Complementary Approaches to Imaging Subcellular Lipid Architectures in Live Bacteria Using Phosphorescent Iridium Complexes and Raman Spectroscopy

A family of three neutral iridium(III) tetrazolato complexes are investigated as bacterial imaging agents. The complexes offer a facile tuning of the emission colour from green (520 nm) to red (600 nm) in aqueous media, while keeping the excitation wavelength unchanged. The three complexes do not inhibit the bacterial growth of Bacillus Cereus, used as a model in this study, and exhibit extremely fast cellular uptake. After a minute incubation time, the nontoxic complexes show subcellular localisation in spherical structures identified as lipid vacuoles. Confocal Raman imaging has been exploited for the first time on live bacteria, to provide direct and label-free mapping of the lipid-enriched organelles within B. cereus, complementing the use of luminescent probes. Examination of the Raman spectra not only confirmed the presence of lipophilic inclusions in B. cereus but offered additional information about their chemical composition, suggesting that the lipid vacuoles may contain polyhydroxybutyrate (PHB).     

The single-mode rate equations for semiconductor lasers with thermal effects

A mathematical model describing the coupling of electrical,optical and thermal effects in semiconductor lasers is introduced.Numerical and asymptotic solutions are derived, including expressionsfor key physical quantities such as the initial time delay,the frequency of spike oscillation and the temperature rise,together with its influence on the photon density, the electronconcentration and the threshold current. The consequences ofthermal effects in reducing efficiency are thus quantified.     

Field testing of collection and measurement of radioxenon for the Comprehensive Test Ban Treaty

Pacific Northwest National Laboratory, with guidance and support from the U.S. Department of Energy's NN-20 Comprehensive Test Ban Treaty (CTBT) Research and Development program, has developed and demonstrated a fully automatic sampler-analyzer (ARSA) for the collection and quantitative measurement of the four xenon radionuclides,^131mXe (11.9 d),^133mXe (2.19 d),¹³³Xe (5.24 d), and¹³⁵Xe (9.10 h), in the atmosphere. These radionuclides are important signatures in monitoring for compliance to a CTBT, and may have applications in stack monitoring and other areas where xenon radionuclides are present. The activity ratios between certain of these radionuclides permit discrimination between radioxenon originating from nuclear detonations and that from nuclear reactor operations, nuclear fuel reprocessing, or from medical isotope production and usage. With the ARSA system, xenon is continuously and automatically separated from the atmosphere at flow rates of about 100 lpm by sorption-bed techniques. Samples collected in 8 hours are automatically analyzed by electron-photon coincidence spectrometry to provide detection sensitivities as low as 100 μBq/m³ of air. This sensitivity is about 10-fold better than achieved with reported laboratory-based procedures¹ for the short time collection intervals of interest. Gamma-ray energy spectra and gas analysis data are automatically collected.     

GC-MS analysis of ethanol and other volatile compounds in micro-volume blood samples—quantifying neonatal exposure

A static headspace gas chromatography coupled mass spectrometry (GC-MS) method was developed and fully validated for the quantitative measurement of acetaldehyde, acetone, methanol, ethanol and acetic acid in the headspace of micro-volumes of blood using n-propanol as an internal standard. The linearity of the method was established over the range 0.2–100 mg/L (R ²?>?0.99) and the limits of detection were 0.1–0.2 mg/L and lower limits quantification 0.5–1 mg/L. Precision and accuracies fell within acceptable limits (20 % for LLOQ and 15 %) for both intra- and inter-day analyses for all compounds except acetaldehyde which had inter-day variability of ≤25 %. The method was applied to analyse blood samples from neonatal patients receiving courses of ethanol excipient containing medications. Baseline levels of acetaldehyde, acetone, methanol and ethanol could be measured in patients before dosing commenced and an increase in levels of some volatiles were observed in several neonates after receiving ethanol-containing medications.     

Biosynthesis of L-p-hydroxyphenylglycine, a non-proteinogenic amino acid constituent of peptide antibiotics

BACKGROUND: The non-proteinogenic amino acid p-hydroxyphenylglycine is a crucial component of certain peptidic natural products synthesized by a non-ribosomal peptide synthetase mechanism. In particular, for the vancomycin group of antibiotics p-hydroxyphenylglycine plays a structural role in formation of the rigid conformation of the central heptapeptide aglycone in addition to being the site of glycosylation. Initial labeling studies suggested tyrosine was a precursor of p-hydroxyphenylglycine but the specific steps in p-hydroxyphenylglycine biosynthesis remained unknown. Recently, the sequencing of the chloroeremomycin gene cluster from Amycolatopsis orientalis gave new insights into the biosynthetic pathway and allowed for the prediction of a four enzyme pathway leading to L-p-hydroxyphenylglycine from the common metabolite prephenate. RESULTS: We have characterized three of the four proposed enzymes of the L-p-hydroxyphenylglycine biosynthetic pathway. The three enzymes are encoded by open reading frames (ORFs) 21, 22 and 17 (ORF21: [PCZA361.1, O52791, CAA11761]; ORF22: [PCZA361. 2, O52792, CAA11762]; ORF17: [PCZA361.25, O52815, CAA11790]), of the chloroeremomycin biosynthetic gene cluster and we show they have p-hydroxymandelate synthase, p-hydroxymandelate oxidase and L-p-hydroxyphenylglycine transaminase activities, respectively. CONCLUSIONS: The L-p-hydroxyphenylglycine biosynthetic pathway shown here is proposed to be the paradigm for how this non-proteinogenic amino acid is synthesized by microorganisms incorporating it into peptidic natural products. This conclusion is supported by the finding of homologs for the four L-p-hydroxyphenylpyruvate biosynthetic enzymes in four organisms known to synthesize peptidic natural products that contain p-hydroxyphenylglycine. Three of the enzymes are proposed to function in a cyclic manner in vivo with L-tyrosine being both the amino donor for L-p-hydroxyphenylglycine and a source of p-hydroxyphenylpyruvate, an intermediate in the biosynthetic pathway.     

