CRYSTALLIZATION AND MECHANICAL PROPERTIES OF POLYPROPYLENE FILLED WITH SiO2 NANOPARTICLES

Oleic acid （OA）-modified SiO2 （OA-m-SiO2） nanoparticles were prepared using surface modification method. Infrared spectroscopy （IR） was used to investigate the structure of the OA-m-SiO2 nanoparticles, and the result showed that OA attached onto the surface of SiO2 nanoparticles through esterification. Effect of OA concentration on the dispersion stability of OA-m-SiO2 in heptane was also studied, and the result indicated that OA-m-SiO2 nanoparticles were dispersed in heptane more stably than the unmodified ones. OA-m-SiO2 nanoparticles can also be dispersed in polypropylene （PP） matrix in nano-scale. The effect of OA-m-SiO2 on crystallization of PP was studied by means of DSC. It was found that the introduction of OA-m-SiO2 resulted in significant increase in the crystallization temperature, crystallization degree and crystallization rate of PP, and OA-m-SiO2 could effectively induce the formation of β-crystal PP. Effect of OA-m-SiO2 content on mechanical properties of PP/OA-m-SiO2 nanocomposites was also studied. The results show that OA-m-SiO2 can significantly improve the mechanical properties of PP.     

Doublet Chirality Transfer and Reversible Helical Transition in Poly(3,5‐disubstituted phenylacetylene)s with Pyrene as a Probe Unit†

A novel doublet chirality transfer (DCT) model was demonstrated in cis poly(3,5‐disubstituted phenylacetylene)s, i.e., S‐I , R‐I , and S‐I‐NMe . The chiral message from the stereocenter of alkylamide substituent at 3‐position induced the polyene backbone to take cis‐transoid helical conformation with a predominant screw sense. And in turn the helical backbone acted as a scaffold to orient the pyrene probes, which was linked to phenyl rings through 5‐position, to array in an asymmetric manner. A combinatory analyses of ¹H NMR, Raman, FTIR, UV‐vis absorption, CD, and computer simulation suggested that the main‐chain stereostructure, solvent nature, and intramolecular hydrogen bonds played important and complex roles on DCT. High cis‐structure content and intramolecular hydrogen bonds were beneficial for the realization of DCT. Reversible helix‐helix transition was observed in S‐I by changing the nature of solvents. In DMF, S‐I adopted a relatively contracted helix, where the main chain exhibited strong optical activity, but that of pyrene was weak. In contrast, a relatively stretched helix formed in CHCl₃, in which the optical activity of pyrene was much larger, whereas that of the polyene backbone was the weakest. This helix‐helix transition was attributed to the intramolecular hydrogen bonds, which was confirmed by solution‐state FTIR spectra and computer calculations.     

Multi-Step Continuous-Flow Organic Synthesis: Opportunities and Challenges

Continuous-flow multi-step synthesis takes the advantages of microchannel flow chemistry and may transform the conventional multi-step organic synthesis by using integrated synthetic systems. To realize the goal, however, innovative chemical methods and techniques are urgently required to meet the significant remaining challenges. In the past few years, by using green reactions, telescoped chemical design, and/or novel in-line separation techniques, major and rapid advancement has been made in this direction. This minireview summarizes the most recent reports (2017–2020) on continuous-flow synthesis of functional molecules. Notably, several complex active pharmaceutical ingredients (APIs) have been prepared by the continuous-flow approach. Key technologies to the successes and remaining challenges are discussed. These results exemplified the feasibility of using modern continuous-flow chemistry for complex synthetic targets, and bode well for the future development of integrated, automated artificial synthetic systems.     

A Mechanistic Switch in C-H Bond Activation by Elusive Fe\begin{document}$^\text{V}$\end{document}(O)(TAML) Reaction Intermediate: A Theoretical Study

The divergent behavior of C-H bond oxidations of aliphatic substrates compared to those of aromatic substrates shown in Gupta's experiment was mechanistically studied herein by means of density functional theory calculations. Our calculations reveal that such difference is caused by different reaction mechanisms between two kinds of substrates (the aliphatic cyclohexane, 2, 3-dimethylbutane and the aromatic toluene, ethylbenzene and cumene). For the aliphatic substrates, C-H oxidation by the oxidant Fe\begin{document}$^{\rm{V}}$\end{document}(O)(TAML) is a hydrogen atom transfer process; whereas for the aromatic substrates, C-H oxidation is a proton-coupled electron transfer (PCET) process with a proton transfer character on the transition state, that is, a proton-coupled electron transfer process holding a proton transfer-like transition state (PCET(PT)). This difference is caused by the strong \begin{document}$\pi$\end{document}-\begin{document}$\pi$\end{document} interactions between the tetra-anionic TAML ring and the phenyl ring of the aromatic substrates, which has a "pull" effect to make the electron transfer from substrates to the Fe=O moiety inefficient.     

