Development of miniature base editors using engineered IscB nickase.

As a miniature RNA-guided endonuclease, IscB is presumed to be the ancestor of Cas9 and to share similar functions. IscB is less than half the size of Cas9 and thus more suitable for in vivo delivery. However, the poor editing efficiency of IscB in eukaryotic cells limits its in vivo applications. Here we describe the engineering of OgeuIscB and its corresponding ωRNA to develop an IscB system that is highly efficient in mammalian systems, named enIscB. By fusing enIscB with T5 exonuclease (T5E), we found enIscB-T5E exhibited comparable targeting efficiency to SpG Cas9 while showing reduced chromosome translocation effects in human cells. Furthermore, by fusing cytosine or adenosine deaminase with enIscB nickase, we generated miniature IscB-derived base editors (miBEs), exhibiting robust editing efficiency (up to 92%) to induce DNA base conversions. Overall, our work establishes enIscB-T5E and miBEs as versatile tools for genome editing.

In Situ Charge Modification within Prussian Blue Analogue Nanocubes by Plasma for Oxygen Evolution Catalysis.

A targeted defect-induced strategy of metal sites in a porous framework is an efficient avenue to improve the performance of a catalyst. However, achieving such an activation without destroying the ordered framework is a major challenge. Herein, a dielectric barrier discharge plasma can etch the Fe(CN)6 group of the NiFe Prussian blue analogue framework in situ through reactive oxygen species generated in the air. Density functional theory calculations prove that the changed local electronic structure and coordination environment of Fe sites can significantly improve oxygen evolution reaction catalytic properties. The modified NiFe Prussian blue analogue is featured for only 316 mV at a high current density (100 mA cm-2), which is comparable to that of commercial alkaline catalysts. In a solar cell-driven alkaline electrolyzer, the overall electrolysis efficiency is up to 64% under real operation conditions. Over 80 h long-time continuous test under 100 mA cm-2 highlights superior durability. The density functional theory calculations confirm that the formation of OOH* is the rate-determining step over Fe sites, and Fe(CN)6 vacancy and extra oxygen atoms can introduce charge redistribution to the catalyst surface, which finally enhances the oxygen evolution reaction catalytic properties by reducing the overpotential by 0.10 V. Both experimental and theoretical results suggest that plasma treatment strategy is useful for modifying the skeletal material nondestructively at room temperature, which opens up a broad prospect in the field of catalyst production.

Metalation of a Hierarchical Self-Assembly Consisting of π-Stacked Cubes through Single-Crystal-to-Single-Crystal Transformation.

Single-crystal-to-single-crystal metalation of organic ligands represents a novel method to prepare metal-organic complexes, but remains challenging. Herein, a hierarchical self-assembly {(H12L8)·([N(C2H5)4]+)3·(ClO4-)15·(H2O)32} (1) (L = tris(2-benzimidazolylmethyl) amine) consisting of π-stacked cubes which are assembled from eight partially protonated L ligands is obtained. By soaking the crystals of compound 1 in the aqueous solution of Co(SCN)2, the ligands coordinate with Co2+ ions stoichiometrically and ClO4- exchange with SCN- via single-crystal-to-single-crystal transformation, leading to {([CoSCNL]+)8·([NC8H20]+)3·(SCN)11·(H2O)13} (2).

Trapping an Ester Hydrate Intermediate in a π-Stacked Macrocycle with Multiple Hydrogen Bonds.

Ester hydrates, as the intermediates of the esterification between acid and alcohol, are very short-lived and challenging to be trapped. Therefore, the crystal structures of ester hydrates have rarely been characterized. Herein, we present that the mono-deprotonated ester hydrates [CH3OSO2(OH)2]-, serving as the template for the self-assembly of a π-stacked boat-shaped macrocycle (CH3OSO2(OH)2)0.67(CH3OSO3)1.33@{[ClLCoII]6}·Cl4·13CH3OH·9H2O (1) (L = tris(2-benzimidazolylmethyl) amine), can be trapped in the host by multiple NH···O hydrogen bonds. In the solution of CoCl2, L, and H2SO4 in MeOH, HSO4- reacts with MeOH, producing [CH3OSO3]- via the ester hydrate intermediate of [CH3OSO3(OH)2]-. Both the product and the intermediate serve as the template directing the self-assembly of the π-stacked macrocycle, in which the short-lived ester hydrate is firmly trapped and stabilized, as revealed by single-crystal analysis.

A Cas9-transcription factor fusion protein enhances homology-directed repair efficiency.

