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181.
Nicolas Le Moigne Emilie Montes Catherine Pannetier Herman Höfte Patrick Navard 《Macromolecular Symposia》2008,262(1):65-71
The dissolution of cotton fibres has been studied at different development stages before and after the onset of secondary wall deposition in solvents of varying quality. We show that the dissolution of the primary wall is inefficient even in good solvents. In moderately good solvents, the inside of the secondary wall dissolves by fragmentation, whereas the outside of the secondary wall swells. These data demonstrate the existence of a centripetal radial gradient in the dissolution capacity within the fibre, which must be related to age-dependent structural variation in the cell wall layers. 相似文献
182.
Takashi Nagano Dr. Jiři Pospíšil Dr. Guillaume Chollet Dr. Saskia Schulthoff Volker Hickmann Dipl.‐Chem. Emilie Moulin Dr. Jennifer Herrmann Dipl.‐Chem. Rolf Müller Prof. Alois Fürstner Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(38):9697-9706
A multitasking C‐silylation strategy using the readily available compound 26 as a surrogate for cinnamic acid represents the key design element of a total synthesis of all known members of the ipomoeassin family of resin glyosides. This protecting group maneuver allows the unsaturated acids decorating the glucose subunit of the targets to be attached at an early phase of the synthesis, prevents their participation in the ruthenium‐catalyzed ring‐closing metathesis (RCM) used to form the macrocyclic ring, and protects them against reduction during the hydrogenation of the resulting cycloalkene over Wilkinson’s catalyst. As the C‐silyl group can be concomitantly removed with the O‐TBS substituent using tris(dimethylamino)sulfonium difluorotrimethylsilicate (TASF) in acetonitrile, no separate protecting group manipulations were necessary in the final stages, thus contributing to a favorable overall “economy of steps”. In addition to the naturally occurring ipomoeassins, a small set of synthetic analogues has also been prepared by “diverted total synthesis”. The cytotoxicity of these compounds was assayed with two different cancer cell lines. The recorded data confirm previous findings that the acylation‐ and oxygenation pattern of these amphiphilic glycoconjugates is highly correlated with their biological activity profile. Ipomoeassin F turned out to be the most promising member of the series, showing IC50 values in the low nanomolar range. 相似文献
183.
184.
Banide EV Ortin Y Seward CM Harrington LE Müller-Bunz H McGlinchey MJ 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(12):3275-3286
1-Phenyl-3,3-biphenyleneallene (2), the base-catalyzed rearrangement product of 9-phenylethynylfluorene (1) yields a yellow, head-to-tail dimer 6 that, upon gentle warming, is converted to the red tail-to-tail isomer trans-3,4-diphenyl-1,2-bis(fluorenylidene)cyclobutane (7), in which the two fluorenylidene moieties severely overlap. The helical sense of the fluorenylidene moieties in 7 matches that of the phenyl substituents, and the interplanar angle between the fluorenylidene moieties is 41 degrees . At 80 degrees C, 6 isomerizes to orange cis-3,4-diphenyl-1,2-bis(fluorenylidene)cyclobutane (8), which at 110 degrees C is converted to orange trans diastereomer 9, whereby the helicity of the overlapping fluorenylidene moieties is reversed from that in 7 such that they are aligned with the ring hydrogen atoms, and the interplanar angle between the fluorenylidene moieties is now 60 degrees . At 180 degrees C, 6 rearranges to dispirodihydrotetracene 3 and blue, electroluminescent diindenotetracene 4, which is readily oxidized to peroxide 5. In the solid state, both 3 and 4 adopt structures with Ci symmetry (only an inversion center) such that the central polycyclic framework is nonplanar. Deprotonation of yellow head-to-tail allene dimer 6 with tBuOK in DMSO and reprotonation with HOAc yields the [1,3]-hydrogen migration product 10, in which the proton originally on the cyclobutane ring is now sited at C9 on the exocyclic fluorenyl substituent. Analogously, deprotonation and reprotonation of orange dimer 9 furnishes [1,3]-hydrogen migration product 11. Side product 17, formed during the synthesis of 1 from 9-phenylethynylfluoren-9-ol, BF3 and Et3SiH, was shown to be a silyl-indene spiro-linked to C9 of fluorene. All products were characterized by NMR spectroscopy and X-ray crystallography, and the mechanisms of these interconversions are discussed. 相似文献
185.
