Termini restraining of small membrane proteins enables structure determination at near-atomic resolution

Small membrane proteins are difficult targets for structural characterization. Here, we stabilize their folding by restraining their amino and carboxyl termini with associable protein entities, exemplified by the two halves of a superfolder GFP. The termini-restrained proteins are functional and show improved stability during overexpression and purification. The reassembled GFP provides a versatile scaffold for membrane protein crystallization, enables diffraction to atomic resolution, and facilitates crystal identification, phase determination, and density modification. This strategy gives rise to 14 new structures of five vertebrate proteins from distinct functional families, bringing a substantial expansion to the structural database of small membrane proteins. Moreover, a high-resolution structure of bacterial DsbB reveals that this thiol oxidoreductase is activated through a catalytic triad, similar to cysteine proteases. Overall, termini restraining proves exceptionally effective for stabilization and structure determination of small membrane proteins

Metallic nanocatalysis : an accelerating seamless integration with nanotechnology

Rapidly growing research interests surround heterogeneous nanocatalysis, in which metal nanoparticles (NPs) play a pivotal role as structure-sensitive active centers. With advances in nanotechnology, the morphology of metal NPs can be precisely controlled, which can provide well-defined models of nanocatalysts for understanding and optimizing the structure–reactivity correlations and the catalytic mechanisms. Benefiting from this, further credible evidence can be acquired on well-defined nanocatalysts rather than common multiphase systems, which is of great significance for the design and practical application of active metal nanocatalysts. Numerous studies demonstrate that enhanced structure-sensitive catalytic activity and selectivity are dependent not only on an increased surface-to-volume ratio and special surface atom arrangements, but also on tailored metal–metal and metal–organic–ligand interfaces, which is ascribed to the size, shape, composition, and ligand effects. Size–reactivity relationships and underlying size-dependent metal–oxide interactions are observed in many reactions. For bimetallic nanocatalysts, the composition and nanostructure play critical roles in regulating reactivities. Crystal facets favor individual catalytic selectivity and rates via distinct reaction pathways occurring on diverse atomic arrangements, both to low-index and high-index facets. High-index facets exhibit superior reactivities owing to their high-energy active sites, which facilitate rapid bond-breaking and new bond generation. Additionally, organic ligands may enhance the catalytic activity and selectivity of metal nanocatalysts via changing the adsorption energies of reactants and/or reaction energy barriers. Furthermore, atomically dispersed metals, especially single-atom metallic catalysts, have emerged recently, which can achieve better specific catalytic activity compared to conventional nanostructured metallic catalysts due to the low-coordination environment, stronger interaction with supports, and maximum service efficiency. Here, recent progress in shaped metallic nanocatalysts is examined and several parameters are discussed, as well as finally highlighting single-atom metallic catalysts and some perspectives on nanocatalysis. The integration of nanotechnology and nanocatalysis has been shaping up and, no doubt, the combination of sensitive characterization techniques and quantum calculations will play more important roles in such processes

Nickel–cobalt catalyst supported on TiO2-coated SiO2 spheres for CO2 methanation in a fluidized bed

Carbon dioxide (CO2) methanation, which is the reduction of carbon dioxide to methane by hydrogen generated from renewable energy, is a promising process for carbon recycling. Towards large-scale implementation, (i) fluidized beds, which have excellent heat transfer, are promising to perform the highly exothermic reaction; and (ii) catalysts suitable for long-term use in fluidized beds are needed. In this study, a novel Nisingle bondCo bimetal catalyst supported on TiO2-coated SiO2 spheres (NiCo/TiO2@SiO2) was rationally designed and evaluated for CO2 methanation in fluidized bed reactor. The results demonstrate that NiCo/TiO2@SiO2 exhibited high CO2 conversion with CH4 selectivity of greater than 95%. Moreover, the superior performance was sustained for more than 100 h in the fluidized bed reactor, affirming the long-term stability of the catalyst. Comprehensive characterizations were conducted to understand the relationship between structure and performance. This study is expected to be valuable for the potential implementation of the CO2 methanation process in fluidized beds.National Research Foundation (NRF)This project is funded by the National Research Foundation (NRF), Prime Minister's Office, Singapore under its Campus for Research Excellence and Technological Enterprise (CREATE) program, and the 2nd Intra-CREATE Seed Collaboration Grant (NRF2017-ITS002-013)

低相对分子质量线型和星形聚乳酸及其共聚物多元醇的合成、结构与性能

Various of polylactide (PLA) and poly(lactide-co-caprolactone) (P(LA-co-CL)) polyols with different structures and molecular weight were synthesized by polymerization of lactide or/and caprolactone in the present of different chain transferring agents using SnOct_2 as catalyst. The structure and molecular weight(M_n) of the resulted polyols were characterized by FT-IR, ~1H-NMR and GPC. The M_n of PLA and P(LA-co-CL) polyols is very close to theoretical values and in a narrow distribution. Moreover, the polymerization rate of lactide is very fast in the present of chain transferring agents at 160 ℃, and the conversion of lactide is above 95% after 10 min and after that the M_n of PLA polyols keeps unchanged. The thermal properties of the resulted PLA and P(LA-co-CL) polyols were investigated by DSC and TGA. The glass transition temperature (T_g) of PLA polyols increases with increasing M_n; the introduction of caprolactone can decrease T_g effectively and enhance the thermal stability of PLA polyols