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MnO 2 is a promising cathode for aqueous Zn batteries. However, the cycling stability is seriously hindered by active material dissolution, and the pre-addition of Mn 2+ salts in electrolytes is widely required. Herein, we propose a structural engineering strategy for MnO 2 to enhance the capacity contribution from the reversible two-electron transfer reaction of MnO 2 /Mn 2+ and realize stable cycling in Mn 2+ -free electrolytes. By compositing with MoO 3 , MnO 2 exhibits weakened Mn-O bonds, more oxygen vacancies, spontaneous generation of structural water, and thus a lowered energy barrier for Mn release during discharge. Meanwhile, the composite material presents stronger electrostatic attractions for dissolved Mn 2+ , which ensures highly reversible re-deposition during charge. As a result, the mass ratios between materials undergoing reversible two-electron and one-electron transfer reactions increase from 0.85 in MnO 2 to 1.68 in the MnO 2 /MoO 3 composite material. In the ZnSO 4 electrolyte, the MnO 2 /MoO 3 cathode achieves 92.6% capacity retention after 300 cycles at 0.1 A g -1 (>1900 h), superior to 62.7% for MnO 2 . MnO 2 /MoO 3 also retains 80.1% capacity after 16 000 cycles at 1 A g -1 (>3200 h). This work presents an effective path to realize stable cycling of MnO 2 in Zn batteries.

Aqueous rechargeable Zn-manganese dioxide (Zn-MnO 2 ) hybrid batteries based on dissolution-deposition mechanisms exhibit ultrahigh capacities and energy densities due to the two-electron transformation between MnO 2 /Mn 2+ . However, the reported Zn-MnO 2 hybrid batteries usually use strongly acidic and/or alkaline electrolytes, which may lead to environmental hazards and corrosion issues of the Zn anodes. Herein, we propose a new Zn-MnO 2 hybrid battery by adding Al 3+ into the sulfate-based electrolyte. The hybrid battery undergoes reversible MnO 2 /Mn 2+ transformation and exhibits good electrochemical performances, such as a high discharge capacity of 564.7 mAh g -1 with a discharge plateau of 1.65 V, an energy density of 520.8 Wh kg -1 , and good cycle life without capacity decay upon 2000 cycles. Experimental results and theoretical calculation suggest that the aquo Al 3+ with Brønsted weak acid nature can act as the proton-donor reservoir to maintain the electrolyte acidity near the electrode surface and prevent the formation of Zn 4 (OH) 6 (SO 4 )·0.5H 2 O during discharging. In addition, Al 3+ doping during charging introduces oxygen vacancies in the oxide structure and weakens the Mn-O bond, which facilitates the dissolution reaction during discharge. The mechanistic investigation discloses the important role of Al 3+ in the electrolyte, providing a new fundamental understanding of the promising aqueous Zn-MnO 2 batteries.

Molybdenum oxide provides high theoretical capacity, but the moderate charge transfer kinetics and cycle life have limited the applications for capacitive energy storage. Herein, the electrochemical performance of molybdenum oxide is modified by tuning the active redox couple through an electrochemical activation process. The activated electrode K-MoO x with a 10 mg cm -2 loading shows excellent pseudocapacitive behavior within the large potential range of -1.2-0 V and delivers 313 F g -1 capacitance at 5 mA cm -2 . It also presents an ultrastable cycle life, with a 98% capacitance retention after 10,000 cycles. The activation process involves the insertion of K + into MoO x , which modifies the Mo electronic structure and introduces Mo 4+ sites according to X-ray photoelectron spectroscopy. As a result, the charge storage redox couple shifts from Mo 5+ /Mo 6+ to Mo 4+ /Mo 5+ , with the latter delivering higher electrochemical activity due to improved conductivity. Electrochemical impedance spectroscopy also suggests faster ion diffusions and thus higher power capability in K-MoO x , resulting in the enhanced performance. A 2.4 V asymmetric supercapacitor is assembled using K-MoO x as the anode with a MnO x cathode. The work demonstrates a feasible and facile strategy to promote the pseudocapacitive behavior of metal oxide materials.

