Facile one-step extraction and oxidative carboxylation of cellulose nanocrystals through hydrothermal reaction by using mixed inorganic acids

A facile and efficient approach to prepare carboxylated cellulose nanocrystals (CCNCs) is presented through a novel one-step hydrothermal procedure by using a mixed acid system of hydrochloric acid and nitric acid (HCl/HNO₃). The as-prepared cellulose nanoparticles were characterized by scanning electron microscopy, wide angle X-ray diffraction, conductometric titrations, Fourier transform infrared spectrometry and thermal gravimetric analysis. The results showed that the combination of the mixed acid and hydrothermal reaction can speed up the process of CCNC preparation, and then high quality of the product could be obtained at relatively low acid concentration. It is found that the addition of nitric acid could not only promote the conversion of surface groups on the cellulose nanocrystals (CNCs), but also have significant influences on the yield, particle size and microstructure of CNCs. For the volume ratio of HCl/HNO₃ of 7:3, the as-prepared CCNCs exhibited the largest length to diameter ratio and narrowest dimension distributions as well as maximum degree of oxidation of 0.12. In addition, high dispersion stability for the CCNCs could be observed due to the existence of negative carboxyl groups. This approach based on one-step oxidative carboxylation greatly simplified the preparation of CCNCs with high yield and high crystallinity under mild hydrothermal condition.     

基于合成方法学研究的有机化学实验教学改革与实践——以苯甲酸乙酯制备为例

以苯甲酸乙酯的制备实验为例,将合成方法学研究引入有机化学实验教学。采取抽签方式确定每个学生的实验内容,通过考查加热方式(电热套或微波辐射加热)、溶剂(甲苯或环己烷)以及反应时间对实验结果的影响,使学生了解科学研究的方法,并通过文献查阅及实验结果分析讨论等教学实践环节提高学生的创新思维和科研能力。     

Stability of the traveling waves for the derivative Schrödinger equation in the energy space

In this paper, we continue the study of the dynamics of the traveling waves for nonlinear Schrödinger equation with derivative (DNLS) in the energy space. Under some technical assumptions on the speed of each traveling wave, the stability of the sum of two traveling waves for DNLS is obtained in the energy space by Martel–Merle–Tsai’s analytic approach in Martel et al. (Commun Math Phys 231(2):347–373, 2002, Duke Math J 133(3):405–466, 2006). As a by-product, we also give an alternative proof of the stability of the single traveling wave in the energy space in Colin and Ohta (Ann Inst Henri Poincaré Anal Non Linéaire 23(5):753–764, 2006), where Colin and Ohta made use of the concentration-compactness argument.     

Novel phosphorescent neutral iridium(III) complex with the steric hindrance for highly efficient red organic light-emitting diodes

A novel and highly efficient thiophenquinolone-based red iridium(III) complex bearing a bulky fluorophenyl moiety is designed and synthesized. The complex shows intensive red phosphorescence (596 nm with shoulder at 642 nm), high photoluminescence efficiency (0.62) and broad full width at half maximum (81 nm). The bulky fluorophenyl moiety introduced into the complex could improve the efficiency of electroluminescence with the maximum current efficiency, power efficiency and the external quantum efficiency up to 29.0 cd/A, 30.4 lm/W and 17.6% due to the effective steric hindrance in solid states.     

Intermolecular H···O═C bonds induced 2D self‐assembly of thiophene based diketopyrrolopyrrole derivative

Compounds with diketopyrrolopyrrole (DPP) and thiophene moieties have attracted considerable attention because of their promising charge transport properties. The molecular conformation and self‐assembly of 2,5‐dihexadecyl‐3,6‐di(thiophen‐2‐yl)‐2,5‐dihydropyrrolo[3,4‐c]pyrrole‐1,4‐dione (TDPP‐C16) molecule have been investigated by scanning tunneling microscopy and density functional theory alculation. The TDPP‐C16 molecules adsorb with their optimized S‐shaped conformation and form a zipper‐like pattern on highly oriented pyrolytic graphite surface. R and S rotated structures are observed. The nanostructure is dominated by intermolecular double hydrogen bonds between C═O of the DPP units and hydrogen atom of thiophene rings in the neighboring molecules in each row. Atomic force microscopy and density functional theory calculation also display the existence of strong intermolecular hydrogen bonding. The results provide molecular evidence for the intermolecular interactions of the surface structure, which could benefit to the design of the organic semiconducting materials and understanding of underlying principle of charge transfer process. Copyright © 2017 John Wiley & Sons, Ltd.     

