Catalytic uses of helicenes displaying phosphorus functions

This review presents an updated state of art of the catalytic uses of chiral phosphorus compounds characterized by a helical scaffold as the key stereogenic element of their structures. These include both helical scaffolds with appended phosphorus functions and helical scaffolds with embedded phosphorus-containing rings (phosphahelicenes). Catalytic applications of helical phosphines in both transition metal catalysis and organocatalysis are presented.     

Spectroscopic investigation on chirality transfer in additive-driven self-assembly of block polymers

Chiral supramolecules prepared by the additive-driven self-assembly of block copolymers provide a facile method to construct helical nanostructures. In this study, we investigated the chiral transfer from chiral tartaric acid to poly(styrene)-b-poly(ethylene oxide) using small-angle X-ray scattering, transmission electron microscopy, circular dichroism, and vibrational circular dichroism. The results showed that the chirality was transferred to both the segments of block copolymer irrespective of the interaction with the chiral additives and formation of helical phase structure. However, the chirality transfer was carried out using different methods: for poly(ethylene oxide) segments, the chirality transfer was carried out via direct hydrogen bond formation; for polystyrene segments, the chirality transfer was carried out via the cooperative motion of block copolymers during the thermal annealing.     

挠率对螺旋管道内二次流的二阶效应

本文用螺旋坐标系和摄动法研究了在螺旋管道内的低雷诺数(R<17/(8~(1/2)))不可压缩流体的定常粘性流动,给出了完全的二阶摄动解。结果表明管道挠率在二阶摄动解时对二次涡有偏转和扭曲效应。本文还发现当雷诺数从很小值逐渐增大时,两次涡位置发生由左右相对到上下相对的有趣旋转。     

Determination of thymopentin in beagle dog blood by liquid chromatography with tandem mass spectrometry and its application to a preclinical pharmacokinetic study

The pentapeptide thymopentin (Arg‐Lys‐Asp‐Val‐Tyr, RKDVY) corresponds to amino acids 32–36 of the 49 amino acid immunomodulatory polypeptide, thymopoietin, whose biological activity is partially reproduced. Thymopentin is widely used in the clinic and represents a promising target for drug design but bioanalytical and pharmacokinetic data are limited due to its enzymatic instability. This paper reports a rapid and sensitive method based on liquid chromatography with tandem mass spectrometry for the determination of thymopentin in beagle dog blood. To inactivate peptidases and stabilize thymopentin, acetonitrile was added to blood samples immediately after collection followed by addition of stable isotope‐labeled thymopentin as internal standard and washing with dichloromethane. Chromatography was carried out on an Ascentis Express Peptide ES‐C₁₈ column using gradient elution with methanol and aqueous 0.1% formic acid at a flow rate of 0.6 mL/min. Positive electrospray ionization mass spectrometry with selected reaction monitoring achieved linearity in the range of 1.5–800 ng/mL with good accuracy/precision and minimal matrix effects. The method was successfully applied to a pharmacokinetic study in beagle dogs after intravenous administration of 0.2 mg/kg thymopentin.     

Open tubular capillary column for the separation of cytochrome C tryptic digest in capillary electrochromatography

A silica capillary of 50 μm internal diameter and 500 mm length (416 mm effective length) was chemically modified with 4‐(trifluoromethoxy) phenyl isocyanate in the presence of dibutyl tin dichloride as catalyst. Sodium diethyl dithiocarbamate was reacted with the terminal halogen of the bound ligand to incorporate the initiator moiety, and in situ polymerization was performed using a monomer mixture of styrene, N‐phenylacrylamide, and methacrylic acid. The resultant open tubular capillary column immobilized with the copolymer layer was used for the separation of tryptic digest of cytochrome C in capillary electrochromatography. The sample was well eluted and separated into many components. The elution patterns of tryptic digest of cytochrome C were studied with respect to pH and water content in the mobile phase. This preliminary study demonstrates that open tubular capillary electrochromatography columns with a modified copolymer layer composed of proper nonpolar and polar units fabricated by reversible addition‐fragmentation transfer polymerization can be useful as separation media for proteomic analysis.     

Stereocontrolled Synthesis of Unnatural Tetrapeptides Containing L‐Valine Units. Part 3

The stereoselective synthesis of the new nonproteinogenic branched tetrapeptides 9a – 9d and 15a , b , containing two L ‐valine units and unnatural α‐amino acids, was accomplished starting from the chiral synthon 1a , a monolactim ether easily obtained from L ‐valine.     

Low eccentricity elliptical fibers with helical windings under slow-wave consideration—Some special cases

Analytical investigation of the lightwave propagation through dielectric elliptical fibers with conducting helical windings on the core-clad boundary is presented under the consideration of slow-wave approximation. The analysis essentially requires the use of elliptical coordinate system. Mathieu and the modified Mathieu functions are used as the representatives of the electromagnetic fields within the structure. Field components in the different sections of the guide are presented, and the characteristic dispersion relations for the system are deduced for 0° and 90° pitch angles. The investigation reveals that the pitch angle has ultimately no effect on the dispersion relations for their selected values. The effect of core ellipse eccentricity on the dispersion characteristics is presented for two different operating wavelengths, and considering different values of the core major axis length.     

Predetermined Chirality at Metal Centers

Asymmetric synthesis in coordination chemistry was described very clearly by Smirnoff in 1920, but, contrary to the development in organic chemistry, it was almost completely neglected for several decades. The interest in chirality in coordination chemistry (see the stereoview of [Ru(bpy)₃]²⁺) has increased rapidly in recent times as a consequence of developments in several fields where chirality is important (polynuclear systems, supramolecular structures, and enantioselective catalysis). Here we show many examples of how, through the choice of ligand, the configuration of a metal center or the chirality of a helicate can be predetermined.     

Template‐Directed Self‐Recognition of Alkyl‐Bridged Bis(catechol) Ligands in the Formation of Helicate‐Type Complexes

A controlling influence on the self‐assembly in the complexation reaction of a mixture of methylene‐ and ethylene‐bridged bis(catechol) ligands ( 1 ‐H₄ and 2 ‐H₄, respectively) with titanium(IV ) ions is exerted by alkali metal cations (see scheme). Thus, not a complicated mixture of complexes, but as a result of a self‐recognition of the ligands only well‐defined products are formed.     

Synthesis and Biological Evaluation of a Cyclo-β-tetrapeptide as a Somatostatin Analogue

Short β -peptides can mimic natural peptide hormones , as has been shown with a cyclo-β-tetrapeptide ( 1 ) that displays micromolar affinity to human somatostatin receptors. β-Peptides are thus a promising new class of peptidomimetics with potential high bioavailability due to their excellent resistance against proteases.