The degradation or dendrite formation of zinc metal electrodes has shown to limit the cycle life of rechargeable aqueous zinc batteries, and a few anode protection methods are proposed. We herein demonstrate that, except for external protections, a simple design of an electrolyte can effectively promote stable and facile Zn stripping/plating from/on zinc electrodes. By using Zn(ClO 4 ) 2 in the aqueous electrolyte, reversible Zn stripping/plating is achieved for over 3000 h at 1 mA cm -2 current density and 1 mA h cm -2 capacity, superior to the conventional ZnSO 4 electrolyte. The overpotential is constant within each cycle and only increases slightly with the increase of current densities. The excellent performance is guaranteed by the controlled formation of a Cl - containing layer, which limits continuous side reactions. The Zn(ClO 4 ) 2 electrolyte shows anodic stability up to 2.4 V, and excellent electrochemical performance is achieved for an example cell with the VO 2 cathode, confirming the applicability of the electrolyte for Zn batteries.

Recent research on the structure and mechanism of DNA polymerases has continued to generate fundamentally important features, including a noncanonical pathway involving "prebinding" of metal-bound dNTP (MdNTP) in the absence of DNA. While this noncanonical mechanism was shown to be a possible subset for African swine fever DNA polymerase X (Pol X) and human Pol λ, it remains unknown whether it could be the primary pathway for a DNA polymerase. Pol μ is a unique member of the X-family with multiple functions and with unusual Mn 2+ preference. Here we report that Pol μ not only prebinds MdNTP in a catalytically active conformation but also exerts a Mn 2+ over Mg 2+ preference at this early stage of catalysis, for various functions: incorporation of dNTP into a single nucleotide gapped DNA, incorporation of rNTP in the nonhomologous end joining (NHEJ) repair, incorporation of dNTP to an ssDNA, and incorporation of an 8-oxo-dGTP opposite template dA (mismatched) or dC (matched). The structural basis of this noncanonical mechanism and Mn 2+ over Mg 2+ preference in these functions was analyzed by solving 19 structures of prebinding binary complexes, precatalytic ternary complexes, and product complexes. The results suggest that the noncanonical pathway is functionally relevant for the multiple functions of Pol μ. Overall, this work provides the structural and mechanistic basis for the long-standing puzzle in the Mn 2+ preference of Pol μ and expands the landscape of the possible mechanisms of DNA polymerases to include both mechanistic pathways.

Metal oxides have attracted renewed interest as promising electrode materials for high energy density supercapacitors. However, the electrochemical performance of metal oxide materials deteriorates significantly with the increase of mass loading due to their moderate electronic and ionic conductivities. This limits their practical energy. Herein, we perform a morphology and phase-controlled electrodeposition of MnO 2 with ultrahigh mass loading of 10 mg cm -2 on a carbon cloth substrate to achieve high overall capacitance without sacrificing the electrochemical performance. Under optimum conditions, a hierarchical nanostructured architecture was constructed by interconnection of primary two-dimensional ε-MnO 2 nanosheets and secondary one-dimensional α-MnO 2 nanorod arrays. The specific hetero-nanostructures ensure facile ionic and electric transport in the entire electrode and maintain the structure stability during cycling. The hierarchically structured MnO 2 electrode with high mass loading yields an outstanding areal capacitance of 3.04 F cm -2 (or a specific capacitance of 304 F g -1 ) at 3 mA cm -2 and an excellent rate capability comparable to those of low mass loading MnO 2 electrodes. Finally, the aqueous and all-solid asymmetric supercapacitors (ASCs) assembled with our MnO 2 cathode exhibit extremely high volumetric energy densities (8.3 mWh cm -3 at the power density of 0.28 W cm -3 for aqueous ASC and 8.0 mWh cm -3 at 0.65 W cm -3 for all-solid ASC), superior to most state-of-the-art supercapacitors.

The vast majority of in vitro structural and functional studies of the activation mechanism of protein kinases use the kinase domain alone. Well-demonstrated effects of regulatory domains or allosteric factors are scarce for serine/threonine kinases. Here we use a site-specifically phosphorylated SCD1-FHA1-kinase three-domain construct of the serine/threonine kinase Rad53 to show the effect of phospho-priming, an in vivo regulatory mechanism, on the autophosphorylation intermediate and specificity. Unphosphorylated Rad53 is a flexible monomer in solution but is captured in an asymmetric enzyme:substrate complex in crystal with the two FHA domains separated from each other. Phospho-priming induces formation of a stable dimer via intermolecular pT-FHA binding in solution. Importantly, autophosphorylation of unprimed and phospho-primed Rad53 produced predominantly inactive pS350-Rad53 and active pT354-Rad53, respectively. The latter mechanism was also demonstrated in vivo. Our results show that, while Rad53 can display active conformations under various conditions, simulation of in vivo regulatory conditions confers functionally relevant autophosphorylation.

