Local Electric Field Effect of TMI (Fe, Co, Cu)-BEA on N₂O Direct Dissociation

Zeolite catalyst consists of an infinite network of TO₄ tetrahedra (T = Si, Al, etc.) having various physic-chemical properties, among which the electric field effect (EFE) constituting one of the most important properties plays a major role in the heterogeneously catalytic reactions. However, up to now few works have been devoted to establishing the relationship between EFE and related catalytic behavior for the zeolite catalyst. In light of that, the present work systematically investigated the local electric field effect of the transition-metal-ion modified β zeolites [TMI (Fe, Co, Cu)-BEA] during N₂O direct decomposition based on Mulliken charge transfer (CT) analysis, frontier molecular orbital analysis (FMO), and diffuse reflectance infrared Fourier transform spectra (DRIFTS). For the O₂ formation mechanism, the EFEs of TMI-BEA and formed αO greatly influenced adsorption and further activation of N₂O through the CT, which was quantitatively determined by the FMO gaps between TMI-BEA and N₂O. For the NO_<i>x</i> formation mechanism, the weak EFEs of Fe-BEA and formed αO during N₂O adsorption through its N end gave a clue of low NO selectivity of Fe-BEA. The EFE investigation of zeolite catalyst facilitates the deeper understanding of the reaction mechanism and clarifies the principle for catalyst design

Theoretical Insight into the Mechanisms and Regioselectivity of [4 + 3] and [4 + 1] Annulations of Enals with Azoalkenes Catalyzed by N‑Heterocyclic Carbenes

The reaction mechanisms on the NHC-catalyzed [4 + 3] and [4 + 1] annulations of enals with azoalkenes have been theoretically investigated with the aid of the density functional theory calculations. It is found that the additives play an important role in promoting proton transfer and dehydration. The impacts of catalysts (<b>NHC-A</b> and <b>NHC-B</b>) and substituent groups on the regioselectivity were rationalized. The origin of the regioselectivity involved in these reactions was probed by performing distortion–interaction analysis. For reaction A with <b>NHC-A</b> as the catalyst and Boc group as the substituent, the regioselectivity is predicted to be determined by the interaction energy of <b>3</b> with <b>R</b>_<b>2</b>^<b>′</b> in <b>TS</b>_<b>3</b>^<b>A</b> versus <b>TS</b>_<b>8</b>^<b>A</b>. For reaction B with <b>NHC-B</b> as the catalyst and Boc group as the substituent, the unstable boat-type conformation versus the stable chair-type conformation involved in the <b>NHC-B</b> moiety accounts for the regioselectivity. In reaction C with <b>NHC-A</b> as the catalyst and Ts group as the substituent, distortion energies of <b>3</b> and <b>R</b>_<b>2</b>^<b>′</b> in <b>TS</b>_<b>3</b>^<b>C</b> versus <b>TS</b>_<b>6</b>^<b>C</b> are found to be the major reason delivering regioselectivity even higher than that of reaction A

Theoretical Insight into the Mechanisms and Regioselectivity of [4 + 3] and [4 + 1] Annulations of Enals with Azoalkenes Catalyzed by N‑Heterocyclic Carbenes

The reaction mechanisms on the NHC-catalyzed [4 + 3] and [4 + 1] annulations of enals with azoalkenes have been theoretically investigated with the aid of the density functional theory calculations. It is found that the additives play an important role in promoting proton transfer and dehydration. The impacts of catalysts (<b>NHC-A</b> and <b>NHC-B</b>) and substituent groups on the regioselectivity were rationalized. The origin of the regioselectivity involved in these reactions was probed by performing distortion–interaction analysis. For reaction A with <b>NHC-A</b> as the catalyst and Boc group as the substituent, the regioselectivity is predicted to be determined by the interaction energy of <b>3</b> with <b>R</b>_<b>2</b>^<b>′</b> in <b>TS</b>_<b>3</b>^<b>A</b> versus <b>TS</b>_<b>8</b>^<b>A</b>. For reaction B with <b>NHC-B</b> as the catalyst and Boc group as the substituent, the unstable boat-type conformation versus the stable chair-type conformation involved in the <b>NHC-B</b> moiety accounts for the regioselectivity. In reaction C with <b>NHC-A</b> as the catalyst and Ts group as the substituent, distortion energies of <b>3</b> and <b>R</b>_<b>2</b>^<b>′</b> in <b>TS</b>_<b>3</b>^<b>C</b> versus <b>TS</b>_<b>6</b>^<b>C</b> are found to be the major reason delivering regioselectivity even higher than that of reaction A

