Wei-Jian Xu

Cathepsin L function in insect moulting: molecular cloning and functional analysis in cotton bollworm, Helicoverpa armigera

Moulting is an essential process of insect development but little is known about cysteine proteases in the process. Here, we detail a proteolytic activity profile from fifth larval instar to new pupae of the lepidopteran Helicoverpa armigera. At fifth to sixth instar moulting, the activities were significantly higher than those in non‐moulting stages, and were inhibited by the cysteine protease inhibitor, 2S, 3S‐trans‐epoxysuccinyl‐L‐leucylamido‐3‐methylbutane ethyl ester (E‐64), or by the cathepsin L‐selective inhibitor CLIK148. Further, a 1513 bp cathepsin L cDNA (Har‐CL) was isolated from the H. armigera larval cuticle and epidermis layer. Har‐CL gene expression, which is correlated closely with ecdysone, was higher during larval moulting. Injection of E‐64 or CLIK148 resulted in delayed fifth to sixth instar moulting, suggesting an essential role for cathepsin L in larval moulting.

Structural phase transitions in perovskite compounds based on diatomic or multiatomic bridges

The structural phase transitions in perovskite compounds were revived in the past decade by the emergence of a large number of perovskite compounds based on diatomic or multiatomic bridges, e.g. CN−, N3−, HCOO−, SCN−, and N(CN)2−, with various interesting properties for possible applications such as in dielectric switches, ferroelectrics, and multiferroics. Compared with the well-studied perovskite oxides and halides, these new perovskite compounds with larger bridges give rise to an increase in the complexity of structural variations as well as an opportunity to tailor the physical properties by taking advantage of the designable and tunable characteristics of the metal species, bridging ligands, and guest cation components. Here, we highlight the recent advances on the thermally-induced structural phase transitions of the perovskite compounds based on the diatomic or multiatomic bridges, focusing on the important role of the components in the phase transition behaviours as well as the intrinsic switching behaviours of physical properties.

A Molecular Perovskite with Switchable Coordination Bonds for High-Temperature Multiaxial Ferroelectrics

The underlying phase transitions of ferroelectric mechanisms in molecular crystals are mainly limited to order-disorder and displacive types that are not involved in breaking of the chemical bonds. Here, we show that the bond-switching transition under ambient pressure is designable in molecular crystals, and demonstrate how to utilize the weaker and switchable coordination bonds in a novel molecular perovskite, [(CH3)3NOH]2[KFe(CN)6] (TMC-1), to afford a scarce multiaxial ferroelectrics with a high Curie temperature of 402 K and 24 equivalent ferroelectric directions (more than BaTiO3). The high-quality thin films of TMC-1 can be easily fabricated by a simple solution process, and to reveal perfect ferroelectric properties at both macroscopic and microscopic scales, suggesting TMC-1 as a promising candidate for applications in next-generation flexible electronics. The presented molecular assembly strategy, together with the achieved bond-switching ferroelectric mechanism, opens a new avenue for designing advanced ferroelectric materials.

A brilliant cryogenic magnetic coolant: magnetic and magnetocaloric study of ferromagnetically coupled GdF3

The use of paramagnetic molecules as cryogenic coolants usually requires relatively large fields to obtain a practical cooling effect. Thus, research into magnetic molecular materials with larger MCEs in fields of ≤2 T is the main focus in this area. In this work, the crystal structure, magnetic susceptibility and isothermal magnetization for the inorganic framework material GdF3 were measured, and the isothermal entropy change was evaluated up to 9 T. Thanks to the combination of the large isotropic spin of Gd3+, the dense structure and weak ferromagnetic interaction, an extremely large −ΔSm for GdF3 was observed up to 528 mJ cm−3 K−1 for Δμ0H = 9 T, proving it to be an exceptional cryogenic magnetic coolant.

Zeolite CAN and AFI-Type Zeolitic Imidazolate Frameworks with Large 12-Membered Ring Pore Openings Synthesized Using Bulky Amides as Structure-Directing Agents.

