Artificial structures made of stacked two-dimensional crystals have recently been the focus of intense research activity. As in twisted or stacked graphene layers, these structures can show unusual behaviours and new phenomena. Among the various layered compounds that can be exfoliated, transition-metal dichalcogenides exhibit interesting properties governed by their structural symmetry and interlayer coupling, which are highly susceptible to stacking. Here, we obtain-by folding exfoliated MoS2 monolayers-MoS2 bilayers with different stacking orders, as monitored by second harmonic generation and photoluminescence. Appropriate folding can break the inversion symmetry and suppress interlayer hopping, evoking strong valley and spin polarizations that are not achieved in natural MoS2 bilayers of Bernal stacking. It can also enlarge the indirect bandgap by more than 100 meV through a decrease in the interlayer coupling. Our work provides an effective and versatile means to engineer transition-metal dichalcogenide materials with desirable electronic and optical properties.

A novel optical second harmonic generation arises from the stacking order of three centrosymmetric graphene monolayer sheets.

Physical separation of C 2 H 2 from CO 2 on metal−organic frameworks (MOFs) has received substantial research interest due to the advantages of simplicity, security, and energy efficiency. However, that C 2 H 2 and CO 2 exhibit very close physical properties makes their separation exceptionally challenging. Previous work appeared to mostly focused on introducing open metal sites that aims to enhance the C 2 H 2 affinity at desired sites, whereas the reticular manipulation of organic components has rarely been investigated. In this work, by reticulating preselected amino and hydroxy functionalities into isostructural ultramicroporous chiral MOFs Ni 2 (L-asp) 2 (bpy) (MOF-NH 2 ) and Ni 2 (L-mal) 2 (bpy) (MOF-OH)we targeted efficient C 2 H 2 uptake and C 2 H 2 /CO 2 separation, which outperforms most benchmark materials. Explicitly, MOF-OH adsorbs substantial amount of C 2 H 2 with record storage density of 0.81 g mL −1 at ambient conditions, which even exceeds the solid density of C 2 H 2 at 189 K. In addition, MOF-OH gave IAST selectivity of 25 toward equimolar mixture of C 2 H 2 /CO 2 , which is nearly twice higher than that of MOF-NH 2 . Notably, the adsorption enthalpies for C 2 H 2 at zero converge in both MOFs are remarkably low (17.5 kJ mol −1 for MOF-OH and 16.7 kJ mol −1 for MOF-NH 2 ), which to our knowledge are the lowest among efficient rigid C 2 H 2 sorbents. The efficiencies of both MOFs for the separation of C 2 H 2 /CO 2 are validated by multicycle breakthrough experiments. DFT calculations provide molecular-level insight over the adsorption/ separation mechanism. Moreover, MOF-OH can survive in boiling water for at least 1 week and can be easily scaled up to kilograms eco-friendly and economically, which is very crucial for potential industrial implementation.

Natural transport channels (or carriers), such as aquaporins, are a distinct type of biomacromolecule capable of highly effective transmembrane transport of water or ions. Such behavior is routine for biology but has proved difficult to achieve in synthetic systems. Perhaps most significantly, the enantioselective transmembrane transport of biomolecules is an especially challenging problem both for chemists and for natural systems. Herein, a group of homochiral zirconium metal−organic cages with four triangular opening windows have been proposed as artificial biomolecular channels for enantioselective transmembrane transport of natural amino acids. These structurally well-defined coordination cages are assembled from six synthetically accessible BINOL-derived chiral ligands as spacers and four n-Bu 3 -Cp 3 Zr 3 clusters as vertices, forming tetrahedral-shaped architectures that feature an intrinsically chiral cavity decorated with an array of specifically positioned binding sites mediated from phenol to phenyl ether to crown ether groups. Fascinatingly, the transformation of single-molecule chirality to global supramolecular chirality within the space-restricted chiral microenvironments accompanies unprecedented chiral amplification, leading to the enantiospecific recognition of amino acids. By virtue of the highly structural stability and excellent biocompatibility, the orientation-independent cages can be molecularly embedded into lipid membranes, biomimetically serving as single-molecular chiral channels for polar-residue amino acids, with the properties that cage-1 featuring hydroxyl groups preferentially transports the L-asparagine, whereas cage-2 attaching crown ether groups spontaneously favor transporting D-arginine. We therefore develop a new type of self-assembled system that can potentially mimic the functions of transmembrane proteins in nature, which is a realistic candidate for further biomedical applications.

Here we report the formation of an unexpected and unique family of chiral helicates.C rystal structures showt hat these triple-stranded Zn II 2 L 3 complexes are held together by subcomponent assembly of axially chiral diamine-functionalized 1,1'-biphenol ditopic with 2-formylpyridine and Zn II . Specifically,t he molecular helicity of the complexes can be controlled by the absolute configurations of the bimetallic vertices,which has been shown to be homoconfiguration (DD) or mesomeric configuration (DL), depending critically on the bulky groups and length of the spacers.F ascinatingly,i nt his system we can engineer the space-restricted chiral microenvironments with varied polar and apolar moieties,w hich profoundly influence the binding affinities and chiral discrimination properties of the helicates,l eading to highly enantioand helix-sense-selective recognition for chiral amino alcohols (up to 9.35). This work reveals the transformation of singlemolecule chirality to global supramolecular chirality within well-defined helicates and demonstrates that their chiral discrimination are highly dependent on the superior microenvironments.