Thermoresponsive Oligo(ethylene glycol)-Based Polymer Brushes on Polymer Monoliths for All-Aqueous Chromatography

Porous polymer monoliths onto which were grafted a thermoresponsive copolymer, poly­(2-(2-methoxyethoxy)­ethyl methacrylate (MEO₂MA)-<i>co</i>-oligo­(ethylene glycol) methacrylate (OEGMA)), were synthesized by the two-step atom transfer radical polymerization (ATRP) method. The copolymer-grafted monoliths were characterized by elemental analysis, scanning electron microscopy, and mercury intrusion porosimetry. They were further used as the thermoresponsive stationary phase for all-aqueous high-performance liquid chromatography (HPLC). The chromatograms of three steroids demonstrated that the chain length of the grafted copolymer, which was regulated by varying the grafting time, could affect the separation by providing different amounts of hydrophobic interaction sites with analytes. Additionally, the elution profiles of steroids on the stationary phase could also be tuned by the comonomer composition. The results showed that the porous polymer monoliths enabled separation of the test mixture in pure aqueous mobile phase under isocratic conditions. Furthermore, the proposed method provides a simple and promising tool in the design and construction of responsive surfaces for chromatography applications

Exploration of Dependence of Organo-Catalyzed Enantioselective Michael Addition on the Pore Size of Mesoporous Host

Confinement, an effective strategy to improve the enantioselectivity in metal-catalyzed asymmetric synthesis, is a great challenge to the heterogeneous organocatalysis via hydrogen-bonding activation in that hydrogen bonding is more sensitive to the complicated spatial or chemical microenvironment in confined spaces. Here, visible improvement of enantioselectivity has been experimentally achieved on heterogeneous 9-amino (9-deoxy) epiquinine and 9-thiourea epiquinine catalysts in the Michael addition by rationally modulating the pore size of the mesoporous host. The enantiomer excess for heterogeneous 9-thiourea epiquinine is level with the homogeneous counterpart when the support pore size is reduced to an optimized spatial dimension. Theoretical calculations revealed that the immobilization can switch the activation routes, and the hydrogen-bonding interaction between substrate and pore wall influences the energy gap between <i>R</i>/<i>S</i> transition states, well accounting for the dependence of enantioselectivity on the pore size experimentally observed in the heterogeneous organocatalytic Michael addition. The results not only demonstrate significant development in the comprehension of confinement in the heterogeneous asymmetric catalysis but also suggest an original strategy in designing efficient enantioselective heterogeneous catalysts

<i>hOGG1</i> Ser326Cys Polymorphism and Risk of Hepatocellular Carcinoma among East Asians: A Meta-Analysis

