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81.
82.
A comprehensive overview on methods applied for syntheses of β-amino-α-trifluoromethyl alcohols, including stereocontrolled variants, is presented. In addition, reported cases of the exploration of β-amino-α-trifluoromethyl alcohols for the preparation of trifluoromethylated peptidomimetics and other biologically active, fluorinated compounds are discussed. Attractive opportunities for their applications as organocatalysts are also presented. 相似文献
83.
84.
D. Brinkmann 《Applied magnetic resonance》2004,27(1-2):207-213
This presentation gives a personal review of nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) spin-lattice relaxation studies in cuprate superconductors mainly dealing with the YBa2Cu4O8 compound with many examples from the Zürich laboratory. The studies were performed in both the normal and the superconducting state with various NMR isotopes (e.g.,17O,63,65Cu,135,137Ba). The relatively broad signals were mostly obtained by a phase-alternating add-subtract spin-echo technique. We will discuss the general behavior of spin-lattice relaxation in the normal state and the calculation of the dynamic spin including an approach (on the basis of thet-J model) to calculate the relaxation for plane copper, oxygen, and yttrium. An application of the Luttingerliquid model to the relaxation of chain copper in YBa2Cu3O7 and YBa2Cu4O8 is also given. We then will deal with characteristic features of the YBa2Cu4O8 structure: the spin gap, an electronic crossover in the normal state, the single-spin fluid model, and the d-wave pairing. 相似文献
85.
86.
M. Morstein P.R. Willmott H. Spillmann M. Döbeli 《Applied Physics A: Materials Science & Processing》2002,75(6):647-654
High-quality thin films of ZrCyN1-y and the novel tribological material Zr0.8Al0.2CyN1-y have been grown by pulsed reactive crossed-beam laser ablation using Zr and Zr–Al ablation targets, respectively, and a pulsed
gas. The gas mixture provided the carbon and nitrogen for the solid-solution films. Control of the stoichiometry (i.e. y)
was determined by the relative partial pressures of the nitrogen- and carbon-containing gases. It was found that optimal control
of the film chemistry was achieved by using the least thermally reactive gases. In this manner, it was possible to activate
the gas species exclusively by collisions in the gas phase with the ablation-plume particles, thereby decoupling the chemistry
from surface processes. The films were characterized for their chemical, crystallographic, optical, and tribological properties.
All the films had very low impurity levels and a cubic rock salt crystal structure over the entire investigated temperature
range between 100 and 600 °C. Exceedingly high quality epitaxial films could be grown on MgO (001) at 600 °C. Films grown
on stainless steel were polycrystalline. The hardness of the films showed a maximum for both sets for stoichiometries predicted
by a recent theoretical model for hardness based on band-structure calculations. In addition, all the films had an exceptionally
low coefficient of friction versus steel.
Received: 22 August 2001 / Accepted: 3 March 2002 / Published online: 19 July 2002 相似文献
87.
Phase Behavior of a Designed Cyclopropyl Analogue of Monoolein: Implications for Low‐Temperature Membrane Protein Crystallization 下载免费PDF全文
Livia Salvati Manni Dr. Alexandru Zabara Dr. Yazmin M. Osornio Jendrik Schöppe Dr. Alexander Batyuk Prof. Dr. Andreas Plückthun Prof. Dr. Jay S. Siegel Prof. Dr. Raffaele Mezzenga Prof. Dr. Ehud M. Landau 《Angewandte Chemie (International ed. in English)》2015,54(3):1027-1031
Lipidic cubic phases (LCPs) are used in areas ranging from membrane biology to biodevices. Because some membrane proteins are notoriously unstable at room temperature, and available LCPs undergo transformation to lamellar phases at low temperatures, development of stable low‐temperature LCPs for biophysical studies of membrane proteins is called for. Monodihydrosterculin (MDS) is a designer lipid based on monoolein (MO) with a configurationally restricted cyclopropyl ring replacing the olefin. Small‐angle X‐ray scattering (SAXS) analyses revealed a phase diagram for MDS lacking the high‐temperature, highly curved reverse hexagonal phase typical for MO, and extending the cubic phase boundary to lower temperature, thereby establishing the relationship between lipid molecular structure and mesophase behavior. The use of MDS as a new material for LCP‐based membrane protein crystallization at low temperature was demonstrated by crystallizing bacteriorhodopsin at 20 °C as well as 4 °C. 相似文献
88.
Excursion to the World of Heptacyclic Compounds Made of Azulenes and Acetylenedicarboxylates 下载免费PDF全文
Yi Chen Erja Lehto Peter Uebelhart Anthony Linden Hans‐Jürgen Hansen 《Helvetica chimica acta》2015,98(7):913-937
Azulenes and acetylenedicarboxylates react under acid catalysis (Brønsted or Lewis) and form (2aRS,8aSR)‐2a,8a‐dihydrocyclopenta[cd]azulene‐1,2‐dicarboxylates as intermediate products, which then dimerize by central bond‐formation between C(2a1) and C(2′a1) and various peripheral C,C′‐atoms of the dihydroazulene fragments, depending on the substituents present. The reactions are often accompanied by the formation of side‐products, such as 2‐(azulen‐1‐yl)fumarates and ‐maleates and others caused by H‐shifts of the primary intermediates. H‐Shifts between the two tetrahydrocyclopenta[cd]azulene parts of the heptacyclic structures were also found. 相似文献
89.
Some recently described pentapeptides containing the α,α‐disubstituted α‐amino acids Aib and Phe(2Me) have been cyclized in DMF solution using diphenyl phosphorazidate (DPPA), O‐(1H‐benzotriazol‐1‐yl)‐N,N,N′,N′‐tetamethyluronium tetrafluoroborate/1‐hydroxybenzotriazole (TBTU/HOBt), and diethyl phosphorocyanidate (DEPC), respectively, to give the corresponding cyclopentapeptides in fair‐to‐good yields. In the case of peptides with L ‐amino acids, and (R)‐ and (S)‐Phe(2Me), the yields differed significantly in favor of the L /(R) combination. The conformations in the crystals of cyclo(Gly‐Aib‐(R,S)‐Phe(2Me)‐Aib‐Gly) and cyclo(Gly‐(R)‐Phe(2Me)‐Pro‐Aib‐Gly) have been determined by X‐ray crystallography, leading to quite different results. In the latter case, the conformation in solution has been elucidated by NMR studies. 相似文献
90.
Four new Aib‐containing cyclopentapeptides have been synthesized by cyclization of the corresponding linear pentapeptides using the diethyl phosphorocyanidate (DEPC)/EtN(iPr)2 method. The linear precursors were prepared via the ‘azirine/oxazolone method’, i.e., the Aib units were introduced by the reaction of amino acids or peptide acids with a 2,2‐dimethyl‐2H‐azirin‐3‐amine, followed by selective hydrolysis of the terminal amide function. Most remarkably, cyclo[(Aib)5] exists in CDCl3 solution in a symmetrical conformation, i.e., no intramolecular H‐bonds are detectable. 相似文献