An In Situ Reflectance Spectroscopic Investigation to Monitor Two-Dimensional MoS2 Flakes on a Sapphire Substrate

In this work, we demonstrate the application of differential reflectance spectroscopy (DRS) to monitor the growth of molybdenum disulfide (MoS₂) using chemical vapor deposition (CVD). The growth process, optical properties, and structure evolution of MoS₂ were recorded by in-situ DRS. Indeed, blue shifts of the characteristic peak B were discussed with the decrease of temperature. We also obtained the imaginary part of the MoS₂ dielectric constant according to reflectance spectra. This method provides an approach for studying the change of two-dimensional (2D) materials’ dielectric constant with temperature. More importantly, our work emphasizes that the DRS technique is a non-destructive and effective method for in-situ monitoring the growth of 2D materials, which is helpful in guiding the preparation of 2D materials.     

Synthesis of a novel nano-rod-shaped hierarchical silicoaluminophosphate SAPO-11 molecular sieve with enhanced hydroisomerization of oleic acid to iso-alkanes

In this article, a novel nano-rod-shaped SAPO-11 molecular sieve (SAPO-11-A-F) with a thickness of ca. 100 nm was successfully fabricated by the in situ seed-induced steam-assisted method using the cationic surfactant cetyltrimethylammonium bromide (CTAB) as a mesoporous template and a nonionic copolymer poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide), F₁₂₇, as the crystal growth inhibitor. The fabricated nano-rod-shaped SAPO-11-A-F possessed nanocrystalline size, a hierarchical porous structure, and enhanced acidic sites. The added CTAB was mainly used to enhance the mesoporous structure and acid, and F₁₂₇ acted as a grain growth inhibitor. According to the orientation growth mechanism of the molecular sieves, the crystallization mechanism of the nano-rod-shaped hierarchical porous molecular sieves with different crystallization times was investigated. It was found that the nano-rod-shaped molecular sieves were formed by the accumulation of nano-sheets. Compared to three nickel catalysts with different silicoaluminophosphate SAPO-11 molecular sieves in the hydroisomerization of oleic acid to iso-alkanes, the bifunctional catalyst of 7% Ni/SAPO-11-A-F had higher isomeric selectivity (79.8%); in particular, the isomeric octadecane showed stronger selectivity, indicating that the nano-rod-shaped SAPO-11 molecular sieve is more beneficial for the hydrodehydration reaction.

A novel nano-rod-shaped SAPO-11 with a thickness of ca. 100 nm was successfully fabricated by in situ seed-induced steam assisted method using the cationic surfactant CTAB as a mesoporous template and F₁₂₇ as the crystal growth inhibitor.     

One-step solution synthesis of a two-dimensional semiconducting covalent organometallic nanosheet via the condensation of boronic acid

In this work, a 2D covalent organometallic nanosheet (COMS) was designed and successfully synthesized through the one-step conjunction of a terpyridine–metal–terpyridine (TMT) sandwich coordinate motif with borate ester covalent heterocyclic (B₃O₃) linkage via the condensation of boronic acid. The obtained 2D COMS with a cobalt coordination center (2D COMS-Co) showed promising p-type semiconducting properties.

A 2D covalent organometallic nanosheet (COMS-Co) was synthesized through the one-step conjunction of sandwich coordinate motif with covalent heterocyclic linkage via the condensation of boronic acid, and it showed promising semiconducting properties.