Precise gene insertion or replacement in cells and animals that requires incorporation of a foreign DNA template into the genome target site by homology-directed repair (HDR) remains an inefficient process. One of the limiting factors for the inefficiency of HDR lies in the limited chance for colocalization of the donor template and target in the huge genome space. We here present a strategy to enhance HDR efficiency in animal cells by spatial and temporal colocalization of the donor and Cas9 by coupling the CRISPR system with a transcription factor (TF). We first identified that THAP domain-containing 11 (THAP11) can coordinate with CRISPR/Cas9 to increase HDR stably through screening multiple TFs from different species. We next designed donor structures with different fusion patterns with TF-specific DNA-binding motifs and found that appending two copies of THAP11-specific DNA binding motifs to both ends of the double-stranded donor DNA has an optimal effect to promote HDR. The THAP11-fused CRISPR system achieved more than twofold increase in HDR-mediated knock-in efficiency for enhanced green fluorescent protein (EGFP) tagging of endogenous genes in 293T cells. We also demonstrated up to 6-fold increases of knock-in through the combinational use of the TF-fused CRISPR and valnemulin, a recently discovered small-molecule HDR enhancer. This modified CRISPR system provides a simple but highly efficient platform to facilitate CRISPR-mediated KI manipulations.

Ultrahigh thermoelectric performance of Janus α-STe2 and α-SeTe2 monolayers.

Janus α-STe2 and α-SeTe2 monolayers are investigated systematically using first-principles calculations combined with semiclassical Boltzmann transport theory. Janus α-STe2 and α-SeTe2 monolayers are indirect semiconductors with band gaps of 1.20 and 0.96 eV, respectively. It is found that they possess ultrahigh figure of merit (ZT) values of 3.9 and 4.4, respectively, at 500 K, much higher than that of the pristine α-Te monolayer (2.8). The higher ZT values originating from Janus structures reduce lattice thermal conductivities remarkably compared with the pristine α-Te monolayer. The much higher phonon anharmonicity in Janus monolayers leads to significantly lower lattice thermal conductivity. It is also found that electronic thermal conductivity can play an important role in thermoelectric efficiency of materials with quite low lattice thermal conductivity. This work suggests the potential applications of Janus α-STe2 and α-SeTe2 monolayers as thermoelectric materials and highlights that using a Janus structure is an effective way to enhance thermoelectric performance.

From a Metal-Organic Square to a Robust and Regenerable Supramolecular Self-assembly for Methane Purification.

Porous supramolecular assemblies constructed by noncovalent interactions are promising for adsorptive purification of methane because of their easy regeneration. However, the poor stability arising from the weak noncovalent interactions has obstructed their practical applications. Here, we report a robust and easily regenerated polyhedron-based cationic framework assembled from a metal-organic square. This material exhibits a very low affinity for CH4 and N2 , but captures other competing gases (e.g. C2 H6 , C3 H8 , and CO2 ) with a moderate affinity. These results underpin highly selective separation of a range of gas mixtures that are relevant to natural gas and industrial off-gas. Dynamic breakthrough studies demonstrate its practical separation for C2 H6 /CH4 , C3 H8 /CH4 , CO2 /N2 , and CO2 /CH4 . Particularly, the separation time is ≈11 min g-1 for the C2 H6 /CH4 (15/85 v/v) mixture and ≈49 min g-1 for the C3 H8 /CH4 (15/85 v/v) mixture (under a flow of 2.0 mL min-1 ), respectively, enabling its capability for CH4 purification from light alkanes.

Constructing π-Stacked Supramolecular Cage Based Hierarchical Self-Assemblies via π···π Stacking and Hydrogen Bonding.

Constructing supramolecular cages with multiple subunits via weak intermolecular interactions is a long-standing challenge in chemistry. So far, π-stacked supramolecular cages still remain unexplored. Here, we report a series of π-stacked cage based hierarchical self-assemblies. The π-stacked cage (π-MX-cage) is assembled from 16 [MXL]+ ions (M = Mn2+, Co2+; X = Br-, SCN-, Cl-; and L = tris(2-benzimidazolylmethyl)amine) via 18 intermolecular π-stacking interactions. The tetrahedral cage, consisting of four [MXL]+ ions as the vertexes and six pairs of [MXL]+ ions as the edges, features 48 exterior N-H hydrogen bond donors for hydrogen bond formation with guest molecules. By variation of the M2+/X- pair, the π-MX-cage demonstrates unique versatility for incorporating a wide variety of species via different hydrogen-bonding modes during the assembly of hierarchical superstructures. In specific, the π-MnBr-cages encapsulate acetonitrile (CH3CN) or cis-1,3,5-cyclohexanetricarbonitrile (cis-HTN) molecules in the central voids, while a core-shell tetrahedral inorganic cluster [Mn(H2O)6]@([Mn(H2O)4]4[Br42-]6) (Mn@Mn4-cage) is captured within the interstitial regions between cages. The π-CoSCN-cages are capable of stabilizing reactive sulfur-containing species, such as S2O42-, S2O62-, and HSO3- ions, in the hierarchical superstructure. Finally, H2PO4- ions are incorporated between π-CoCl-cages, resulting in an inorganic mesoporous framework. These results provide insights into further exploring the chemistry and hierarchical assembly of supramolecular cages based on π-π stacking intermolecular interactions.

