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We proposed new basic equations and the approximate model for gravitational ventilation through a single openingm which can be incorporated into a ventilation network analysis. The new basic equations are the mass flow balance and the conversion equations of pressure difference and dynamic pressure at an indoor‐outdoor boundary. In order to calculate the mass flow rate by gravitational ventilation using these equations, the following two values at the boundary are required: (1) windward speed, (2) temperature profile. 1. We have shown calculation methods based on the one‐dimensional flow for (1), and used a flow tube model for (2). 2. The neutral pressure level and the inflow‐outflow wind speed can be obtained by steady‐state analysis of basic equations. The coefficients that optimize the calculation results were also shown. 3. We compared the approximate model with the CFD and verified their validity. Finally, the basic characteristics of single‐opening gravitational ventilation were discussed.

The ability to construct metal single-atom catalysts (SACs) asymmetrically coordinated with organic heteroatoms represents an important endeavor toward developing high-performance catalysts over symmetrically coordinated counterparts. Moreover, it is of key importance in creating supporting matrix with porous architecture for situating SACs as it greatly impacts the mass diffusion and transport of electrolyte. Herein, we report the crafting of Fe single atoms with asymmetrically coordinated nitrogen (N) and phosphorus (P) atoms scaffolded by rationally designed mesoporous carbon nanospheres (MCNs) with spoke-like nanochannels for boosting ring-opening reaction of epoxide to produce an array of pharmacologically important β-amino alcohols. Notably, interfacial defects in MCN derived from the use of sacrificial template create abundant unpaired electrons, thereby stably anchoring N and P atoms and in turn Fe atoms on MCN. Importantly, the introduction of P atom promotes the symmetry-breaking of common four N-coordinated Fe sites, resulting in the Fe-N₃P sites on MCN (denoted Fe-N₃P-MCN) with an asymmetric electronic configuration and thus superior catalytic capability. As such, the Fe-N₃P-MCN catalysts manifest a high catalytic activity for ring-opening reaction of epoxide (97% yield) over the Fe-N₃P docked on nonporous carbon surface (91%) as well as the sole Fe-N₄ SACs grounded on the same MCN support (89%). Density functional theory calculations reveal that Fe-N3P SAC lowers the activation barrier for the C–O bond cleavage and the C–N bond formation, thus accelerating the ring-opening of epoxide. Our study provides fundamental and practical insights into developing advanced catalysts in a simple and controllable manner for multistep organic reactions.

RAD52 is important for the repair of DNA double-stranded breaks 1 , 2 , mitotic DNA synthesis 3 – 5 and alternative telomere length maintenance 6 , 7 . Central to these functions, RAD52 promotes the annealing of complementary single-stranded DNA (ssDNA) 8 , 9 and provides an alternative to BRCA2/RAD51-dependent homologous recombination repair 10 . Inactivation of RAD52 in homologous-recombination-deficient BRCA1 - or BRCA2 -defective cells is synthetically lethal 11 , 12 , and aberrant expression of RAD52 is associated with poor cancer prognosis 13 , 14 . As a consequence, RAD52 is an attractive therapeutic target against homologous-recombination-deficient breast, ovarian and prostate cancers 15 – 17 . Here we describe the structure of RAD52 and define the mechanism of annealing. As reported previously 18 – 20 , RAD52 forms undecameric (11-subunit) ring structures, but these rings do not represent the active form of the enzyme. Instead, cryo-electron microscopy and biochemical analyses revealed that ssDNA annealing is driven by RAD52 open rings in association with replication protein-A (RPA). Atomic models of the RAD52–ssDNA complex show that ssDNA sits in a positively charged channel around the ring. Annealing is driven by the RAD52 N-terminal domains, whereas the C-terminal regions modulate the open-ring conformation and RPA interaction. RPA associates with RAD52 at the site of ring opening with critical interactions occurring between the RPA-interacting domain of RAD52 and the winged helix domain of RPA2. Our studies provide structural snapshots throughout the annealing process and define the molecular mechanism of ssDNA annealing by the RAD52–RPA complex. Single-stranded DNA annealing is driven by RAD52 open rings in association with RPA.