Two-dimensional (2D) metal–organic frameworks (MOFs) obtained by using the strong bonding effects between metal ions and organic molecule species have aroused great interest;^1–8 these include coordination nanosheets, which are a class of 2D materials featuring metal complex motifs.^9–12 Covalent bonds are considered to be an effective way to fabricate covalent organic frameworks (COFs) such as COF-1, which is mainly constructed by a phenyl ring and borate ester to form covalent heterocyclic (B₃O₃) linkage.^13–15 Based on the synergistic effects of metal coordination and covalent interactions, Jiang and co-workers demonstrated the important role of central metals in controlling π-electronic functions through Mpc-COF.¹⁶ Nevertheless, the coordination bond forms spontaneously within the ring of the porphyrin heterocycle and not as the linkage between organic components. In addition, the connections made between metal ions and ligand motifs cannot facilitate the proper tuning of the physicochemical properties of the structure.¹⁷ Combining the covalent and coordinate features may provide an opportunity to design new 2D materials and thus, the synergetic enhancement in many unique properties can be achieved. As far as we know, the fabrication of 2D semiconducting materials that combine the covalent heterocyclic linkage and coordinate linkage has not been reported. Therefore, it is a pressing need to construct a functional 2D organic framework through a one-step synthesis strategy, which would be a more attractive approach.Herein, we first proposed an efficient one-step strategy to synthesize a 2D material by the synergy of covalent and organometallic interactions; it was named as a covalent organometallic nanosheet (2D COMS-M, M = cobalt (Co)). The as-proposed 2D COMS-Co was constructed by linking the borate ester covalent heterocyclic (B₃O₃) structure and terpyridine (tpy) metal coordination motif (TMT) (Fig. 1).Open in a separate windowFig. 1(a) Synthesis route of the semiconducting 2D COMS. (b) Design principles of COMS via the condensation of boronic acid. (c) The calculated cross-sectional view of 2D COMS-Co.In order to explore the extended construction of 2D COMS, the self-condensation ligand 4-phenylborate-2,2′; 6′,2′′-terpyridine (L¹) integrated with CoCl₂ as the Co²⁺ carrier was employed through an anhydrous and oxygen-free hydrothermal reaction at 120 °C under argon, and the typical synthesis process is depicted in Fig. 1a (for details, please see ESI^†). Starting from the condensation reaction of boronic acid (Fig. 1b), H₂O could be generated and played a key role in dissolving CoCl₂ and further releasing Co²⁺ ions (CoCl₂ is practically insoluble in mesitylene and dioxane). This was followed by coordination between the terpyridine motifs and the released Co²⁺ ions to obtain 2D COMS. This novel strategy could achieve crystalline 2D materials by self-controlling the release of Co²⁺ through the one-step condensation reaction of boronic acid. The calculated cross-sectional view of 2D COMS-Co indicates that the thickness of the monolayer 2D COMS-Co is 0.69 nm (Fig. 1c). The dual synergistic connecting effects of covalence and coordination in 2D COMS-Co provided nanosheet-like morphology with significant improvement in the semiconducting performance. The hole mobility of the 2D COMS-Co-based FET device could reach to 5.7 × 10⁻⁵ cm² V⁻¹ s⁻¹ with an ON–OFF ratio of 221, which demonstrated the potential application of 2D COMS-Co in semiconducting devices.The scanning electron microscopy (SEM) image (Fig. 2a) reveals that 2D COMS-Co has a uniform micron-sized nanosheet-like structure. Furthermore, the transmission electron microscopy (TEM) image indicates that the as-synthesized 2D COMS-Co consists of few multi-layers. Fig. 2c shows an enlarged image of the selected area visualized with high-resolution TEM (HRTEM), where the section enclosed by white lines depicts lattice fringes. Moreover, the selected area electron diffraction (SAED, inset of Fig. 2c) image shows a circular ring pattern that reveals the well-defined crystalline structure of 2D COMS-Co; these results are in agreement with our X-ray diffraction data (Fig. S2, ESI^†). Most interestingly, the atomic force microscopy (AFM) image (Fig. 2d) clearly demonstrates that the selected thickness of 2D COMS-Co is 2.07 nm, and the resultant thickness is three times less than the calculated value of 0.69 nm (Fig. 1c), indicating its uniform three-layer stacked structure. The above results collectively provide strong evidence of typical 2D features for COMS-Co. Moreover, the high-angle annular dark-field (HAADF) image and the scanning transmission electron microscopy (STEM) elemental mapping further revealed that the C (red), B (cyan), N (green), O (blue) and Co (pink) elements are homogeneously distributed on the selected area of 2D COMS-Co (Fig. 2e–k). The electronic structure of 2D COMS-Co was further characterized by four-probe scanning tunnel microscopy (STM) (please see details in ESI^†). The high-resolution STM imaging revealed that the 2D COMS-Co flake has a layered flake structure with uniformly distributed hexagonal hole morphology and the resultant holes have a diameter of 4.72 nm (Fig. 2l); this observation is in accordance with the proposed structure of 2D COMS-Co (Fig. S8, ESI^†).Open in a separate windowFig. 