共查询到20条相似文献,搜索用时 281 毫秒
1.
Coste A Toumi M Wright K Razafimahaléo V Couty F Marrot J Evano G 《Organic letters》2008,10(17):3841-3844
Pyrroloindoles are a key structural motif found in a wide number of biologically active alkaloids. Intramolecular copper-catalyzed coupling of readily accessible 2-iodo-tryptophan derivatives occurs in excellent yield, affording a wide range of polysubstituted, enantioenriched tetrahydropyrrolo[2,3- b]indoles. Diketopiperazines are also suitable substrates for this cyclization reaction, which affords a straightforward entry to tetra- to hepta-polycyclic systems. 相似文献
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Summary A method for optimization of the mobile phase composition in ion exchange chromatography with a wide range external pH gradient (approx. over 5 pH units) has been formulated. It is shown that programming of various wide range pH profiles which are not impaired by buffer interactions of the mobile phase with sorbent is possible. Utilization of the wide range external pH gradient in cation-exchange chromatography of bovine haemoglobin is also demonstrated. 相似文献
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A wide range of mesophases are induced on treating polycatenar complexes of silver(I) with a wide range of organic solvents. 相似文献
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Summary A simple procedure was developed for preparing wide pore (≦ 40nm) silicas from a common chromatographic silica gel. The effects
of various experimental conditions on pore size, pore volume, and surface area are discussed. The results show that under
controlled conditions a wide variety of wide pore silica packing materials can be prepared.
Presented at the 15th International Symposium on Chromatography, Nürnberg, October 1984 相似文献
5.
Xiao‐Bo Ding Daniel P. Furkert Margaret A. Brimble 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(34):11956-11961
Syn dihydroxyketone motifs are embedded in a wide range of biologically active natural products, however the development of stereoselective synthetic methods to assemble these structures has proven a challenging task. We report a highly diastereoselective method for the synthesis of syn dihydroxyketones from propargylic alcohols, with wide scope for application in natural product synthesis. The reaction sequence involves regioselective cyclisation of propargylic alcohols with incorporation of a triketone to give enol dioxolanes that are then diastereoselectively epoxidised to form unusual spiroepoxide intermediates. Hydrolysis affords syn dihydroxyketones as essentially single diastereisomers. The reaction sequence is operationally simple, of wide substrate scope, and remarkably can be efficiently carried out as a one‐pot process with no loss of overall yield or diastereoselectivity. 相似文献
6.
In x-ray fluorescence spectrometry, matrix effects have to be corrected. The empiric equations, the theoretical coefficients and the fundamental parameters can be applied in the purpose. The classical matrix correction models include mainly Lachance-Trail,Rousseau, De Jongh, Claisse-Quentin, COLA algorithms,etc. The good results can be obtained by using a number of standards or the theoretical Alpha coefficients if the range of component concentrations in samples is not very wide. When unknown samples with a wide range of concentrations are predicted, a recalculation process of the theoretical Alpha coefficients has to be made. In addition, a spline function may be chosen to split wide range in several segments. 相似文献
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Francis M. Mirabella 《Journal of Polymer Science.Polymer Physics》1985,23(5):861-871
The use of band-ratioing techniques in internal reflection spectroscopy (IRS) for a wide variety of polymer surface composition and orientation measurements is discussed. It is shown that quantitative data can be obtained under a wide range of experimental conditions. The effects of variations in sample contact, internal reflection element, and angle of incidence are considered in detail. The applicability and limitations of calibration procedures for the determination of surface composition under various experimental conditions are considered. The requirements for obtaining quantitative results by IRS are shown to be far more lenient than is typically assumed. 相似文献
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I. K. Khairullin A. G. Sinaiskii I. V. Dal’gren M. P. Pomanskaya I. I. Khairullin M. A. Chebotarev 《Polymer Science Series D》2013,6(1):72-76
Results are presented of investigations devoted to the creation of polymer compositions using oligomeric urethane-siloxane rubbers as basic polymers (foreign analogs are STO, SPUR or STP polymers). The sealants developed based on these binding materials exhibit a wide range of rates of curing, good physicomechanical characteristics, and high adhesion to various substrates. The corresponding low-, medium-, and high-modulus polymer compositions may find wide application in automobile and transport engineering, shipbuilding, the construction industry, and other fields. 相似文献
11.