The electron transfer process (ETP) is able to avoid the redox cycling of catalysts by capturing electrons from contaminants directly. However, the ETP usually leads to the formation of oligomers and the reduction of oxidants to anions. Herein, the charge-confined Fe single-atom catalyst (Fe/SCN) with Fe-N 3 S 1 configuration was designed to achieve ETP-mediated contaminant activation of the oxidant by limiting the number of electrons gained by the oxidant to generate 1 O 2 . The Fe/SCN-activate periodate (PI) system shows excellent contaminant degradation performance due to the combination of ETP and 1 O 2 . Experiments and DFT calculations show that the Fe/SCN-PI* complex with strong oxidizing ability triggers the ETP, while the charge-confined effect allows the single-electronic activation of PI to generate 1 O 2 . In the Fe/SCN + PI system, the 100% selectivity dechlorination of ETP and the ring-opening of 1 O 2 avoid the generation of oligomers and realize the transformation of large-molecule contaminants into small-molecule biodegradable products. Furthermore, the Fe/SCN + PI system shows excellent anti-interference ability and application potential. This work pioneers the generation of active species using ETP’s electron to activate oxidants, which provides a perspective on the design of single-atom catalysts via the charge-confined effect. In the electron transfer process, contaminants always form oligomers due to the lack of ROS. Here, the authors achieved electron transfer mediated activation of periodate by contaminants to generate 1 O 2 by charge confined single-atom catalyst.

The sustainable production of value-added N-heterocycles from available biomass allows to reduce the reliance on fossil resources and creates possibilities for economically and ecologically improved synthesis of fine and bulk chemicals. Herein, we present a unique Ru 1 Co NP /HAP surface single-atom alloy (SSAA) catalyst, which enables a new type of transformation from the bio-based platform chemical furfural to give N-heterocyclic piperidine. In the presence of NH 3 and H 2 , the desired product is formed under mild conditions with a yield up to 93%. Kinetic studies show that the formation of piperidine proceeds via a series of reaction steps. Initially, in this cascade process, furfural amination to furfurylamine takes place, followed by hydrogenation to tetrahydrofurfurylamine (THFAM) and then ring rearrangement to piperidine. DFT calculations suggest that the Ru 1 Co NP SSAA structure facilitates the direct ring opening of THFAM resulting in 5-amino-1-pentanol which is quickly converted to piperidine. The value of the presented catalytic strategy is highlighted by the synthesis of an actual drug, alkylated piperidines, and pyridine. The synthesis of nitrogen-containing heterocycles from biomass is scarcely known. Here, the authors report a strategy for the N-heterocyclic piperidines synthesis by one-pot amination of the bio-based furfural utilizing a Ru 1 Co NP /HAP surface single-atom alloy catalyst.

Sterically congested C–O and C–N bonds are ubiquitous in natural products, pharmaceuticals, and bioactive compounds. However, the development of a general method for the efficient construction of those sterically demanding covalent bonds still remains a formidable challenge. Herein, a photoredox-driven ring-opening C( sp 3 )–heteroatom bond formation of arylcyclopropanes is presented, which enables the construction of structurally diversified while sterically congested dialkyl ether, alkyl ester, alcohol, amine, chloride/fluoride, azide and also thiocyanate derivatives. The selective single electron oxidation of aryl motif associated with the thermodynamic driving force from ring strain-release is the key for this transformation. By this synergistic activation mode, C–C bond cleavage of otherwise inert cyclopropane framework is successfully unlocked. Further mechanistic and computational studies disclose a complete stereoinversion upon nucleophilic attack, thus proving a concerted S N 2-type ring-opening functionalization manifold, while the regioselectivity is subjected to an orbital control scenario. The development of new methodologies for the construction of C( sp 3 )–heteroatom bonds under mild conditions is desirable. Here the authors report the formation of C( sp 3 )–heteroatom bonds via ring opening of arylcyclopropanes enabled by photoredox catalysis.

