Accelerated Nuclear Magnetic Resonance Spectroscopy with Deep Learning

Nuclear magnetic resonance (NMR) spectroscopy serves as an indispensable tool in chemistry and biology but often suffers from long experimental times. We present a proof-of-concept of the application of deep learning and neural networks for high-quality, reliable, and very fast NMR spectra reconstruction from limited experimental data. We show that the neural network training can be achieved using solely synthetic NMR signals, which lifts the prohibiting demand for a large volume of realistic training data usually required for a deep learning approach.     

Photoenzymatic Hydrogenation of Heteroaromatic Olefins Using ‘Ene’‐Reductases with Photoredox Catalysts

Flavin‐dependent ‘ene’‐reductases (EREDs) are highly selective catalysts for the asymmetric reduction of activated alkenes. This function is, however, limited to enones, enoates, and nitroalkenes using the native hydride transfer mechanism. Here we demonstrate that EREDs can reduce vinyl pyridines when irradiated with visible light in the presence of a photoredox catalyst. Experimental evidence suggests the reaction proceeds via a radical mechanism where the vinyl pyridine is reduced to the corresponding neutral benzylic radical in solution. DFT calculations reveal this radical to be “dynamically stable”, suggesting it is sufficiently long‐lived to diffuse into the enzyme active site for stereoselective hydrogen atom transfer. This reduction mechanism is distinct from the native one, highlighting the opportunity to expand the synthetic capabilities of existing enzyme platforms by exploiting new mechanistic models.     

An effective lactic acid-modified Hβ zeolite for synthesis of bis(indolyl)methanes

Excellent activity and stability have been observed for a lactic acid-modified Hβ (LA-Hβ) zeolite in the synthesis of bis(indolyl)methanes by Friedel–Crafts alkylation of indole with aldehydes. It is proposed that lactic acid treatment is appropriate for dealumination of Hβ zeolite, and results in a LA-Hβ zeolite with greater surface area, fewer weak acid sites, and more moderately-strong acid sites, as confirmed by the Brunauer–Emmett–Teller method, inductively coupled plasma emission spectrometry, and temperature-programmed desorption of NH₃. Moreover, both electronic and steric effects of substituents on the aromatic ring of the aldehydes were found to be important in this reaction.     

Aerothermal dynamic failure of infrared window in high-speed aircraft

红外罩材料包括红外罩增透保护膜和基底材料, 是高速导弹结构--功能一体化的关键部件, 应用极为广泛. 但是, 红外罩材料通常工作于恶劣的外界环境下, 处于复杂的热力混合作用状态, 可能导致窗口失效, 因此对红外罩材料热力响应和失效的研究具有重要的科学研究价值和工程实际意义.本文针对高速飞行器环境下红外罩材料的气动热力失效机制, 从典型材料的特性及制备、气动热力响应机理及分析、红外罩材料的结构性和功能性失效等方面总结相关学者的研究成果, 并对今后的发展趋势进行展望.     

A nanoflower shaped gold-palladium alloy on graphene oxide nanosheets with exceptional activity for electrochemical oxidation of ethanol

We report on a new and facile method for the preparation of well-dispersed gold-palladium (AuPd) flower-shaped nanostructures on sheets of graphene oxide (GO). Transmission electron microscopy and high angle annular dark field STEM were used to characterize the morphology and composition of the new nanohybrids. The AuPd/GO composites display high electrocatalytic activity for the oxidation of ethanol in strongly alkaline medium as examined by cyclic voltammetry and chronoamperometry. Both the current density (13.16 mA?·?cm^?2 at a working potential of ?0.12 V) and the long-time stability are superior to a commercial Pd-on-carbon catalyst which is attributed to the cooperative action of the catalytic activities of Au and Pd, and the good dispersion of the alloy on the nanosheets.

Trishomoaromatic (B3N3Ph6) Dianion: Characterization and Two‐Electron Reduction

Benzene, a common aromatic compound, can be converted into an unstable antiaromatic 8π‐electron intermediate through two‐electron reduction. However, as an isoelectronic equivalent of benzene, borazine (B₃N₃Ph₆), having weak aromaticity, undergoes a totally different two‐electron reduction to afford (B₃N₃R₆)^2? homoaromatic compounds. Reported here is the synthesis of homoaromatic (B₃N₃Ph₆)^2? by the reduction of B₃N₃Ph₆ with either potassium or rubidium in the presence of 18‐crown‐6 ether. Theoretical investigations illustrate that two electrons delocalize over the three boron atoms in (B₃N₃Ph₆)^2?, which is formed by the geometric and orbital reorganization and exhibits (π,σ)‐mixed homoaromaticity. Moreover, (B₃N₃Ph₆)^2? can act as a robust 2e reductant for unsaturated compounds, such as anthracene, chalcone, and tanshinones. This 2e reduction is of high efficiency and selectivity, proceeds under mild reaction conditions, and can regenerate neutral borazine.     

