The catalytic activity of a novel recyclable alkoxypalladium complex in Suzuki reaction

A novel palladium complex based on N,O-ligand was synthesized, which shows a high catalytic activity in the Suzuki cross-coupling reaction without using any phosphine ligand. More importantly, no significant loss of the catalytic activity was observed after six recycles. We suggest that this catalyst has commercial and industrial potential in the future.     

Unveiling the Activity Origin of a Copper‐based Electrocatalyst for Selective Nitrate Reduction to Ammonia

Unveiling the active phase of catalytic materials under reaction conditions is important for the construction of efficient electrocatalysts for selective nitrate reduction to ammonia. The origin of the prominent activity enhancement for CuO (Faradaic efficiency: 95.8 %, Selectivity: 81.2 %) toward selective nitrate electroreduction to ammonia was probed. ¹⁵N isotope labeling experiments showed that ammonia originated from nitrate reduction. ¹H NMR spectroscopy and colorimetric methods were performed to quantify ammonia. In situ Raman and ex situ experiments revealed that CuO was electrochemically converted into Cu/Cu₂O, which serves as an active phase. The combined results of online differential electrochemical mass spectrometry (DEMS) and DFT calculations demonstrated that the electron transfer from Cu₂O to Cu at the interface could facilitate the formation of *NOH intermediate and suppress the hydrogen evolution reaction, leading to high selectivity and Faradaic efficiency.     

一种高压电源谐振升压倍压电路

提出了一种高压电源谐振升压倍压电路,该电路由LC谐振电路与整流电路组成。对该电路的工作模式和稳态输出特性进行了分析;建立了该电路的数学模型：以归一化的形式定量描述了稳态输出电压与电流的增益、短路特性和开路特性、输出纹波与电压降、以及器件上的电应力,并分析了电路品质因数、归一化频率和电容比对输出特性的影响;对该电路进行了仿真与实验研究,仿真结果与实验结果具有很好的一致性,验证了数学模型的正确性。与C-W电路的对比研究结果表明：所提出的电路具有输出电压稳定、输出纹波小、短路特性好以及响应速度快的优点,满足高压小电流的应用需求。     

Constructing Efficient and Thermostable Red-NIR Emitter via Cross Relaxation and Crystal-Field Engineering of Holmium-Based Perovskite-Type Half Metal

Lanthanide ions, as dopants, have evoked widespread research interest owing to the rich optical, magnetic, and electrical properties, but their luminescent intensity is always limited by typical concentration quenching. Herein, a holmium-based double perovskite of Cs₂NaHoCl₆ is reported, which surprisingly breaks through this barrier and achieves efficient red-NIR emission by virtue of the large unit cell, low phonon energy, high content of activators, and cross relaxation phenomenon between Ho³⁺. The heavy Ho³⁺ also endows the intriguing half-metallic nature with a down-spin conducting band and an up-spin insulating band. After performing ion doping on crystallographic sites of Na⁺ and Ho³⁺, the photoluminescence quantum yield of such red-NIR emitter under 450 nm excitation is dramatically promoted to 82.3%, benefiting from the improved crystal field environment that alleviates the parity forbidden rule and suppresses non-radiative recombination loss. Furthermore, the heat-favorable phonon-assisted population processes enable the robust photostability against thermal quenching. By combining a 450 nm chip, the red-NIR light-emitting diodes are fabricated, in which the wide-coverage NIR emissions are ideally suited for medical light source, night vision, nondestructive examination, and transmission imaging. It is believed that this work will open an avenue for enhancing the fluorescence of lanthanide ions and developing advanced spintronic materials.     

HPLC法测定土圞儿根皮和块根中的西瑞香素

建立高效液相色谱法测定土圞儿根皮和块根中西瑞香素含量的方法。采用Kromasil C18色谱柱(250mm×4.6 mm,5μm),以甲醇–0.2%磷酸水溶液(56∶44)为流动相等度洗脱,流量为1.0 m L/min,柱温为35℃,检测波长为345 nm。西瑞香素的质量浓度在20~100μg/m L内与色谱峰面积呈现良好的线性关系,线性相关系数r=0.999 9,方法精密度(RSD)为1.23%(n=6)。根皮样品、块根样品的加标回收率分别为98.8%,98.2%,测定结果的相对标准偏差分别为1.30%,2%(n=6)。该方法快速可靠,可用于土圞儿药材的质量控制。     

亚纯函数的差分多项式

假设函数f(z)是亚纯函数,H(z,f)是关于f(z)的差分多项式,s(z)是关于f(z)的小函数,考察了差分多项式f(z)~nH(z,f)-s(z)的零点分布问题.首先得到了差分多项式f(z)~nH(z,f)-s(z)的零点计数函数和函数f(z)的特征函数以及极点计数函数之间的一些不等式估计,再根据这些不等式,建立了Hayman关于亚纯函数的一个经典结果的差分模拟.     

