Programmed Site‐Selective Palladium‐Catalyzed Arylation of Thieno[3,2‐b]thiophene

Mono‐, di‐, tri‐, and tetraarylated thieno[3,2‐b ]thiophenes were synthesized by direct site‐selective Pd‐catalyzed C−H activation reactions with various aryl bromides in the presence of a phosphine‐free Pd(OAc)₂/KOAc catalyst system in N ,N ‐dimethylacetamide (DMAc). The arylation of 2‐arylthieno[3,2‐b ]thiophene took place at the C3 position if the 2‐aryl substituents possessed electron‐withdrawing groups and at the C5 position if they were bulky and possessed electron‐donating groups.     

The nature of synergistic effects in transition metal oxides/in-situ intermediate-hydroxides for enhanced oxygen evolution reaction

Oxygen evolution reaction is highly important for hydrogen production via water splitting but requires ～0.22 V onset overpotential, resulting in at least 15% extra energy consumption even utilized with the benchmark hetero-doped transition-metal hydroxide catalysts. The lack of fundamental understanding on catalyst behaviour and on synergistic mechanisms limit the breakthrough for material design. Here, we systematically summarise a variety of investigations and arguments on the mechanism from the microscale (optimal octahedral intermediate with six M?O coordination) to atomic scale (the active site behaviour). The electron–orbital scale (e_g) is further described for the intrinsic OER activity. The synergistic effect may also lead to a short-cut pathway of lattice-oxygen-mediated mechanism to achieve a smaller overpotential. This review provides a theoretical reference for the design of advanced catalysts.     

双原子位点M-N-C电催化剂在CO2还原反应中活性位点的最佳分布

双原子位点M-N-C催化剂是催化CO₂还原反应(CO₂RR)性能最佳的催化剂之一. 然而, 目前的研究主要集中于M-N-C活性中心原子类型的调控, 低估了活性位点的配位模式及分布对其催化性能的影响. 本文选取典型的双原子位点M-N-C催化剂(NiFe-N-C)为研究对象, 采用密度泛函理论方法探究了9种活性位点具有不同配位环境的NiFe-N-C催化剂电催化CO₂RR的反应机理. 结果表明, 随着金属原子配位数、 双原子位点间距离的增加, M-N-C催化剂的稳定性、 催化CO₂还原至CO的活性及抑制氢析出反应的选择性均呈现先升高后下降的趋势. 其中, 金属原子四配位且对称分布的NiFe-N-C-model 3催化剂, 因其双原子位点的强相互作用表现出最优的催化性能.     

Fuzzy reliability analysis of aseismic structures

The structural reliability analysis taking account of the fuzziness in both earthquake loads and structural resistances is put forward in this paper. For this purpose, the concepts such as fuzzy earthquake intensity, fuzzy response spectrum, fuzzy structural response and satisfaction degree to fuzzy-random constraint are defined. This procedure may be taken as a basis for establishing a more rational optimum design of structures.     

Evaluation of a multi‐fiber exchange solid‐phase microextraction system and its application to on‐site sampling

Until recently, multiple solid‐phase microextraction fibers could not be automatically desorbed in a single gas chromatographic sequence without manual intervention from an operator. This drawback had been a critical issue, particularly during the analysis of numerous on‐site samples taken with various fiber assemblies. Recently, a Multi‐Fiber Exchange system, designed to overcome this flaw found in other commercially available autosamplers, was released. In the current research, a critical evaluation of the Multi‐Fiber Exchange system performance in terms of storage stability and long‐term operation is presented. It was established in the course of our research that the Multi‐Fiber Exchange system can operate continuously and precisely for multiple extraction/injection cycles. However, when the effect of residence time of commercial fibers on the Multi‐Fiber Exchange tray was evaluated, results showed that among the evaluated fiber coatings, Carboxen/polydimethylsiloxane was the only coating capable of efficient storage on the tray for up to 24 h after field sampling without suffering significant loss of analytes (≤10% for benzene, toluene, ethylbenzene, o‐xylene, decane, and limonene). Additionally, the system capability for high‐throughput analysis was demonstrated by the unattended desorption of multiple fibers after on‐site sampling of toluene, indoor air levels, in a polymer synthesis lab.     

Effect of Chain Topology of Polyethylenimine on Physisorption and Chemisorption of Carbon Dioxide

Polyethylenimine (PEI) is a promising candidate for CO₂ capture. In this work, the physisorption and chemisorption of CO₂ on various low‐molecular‐weight PEIs are investigated to identify the effect of chain architecture on sorption. The reliability of theoretical calculations are partially supported by our experimental measurements. Physisorption is calculated independently by the reference interaction‐site model integral equation theory; chemisorption is distinguished from the total sorption given by the quantum density functional theory. It is shown that, as the chain length increases, both chemisorption and physisorption drop off nonlinearly, but the decay amplitude of chemisorption is more apparent. Conversely, as the amine group approaches the central triamine unit of each oligomer, the sorption capacity decreases, affecting the sorption equilibrium in a complex way. This arises from the cooperative contribution of an increased steric effect and renormalized electronic distribution.     

Protein photocrosslinking reveals dimer of dimers formation on MarR protein in Escherichia coli

The multiple antibiotic resistance regulatory protein(MarR) binds to two promoter sites on the marO operator in Escherichia coli.Our study showed that more than one MarR dimer proteins bound to either of its two promoter sites(Site I and Site II),suggesting that MarR might form higher complexes than homodimers when bound to DNA inside E.coli cells.To further verify this hypothesis,we site-specifically incorporated a photocrosslinking probe at the interface between two MarR dimer proteins.Photolysis in living E.coli cells revealed a covalent linkage between the two interdimer subunits of MarR,suggesting that MarR forms dimer of dimers in vivo.