Zhijun Du

An Optically Active Polymer for Broad-Spectrum Enantiomeric Recognition of Chiral Acids

Recognition of enantiomers of chiral acids by anion-π or lone pair-π interactions has not yet been investigated but is a significant and attractive challenge. This study reports an optically active polymer-based supramolecular system with capabilities of discriminating enantiomers of various chiral acids. The polymer featuring alternate π-acidic naphthalenediimides (NDIs) and methyl l-phenylalaninates in the backbone exhibits an unprecedented slow self-assembly process that is susceptible to perturbation by various chiral acids. Thus, the combination of anion-π or lone pair-π interactions and sensitivity of the polymeric self-assembly process to external chiral species endows the system with recognition capabilities. This is the first time that anion-π or lone pair-π interactions have been applied in the recognition of enantiomers of various chiral acids with a single system. The results shed light on new strategies for material design by integrating π-acidic aromatic systems and chiral building blocks to afford relevant advanced functions.

Dehydrogenation and dehalogenation of amines in MALDI‐TOF MS investigated by isotopic labeling

Secondary and tertiary amines have been reported to form [M-H](+) that correspond to dehydrogenation in matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS). In this investigation, we studied the dehydrogenation of amines in MALDI-TOF MS by isotopic labeling. Aliphatic amines were labeled with deuterium on the methylene of an N-benzyl group, which resulted in the formation of [M-D](+) and [M-H](+) ions by dedeuteration and dehydrogenation, respectively. This method revealed the proton that was removed. The spectra of most tertiary amines with an N-benzyl group showed high-intensity [M-D](+) and [M-H](+) ion peaks, whereas those of secondary amines showed low-intensity ion peaks. Ratios between the peak intensities of [M-D](+) and [M-H](+) greater than 1 suggested chemoselective dehydrogenation at the N-benzyl groups. The presence of an electron donor group on the N-benzyl groups enhanced the selectivity. The dehalogenation of amines with an N-(4-halobenzyl) group was also observed alongside dehydrogenation. The amino ions from dehalogenation can undergo second dehydrogenation. These results provide the first direct evidence about the position at which dehydrogenation of an amine occurs and the first example of dehalogenation of haloaromatic compounds in MALDI-TOF MS. These results should be helpful in the structural identification and elucidation of synthetic and natural molecules.

Sequence‐Dependent Self‐Assembly of Chiral Polyimides

Sequence-defined chiral polyimides comprising identical asymmetric diamine monomers arranged in different directions along the main chain were designed and prepared. These new sequence-defined polymers exhibit sequence-dependent self-assembly behaviors and responses to ibuprofen enantiomers, as revealed by their chiroptical spectra and gelation properties. For the first time, the self-assembly of polymers and their interactions with guest molecules have been successfully controlled by means of the directional arrangement of the monomers in their polymer backbones.

4-Dimethylaminopyridine-catalyzed dynamic kinetic resolution in asymmetric synthesis of P-chirogenic 1,3,2-oxazaphospholidine-2-oxides

Excellent diastereoselectivity (dr value up to 100 : 0) was achieved in DMAP-catalyzed P–N bond formation in the synthesis of P-chirogenic organophosphines from phenylphosphonic dichloride (PhP(O)Cl2) and (S)-2-pyrrolidinemethanol derivatives. Investigations using NMR spectroscopy and calculations revealed the formation of a bimolecular complex from (PhP(O)Cl2) and revealed DMAP as an ‘active phosphonyl’ that was converted to the P–N bonded compound with a significant preference for one of two diastereomers through dynamic kinetic resolution. These results present for the first time the mechanism of conversion from an achiral phosphorus centre to a P-stereogenic centre by direct stereoselective reaction at the phosphorus centre.

Surface modification of high-performance polyimide fibres by using a silane coupling agent

ABSTRACT The silane coupling agent 3-aminopropyltriethoxysilane (KH-550) was used to modify the surface of two kinds of high-performance polyimide (PI) fibres (i.e., PI-1 and PI-2). The surface chemical composition, morphologies and roughness of modified PI fibres were characterised by XPS, SEM and AFM. Results showed that the elemental ratio between O and C, the surface oxygen concentration and the surface roughness increased with KH-550 concentration. However, the interfacial shear strength (IFSS) and interlaminar shear strength (ILSS) values of PI fibre/epoxy resin composites increased and then decreased with KH-550 concentration. When KH-550 concentration was increased to 4 wt%, the IFSS and ILSS values reached their maximum point. At this point, the IFSS values were found increase by 17.3% and 8.3% for PI-1 and PI-2, respectively, compared with their pristine state. Meanwhile, the ILSS values of PI-1- and PI-2-reinforced composites were found increase by 22.4% and 24.1%, respectively. Graphical Abstract GRAPHICAL ABSTRACT

Hexagonal Lyotropic Liquid Crystal from Simple “Abiotic” Foldamers

Abstract The motivation of foldamer chemistry is to identify novel building blocks that have the potential to imitate natural species. Peptides and peptide mimetics can form stable helical conformations and further self‐assemble into diverse aggregates in water, where it is difficult to isolate a single helix. In contrast, most “abiotic” foldamers may fold into helical structures in solution, but are difficult to assemble into tertiary ones. It remains a challenge to obtain “abiotic” species similar to peptides. In this paper, a novel foldamer scaffold, in which p‐phenyleneethynylene units are linked by chiral carbon atoms, was designed and prepared. In very dilute solutions, these oligomers were random coils. The hexamer and octamers could form a hexagonal lyotropic liquid crystal (LC) in CH2Cl2 when the concentrations reached the critical values. The microscopic observations indicated that they could assemble into the nanofibers in the LC. Interestingly, after some LC phases were diluted at room temperature, the nanofibers could be preserved. The good stabilities of the assemblies are possibly attributed to a more compact backbone and more rigid side chains.