Performance evaluation of the zero‐multipole summation method in modern molecular dynamics software

The zero‐multiple summation method (ZMM) is a cutoff‐based method for calculating electrostatic interactions in molecular dynamics simulations, utilizing an electrostatic neutralization principle as a physical basis. Since the accuracies of the ZMM have been revealed to be sufficient in previous studies, it is highly desirable to clarify its practical performance. In this paper, the performance of the ZMM is compared with that of the smooth particle mesh Ewald method (SPME), where the both methods are implemented in molecular dynamics software package GROMACS. Extensive performance comparisons against a highly optimized, parameter‐tuned SPME implementation are performed for various‐sized water systems and two protein–water systems. We analyze in detail the dependence of the performance on the potential parameters and the number of CPU cores. Even though the ZMM uses a larger cutoff distance than the SPME does, the performance of the ZMM is comparable to or better than that of the SPME. This is because the ZMM does not require a time‐consuming electrostatic convolution and because the ZMM gains short neighbor‐list distances due to the smooth damping feature of the pairwise potential function near the cutoff length. We found, in particular, that the ZMM with quadrupole or octupole cancellation and no damping factor is an excellent candidate for the fast calculation of electrostatic interactions. © 2018 Wiley Periodicals, Inc.     

HPLC-MS/MS法测定婴幼儿配方乳粉中胆碱、左旋肉碱、牛磺酸与肌醇

建立了一种同时测定婴幼儿配方乳粉中4种可选择成分(胆碱、左旋肉碱、牛磺酸和肌醇)的高效液相色谱-串联三重四极杆质谱(HPLC-MS/MS)分析方法。样品经温水溶解后用亚铁氰化钾和乙酸锌沉淀蛋白,上清液过滤后采用HSS T3色谱柱分离,三重四极杆质谱仪检测,胆碱和左旋肉碱使用内标法定量,牛磺酸和肌醇使用外标法定量。在最优化条件下,胆碱和左旋肉碱在0.01~2.0 mg/L范围内,牛磺酸和肌醇在0.1~2.0 mg/L范围内呈良好的线性关系,相关系数均大于0.997;胆碱和左旋肉碱的检出限均为1.5 mg/kg,牛磺酸和肌醇的检出限均为15 mg/kg。4种化合物的回收率为87.5%~102.4%,相对标准偏差(RSD,n=6)为3.0%~7.3%。该方法灵敏度高、净化效果好、定量准确,适用于婴幼儿配方乳粉中胆碱、左旋肉碱、牛磺酸和肌醇的同时快速检测。     

高效毛细管电泳法测定泳池中尿液指示物乙酰磺胺酸钾

建立了高效毛细管电泳测定游泳池水中新型尿液指示物乙酰磺胺酸钾含量的新方法。采用内壁无涂层熔融石英毛细管(60.2 cm×75μm,有效长度50 cm)进行分离,缓冲液为10 mmol/L硼砂溶液(pH 9.3),分离电压为24 k V,进样时间为20 s,检测波长为226 nm。取游泳池水样过滤,经固相萃取小柱浓缩富集后直接进样分析。结果显示:在优化条件下,乙酰磺胺酸钾在0.2~100.0 mg/L质量浓度范围内线性良好(r=0.999 8),检出限为50.0μg/L,迁移时间和峰高的相对标准偏差(RSD)分别为0.73%和1.8%,加标回收率为96.0%~103.6%。该方法简单快速、准确可靠,适用于游泳池水中乙酰磺胺酸钾的检测。     

纳米多孔双金属氧化物NiCo2O4的制备及其电化学性能

采用快速凝固与脱合金化相结合的方法制备纳米多孔Ni、Ni-Co合金,分别经腐蚀与退火获得纳米多孔NiO、NiCo_2O_4,采用XRD、SEM、TEM、N_2吸附-脱附等对多孔NiO、NiCo_2O_4电极的物相、形貌结构、孔径分布进行表征,并通过循环伏安、恒电流充放电等方法测试多孔电极的电化学性能。结果表明,得到的纳米多孔NiO具有均匀的"泥裂"式结构,在1A·g~(-1)电流密度下比电容为375 F·g~(-1),当电流密度增加至20 A·g~(-1)时的比容保持率为67.5%,在4 A·g~(-1)电流密度下循环充放电1 000次,比容保持率为81.7%;NiCo_2O_4形成典型的开放式纳米多孔双连续结构,其在1A·g~(-1)电流密度下比电容为674 F·g~(-1),当电流密度增加至20 A·g~(-1),比容保持率达72.0%;在4 A·g~(-1)电流密度下循环充放电1 000次,比容保持率达92.9%,双连续纳米多孔结构及其提供的机械稳定性,使得NiCo_2O_4表现出更为优异的超电容性能。     