Using bulky amides as the structure-directing agents (SDAs) is an alternative synthetic strategy for the exploration of crystalline large pore (≥12-membered ring) zeolitic imidazolate frameworks (ZIFs). Specifically, by using the bulky amides, dibutylformamide (DBF) and dipropylformamide (DPF) as solvent and imidazole (Im) as a ligand, two ZIFs mimicking the CAN and AlPO-5 (AFI) zeotypes with 12-membered ring (MR) pore openings were synthesized, and denoted as CAN-[Zn(Im)2] and AFI-[Zn(Im)2], respectively. These two materials are the first known examples of Zn(Im)2 polymorphs with 12-MR pores and AFI-[Zn(Im)2] has the largest pore apertures reported to date for ZIF materials. The concept that the bulky amides used were not simply acting as the solvent, but were in fact acting as SDAs or templates during the synthesis of the large pore ZIFs, was suggested by the closeness of the geometrical fit between the guest DBF and the can cages (composite building units) of the CAN-[Zn(Im)2].

Importing spontaneous polarization into a Heisenberg ferromagnet for a potential single-phase multiferroic

A novel two-dimensional Heisenberg ferromagnet with a flexible organic layer, [C6H5(CH2)4NH3]2[CuCl4], undergoes ferroelastic, ferroelectric and ferromagnetic transitions at 337, 143 and 7.8 K, respectively. The ferromagnet was characterized by variable-temperature thermal measurements, in situ single-crystal X-ray structure analyses, anisotropic dielectric measurements, and pyroelectric and magnetic analyses. Differing from the other layered perovskite-like compounds, this compound revealed an extraordinary distorted polar structure with five times the cell volume at its polar phase because of the flexibility of the organic layer. Hence, this presents an approach to introduce spontaneous electric polarization into the Heisenberg ferromagnet for single-phase multiferroics. Moreover, due to the cooperation between the frozen [C6H5(CH2)4NH3]+ cations and the tilting of the CuCl6 octahedra, this potential multiferroic compound simultaneously exhibits dielectric and magnetic bistabilities during both the ferroelastic and ferroelectric transitions.

Order–disorder phase transition in the first thiocyanate-bridged double perovskite-type coordination polymer: [NH4]2[NiCd(SCN)6]

The first thiocyanate-bridged double perovskite-type coordination polymer [NH4]2[NiCd(SCN)6] is reported here, which undergoes a reversible structural phase transition at around 120 K. An order–disorder mechanism for this transition is disclosed by X-ray structural analyses, dielectric measurement, as well as molecular dynamics simulations.

Room-temperature optic-electric duple bistabilities induced by plastic transition

We disclosed that acetamidinium perchlorate is a plastic crystal undergoing a near-room-temperature plastic transition. Thanks to drastic symmetry breaking during the plastic transition, it displays remarkable nonlinear optical switching with a high on/off contrast and a superior reversibility, as well as rapid dielectric switching between the high and low dielectric states.

Deformable Mn(III)–Schiff-base dimer for anomalously large positive and negative anisotropic thermal expansions

A new molecular crystal with supramolecular layers assembled by a Mn(III)–Schiff-base dimer and fumaric acid was investigated by means of variable-temperature single-crystal structural analyses. The Mn(III)–Schiff-base dimer reveals remarkable thermally-induced deformation and hence causes anomalously large positive and negative anisotropic thermal expansions in the supramolecular layers, providing a new type of promising weak supramolecular synthon for designing sensitive thermomechanical actuators.

Thermal-induced reversible ferroelastic phase transition in a new bromethyl-substituted molecular rotor

A new bromethyl-substituted molecular rotor, [Cu(dabcoCH2Br)(H2O)Br3] (dabcoCH2Br+=1-(2-bromethyl)-1,4-diazoniabicyclo[2.2.2]octane cation), which belongs to a family of halomethyl-substituted molecular rotors, was synthesized and structurally characterized. The reversible phase transition at ca. 250 K was well established for this molecular rotor by thermal analyses, variable-temperature X-ray diffraction, and variable temperature dielectric measurements. The order-disorder transformation of the rotator part (dabco moiety) causes ferroelastic phase transition with an Aizu notation of mmmF2/m from high-temperature orthorhombic phase (Pbnm) to low-temperature monoclinic phase (P21/n). More important, in reference to the density functional theory calculations and structural analyses, the key factors to tune the phase transition behaviors are discussed in detail for this family of halomethyl-substituted molecular rotors.