Synthesis and Chirality Control of Bulk Crystals and Nanocrystals: From a Right-Handed Nonpolar Chain to a Left-Handed Polar Chain

Both bulk crystals and nanocrystals of two helical complexes, [Cu­(μ₂-L)­(H₂O)]_<i>n</i> (<b>1</b>) and {[Cu­(μ₂-L)­(H₂O)]·2H₂O}_<i>n</i> (<b>2</b>) (H₂L = thiazolidine-2,4-dicarboxylic acid), have been synthesized with the chiralities of right-handedness (<b>1</b>) and left-handedness (<b>2</b>), respectively. 4-Cyanopyridine and poly­(vinylpyrrolidone) (PVP) have been applied to control the synthesis of complexes with different helicities in bulk-crystal and nanocrystal forms, respectively. <b>2</b> can be irreversibly transformed to <b>1</b> under heating. Associated with the conformation changing, the symmetry alters between nonpolar and polar space groups

Liquid Chromatography Tandem Mass Spectrometry Combined with Fourier Transform Mid-Infrared Spectroscopy and Chemometrics for Comparative Analysis of Raw and Processed <i>Gentiana rigescens</i>

<div><p>Herbal medicines have been shown to change chemical constituents upon different processing approaches, which might lead to different pharmacological activities and therapeutic effects. In this study, raw and processed <i>Gentiana rigescens</i> (wine-, vinegar-, and salt water-processed) were extracted and profiled by ultra-fast liquid chromatography tandem mass spectrometry (UFLC–MS/MS) and Fourier transform mid-infrared spectroscopy (FT-MIR). Hierarchical cluster analysis (HCA) based on FT-MIR revealed potential relationships between raw and processed samples, while the processed sample displayed chemical variation. Partial least-squares discriminate analysis (PLS-DA) was used for screening the marker metabolites. The results indicated that UFLC–UV-MS/MS and FT-MIR fingerprints with chemometrics could effectively evaluate the quality of <i>G. rigescens</i> under different processed approaches. Eight compounds were selected as potential marker metabolites for contributing to the most effective classification of raw and processed samples. In addition, these potential marker metabolites were tentatively identified by matching mass information with the fragmentation patterns of the published literature or standard compounds. These results revealed that UFLC–UV-MS/MS and FT-MIR methods coupled with chemometrics could provide an effective platform for monitoring quality variations of <i>G. rigescens</i> under different processed approaches.</p></div

Mechanical Bond-Induced Radical Stabilization

A homologous series of [2]­rotaxanes, in which cyclobis­(paraquat-<i>p</i>-phenylene) (CBPQT⁴⁺) serves as the ring component, while the dumbbell components all contain single 4,4′-bipyridinium (BIPY²⁺) units centrally located in the midst of oligomethylene chains of varying lengths, have been synthesized by taking advantage of radical templation and copper-free azide–alkyne 1,3-dipolar cycloadditions in the formation of their stoppers. Cyclic voltammetry, UV/vis spectroscopy, and mass spectrometry reveal that the BIPY^•+ radical cations in this series of [2]­rotaxanes are stabilized against oxidation, both electrochemically and by atmospheric oxygen. The enforced proximity between the BIPY²⁺ units in the ring and dumbbell components gives rise to enhanced Coulombic repulsion, destabilizing the ground-state co-conformations of the fully oxidized forms of these [2]­rotaxanes. The smallest [2]­rotaxane, with only three methylene groups on each side of its dumbbell component, is found to exist under ambient conditions in a monoradical state, a situation which does not persist in acetonitrile solution, at least in the case of its longer analogues. ¹H NMR spectroscopy reveals that the activation energy barriers to the shuttling of the CBPQT⁴⁺ rings over the BIPY²⁺ units in the dumbbells increase linearly with increasing oligomethylene chain lengths across the series of [2]­rotaxanes. These findings provide a new way of producing highly stabilized BIPY^•+ radical cations and open up more opportunities to use stable organic radicals as building blocks for the construction of paramagnetic materials and conductive molecular electronic devices