are dependent on the presence of multi phases. The observed changes in cell volume and resistivity can both be explained by a change in the oxygen concentration in the range 0 to 0.15.     

Kinetics of n-propylaminolysis of some oxime ethers in 1:1 aqueous acetonitrile

Kinetic studies on the cleavage of the C–O bond of O-(2,4-dinitrophenyl)-substituted cyclohexanone, acetophenone, benzophenone and 4-bromobenzophenone oxime by n-propylamine in 11 aqueous acetonitrile has been reported. Base catalysis being absent, these second order nucleophilic substitution reactions are specific acid catalyzed. The catalytic rate coefficients are calculated and a probable mechanism proposed.

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C–O O-(2,4-)- , , 4- - - (11). . .

     

Binding of leucomycin and its derivatives to E. Coli ribosomes

Structure-activity relationships have been discussed for inhibition of [¹⁴C] erythromycin binding to Escherichia coli ribosomes by leucomycin and its acyl derivatives in the light of the Fujita-Ban de novo model. The group contributions of various substituents show that acylation at position 4″ of the mycarose moiety of leucomycin increases affinity for binding of leucomycins to ribosomes. It is also indicated that unlike at position 2' in mycaminose region a free hydroxyl at position 9 of the lactone ring is not important for binding to ribosomes.     

Linear free energy relationships implicate three modes of binding for fluoroaromatic inhibitors to a mutant of carbonic anhydrase II

[figure: see text] Linear free energy relationships between binding affinity and hydrophobicity for a library of fluoroaromatic inhibitors of F131V carbonic anhydrase II (CA) implicate three modes of interaction. X-ray crystal structures suggest that F131 interacts with fluoroaromatic inhibitors, while P202, on the opposite side of the active site cleft, serves as the site of the hydrophobic contact in the case of the F131V mutant. 2-Fluorinated compounds bind more tightly, perhaps due to the field effect of the nearby fluorine on the acidity of the amide proton.     

USE OF A pH-STAT DILUTION TO DETERMINE CRITICAL MICELLE CONCENTRATIONS AND COUNTERION CONCENTRATIONS OF IONIC MICELLES1

The use of a pH-stat to determine the critical micelle concentration (c.m.c.) of ionic micellar solutions is described. Counterion is released with the dilution of an ionic micellar solution at all concentrations above the c.m.c. The titration of the released counterion permits the evaluation of the c.m.c. and the associated amount of counterion for any concentration above the c.m.c. The diluent is the same medium in which the micelle is dissolved. Thus any ionic strength, ion composition, or pH may be used. Examples of the method to determine the c.m.c. of promethazine hydrochloride in water and of tetracaine hydrochloride in 0.128 N NaCl as a function of pH are given. Also the c.m.c of promethazine hydrochloride - Tween 80 mixtures was examined as a function of mole fraction.     

Calcium(II)-selective potentiometric sensor based on p -isopropylcalix6arene in PVC matrix

In Japan, large amounts of fertilizer nitrogen are applied to tea plantations. We collected samples of tea plantation soil each season for a year. Samples were analyzed for their contents of various inorganic chemicals and total N. Nitrogen was present mainly in the top 0 to 30?cm of soil. However, at times the concentration of nitrate N in the soil water was more than 35?mg?L^?1, even in the deepest layers. The contents of various metal elements in the soil were examined. Ba, Fe, Sr and Zn contents were high in the top 0 to 30?cm of soil. But Al and Mn contents were not always high in the top 0 to 30?cm of soil. From the correlation analysis among contents of various inorganic chemicals, it was suggested that increased leaching of Al, Mn, and Zn from tea plantation soil occurred with increased nitrate N concentration.