Improving the flame retardancy of polyamide 6 by incorporating hexachlorocyclotriphosphazene modified MWNT

A nitrogen‐, phosphorus‐ and chlorine‐containing flame retardant, hexachlorocyclotriphosphazene (HCTP), has been covalently grafted onto the surface of multi‐wall carbon nanotubes (MWNT) to obtain MWNT‐HCTP. Polyamide 6 (PA6)/MWNT composites were then prepared via melt compounding. The flammability of PA6/MWNT composite was characterized by cone calorimetry, limiting oxygen index (LOI) and UL‐94 tests. The results showed that peak heat release rate of samples containing 3 wt% MWNT‐HCTP was only 460 kW/m², which decreased by 35.2% compared with that of a neat PA6 sample. The LOI value was increased from 22.7% to 26.5%, and UL‐94 test performance was also significantly improved by the presence of MWNT‐HCTP. Scanning electron microscope (SEM) and optical microscope analysis showed that modified MWNT had a better dispersion and compatibility in PA6 than unmodified MWNT. The composition of residue chars and volatile products was investigated by SEM/energy dispersive X‐ray spectroscopy, Fourier transform infrared spectroscopy (FTIR) and thermogravimetric‐FTIR, respectively. It was proposed that grafted HCTP was mainly functioned in the condensed phase, where P, N can synergistically promote char formation and Cl element can catch free radicals to terminate the chain reaction during combustion of the PA6 composite. Copyright © 2014 John Wiley & Sons, Ltd.     

Experimental research of effects of different rotation radii on the growth rate of potassium dihydrogen phosphate crystals

Comparing with the traditional concentric rotation method (rotation radius is 0 cm), the effects of different rotation radii on the growth rate of KDP crystals were studied by experimental methods. It was found that with the increase of rotation radius from 0 cm, the growth rate of each direction of crystals first increased and then decreased in a size‐unchanged vessel. The smaller the distance between the crystal and vessel wall, the less the growth rate. This phenomenon was named the “wall collision effect”. Also, the value of growth rate reached a maximum when the rotation radius was about half of its allowable largest value in the size‐unchanged vessel. In addition, an increase of the rotation radius could improve the crystal growth rate under the same linear velocity of crystal movement. Finally, the uniformity of crystal growth has also been analyzed compared with the concentric rotation radius. It was found that the uniformity of crystal growth was best when the rotation radius was half of its allowable maximum value, and it was more conducive to the actual application of KDP crystals.     

ω-芋螺毒素的定量构效关系与虚拟筛选

ω-芋螺毒素属于海洋生物活性多肽,由24-31个氨基酸残基组成.特异性作用于电压敏感的钙离子通道(VGCCs),能够直接开发成药物或作为先导化合物进行新药开发.本文应用新型氨基酸残基结构描述符cscales和遗传偏最小二乘算法,对ω-芋螺毒素进行定量构效关系(QSAR)研究,并设计、构建了容量为2244个化合物的N-型和P/Q-型VGCC拮抗剂虚拟组合多肽库,然后分别采用QSAR模型预测和相似性搜索方法对组合多肽库进行了虚拟筛选.研究结果表明,建立的N-型和P/Q-型VGCC拮抗剂QSAR模型均具有较好的预测能力,交叉验证相关系数(CV-r2)均大于0.89.主成分分析和聚类分析结果表明,虚拟组合多肽库中化合物具有较好的结构多样性和差异性.通过虚拟筛选,得到了具有高预测活性的6个N-型和19个P/Q-型钙离子通道拮抗剂,为进一步的合成和活性评价奠定了理论基础.同时,本文建立的多肽QSAR预测模型和虚拟筛选策略,为其它多肽类化合物的定量构效关系研究和虚拟筛选提供了参考.     