Machine learning phase transitions of the three-dimensional Ising universality class

Exploration of the QCD phase diagram and critical point is one of the main goals in current relativistic heavy-ion collisions. The QCD critical point is expected to belong to a three-dimensional (3D) Ising universality class. Machine learning techniques are found to be powerful in distinguishing different phases of matter and provide a new way to study the phase diagram. We investigate phase transitions in the 3D cubic Ising model using supervised learning methods. It is found that a 3D convolutional neural network can be trained to effectively predict physical quantities in different spin configurations. With a uniform neural network architecture, it can encode phases of matter and identify both second- and first-order phase transitions. The important features that discriminate different phases in the classification processes are investigated. These findings can help study and understand QCD phase transitions in relativistic heavy-ion collisions.     

A kinetic study of product cleavage reactions from the solid phase by a biocompatible and removable cleaving reagent, HCl

TFA has been widely used as a cleaving reagent in solid-phase organic synthesis. However, it is difficult to remove from the final product, and it is toxic to various cells. To search for an alternative, we studied the kinetics of HCl cleavage reactions of 18 resin-bound compounds on various linkers. HCl is very easy to remove completely from samples, and the residual HCl does not have a toxic effect in cell assays. Most compounds studied in this work can be easily cleaved using a low concentration of HCl (0.9-2.3%) and the minimal amount of time (60-90 min). Even in the most difficult case, a moderate 8% HCl and an extended time (10-15 h) are enough to cleave the product. Therefore, our kinetic studies establish HCl as a biocompatible, removable, and effective substitute for TFA when final compounds are used for biological screening and drug discovery.     

Morphology controlled nanostructures self-assembled from phthalocyanine derivatives bearing alkylthio moieties: effect of sulfur-sulfur and metal-ligand coordination on intermolecular stacking

To investigate the effect of sulfur-sulfur and metal-ligand coordination on the molecular structure and morphology of self-assembled nanostructures, metal-free 2,3,9,10,16,17,23,24-octakis(isopropylthio)phthalocyanine H(2)Pc(β-SC(3)H(7))(8) (1) and its copper and lead congeners CuPc(β-SC(3)H(7))(8) (2) and PbPc(β-SC(3)H(7))(8) (3) are synthesized and fabricated into organic nanostructures by a phase-transfer method. The self-assembly properties are investigated by electronic absorption and Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Experimental results reveal different molecular packing modes in these aggregates, which in turn result in self-assembled nanostructures with different morphologies ranging from nanobelts for 1 through nanoribbons for 2 to cluster nanoflowers for 3. Intermolecular π-π and sulfur-sulfur interactions between metal-free phthalocyanine 1 lead to the formation of nanobelts. The additional Cu-S coordination bond between the central copper ion of 2 and the sulfur atom of the adjacent molecule of 2 in cooperation with the intermolecular π-π stacking interaction increases the intermolecular interaction, and results in the formation of long nanoribbons for 2. In contrast to compounds 1 and 2, the special molecular structure of complex 3, together with the intermolecular π-π stacking interaction and additional Pb-S coordination bond, induces the formation of Pb-connected pseudo-double-deckers during the self-assembly process, which in turn further self-assemble into cluster nanoflowers. In addition, good semiconducting properties of the nanostructures fabricated from phthalocyanine derivatives 1-3 were also revealed by I-V measurements.     

ON DIFFERENCE EQUATIONS RELATING TO GAMMA FUNCTION

We consider the existence, the growth, poles, zeros, fixed points and the Borel exceptional value of solutions for the following difference equations relating to Gamma function y(z + 1) -y(z) = R(z) and y(z + 1) = P (z)y(z).