Improved models for the phase behaviour of hydrogen fluoride: chain and ring aggregates in the SAFT approach and the AEOS model

Hydrogen fluoride presents one of the strongest hydrogen bonds known. Ring aggregates exist both in the vapour and liquid phases at low temperatures resulting in an anomalously high low-temperature vapour pressure. The effect of ring-like aggregates on the vapour—liquid phase equilibria of associating fluids is studied within the framework of the statistical associating fluid theory (SAFT) and in the chemical model of Lencka and Anderko (AEOS). The SAFT approach incorporates separate contributions to describe chain formation, association (hydrogen bonding), and long range dispersion forces. The treatment of the association interactions stems from the thermodynamic perturbation theory of Wertheim. At the first level of approximation the contribution of ring-like aggregates is neglected and only chain- and treelike structures are treated. In this work an earlier extension of the approach to incorporate ring aggregates is used to model the phase behaviour of hydrogen fluoride. The chemical model of Lencka and Anderko for associating fluids is also considered together with a modification that takes into account the formation of ring aggregates. Vapour pressures and coexistence densities are examined together with heats of vapourization, and the calculations are compared with experimental data.     

Electron spin resonance studies of 199HgH, 201HgH, 199HgD and 201HgD isolated in neon and argon matrices at 4K: an electronic structure investigation

Various isotopomers of the mercury hydride radical (HgH) have been generated in a microwave discharge and trapped in neon and argon matrices at 4 K for electron spin resonance (ESR) investigations. Both the dipolar (A_dip) and isotropic (A_iso) components of the nuclear hyperfine interactions have been directly measured for ¹⁹⁹Hg, ²⁰¹Hg, H and D. Electronic structure information for HgH in its X²Σ ground state obtained from the hyperfine data is compared with theoretical results from several different computational methods. The hyperfine interactions in HgH are unusually large with A_iso(¹⁹⁹Hg) = 6859(3), A_dip(¹⁹⁹Hg) = 446(3), A_iso(H) = 730(2) and A_dip(H) = 0(2) MHz. A standard analysis of the hyperfine interactions demonstrates the need for a more in-depth theoretical treatment of HgH that should include relativistic effects. An interesting shift in spin density is observed when deuterium replaces hydrogen in HgH. The decreased spin density on deuterium, which was demonstrated in earlier studies, can now be more fully investigated since these new measurements confirm an associated increase in spin density on mercury     

All optical electron injector using an intense ultrashort pulse laser and a solid wire target

Energetic electron bunches were generated by irradiating a solid tungsten wire 13 μm wide with 50 femtosecond pulses at an intensity of ∼3×10¹⁸ W/cm². The electron yield, energy spectrum and angular distribution were measured. These energetic electron bunches are suitable for injection into a laser driven plasma accelerator. An all-optical electron injector based on this approach could simplify timing and alignment in future laser-plasma accelerator experiments. PACS 41.75.Ht; 41.75.Lx; 52.38.Kd; 52.38.Ph     

Effect of light on self-assembly of aqueous mixtures of sodium dodecyl sulfate and a cationic, bolaform surfactant containing azobenzene

We report light and small-angle neutron scattering measurements that characterize microstructures formed in aqueous surfactant solutions (up to 1.0 wt % surfactant) containing mixtures of sodium dodecyl sulfate (SDS) and the light-sensitive bolaform surfactant, bis(trimethylammoniumhexyloxy)azobenzene dibromide (BTHA) as a function of composition, equilibration time, and photostationary state (i.e., solutions rich in cis-BTHA or trans-BTHA). We observed formation of vesicles in both SDS-rich and trans-BTHA-rich regions of the microstructure diagram, with vesicles present over a particularly broad range of compositions for trans-BTHA-rich solutions. Illumination of mixtures of BTHA and SDS with a broadband UV light source leads to formation of photostationary states where the fraction of BTHA present as cis isomer (75-80% cis-BTHA) is largely independent of the mixing ratio of SDS and BTHA. For a relatively limited set of mixing ratios of SDS and BTHA, we observed UV illumination of SDS-rich vesicles to result in the reversible transformation of the vesicles to micellar aggregates and UV illumination of BTHA-rich vesicles to result in irreversible precipitation. Surprisingly, however, for many mixtures of trans-BTHA and SDS that formed solutions containing vesicles, illumination with UV light (which was confirmed to lead to photoisomerization of BTHA) resulted in only a small decrease in the number of vesicles in solution, relatively little change in the sizes of the remaining vesicles, and coexistance of the vesicles with micelles. These observations are consistent with a physical model in which the trans and cis isomers of BTHA present at the photostationary state tend to segregate between the different microstructures coexisting in solution (e.g., vesicles rich in trans-BTHA and SDS coexist with micelles rich in cis-BTHA and SDS). The results presented in this paper provide guidance for the design of light-tunable surfactants systems.