Lattice Strain Engineering on Metal-Organic Frameworks by Ligand Doping to Boost the Electrocatalytic Biomass Valorization.

As an efficient and environmental-friendly strategy, electrocatalytic oxidation can realize biomass lignin valorization by cleaving its aryl ether bonds to produce value-added chemicals. However, the complex and polymerized structure of lignin presents challenges in terms of reactant adsorption on the catalyst surface, which hinders further refinement. Herein, NiCo-based metal-organic frameworks (MOFs) are employed as the electrocatalyst to enhance the adsorption of reactant molecules through π-π interaction. More importantly, lattice strain is introduced into the MOFs via curved ligand doping, which enables tuning of the d-band center of metal active sites to align with the reaction intermediates, leading to stronger adsorption and higher electrocatalytic activity toward bond cleavage within lignin model compounds and native lignin. When 2'-phenoxyacetophenone is utilized as the model compound, high yields of phenol (76.3%) and acetophenone (21.7%) are achieved, and the conversion rate of the reactants reaches 97%. Following pre-oxidation of extracted poplar lignin, >10 kinds of phenolic compounds are received using the as-designed MOFs electrocatalyst, providing ≈12.48% of the monomer, including guaiacol, vanillin, eugenol, etc., and p-hydroxybenzoic acid dominates all the products. This work presents a promising and deliberately designed electrocatalyst for realizing lignin valorization, making significant strides for the sustainability of this biomass resource.

Electrocatalytic Lignin Valorization into Aromatic Products via Oxidative Cleavage of Cα-Cß Bonds.

Lignin is the most promising candidate for producing aromatic compounds from biomass. However, the challenge lies in the cleavage of C-C bonds between lignin monomers under mild conditions, as these bonds have high dissociation energy. Electrochemical oxidation, which allows for mild cleavage of C-C bonds, is considered an attractive solution. To achieve low-energy consumption in the valorization of lignin, the use of highly efficient electrocatalysts is essential. In this study, a meticulously designed catalyst consisting of cobalt-doped nickel (oxy)hydroxide on molybdenum disulfide heterojunction was developed. The presence of molybdenum in a high valence state promoted the adsorption of tert-butyl hydroperoxide, leading to the formation of critical radical intermediates. In addition, the incorporation of cobalt doping regulated the electronic structure of nickel, resulting in a lower energy barrier. As a result, the heterojunction catalyst demonstrated a selectivity of 85.36% for cleaving the Cα-Cß bond in lignin model compound, achieving a substrate conversion of 93.69% under ambient conditions. In addition, the electrocatalyst depolymerized 49.82 wt% of soluble fractions from organosolv lignin (OL), resulting in a yield of up to 13 wt% of aromatic monomers. Significantly, the effectiveness of the prepared electrocatalyst was also demonstrated using industrial Kraft lignin (KL). Therefore, this research offers a practical approach for implementing electrocatalytic oxidation in lignin refining.

Switch of cell migration modes orchestrated by changes of three-dimensional lamellipodium structure and intracellular diffusion.

Cell migration plays important roles in many biological processes, but how migrating cells orchestrate intracellular molecules and subcellular structures to regulate their speed and direction is still not clear. Here, by characterizing the intracellular diffusion and the three-dimensional lamellipodium structures of fish keratocyte cells, we observe a strong positive correlation between the intracellular diffusion and cell migration speed and, more importantly, discover a switching of cell migration modes with reversible intracellular diffusion variation and lamellipodium structure deformation. Distinct from the normal fast mode, cells migrating in the newly-found slow mode have a deformed lamellipodium with swollen-up front and thinned-down rear, reduced intracellular diffusion and compartmentalized macromolecule distribution in the lamellipodium. Furthermore, in turning cells, both lamellipodium structure and intracellular diffusion dynamics are also changed, with left-right symmetry breaking. We propose a mechanism involving the front-localized actin polymerization and increased molecular crowding in the lamellipodium to explain how cells spatiotemporally coordinate the intracellular diffusion dynamics and the lamellipodium structure in regulating their migrations.

Responses of maize (Zea mays L.) seedlings growth and physiological traits triggered by polyvinyl chloride microplastics is dominated by soil available nitrogen.

