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181.
A series of eleven specially designed benzotriazole monoazo dyes for use in surface enhanced resonance Raman scattering studies are reported. Unlike previous benzotriazole dyes produced for SERRS, these dyes have been synthesised to be trifunctional in nature. The presence of the benzotriazole moiety provides surface complexing properties, the azo linkage provides the colour and hence extra sensitivity and the nucleophilic amine group enables further functionalisation. 相似文献
182.
Eberendu AR Luta G Edwards JA McAnalley BH Davis B Rodriguez S Henry CR 《Journal of AOAC International》2005,88(3):684-691
Aloe vera inner leaf gel has been used as a medicinal remedy for many years. Yet some aloe products do not demonstrate beneficial effects, indicating that poor quality products are reaching the market. Therefore, an efficient and accurate method is needed to evaluate the quality of aloe products. This paper describes a quick, quantitative colorimetric assay that has been developed for the determination of glucomannan in aloe gel and products. With this method, interference by non-aloe polysaccharides or other extraneous components was absent or negligible. Data indicate that the glucomannan can be determined at parts per million (mg/L) in aqueous solutions with an accuracy of 100 +/- 5% at a 10 mg/L concentration. The correlation coefficient is 0.999, and linearity is from 0.9 to 72.7 mg/L in the test solution. The method is inexpensive, simple, sensitive, and reproducible. This method was applied to determine the polysaccharide content of commercial aloe products. Both qualitative and quantitative information can be obtained in about 5 min. 相似文献
183.
Alexis D.C. Parenty 《Tetrahedron》2005,61(35):8410-8418
Secondary amines and thiols undertake a substitution reaction on the side chain of 2-bromoethyl-pyridinium derivatives ‘directed’ by an intramolecular re-arrangement. Experimental investigations strongly indicate that the reaction is initiated by an alpha addition of the nucleophile onto the iminium moiety of the N-heteroaromatic cation, followed by a cyclisation and an oxidative ring opening. This novel substitution process is able to occur with less reactive nucleophiles that would not undergo conventional substitution with ‘isolated’ bromoethyl moieties. 相似文献
184.
The wetting and moisture up-take behaviour, as well as the electrokinetic properties of various lignocellulosic fibres were
characterised. Knowledge of surface and water uptake properties of this kind of materials will help to tailor their potential
use in different end user applications. The surface tension of the fibres was determined from wetting measurements using the
capillary rise technique. The wetting data were used to determine the surface tension of the fibres. Our results show that
the surface tension of the lignocellulosic fibres is a linear function of their cellulose content. Zeta-potential measurements
were exploited to characterise the surface chemistry of the fibres. Measuring the zeta-potential as function of time enables
the rapid assessment of the water up-take, i.e. the swelling behaviour of the fibres. The results obtained by the zeta potential
measurements correlate, with the exception of flax, in a linear manner with the results obtained from conventional moisture
uptake measurements. Even though all lignocellulosic fibres are very hydrophilic due to the presence of polar oxygen containing
groups they have different grades of hydrophilicity, which is also reflected in the different water uptake capabilities measured.
The wetting, moisture uptake and electrokinetic properties of the lignocellulosic fibres are determined by the availability
of the surface functional groups present, which is usually consequence of the processes used to separate, and extract the
fibres from the plant (retting), as well as any further processing used to improve the fibre quality. 相似文献
185.
4-Chloro-2(H)-pyran-2-one undergoes thermal Diels-Alder cycloaddition with electron-deficient dienophiles to afford, without any significant selectivity, 6-endo- and 5-endo-substituted bicyclic lactone cycloadducts. In contrast to 3- and 5-bromo-2(H)-pyran-2-one, 4-chloro-2(H)-pyran-2-one does not undergo thermal cycloadditions with electron-rich dienophiles. The regio- and stereochemical preferences of the cycloadditions of 4-chloro-2(H)-pyran-2-one and other related 2(H)-pyran-2-ones are investigated computationally. Calculations were carried out on the transition states leading to the four possible regio- and stereoisomeric cycloadducts using density functional theory (B3LYP/6-31G). These studies allow prediction of the regio- and stereoselectivity in these reactions which are in line with experimental observations. 相似文献
186.
187.
188.
Alexis Michel 《Mathematische Zeitschrift》1999,230(3):451-470
Let E be an elliptic curve with complex multiplication over the ring of integers of an imaginary quadratic field K. Denote by p an odd prime that splits into in and by the unique -extension of K totally ramified above . It is well-known that the Selmer group attached to any finite extension of is analogous to the minus part of the p-class group of divisors of the cyclotomic - extensions of CM number fields. One of the most striking examples of this analogy is the existence of a translation formula à la Kida for the codimension of the Selmer group at the top of the tower. In this article we carry on the analogy with the presentations
of results similar to those proven by Gold and Madan in the cyclotomic case (see [8]), which were the continuation of Kida's
work. More precisely, we describe the -structure of the Selmer group when G is a cyclic group of order p or . In addition, we study the modular representation of G on the subgroup of points of order p of the Selmer group, when G is cyclic of order .
Received December 3, 1997 相似文献
189.
Lilian Geniller Dr. Marc Taillefer Dr. Florian Jaroschik Dr. Alexis Prieto 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(43):e202201495
The first photo-mediated process enabling the generation of halide radicals by Halogen-Atom Transfer (XAT) is described. Contrary to radical transformations involving XAT reactivity, which exploit stable carbon radicals, this unique approach uses 1,2-dihaloethanes for the generation of unstable carbon radicals by XAT. These transient radicals then undergo β-scission with release of ethylene and formation of more stable halide radicals which have been used in selective hydrohalogenations of a large number of unsaturated hydrocarbons, including Michael acceptors, unactivated alkenes and alkynes. This hydrohalogenation is tolerant of a broad range of functionalities and is believed to proceed through a radical-chain manifold that propagates by the use of silane derivatives. 相似文献
190.
Catalytic Upgrading of Biomass‐Derived Methyl Ketones to Liquid Transportation Fuel Precursors by an Organocatalytic Approach
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Dr. Shylesh Sankaranarayanapillai Dr. Sanil Sreekumar Joseph Gomes Adam Grippo George E. Arab Prof. Martin Head‐Gordon Prof. F. Dean Toste Prof. Alexis T. Bell 《Angewandte Chemie (International ed. in English)》2015,54(15):4673-4677
A highly efficient water‐tolerant, solid‐base catalyst for the self‐condensation of biomass‐derived methyl ketones to jet‐diesel fuel precursors was developed by grafting site‐isolated secondary amines on silica‐alumina supports. It is shown that apart from the nature and density of amine groups and the spatial separation of the acidic and basic sites, the acidity of the support material plays a critical role in defining the catalytic activity. It is also found that a combination of weakly acidic silanol/aluminol with secondary amine groups can mimic proline catalysts and are more effective in catalyzing the selective dimerization reaction than the combination of amines with organic acids. In situ FTIR measurements demonstrate that acidic groups activate methyl ketones through their carbonyl groups leading to a favorable C? C bond formation step involving an enamine intermediate. DFT analysis of the reaction pathway confirms that C? C bond formation is the rate‐limiting step. 相似文献