Coexistence of domains with distinct order and polarity in fluid bacterial membranes

In this study we sought the detection and characterization of bacterial membrane domains. Fluorescence generalized polarization (GP) spectra of laurdan-labeled Escherichia coli and temperature dependencies of both laurdan's GP and fluorescence anisotropy of 1,3-diphenyl-1,3,5-hexatriene (DPH) (rDPH) affirmed that at physiological temperatures, the E. coli membrane is in a liquid-crystalline phase. However, the strong excitation wavelength dependence of rlaurdan at 37 degrees C reflects membrane heterogeneity. Time-resolved fluorescence emission spectra, which display distinct biphasic redshift kinetics, verified the coexistence of two subpopulations of laurdan. In the initial phase, <50 ps, the redshift in the spectral mass center is much faster for laurdan excited at the blue edge (350 nm), whereas at longer time intervals, similar kinetics is observed upon excitation at either blue or red edge (400 nm). Excitation in the blue region selects laurdan molecules presumably located in a lipid domain in which fast intramolecular relaxation and low anisotropy characterize laurdan's emission. In the proteo-lipid domain, laurdan motion and conformation are restricted as exhibited by a slower relaxation rate, higher anisotropy and a lower GP value. Triple-Gaussian decomposition of laurdan emission spectra showed a sharp phase transition in the temperature dependence of individual components when excited in the blue but not in the red region. At least two kinds of domains of distinct polarity and order are suggested to coexist in the liquid-crystalline bacterial membrane: a lipid-enriched and a proteolipid domain. In bacteria with chloramphenicol (Cam)-inhibited protein synthesis, laurdan showed reduced polarity and restoration of an isoemissive point in the temperature-dependent spectra. These results suggest a decrease in membrane heterogeneity caused by Cam-induced domain dissipation.     

Photoinduced decomposition of the polybromostyryl carbanions

The photoinduced decay in THF of the sodium salt of the polybromostyryl carbanions (PS_B?) was investigated in vacuum at ?78°C. Maximal rates of decay were obtained when the wavelength of the incident light corresponded to the absorption maximum of the PS_B? at 495 nm. The quantum yield of the process was found to be 13 eq./Einstein. Products of the photostimulated decompositions at ?78°C were found to be different from those obtained as result of the “dark” thermal decomposition at –20°C. Decomposition of the PS_B? carbanions was accompanied by evolution of Br^? anions and by formation of polyaryl carbanions absorbing in the 270- to 400-nm range. The mechanism of the photoinduced decomposition of PS_B?, though basically analogous to the S_RN1 reaction mechanism, was found to differ significantly from the latter. The intramolecular dissociative electron transfer was assumed to represent its initiation step. Its propagation was attributed to the addition of PS_B? to the initially formed biradicals, ejection of Br^? from the resulting radical anions, and intramolecular electron transfer yielding polybromostyryl radicals. Products of the photoinduced decomposition of PS_B? remained soluble in THF when the intensity of the incident light was relatively weak, though their molecular weight distribution broadened. Insoluble, highly crosslinked polymers were obtained when the intensity of the incident light was very high.     

Identification of phenylbutyrylglutamine,a new metabolite of phenylbutyrate metabolism in humans

Phenylbutyrate is used in humans for treating inborn errors of ureagenesis, certain forms of cancer, cystic fibrosis and thalassemia. The known metabolism of phenylbutyrate leads to phenylacetylglutamine, which is excreted in urine. We have identified phenylbutyrylglutamine as a new metabolite of phenylbutyrate in human plasma and urine. We describe the synthesis of phenylbutyrylglutamine and its assay by gas chromatography/mass spectrometry as a tert-butyldimethylsilyl or methyl derivative, using standards of [(2)H(5)]phenylbutyrylglutamine and phenylpropionylglutamine. After administration of phenylbutyrate to normal humans, the cumulative urinary excretion of phenylacetate, phenylbutyrate, phenylacetylglutamine and phenylbutyrylglutamine amounts to about half of the dose of phenylbutyrate. Thus, additional metabolites of phenylbutyrate are yet to be identified.     

Rapid estimation of biochemical oxygen demand

The feasibility of using columnar reactors containing immobilized microorganisms for the rapid estimation of BOD was demonstrated in this study. Dilutions of three types of industrial effluents were tested by the BOD₅ test and by this experimental system. A high degree of correlation (r = 0.98) was observed between results of the two tests. The mean standard error of estimation of the experimental system was 11%.     