As a burgeoning pollutant, microplastics (MPs) has elicited global concern. However, ecological effects and mechanisms of MPs on plant-soil system are still poorly understood. In the present study, the impacts of polyvinyl chloride microplastics (PVC-MPs) on maize (Zea mays L.) seedlings growth and physiological traits and soil properties were discussed through a 30-day pot experiment. Results showed that PVC-MPs had greater toxicity effect on seedlings shoot biomass than root biomass. To defense the impact of PVC-MPs, the superoxide dismutase and catalase activities in seedlings leaf were stimulated. Moreover, the adhesion of MPs on soil particles increased, and soil microorganism, enzymes, and nutrients were altered significantly with increasing content of PVC-MPs. Notably, soil nitrate nitrogen decreased significantly with increasing content of PVC-MPs, whereas soil ammonium nitrogen was promoted under lower contents (0.1% and 1%) of PVC-MPs. Redundancy analysis indicated that soil nitrate nitrogen and ammonium nitrogen can explain 87.4% and 7.7% of variation in maize seedlings growth and physiological traits, respectively. These results display that maize seedlings shoot is more susceptible to the impact of PVC-MPs and soil available nitrogen is the primary limiting factor on maize seedlings growth and physiological traits triggered by PVC-MPs. Impacts of PVC-MPs on maize seedlings growth and physiological traits by nitrogen depletion lead to the possible yield and economic loess and potential risks due to the over use of nitrogen fertilizers.

Quantifying transport dynamics with three-dimensional single-particle tracking in adherent cells.

Intracellular transport plays an important role in maintaining the physiological functions of cells. Here, we describe a protocol for 3D single-particle tracking within living cells. We detail the use of a two-focal imaging system and the analytical steps for quantifying 3D transport dynamics. This protocol can be used to characterize the intracellular diffusion and trafficking of macromolecules, nanoparticles, and endocytic vesicles in adherent cells. For complete details on the use and execution of this protocol, please refer to Jiang et al. (2022).

Spatiotemporal three-dimensional transport dynamics of endocytic cargos and their physical regulations in cells.

Intracellular transport, regulated by complex cytoarchitectures and active driving forces, is crucial for biomolecule translocations and relates to many cellular functions. Despite extensive knowledge obtained from two-dimensional (2D) experiments, the real three-dimensional (3D) spatiotemporal characteristics of intracellular transport is still unclear. With 3D single-particle tracking, we comprehensively studied the transport dynamics of endocytic cargos. With varying timescale, the intracellular transport changes from thermal-dominated 3D-constrained motion to active-dominated quasi-2D motion. Spatially, the lateral motion is heterogeneous with peripheral regions being faster than perinuclear regions, while the axial motion is homogeneous across the cells. We further confirmed that such anisotropy and heterogeneity of vesicle transport result from actively directed motion on microtubules. Strikingly, inside the vesicles, we observed endocytic nanoparticles make diffusive motions on their inner membranes when microtubules are absent, suggesting endocytic cargos are normally localized at the inner vesicle membranes through a physical connection to the microtubules outside during transport.

Metal-Free Boron/Phosphorus Co-Doped Nanoporous Carbon for Highly Efficient Benzyl Alcohol Oxidation.

An in-depth understanding of the electronic structures of catalytically active centers and their surrounding vicinity is key to clarifying the structure-activity relationship, and thus enabling the design and development of novel metal-free carbon-based materials with desired catalytic performance. In this study, boron atoms are introduced into phosphorus-doped nanoporous carbon via an efficient strategy, so that the resulting material delivers better catalytic performance. The doped B atoms alter the electronic structures of active sites and cause the adjacent C atoms to act as additional active sites that catalyze the reaction. The B/P co-doped nanoporous carbon shows remarkable catalytic performance for benzyl alcohol oxidation, achieving high yield (over 91% within 2 h) and selectivity (95%), as well as low activation energy (32.2 kJ mol-1 ). Moreover, both the conversion and selectivity remain above 90% after five reaction cycles. Density functional theory calculations indicate that the introduction of B to P-doped nanoporous carbon significantly increases the electron density at the Fermi level and that the oxidation of benzyl alcohol occurs via a different reaction pathway with a very low energy barrier. These findings provide important insights into the relationship between catalytic performance and electronic structure for the design of dual-doped metal-free carbon catalysts.

Molecule Confined Isolated Metal Sites Enable the Electrocatalytic Synthesis of Hydrogen Peroxide.

The direct synthesis of hydrogen peroxide (H2 O2 ) through the two-electron oxygen reduction reaction is a promising alternative to the industrial anthraquinone oxidation process. Selectivity to H2 O2 is however limited by the four-electron pathway during oxygen reduction. Herein, it is reported that aminoanthraquinone confined isolated metal sites on carbon supports selectively steer oxygen reduction to H2 O2 through the two-electron pathway. Confining isolated NiNx sites under aminoanthraquinone increases the selectivity to H2 O2 from below 55% to above 80% over a wide potential range. Spectroscopy characterization and density functional theory calculations indicate that isolated NiNx sites are confined within a nanochannel formed between the molecule and the carbon support. The confinement reduces the thermodynamic barrier for OOH* desorption versus further dissociation, thus increasing the selectivity to H2 O2 . It is revealed how tailoring noncovalent interactions beyond the binding site can empower electrocatalysts for the direct synthesis of H2 O2 through oxygen reduction.

