Selenoglycosides in silico: ab initio-derived reparameterization of MM4, conformational analysis using histo-blood group ABH antigens and lectin docking as indication for potential of bioactivity

The identification of glycan epitopes such as the histo-blood group ABH determinants as docking sites for bacterial/viral infections and signals in growth regulation fuels the interest to develop non-hydrolysable mimetics for therapeutic applications. Inevitably, the required substitution of the linkage oxygen atom will alter the derivative’s topology. Our study addresses the question of the impact of substitution of oxygen by selenium. In order to characterize spatial parameters and flexibility of selenoglycosides, we first performed ab initio calculations on model compounds to refine the MM4 force field. The following application of the resulting MM4R version appears to reduce the difference to ab initio data when compared to using the MM4 estimator. Systematic conformational searches on the derivatives of histo-blood group ABH antigens revealed increased flexibility with acquisition of additional low-energy conformer(s), akin to the behavior of S-glycosides. Docking analysis using the Glide program for eight test cases indicated potential for bioactivity, giving further experimental investigation a clear direction to testing Se-glycosides as lectin ligands.     

Proof of Principle Experiments on Direct Generation of the $hbox{TE}_{11}$ Mode in a Coaxial Vircator

Experiments on a coaxial vircator with a sectioned emitter are reported. The emitting area is sectioned to form two opposing emitters in order to favor growth of the $hbox{TE}_{11}$ mode and inhibit growth of the $hbox{TM}_{01}$ mode that is usually excited in a coaxial vircator. Experiments are performed using a compact 320-J 400-kV Marx generator and a compact coaxial vircator built in a standard 8$^{primeprime}$ vacuum tube. The radiated magnetic-field strength is measured by means of four free-field (B-dot) probes, and experiments show that sectioning the emitter does, in fact, lead to generation of the $hbox{TE}_{11}$ mode.      

Combined Extraction and Electrochemical Detection of Amines and Phenols Using Microelectrodes in Organic Solvents

A straightforward approach for liquid‐liquid extractive detection of aromatic amines and phenols is described based on the spontaneous transfer of the molecule from the aqueous to an organic phase and subsequent electrochemical detection in the latter phase using a microelectrode. It is demonstrated that the extent of the transfer can be modified by altering the pH of the aqueous solution and the organic solvent. It is also concluded that the presence of an ion‐pair formation agent does not increase the transfer yield for 4‐chloroaniline and phenol. The present approach combines liquid‐liquid sample clean‐up and quantification into a single step which significantly facilitates determinations of aromatic amines and phenols present in complex samples.     

Strong phonon replicas in be 1s photoemission spectra

The Be 1s core level photoemission line from metallic Be is shown to contain unexpected internal fine structure. We argue that this fine structure is caused by intrinsic excitation of a narrow band of optical phonons in the 1s photoemission process. The general importance of the present results for high resolution core level photoemission investigations of metals is pointed out.     

Precise polarographic determination of the stability constants of cadmium and lead with oxalate and sulphate

Precise polarographic determinations of the stability constants of some complexes of lead and cadmium with oxalate and sulphate were made using differential-pulse polarography, normal- pulse polarography and direct-current polarography at three different concentrations of the metal ions in the range 1 × 10^?4 to 9 × 10^?8 M. The stability constants, evaluated with the DeFord-Hume procedure, at the different metal ion concentrations and using the different techniques are in good agreement with each other and with literature values. In the calculations corrections were made for changes in liquid-junction potentials and the effect of alterations in the diffusion coefficient of the reactant was also considered for diffusion towards a spherical electrode. For metal ion concentrations above approximately 10^?6 M the precision of the determinations of the half-wave potentials and of the calculations of the stability constants approaches that commonly obtained in potentiometric measurements on similar systems.     

Surface segregation and mixed valency in dilute Yb-Al interdiffusion compounds

Photoemission experiments on mixed valent Yb-Al compounds prepared by diffusing Yb into an Al(110) single crystal are reported. At high Yb concentrations surface core level peaks reveal a purely divalent surface in agreement with recent results for single crystal YbAl₂. In the dilute limit, when the intensity from bulk Yb is reduced below the limit of detection, a surface layer of divalent Yb still persists and a surface segregation of Yb in Al is made evident. When the bulk concentration of Yb is reduced the bulk mean valence increases. For diluted samples, when the formation of YbAl₃ in a surrounding of elemental Al is expected, Yb is still in a mixed valent state. The highly resolved structures from trivalent Yb are compared with a recent calculation of the 4f¹³ → 4f¹² multiplet pattern.     

Single-pulse two-dimensional temperature imaging in flames by degenerate four-wave mixing and polarization spectroscopy

We introduce a novel and simple experimental arrangement for single-pulse two-dimensional temperature mapping in flames by the coherent imaging techniques, degenerate four-wave mixing and polarization spectroscopy, utilizing a dual-wavelength dye laser and a diffraction grating. Each pulse of this dye laser consists of two wavelengths which were tuned to resonance with two different rotational transitions in theQ ₁ branch of theA ² –X ² (0, 0) band of the OH radical. A typical coherent imaging geometry where a sheet-shaped pump beam crossed an unfocused probe beam, was used. The two generated images of OH signal distributions were spatially separated by a diffraction grating and simultaneously detected on a single CCD chip. The two-dimensional single-pulse temperature map was extracted from these images. The precision of the methods is examined and a comparison between degenerate four-wave mixing and polarization spectroscopy is made.