Alkali Metal and Trimethylsilyl Carbamoselenothioates – Synthesis,Structure, and some Reactions

This paper describes the synthesis and some reactions of potassium, rubidium, cesium and trimethylsilyl carbamoselenothioates. The potassium salts were synthesized in 70–80 % yields by reacting the corresponding thiocarbamoyl chlorides with potassium selenide in acetonitrile. Furthermore, the rubidium and cesium salts were obtained in good yields by treating the trimethylsilyl esters with the corresponding metal fluorides. The crystal structure of acetonitrile‐solvated potassium N,N‐dimethylcarbamoselenothioate consisted of dimeric units, featuring μ‐carbamoselenothioate anions associated with potassium cations that are located on the upper and lower sides of a plane involving two opposing carbamoselenothioate groups. These heavier alkali metal salts readily reacted with alkyl halides to give both S‐ and Se‐alkyl esters. The reaction of the potassium salts with trimethylsilyl chlorides forms S‐ and Se‐trimethylsilyl carbamoselenothioates which are in equilibrium. The reaction of the salts and silyl esters with organo Group‐14 and ‐15 elements halides gave exclusively the corresponding Se‐substituted products in good yields.     

Investigation of Novel Peptide Chiral Selectors Prepared by Solid-Phase Synthesis with a tert-Butoxycarbonyl Amino Acid

A new class of chiral stationary phases (CSP) with peptide chiral selectors was prepared by solid-phase synthesis with a tert-butoxycarbonyl-L-amino acid on silica. The type of amino acid that is favorable for this class of CSP is discussed. Using the CSP with the phenylalanine peptide selector, the effect of peptide length on the enantioselectivity was investigated in normal-phase mode. The applicability of the CSP with a phenylalanine peptide to chiral ligand-exchange chromatography was also examined.

     

Self-assembled arrays of silica particles on the patterns reflecting the phase-separated structures of mixed Langmuir–Blodgett films

In this study, we constructed self-assembled arrays of silica particles on the micro- and nanopatterns of functionalized templates fabricated from phase-separated mixed Langmuir–Blodgett (LB) films. Electrostatic interaction between the carboxylic groups of silica particles and amino groups on the functionalized templates results in the formation of the self-assembled arrays of silica particles. The patterns of the silica particle arrays can be designed by controlling the phase-separated structures of the original mixed LB films.     

Associative desorption of adsorbed oxygen promoted by translational energy of incident O2 molecules

Effects of the translational energy of incident oxygen molecules on surface processes from dissociative adsorption to subsequent associative desorption on Pt(1 1 1) have been investigated by means of supersonic molecular beam scattering. The reaction rate of associative desorption increases with the incident translational energy. The enhanced associative desorption can be attributed to nonthermal diffusion of dissociated oxygen, promoted by the translational energy of incoming molecules.     

Active compensation of rf-pulse transients

A new approach to compensate rf-pulse transients is proposed. Based on the idea of the response theory of a linear system, a formula is derived to obtain the required excitation voltage profile back from the intended target rf-pulse shape. The validity of the formula is experimentally confirmed by monitoring the rf-field created inside the sample coil with a pickup coil. Since this approach realizes accurate rf-pulse shapes without reducing the Q-factor of the tank circuit of the probe, it can be used not only to suppress the transient tail of the rf-pulse, but also as a general concept for accurate rf-pulsing.     

Multispectral Image Compression for Improvement of Colorimetric and Spectral Reproducibility by Nonlinear Spectral Transform

The article proposes a multispectral image compression scheme using nonlinear spectral transform for better colorimetric and spectral reproducibility. In the method, we show the reduction of colorimetric error under a defined viewing illuminant and also that spectral accuracy can be improved simultaneously using a nonlinear spectral transform called Labplus, which takes into account the nonlinearity of human color vision. Moreover, we show that the addition of diagonal matrices to Labplus can further preserve the spectral accuracy and has a generalized effect of improving the colorimetric accuracy under other viewing illuminants than the defined one. Finally, we discuss the usage of the first-order Markov model to form the analysis vectors for the higher order channels in Labplus to reduce the computational complexity. We implement a multispectral image compression system that integrates Labplus with JPEG2000 for high colorimetric and spectral reproducibility. Experimental results for a 16-band multispectral image show the effectiveness of the proposed scheme.     

Chemical synthesis of ComX pheromone and related peptides containing isoprenoidal tryptophan residues

The ComX pheromone is a post-translationally modified oligopeptide that stimulates natural genetic competence controlled by quorum sensing in Bacillus subtilis. Recently, the structure of the ComX_RO-E-2 pheromone produced by strain RO-E-2 was determined. Based on the NMR analysis, a geranyl group is bound to the tryptophan residue, which results in the formation of a tricyclic ring structure. It was proposed that one of the four possible stereochemical isomers was based on a conformational search for model compounds and the assumption that amino acid residues in the natural pheromone have the l-configuration. All possible modified tryptophan residues and the corresponding ComX_RO-E-2 peptides were synthesized to confirm the precise stereochemistry. Here, the synthesis of the modified tryptophan derivatives was reported in detail. It was succeeded in synthesizing four optically active modified tryptophan methyl esters from which the four diastereomeric ComX_RO-E-2 peptides were prepared. Since only one of the four diastereomers was spectroscopically identical to the natural pheromone and exhibited biological activity, the absolute structure of the ComX_RO-E-2 pheromone was able to be established unambiguously. Furthermore, it was noticed that two other bioactive pheromones were present in the culture broth that were co-purified with ComX_RO-E-2 pheromone. These pheromones were presumed to be the N-terminal truncated peptides of ComX_RO-E-2 pheromone, i.e., [2-6]ComX_RO-E-2 and [3-6]ComX_RO-E-2, by LC-MS and NMR analyses. Using Fmoc solid-phase peptide synthesis, ComX_RO-E-2 pheromone and the [2-6]ComX_RO-E-2 and [3-6]ComX_RO-E-2 peptides were prepared. The synthetic peptides were identical to the natural pheromones and also showed significant biological activity.