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991.
We demonstrate here seven pure cyclic samples,which belongs to two series of oligoesters,cyclic oligo(trimethylene terephthalate)s(COTTs) and cyclic oligo(butylene terephthalate)s(COBTs),showing odd-even effect of degree of oligomerization(repeating units number) on properties.The pentamer of COTT and trimer of COBT show much lower melting temperature,and the trimer of COTT and trimer of COBT show significant lower refractive index,which can be ascribed to the low packing density of cyclic oligoesters with odd number of degree of oligomerization.Our results reveal the discrete property change as a function of cyclic size of oligomers,which can be used to design materials with special properties. 相似文献
992.
Hsiao-Chien Chen Yi-Ming Tu Chung-Che Hou Yu-Chen Lin Ching-Hsiang Chen Kuang-Hsuan Yang 《Analytica chimica acta》2015
A water-dispersible multi-walled carbon nanotubes (MWCNTs) derivative, MWCNTs-1-one-dihydroxypyridine (MWCNTs-Py) was synthesis via Friedel–Crafts chemical acylation. Raman spectra demonstrated the conjugated level of MWCNTs-Py was retained after this chemical modification. MWCNTs-Py showed dual hydrogen peroxide (H2O2) and glucose detections without mutual interference by adjusting pH value. It was sensitive to H2O2 in acidic solution and displayed the high performances of sensitivity, linear range, response time and stability; meanwhile it did not respond to H2O2 in neutral solution. In addition, this positively charged MWCNTs-Py could adsorb glucose oxidase (GOD) by electrostatic attraction. MWCNTs-Py-GOD/GC electrode showed the direct electron transfer (DET) of GOD with a pair of well-defined redox peaks, attesting the bioactivity of GOD was retained due to the non-destroyed immobilization. The high surface coverage of active GOD (3.5 × 10−9 mol cm−2) resulted in exhibiting a good electrocatalytic activity toward glucose. This glucose sensor showed high sensitivity (68.1 μA mM−1 cm−2) in a linear range from 3 μM to 7 mM in neutral buffer solution. The proposed sensor could distinguish H2O2 and glucose, thus owning high selectivity and reliability. 相似文献
993.
994.
Self‐Guided Supramolecular Cargo‐Loaded Nanomotors with Chemotactic Behavior towards Cells 下载免费PDF全文
Fei Peng Yingfeng Tu Dr. Jan C. M. van Hest Dr. Daniela A. Wilson 《Angewandte Chemie (International ed. in English)》2015,54(40):11662-11665
Delivery vehicles that are able to actively seek and precisely locate targeted tissues using concentration gradients of signaling molecules have hardly been explored. The directed movement toward specific cell types of cargo‐loaded polymeric nanomotors along a hydrogen peroxide concentration gradient (chemotaxis) is reported. Through self‐assembly, bowl‐shaped poly(ethylene glycol)‐b‐polystyrene nanomotors, or stomatocytes, were formed with platinum nanoparticles entrapped in the cavity while a model drug was encapsulated in the inner compartment. Directional movement of the stomatocytes in the presence of a fuel gradient (chemotaxis) was first demonstrated in both static and dynamic systems using glass channels and a microfluidic flow. The highly efficient response of these motors was subsequently shown by their directional and autonomous movement towards hydrogen peroxide secreting neutrophil cells. 相似文献
995.
Silver‐Catalyzed Cross‐Coupling of Isocyanides and Active Methylene Compounds by a Radical Process 下载免费PDF全文
Jianquan Liu Zhenhua Liu Dr. Peiqiu Liao Dr. Lin Zhang Prof. Tao Tu Prof. Xihe Bi 《Angewandte Chemie (International ed. in English)》2015,54(36):10618-10622
Isocyanides are versatile building blocks, and have been extensively exploited in C? H functionalization reactions. However, transition‐metal‐catalyzed direct C? H functionalization reactions with isocyanides suffer from over‐insertion of isocyanides. Reported herein is a radical coupling/isomerization strategy for the cross‐coupling of isocyanides with active methylene compounds through silver‐catalysis. The method solves the over‐insertion issue and affords a variety of otherwise difficult to synthesize β‐aminoenones and tricarbonylmethanes under base‐ and ligand‐free conditions. This report presents a new fundamental C? C bond‐forming reaction of two basic chemicals. 相似文献
996.