2Morphological characterization of 2D COMS-Co. (a) SEM image of powder. (b) TEM image. (c) HRTEM image (d) AFM image. (e) HAADF image. (f–k) STEM elemental mapping. (l) STM image.Due to the covalence and coordination effects, the absorption peak of 2D COMS-Co obtained from the UV-vis measurements (Fig. 3a) is red-shifted in comparison to that for ligand L¹, and the optical band gap is calculated to be 1.85 eV. Furthermore, density functional theory (DFT) calculations revealed that the highest occupied molecular orbital (HOMO) of 2D COMS-Co was dominated by the π orbital of the B₃O₃ linkage and the phenyl ring, whereas the π* orbital of TMT was responsible for the lowest unoccupied molecular orbital (LUMO). Additionally, the calculated electronic band gap of 2D COMS-Co was 1.89 eV, which was in accordance with the optical band gap, confirming the successful synthesis of 2D COMS-Co. Fig. 3b displays the X-ray photoelectron spectroscopy (XPS) spectrum of 2D COMS-Co, in which the appearance of the binding energy peak at 192.2 eV is significantly different from that for L¹ (191.1 eV), which can be ascribed to the –C–B–O₂ structure.^18,19 Compared to the observation for L¹, the N 1s peak for 2D COMS-Co shifted to a higher binding energy value (399.2 eV for COMS-Co and 397.5 eV for L¹). The skewing of the peaks toward higher binding energy was induced by the contribution of N atoms in terpyridine to the metal center. Therefore, the XPS results clearly provide evidence of the existence of both covalent and coordination effects in the as-prepared 2D COMS-Co. The Fourier transform infrared (FT-IR) spectra in Fig. 3c show that the –B(OH)₂ bands (around 3500 cm⁻¹) of the ligand L¹ are significantly attenuated compared to that observed for 2D COMS-Co. In addition, the B–O stretching vibrations at 1351 cm⁻¹ can be observed for 2D COMS-Co but not for L¹.^13,20–22 Thus, the above results show that the expected B₃O₃ rings for 2D COMS-Co have indeed been formed. Notably, the nitrogen adsorption–desorption isotherms reveal that the Brunauer–Emmett–Teller (BET) specific surface area of 2D COMS-Co is as high as 598 m² g⁻¹ (Fig. 3d); it surpasses those of other layered materials, including the reported graphene oxide paper (10 m² g⁻¹), clays (10 to 100 m² g⁻¹), and pillared clays (50 to 300 m² g⁻¹), and is in the range of the values of the most porous zeolites and many porous carbons.^13,23 This drastic enhancement can be assigned to the uniform porous structure of the as-synthesized 2D COMS-Co.Open in a separate windowFig. 3(a) UV-vis spectra of L¹ and 2D COMS-Co (left), electron distribution on HOMO/LUMO and the orbital energy gap (right). (b) XPS B 1s and N 1s spectra of L¹ and 2D COMS-Co. (c) FT-IR spectra of L¹ and 2D COMS-Co. (d) N₂ adsorption and desorption isotherms of 2D COMS-Co (inset: stacking porous view).The above results show that the 2D COMS-Co units arranged in periodic strips can provide conducting pathways for charge carrier transport through TMT and central cobalt ions. 2D COMS-Co was employed to function as the active semiconducting channel in a field-effect transistor (FET) device. As shown in Fig. 4a, the individual 2D COMS-Co sample is deposited on an Si wafer as the semiconducting layer to construct the FET device. The 2D COMS-Co-based FET device delivered hole mobility of 5.7 × 10⁻⁵ cm² V⁻¹ S⁻¹ and an ON/OFF ratio of 221, which were comparable with those of previously reported 2D MOFs (Table S1^†). Therefore, these results collectively demonstrate the potential application of 2D COMS-Co in semiconducting devices.Open in a separate windowFig. 4(a) Schematic of the FET device employing 2D COMS-Co as the semiconducting layer. (b) Transfer curve of the 2D COMS-Co-based FET device with the inset showing an optical and model diagram of the device; V_G is the gate-source voltage and I_D is the drain current.In summary, a novel two-dimensional covalent organometallic nanosheet (COMS) was designed and successfully synthesized through the strategy of one-step conjunction of a TMT sandwich coordinate motif with B₃O₃ linkage. This facile strategy could achieve crystalline 2D COMS-Co by self-controlling the release of Co²⁺ through a one-step condensation reaction of boronic acid. The systematic characterization demonstrated the successful preparation of porous and crystalline 2D COMS-Co. Particularly, the as-prepared 2D COMS-Co-based FET device presented hole mobility of 5.7 × 10⁻⁵ cm² V⁻¹ S⁻¹ and an ON/OFF ratio of 221, which demonstrated the potential application of 2D COMS-Co in semiconducting devices. Therefore, we envision that this work will open a new avenue for the synthesis of two-dimensional semiconducting covalent organometallic materials by using covalence and coordination dual synergistic connection effects via a one-step facile strategy.     

