Criegee intermediates are important atmospheric oxidants, and quantitative kinetics for stabilized Criegee intermediates are key parameters for atmospheric modeling but are still limited. Here we report barriers and rate constants for unimolecular reactions of s-cis-syn-acrolein oxide (scsAO), in which the vinyl group makes it a prototype for Criegee intermediates produced in the ozonolysis of isoprene. We find that the MN15-L and M06-2X density functionals have CCSD(T)/CBS accuracy for the unimolecular cyclization and stereoisomerization of scsAO. We calculated high-pressure-limit rate constants by the dual-level strategy that combines (a) high-level wave function-based conventional transition-state theory (which includes coupled-cluster calculations with quasiperturbative inclusion of quadruple excitations because of the strongly multiconfigurational character of the electronic wave function) and (b) canonical variational transition-state theory with small-curvature tunneling based on a validated density functional. We calculated pressure-dependent rate constants both by system-specific quantum Rice-Ramsperger-Kassel theory and by solving the master equation. We report rate constants for unimolecular reactions of scsAO over the full range of atmospheric temperature and pressure. We found that the unimolecular reaction rates of this larger-than-previously studied Criegee intermediate depend significantly on pressure. Particularly, we found that falloff effects decrease the effective unimolecular cyclization rate constant of scsAO by about a factor of 3, but the unimolecular reaction is still the dominant atmospheric sink for scsAO at low altitudes. The large falloff caused by the inclusion of the stereoisomerization channel in the master equation calculations has broad implications for mechanistic analysis of reactions with competitive internal rotations that can produce stable rotamers.
Abstract Lithium‐metal batteries suffer from short cycle life and poor safety due to uncontrolled dendrite growth at Li anodes. An advanced solid‐electrolyte interphase (SEI) with homogeneous chemical composition and physical structure holds great promise to address the issues. Herein, a new surface bromination approach is proposed for stabilizing SEI of Li anode via a scalable dip‐coating method. A lithium bromide‐enriched SEI is readily created on Li metal from chemical passivation by bromooctane. In‐situ optical microscopy reveals the crucial role of LiBr in inhibiting dendritic Li growth. The mechanistic investigations suggest the crystal facet (111) of LiBr provides high adsorption energy and low diffusion barriers for Li + ions. The incorporation of LiBr into SEI guarantees the stable cycling of Li irrespective of with ether or carbonate electrolytes, and the SEI is endurable at extremely low or high temperatures. The symmetric cell of the LiBr modified Li delivers a long lifespan of 2400 h with an overpotential less than 15 mV at 0.5 mA cm ‐2 , 1 mAh cm ‐2 . When paired with commercial cathodes, decent cycling retention and rate capability are available as well. This work demonstrates a feasible strategy for the development of stable Li‐metal batteries.
Here we report two-dimensional (2D) single-crystalline holey-graphyne (HGY) created an interfacial two-solvent system through a Castro-Stephens coupling reaction from 1,3,5-tribromo-2,4,6-triethynylbenzene. HGY is a new type of 2D carbon allotrope whose structure is comprised of a pattern of six-vertex and eight-vertex rings. The carbon-carbon 2D network of HGY is alternately linked between benzene rings and sp (carbon-carbon triple bond) bonding. The ratio of the sp over sp2 bonding is 50%. It is confirmed that HGY is stable by DFT calculation. The vibrational, optic, and electric properties of HGY are investigated theoretically and experimentally. It is a p-type semiconductor that embraces a natural direct band gap (~ 1.0 eV) with high hole mobility and electron mobility at room temperature. This report is expected to help develop a new types of carbon-based semiconductor devices with high mobility.
Abstract Single‐atom catalysts (SACs) have become the forefront of energy conversion studies, but unfortunately, the origin of their activity and the interpretation of the synchrotron spectrograms of these materials remain ambiguous. Here, systematic density functional theory computations reveal that the edge sites—zigzag and armchair—are responsible for the activity of the graphene‐based Co (cobalt) SACs toward hydrogen evolution reaction (HER). Then, edge‐rich (E)‐Co single atoms (SAs) were rationally synthesized guided by theoretical results. Supervised learning techniques are applied to interpret the measured synchrotron spectrum of E‐Co SAs. The obtained local environments of Co SAs, 65.49% of Co‐4N‐plane, 13.64% in Co‐2N‐armchair, and 20.86% in Co‐2N‐zigzag, are consistent with Athena fitting. Remarkably, E‐Co SAs show even better HER electrocatalytic performance than commercial Pt/C at high current density. Using the joint effort of theoretical modeling, thorough characterization of the catalysts aided by supervised learning, and catalytic performance evaluations, this study not only uncovers the activity origin of Co SACs for HER but also lays the cornerstone for the rational design and structural analysis of nanocatalysts.
Abstract L-Asparaginase is an enzyme successfully being used in the treatment of acute lymphoblastic leukemia, acute myeloid leukemia, and non-Hodgkin’s lymphoma. However, some disadvantages still limit its full application potential, e.g., allergic reactions, pancreatitis, and blood clotting impairment. Therefore, much effort has been directed at improving its performance. A popular strategy is to randomly conjugate L-asparaginase with mono-methoxy polyethylene glycol, which became a commercial FDA approved formulation widely used in recent years. To improve this formulation by PEGylation, herein we performed cysteine-directed site-specific conjugation of the four L-asparaginase subunits to prevent dissociation-induced loss of activity. The conjugation sites were selected at surface-exposed positions on the protein to avoid affecting the catalytic activity. Three conjugates were obtained using different linear PEGs of 1000, 2000, and 5000 g/mol, with physical properties ranging from a semi-solid gel to a fully soluble state. The soluble-conjugate exhibited higher catalytic activity than the non-conjugated mutant, and the same activity than the native enzyme. Site-specific crosslinking of the L-asparaginase subunits produced a higher molecular weight conjugate compared to the native tetrameric enzyme. This strategy might improve L-asparaginase efficiency for leukemia treatment by reducing glomerular filtration due to the increase in hydrodynamic size thus extending half-live, while at the same time retaining full catalytic activity.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
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