Diffusion Behaviors of Integrins in Single Cells Altered by Epithelial to Mesenchymal Transition.

Cell morphology and migration depend critically on the adhesions on the extracellular matrix (ECM), determined by the transmembrane protein integrins. The epithelial to mesenchymal transition (EMT) is a prominent transformation process in which adherent cells acquire a mesenchymal phenotype and a promoted migration. EMT plays important roles in embryonic development and cancer metastasis, and its hallmarks include the acquisition of front-back cell polarity and loss of cell-cell contact. However, how integrins dynamically regulate cell-ECM adhesions and cellular behaviors during EMT is still unclear. Using single-particle tracking of ß1-integrins labeled with quantum dots, the temporal-spatial on-membrane dynamics of integrins in the EMT of MCF10A cells is revealed. ß1-integrins exhibit significantly enhanced dynamics, which temporally behave more diffusive and less immobilized, and spatially become distributed asymmetrically with front regions being more dynamic. These dynamic alterations are shown to arise from microtubule remodeling in EMT. The results shed new light on the EMT mechanism from the cell-ECM adhesion perspective, and suggest that the enhanced integrin diffusion may represent as a new hallmark of EMT.

H2A mono-ubiquitination differentiates FACT's functions in nucleosome assembly and disassembly.

The histone chaperone FACT (FAcilitates Chromatin Transcription) plays an essential role in transcription and DNA replication by its dual functions on nucleosome assembly to maintain chromatin integrity and nucleosome disassembly to destabilize nucleosome and facilitate its accessibility simultaneously. Mono-ubiquitination at Lysine 119 of H2A (ubH2A) has been suggested to repress transcription by preventing the recruitment of FACT at early elongation process. However, up to date, how ubH2A directly affects FACT on nucleosome assembly and disassembly remains elusive. In this study, we demonstrated that the dual functions of FACT are differently regulated by ubH2A. The H2A ubiquitination does not affect FACT's chaperone function in nucleosome assembly and FACT can deposit ubH2A-H2B dimer on tetrasome to form intact nucleosome. However, ubH2A greatly restricts FACT binding on nucleosome and inhibits its activity of nucleosome disassembly. Interestingly, deubiquitination of ubH2A rescues the nucleosome disassembly function of FACT to activate gene transcription. Our findings provide mechanistic insights of how H2A ubiquitination affects FACT in breaking nucleosome and maintaining its integrity, which sheds light on the biological function of ubH2A and various FACT's activity under different chromatin states.

High-Loading, Well-Dispersed Phosphorus Confined on Nanoporous Carbon Surfaces with Enhanced Catalytic Activity and Cyclic Stability.

Phosphorus-doped carbon materials are promising alternatives to noble metal-based catalysts for the highly selective oxidation of benzyl alcohol to benzaldehyde, but it is challenging to achieve high loadings of high-activity P dopants in metal-free catalysts. Here, the preparation of high-loading and well-dispersed P atoms confined to the surfaces of cellulose-derived carbon via a dissolving-doping strategy is reported. In this method, cellulose is dissolved in phosphoric acid to generate a cellulose-phosphoric supramolecular collosol, which is then directly carbonized. The as-prepared carbon possesses a high specific surface area of 1491 cm3 g-1 and a high P content of 8.8 wt%. The P-doped nanoporous carbon shows a superior catalytic activity and cyclic stability toward benzyl alcohol oxidation, with a high turnover frequency of 3.5 × 10-3 mol g-1 h-1 and a low activation energy of 35.6 kJ mol-1 . Experimental results and theoretical calculations demonstrate that the graphitic C3 PO species is the leading catalytic active center in this material. This study provides a novel strategy to prepare P dopants in nanoporous carbon materials with excellent catalytic performance.

Endogenous Bos taurus RECQL is predominantly monomeric and more active than oligomers.