Influence of polypropylene topological structure evolution during melt branching reactive processing on its melt performances

Gel‐free long‐chain‐branched polypropylene (LCBPP) was prepared by the melt radical branching reaction in the presence of peroxide initiator 2,5‐dimethyl‐2,5‐di(tert‐butylperoxy) hexane peroxide, zinc dimethyldithiocarbamate, and trimethylolpropane triacrylate in a torque rheometer. It could be inferred that recombination between PP chains via radical coupled reaction took place and trimethylolpropane triacrylate was grafted onto PP backbone by the torque curves and Fourier transformed infrared spectroscopy results. The presence of long chain branches (LCB) for modified PP was verified by the gel permeation chromatography measurements and vGP plots. On the other hand, it was found that the topological structure of PP chains transformed from linear form to a long star‐like shape during the reaction progress, and the topological structure was directly determined by the radical reaction time. The topological structure of PP would further impact its melt behaviour. After complete melting of raw PP, “sparse and long” LCBPP firstly generated which possessed high melt strength owing to the increasing entanglement of long branching chains. And at the time corresponding to the summit of reaction peak on the torque curve, the modified LCBPP possess the highest melt strength owing to its long star topological structure. While as reaction time was prolonged, severe degradation of the LCBPPs would take place under too long mixing time and “dense and short” branches generated due to the residual radicals, with a sharp decline in melt strength.     

Structural transformation from shish‐kebab crystals to micro‐fibrils through hot stretching process of gel‐spun ultra‐high molecular weight polyethylene fibers with high concentration solution

Structural evolution of gel‐spun ultra‐high molecular weight polyethylene fibers with high concentration solution via hot stretching process was investigated by in situ small‐angle X‐ray scattering, in situ wide‐angle X‐ray diffraction measurements, scanning electron microscopy, and differential scanning calorimetry. With the increase of stretching strain, the long period continuously increases at relative lower stretching temperature, while it first increases and then decreases rapidly at relative higher stretching temperature. The kebab thickness almost keeps constant during the whole hot‐stretching process and the kebab diameter continually decreases for all stretching temperatures. Moreover, the length of shish decreases slightly and the shish quantity increases although there is almost no change in the diameter of shish crystals during the hot stretching process. The degree of crystal orientation at different temperatures is as high as above 0.9 during the whole stretching process. These results indicate that the shish‐kebab crystals in ultra‐high molecular weight polyethylene fibers can transform continuously into the micro‐fibril structure composed mostly of shish crystals through the hot stretching process. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 225–238     

Efficient analysis of phytochemical constituents in the peel of Chinese wild citrus Mangshanju (Citrus reticulata Blanco) by ultra high performance liquid chromatography–quadrupole time‐of‐flight‐mass spectrometry

An efficient ultra high‐performance liquid chromatography coupled with quadrupole time‐of‐flight mass spectrometry method was developed for separation and profiling of phytochemical constituents of Chinese wild mandarin Mangshanju (Citrus reticulata Blanco). All constituents were well separated within 16 min. Based on retention times, accurate mass, MS^E fragments, and/or reference standards as well as databases, a total of 81 compounds were unambiguously identified or tentatively assigned including flavonoid glycosides, acylated flavonoid glycosides, flavones, polymethoxylated flavonoids, and limonoids as well as four other compounds. Among them, 22 polymethoxylated flavones and ten polymethoxylated flavanones/chalcones were identified in Mangshanju, more types than other citrus reported before. A basic procedure for identifying flavonoid‐O‐glycosides and the aglycones including polymethoxylated flavonoids was proposed. In addition, this method was successfully used to analyze another four mandarin germplasms, Cenxi suan ju, Xipi gousi gan, Nanfeng miju, and Or, showing that Mangshanju contained two characteristic compounds distinct from the other four citrus species. This study systematically profiled phytochemical constituents of Mangshanju, which was helpful for further utilization of Mangshanju owing to its abundant bioactive compounds.     

