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131.
Christian Amatore Prof. Stéphane Arbault Dr. Imelda Bonifas Dr. Frédéric Lemaître Dr. Yann Verchier 《Chemphyschem》2007,8(4):578-585
Several previous reports have discussed the effects of external osmolarity on vesicular exocytotic processes. However, few of these studies considered hypotonic conditions on chromaffin cells. Herein, the exocytosis of catecholamines by chromaffin cells was investigated in a medium of low osmolarity (200 mOsm) by amperometry at carbon fiber microelectrodes. It is observed that the frequency of the exocytotic events is significantly higher under hypotonic conditions than under physiological conditions (315 mOsm). This further confirms that the swelling of the polyelectrolytic matrix (which follows ionic exchanges) contained in dense core vesicles is the energetic driving force of the exocytotic phenomenon, being favored by a lower osmolarity. The mean amount of catecholamines released during secretory events also increases importantly under the hypotonic condition. This may be rationalized by the coexistence of two distinct populations of dense core vesicles with a relative content ratio of 4.7. The larger content population is favored under hypotonic conditions but plays only a side role under isotonic conditions. 相似文献
132.
A common precursor, tetronic acid, was used in the synthesis of several vulpinic acids and pulvinic acids, which are pigments found in several lichens and mushrooms. The key features of this method are a two-step alkylidenation of benzyl tetronate and a Suzuki-Miyaura cross-coupling. The synthesis of several natural products, vulpinic acid, pinastric acid, xerocomic acid is described. 相似文献
133.
Bin Luo Jean-Fran?ois Aujol Yann Gousseau Sa?d Ladjal Henri Ma?tre 《IEEE transactions on image processing》2007,16(10):2503-2514
We study the problem of finding the characteristic scale of a given satellite image. This feature is defined so that it does not depend on the spatial resolution of the image. This is a different problem than achieving scale invariance, as often studied in the literature. Our approach is based on the use of a linear scale space and the total variation (TV). The critical scale is defined as the one at which the normalized TV reaches its maximum. It is shown experimentally, both on synthetic and real data, that the computed characteristic scale is resolution independent. 相似文献
134.
Dr. Ko Urushibara Dr. Yann Ferrand Prof. Zhiwei Liu Dr. Kosuke Katagiri Dr. Masatoshi Kawahata Estelle Morvan Ryan D'Elia Prof. Vojislava Pophristic Prof. Aya Tanatani Prof. Ivan Huc 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(43):11205-11215
The alkylation of some secondary amide functions with a dimethoxybenzyl (DMB) group in oligomers of 8-amino-2-quinolinecarboxylic acid destabilizes the otherwise favored helical conformations, and allows for cyclization to take place. A cyclic hexamer and a cyclic heptamer were produced in this manner. After DMB removal, X-ray crystallography and NMR show that the macrocycles adopt strained conformations that would be improbable in noncyclic species. The high helix folding propensity of the main chain is partly expressed in these conformations, but it remains frustrated by macrocyclization. Despite being homomeric, the macrocycles possess inequivalent monomer units. Experimental and computational studies highlight specific fluxional pathways within these structures. Extensive simulated annealing molecular dynamics allow for the prediction of the conformations for larger macrocycles with up to sixteen monomers. 相似文献
135.
Peter M. Chapple Julien Cartron Ghanem Hamdoun Samia Kahlal Marie Cordier Hassan Oulyadi Jean-Franois Carpentier Jean-Yves Saillard Yann Sarazin 《Chemical science》2021,12(20):7098
The first families of alkaline-earth stannylides [Ae(SnPh3)2·(thf)x] (Ae = Ca, x = 3, 1; Sr, x = 3, 2; Ba, x = 4, 3) and [Ae{Sn(SiMe3)3}2·(thf)x] (Ae = Ca, x = 4, 4; Sr, x = 4, 5; Ba, x = 4, 6), where Ae is a large alkaline earth with direct Ae–Sn bonds, are presented. All complexes have been characterised by high-resolution solution NMR spectroscopy, including 119Sn NMR, and by X-ray diffraction crystallography. The molecular structures of [Ca(SnPh3)2·(thf)4] (1′), [Sr(SnPh3)2·(thf)4] (2′), [Ba(SnPh3)2·(thf)5] (3′), 4, 5 and [Ba{Sn(SiMe3)3}2·(thf)5] (6′), most of which crystallised as higher thf solvates than their parents 1–6, were established by XRD analysis; the experimentally determined Sn–Ae–Sn′ angles lie in the range 158.10(3)–179.33(4)°. In a given series, the 119Sn NMR chemical shifts are slightly deshielded upon descending group 2 from Ca to Ba, while the silyl-substituted stannyls are much more shielded than the phenyl ones (δ119Sn/ppm: 1′, −133.4; 2′, −123.6; 3′, −95.5; 4, −856.8; 5, −848.2; 6′, −792.7). The bonding and electronic properties of these complexes were also analysed by DFT calculations. The combined spectroscopic, crystallographic and computational analysis of these complexes provide some insight into the main features of these unique families of homoleptic complexes. A comprehensive DFT study (Wiberg bond index, QTAIM and energy decomposition analysis) points at a primarily ionic Ae–Sn bonding, with a small covalent contribution, in these series of complexes; the Sn–Ae–Sn′ angle is associated with a flat energy potential surface around its minimum, consistent with the broad range of values determined by experimental and computational methods.The complete series of heterobimetallic alkaline-earth distannyls [Ae{SnR3}2·(thf)x] (Ae = Ca, Sr, Ba) have been prepared for R = Ph and SiMe3, and their bonding and electronic properties have been comprehensively investigated. 相似文献
136.