There is broad consensus that RecQ family helicase is a high-order oligomer that dissociates into a dimer upon ATP binding. This conclusion is based mainly on studies of highly purified recombinant proteins, and the oligomeric states of RecQ helicases in living cells remain unknown. We show here that, in contrast to current models, monomeric RECQL helicase is more abundant than oligomer/dimer forms in living cells. Further characterization of endogenous BtRECQL and isolated monomeric BtRECQL using various approaches demonstrates that both endogenous and recombinant monomeric BtRECQL effectively function as monomers, displaying higher helicase and ATPase activities than dimers and oligomers. Furthermore, monomeric BtRECQL unfolds intramolecular G-quadruplex DNA as efficiently as human RECQL and BLM helicases. These discoveries have implications for understanding endogenous RECQL oligomeric structures and their regulation. It is worth revisiting oligomeric states of the other members of the RecQ family helicases in living cells.

Tuning of lattice oxygen reactivity and scaling relation to construct better oxygen evolution electrocatalyst.

Developing efficient and low-cost electrocatalysts for oxygen evolution reaction is crucial in realizing practical energy systems for sustainable fuel production and energy storage from renewable energy sources. However, the inherent linear scaling relation for most catalytic materials imposes a theoretical overpotential ceiling, limiting the development of efficient electrocatalysts. Herein, using modeled NaxMn3O7 materials, we report an effective strategy to construct better oxygen evolution electrocatalyst through tuning both lattice oxygen reactivity and scaling relation via alkali metal ion mediation. Specifically, the number of Na+ is linked with lattice oxygen reactivity, which is determined by the number of oxygen hole in oxygen lone-pair states formed by native Mn vacancies, governing the barrier symmetry between O-H bond cleavage and O-O bond formation. On the other hand, the presence of Na+ could have specific noncovalent interaction with pendant oxygen in *OOH to overcome the limitation from linear scaling relation, reducing the overpotential ceiling. Combining in situ spectroscopy-based characterization with first-principles calculations, we demonstrate that an intermediate level of Na+ mediation (NaMn3O7) exhibits the optimum oxygen evolution activity. This work provides a new rational recipe to develop highly efficient catalyst towards water oxidation or other oxidative reactions through tuning lattice oxygen reactivity and scaling relation.

Crystal structures of N-terminally truncated telomerase reverse transcriptase from fungi‡.

Telomerase plays critical roles in cellular aging, in the emergence and/or development of cancer, and in the capacity for stem-cell renewal, consists of a catalytic telomerase reverse transcriptase (TERT) and a template-encoding RNA (TER). TERs from diverse organisms contain two conserved structural elements: the template-pseudoknot (T-PK) and a helical three-way junction (TWJ). Species-specific features of the structure and function of telomerase make obtaining a more in-depth understanding of the molecular mechanism of telomerase particularly important. Here, we report the first structural studies of N-terminally truncated TERTs from Candida albicans and Candida tropicalis in apo form and complexed with their respective TWJs in several conformations. We found that Candida TERT proteins perform only one round of telomere addition in the presence or absence of PK/TWJ and display standard reverse transcriptase activity. The C-terminal domain adopts at least two extreme conformations and undergoes conformational interconversion, which regulates the catalytic activity. Most importantly, we identified a conserved tertiary structural motif, called the U-motif, which interacts with the reverse transcriptase domain and is crucial for catalytic activity. Together these results shed new light on the structure and mechanics of fungal TERTs, which show common TERT characteristics, but also display species-specific features.

DNA polymerase Gp90 activities and regulations on strand displacement DNA synthesis revealed at single-molecule level.

Strand displacement DNA synthesis (SDDS) is an essential step in DNA replication. With magnetic tweezers, we investigated SDDS kinetics of wild-type gp90 and its exonuclease-deficient polymerase gp90 exo- at single-molecule level. A novel binding state of gp90 to the fork flap was confirmed prior to SDDS, suggesting an intermediate in the initiation of SDDS. The rate and processivity of SDDS by gp90 exo- or wt-gp90 are increased with force and dNTP concentration. The rate and processivity of exonuclease by wt-gp90 are decreased with force. High GC content decreases SDDS and exonuclease processivity but increases exonuclease rate for wt-gp90. The high force and dNTP concentration and low GC content facilitate the successive SDDS but retard the successive exonuclease for wt-gp90. Furthermore, increasing GC content accelerates the transition from SDDS or exonuclease to exonuclease. This work reveals the kinetics of SDDS in detail and offers a broader cognition on the regulation of various factors on SDDS at single-polymerase level.

Enlarging the π-Conjugation of Cobalt Porphyrin for Highly Active and Selective CO2 Electroreduction.

