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161.
Yu‐Hao Li Shaoping Zheng Dr. Yves‐Marie Legrand Dr. Arnaud Gilles Dr. Arie Van der Lee Dr. Mihail Barboiu 《Angewandte Chemie (International ed. in English)》2018,57(33):10520-10524
Self‐assembled alkyl‐ureido‐benzo‐15‐crown‐5‐ethers are selective ionophores for K+ cations, which are preferred to Na+ cations. The transport mechanism is determined by the optimal coordination rather than classical dimensional compatibility between the crown ether hole and the cation diameter. Herein, we demonstrate that systematic changes of the structure lead to unexpected modifications in the cation‐transport activity and suffice to produce adaptive selection. We show that the main contribution to performance arises from optimal constraints on the conformational freedom, which are determined by the binding macrocycles, the nature of the hydrogen‐bonding groups, and the hydrophobic tails. Simple changes to the flexible 15‐crown‐5‐ether lead to selective carriers for Na+. Hydrophobic stabilization of the channels through mutual interactions between lipids and variable hydrophobic tails appears to be an important cause of increased activity. Oppositely, restricted translocation is achieved when constrained hydrogen‐bonded macrocyclic relays are less dynamic in a pore superstructure. 相似文献
162.
Coulbois Thierry; Hilion Arnaud; Lustig Martin 《Journal London Mathematical Society》2008,78(3):755-766
We study the map which associates to a current its support (whichis a lamination). We show that this map is Out(FN)-equivariant,not injective, not surjective and not continuous. However itis semi-continuous and almost surjective in a suitable sense.Given an -tree T (with dense orbits) in the boundary of outerspace and a current µ carried by the dual lamination ofT, we define a dual pseudo-distance dµ on T. When thetree and the current come from a measured geodesic laminationon a surface with boundary, the dual distance is the originaldistance of the tree T. In general, such a good correspondencedoes not occur. We prove that when the tree T is the attractivefixed point of a non-geometric irreducible, with irreduciblepowers, outer automorphism, the dual lamination of T is uniquelyergodic and the dual distance dµ is either zero or infinitethroughout T. 相似文献
163.
A one step synthesis of (di)alkylamino-substituted 1,2,4,5-tetrazines direct from 3,6-disubstituted-1,2-dihydro-1,2,4,5-tetrazine precursors is described. A comparative study revealed that the described method not only avoids the up-to-now required oxidation step but also lower reaction times and/or temperatures compared to usual protocols. The efficiency of the reaction was highlighted by a practical synthesis of 3,6-bis(methylamino)-1,2,4,5-tetrazine using aqueous methylamine. Other primary and secondary amines were also found to give disubstitution products when reacted with 3,6-bis(methylsulfanyl)-1,2,4,5-dihydrotetrazine. 相似文献
164.
Salaün A Mocquet C Perochon R Lecorgne A Le Grel B Potel M Le Grel P 《The Journal of organic chemistry》2008,73(21):8579-8582
The cyclization of aza-beta(3)-tetrapeptides gives access to new CTP (cyclotetrapeptide) analogues. These stereocontrolled templates are assembled without any asymmetric synthesis. X-ray crystallographic structure and NMR analysis show that the macrocyclic scaffold is characterized by a fully cooperative intramolecular H-bond network, in sharp contrast with the nanotubular assemblies observed for beta(3)-cyclotetrapeptides. This folding property reduces considerably the polarity of aza-beta(3)-tetrapeptides and should be useful in addressing intracellular targets. 相似文献
165.
Haak RM Berthiol F Jerphagnon T Gayet AJ Tarabiono C Postema CP Ritleng V Pfeffer M Janssen DB Minnaard AJ Feringa BL de Vries JG 《Journal of the American Chemical Society》2008,130(41):13508-13509
The direct chemo-enzymatic DKR of racemic beta-haloalcohols is reported, yielding the corresponding optically active epoxides in a single step. The mutant haloalcohol dehalogenase HheC Cys153Ser Trp249Phe is used for the asymmetric ring closure, whereas racemization of the remaining enantiomer of the haloalcohol is achieved using the new iridacycle 3, one of the most effective racemization catalysts to date for beta-haloalcohols. 相似文献
166.
Audrey Boutonnet Arnaud Morin Pierre Petit Patricia Vicendo Véréna Poinsot François Couderc 《Analytica chimica acta》2016
Pulsed lasers are widely used in capillary electrophoresis (CE) studies to provide laser induced fluorescence (LIF) detection. Unfortunately pulsed lasers do not give linear calibration curves over a wide range of concentrations. While this does not prevent their use in CE/LIF studies, the non-linear behavior must be understood. Using 7-hydroxycoumarin (7-HC) (10–5000 nM), Tamra (10–5000 nM) and tryptophan (1–200 μM) as dyes, we observe that continuous lasers and LEDs result in linear calibration curves, while pulsed lasers give polynomial ones. The effect is seen with both visible light (530 nm) and with UV light (355 nm, 266 nm). In this work we point out the formation of byproducts induced by pulsed laser upon irradiation of 7-HC. Their separation by CE using two Zeta LIF detectors clearly shows that this process is related to the first laser detection. All of these photodegradation products can be identified by an ESI-/MS investigation and correspond to at least two 7HC dimers. By using the photodegradation model proposed by Heywood and Farnsworth (2010) and by taking into account the 7-HC results and the fact that in our system we do not have a constant concentration of fluorophore, it is possible to propose a new photochemical model of fluorescence in LIF detection. The model, like the experiment, shows that it is difficult to obtain linear quantitation curves with pulsed lasers while UV-LEDs used in continuous mode have this advantage. They are a good alternative to UV pulsed lasers. An application involving the separation and linear quantification of oligosaccharides labeled with 2-aminobezoic acid is presented using HILIC and LED (365 nm) induced fluorescence. 相似文献
167.
168.
Inside Cover: Kinetics of Reactive Modules Adds Discriminative Dimensions for Selective Cell Imaging (ChemPhysChem 10/2016) 下载免费PDF全文
169.
170.
The short and efficient asymmetric synthesis of (-)-1-hydroxyquinolizidinone was achieved in seven steps and 25.2% overall yield from readily available 5-chloropentanal. It is a key intermediate in the formal syntheses of (-)-homopumilotoxin 223G and (-)-epiquinamide. 相似文献