A novel SiO monolayer with a negative Poisson's ratio and Dirac semimetal properties.

Although a number of interesting physical properties such as a negative Poisson's ratio (NPR) and Dirac semimetal (DS) properties have been recently predicted in two-dimensional (2D) materials, the realization of a 2D material that exhibits both of these DS and NPR features has rarely been reported. Here by adopting particle swarm optimization (PSO) algorithms combined with first-principles methods, we successfully construct a novel SiO monolayer (Pmna), the dynamic and thermal stability of which was characterized using phonon spectrum calculations and molecular dynamics simulations. In particular, Young's modulus and Poisson's ratio calculations showed that the Pmna monolayer exhibits high mechanical anisotropy with an in-plane NPR originating from its puckered atomic arrangement. More notably, the band structure of the Pmna monolayer possesses zero bandgap with four Dirac cones in its first Brillouin zone, exhibiting a DS feature. From the calculations of orbital-resolved band structures, the Dirac cone was revealed to originate from the orbital hybridization of Si and O atoms. The Pmna monolayer is the first 2D structure in the Si-O system that has both an NPR and Dirac semi-metal properties, providing a new model for exploring 2D multifunctional materials.

Comparative investigation of the thermal transport properties of Janus SnSSe and SnS2 monolayers.

Recently, Janus two-dimensional (2D) materials as a new member of 2D derivatives have been receiving much attention due to their novel properties. In this work, the lattice thermal conductivity κL of the Janus SnSSe monolayer is investigated based on first-principles calculations, while that of the SnS2 monolayer is studied for comparison. It is found the the κL values of SnSSe and SnS2 are 13.3 and 11.0 W m-1 K-1 at room temperature, and acoustic branches dominate their thermal transport. Weaker phonon anharmonicity in SnSSe leads to a slightly higher κL, though it has weaker phonon harmonicity. The smaller Grüneisen parameters of TA and LA phonons lower than 1 THz in SnSSe indicate weaker phonon anharmonicity, resulting in a higher κL. Finally, the size effect and boundary effect are also investigated, exhibiting that the κL can further decrease at the nanoscale. Our work suggests that Janus SnSSe and SnS2 have a much lower κL compared with conventional transition metal dichalcogenides (TMDs) and are potential competitors in the thermoelectric field.

Two-dimensional carbon dioxide with high stability, a negative Poisson's ratio and a huge band gap.

Carbon dioxide (CO2) normally exists in a gaseous molecular state under ambient conditions, while two-dimensional (2D) crystals of CO2 have not been reported yet. In this work, based on density functional theory and the particle swarm optimization method, we unveil two CO2 2D crystals with space groups of P4[combining macron]M2 and Amm2. Our results show that these structures have excellent thermal, dynamic, and mechanical stability. The new structures are insulators with an indirect or direct band gap, while the indirect band gap can be tuned to be direct with small uniaxial strains. More importantly, the P4[combining macron]M2 structure has an in-plane negative Poisson's ratio, which is due to the interaction of the lattice symmetry and the local CO4 tetrahedron symmetry. In addition, the Amm2 sheet has a very large electronic band gap (>9 eV), which is the largest in all known 2D materials. Enthalpy curves indicate that these 2D structures may be obtained from the ambient phase of CO2 under high pressure. This work presents new structures of CO2, and because of their excellent performance in terms of stability, mechanical and electronic properties, they potentially have broad applications.

A covalent capillary coating of diazoresin and polyglycerol dendrimer for protein analysis using capillary electrophoresis.

Overcoming proteins adsorption on the inner surface of capillary has attracted increasing attention recently. By using the unique photochemistry reaction of diazoresin (DR), a new covalent capillary coating was prepared on the fused-silica capillary through layer-by-layer self-assembly of DR with polyglycerol (PG) dendrimer. The separation performance of covalently DR/PG-dendrimer coated capillary noticeably exceeded the bare capillary and the noncovalently linked DR/PG-dendrimer capillary. A baseline separation of lysozyme, myoglobin, bovine serum albumin, and ribonuclease A was achieved using CE within 20 min. Besides, the covalently linked DR/PG-dendrimer coating has the remarkable stability and reproducibility. Especially, compared with the traditional method which use highly toxic and moisture-sensitive silane coupling agent, this method seems to be a simple and environmental friendly way to prepare the covalently coated capillaries for CE.

