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排序方式: 共有214条查询结果,搜索用时 15 毫秒
71.
72.
甘氨酸衍生化β-环糊精键合硅胶液相色谱固定相的合成与评价 总被引:1,自引:0,他引:1
β-环糊精键合硅胶经对甲苯磺酰化后,与甘氨酸反应得到甘氨酸衍生化β-环糊精键合硅胶固定相(GCDS)。考察了GCDS对位置异构体、丹磺酰化氨基酸异构体、苯丙酸类药物等的分离性能,研究了流动相中甲醇浓度、pH以及柱温对色谱保留行为的影响。 相似文献
73.
Yuen Ping Tan Kylie A. Agnew-Francis Julian Hofmann Dr. Andrei I. Savchenko Dr. Scott R. Lafontaine Prof. Glen M. Boyle Prof. Paul V. Bernhardt Prof. James A. Fraser Prof. Thomas H. Shellhammer Prof. Craig M. Williams 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(7):1653-1660
Dysphania is an abundant genus of plants, many of which are endemic to the Australian continent, occurring primarily in arid and temperate zones. Despite their prevalence, very few investigations into the phytochemistry of native Dysphania have been undertaken. Described herein, is the isolation and elucidation of two enantiomeric diastereomers of humulene diepoxide C from D. kalpari and D. rhadinostachya, of which unassigned diastereomers of humulene diepoxide C have been previously reported as components in beer brewed from aged hops. In addition, two (+)-humulene diepoxiols (humulene diepoxiol C-I and C-II) were isolated from D. rhadinostachya. Analysis of Chinook hops oil confirmed the presence of both humulene diepoxide C-I and C-II as trace components, and in turn enabled GC-MS peak assignment to the relative stereochemistry. Anticancer assays did not reveal any significant activity for the (+)-humulene diepoxides. Antifungal assays showed good activity against a drug-resistant strain of C. auris, with MIC50 values of 8.53 and 4.91 μm obtained for (+)-humulene diepoxide C-I and C-II, respectively. 相似文献
74.
H. Allouchi A. Belaaraj M. Cotrait E. Lafontaine P. Judeinstein J.-P. Bayle 《Liquid crystals》2013,40(8):1087-1096
The crystal structures of two mesogenic compounds having two neighbouring lateral alkoxy chains in the central part of the molecules have been solved. In both structures, the common four ring central core is extended and quite rigid with a total length close to 28.5 Å. All the molecules are strictly parallel because of the P1 space group; the molecular arrangement is characteristic of a nematogenic system. In these structures, the lateral alkoxy chains are folded back to the core; they exhibit slightly different conformations and are quite disordered. The 13C chemical shift of the first -OCH2- within the lateral chains can probe the mean conformation of the chain in the nematic phase. This chemical shift is independent of the compound. Nevertheless, in the solid phase, this chemical shift is dependent on small geometrical changes due to the influence of the oxygen in the neighbouring lateral chain. In addition, temperature cycling of the sample leads to different crystalline solid forms as evidenced by DSC and NMR studies. 相似文献
75.
用低温溶剂热法合成了2种分立结构的有机杂化硫代碲(Ⅳ)酸盐化合物(H2en)TeS3(1)和[Ni(en)3]TeS3(2)(en=乙二胺),通过X-射线单晶衍射,红外光谱,元素分析等手段对它们的结构进行了表征。晶体结构解析结果表明:2个化合物均属单斜晶系,空间群分别为P21和P21/c。化合物1和2具有孤立三角锥[TeS3]2-阴离子,化合物1的平衡阳离子为双质子化乙二胺[H2en]2+,阴离子基团[TeS3]2-和阳离子基团[H2en]2+之间通过N-H…S氢键连接。化合物2的阳离子基团为过渡金属Ni与乙二胺的配合物[Ni(en)3]2+。另外,对该2种晶体进行了紫外-可见漫反射光谱测试和热重分析。 相似文献
76.
