Quadruply BN-Fused Tetrathia[8]circulenes with Flexible Frameworks: Synthesis,Structures and Properties

Quadruply BN-fused tetrathia[8]circulenes were synthesized through four-fold electrophilic borylation. The single-crystal X-ray diffraction analysis revealed that the BN-fused tetrathia[8]circulene with peripheral phenyl groups exhibits crystal polymorphism, in which the circulene core adopts both planar and saddle conformations in the solid state. The experimental and theoretical studies revealed that the weaker aromaticity of azaborine compared with benzene renders the flexibility of the BN-fused tetrathia[8]circulenes.     

Enthalpically and Entropically Favorable Self-Assembly: Synthesis of C4h-Symmetric Tetraazatetrathia[8]circulenes by Regioselective Introduction of Pyridine Rings

Self-assembly of π-conjugated molecules in solution generally occurs owing to either an enthalpic or an entropic gain; however, designing π-conjugated systems that simultaneously exhibit enthalpically and entropically favorable self-assembly behavior is challenging. Herein, the self-assembly behavior of tetraazatetrathia[8]circulenes is disclosed, which is driven by both enthalpy and entropy. Single-crystal X-ray diffraction analysis demonstrated that molecules of these tetraazatetrathia[8]circulenes form face-to-face stacked dimers with a 1D columnar structure owing to the circularly arranged dipole moments. Importantly, concentration- and temperature-dependent ¹H NMR spectra revealed that the formation of self-assemblies of tetraazatetrathia[8]circulenes in chloroform and methanol is favored by both enthalpic and entropic factors. The unique association behavior is due to the presence of sp²-hybridized nitrogen atoms, which weakly coordinate to the hydrogen atoms of these solvents and reduce the π-electron density of the circulene cores.     

Single-Step N-Terminal Modification of Proteins via a Bio-Inspired Copper(II)-Mediated Aldol Reaction

The chemical modification of proteins is an effective technique for manipulating the properties and functions of proteins, and for creating protein-based materials. The N-terminus is a promising target for single-site modification that provides modified proteins with uniform structures and properties. In this paper, a copper(II)-mediated aldol reaction with 2-pyridinecarboxaldehyde (2-PC) derivatives is proposed as an operationally simple method to selectively modify the N-terminus of peptides and proteins at room temperature and physiological pH. The copper(II) ion activates the N-terminal amino acids by complexation with an imine of the N-terminal amino acid and 2-PCs, realizing the selective formation of the nucleophilic intermediate at the N-terminus. This results in a stable carbon-carbon bond between the 2-PCs and the α-carbon of various N-terminal amino acids. The reaction is applied to four different proteins, including biopharmaceuticals such as filgrastim and trastuzumab. The modified trastuzumab retains the human epidermal growth factor receptor 2 recognition activity.     

Evolution of long-period stacking order (LPSO) in Mg97Zn1Gd2 cast alloys viewed by HAADF-STEM multi-scale electron tomography

We have studied three-dimensional (3D) structures and growth processes of 14H-type long-period stacking order (LPSO) formed in Mg₉₇Zn₁Gd₂ cast alloys by single tilt-axis electron tomography (ET) using high-angle annular dark-field scanning transmission electron microscopy. Evolution of the solute-enriched stacking faults (SFs) and the 14H LPSO by ageing were visualised in 3D with a high spatial resolution in multi-scale fields of views from a few nanometres to ~10 μm. Lateral growth of the solute-enriched SFs and the LPSO in the (0?0?0?1)_Mg plane is notable compared to the out-of-plane growth in the [0?0?0?1]_Mg direction. The 14H LPSO grows at the cost of decomposition of the (Mg, Zn)₃Gd-type precipitates, and accompany a change of in-plane edge angles from 30 to 60°. We have updated the Time–Temperature–Transformation diagram for precipitation in Mg₉₇Zn₁Gd₂ alloys: starting temperatures of both solute-enriched SFs and LPSO formation shifted to a shorter time side than those in the previous diagram.     

Measurement technique for depth profiling in time-domain low-coherence interferometer

A measurement technique for depth profiling in a time-domain low-coherence interferometer has been proposed. The spatial variation of the optical path caused by a diffraction grating in the Littrow configuration produces a white-light interferogram. A one-dimensional charge-coupled device (1D-CCD) detector is used to measure the undersampled white-light interferogram. The position of the reflective boundary is calculated from the rate of phase change with spatial frequency, which is based on the sub-Nyquist sampling of the white-light interferogram in the frequency domain.     

One‐Pot Stereoselective Synthesis of 2‐Acylaziridines and 2‐Acylpyrrolidines from N‐(Propargylic)hydroxylamines

The stereoselective direct transformation of N‐(propargylic)hydroxylamines into cis‐2‐acylaziridines was achieved by the combined use of AgBF₄ and CuCl. Copper salts were found to promote the transformation of the intermediary 4‐isoxazolines into 2‐acylaziridines and both 3‐aryl‐ and 3‐alkyl‐substituted 2‐acylaziridines could be prepared by using this method. Furthermore, subsequent 1,3‐dipolar cycloaddition of azomethine ylides that were generated in situ from the intermediary 2‐acylaziridines with maleimides was achieved in a stereoselective one‐pot procedure to afford the corresponding 2‐acylpyrrolidines, which consisted of an octahydropyrrolo[3,4‐c]pyrrole skeleton.