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91.
Base‐Induced Reactions of p ‐ Menthane‐ and Pinane‐Derived Epoxyesters – Coconut Fragrance The base‐induced isomerization of p‐menthane‐ and pinane‐derived epoxy esters was studied. The reaction is dependent on the structure of the terpene compound, the nature of the base, and experimental conditions. Among all the new synthesized compounds, one, 6a , emits a very strong fragrance of coconut. In the structure of this tricyclic lactone, the presence of a methyl substituent is essential. 相似文献
92.
93.
A computational study of physical and biological characterization of common UV sources and filters,and their relevance for substituting sunlight 总被引:3,自引:0,他引:3
Sunlight is the most important environmental UV source, affecting not only human health but also the whole terrestrial ecosystem. The use of artificial sources is advantageous since it is independent of geographical location and seasonal variations, however, in some photobiological/photochemical studies the choice of a specific UV source in relation to the biological end-point studied is sometimes questionable. Furthermore, it is often difficult to compare the results obtained in different laboratories due to 'slight' differences in the physical characteristics of the UV sources used. In an attempt to address these issues we calculated and compared the physical characteristics and the biological efficiency in UV-B and UV-A regions for two biological end-points (CPD and Fpg-sensitive sites formation) for frequently used UV-B, UV-A sources and solar light simulators (SLS). Our calculation shows that FS20 lamp is appropriate for studying the biological effects of UV-B radiation although differences in spectral characteristics of the associated filters may lead to at least 2-fold yields in CPD production. Furthermore, the use of a SLS with a Kodacel filter alone is inadequate for studying environmental UV effects. A metal-halide source with a Schott WG345 filter is appropriate for studies on biological effects due to UV-A region. Relative exposure duration was calculated to achieve equal amount of CPD or Fpg-sensitive sites, provided equal, total UV-(A+B) irradiance for the different UV sources. 相似文献
94.
Ralph J. Faudree Evelyne Flandrin Michael S. Jacobson Jenő Lehel Richard H. Schelp 《Graphs and Combinatorics》2000,16(4):399-410
It will be shown that if G is a graph of order n which contains a triangle, a cycle of length n or n−1 and at least cn odd cycles of different lengths for some positive constant c, then there exists some positive constant k=k(c) such that G contains at least kn
1/6 even cycles of different lengths. Other results on the number of even cycle lengths which appear in graphs with many different
odd length cycles will be given.
Received: October 15, 1997 相似文献
95.
Filip Van Lijsebetten Kevin De Bruycker Evelyne Van Ruymbeke Johan M. Winne Filip E. Du Prez 《Chemical science》2022,13(43):12865
Dynamic covalent networks present a unique opportunity to exert molecular-level control on macroscopic material properties, by linking their thermal behaviour to the thermodynamics and kinetics of the underlying chemistry. Yet, existing methods do not allow for the extraction and analysis of the influence of local differences in chemical reactivity caused by available reactants, catalysts, or additives. In this context, we present a rheological paradigm that allows us to correlate the composition of a reactive polymer segment to a faster or slower rate of network rearrangement. We discovered that a generalised Maxwell model could separate and quantify the dynamic behaviour of each type of reactive segment individually, which was crucial to fully comprehend the mechanics of the final material. More specifically, Eyring and Van ''t Hoff analysis were used to relate possible bond catalysis and dissociation to structural changes by combining statistical modelling with rheology measurements. As a result, precise viscosity changes could be measured, allowing for accurate comparison of various dynamic covalent network materials, including vitrimers and dissociative networks. The herein reported method therefore facilitated the successful analysis of virtually any type of rate-enhancing effect and will allow for the design of functional and fast (re)processable materials, as well as improve our ability to predict and engineer their properties for future applications.A novel characterisation method is presented to link molecular reactivity changes to material properties of reprocessable thermosets with unique performance. 相似文献
96.
Christoph Kieninger Evelyne Deery Andrew D. Lawrence Maren Podewitz Klaus Wurst Emi Nemoto‐Smith Florian J. Widner Joseph A. Baker Steffen Jockusch Christoph R. Kreutz Klaus R. Liedl Karl Gruber Martin J. Warren Bernhard Krutler 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(31):10869-10873
97.
Antiplasmodial activity of three bisbenzylisoquinoline alkaloids from the tuber of Stephania rotunda
Chea A Bun SS Azas N Gasquet M Bory S Ollivier E Elias R 《Natural product research》2010,24(18):1766-1770
Three bisbenzylisoquinoline alkaloids were isolated for the first time from Stephania rotunda tuber. Their structures were elucidated by spectroscopic methods and their antiplasmodial activity was investigated in vitro on chloroquine resistant Plasmodium falciparum strain W2. These alkaloids were identified as 2-norcepharanthine (1), cepharanoline (2) and fangchinoline (3). In vitro, they displayed significant antiplasmodial activity with inhibitory concentration 50 values of 0.3, 0.2 and 0.3 μM. 相似文献
98.
Julien Hanss Evelyne Veuillet Kamel Adjout Julien Besle Lionel Collet Hung Thai-Van 《BMC neuroscience》2009,10(1):23-11
Background
In normal-hearing subjects, monaural stimulation produces a normal pattern of asynchrony and asymmetry over the auditory cortices in favour of the contralateral temporal lobe. While late onset unilateral deafness has been reported to change this pattern, the exact influence of the side of deafness on central auditory plasticity still remains unclear. The present study aimed at assessing whether left-sided and right-sided deafness had differential effects on the characteristics of neurophysiological responses over auditory areas. Eighteen unilaterally deaf and 16 normal hearing right-handed subjects participated. All unilaterally deaf subjects had post-lingual deafness. Long latency auditory evoked potentials (late-AEPs) were elicited by two types of stimuli, non-speech (1 kHz tone-burst) and speech-sounds (voiceless syllable/pa/) delivered to the intact ear at 50 dB SL. The latencies and amplitudes of the early exogenous components (N100 and P150) were measured using temporal scalp electrodes. 相似文献99.
We consider the Schrödinger system with Newton-type interactions that was derived by R. Klein, A. Majda and K. Damodaran (1995) [17] to modelize the dynamics of N nearly parallel vortex filaments in a 3-dimensional homogeneous incompressible fluid. The known large time existence results are due to C. Kenig, G. Ponce and L. Vega (2003) [16] and concern the interaction of two filaments and particular configurations of three filaments. In this article we prove large time existence results for particular configurations of four nearly parallel filaments and for a class of configurations of N nearly parallel filaments for any N?2. We also show the existence of travelling wave type dynamics. Finally we describe configurations leading to collision. 相似文献
100.
Larcher D Delobel B Dantras-Laffont L Simon E Blach JF Baudrin E 《Inorganic chemistry》2010,49(23):10949-10955
In this paper, we detailed the formation/evolution of precipitates in alcoholic media containing Co(II+) and Li(+) species, together with the evolution of the composition and structure/texture of the resulting solid phases during the aging process at controlled constant temperature. While the end product is found to be well-crystallized HT-LiCoO(2), its formation is shown to result from a two-step process enlisting the initial fast precipitation of β-HCoO(2) and then its slow dissolution followed by recrystallization of the lithium-containing material. These results were obtained through combined X-ray diffraction, Raman and IR spectroscopy, elemental and oxidation-state analysis, and high-resolution transmission electron microscopy/selected-area electron diffraction observations. Depending on the cationic concentration, the size of the precipitated material can be controlled within the nanometric range. The electrochemical performances of these aged materials are slightly improved compared to those of the directly precipitated ones that we previously reported. The main limitation of these materials remains the presence of surface protons. 相似文献