Jyoti Rani Sanjiv Kumar Monika Saini Jyoti Mundlia Prabhakar Kumar Verma 《Research on Chemical Intermediates》2016,42(9):6777-6804
Pyrimidine and its derivatives play a wide role in drug discovery processes and have considerable chemical significance and biological activities. Pyrimidines are the building blocks of many natural compounds such as vitamins, liposacharides, and antibiotics. Pyrimidine is used as parent substance for the synthesis of a wide variety of heterocyclic compounds and raw material for drug synthesis and is also crucial in the theoretical development of heterocyclic chemistry and in organic synthesis. Pyrimidine derivatives are vital in several biological activities, i.e. antihypertensive, anticancer, antimicrobial, anti-inflammatory, and antioxidant activity. This creates interest among researchers who have synthesized a variety of pyrimidine derivatives. 相似文献
12.
The influence of short-chain alcohol on the aggregation behavior of Sodium Dodecyl Sulfate (SDS) is investigated within a wide range of alcohol concentration by potentiometric technique. It is observed that aggregation behavior of SDS is a function of alcohol concentration. Variation of micellization parameters are studied in a wide range of alcohol concentration and the trend of changing of micellization parameters have been investigated. The variations of micellization parameters show several regularities. Finally, the relationships between these regularities and alcohol-surfactant interactions have been explained. 相似文献
13.
An efficient one-pot synthetic approach to access a variety of 3-(indol-3-yl)quinoxalin-2-ones from various quinoxalin-2-ones and very wide scope of indoles through TfOH-catalyzed Friedel-Crafts type coupling reaction in DMF has been developed. Only 10 mol % Brønsted acid as a catalyst, air as an oxidizer, and very wide range of substrates are the prominent advantages of this method. 相似文献
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Circular dichroism and absorption are calculated for one-dimensional chiral soft substance (a cholesteric liquid crystal, CLC) cells with an isotropic defect layer. The photonic density of states (PDS), circular dichroism, absorption and emission dependencies are calculated as functions of the parameters characterising absorption and gain. The absorption and gain effects in chiral photonic systems with a defect layer are established and it is shown that in some cases the subject system can work as: a low threshold laser, a multi-position trigger, a total wide/narrow band absorber, a wide/narrow band filter/mirror, etc. This work demonstrates the effects of absorption and emission in photonic crystal (PC) layers, and offers a novel approach to understanding of tunable soft photonic substances. 相似文献
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F M Pohl 《Angewandte Chemie (International ed. in English)》1972,11(10):894-896
In globular proteins, the complicated steric arrangement of the polypeptide chain is determined by several interdependent cooperative interactions. These macromolecules are capable of reacting to changes in the environmental conditions such as temperature and pressure or the concentration of a wide range of compounds by changing their conformation and hence their biological and chemical properties. They are thus suitable for regulation processes or information storage in solution with a wide range of time constants. Environmental effects of this kind can be followed and explained in part at the molecular level by investigation of the time-dependent reversible unfolding of a number of proteins that can be described to a good approximation by a strongly cooperative “all-or-none” transition between two states. 相似文献
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E. Paillard F. Toulgoat R. Arvai C. Iojoiu L. Cointeaux M. Medebielle F. Alloin B. Langlois J.-Y. Sanchez 《Journal of fluorine chemistry》2011,132(12):1213-1218
This paper reports both on a general multistep synthesis of a wide family of aryl substituted perfluorosulfonimides and on a preliminary electrochemical investigation of two lithium salts hosted by a poly(oxyethylene) homopolymer. Both salts have a cationic transference number more than twice that of LiTFSI. Additionally, one of these salts exhibits markedly higher cationic conductivities than POE/LiTFSI electrolytes. These preliminary data are very encouraging as, thanks to the aryl moiety, a wide variety of salts can be considered in order to still improve the performances of polymer electrolytes. 相似文献
20.
G B Lockwood 《Journal of chromatography. A》2001,936(1-2):23-31
The commercial importance of the volatile mono- and sesqui-terpenoids has resulted in a wide range of techiques being used for extraction, concentration, chromatography, and characterisation of constituents. The major chromatographic technique is gas chromatography, and tandem techniques of chromatography linked to further chromatography and spectroscopy, allow much increased resolution, and greater ease of characterisation of terpenes. A wide range of extraction techniques are discussed, and suitability for particular matrices and sample sizes outlined. Chromatography operating conditions and stationary phases, and techniques for solute identification are laid out. A number of applications of terpene analysis in many different matrices are discussed. 相似文献