Moulin E Barluenga S Totzke F Winssinger N 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(34):8819-8834
Pochonins A-F were recently characterized as six new members of the naturally occurring family of 14-membered resorcylic acid lactones. As there are a high number of ATPase and kinase inhibitors among natural resorcylic lactones, a library based on the pochonin scaffold, with five points of diversity, was prepared which includes diversity beyond that of the natural analogues. The library was synthesized by using solid-supported reagents amenable to automation. Testing the library for its inhibition against a panel of 24 kinases at 10 microM afforded a >14 % hit rate. These results demonstrate the potential of the resorcylides towards the inhibition of therapeutically relevant kinases. 相似文献
186.
Montse Lpez‐Martínez Manuel Lpez‐Ortiz Maria Elena Antinori Emilie Wientjes Alba Nin‐Hill Carme Rovira Roberta Croce Ismael Díez‐Prez Pau Gorostiza 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(38):13414-13418
The transport of electrons along photosynthetic and respiratory chains involves a series of enzymatic reactions that are coupled through redox mediators, including proteins and small molecules. The use of native and synthetic redox probes is key to understanding charge transport mechanisms and to the design of bioelectronic sensors and solar energy conversion devices. However, redox probes have limited tunability to exchange charge at the desired electrochemical potentials (energy levels) and at different protein sites. Herein, we take advantage of electrochemical scanning tunneling microscopy (ECSTM) to control the Fermi level and nanometric position of the ECSTM probe in order to study electron transport in individual photosystem I (PSI) complexes. Current–distance measurements at different potentiostatic conditions indicate that PSI supports long‐distance transport that is electrochemically gated near the redox potential of P700, with current extending farther under hole injection conditions. 相似文献
187.
We present for the first time a Nd:YVO(4) laser emitting at 1064 nm intracavity pumped at 912 nm by a Nd:GdVO(4) laser. We carried out a model to design the system properly, and laser performance was experimentally investigated. Intracavity sum-frequency mixing at 912 and 1064 nm was then realized in a BiBO crystal to reach the blue range. We obtained a cw output power of 155 mW at 491 nm with a pump laser diode emitting 20 W at 808 nm. 相似文献
188.
Nonnegative matrices with the property that the group inverse of the matrixis equal to a power of the matrix are characterized. The special case of the Moore- Penrose inverse is considered. The situation when the matrix is stochastic is examined. 相似文献
189.
Fennell Burns Miroslav Fiedler Emilie Haynsworth 《Linear algebra and its applications》1974,8(6):547-559
Some results are obtained relating topological properties of polyhedral cones to algebraic properties of matrices whose columns are the extremal vectors of the cone. In addition, several characterizations of positive operators on polyhedral cones are given. 相似文献
190.
Emilie Devijver 《Advances in Data Analysis and Classification》2017,11(2):243-279
Finite mixture regression models are useful for modeling the relationship between response and predictors arising from different subpopulations. In this article, we study high-dimensional predictors and high-dimensional response and propose two procedures to cluster observations according to the link between predictors and the response. To reduce the dimension, we propose to use the Lasso estimator, which takes into account the sparsity and a maximum likelihood estimator penalized by the rank, to take into account the matrix structure. To choose the number of components and the sparsity level, we construct a collection of models, varying those two parameters and we select a model among this collection with a non-asymptotic criterion. We extend these procedures to functional data, where predictors and responses are functions. For this purpose, we use a wavelet-based approach. For each situation, we provide algorithms and apply and evaluate our methods both on simulated and real datasets, to understand how they work in practice. 相似文献