<div><p>Background</p><p>The <i>hOGG1</i> gene encodes a DNA glycosylase enzyme responsible for DNA repair. The Ser326Cys polymorphism in this gene may influence its repair ability and thus plays a role in carcinogenesis. Several case-control studies have been conducted on this polymorphism and its relationship with the risk of hepatocellular carcinoma (HCC) among East Asians. However, their results are inconsistent.</p><p>Methods</p><p>We performed a meta-analysis of published case-control studies assessing the association of the <i>hOGG1</i> Ser326Cys polymorphism with HCC risk among East Asians. PubMed, EMBASE, SCI, BIOSIS, CNKI and WanFang databases were searched. A random-effect model was used to calculate odds ratios (ORs) and 95% confidence intervals (95% CIs). Analyses were conducted for additive, dominant and recessive genetic models.</p><p>Results</p><p>Eight studies were identified involving 2369 cases and 2442 controls assessing the association of the <i>hOGG1</i> Ser326Cys polymorphism with HCC risk among East Asians. Applying a dominant genetic model, only in the Chinese population, the Cys allele was significantly associated with increased risk of HCC (OR 1.56, 95% CI 1.12–2.17). However, two studies influenced this finding according to sensitivity analysis. Furthermore, considerable heterogeneity and bias existed among Chinese studies.</p><p>Conclusion</p><p>There is limited evidence to support that the <i>hOGG1</i> Ser326Cys polymorphism is associated with HCC risk among East Asians. Well-designed and large-sized studies are required to determine this relationship.</p></div

Electrosynthesis of Trisubstituted 2‑Oxazolines via Dehydrogenative Cyclization of β‑Amino Arylketones

An electrochemically intramolecular functionalization of C­(sp³)–H bonds with masked oxygen nucleophiles was developed. With KI as the catalyst and electrolyte, diverse trisubstituted 2-oxazolines were constructed in good to excellent yields. This newly developed electrochemical dehydrogenative approach features external oxidant-free and additive-free conditions

Enhanced Electrochemical Performance of LiNi_0.5Mn_1.5O₄ Cathode Material by YPO₄ Surface Modification

Cathode material LiNi_0.5Mn_1.5O₄ (LNMO) for lithium-ion batteries is successfully synthesized by a sol–gel method and is further modified by a thin layer of YPO₄ (1, 3, and 5 wt %) through a simple wet chemical strategy. Physical characterizations indicate that the YPO₄ nanolayer has a little impact on the cathode structure. Electrochemical optimization reveals that the 3 wt % YPO₄-coated LNMO could still deliver a high specific capacity of 107 mAh g^–1 after 240 cycles, with a capacity retention of 77.5%, much higher than that of the pristine electrode. Electrochemical impedance spectroscopy (EIS) analysis proves that the rapid increase of surface impedance could be suppressed by the YPO₄ coating layer and thus facilitates the surface kinetics behavior in repeated cycling. Through further material aging experiments, the improvement of electrochemical performances could be attributed to the formation of Lewis acid YF₃, converted from the YPO₄ coating layer in the LiPF₆-based electrolyte, which not only scavenges the surface insulating alkaline species with a high acidity but also accelerates ion exchange on the material surface and thus helps to generate the solid solution Li–Ni–Mn–Y–O on the surface of YPO₄-coated LNMO

Nucleosome positioning changes during human embryonic stem cell differentiation

<p>Nucleosomes are the basic unit of chromatin. Nucleosome positioning (NP) plays a key role in transcriptional regulation and other biological processes. To better understand NP we used MNase-seq to investigate changes that occur as human embryonic stem cells (hESCs) transition to nascent mesoderm and then to smooth muscle cells (SMCs). Compared to differentiated cell derivatives, nucleosome occupancy at promoters and other notable genic sites, such as exon/intron junctions and adjacent regions, in hESCs shows a stronger correlation with transcript abundance and is less influenced by sequence content. Upon hESC differentiation, genes being silenced, but not genes being activated, display a substantial change in nucleosome occupancy at their promoters. Genome-wide, we detected a shift of NP to regions of higher G+C content as hESCs differentiate to SMCs. Notably, genomic regions with higher nucleosome occupancy harbor twice as many G↔C changes but fewer than half A↔T changes, compared to regions with lower nucleosome occupancy. Finally, our analysis indicates that the hESC genome is not rearranged and has a sequence mutation rate resembling normal human genomes. Our study reveals another unique feature of hESC chromatin, and sheds light on the relationship between nucleosome occupancy and sequence G+C content.</p

Sensitivity analysis using the one-study remove approach.

<p>OR, odds ratio; CI, confidence interval.</p