A couple of novel crystalline aluminum(III) derivatives containing tridentate Schiff base ligand (HL) and β‐diketones (acetylacetone = acac, benzoylacetone = bnzac, and dibenzoylmethane = dbnz), namely, [Al(L)bnzac] [Al1], [Al(L)dnbz] [Al2], and [Al(L)acac] [Al3], are synthesized and characterized using different spectroscopic techniques and elemental analysis. Single crystal X‐ray diffraction analysis of Al2 and Al3 exhibits hexacoordinated geometry around aluminum center atom which is also confirmed using density functional theory (DFT). The ring‐opening polymerization (ROP) of caprolactone is evaluated to determine the catalytic potential of the complexes Al1–Al3 in the absence and presence of benzyl alcohol (BnOH). The effect of time and temperature is also examined and found that lesser steric effects of the ancillary ligand causes a higher polymerization rate. Gel permeation chromatography (GPC) is used to determine the molecular weight (Mn & Mw) and dispersity (Đ) values of polycaprolactone. Within first 2 h, Al3 exhibits excellent catalytic activity with 99% conversion at 110 °C (MnGPC = 1948 gmol−1, MwGPC = 2865 gmol−1, and Đ = 1.47). An end‐group study is performed using matrix‐assisted laser desorption ionization‐time of flight (MALDI‐TOF) spectrometry, and 1H NMR spectral analysis. Also, PCL is characterized using elemental, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) analyses. First‐order kinetics are found in the monomer aligned with the activated monomer mechanism for the catalysts. Ring‐opening polymerization of ε‐caprolactone using Al(III) heteroleptic complexes containing tridentate Schiff base ligand and β‐diketones is evaluated to determine the catalytic potential of Al(III) complexes in absence as well as in presence of benzyl alcohol.

Soft porous organic crystals with stimuli‐responsive single‐crystal‐to‐single‐crystal (SCSC) transformations are important tools for unraveling their structural transformations at the molecular level, which is of crucial importance for the rapid development of stimuli‐responsive systems. Carefully balancing the crystallinity and flexibility of materials is the prerequisite to construct advanced organic crystals with SCSC, which remains challenging. Herein, a squaraine‐based soft porous organic crystal (SPOC‐SQ) with multiple gas‐induced SCSC transformations and temperature‐regulated gate‐opening adsorption of various C1‐C3 hydrocarbons is reported. SPOC‐SQ is featured with both crystallinity and flexibility, which enable pertaining the single crystallinity of the purely organic framework during accommodating gas molecules and directly unveiling gas‐framework interplays by SCXRD technique. Thanks to the excellent softness of SPOC‐SQ crystals, multiple metastable single crystals are obtained after gas removals, which demonstrates a molecular‐scale shape‐memory effect. Benefiting from the single crystallinity, the molecule‐level structural evolutions of the SPOC‐SQ crystal framework during gas departure are uncovered. With the unique temperature‐dependent gate‐opening structural transformations, SPOC‐SQ exhibits distinctly different absorption behaviors towards C3H6 and C3H8, and highly efficient and selective separation of C3H6/C3H8 (v/v, 50/50) is achieved at 273 K. Such advanced soft porous organic crystals are of both theoretical values and practical implications. By balancing the crystallinity and flexibility, multiple gases‐induced single‐crystal‐to‐single‐crystal (SCSC) transformations of a novel soft porous organic crystal (SPOC) are discovered for not only elucidation of gas‐framework interplays and molecular‐scale shape‐memory effect at molecular level but also highly selective separation of propylene/propane, demonstrating the crucial significance of stimuli‐responsive SCSC transformations in guiding development of stimuli‐responsive systems.

Spirothiopyran (STP) is particularly attractive when used as a mechanophore to endow polymers with both damage-signaling and self-reinforcing capacity. It is, however, not clear the actual force required to induce the cycloreversion of STP into ring-opened thiomerocyanine (TMC), which reacts spontaneously with activated C-C bonds. Here, we used atomic force microscopy (AFM)-based single molecule force spectroscopy (SMFS) to study the mechanochemistry of STP mechanophore. It is found that the ring-opening of STP at room temperature requires forces of ∼ 200–400 pN, depending on the pulling speed. In addition, the reversibility of STP to TMC isomerization is demonstrated. Finally, mechanochemically induced intermolecular Click addition is achieved in single molecule level by pulling STP in the presence of maleimide.