F. Perez P. Judeinstein J. P. Bayle H. Allouchi M. Cotrait E. Lafontaine 《Liquid crystals》1996,21(6):855-864
A new homologous series of 4-(4-chlorobenzoyloxy)-2-alkoxy-3-methyl-4'-(4-trans-pentyl-cyclohexanoyloxy) azobenzenes has been synthesized. These compounds contain four rings in the main core, a lateral alkoxy branch and an adjacent lateral methyl group on one inner ring. They present a large nematic range and a solid-solid phase transition for the first members of the series. The crystal structures of two similar compounds containing a lateral butoxy chain have been solved. The HM4 compound (C31H33N2O5Cl) is derived from the series, but does not have the terminal pentyl chain while the PM4 compound (C36H43N2O5Cl) possesses this terminal chain. HM4 and PM4 crystallize, respectively, in P21/c (Z = 4) and P1 (Z = 2) space groups. The final reliability factors are R = 0.138 for HM4 (the terminal cyclohexyl ring is largely disordered) and R = 0.041 for PM4, for 2204 and 1963 observed reflections, respectively. The four ring central core is linear and rigid for both compounds. The conformation of the butyloxy side chain branched on one of the central phenyl rings is very dependent on the terminal substituent, as it is found in a largely bent conformation in HM4 and in an extended conformation in PM4. To monitor the lateral chain conformation in the solid and nematic phase, we have used the -OCH2- resonance in the 13C MAS NMR spectra. The temperature dependence of this resonance has indicated that the solid-solid transition encountered for the first members of the series is associated with a change of the lateral chain conformation within the solid phase. At the solid-nematic transition, the change of the chain conformation involving the first segment of the lateral chain is far less pronounced. When this solid-solid phase transition disappears for the last members of the series, this change in the conformation occurs at the solid-nematic transition. 相似文献
77.
78.
用十二胺-N乙酸-N亚甲基膦酸(DAPA)改性氧化锆制备了一种新的锆基质色谱固定相(DAPAZ),研究发现,DAPA在氧化锆表面有两种结合方式:红外光谱中1611cm^-1处的特征吸收表明羧基主要与胺基形成偶极离子,以羧酸根离子形式存在,大部分的DAPA分子通过膦酸基团与氧化锆结合;而与钼酸的显色反应则表明有少量DAPA以羧居与氧化锆结合,另外,对固定相的屏蔽效应、碱性条件(pH9.5)下的稳定性等色谱性能的研究也证实这两种吸附方式同时存在,但以膦酸基结合为主。 相似文献
79.
Abstract Management and conservation of exploited populations have been a central issue in theoretical and empirical studies. In this work, it is shown that threshold policies can induce cyclic behavior in an otherwise exploited stable population as a consequence of the combination of harvest pressure and excessively protective threshold densities. Moreover, the dynamical outcomes generated by these extremely protective policies may vary according to the initial densities. These results may be of significant concern in conservation as well as in management of exploited population. 相似文献
80.
P. A. S. JORGE P. CALDAS J. C. G. ESTEVES DA SILVA C. C. ROSA A. G. OLIVA J. L. SANTOS 《Fiber and Integrated Optics》2013,32(3-4):201-225
Abstract A scheme for the simultaneous determination of temperature and analyte concentration for application in luminescence-based chemical sensors is proposed. This scheme is applied to an optical oxygen sensor, which is based on the quenching of the fluorescence of a ruthenium complex. Temperature measurement is performed using the excitation radiation and an absorption long-pass filter. Preliminary results are presented that show the viability of an oxygen measurement that is independent of temperature and optical power level. The possibility of self-referenced temperature measurements with semiconductor nanoparticles is also investigated. In order to optimize the sensor design, several different optical fiber probe geometries for oxygen sensing are tested and compared, including different methods of coupling radiation into the optical fiber system. Polyvinyl alcohol (PVA) and polyacrylamide membranes are tested as supports for sensor immobilization in fiber-optical pH sensing devices in aqueous solution. Some results are presented that show the feasibility of using fiber-optical pH indicators for remote monitoring. 相似文献