No abstract

The CRISPR-Cas systems, as exemplified by CRISPR-Cas9, are RNA-guided adaptive immune systems used by bacteria and archaea to defend against viral infection. The CRISPR-Cpf1 system, a new class 2 CRISPR-Cas system, mediates robust DNA interference in human cells. Although functionally conserved, Cpf1 and Cas9 differ in many aspects including their guide RNAs and substrate specificity. Here we report the 2.38 Å crystal structure of the CRISPR RNA (crRNA)-bound Lachnospiraceae bacterium ND2006 Cpf1 (LbCpf1). LbCpf1 has a triangle-shaped architecture with a large positively charged channel at the centre. Recognized by the oligonucleotide-binding domain of LbCpf1, the crRNA adopts a highly distorted conformation stabilized by extensive intramolecular interactions and the (Mg(H2O)6)(2+) ion. The oligonucleotide-binding domain also harbours a looped-out helical domain that is important for LbCpf1 substrate binding. Binding of crRNA or crRNA lacking the guide sequence induces marked conformational changes but no oligomerization of LbCpf1. Our study reveals the crRNA recognition mechanism and provides insight into crRNA-guided substrate binding of LbCpf1, establishing a framework for engineering LbCpf1 to improve its efficiency and specificity for genome editing.

Nonaqueous rechargeable lithium–oxygen batteries (LOBs) are one of the most promising candidates for future electric vehicles and wearable/flexible electronics. However, their development is severely hindered by the sluggish kinetics of the ORR and OER during the discharge and charge processes. Here, we employ MOF-assisted spatial confinement and ionic substitution strategies to synthesize Ru single atoms riveted with nitrogen-doped porous carbon (Ru SAs-NC) as the electrocatalytic material. By using the optimized Ru0.3 SAs-NC as electrocatalyst in the oxygen-breathing electrodes, the developed LOB can deliver the lowest overpotential of only 0.55 V at 0.02 mA cm–2. Moreover, in-situ DEMS results quantify that the e–/O2 ratio of LOBs in a full cycle is only 2.14, indicating a superior electrocatalytic performance in LOB applications. Theoretical calculations reveal that the Ru–N4 serves as the driving force center, and the amount of this configuration can significantly affect the internal affinity of intermediate species. The rate-limiting step of the ORR on the catalyst surface is the occurrence of 2e– reactions to generate Li2O2, while that of the OER pathway is the oxidation of Li2O2. This work broadens the field of vision for the design of single-site high-efficiency catalysts with maximum atomic utilization efficiency for LOBs.

Conductive polymer hydrogels are receiving considerable attention in applications such as soft robots and human-machine interfaces. Herein, a transparent and highly ionically conductive hydrogel that integrates sensing, UV-filtering, water-retaining, and anti-freezing performances is achieved by the organic combination of tannic acid-coated hydroxyapatite nanowires (TA@HAP NWs), polyvinyl alcohol (PVA) chains, ethylene glycol (EG), and metal ions. The highly ionic conductivity of the hydrogel enables tensile strain, pressure, and temperature sensing capabilities. In particular, in terms of the hydrogel strain sensors based on ionic conduction, it has high sensitivity (GF = 2.84) within a wide strain range (350%), high linearity (R 2 = 0.99003), fast response (≈50 ms) and excellent cycle stability. In addition, the incorporated TA@HAP NWs act as a nano-reinforced filler to improve the mechanical properties and confer a UV-shielding ability upon the hydrogel due to its size effect and the characteristics of absorbing ultraviolet light waves, which can reflect and absorb short ultraviolet rays and transmit visible light. Meanwhile, owing to the water-locking effect between EG and water molecules, the hydrogel exhibits freezing resistance at low temperatures and moisture retention at high temperatures. This biocompatible and multifunctional conductive hydrogel provides new ideas for the design of novel ionic skin devices.

