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981.
982.
Yuta Suzuki Tetsuhiro NemotoShun-ichi Nakano Zengduo ZhaoYuta Yoshimatsu Yasumasa Hamada 《Tetrahedron letters》2014
A novel method for synthesizing 4,5-fused tricyclic quinoline derivatives based on an acid-promoted intramolecular Friedel–Crafts allenylation of anilines. Using aryl group-substituted propargyl alcohol derivatives with a meta-substituted N-Boc aniline unit as substrates, a four-step reaction sequence involving an acid-promoted intramolecular Friedel–Crafts allenylation of anilines, an acid-promoted intramolecular C–N bond formation, deprotection of the Boc group, and air oxidation proceeded in a single pot, producing the corresponding 4,5-fused tricyclic quinoline derivatives in 31–84% yield. 相似文献
983.
Marko Stojkovic Israel Joel Koenka Wolfgang Thormann Peter C. Hauser 《Electrophoresis》2014,35(4):482-486
A CE system featuring an array of 16 contactless conductivity detectors was constructed. The detectors were arranged along 70 cm length of a capillary with 100 cm total length and allow the monitoring of separation processes. As the detectors cannot be accommodated on a conventional commercial instrument, a purpose built set‐up employing a sequential injection manifold had to be employed for automation of the fluid handling. Conductivity measurements can be considered universal for electrophoresis and thus any changes in ionic composition can be monitored. The progress of the separation of Na+ and K+ is demonstrated. The potential of the system to the study of processes in CZE is shown in two examples. The first demonstrates the differences in the developments of peaks originating from a sample plug with a purely aqueous background to that of a plug containing the analyte ions in the buffer. The second example visualizes the opposite migration of cations and anions from a sample plug that had been placed in the middle of the capillary. 相似文献
984.
Adaptive lambda square dynamics simulation: An efficient conformational sampling method for biomolecules 下载免费PDF全文
A novel, efficient sampling method for biomolecules is proposed. The partial multicanonical molecular dynamics (McMD) was recently developed as a method that improved generalized ensemble (GE) methods to focus sampling only on a part of a system (GEPS); however, it was not tested well. We found that partial McMD did not work well for polylysine decapeptide and gave significantly worse sampling efficiency than a conventional GE. Herein, we elucidate the fundamental reason for this and propose a novel GEPS, adaptive lambda square dynamics (ALSD), which can resolve the problem faced when using partial McMD. We demonstrate that ALSD greatly increases the sampling efficiency over a conventional GE. We believe that ALSD is an effective method and is applicable to the conformational sampling of larger and more complicated biomolecule systems. © 2013 Wiley Periodicals, Inc. 相似文献
985.
Neomacrophorins I (1), II (2), and III (3) were isolated from the culture broth of Trichoderma sp. 1212-03, which was collected at Shirakami Mountainous area in Japan. Structural analyses disclosed that these resemble known macrophorins but possess axial-hydroxy group at C3 as well as different side chains at C7′. These are diastereomeric forms of macrophorins for 5′,6′-epoxide functionality. The NMR analyses suggested their relative configurational relationship between the C1–C15 drimene and C1′–C7′ epoxyquinone moieties. ECD spectral discussions verified them particularly for C5′,C6′-epoxyquinone (1), C5′,C6′-epoxysemiquinone (2 and 3), and 2″,3″-dihydroxybutanoate moiety in 1 and 2. The configuration of C3″-stereocenter of 3 was determined by chiral GC–MS after converting into methyl (S)-3″-hydroxybutanoate by basic of 3 methanolysis. Biological assays disclosed that 1 induces hyphal branching of Cochliobolus miyabeanus as well as cytotoxicity against human colorectal cancer COLO 201. 相似文献
986.
Kazuaki Z. Takahashi 《Journal of computational chemistry》2014,35(11):865-875
In our previous study (Takahashi et al., J. Chem. Theory Comput. 2012, 8, 4503), we developed the linear‐combination‐based isotropic periodic sum (LIPS) method. The LIPS method is based on the extended isotropic periodic sum theory that produces a ubiquitous interaction potential function to estimate homogeneous and heterogeneous systems. The LIPS theory also provides the procedure to design a periodic reaction field. To demonstrate this, in the present work, a novel reaction field of the LIPS method was developed. The novel reaction field was labeled LIPS‐SW, because it provides an interaction potential function with a shape that resembles that of the switch function method. To evaluate the ability of the LIPS‐SW method to describe in homogeneous and heterogeneous systems, we carried out molecular dynamics (MD) simulations of bulk water and water–vapor interfacial systems using the LIPS‐SW method. The results of these simulations show that the LIPS‐SW method gives higher accuracy than the conventional interaction potential function of the LIPS method. The accuracy of simulating water–vapor interfacial systems was greatly improved, while that of bulk water systems was maintained using the LIPS‐SW method. We conclude that the LIPS‐SW method shows great potential for high‐accuracy, high‐performance computing to allow large scale MD simulations. © 2014 Wiley Periodicals, Inc. 相似文献
987.