Characterization and simultaneous quantification of biological aporphine alkaloids in Litsea cubeba by HPLC with hybrid ion trap time‐of‐flight mass spectrometry and HPLC with diode array detection 下载免费PDF全文
Qiang Guo Yunfang Zhao Xiaoli Gao Xingyun Chai Pengfei Tu 《Journal of separation science》2015,38(15):2614-2624
The root and rhizome of Litsea cubeba (Lour) Pers., named ‘Dou‐chi‐jiang’ in Chinese, has been traditionally used for treatment of cardiovascular and cerebrovascular diseases, rheumatic arthralgia, and other diseases in China. Aporphine alkaloids are its characteristic ingredients and responsible for its bioactivities, especially anti‐inflammatory and analgesic effects. A sensitive and reliable high‐performance liquid chromatography with diode array detection‐tandem mass spectrometry method was developed for characterization and simultaneous determination of biological aporphine alkaloids in ‘Dou‐chi‐jiang’. The optimized chromatographic conditions were performed on an Eclipse XDB C18 column with a gradient of acetonitrile/water containing 0.1% formic acid as the mass spectrometry mobile phase and acetonitrile/water containing 0.2% diethylamine (pH 3.10, adjusted by acetic acid) as the liquid chromatography mobile phase. The fragmentation pathways by loss of CO, ·CH3, ·NH3, and ·NH2CH3 were detected as characteristic for aporphine alkaloids. Based on these characteristics, total 12 analogues were identified. The quantification method was validated in terms of linearity, precision, and accuracy for six major aporphine alkaloids, which was successfully applied for simultaneous determination in ten batches of samples. The established method is simple, rapid, and specific for characterization and quantitation of aporphine alkaloids in ‘Dou‐chi‐jiang’ and other traditional Chinese medicines rich in this kind of ingredient. 相似文献
997.
Yang Li Dr. Yuan-Yuan An Jian-Zhong Fan Xiao-Xu Liu Xin Li Prof. Dr. F. Ekkehardt Hahn Prof. Dr. Yao-Yu Wang Prof. Dr. Ying-Feng Han 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(25):10159-10166
A series of supramolecular assemblies of types [Ag8( L )4](PF6)8 and [Ag4( L )2](PF6)4, obtained from the tetraphenylethylene (TPE) bridged tetrakis(1,2,4-triazolium) salts H4-L(PF6)4 and AgI ions, is described. The assembly type obtained dependends on the N-wingtip substituents of H4-L(PF6)4. Changes in the lengths of the N4-wingtip substituents enables controlled formation of assemblies with either [Ag4( L )2](PF6)4 or [Ag8( L )4](PF6)8 stoichiometry. The molecular structures of selected [Ag8( L )4](PF6)8 and [Ag4( L )2](PF6)4 assemblies were determined by X-ray diffraction analyses. While H4- L (PF6)4 does not exhibit fluorescence in solution, their tetra-NHC (NHC=N-heterocyclic carbene) assemblies do upon NHC–metal coordination. Upon irradiation, all assemblies undergo a light-induced, supramolecule-to-supramolecule structural transformation by an oxidative photocyclization involving phenyl groups of the TPE core, resulting in a significant change of the luminescence properties. 相似文献
998.
We report some key results in the theoretical investigations of configurations of lipid membranes and present several challenges in this field,which involve(i)the exact solutions to the shape equation of lipid vesicles,(ii)the exact solutions to the governing equations of open lipid membranes,(iii)the neck condition of two-phase vesicles in the budding state,(iv) the nonlocal theory of membrane elasticity,and(v)the relationship between the symmetry and the magnitude of the free energy. 相似文献
999.
We investigated the characteristics and the mechanism of Pt/La2O3/Pt resistance switching memory with a set of measurements. The La2O3 films were determined as nano‐poly‐crystalline (diameter of the nanocrystals 5–10 nm) by XRD and HRTEM analysis. The Pt/La2O3/Pt device exhibited excellent resistive switching properties, including low switching voltage (<2 V), large low/high resistance ratio (>108), and good cycling endurance property. The conduction mecha‐ nisms of the Pt/La2O3/Pt device were revealed with current–voltage characteristics, which are different in the low and high resistance states. Furthermore, XPS analysis and temperature‐dependent resistance measurement in the low resistance state showed that the conducting filaments in the Pt/La2O3/Pt device are mainly affected by oxygen defects rather than metallic La. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
1000.
J. J. Miau H. W. Tsai Y. J. Lin J. K. Tu C. H. Fang M. C. Chen 《Experiments in fluids》2011,51(4):949-967
Experiments were conducted for 2D circular cylinders at Reynolds numbers in the range of 1.73 × 105–5.86 × 105. In the experiment, two circular cylinder models made of acrylic and stainless steel, respectively, were employed, which
have similar dimensions but different surface roughness. Particular attention was paid to the unsteady flow behaviors inferred
by the signals obtained from the pressure taps on the cylinder models and by a hot-wire probe in the near-wake region. At
Reynolds numbers pertaining to the initial transition from the subcritical to the critical regimes, pronounced pressure fluctuations
were measured on the surfaces of both cylinder models, which were attributed to the excursion of unsteady flow separation
over a large circumferential region. At the Reynolds numbers almost reaching the one-bubble state, it was noted that the development
of separation bubble might switch from one side to the other with time. Wavelet analysis of the pressure signals measured
simultaneously at θ = ±90° further revealed that when no separation bubble was developed, the instantaneous vortex-shedding frequencies could
be clearly resolved, about 0.2, in terms of the Strouhal number. The results of oil-film flow visualization on the stainless
steel cylinder of the one-bubble and two-bubble states showed that the flow reattachment region downstream of a separation
bubble appeared not uniform along the span of the model. Thus, the three dimensionality was quite evident. 相似文献