Rational design and bottom-up synthesis based on the structural topology is a promising way to obtain two-dimensional metal–organic frameworks (2D MOFs) in well-defined geometric morphology. Herein, a topology-guided bottom-up synthesis of a novel hexagonal 2D MOF nanoplate is realized. The hexagonal channels constructed via the distorted (3,4)-connected Ni2(BDC)2(DABCO) (BDC = 1,4-benzene­dicarboxylic acid, DABCO = 1,4-diazabicyclo[2.2.2]­octane) framework serve as the template for the specifically designed morphology. Under the inhibition and modulation of pyridine through a substitution–suppression process, the morphology can be modified from hexagonal nanorods to nanodisks and to nanoplates with controllable thickness tuned by the dosage of pyridine. Subsequent pyrolysis treatment converts the nanoplates into a N-doped Ni@carbon electrocatalyst, which exhibits a small overpotential as low as 307 mV at a current density of 10 mA cm–2 in the oxygen evolution reaction.

No abstract

3D ordered meso-macroporous (3DOMM) Ce0.2Zr0.8O2 (CZO) was successfully synthesized by a combined method of evaporation-induced interfacial self-assembly (EISA) and colloidal crystal templates (CCT). The multifunctional catalysts of spinel-type Pd x Co3–x O4 nanoparticles (NPs) supported on 3DOMM CZO were fabricated by a gas bubbling assisted coprecipitation (GBCP) method. The relationship between nanostructure (hierarchical pore and spinel-type active phase) and activity during catalytic soot oxidation was studied by the techniques of SEM, TEM, XPS, H2-TPR, NO oxidation, soot-TPO, and so on. The 3DOMM structure with a larger surface area and total pore volume increases the amount of supported active sites and enhances the contact efficiency between reactants (soot, O2, and NO) and catalysts. Spinel-type Pd x Co3–x O4 (AB2O4) binary active sites by substitution for Co2+ (A site) with Pd2+ cations are beneficial for improving activation efficiency for gaseous reactants (NO and O2). The novel nanocatalysts of 3DOMM CZO-supported spinel-type Pd x Co3–x O4 NPs exhibited superb catalytic performance and strong nanostructure-dependent activity for soot oxidation under loose contact of soot with catalyst. For instance, the T 10, T 50, and T 90 values of 3DOMM PdCo2O4/CZO catalyst with the highest catalytic activity (TOF = 2.56 h–1) are only 313, 367, and 404 °C, respectively. The NO2-assisted catalytic mechanism for soot oxidation is studied and proposed by in situ Raman spectra, and the role of spinel-type PdCo2O4 binary active sites is revealed. 3DOMM Pd x Co3–x O4/CZO catalysts are decent systems for soot oxidation, and the easy preparation technology has the potential for application to catalysts with other element compositions.

The rational design of excellent electrocatalysts is significant for triggering the slow kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in rechargeable metal–air batteries. Hereby, we report a bifunctional catalytic material with core–shell structure constructed by Co3O4 nanowire arrays as cores and ultrathin NiFe-layered double hydroxides (NiFe LDHs) as shells (Co3O4@NiFe LDHs). The introduction of Co3O4 nanowires could provide abundant active sites for NiFe LDH nanosheets. Most importantly, the deposition of NiFe LDHs on the surface of Co3O4 can modulate the surface chemical valences of Co, Ni, and Fe species via changing the electron donor and/or electron absorption effects, finally achieving the balance and optimization of ORR and OER properties. By this core–shell design, the maximum ORR current densities of Co3O4@NiFe LDHs increase to 3–7 mA cm–2, almost an order of magnitude increases compared to pure NiFe LDH (0.45 mA cm–2). Significantly, an OER overpotential as low as 226 mV (35 mA cm–2) is achieved in the designed core–shell catalyst, which is comparable to and/or even better than those of commercial Ir/C. Hence, the primary zinc–air battery employing Co3O4@NiFe LDH as an air electrode achieves a high specific capacity (667.5 mA h g–1) and first-class energy density (797.6 W h kg–1); the rechargeable battery can show superior reversibility, excellent stability, and voltage gaps of ∼0.8 V (∼60% of round-trip efficiency) in >1200 continuous cycles. Furthermore, the flexible quasi-solid-state zinc–air battery with bendable ability holds practical potential in portable and wearable electronic devices.