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71.
This Note deals with the modeling of a structure made of straight elastic rods whose thickness tends to 0. We show that, upon an adequate scaling, the infimum of the total elastic energy tends to the minimum of a functional which depends on fields defined on the centerlines of the rods. 相似文献
72.
Tony Chave Sergei I. Nikitenko Dominique Granier Thomas Zemb 《Ultrasonics sonochemistry》2009,16(4):481-487
Herein, we report the sonochemical reactions with MSU-X mesoporous alumina (m-Al2O3) in aqueous solutions. Sonication (f = 20 kHz, I = 30 W cm?2, Waq = 0.67 W mL?1, T = 36–38 °C, Ar) causes significant acceleration of m-Al2O3 dissolution in the pH range of 4–11. Moreover, power ultrasound has a dramatic effect on the textural properties and phase composition of m-Al2O3. Short-time sonication at pH = 4 leads to the formation of nanorods and nanofibers of boehmite, AlO(OH). Prolonged ultrasonic treatment causes high aspect morphology transformation to aggregated nanosheets in weakly acid solutions or plated nanocrystals in alkaline solutions. Sonochemical products in alkaline medium are composed principally from boehmite and small amounts of bayerite, Al(OH)3. Silent hydrolysis of m-Al2O3 yields boehmite at pH = 4 and bayerite at pH = 11. The effect of ultrasound on the textural properties of mesoporous alumina as well as on the transformation of nanosized bayerite to boehmite can be consistently attributed to the transient strong heating of the liquid shell surrounding the cavitation bubble which caused the chemical processes similar to those occurred during hydrothermal treatment. 相似文献
73.
An efficient one-step synthesis of 1,1-dipfienyl-1-silacyclopent-3-ene 1 is reported. 相似文献
74.
Easy two‐step synthesis of a series of dithiines was performed from succinic anhydride via cyclization of the corresponding 4‐(alkylamino)‐4‐oxobutanoic acids (succinamic acids). The reaction, carried out in polar aprotic solvents, gave 4,8‐dithiine‐indacene‐1,3,5,7‐tetraones (diimides 3) via 3,7‐bis‐4,8‐dithia‐indacene‐1,5‐diones (diisoimides 2), which could be isolated. Surprisingly, in this reaction, thionyl chloride appeared as an oxidant, and this process seemed to be useful for the syntheses of S‐containing heterocyclic compounds such as 1,4‐dithiins. A mechanistic pathway was considered. 相似文献
75.
A two-step synthesis of a set of arylmenthones 3 from R(+)-pulegone 2 via their silylenolethers 4 is proposed leading in high yields to 8-arylmenthols 1. 相似文献
76.
Alain Valla Nathalie Méheux Dominique Cartier Benoist Valla Laurent Dufossé 《合成通讯》2013,43(2):184-190
A synthesis of a new C-15 phosphorus ylide from a C-14 enaminone is reported. This reagent, which undergoes selective 1,2- or 1,4-additions with saturated and unsaturated aldehydes, may find some synthetic use for the preparation of β-end-group retinoid derivatives. 相似文献
77.
Pascal Munier Marie-Béatrice Giudicelli Dominique Picq et Daniel Anker 《Journal of carbohydrate chemistry》2013,32(8):1225-1230
Abstract L'hydrolyse acide des acétals et en particulier des osides fait intervenir un carbocation intermédiaire stabilisé par l'oxygène voisin; un substituant électroattracteur en α de l'atome d'oxygène ou de carbone d'un tel cation déstabilise cedernier et rend l'hydrolyse des acétals plus difficile. C'est ainsi que pour un 2-méthoxy-tétrahydropyrane, le remplacement en C-6 d'un groupement CH2OH par CO2Et1 provoque une diminution de la vitesse d'hydrolyse d'un facteur de 200. Il est également bien connu que les 2-désoxy glycosides sont hydrolysés bien plus rapidement que leurs analogues 2-hydroxylés. Le même résultat est obtenu avec un atome d'halogène; c'est ainsi que Horton et coll.2 en introduisant un atome d'iode en position 2′ d'analogues de la daunorubicine et de l'adriamycine ont pu augmenter leur efficacité in vivo. Compte tenu de la taille réduite de l'atome de fluor qui modifie peu l'encombrement de la molécule, plusieurs travaux ont été consacrés à l'introduction d'un fluor en position 2 d'osides pour ralentir leur vitesse d'hydrolyse in vivo. 3-5 Cette même démarche a conduit d'autres auteurs à synthétiser des 2,2-difluorosucres.6 On pouvait donc envisager de remplacer l'hydrogène en C-1 de certains sucres par un groupement trifluorométhyle pour obtenir ainsi une nouvelle classe d'osides, dont la liaison osidique serait très stabilisée, ce qui devrait accroître leur durée de vie in vivo; on sait en effet 7 que les acétals de trifluorométhylcétones sont très difficiles à hydrolyser. Nous avons récemment décrit8 l'obtention des composés 1 et 9 et, on pouvait envisager de substituer l'hydroxyle anomérique de tels 2-uloses par divers nucléophiles. Les substitution nucléophiles en α d'un groupe CF3 sont difficiles9,10 et font en général intervenir un carbocation du type CF3-C+R1-XR2 stabilisé par un hétéroatome X(O, S)11-15 ou par un phényle.9 Ce carbocation est formé dans quelques cas par voie électrochimique,14-15 mais, dans la plupart des travaux, il résulte soit de la rupture d'une liaison CR1-Y assistée par un acide de Lewis soit de la solvolyse de cette liaison.9 Pour éviter l'emploi d'un acide de Lewis incompatible avec des groupes protecteurs acido-sensibles, nous avons mésylé l'hydroxyle anomérique pour obtenir un meilleur groupe partant. Nous décrivons dans cette note les résultats préliminaires obtenus principalement par action de divers nucléophiles sur ces mésylates. 相似文献
78.
