Probing the transmembrane potential of bacterial cells by voltage-sensitive dyes.

Fluorescent dyes have been widely employed as optical indicators of the membrane potential difference in cells, isolated organelles and lipid vesicles that are too small to make microelectrode measurements feasible. We describe here the application of a carbocyanine dye, 3,3'-dipropylthiodicarbocyanine iodide [DiS-C3-(5)], to monitor the transmembrane potential changes induced by a variation of the K+ concentration for the cells of Escherichia (E.) coli and photosynthetic bacterium Rhodospirillum (R.) rubrum. The cells were first incubated in buffers containing DiS-C3-(5) and K+ ions of various concentrations until the fluorescence intensity reached a constant value. Valinomycin was then added to the solution, which caused changes in the fluorescence intensity, depending on the K+ concentrations. The membrane potential is shown to have a linear relationship with the fluorescence intensity of DiS-C3-(5). The results demonstrate that the K+ concentrations inside intact cells are 4.6 mM and 5.3 mM for E. coli and R. rubrum, respectively. The diffusion potentials of K+ ions were determined using the Nernst equation over the range of -1.3 mV to 44 mV, corresponding to K+ concentrations of 5 mM -25 mM outside of the cells.     

Barbaloin stimulates growth of Eubacterium sp. strain BAR, a barbaloin-metabolizing bacterium from human feces

Eubacterium sp. strain BAR, isolated from human feces, transformed barbaloin to aloe-emodin anthrone in a basal medium lacking carbohydrate. Barbaloin remarkably stimulated the growth of strain BAR in the basal medium, the stimulative extent of the growth depending on the amount of barbaloin added. The addition of D-glucose, D-galactose, maltose, cellobiose, sucrose or D-amygdalin to the basal medium containing barbaloin caused a decrease of the growth stimulated by barbaloin to the growth level with each sugar, resulting in a complete inhibition of the barbaloin transformation. On the other hand, the addition of D-fructose, which itself stimulated the growth of strain BAR, further increased the growth in the presence of barbaloin and little inhibited barbaloin transformation. Nojirimycin bisulfite, a specific inhibitor of glucosidases, potently inhibited the growth with barbaloin, but did not affect the growth with glucose or cellobiose. Also, nojirimycin bisulfite completely inhibited the transformation of barbaloin to aloe-emodin anthrone. These results indicate that a unique enzyme capable of cleaving the C-glycosyl bond is induced in strain BAR by barbaloin and, consequently, strain BAR grows by utilizing as a nutrient the carbohydrate liberated from barbaloin. It is further suggested that the barbaloin-cleaving enzyme is inhibited by nojirimycin bisulfite and that the induction of the enzyme is repressed with D-glucose and D-galactose.     

Curcumol and its one-step formation from curdione

The absolute stereochemistry of curcumol ( 1 ) is confirmed on the basis of the spectroscopic data. The existence of two conformations in curdione ( 4 ) is revealed by nOe experiments at ambient temperature. One-step conversion of 4 into 1 stereospecifically proceeds via the ene-reaction without epimerization at any asymmetric center in 4 .     

Highly stereoselective reduction of β-oxosulfonium salts ---synthesis of trans epoxides---

Alkylation of α-methylthio or α-phenylthio ketones 1 with trimethyloxonium tetrafluoroborate and the reduction of the resulting sulfonium salts 5 with naBH₄ followed by the base treatment afforded trans-epoxides 8 with high stereoselectivity.     

Electron-transfer chain-substitution in hydrodemercuration of alkylmercury(II) compounds with n-benzyl-1,4-dihydronicotinamide

Reduction of alkylmercury(II) acetates with N-benzyl-1,4-dihydronicotinamide (BNAH) proceeds through electron-transfer chain-substitution mechanism. The rate constant of hydrogen transfer from BNAH to alkyl radical was estimated as in the order of 10⁵ 1/mol·sec.     

USEFUL PHOTOLUMINESCENCE PROBES OF MICELLAR SYSTEMS—CYCLIC AZOALKANES AS FLUORESCENCE ACCEPTORS AND 1,5-DIMETHYLNAPHTHALENE AS A FLUORESCENCE DONOR

Abstract— Certain cyclic azoalkanes are shown to exhibit substantial fluorescence intensity and attractive absorption parameters in detergent solutions. Quenching of the fluorescence of detergent solutions of 1,5-dimethylnaphthalene by these bicyclic azoalkanes has been investigated and is found to provide a useful system to study properties of micellar systems.     

Polarization mode conversion in YIG rib waveguide

This paper describes the experimental results on the orthogonally polarized mode conversion in a YIG rib channel waveguide, in which a small magnetic field induced around the electrode deposited on the waveguide was used. The dependence of mode conversion efficiency on the coupling length and the effect of a d.c. bias field applied to the waveguide were investigated. The Faraday rotation angle of the fabricated YIG rib channel waveguide was found to be 160° cm^–1, which was a reasonable value compared with that in the YIG planar waveguide reported previously. Furthermore, an increase in conversion efficiency and a decrease in switching time were found in the presence of a d.c. magnetic bias field.     

Gradient-index glass rods of PbO---K2O---B2O3---SiO2 system prepared by the sol-gel process

A glass rod of the PbO---K₂O---B₂O₃---SiO₂ system having a radial gradient of refractive index has been prepared by the sol-gel process using aqueous solutions of lead acetate and potassium nitrate as the sources for index-modifying cations. A gel prepared by gelatinizing a sol from the mixture of tetramethoxysilane, tetraethoxysilane, and the aqueous solutions of boric acid and lead acetate was placed in an aqueous solution of potassium nitrate to form the concentration gradient of modifier cations by diffusion through the micropores of the gel. The glass rod of about 7 mm in diameter obtained by drying and sintering the gel had a refractive index of parabolic profile changing from the center toward the perimeter with a maximum difference of about 0.04.