Total Chemical Synthesis of Biologically Active Fluorescent Dye‐Labeled Ts1 Toxin

Ts1 toxin is a protein found in the venom of the Brazilian scorpion Tityus serrulatus. Ts1 binds to the domain II voltage sensor in the voltage‐gated sodium channel Nav and modifies its voltage dependence. In the work reported here, we established an efficient total chemical synthesis of the Ts1 protein using modern chemical ligation methods and demonstrated that it was fully active in modifying the voltage dependence of the rat skeletal muscle voltage‐gated sodium channel rNav1.4 expressed in oocytes. Total synthesis combined with click chemistry was used to label the Ts1 protein molecule with the fluorescent dyes Alexa‐Fluor 488 and Bodipy. Dye‐labeled Ts1 proteins retained their optical properties and bound to and modified the voltage dependence of the sodium channel Nav. Because of the highly specific binding of Ts1 toxin to Nav, successful chemical synthesis and labeling of Ts1 toxin provides an important tool for biophysical studies, histochemical studies, and opto‐pharmacological studies of the Nav protein.     

Double‐Wall Carbon Nanotube–Porphyrin Supramolecular Hybrid: Synthesis and Photophysical Studies

Double‐wall carbon nanotubes (DWCNTs) with pyridyl units covalently attached to the external wall through isoxazolino linkers and carboxylic groups that have been esterified by pentyl chains are synthesized. The properties of these modified DWCNTs are then compared with an analogous sample based on single‐wall carbon nanotubes (SWCNTs). Raman spectroscopy shows the presence of characteristic radial breathing mode vibrations, confirming that the samples partly retain the integrity of the nanotubes in the case of DWCNTs, including the internal and external nanotubes. Quantification of the pyridyl content for both samples (DWCNT and SWCNT derivatives) is based on X‐ray photoelectron spectroscopy and thermogravimetric profiles, showing very similar substituent load. Both pyridyl‐containing nanotubes (DWCNTs and SWCNTs) form a complex with zinc porphyrin (ZnP), as evidenced by the presence of two isosbestic points in the absorption spectra of the porphyrin upon addition of the pyridyl‐functionalized nanotubes. Supramolecular complexes based on pyridyl‐substituted DWCNTs and SWCNTs quench the emission and the triplet excited state identically, through an energy‐transfer mechanism based on pre‐assembly of the ground state. Thus, the presence of the intact inner wall in DWCNTs does not influence the quenching behavior, with respect to SWCNTs, for energy‐transfer quenching with excited ZnP. These results sharply contrast with previous ones referring to electron‐transfer quenching, in which the double‐wall morphology of the nanotubes has been shown to considerably reduce the lifetime of charge separation, owing to faster electron mobility in DWCNTs compared to SWCNTs.     

Modelling of a tubular solid oxide fuel cell with different designs of indirect internal reformer

The cell performance and temperature gradient of a tubular solid oxide fuel cell with indirect internal reformer(IIR-SOFC) fuelled by natural gas, containing a typical catalytic packed-bed reformer, a catalytic coated wall reformer, a catalytic annular reformer, and a novel catalytic annular-coated wall reformer were investigated with an aim to determine the most efficient internal reformer system. Among the four reformer designs, IIR-SOFC containing an annular-coated wall reformer exhibited the highest performance in terms of cell power density(0.67 W cm-2)and electrical efficiency(68%) with an acceptable temperature gradient and a moderate pressure drop across the reformer(3.53×10-5kPa).IIR-SOFC with an annular-coated wall reformer was then studied over a range of operating conditions: inlet fuel temperature, operating pressure, steam to carbon(S : C) ratio, gas flow pattern(co-flow and counter-flow pattern), and natural gas compositions. The simulation results showed that the temperature gradient across the reformer could not be decreased using a lower fuel inlet temperature(1223 K–1173 K)and both the power density and electrical efficiency of the cell also decreased by lowering fuel inlet temperature. Operating in higher pressure mode(1-10 bar) improved the temperature gradient and cell performance. Increasing the S : C ratio from 2 : 1 to 4 : 1 could decrease the temperature drop across the reformer but also decrease the cell performance. The average temperature gradient was higher and smoother in IIR-SOFC under a co-flow pattern than that under a counter-flow pattern, leading to lower overpotential and higher cell performance. Natural gas compositions significantly affected the cell performance and temperature gradient. Natural gas containing lower methane content provided smoother temperature gradient in the system but showed lower power density and electrical efficiency.     