Dominique Lafont Paul Boullanger Yves Chevalier 《Journal of carbohydrate chemistry》2013,32(4-5):533-550
Abstract Twelve N-acetyl or NH2-free D-glucosaminyl bolaamphiphiles have been synthesized by the intermediate of N-allyloxycarbonyl-d-glucosaminyl precursors. Thus, glycosylation of α,ω-diols with 1,3,4,6-tetra-O-acetyl-2-allyloxycarbonylamino-2-deoxy-β-d-glucopyranose (1) gave the bis(glycosides) 2a-h in good yields and without column chromatography. Alkaline treatment of these derivatives followed by acetylation gave the peracetylated N-acetyl compounds 3a-h which were further deprotected by the Zemplén deacetylation procedure to the N-acetyl-d-glucosaminyl bolaamphiphiles 4a-h. The bis(glycosides) 2c,d,g were also transformed into the O-acetylated amino-free derivatives 5c,d,g by chemospecific deprotection of the N-allyloxycarbonyl groups with palladium (0). Further deprotection of the ester functions led to the completely deprotected bolaamphiphiles 7c,d,g with high yields. Fully deprotected compounds 7a,d,g,h were also obtained from 2a,d,g,h by alkaline treatment and purification by column chromatography. Surface tension measurements were realized for aqueous solutions containing the soluble bolaamphiphiles. 相似文献
79.
Dr. Matthieu Fonvielle Dénia Mellal Delphine Patin Maxime Lecerf Dr. Didier Blanot Dr. Ahmed Bouhss Dr. Marco Santarem Dr. Dominique Mengin‐Lecreulx Dr. Matthieu Sollogoub Dr. Michel Arthur Dr. Mélanie Ethève‐Quelquejeu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(4):1357-1363
Peptidyl–RNA conjugates have various applications in studying the ribosome and enzymes participating in tRNA‐dependent pathways such as Fem transferases in peptidoglycan synthesis. Herein a convergent synthesis of peptidyl–RNAs based on Huisgen–Sharpless cycloaddition for the final ligation step is developed. Azides and alkynes are introduced into tRNA and UDP‐MurNAc‐pentapeptide, respectively. Synthesis of 2′‐azido RNA helix starts from 2′‐azido‐2′‐deoxyadenosine that is coupled to deoxycytidine by phosphoramidite chemistry. The resulting dinucleotide is deprotected and ligated to a 22‐nt RNA helix mimicking the acceptor arm of Ala‐tRNAAla by T4 RNA ligase. For alkyne UDP‐MurNAc‐pentapeptide, meso‐cystine is enzymatically incorporated into the peptidoglycan precursor and reduced, and L ‐Cys is converted to dehydroalanine with O‐(mesitylenesulfonyl)hydroxylamine. Reaction of but‐3‐yne‐1‐thiol with dehydroalanine affords the alkyne‐containing UDP‐MurNAc‐pentapeptide. The CuI‐catalyzed azide alkyne cycloaddition reaction in the presence of tris[(1‐hydroxypropyl‐1H‐1,2,3‐triazol‐4‐yl)methyl]amine provided the peptidyl‐RNA conjugate, which was tested as an inhibitor of non‐ribosomal FemXWv aminoacyl transferase. The bi‐substrate analogue was found to inhibit FemXWv with an IC50 of (89±9) pM , as both moieties of the peptidyl–RNA conjugate contribute to high‐affinity binding. 相似文献
80.
Dr. Chih‐Kai Liang Dr. Galina V. Dubacheva Dr. Thierry Buffeteau Dr. Dominique Cavagnat Dr. Philippe Hapiot Dr. Bruno Fabre Prof. James H. R. Tucker Dr. Dario M. Bassani 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(38):12748-12758
The synthesis of an anthracene‐bearing photoactive barbituric acid receptor and its subsequent grafting onto azide‐terminated alkanethiol/Au self‐assembled monolayers by using an CuI‐catalyzed azide–alkyne reaction is reported. Monolayer characterization using contact‐angle measurements, electrochemistry, and spectroscopic ellipsometry indicate that the monolayer conversion is fast and complete. Irradiation of the receptor leads to photodimerization of the anthracenes, which induces the open‐to‐closed gating of the receptor by blocking access to the binding site. The process is thermally reversible, and polarization‐modulated IR reflection–absorption spectroscopy indicates that photochemical closure and thermal opening of the surface‐bound receptors occur in 70 and 100 % conversion, respectively. Affinity of the open and closed surface‐bound receptor was characterized by using force spectroscopy with a barbituric‐acid‐modified atomic force microscope tip. 相似文献