Synthesis and properties of porous CLEAs lipase by the calcium carbonate template method and its application in biodiesel production

In this work, porous cross-linked enzyme aggregates (p-CLEAs) were synthesized by the in situ co-precipitation method using CaCO₃ microparticles as templates. The preparation procedure involved the immobilization of crude lipase as CLEAs via precipitation with ammonium sulfate and entrapping these lipase molecules into the CaCO₃ templates, followed by DTT (dithiothreitol)-induced assembly of lipase molecules to form lipase microparticles (lipase molecules were assembled into microparticles internally using disulfide bonds within the lipase molecules as the molecular linkers and stimulated by dithiothreitol); finally, the removal of CaCO₃ templates was performed by EDTA to form pores in CLEAs. The scanning electron microscopy analysis of p-CLEAs showed a porous structure. p-CLEAs showed obvious improvement in thermal stability (after incubation at 65 °C, p-CLEAs lipase retained 86% relative activity, while free lipase retained only 33.67%) and pH stability (p-CLEAs relative activity was over 90% while for free lipase, the relative activity ranged from 72% to 89% from pH 6 to 9) than free lipase and could hold relatively high activity retention without activity loss at 4 °C for more than six months. The application of p-CLEAs in producing biodiesel showed a higher degree of conversion. The conversion of fatty acid methyl ester (FAME) was 89.7%; this value was higher by approximately 7.4% compared to that of the conventional CLEAs under the optimized conditions of a methanol–oil molar ratio of 6 : 1, with a p-CLEAs lipase dose of 20% and water content of 3% at 45 °C for 24 h. The FAME conversion remained greater than 70% even after reusing the p-CLEAs lipase for 8 reactions. The results demonstrated that the p-CLEAs lipase is suitable for applications in the preparation of biodiesel.

Porous cross-linked enzyme aggregates (p-CLEAs) were synthesized. This p-CLEAs presented a complete structure with abundant channels, large specific surface and more efficient catalytic effect compared with conventional CLEAs.     

Role of Angptl4 in vascular permeability and inflammation

Background

Angptl4 is a secreted protein involved in the regulation of vascular permeability, angiogenesis, and inflammatory responses in different kinds of tissues. Increases of vascular permeability and abnormality changes in angiogenesis contribute to the pathogenesis of tumor metastasis, ischemic-reperfusion injury. Inflammatory response associated with Angptl4 also leads to minimal change glomerulonephritis, wound healing. However, the role of Angptl4 in vascular permeability, angiogenesis, and inflammation is controversy. Hence, an underlying mechanism of Angptl4 in different kind of tissues needs to be further clarified.

Methods

Keywords such as angptl4, vascular permeability, angiogenesis, inflammation, and endothelial cells were used in search tool of PUBMED, and then the literatures associated with Angptl4 were founded and read.

Results

Data have established Angptl4 as the key modulator of both vascular permeability and angiogenesis; furthermore, it may also be related to the progression of metastatic tumors, cardiovascular events, and inflammatory diseases. This view focuses on the recent advances in our understanding of the role of Angptl4 in vascular permeability, angiogenesis, inflammatory signaling and the link between Angptl4 and multiple diseases such as cancer, cardiovascular diseases, diabetic retinopathy, and kidney diseases.