以同向啮合双螺杆挤出机为反应器,采用苯乙烯和异戊二烯为聚合单体,以正丁基锂为引发剂,采用三次加料法合成苯乙烯/异戊二烯/苯乙烯(SIS)三嵌段热塑性弹性体.氢核磁共振(1H NMR)谱分析结果表明,共聚物中聚异戊二烯嵌段以1,4-结构为主.采用四氧化锇催化双氧水氧化降解聚合物分子链,利用凝胶渗透色谱对氧化降解后的聚苯乙烯碎片进行分析,证明共聚物分子为(聚苯乙烯-聚异戊二烯-聚苯乙烯)(PS-PI-PS)三嵌段结构.动态力学分析(DMA)及透射电子显微镜(TEM)分析结果表明,SIS具有两相分离结构.拉伸试验结果表明,共聚物拉伸强度与苯乙烯含量有关. 相似文献
988.
989.
Rapid quantitative analysis of individual anthocyanin content based on high‐performance liquid chromatography with diode array detection with the pH differential method 下载免费PDF全文
Huayin Wang 《Journal of separation science》2014,37(18):2535-2544
A new quantitative technique for the simultaneous quantification of the individual anthocyanins based on the pH differential method and high‐performance liquid chromatography with diode array detection is proposed in this paper. The six individual anthocyanins (cyanidin 3‐glucoside, cyanidin 3‐rutinoside, petunidin 3‐glucoside, petunidin 3‐rutinoside, and malvidin 3‐rutinoside) from mulberry (Morus rubra) and Liriope platyphylla were used for demonstration and validation. The elution of anthocyanins was performed using a C18 column with stepwise gradient elution and individual anthocyanins were identified by high‐performance liquid chromatography with tandem mass spectrometry. Based on the pH differential method, the high‐performance liquid chromatography peak areas of maximum and reference absorption wavelengths of anthocyanin extracts were conducted to quantify individual anthocyanins. The calibration curves for these anthocyanins were linear within the range of 10–5500 mg/L. The correlation coefficients (r2) all exceeded 0.9972, and the limits of detection were in the range of 1–4 mg/L at a signal‐to‐noise ratio ≥5 for these anthocyanins. The proposed quantitative analysis was reproducible with good accuracy of all individual anthocyanins ranging from 96.3 to 104.2% and relative recoveries were in the range 98.4–103.2%. The proposed technique is performed without anthocyanin standards and is a simple, rapid, accurate, and economical method to determine individual anthocyanin contents. 相似文献
990.
Ultra‐trace level determination of diquat and paraquat residues in surface and drinking water using ion‐pair liquid chromatography with tandem mass spectrometry: A comparison of direct injection and solid‐phase extraction methods 下载免费PDF全文
Jin‐Aa Oh Jun‐Bae Lee Soo‐Hyung Lee Ho‐Sang Shin 《Journal of separation science》2014,37(20):2900-2910
Direct injection and solid‐phase extraction methods for the determination of diquat and paraquat in surface and drinking water were developed using liquid chromatography with tandem mass spectrometry. The signal intensities of analytes based on six ion‐pairing reagents were compared with each other, and 12.5 mM nonafluoropentanoic acid was selected as the best suited amongst them. A clean‐up method was developed using Oasis hydrophilic–lipophilic balance; this was compared to the direct injection method, with respect to limits of detection, interference, precision, and accuracy. Limits of quantification of diquat and paraquat were 0.03 and 0.01 μg/L using the direct injection method, and 0.002 and 0.001 μg/L using the hydrophilic–lipophilic balance method. When the hydrophilic–lipophilic balance method was used to analyze target compounds in 114 surface water and 30 drinking water samples, paraquat and diquat were detected within a concentration range of 0.001–0.12 and 0.002–0.038 μg/L in surface water, respectively. When the direct injection method was used to analyze target compounds in the same samples, the detected concentrations of paraquat and diquat were within 25% in samples being >0.015 μg/L using the hydrophilic–lipophilic balance method. The liquid chromatography with tandem mass spectrometry method using direct injection can thus be used for routine monitoring of paraquat and diquat in surface and drinking water. 相似文献