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Hang Yin Qian Cheng Roselyne Rosas Prof. Stéphane Viel Dr. Valérie Monnier Prof. Laurence Charles Prof. Didier Siri Dr. Didier Gigmes Dr. Olivier Ouari Prof. Ruibing Wang Dr. Anthony Kermagoret Dr. David Bardelang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(54):12552-12559
A viologen derivative carrying a benzimidazole group ( V-P-I 2+; viologen–phenylene–imidazole V-P-I ) can be dimerized in water using cucurbit[8]uril (CB[8]) in the form of a 2:2 complex resulting in a negative shift of the guest pKa, by more than 1 pH unit, contrasting with the positive pKa shift usually observed for CB-based complexes. Whereas 2:2 complex protonation is unclear by NMR, silver cations have been used for probing the accessibility of the imidazole groups of the 2:2 complexes. The protonation capacity of the buried imidazole groups is reduced, suggesting that CB[8] could trigger proton release upon 2:2 complex formation. The addition of CB[8] to a solution containing V-P- I 3+ indeed released protons as monitored by pH-metry and visualized by a coloured indicator. This property was used to induce a host/guest swapping, accompanied by a proton transfer, between V-P-I 3+ ⋅ CB[7] and a CB[8] complex of 1-methyl-4-(4-pyridyl)pyridinium. The origin of this negative pKa shift is proposed to stand in an ideal charge state, and in the position of the two pH-responsive fragments inside the two CB[8] which, alike residues engulfed in proteins, favour the deprotonated form of the guest molecules. Such proton release triggered by a recognition event is reminiscent of several biological processes and may open new avenues toward bioinspired enzyme mimics catalyzing proton transfer or chemical reactions. 相似文献
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In a recent paper [17] we proposed a stochastic algorithm which generates optimal probabilities for the decompression of
an image represented by the fixed point of an IFS system (SAOP). We show here that such an algorithm is in fact a non trivial
example of Generalized Random System with Complete Connections. We also exhibit a generalization which could represent the
solution to the inverse problem for an image with grey levels, if a fixed set of contraction maps is available.
Received: 1 July 2002 相似文献
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We obtain a simple derivation of Korzhik's result on the burst distribution of a linear code. 相似文献
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Gérard Audran Matisse Bim Batsiandzy Ibanou Paul Brémond Sylvain R. A. Marque Germain Obame Valérie Roubaud Didier Siri 《Journal of Physical Organic Chemistry》2014,27(5):387-391
In a recent work (Org. Lett. 2012, 14, 358–361), we showed that the activation by benzylation of alkoxyamine 1 (diethyl (1‐(tert‐butyl(1‐(pyridin‐4‐yl)ethoxy)amino)‐2,2‐dimethylpropyl)phosphonate) afforded a surprisingly large C–ON bond homolysis rate constant kd. Taking advantage of the easy preparation of para‐X‐benzyl‐activated alkoxyamines 2 and of the presence of a shielding methylene group between the two aromatic moieties, we investigated the long range (10 bonds between the X group and the C–ON bond) polar effect for X = H, F, OMe, CN, NO2, NMe2, +NHMe2,Br?. It was observed that the effect was weak (4‐fold) and mainly due to the zwiterionic mesomeric forms generated by the presence of group X on the para position, i.e. kd increased for CN and NO2 and decreased for OMe, NMe2 and +NMe2H,Br?. DFT calculations at the B3LYP/6‐31G(d,p) level were performed to determine orbital interactions (natural bond orbital (NBO) analysis), Mulliken and NBO charges which support the reactivity described. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
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Escoubet S Gastaldi S Timokhin VI Bertrand MP Siri D 《Journal of the American Chemical Society》2004,126(39):12343-12352
Thiols mediate the radical isomerization of allylic amines into enamines. The reaction results in the cleavage of the allylic C-N bond, after treatment with aqueous HCl. The mechanism involves the abstraction of an allylic hydrogen alpha to nitrogen by thiyl radical, followed by a return hydrogen transfer from the thiol to the carbon gamma to nitrogen in the intermediate allylic radical. The scope and limitations of the reaction with respect to the nature of the thiol, to the structure of the allylic chain, and to the nature of the substituents at nitrogen were investigated. The experimental results were interpreted on the ground of DFT calculations of the C-Halpha BDE in the starting allylic amines, and of the C-Hgamma BDE in the resulting enamines. The efficiency of the initial hydrogen transfer is the first requirement for the reaction to proceed. A balance must be found between the S-H BDE and the two above-mentioned C-H BDEs. The incidence of stereoelectronic factors was analyzed through NBO calculations performed on the optimized geometries of the starting allylic amines. Additional calculations of the transition structures and subsequent tracing of the reaction profiles were performed for the abstraction of Halpha from both the allyl and the prenyl derivatives by p-TolS(*). The latter allowed us to estimate the rate constant for the abstraction of hydrogen by thiyl radical from an N-prenylamine and an N-allylamine. 相似文献
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We accidentally found that the F→OH conversion by direct hydroxylation of electron deficient aryls above 150 °C allows the isolation of the precursors of novel quinonemonoimines 9, previously unknown. 相似文献