Conclusions

Taken together, Angptl4 modulates vascular permeability, angiogenesis, inflammatory signaling, and associated diseases. The use of Angptl4-modulating agents such as certain drugs, food constituents (such as fatty acids), nuclear factor (such as PPARα), and bacteria may treat associated diseases such as tumor metastasis, ischemic-reperfusion injury, inflammation, and chronic low-grade inflammation. However, the diverse physiological functions of Angptl4 in different tissues can lead to potentially deleterious side effects when used as a therapeutic target. In this regard, a better understanding of the underlying mechanisms for Angptl4 in different tissues is necessary.     

下消化道出血诊治指南（2020）

下消化道出血（lower gastrointestinal bleeding, LGIB）的定义为屈氏韧带以远的肠道出血,包括小肠出血和结直肠出血。LGIB临床常见,占全部消化道出血的20%～30%。但由于各种原因,对LGIB的研究却不及上消化道出血深入,相关指南和共识亦较少。此外,近年来内镜和影像技术快速发展,逐渐发现小肠出血的临床特点、诊疗方法和转归均不同于结直肠出血。因此,由中华医学会消化内镜学分会结直肠学组、中国医师协会消化医师分会结直肠学组、国家消化系统疾病临床医学研究中心牵头制定了《下消化道出血诊治指南（2020）》,本指南结合最新的国内外临床研究结论及专家意见,结合我国实际,分别对小肠出血和结直肠出血的临床诊治进行了规范和推荐,旨在进一步规范LGIB的诊治流程。     

结直肠侧向发育型肿瘤癌变的内镜学特征

目的 探讨结直肠侧向发育型肿瘤（laterally spreading tumor,LST）癌变的独立预测因素。方法 回顾性收集于2013年6月—2019年3月在首都医科大学附属北京友谊医院因结直肠LST行内镜治疗患者的性别、年龄、体重指数、吸烟史、病变的内镜学特征和病理学特点。用单因素分析寻找癌变的影响因素,对于其中差异有统计学意义的因素再纳入多因素Logistic回归分析。结果 共纳入了323例患者341处病变。假凹陷型LST的癌变率最高[85.48%（53/62）],其次为结节混合型[76.97%（117/152）],均显著高于颗粒均一型[29.51%（18/61）,P均＜0.001]和扁平隆起型[24.24%（16/66）,P均＜0.001]。单因素分析显示,假凹陷型（P＜0.001,OR=18.40,95%CI：7.46～45.42）、结节混合型（P＜0.001,OR=10.45,95%CI：5.30～20.58）、位于直乙部位（P＜0.001,OR=2.33,95%CI：1.47～3.69）、直径≥2 cm（P＜0.001,OR=2.60,95%CI：1.60～4.00）是病变发生癌变的危险因素。多因素Logistic回归分析表明,假凹陷型（P＜0.001,OR=17.51,95%CI：7.06～43.43）、结节混合型（P＜0.001,OR=8.25,95%CI：4.07～16.73）、直径≥2 cm（P=0.032,OR=1.80,95%CI：1.05～3.08）是结直肠LST发生癌变的独立预测因素。结论 当LST为假凹陷型、结节混合型或直径≥2 cm时病变发生癌变的风险高,需要采取整块切除的方式治疗。     

内镜下磁吻合术治疗先天性食管狭窄一例

采用传统手术方法治疗儿童先天性食管狭窄较困难且并发症多。本文报道1例利用磁吻合术实现儿童先天性食管狭窄微创治疗的临床经验。通过消化道内镜和胃造瘘方法将两个圆环状永磁体分别植入食管狭窄部位近、远端食管腔内,磁体对食管狭窄部位产生持续压榨作用以疏通食管。磁吻合术后1 d内磁环即完成良好对位,术后14 d胃造瘘口取出磁体,食管造影显示吻合口通畅情况良好,术后3个月复查食管造影通畅情况良好,随访6个月未发生任何并发症。