Field-Induced Slow Magnetic Relaxation in an Octacoordinated Fe(II) Complex with Pseudo-D2d Symmetry: Magnetic, HF-EPR, and Theoretical Investigations.

An octacoordinated Fe(II) complex, [FeII(dpphen)2](BF4)2·1.3H2O (1; dpphen = 2,9-bis(pyrazol-1-yl)-1,10-phenanthroline), with a pseudo-D2d-symmetric metal center has been synthesized. Magnetic, high-frequency/-field electron paramagnetic resonance (HF-EPR), and theoretical investigations reveal that 1 is characterized by uniaxial magnetic anisotropy with a negative axial zero-field splitting (ZFS) (D ≈ -6.0 cm-1) and a very small rhombic ZFS (E ≈ 0.04 cm-1). Under applied dc magnetic fields, complex 1 exhibits slow magnetic relaxation at low temperature. Fitting the relaxation time with the Arrhenius mode combining Orbach and tunneling terms affords a good fit to all the data and yields an effective energy barrier (17.0 cm-1) close to the energy gap between the ground state and the first excited state. The origin of the strong uniaxial magnetic anisotropy for 1 has been clearly understood from theoretical calculations. Our study suggests that high-coordinated compounds featuring a D2d-symmetric metal center are promising candidates for mononuclear single-molecule magnets.

Advances in site-specific integration of transgene in animal genome.

The traditional transgenic technologies, such as embryo microinjection, transposon-mediated integration, or lentiviral transfection, usually result in random insertions of the foreign DNA into the host genome, which could have various disadvantages in the establishment of transgenic animals. Therefore, a strategy for site-specific integration of a transgene is needed to generate genetically modified animals with accurate and identical genotypes. However, the efficiency for site-specific integration of transgene is very low, which is mainly caused by two issues. The first one is the low efficiency of inducing double-strand break (DSB) at the target site of host genome in the initial process. The second one is the low efficiency of homologous recombination repair (HDR) between the target site and the donor plasmid carrying homologous arm and foreign genes. HDR is the most common mechanism for site-specific integration of a transgene. DSBs can stimulate DNA repair mainly by two competitive mechanisms, HDR and nonhomologous end joining (NHEJ). Hence, activation of HDR or inhibition of NHEJ can promote the HDR in the integration processes, thereby optimizing a specific targeting of the transgene. In this review, we summarize the recent advances in strategies for improving the site-specific integration of foreign transgene in transgenic technologies.

Effects of parameters, plasmid dosages and topological structures on transfection efficiency of porcine fetal fibroblasts using different electroporators.

To obtain an ideal transfection efficiency of porcine fetal fibroblasts, fluorescence activated cell sorting (FACS) was used to optimize parameters for transfection of porcine fetal fibroblasts (PFFs) with ECM? 830, NEPA 21 and Nucleofector? 2b in different conditions such as electroporation parameters, plasmid dosages and topological structures. The results show that the optimum poring pulse parameter of NEPA 21 is voltage 200 V, continuous 3 ms, interval 50 ms, 3 times, voltage attenuation range of 10%; and the transfection efficiency of Nucleofector? 2b is highest under U-023 program. Under the optimum conditions, FACS analysis demonstrates that Nucleofector? 2b and ECM? 830 have the highest transfection efficiency when transfecting 10 µg supercoiled plasmids into PFFs, and 8 µg for NEPA 21. Supercoiled plasmids show higher transfection efficiencies than linearized plasmids. Moreover, Nucleofector? 2b has the highest transfection efficiency among the three electroporation instruments. This study paves the way to generate transgenic or gene editing pigs with high efficiency.

Anisotropic Change in the Magnetic Susceptibility of a Dynamic Single Crystal of a Cobalt(II) Complex.

Atypically anisotropic and large changes in magnetic susceptibility, along with a change in crystalline shape, were observed in a CoII complex at near room temperature. This was achieved by combining oxalate molecules, acting as rotor, and a CoII ion with unquenched orbital angular momentum. A thermally controlled 90° rotation of the oxalate counter anion triggered a symmetry-breaking ferroelastic phase transition, accompanied by contraction-expansion behavior (ca. 4.5 %) along the long axis of a rod-like single crystal. The molecular rotation induced a minute variation in the coordination geometry around the CoII ion, resulting in an abrupt decrease and a remarkable increase in magnetic susceptibility along the direction perpendicular and parallel to the long axis of the crystal, respectively. Theoretical calculations suggested that such an unusual anisotropic change in magnetic susceptibility was due to a substantial reorientation of magnetic anisotropy induced by slight disruption in the ideal D3 coordination environment of the complex cation.