聚(苯乙烯-二乙烯苯)树脂对聚乙二醇的吸附研究

制备了聚(苯乙烯-二乙烯苯)树脂NDA-150,并将其应用于聚乙二醇(PEG)模拟废水处理。研究了投加量、p H值、温度及时间对PEG去除效果的影响。实验结果表明,最佳投加量为0.4g/L,此时吸附量Qe为35mg/g;初始p H值对吸附过程的影响可忽略不计,最佳温度为293K,吸附等温线可使用Freundlich方程很好地拟合。PEG在NDA-150树脂上吸附的ΔH,ΔG以及ΔS的计算结果表明,吸附过程是自发的放热过程,且熵是增加的。整个吸附过程约在24h左右达到平衡,吸附动力学数据符合拟二级动力学方程。     

氧化锆口腔种植体的动态植入过程分析与设计

在牙科种植领域常使用的种植体材料多为纯钛或钛合金, 然而钛金属种植体存在美学缺陷及潜在的致敏可能等问题. 氧化锆陶瓷由于其高强度、美观性与生物相容性被认为是钛金属种植体的理想替代品, 但目前国内对于氧化锆种植体的研究仍处于起步阶段. 本文通过对氧化锆种植体及骨组织进行有限元建模, 并对种植体的动态植入过程进行仿真, 分析了骨组织内部的应力-应变状况. 结果发现, 随着植入深度的增加, 种植体与骨组织的接触面积增大, 松质骨内应力增加. 考虑到骨组织的具体结构, 将松质骨内的最大应力-应变作为分析的主要对象, 结合损伤分析, 对种植体模型进行了优化. 此外, 还设计了3种具有自攻刃设计的种植体模型, 分别进行应力应变分析后确定了最优设计. 之后建立了具有自攻刃设计的种植体模型, 并模拟了临床的3种植入方案: 螺纹成形、螺纹切割、螺纹成形与切割进行分析, 通过分析得到螺纹成形与切割种植方案更为安全的结论. 本文结果可以指导氧化锆种植体的结构设计以及植入时的条件设定等, 为我国自主研发的氧化锆种植体进行了理论指导, 为其早日进行临床应用指明了方向.      

Arsenic(II) sulfide quantum dots prepared by a wet process from its bulk

Arsenic(II) sulfide nanocrystals were fabricated by a wet process from its bulk through cluster-mediate transformation. The bulk arsenic(II) sulfide can be easily dissolved in ethylenediamine to form a solution-like cluster (As4S4-NH2C2H4NH2)). The cluster can be transformed to nanocrystals assisted by consumption of ethylenediamine in protic polar solvents with mild thermal treatment. The nanocrystals show size-dependent fluorescence ranging from UV to the blue, two photon fluorescence as well as cytotoxic effects on cancer cells.     

Aggregation and supramolecular chirality of achiral amphiphilic metalloporphyrins

Metalloporphyrin derivatives with three hydrophobic dodecyl chains and a hydrophilic ester or carboxylic acid substituent were designed in order to clarify the effect of the central metal ions on the aggregation as well as the supramolecular chirality in the Langmuir-Schaefer films. All the metalloporphyrins showed good spreading behavior on water surface and can be transferred onto solid substrates. The transferred films were characterized by a variety of methods including UV-visible spectroscopy, circular dichroism (CD) spectroscopy, FTIR spectroscopy, atomic force microscopy (AFM) and scanning electron microscope (SEM) measurements. It has been found that the copper derivative forms J-aggregates as well as H-aggregates in the film. Moreover, the film showed strong CD signals. Change from the ester substitution to carboxylic acid caused the decrease of the supramolecular chirality. On the contrary, the zinc derivative showed only a negligible CD signal although the corresponding free base could assemble into a chiral assembly. A possible mechanism for the subtle relationship between supramolecular chirality and molecular structures has been proposed.