Determination of ammonium in river water and sewage samples by capillary zone electrophoresis with direct UV detection

We developed capillary zone electrophoresis (CZE) with direct UV detection for determination of ammonium in environmental water samples. Ammonium in the samples was partly converted into ammonia in the alkaline background electrolyte (BGE) during migration and was detected by molecular absorption of ammonia at 190 nm in approximately 7 min. The limit of detection (LOD) for ammonium was 0.24 mg/l (as nitrogen) at a signal-to-noise ratio of three. The respective values of the relative standard deviation (RSD) of peak area, peak height, and migration time for ammonium were 2.1, 1.8, and 0.46%. Major alkali and alkaline earth metal ions coexisting in the samples did not interfere with ammonium determination by the proposed method. The proposed method determined ammonium in surface water and sewage samples. The results were compared to those obtained using ion chromatography (IC).     

Synthesis of axinohydantoins

A short synthesis of the hydantoin-containing marine sponge metabolites axinohydantoins is described. A key feature of the synthesis is a putative biomimetic, intramolecular cyclization of alpha-functionalized imidazolone 5, which affords the tricyclic pyrroloazepinone framework comprising 6. In addition, the conversion of imidazolones to alpha,beta-unsaturated hydantoins is outlined and represents a new approach to these heterocyclic systems.     

(15N) acetamide in polar solvents: Hindered internal rotation and intermolecular interactions

The ¹H spectrum of (¹⁵N)acetamide has been measured in dimethyl sulphoxide (DMSO), methyl propyl ketone (MPK), 1,3-dioxane, 1,4-dioxane, D₂O, acetonitrile and pyridine-d₅ at various temperature intervals within the range of 278–343 K. From the temperature dependence of the NMR spectra of the amide protons, the free energy of activation, ΔG^≠, for hindered rotation about the central C? N bond was determined by means of total line shape analysis in the four solvents DMSO, MPK and the two dioxanes. Observed values of ΔG^≠ (298 K) (72.7 in DMSO, 70.1 in MPK, 70.0 in 1,3-dioxane and 70.1 kJ mol¹ in 1,4-dioxane) were not very sensitive to the choice of solvent or concentration. The concentration dependence of the internal chemical shift between the amide protons was studied in MPK, D₂O, acetonitrile and pyridine-d₅. The free energy of activation and the internal chemical shift are discussed on the basis of solvent-amide and amide–amide specific hydrogen bonding interactions, and in comparison to the results of molecular orbital calculations.     

Unsteady Falkner-Skan flow

Zusammenfassung Mittels des Differenzenverfahrens wurden instationäre, laminare Grenzschichten längs eines Keiles (von verschiedenen Keilwinkeln ) gerechnet, der plötzlich aus der Ruhe herausbewegt wird. Es ist bemerkenswert, daß im Fall >0.6 die Grenzschicht an der betreffenden Stelle der Keilwand bereits vor der Ankunft der an der Vorderkante entstehenden Störungen fast stationär wird, und daß, wenn die -Zahl sich dem Wert –0.1988 nähert, es doch eine beträchtliche Zeit braucht vom Vorüberziehen dieser Störungen bis zum Erreichen des stationären Zustandes der Grenzschicht.     

A novel type secoiridoid glucoside,hydrangenoside a from Hydrangea macrophylla

Hydrangenoside A, isolated along with its three congeners from Hydrangea macrophylla, was proved to have a novel type of structure which is thought to be biosynthesized through an aldol-type condensation of secologanin with a unit formed by the shikimate-malonate route followed by decarboxylation.     

Photon number squeezing of ultrabroadband laser pulses generated by microstructure fibers

To the best of our knowledge, we demonstrate for the first time the generation of photon number squeezing by spectral filtering for ultrabroadband light generated by microstructure fibers at 800 nm. A maximum squeezing of 4.6 dB is observed, corresponding to 10.3 dB after correcting for detection losses. We numerically analyzed the quantum dynamics of ultrashort laser pulse propagation through optical fibers by solving a nonlinear quantum Schr?dinger equation that included Raman scattering, especially for the quantum correlation of photon number fluctuation among frequency modes in broadband pulses.     

Compaction of single-chain DNA by histone-inspired nanoparticles

We elaborated a versatile experimental model of chromatin which consists of a single chain of long duplex DNA that interacts with well-defined cationic nanoparticles of various sizes. We found that the DNA compaction by nanoparticles is stepwise and progressive at the single-chain level. It is controlled by the ability of DNA to wrap nanoparticles, which is more efficient for larger particles and, similar to DNA-histone interaction, is optimal at a physiological salt concentration.     

Micellar cobaltporphyrin nanorods in alcohols

Cobalt(II) meso-tetrakis(4-hexadecylamidophenyl)porphyrin self-assembles in ethanol/1-propanol 2/1 (v/v) to form a rodlike micelle with nanoscale dimensions; the nanorod is a face-to-face aggregate having a hydrophobic corona around a polar core and is thus characterized as a reverse micelle.     

Control of bacteria adhesion by cell-wall engineering

UDP-MurNAc-pentapeptide derivative bacterial cell-wall precursors were synthesized as effective tools for surface display on living bacteria. Lactobacilli were incubated in the ketone-modified precursor-containing medium, and the ketone moiety was displayed on the bacterial surface through cell-wall biosynthesis. Oligomannose was coupled with the ketone moiety on the bacterial surface via a aminooxyl linker, thereby displaying this oligosaccharide on the surface of the bacteria. The increase in the adhesion of the sugar-displaying bacteria onto a concanavalin A-attached film compared to that of native bacteria was confirmed by microscopic observation and surface plasmon resonance measurement. The incorporation of the artificial cell-wall precursors was enhanced when incubated with fosfomycin, an inhibitor of cell-wall precursor biosynthesis.