Solvability of finite groups

H is called an ? _p -embedded subgroup of G, if there exists a p-nilpotent subgroup B of G such that H _p ∈ Syl _p (B) and B is ? _p -supplemented in G. In this paper, by considering prime divisor 3, 5, or 7, we use ? _p -embedded property of primary subgroups to investigate the solvability of finite groups. The main result is follows. Let E be a normal subgroup of G, and let P be a Sylow 5-subgroup of E. Suppose that 1 < d ? |P| and d divides |P|. If every subgroup H of P with |H| = d is ?₅-embedded in G, then every composition factor of E satisfies one of the following conditions: (1) I/C is cyclic of order 5, (2) I/C is 5′-group, (3) I/C ? A₅.     

A new condition for solvable groups

A subgroup H of G is called complemented in G if there exists a subgroup K of G such that $G=HK$ and $H\cap K=1$. The aim of this paper is to prove the following: A finite group G is solvable if and only if its Sylow 3-, 5- and 7-subgroups are complemented in G.     

Pure Ion Chromatograms Combined with Advanced Machine Learning Methods Improve Accuracy of Discriminant Models in LC–MS-Based Untargeted Metabolomics

Untargeted metabolomics based on liquid chromatography coupled with mass spectrometry (LC–MS) can detect thousands of features in samples and produce highly complex datasets. The accurate extraction of meaningful features and the building of discriminant models are two crucial steps in the data analysis pipeline of untargeted metabolomics. In this study, pure ion chromatograms were extracted from a liquor dataset and left-sided colon cancer (LCC) dataset by K-means-clustering-based Pure Ion Chromatogram extraction method version 2.0 (KPIC2). Then, the nonlinear low-dimensional embedding by uniform manifold approximation and projection (UMAP) showed the separation of samples from different groups in reduced dimensions. The discriminant models were established by extreme gradient boosting (XGBoost) based on the features extracted by KPIC2. Results showed that features extracted by KPIC2 achieved 100% classification accuracy on the test sets of the liquor dataset and the LCC dataset, which demonstrated the rationality of the XGBoost model based on KPIC2 compared with the results of XCMS (92% and 96% for liquor and LCC datasets respectively). Finally, XGBoost can achieve better performance than the linear method and traditional nonlinear modeling methods on these datasets. UMAP and XGBoost are integrated into KPIC2 package to extend its performance in complex situations, which are not only able to effectively process nonlinear dataset but also can greatly improve the accuracy of data analysis in non-target metabolomics.     

Experimental Investigation on the Mass Diffusion Behaviors of Calcium Oxide and Carbon in the Solid-State Synthesis of Calcium Carbide by Microwave Heating

Microwave (MW) heating was proven to efficiently solid-synthesize calcium carbide at 1750 °C, which was about 400 °C lower than electric heating. This study focused on the investigation of the diffusion behaviors of graphite and calcium oxide during the solid-state synthesis of calcium carbide by microwave heating and compared them with these heated by the conventional method. The phase compositions and morphologies of CaO and C pellets before and after heating were carefully characterized by inductively coupled plasma spectrograph (ICP), thermo gravimetric (TG) analyses, X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The experimental results showed that in both thermal fields, Ca and C inter-diffused at a lower temperature, but at a higher temperature, the formed calcium carbide crystals would have a negative effect on Ca diffusion to carbon. The significant enhancement of MW heating on carbon diffusion, thus on the more efficient synthesis of calcium carbide, manifested that MW heating would be a promising way for calcium carbide production, and that a sufficient enough carbon material, instead of CaO, was beneficial for calcium carbide formation in MW reactors.