Fluorescence resonance energy transfer in CdSe/ZnS-DNA conjugates: probing hybridization and DNA cleavage

Nucleic-acid-functionalized CdSe/ZnS quantum dots (QDs) were hybridized with the complementary Texas-Red-functionalized nucleic acid. The hybridization was monitored by following the fluorescence resonance energy transfer from the QDs to the dye units. Treatment of the QD/dye DNA duplex structure with DNase I resulted in the cleavage of the DNA and the recovery of the fluorescence properties of the CdSe/ZnS QDs. The luminescence properties of the QDs were, however, only partially recovered due to the nonspecific adsorption of the dye onto the QDs. Similarly, nucleic-acid-functionalized Au nanoparticles (Au NPs) were hybridized with the complementary Texas-Red-labeled nucleic acid. The hybridization was followed by the fluorescence quenching of the dye by the Au NPs. Treatment of the Au NP/dye DNA duplex with DNase I resulted in the cleavage of the DNA and the partial recovery of the dye fluorescence. The incomplete recovery of the dye fluorescence originated from the nonspecific binding of the dye units to the Au NPs. The nonspecific binding of the dye to the CdSe/ZnS QDs and the Au NPs is attributed to nonprotected surface vacancies in the two systems.     

Rate constants for the reactions of Ar+ with CO2 and SO2 as a function of temperature (300–1500 K)

We have measured the rate constants for the reactions of Ar⁺ with CO₂ and SO₂ from 300 to 1500 K in a high temperature flowing afterglow. For the reaction with CO₂, we have found that all modes of energy, i.e., translation, rotation, and vibration, affect the rate constant to the same degree up to a total energy of 0.4 eV. Above 0.4 eV total energy, internal energy decreases the rate constants more effectively than does translational energy. For the reaction of Ar⁺ with SO₂, the rate constants go through a minimum at about 900 K. By comparing our results to drift tube data, we derive rate constants for reaction from the υ=0 and υ>0 vibrational levels. At low energy, the vibrationally excited SO₂ molecules react with Ar⁺ approximately twice as fast as the ground state molecules. Both vibrational modes have similar temperature dependences.     

Characterization of an orphan Ra–Be neutron source

Journal of Radioanalytical and Nuclear Chemistry - An orphan radium-beryllium (Ra–Be) neutron source (Nuclear Chicago Corporation) detected inside a scrap metal shipping container, was seized...     

The prediction of the coefficient of restitution between impacting spheres and finite thickness plates undergoing elastoplastic deformations and wave propagation

Nonlinear Dynamics - The coefficient of restitution (COR) is a pragmatic analytical tool needed to solve impact problems. The coefficient is customarily obtained empirically by executing...     

Templated Grain Growth of Textured Piezoelectric Ceramics

Crystallographic texturing of polycrystalline ferroelectric ceramics offers a means of achieving significant enhancements in the piezoelectric response. Templated grain growth (TGG) enables the fabrication of textured ceramics with single crystal-like properties, as well as single crystals. In TGG, nucleation and growth of the desired crystal on aligned single crystal template particles results in an increased fraction of oriented material with heating. To facilitate alignment during forming, template particles must be anisometric in shape. To serve as the preferred sites for epitaxy and subsequent oriented growth of the matrix, the template particles need to be single crystal and chemically stable up to the growth temperature. Besides templating the growth process, the template particles may also serve as seed sites for phase formation of a reactive matrix. This process, referred to as Reactive TGG (RTGG), has been used to obtain highly oriented Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃, Sr_0.53Ba_0.47Nb₂O₆, and (Na_1/2Bi_1/2)TiO₃-BaTiO₃. Highly oriented Bi₄Ti₃O₁₂, Sr₂Nb₂O₇, CaBi₄Ti₄O₁₅, Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃, Sr_0.53Ba_0.47Nb₂O₆ and (Na_1/2Bi_1/2)TiO₃-BaTiO₃ ceramics have been produced by TGG. The resulting ceramics show texture levels up to 90%, and significant enhancements in the piezoelectric properties relative to randomly oriented ceramics with comparable densities. For example, piezoelectric coefficients of textured piezoelectrics are from 2 to 3 times higher than polycrystalline ceramics and as high as 90% of the single crystal values. In textured PMN-PT, a low field (< 5 kV/cm) piezoelectric coefficient (d ₃₃) of ～1600 pC/N was obtained with > 0.3% strain (at 50 kV/cm). The high field dielectric and electromechanical properties of textured perovskites are more hysteretic than those of single crystals, probably as a result of clamping by the residual template particles, residual random grains, the presence of non-ferroelectric second phases, and a wide orientation distribution. Lateral clamping of one grain by another may also be an important factor in fiber-textured samples. Means to further improve the quality of texture and thus properties of textured piezoelectric ceramics by TGG are presented.