Jean-Daniel Malcor Yann BrouilletteJulien Graffion Kim SpielmannNicolas Masurier Ludovic T. MaillardJean Martinez Vincent Lisowski 《Tetrahedron》2014
A convenient synthesis of pyrrolo[3,2-d][1,3]oxazine-2,4-dione 4 is described and its reactivity towards various nucleophiles studied. The regioselective ring opening of anhydride 4 or its N-alkylated analog 25 in the presence of alanine or proline afforded, respectively, imidazolidinedione 22 and N-protected pyrrolo[3,2-e][1,4]diazepines 30 and 31 in a one-pot process. In a last part of this study, an alternative route to produce a library of eight non protected pyrrolo[3,2-e][1,4]diazepine-2,5-diones 35a–h is described to overcome the limited reactivity of anhydride 4. 相似文献
137.
Bauer RC Gloaguen Y Lutz M Reek JN de Bruin B van der Vlugt JI 《Dalton transactions (Cambridge, England : 2003)》2011,40(35):8822-8829
The synthesis of a new, all-phosphorus pincer PP(NEt2)P ligand L3(NEt2), which is derived from 2-indolylphosphine and features a central N(2)P(NEt(2)) core, is described. This 'PPP' species shows coordination toward Rh as a neutral trisphosphine ligand. Tridentate diphenylphosphine-derived PP(H)P ligands L1(H) and L2(H), featuring a secondary phosphine core, show 'ambivalent' coordination, acting as persistent neutral triphosphine ligands with Rh, and as easily-formed monoanionic phosphido(bisphosphine) pincer ligands toward Pd. These subtle differences, which might be more general for group 9 and 10 metal complexes with this ligand set, are explained by comparative DFT calculations (BP86; def2-TZVP level of theory) for the Rh and Pd species involved, including those with the structurally related PN(H)P ligands. The optimized structure for complex PdCl(L2) indicates minimal overlap of available Pd d-orbitals with the lone pair of the central, deprotonated phosphorus atom (formally a phosphido fragment), suggesting that it behaves predominantly like a bulky phosphine instead of a phosphido fragment. 相似文献
138.
Pointillart F Le Gal Y Golhen S Cador O Ouahab L 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(37):10397-10404
The reactions between the [Ln(tta)(3)]·2H(2)O precursors (tta(-)=2-thenoyltrifluoroacetonate anion) and the tetrathiafulvalene-3-pyridine-N-oxide ligands (L(1)) lead to dinuclear complexes of formula [{Ln(tta)(3)(L(1))}(2)]·xCH(2)Cl(2) (x=0.5 for Ln=Dy(III) (1) and x=0 for Ln=Gd(III) (2)). The crystal structure reveals that two {Ln(tta)(3)} moieties are bridged by two donors through the nitroxide groups. The Dy(III) centre adopts a distorted square antiprismatic oxygenated polyhedron structure. The antiferromagnetic nature of the exchange interaction between the two Dy(III) ions has been determined by two methods: 1) an empirical method using the [Dy(hfac)(3)(L(2))(2)] mononuclear complex as a model (3) (hfac(-)=1,1,1,5,5,5-hexafluoroacetylacetonate anion, L(2)=tetrathiafulvaleneamido-2-pyridine-N-oxide ligand), and 2) assuming an Ising model for the Dy(III) ion giving an exchange energy of -2.30 cm(-1), g=19.2 in the temperature range of 2-10 K. The antiferromagnetic interactions have been confirmed by a quantitative determination of J for the isotropic Gd(III) derivative (J=-0.031 cm(-1), g=2.003). Compound 1 displays a slow magnetisation relaxation without applied external magnetic fields. Alternating current susceptibility shows a thermally activated behaviour with pre-exponential factors of 5.48(4)×10(-7) s and an energy barrier of 87(1) K. The application of an external field of 1.6 kOe compensates the antiferromagnetic interactions and opens a new quantum tunnelling path. 相似文献
139.
Audrey Cassen Yann Gloaguen Laure Vendier Carine Duhayon Amalia Poblador‐Bahamonde Christophe Raynaud Eric Clot Gilles Alcaraz Sylviane Sabo‐Etienne 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2014,126(29):7699-7703
Tuning the nature of the linker in a L∼BHR phosphinoborane compound led to the isolation of a ruthenium complex stabilized by two adjacent, δ‐C H and ε‐Bsp2 H, agostic interactions. Such a unique coordination mode stabilizes a 14‐electron “RuH2P2” fragment through connected σ‐bonds of different polarity, and affords selective B H, C H, and B C bond activation as illustrated by reactivity studies with H2 and boranes. 相似文献
140.
Dr. Michael L. Singleton Geert Pirotte Dr. Brice Kauffmann Dr. Yann Ferrand Dr. Ivan Huc 《Angewandte Chemie (International ed. in English)》2014,53(48):13140-13144
The postsynthetic modulation of capsules based on helical aromatic oligoamide foldamers would be a powerful approach for controlling their receptor properties without altering the initial monomer sequences. With the goal of developing a method to increase the size of a cavity within a helix, a single‐helical foldamer capsule was synthesized with a wide‐diameter central segment that was designed to intercalate with a second shorter helical strand. Despite the formation of stable double‐helical homodimers (Kdim>107 M ?1) by the shorter strand, when it was mixed with the single‐helical capsule sequence, a cross‐hybridized double helix was formed with Ka>105 M ?1. This strategy makes it possible to direct the formation of double‐helical heterodimers. On the basis of solution‐ and solid‐state structural data, this intercalation resulted in an increase in the central‐cavity size to give a new interior volume of approximately 150 Å3. 相似文献