Chiral separation of amide conjugates of jasmonic acid by liquid chromatography

Summary Synthetic amide conjugates of (−)-jasmonic acid and its (+)-enantiomer were resolved by means of chiral liquid chromatography. The diastereomeric pairs prepared by chemical reaction of (±)-jasmonic acid with a series of (S)- or (R)-amino acids and with some (S)-amino acid alcohols were completely separated on Chiralpak AS using a mixture of n-hexane/2-propanal as mobile phase. The retention data indicate that the (−)-jasmonic acid conjugates eluted faster than those of the (+)-enantiomer, independent on the configuration of the bound amino acid. Likewise, enantiomeric derivatives of (±)-jasmonic acid and non-chiral amino acids were completely separated on the chiral stationary phase and showed the same elution sequence. The resolution factors,Rs, were found to range between 1.13 and 6.64. The separated compounds were chiropatically analyzed by measurement of the circular dichroism. Presented at the 21^st ISC held in Stuttgart, Germany, 15^th–20^th September, 1996     

A Set of Homo‐Oligomeric Standards Allows Accurate Protein Counting

Techniques based on fluorescence microscopy are increasingly used to count proteins in cells, but few stoichiometrically well‐defined standards are available to test their accuracy. A selection of bacterial homo‐oligomers were developed that contain 10–24 subunits and fully assemble when expressed in mammalian cells, and they can be used to easily validate/calibrate molecular counting methods. The utility of these standards was demonstrated by showing that nuclear pores contain 32 copies of the Nup107 complex.     

Second- and higher-order data generation and calibration: A tutorial

An introduction to multi-way calibration based on second- and higher-order data generation and processing is provided, with emphasis on practical experimental aspects. After a discussion concerning a proper nomenclature scheme, a suitable classification of the obtainable data, and the general features of the available algorithms and their underlying models, a series of examples is discussed in detail, with the purpose of illustrating the great potentiality of the field for the analytical community. Emphasis is directed toward the most popular multi-way data, i.e., second-order or matrix data, which can be conveniently measured in a variety of instruments. Third-order data are being increasingly studied and are also discussed, along with the less explored field of fourth-order data. The estimation of figures of merit, which analysts need to report during method development, is now sufficiently mature to be provided for the general audience.     

Additional insights from very‐high‐resolution 13C NMR spectra of long‐chain n‐alkanes

New information has been obtained from very‐high‐resolution ¹³C NMR studies of a series of long‐chain n‐alkanes. These compounds are fundamentally important in the petroleum industry and are essential to the life of some plants, flowers, and insects. At least partial resolution of the ten different ¹³C NMR signals of n‐C₂₀H₄₂ is observed at 11.7 T for solutions in C₆D₆ or C₆D₅CD₃. A ¹³C T₁ inversion‐recovery experiment provides much more detailed information than in previous studies of long‐chain n‐alkanes, demonstrates a steady increase in the relaxation times of the ten different carbons proceeding from the middle to the end of the chain because of segmental motion, and thus confirms the assignments for the interior carbons. In contrast, there is significant overlap for the signals for C‐7 and the more interior carbons in a solution of n‐C₁₆ or longer chain alkanes in CDCl₃. Not only are the chemical shifts sensitive to the solvent used, but also the relative chemical shifts change. Signals for the interior carbons of the odd‐number alkanes in CDCl₃ are better resolved than in the spectra of their even‐number counterparts. Some mixed aromatic solvent systems give increased dispersion of the cluster of C‐6 through C‐10 signals of n‐C₂₀H₄₂, n‐C₂₁H₄₄, and n‐C₂₂H₄₆. However, none of the solvents used could even partially resolve the C‐10 and C‐11 signals of n‐C₂₁H₄₄ or n‐C₂₂H₄₆ at 11.7 T, which may result from a different distribution of conformers for n‐C₂₁H₄₄ or n‐C₂₂H₄₆ than for n‐C₂₀H₄₂ and shorter n‐alkanes. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis of Dibenzofuran Derivatives from Spirodihydrocoumarins

effective and straightforward route has been accomplished for the synthesis of hexahydrodibenzofurans based on rearrangement of a spirodihydrocoumarin.     

A Wavenumber,Intensity, and Resolution Standard for High Resolution Ultraviolet/Visible Fourier Transform Spectroscopy

Abstract

The Re I (527. 55 nm, 18955 cm^?1) emission line from a hollow cathode lamp (HCL) is proposed as a standard for wavenumber accuracy and precision, resolution accuracy and precision and intensity precision. The Los Alamos Fourier transform spectrometer measured the HCL emission at high resolution (0. 026 cm^?1). The advantages of this spectral line to other emission standards is discussed.     

A Comparison of the High Resoluton Crystal Structures of the π- Molecuar Complexes of Anthracene and Phenothiazine with Pyromellitic Dianhydride

The π-molecular complexes formed by aromatic molecules with three rings tend to form crystals of high purity and are therefore ideal for solid state spectroscopic and photocurrent studies. We have therefore undertaken an investigation of the detailed structures of a number of such complexes in order to facilitate the interpretation of such data and other physical properties and in order to better understand the large changes in physical properties generated by small changes in composition and molecular packing. The piezoreflection spectra of the anthracene-pyromellitic dianhydride complex (A-PMDA) has been studied by Eckhardt and Merski (1973). The photo-current excitation spectra of A-PMDA was reported by Karl and Ziegler (1975) and more recently the preparation, optical properties, absorption and photoconductivity properties of phenothiazine-pyromellitic dianhydride have also been studied. (Anthonj, Karl, Robertson and Stezowski, 1979).     

Resolution of (D,L)-Phenylalanine in Biphasic System by α-Chymotrypsin Immobilized on Superparamagnetic Nanogels

α-Chymotrypsin immobilized on super paramagnetic nanogels covered with carboxyl groups, exhibited high stereoselectivity in kinetic resolution of racemic phenylalanine in toluene/water biphasic system, and even improved reusability over its parent free enzyme. The results also showed that the addition of ionic liquid to water phase could enhance the stereoselectivity of the immobilized enzyme to a certain extent while the conversion yield decreased. The long-term stability allows the supported enzyme with nano-scaled dimension to use in continuous chiral resolution reaction, which opens a new horizon for enzymatic chiral resolution in large-scale production.     

Merging Gradient-Based Methods to Improve Benchtop NMR Spectroscopy: A New Tool for Flow Reaction Optimization

Emerging low cost, compact NMR spectrometers that can be connected in-line to a flow reactor are suited to study reaction mixtures. The main limitation of such spectrometers arises from their lower magnetic field inducing a reduced sensitivity and a weaker spectral resolution. For enhancing the spectral resolution, the merging of Pure-Shift methods recognized for line narrowing with solvent elimination schemes was implemented in the context of mixtures containing protonated solvents. One more step was achieved to further enhance the resolution power on compact systems, thanks to multiple elimination schemes prior to Pure-Shift pulse sequence elements. For the first time, we were able to remove up to 6 protonated solvent signals simultaneously by dividing their intensity by 500 to 1700 with a concomitant spectral resolution enhancement for signals of interest from 9 to 12 as compared to the standard 1D ¹H. Then, the potential of this new approach was shown on the flow synthesis of a complex benzoxanthenone structure.