Heterogeneous molecular catalysts have attracted considerable attention as carbon dioxide reduction reaction (CO2 RR) electrocatalysts. The π-electron system of conjugated ligands in molecular catalysts may play an important role in determining the activity. In this work, by enlarging π-conjugation through appending more aromatic substituents on the porphyrin ligand, altered π-electron system endows the as-prepared 5,10,15,20-tetrakis(4-(pyren-1-yl)phenyl)porphyrin CoII with high Faradaic efficiency (ca. 95 %) for CO production, as well as high turnover frequency (2.1 s-1 at -0.6 V vs. RHE). Density functional theory calculation further suggests that the improved electrocatalytic performance mainly originates from the higher proportion of Co d z 2 orbital and the CO2 π* orbital in the HOMO of the (Co-porphyrin-CO2 )- intermediate with larger π-conjugation, which facilitates the CO2 activation. This work provides strong evidence that π-conjugation perturbation is effective in boosting the CO2 RR.

Structural and functional studies of SF1B Pif1 from Thermus oshimai reveal dimerization-induced helicase inhibition.

Pif1 is an SF1B helicase that is evolutionarily conserved from bacteria to humans and plays multiple roles in maintaining genome stability in both nucleus and mitochondria. Though highly conserved, Pif1 family harbors a large mechanistic diversity. Here, we report crystal structures of Thermus oshimai Pif1 (ToPif1) alone and complexed with partial duplex or single-stranded DNA. In the apo state and in complex with a partial duplex DNA, ToPif1 is monomeric with its domain 2B/loop3 adopting a closed and an open conformation, respectively. When complexed with a single-stranded DNA, ToPif1 forms a stable dimer with domain 2B/loop3 shifting to a more open conformation. Single-molecule and biochemical assays show that domain 2B/loop3 switches repetitively between the closed and open conformations when a ToPif1 monomer unwinds DNA and, in contrast with other typical dimeric SF1A helicases, dimerization has an inhibitory effect on its helicase activity. This mechanism is not general for all Pif1 helicases but illustrates the diversity of regulation mechanisms among different helicases. It also raises the possibility that although dimerization results in activation for SF1A helicases, it may lead to inhibition for some of the other uncharacterized SF1B helicases, an interesting subject warranting further studies.

Structural tuning of heterogeneous molecular catalysts for electrochemical energy conversion.

Heterogeneous molecular catalysts based on transition metal complexes have received increasing attention for their potential application in electrochemical energy conversion. The structural tuning of first and second coordination spheres of complexes provides versatile strategies for optimizing the activities of heterogeneous molecular catalysts and appropriate model systems for investigating the mechanism of structural variations on the activity. In this review, we first discuss the variation of first spheres by tuning ligated atoms; afterward, the structural tuning of second spheres by appending adjacent metal centers, pendant groups, electron withdrawing/donating, and conjugating moieties on the ligands is elaborated. Overall, these structural tuning resulted in different impacts on the geometric and electronic configurations of complexes, and the improved activity is achieved through tuning the stability of chemisorbed reactants and the redox behaviors of immobilized complexes.

Curaxin-Induced DNA Topology Alterations Trigger the Distinct Binding Response of CTCF and FACT at the Single-Molecule Level.

The candidate anticancer drug curaxins can insert into DNA base pairs and efficiently inhibit the growth of various cancers. However, how curaxins alter the genomic DNA structure and affect the DNA binding property of key proteins remains to be clarified. Here, we first showed that curaxin CBL0137 strongly stabilizes the interaction between the double strands of DNA and reduces DNA bending and twist rigidity simultaneously, by single-molecule magnetic tweezers. More importantly, we found that CBL0137 greatly impairs the binding of CTCF but facilitates trapping FACT on DNA. We revealed that CBL0137 clamps the DNA double helix that may induce a huge barrier for DNA unzipping during replication and transcription and causes the distinct binding response of CTCF and FACT on DNA. Our work provides a novel mechanical insight into CBL0137's anticancer mechanisms at the nucleic acid level.

Anodic Oxidation Enabled Cation Leaching for Promoting Surface Reconstruction in Water Oxidation.

A rational design for oxygen evolution reaction (OER) catalysts is pivotal to the overall efficiency of water electrolysis. Much work has been devoted to understanding cation leaching and surface reconstruction of very active electrocatalysts, but little on intentionally promoting the surface in a controlled fashion. We now report controllable anodic leaching of Cr in CoCr2 O4 by activating the pristine material at high potential, which enables the transformation of inactive spinel CoCr2 O4 into a highly active catalyst. The depletion of Cr and consumption of lattice oxygen facilitate surface defects and oxygen vacancies, exposing Co species to reconstruct into active Co oxyhydroxides differ from CoOOH. A novel mechanism with the evolution of tetrahedrally coordinated surface cation into octahedral configuration via non-concerted proton-electron transfer is proposed. This work shows the importance of controlled anodic potential in modifying the surface chemistry of electrocatalysts.