Expanding vinyl ether monomer repertoire for ring-expansion cationic polymerization: Various cyclic polymers with tailored pendant groups

Herein, we clarified the ring-expansion cationic polymerization with a cyclic hemiacetal ester (HAE)-based initiator was versatile in terms of applicable vinyl ether monomers. Although there was a risk that higher reactive vinyl ethers may incur β-H elimination of the HAE-based cyclic dormant species to irreversibly give linear chains, the polymerizations were controlled to give corresponding cyclic polymers from various alkyl vinyl ethers of different reactivities. Functional vinyl ether monomers were also available, and for instance a vinyl ether monomer carrying an initiator moiety for metal-catalyzed living radical polymerization in the pendant allowed construction of ring-linear graft copolymers through the grafting-from approach. Furthermore, ring-based gel was prepared via the addition of divinyl ether at the end of the ring-expansion polymerization, where multi HAE bonds cyclic polymers or fused rings were crosslinked with each other. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3082–3089     

Saturated Heavier Group 14 Compounds as ‐Electron‐Acceptor (Z‐Type) Ligands

This review article describes the chemistry of transition‐metal complexes containing heavier group 14 elements (Si, Ge, and Sn) as the σ‐electron‐acceptor (Z‐type) ligands and discusses the characteristics of bonds between the transition metal and Z‐type ligand. Moreover, we review the iridium hydride mediated cleavage of E–X bonds (E=Si, Ge; X=F, Cl), where the key intermediates are pentacoordinate silicon or germanium compounds bearing a dative M→E bond.     

Gas-Phase Stability of Negatively Charged Organophosphate Metabolites Produced by Electrospray Ionization and Matrix-Assisted Laser Desorption/Ionization

The formation mechanisms of singly and multiply charged organophosphate metabolites by electrospray ionization (ESI) and their gas phase stabilities were investigated. Metabolites containing multiple phosphate groups, such as adenosine 5'-diphosphate (ADP), adenosine 5'-triphosphate (ATP), and D-myo-inositol-1,4,5-triphosphate (IP₃) were observed as doubly deprotonated ions by negative-ion ESI mass spectrometry. Organophosphates with multiple negative charges were found to be unstable and often underwent loss of PO₃ ^–, although singly deprotonated analytes were stable. The presence of fragments due to the loss of PO₃ ^– in the negative-ion ESI mass spectra could result in the misinterpretation of analytical results. In contrast to ESI, matrix-assisted laser desorption ionization (MALDI) produced singly charged organophosphate metabolites with no associated fragmentation, since the singly charged anions are stable. The stability of an organophosphate metabolite in the gas phase strongly depends on its charge state. The fragmentations of multiply charged organophosphates were also investigated in detail through density functional theory calculations.

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Chromatographic behavior of small organic compounds in low‐temperature high‐performance liquid chromatography using liquid carbon dioxide as the mobile phase

Low‐temperature high‐performance liquid chromatography, in which a loop injector, column, and detection cell were refrigerated at –35ºC, using liquid carbon dioxide as the mobile phase was developed. Small organic compounds (polyaromatic hydrocarbons, alkylbenzenes, and quinones) were separated by low‐temperature high‐performance liquid chromatography at temperatures from –35 to –5ºC. The combination of liquid carbon dioxide mobile phase with an octadecyl‐silica (C₁₈) column provided reversed phase mode separation, and a bare silica‐gel column resulted in normal phase mode separation. In both the cases, nonlinear behavior at approximately –15ºC was found in the relationship between the temperature and the retention factors of the analytes (van't Hoff plots). In contrast to general trends in high‐performance liquid chromatography, the decrease in temperature enhanced the separation efficiency of both the columns.     

Measuring the Relative Hydrogen‐Bonding Strengths of Alcohols in Aprotic Organic Solvents

Voltammetric experiments with 9,10‐anthraquinone and 1,4‐benzoquinone performed under controlled moisture conditions indicate that the hydrogen‐bond strengths of alcohols in aprotic organic solvents can be differentiated by the electrochemical parameter ΔE_p^red=|E_p^red(1)?E_p^red(2)|, which is the potential separation between the two one‐electron reduction processes. This electrochemical parameter is inversely related to the strength of the interactions and can be used to differentiate between primary, secondary, tertiary alcohols, and even diols, as it is sensitive to both their steric and electronic properties. The results are highly reproducible across two solvents with substantially different hydrogen‐bonding properties (CH₃CN and CH₂Cl₂) and are supported by density functional theory calculations. This indicates that the numerous solvent–alcohol interactions are less significant than the quinone–alcohol hydrogen‐bonding interactions. The utility of ΔE_p^red was illustrated by comparisons between 1) 3,3,3‐trifluoro‐n‐propanol and 1,3‐difluoroisopropanol and 2) ethylene glycol and 2,2,2‐trifluoroethanol.     

Stereospecific Synthesis of a Dihydroxyethylene Isostere of Cyclohexylalanine Amide, (2S,3R,4S)-4-Amino-5-Cyclohexyl-1-Morpholino-2,3-Pentanediol(ACMP) from a Protected Sugar

ABSTRACT

A transition-state analogue of a renin inhibitor at the scissile site, a dihydroxyethylene isostere of cyclohexylalanine amide, (2S,3R,4S)-4-amino-5-cyclohexyl-1-morpholino-2,3-pentanediol(ACMP), was synthesized from 1,2:5,6-di-O-isopropylidene-α-D-allofuranose stereospecifically.     

Online tool for calculating null points in various inversion recovery sequences

Accurate equations for calculating the inversion time of the null point (TI_null) in inversion recovery (IR) sequences are required for adequate suppression of fat or cerebrospinal fluid (CSF) but are not widely known. The purpose of this study is to elucidate the process of deriving accurate TI_null equations using schematic diagrams that allow the equations to be easily understood, and to devise a convenient online tool for instant calculation of TI_null.     

Chemical and Genetic Study of Ligularia anoleuca and L. veitchiana in Yunnan and Sichuan Provinces of China

Chemical and genetic study of Ligularia anoleuca and L. veitchiana, which belong to section Ligularia, series Speciosae, was carried out. From L. anoleuca samples, collected in Yunnan and Sichuan Provinces of China, a new compound, furanoeremophil‐1(10)‐en‐6α‐ol, was isolated together with known 6β‐{[2‐(hydroxymethyl)prop‐2‐enoyl]oxy}furanoeremophil‐1(10)‐ene and 1β,10β‐epoxy‐6β‐{[2‐(hydroxymethyl)prop‐2‐enoyl]oxy}furanoeremophilane. From L. veitchiana samples, collected in Yunnan Province, euparin, 2‐isopropenyl‐5,6‐dimethoxybenzofuran, and 6‐hydroxy‐3β‐methoxytrementone were isolated. DNA Sequencing of the internal transcribed spacers of the ribosomal RNA gene showed that the two species are not particularly close despite morphological similarities, in agreement with the chemical results.