Helix versus zig-zag: control of supramolecular topology via carboxylic acid conformations in ortho-substituted phenyl amines

ortho-Substituted phenyl amines form supramolecular helices or zig-zag structures, depending on the conformation of the carboxylic acid substituents--which can be controlled by an intramolecular hydrogen-bonding interaction.     

Reactions of gaseous ions. I. Methane and ethylene

At elevated pressures in a mass spectrometer ion source reactions occur between certain ions and the neutral species present. We have studied the various secondary ions formed in methane and ethylene at elevated pressures and have determined the reactions by which they are formed and the rates of these reactions. The rates are all extremely fast. The reaction rates have been treated by classical collision theory and it has been shown that to a fair approximation the cross-sections and reaction rate constants can be predicted from a simple balance of rotational and polarization forces. [Reprinted from J. Am. Chem. Soc. 1957; 79: 2419.] Copyright 1957 by the American Chemical Society and reprinted by permission of the copyright owner.     

Application of matrix solid-phase dispersion in the determination of dibenzo[a,l]pyrene content of experimental animal diets used in a large-scale tumor study.

A method utilizing matrix solid-phase dispersion (MSPD) was developed for isolation and determination of dibenzo[a,l]pyrene (DBP) in experimental rainbow-trout diets used in a large-scale carcinogenesis study. A 0.5 g sample of moist ration containing 0-225 ppm DBP (dry basis) was mixed with 2 g C18 sorbent and benzo[a]pyrene internal standard was added to the mixture. Extraction and clean-up were accomplished in a single step by extracting the sample mixture with hexane-benzene 4:1 from a cartridge containing 2 g Florisil. DBP was quantified by HPLC on a C5 bonded phase column with fluorescence detection. Mean analytical recovery of DBP from control diet spiked at three concentration levels was 101 to 107% with relative standard deviations of 1 to 7%. The limit of detection of DBP was equivalent to 0.014 ppm in the ration. Application of the method to verification of DBP levels in trout rations from the carcinogenesis study is described. Control ration (0 ppm DBP) was screened for possible DBP contamination and none was found. This is the first report on analysis of DBP in experimental animal diets.     

Hyperfine level-crossing spectroscopy of NH2 with dye-laser excitation

Hyperfine structure of a number of levels of the (0, 9, 0) and (0, 10, 0) vibrational states of the à ²A₁ state of NH₂ has been measured using the technique of magnetic level-crossing. A CW dye-laser served as an excitation source. The resolution achieved is ～ 3 MHz. The analyses have been aided by calculations of the relative fields for the level-crossings in terms of the parameters of a model hamiltonian, together with their relative intensities for linear and non-linear excitation. These calculations are presented for I = ½ and 1 for J = 1 ½, 2 ½, 3 ½, and 4 ½.

Hyperfine parameters for the (0, 10, 0) vibrational state are in good agreement with the one set of literature values, obtained using the independent method of intermodulated fluorescence.

We observe an apparent drop of 30 per cent in the Fermi contact parameter between the (0, 10, 0) and (0, 9, 0) levels. However, it is also found that the hyperfine splittings within the (0, 9, 0) state are not completely in accord with the simple model. These observations are briefly discussed in terms of the Renner effect and the s-p hybrid nature of the molecular orbital occupied by the unpaired electron.     

Laser-induced fluorescence studies of HfF+ produced by autoionization

Autoionization of Rydberg states of HfF, prepared using the optical-optical double resonance technique, holds promise to create HfF(+) in a particular Zeeman level of a rovibronic state for an electron electric dipole moment search. We characterize a vibronic band of Rydberg HfF at 54 cm(-1) above the lowest ionization threshold and directly probe the state of the ions formed from this vibronic band by performing laser-induced fluorescence on the ions. The Rydberg HfF molecules show a propensity to decay into only a few ion rotational states of a given parity and are found to preserve their orientation qualitatively upon autoionization. We show empirically that we can create 30% of the total ion yield in a particular ∣J(+), M(+) state and present a simplified model describing autoionization from a given Rydberg state that assumes no angular dynamics.     

Flux through Trehalose Synthase Flows from Trehalose to the Alpha Anomer of Maltose in Mycobacteria

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Highlights? Flux through trehalose synthase (TreS) in mycobacteria is from trehalose to maltose ? The appropriate α anomer is formed by TreS for maltose kinase of the GlgE pathway ? The specificity of TreS for α-maltose is retained with deoxyfluoro analogs ? TreS supports cytosolic/capsular α-glucan but not trehalose mycolate biosynthesis     

Exponential mixing for smooth hyperbolic suspension flows

We present some simple examples of exponentially mixing hyperbolic suspension flows. We include some speculations indicating possible applications to suspension flows of algebraic Anosov systems. We conclude with some remarks about generalizations of our methods.     

A new shunt DC active filter of power supply in a steady high magnetic field facility

A DC active power filter is an indispensable part in a high power and high stability power supply system, especially in the power supply system of the Steady High Magnetic Field Facility, which requires that the current ripple should be limited to 50 parts per million. In view of the disadvantages of the series DC active power filter and shunt Pulse Width Modulation DC active filter, this paper puts forward a novel DC active filter by combining the advantages of the transistor regulator and the shunt type. The structure and principle of the new shunt linear active filter are introduced. Meanwhile, the design of several key components that construct the new shunt linear active filter is also analyzed. The simulation model and an experimental prototype of the shunt linear active filter are developed, and the results verify that the parameter design is reasonable and the shunt active filter has a good filter effect.