熵驱大分子胶体粒子的柱状受限结晶

熵是物理化学的基本状态参量,在统计力学和热力学中处于核心位置.按照玻尔兹曼的微观解释,熵可以由孤立系统微观状态的数目(W)给出,即S=kBlnW,这里kB为玻尔兹曼常数[1,2].根据此公式,微观状态数越多,系统越混乱,熵越大,所以熵常被视作体系无序程度的度量.但熵增仅对应体系微观状态数的增加,与可观测的结构有序程度无关[3~5].在一些典型的软物质体系中,结构越有序熵反而越大,如胶体硬球在随机密堆积点的有序结晶[6]及描述各向异性棒状分子从各向同性相到向列相转变的Onsager原理[7].     

Synthesis and Thermal Performance of Polyurea Microcapsulated Phase Change Materials by Interfacial Polymerization

Microencapsulated phase change materials with paraffin as the core material were synthesized by interfacial polymerization of isophorone diisocyanate with diethylene triamine. The particle size and particle size distribution, morphology, thermal performance and the encapsulation efficiency of the prepared materials were investigated. The results of Fourier transform infrared spectrometer and X-ray photoelectron spectroscopy suggested that the paraffin core was well encapsulated by the polyurea resin. The particle size of the prepared materials decreased and its distribution became narrow with the increase of the emulsification time, stirring speed and emulsifier amount. The thermal gravimetric analysis indicated that the prepared materials exhibited good thermal stability, while the differential scanning calorimetry their high encapsulation efficiency.     

弱碱性离子交换树脂D301分离低浓度甲酸的研究

采用D301弱碱性离子交换树脂对水溶液中低浓度甲酸进行分离。静态条件下考察了时间、温度、振荡速率和树脂用量对分离效果的影响,获得了交换等温线;动态条件下考察了不同高径比、流速、温度、浓度下动态穿透曲线;研究了树脂再生效果与稳定性。初始浓度573mg/L的甲酸废水,在树脂用量2.5g/L、温度35℃、振荡速率160r/min条件下,最大交换量为154.16mg/g;其交换等温线符合Langmuir方程,热力学平衡方程计算得G<0,H=10.25kJ/mol,S>0,表明该吸附过程是自发的、吸热、熵增加的过程。交换过程中颗粒扩散是离子交换的主要速率控制步骤,表观活化能与反应级数分别为5.983kJ/mol和0.378。     

Interfacial Engineering of NiFeP/NiFe-LDH Heterojunction for Effi-cient Overall Water Splitting

In consideration of application prospect of non-noble metallic materials catalysts,the study of exploring more highly effective electrocatalysts has been focuse...     

Polydopamine nanodots are viable probes for fluorometric determination of the activity of alkaline phosphatase via the in situ regulation of a redox reaction triggered by the enzyme

The authors describe an environmentally friendly and fast (~14 min) method for the synthesis of homogeneously distributed fluorescent polydopamine nanodots (PDA-NDs) using KMnO₄ as the oxidant. Alkaline phosphatase (ALP) catalyzes the hydrolysis of ascorbic acid 2-phosphate to release free ascorbic acid which undergoes an in-situ redox reaction with KMnO₄. Depending on the activity of ALP, more or less KMnO₄ is consumed, and this affects the formation of the PDA-NDs. Based on this finding, a sensitive method was worked out to quantify the activity of ALP via real-time formation of fluorescent PDA-NDs. The fluorometric signal (best measured at excitation/emission peaks of 390/500 nm) is linear in the 1 to 50 mU·mL^?1 ALP activity range, and the limit of the detection is as low as 0.94 mU·mL^?1 (based on 3 σ/m). The method was successfully applied to the determination of ALP activity in spiked human serum and in MCF-7 cell lysates. It was also applied in a method to screen for inhibitors of ALP.

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Graphical abstract Schematic of a fluorometric method for the determination of alkaline phosphatase (ALP) activity. The method is based on the in-situ regulation of the formation of fluorescent polydopamine nanodots (PDA-NDs) through the competition between the KMnO₄-induced polymerization of dopamine and ALP-directed ascorbic acid 2-phosphate (Asc-2P) hydrolysis. AA: Ascorbic acid.

     

Generation and Stabilization of a Dinickel Catalyst in a Metal-Organic Framework for Selective Hydrogenation Reactions

Although many monometallic active sites have been installed in metal–organic frameworks (MOFs) for catalytic reactions, there are no effective strategies to generate bimetallic catalysts in MOFs. Here we report the synthesis of a robust, efficient, and reusable MOF catalyst, MOF-NiH, by adaptively generating and stabilizing dinickel active sites using the bipyridine groups in MOF-253 with the formula of Al(OH)(2,2′-bipyridine-5,5′-dicarboxylate) for Z-selective semihydrogenation of alkynes and selective hydrogenation of C=C bonds in α,β-unsaturated aldehydes and ketones. Spectroscopic studies established the dinickel complex (bpy⋅⁻)Ni^II(μ₂-H)₂Ni^II(bpy⋅⁻) as the active catalyst. MOF-NiH efficiently catalyzed selective hydrogenation reactions with turnover numbers of up to 192 and could be used in five cycles of hydrogenation reactions without catalyst leaching or significant decrease of catalytic activities. The present work uncovers a synthetic strategy toward solution-inaccessible Earth-abundant bimetallic MOF catalysts for sustainable catalysis.