Stress-Induced Domain Wall Motion in a Ferroelastic Mn3+ Spin Crossover Complex

Domain wall motion is detected for the first time during the transition to a ferroelastic and spin state ordered phase of a spin crossover complex. Single-crystal X-ray diffraction and resonant ultrasound spectroscopy (RUS) revealed two distinct symmetry-breaking phase transitions in the mononuclear Mn³⁺ compound [Mn(3,5-diBr-sal₂(323))]BPh₄, 1. The first at 250 K, involves the space group change Cc→Pc and is thermodynamically continuous, while the second, Pc→P1 at 85 K, is discontinuous and related to spin crossover and spin state ordering. Stress-induced domain wall mobility was interpreted on the basis of a steep increase in acoustic loss immediately below the the Pc-P1 transition     

A size-modified poisson–boltzmann ion channel model in a solvent of multiple ionic species: Application to voltage-dependent anion channel

We present a new size-modified Poisson–Boltzmann ion channel (SMPBIC) model and use it to calculate the electrostatic potential, ionic concentrations, and electrostatic solvation free energy for a voltage-dependent anion channel (VDAC) on a biological membrane in a solution mixture of multiple ionic species. In particular, the new SMPBIC model adopts a membrane surface charge density and a natural Neumann boundary condition to reflect the charge effect of the membrane on the electrostatics of VDAC. To avoid the singularity difficulties caused by the atomic charges of VDAC, the new SMPBIC model is split into three submodels such that the solution of one of the submodels is obtained analytically and contains all the singularity points of the SMPBIC model. The other two submodels are then solved numerically much more efficiently than the original SMPBIC model. As an application of this SMPBIC submodel partitioning scheme, we derive a new formula for computing the electrostatic solvation free energy. Numerical results for a human VDAC isoform 1 (hVDAC1) in three different salt solutions, each with up to five different ionic species, confirm the significant effects of membrane surface charges on both the electrostatics and ionic concentrations. The results also show that the new SMPBIC model can describe well the anion selectivity property of hVDAC1, and that the new electrostatic solvation free energy formula can significantly improve the accuracy of the currently used formula. © 2019 Wiley Periodicals, Inc.     

Simulating ion channel activation mechanisms using swarms of trajectories

Atomic-level studies of protein activity represent a significant challenge as a result of the complexity of conformational changes occurring on wide-ranging timescales, often greatly exceeding that of even the longest simulations. A prime example is the elucidation of protein allosteric mechanisms, where localized perturbations transmit throughout a large macromolecule to generate a response signal. For example, the conversion of chemical to electrical signals during synaptic neurotransmission in the brain is achieved by specialized membrane proteins called pentameric ligand-gated ion channels. Here, the binding of a neurotransmitter results in a global conformational change to open an ion-conducting pore across the nerve cell membrane. X-ray crystallography has produced static structures of the open and closed states of the proton-gated GLIC pentameric ligand-gated ion channel protein, allowing for atomistic simulations that can uncover changes related to activation. We discuss a range of enhanced sampling approaches that could be used to explore activation mechanisms. In particular, we describe recent application of an atomistic string method, based on Roux's “swarms of trajectories” approach, to elucidate the sequence and interdependence of conformational changes during activation. We illustrate how this can be combined with transition analysis and Brownian dynamics to extract thermodynamic and kinetic information, leading to understanding of what controls ion channel function. © 2019 Wiley Periodicals, Inc.     

Gastroprotective Effects of Inulae Flos on HCl/Ethanol-Induced Gastric Ulcers in Rats

Inulae Flos, the flower of Inula britannica L., is used as a dietary supplement, beverage, and medicine in East Asia. In this study, we evaluated the gastroprotective effects of Inulae Flos extract (IFE) against gastric mucosal lesions induced by hydrochloric acid (HCl)/ethanol in rats and explored its potential mechanisms by measuring antioxidant enzyme activity, mucus secretion, and prostaglandin E₂ (PGE₂) levels. Pretreatment with IFE at doses of 100 and 300 mg/kg significantly inhibited gastric lesions in HCl/ethanol-treated rats. IFE increased the activities of superoxide dismutase and catalase and the levels of glutathione and PGE₂ in gastric tissues. The administration of IFE also significantly increased the gastric wall mucus contents in HCl/ethanol-induced gastric lesions. These findings suggest that IFE has gastroprotective effects against HCl/ethanol-induced gastric lesions and exerts these effects through increased antioxidant levels and gastric mucus secretion. Inulae Flos may be a promising agent for the prevention and treatment of gastritis and gastric ulcers.