Influence of Intermolecular Interactions on Valence Tautomeric Behaviors in Two Polymorphic Dinuclear Cobalt Complexes.

Two polymorphic structures have been well determined in a valence tautomeric (VT) dinuclear cobalt complex. These polymorphs showed distinct thermal- and photomagnetic behavior, and are thus ideal for studying the "pure" intermolecular factors to VT transitions. In polymorph 1A, the VT cations are arranged head-to-waist with their neighbors and exhibit weak π⋅⋅⋅π interactions, resulting in a gradual and incomplete thermal VT transition. In contrast, the cations in polymorph 1B are arranged head-to-tail and exhibit relatively strong π⋅⋅⋅π interactions, leading to an abrupt and complete thermal VT transition with adjustable hysteresis loop at around room temperature. The VT process for both polymorphs can be induced by light, but the light-excited state of 1B⋅2H2 O has a higher thermal relaxation temperature than that of 1A⋅3H2 O.

Establishment of porcine Xist knockout model using CRISPR/Cas9 system.

Somatic cell nuclear transfer technique has great applications in livestock breeding, production of genetically modified animals, rescue of endangered species and treatment of human diseases. However, the currently low efficiency in animals cloning, an average of less than 5%, greatly hindered the rapid development of this technique. Among many factors which affect the efficiency of cloning pigs, X chromosome inactivation is an important one. Moreover, Xist gene is closely related to X chromosome inactivation, suggesting that it may directly or indirectly affects cloning efficiency. In this study, multiple sgRNAs were designed based on the CRISPR/Cas system, and two sites (Target 3 and Target 4) whose mutation efficiency were 1% and 3% at the cellular level were selected. We successfully knocked out Xist with 100% efficiency by microinjecting sgRNAs for Target 3 and Target 4 in embryo. Finally, 6 cloning piglets were born including two Xist-fully-knockout piglets. The follow-up studies on increasing cloning efficiency can be carried out based on the Xist-knockout model.

Thermally Induced Intra-Carboxyl Proton Shuttle in a Molecular Rack-and-Pinion Cascade Achieving Macroscopic Crystal Deformation.

Proton transport via dynamic molecules is ubiquitous in chemistry and biology. However, its use as a switching mechanism for properties in functional molecular assemblies is far less common. In this study, we demonstrate how an intra-carboxyl proton shuttle can be generated in a molecular assembly akin to a rack-and-pinion cascade via a thermally induced single-crystal-to-single-crystal phase transition. In a triply interpenetrated supramolecular organic framework (SOF), a 4,4'-azopyridine (azpy) molecule connects to two biphenyl-3,3',5,5'-tetracarboxylic acid (H4 BPTC) molecules to form a functional molecular system with switchable mechanical properties. A temperature change reversibly triggers a molecular movement akin to a rack-and-pinion cascade, which mainly involves 1) an intra-carboxyl proton shuttle coupled with tilting of the azo molecules and azo pedal motion and 2) H4 BPTC translation. Moreover, both the molecular motions are collective, and being propagated across the entire framework, leading to a macroscopic crystal expansion and contraction.

A Novel Ligustrazine Derivative T-VA Prevents Neurotoxicity in Differentiated PC12 Cells and Protects the Brain against Ischemia Injury in MCAO Rats.

Broad-spectrum drugs appear to be more promising for the treatment of acute ischemic stroke. In our previous work, a new ligustrazine derivative (3,5,6-trimethylpyrazin-2-yl) methyl 3-methoxy-4-[(3,5,6-trimethylpyrazin-2-yl)methoxy]benzoate (T-VA) showed neuroprotective effect on injured PC12 cells (EC50 = 4.249 µM). In the current study, we show that this beneficial effect was due to the modulation of nuclear transcription factor-κB/p65 (NF-κB/p65) and cyclooxygenase-2 (COX-2) expressions. We also show that T-VA exhibited neuroprotective effect in a rat model of ischemic stroke with concomitant improvement of motor functions. We propose that the protective effect observed in vivo is owing to increased vascular endothelial growth factor (VEGF) expression, decreased oxidative stress, and up-regulation of Ca(2+)-Mg(2+) ATP enzyme activity. Altogether, our results warrant further studies on the utility of T-VA for the potential treatment of ischemic brain injuries, such as stroke.