In situ derivatization and hollow‐fiber liquid‐phase microextraction to determine sulfonamides in water using UHPLC with fluorescence detection

A sensitive method for determining sulfonamides in water was developed and validated through in situ derivatization and hollow‐fiber liquid‐phase microextraction with ultra‐high performance liquid chromatography and fluorescence detection. The target sulfonamides were sulfadiazine, sulfacetamide, sulfamerazine, sulfamethazine, sulfamethoxypyridazine, sulfachloropyridazine, sulfamethoxazole, and sulfisoxazole. Following in situ derivatization with fluorescamine, three‐phase hollow‐fiber liquid‐phase microextraction with an S 6/2 polypropylene hollow‐fiber membrane was applied automatically using a multipurpose autosampler. Experimental parameters including derivatization time, choice of organic phase, pH of donor and acceptor phase, stirring rate, extraction temperature and time were optimized. Under optimized conditions, the target sulfonamides achieved excellent linearity with correlation coefficients of 0.9924–0.9994 within the concentration range of 0.05–5 μg/L. The limits of detection of the eight sulfonamides were 3.1–11.2 ng/L, and the limits of quantification were 10.3–37.3 ng/L. Enrichment factors of 0.1 and 5 μg/L sulfonamides spiked in lake water were 14–60, and recoveries were 56–113% with relative standard derivations of 3–19%. Applied with the developed method, sulfamerazine and sulfamethoxazole were measurable in both influent and effluent water of the three sewage treatment plants in Guangzhou, China. The developed method was sensitive and provided an alternative method for simultaneously enriching and quantifying multiple sulfonamides in environmental water.     

Ultrasensitive determination of highly polar trimethyl phosphate in environmental water by molecularly imprinted polymeric fiber headspace solid‐phase microextraction

A sensitive, accurate, and cost effective method for the quantification of trimethyl phosphate, which is highly polar and volatile, in environmental water is presented. Trimethyl phosphate was headspace solid‐phase microextracted on a molecularly imprinted polymeric fiber, and then the fiber was thermally desorbed in the gas chromatograph injector, and the compound was determined. The trimethyl phosphate imprinted polymeric fiber was prepared by copolymerization in a fused silica capillary tube and obtained by removal of the wall of fused silica capillary tube. The monolithic fiber displayed good selectivity toward trimethyl phosphate among its structural analogues. It was thermally stable up to 320°C so that it can withstand the high temperature of the gas chromatograph injector for desorption. The factors influencing the performance of its headspace solid‐phase microextraction were studied. Under the optimal conditions, the method for quantification of trimethyl phosphate in environmental water was well developed. It exhibited significant linearity, the lowest limit of quantification to date, and good recoveries. Using this method, trimethyl phosphate was detected in five out of seven environmental water samples at concentration levels from 0.28 to 1.22 μg/L, illustrating the heavy pollution of trimethyl phosphate in environmental water.     

Hypercrosslinked particles for the extraction of sweeteners using dispersive solid‐phase extraction from environmental samples

This work presents a new extraction material, namely, Q‐100, based on hypercrosslinked magnetic particles, which was tested in dispersive solid‐phase extraction for a group of sweeteners from environmental samples. The hypercrosslinked Q‐100 magnetic particles had the advantage of suitable pore size distribution and high surface area, and showed good retention behavior toward sweeteners. Different dispersive solid‐phase extraction parameters such as amount of magnetic particles or extraction time were optimized. Under optimum conditions, Q‐100 showed suitable apparent recovery, ranging in the case of river water sample from 21 to 88% for all the sweeteners, except for alitame (12%). The validated method based on dispersive solid‐phase extraction using Q‐100 followed by liquid chromatography with tandem mass spectrometry provided good linearity and limits of quantification between 0.01 and 0.1 μg/L. The method was applied to analyze samples from river water and effluent wastewater, and four sweeteners (acesulfame, saccharin, cyclamate, and sucralose) were found in both types of sample.