The mechanism of DNA polymerase (pol) fidelity is of fundamental importance in chemistry and biology. While high-fidelity pols have been well studied, much less is known about how some pols achieve medium or low fidelity with functional importance. Here we examine how human DNA polymerase λ (Pol λ) achieves medium fidelity by determining 12 crystal structures and performing pre-steady-state kinetic analyses. We showed that apo-Pol λ exists in the closed conformation, unprecedentedly with a preformed MgdNTP binding pocket, and binds MgdNTP readily in the active conformation in the absence of DNA. Since prebinding of MgdNTP could lead to very low fidelity as shown previously, it is attenuated in Pol λ by a hydrophobic core including Leu431, Ile492, and the Tyr505/Phe506 motif. We then predicted and demonstrated that L431A mutation enhances MgdNTP prebinding and lowers the fidelity. We also hypothesized that the MgdNTP-prebinding ability could stabilize a mismatched ternary complex and destabilize a matched ternary complex, and provided evidence with structures in both forms. Our results demonstrate that, while high-fidelity pols follow a common paradigm, Pol λ has developed specific conformations and mechanisms for its medium fidelity. Structural comparison with other pols also suggests that different pols likely utilize different conformational changes and microscopic mechanisms to achieve their catalytic functions with varying fidelities.

Highly aligned nanoarchitecture arrays directly grown on conducting substrates open up a new direction to accelerate Faradaic reactions for charge storage as well as address "dead volume" limitations for high-performance pseudocapacitor electrodes. Here we reported the electrochemical fabrication of well-ordered polypyrrole (PPy) nanowire arrays (NWAs) on surfaces of carbon fibers in an untreated carbon cloth to construct hierarchical structures constituted by the three-dimensional conductive carbon fiber skeleton and the atop well-ordered electroactive polymer nanowires. The morphologies, wetting behaviors, and charge-storage performances of the polymer were investigated by scanning electron microscopy, transmission electron microscopy, contact-angle measurement, cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy. The well-ordered PPy NWA electrode exhibited a high specific capacitance of 699 F/g at 1 A/g with excellent rate capability, and 92.4% and 81.5% of its capacitance could be retained at 10 and 20 A/g, respectively. An extremely high energy density of 164.07 Wh/kg could be achieved by the PPy NWAs at a power density of 0.65 kW/kg. It also displayed a quite high energy density of 133.79 Wh/kg at a high power density of 13 kW/kg. The assembled symmetric supercapacitor of PPy NWAs//PPy NWAs also exhibited excellent rate capability, and only 19% of its energy density decreased when the power density increased 20 times from 0.65 to 13 kW/kg.

Electrochemical codeposition of vanadium oxide (V2O5) and polypyrrole (PPy) is conducted from vanadyl sulfate (VOSO4) and pyrrole in their aqueous solution to get V2O5-PPy composite, during which one-dimensional growth of polypyrrole (PPy) is directed. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) are used to characterize the composite, while scanning electron microscopy (SEM) is used to investigate their morphologies. Cyclic voltammetry (CV), chronopotentiometry (CP) for galvanostatic charge-discharge and electrochemical impedance spectroscopy (EIS) are used to study electrochemical activities and pseudocapacitive properties of the composite. The influences of VOSO4 to pyrrole ratio in the electro-codeposition solution on morphologies and pseudocapacitive properties of the composite are discussed. Due to the organic-inorganic synergistic effect, V2O5-PPy composite exhibits good charge-storage properties in a large potential window from -1.4 to 0.6 V vs SCE, with a specific capacitance of 412 F/g at 4.5 mA/cm(2). A model supercapacitor assembled by using the V2O5-PPy composite as the electrode materials displays a high operating voltage of 2 V and so a high energy density of 82 Wh/kg (at the power density of 800 W/kg).