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11.
The design, enantioselective synthesis, and structural characterization of novel bicyclic lactams as peptide mimics of the type VI beta turn is described. The mimics duplicate the conformation of the backbone and disposition of the side-chain atoms of the central two residues of the turn. The Gly L-Pro mimic, lactam 6, was prepared in good overall yield starting from (S)-2-(2'-propenyl)proline. (1)H NMR spectroscopy defined the relative stereochemistry of the substituents and conformational characteristics of the six-membered ring of the lactam; X-ray crystallographic analysis confirmed the conformational and stereochemical assignment. Examination of the crystal structure of lactam 6 revealed that the central amide bond was twisted appreciably out of planarity. The twisting of the amide bond was attributed to angle strain resulting from the presence of the sp(2)-hybridized nitrogen atom at the junction of the two rings. Alkylation of the enolate of the N,N-dimethylformamidine derivative of lactam 6 with benzyl bromide afforded stereoselectively the formamidine 11, a mimic of an L-Phe L-Pro dipeptide in the type VI turn conformation. The efficient synthetic route to highly functionalized peptidomimetics such as 11 will prove highly useful in peptide structure-function studies. 相似文献
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Lu J Qu X Peleckis G Boas JF Bond AM Martin LL 《The Journal of organic chemistry》2011,76(24):10078-10082
The tetrabutylammonium complex with a 2:5 stoichiometry, (n-Bu(4)N)(2)(TCNQ)(5), has been prepared and structurally characterized by X-ray crystallography. Diagnostic bands in the Raman spectrum and signature features in the electrochemistry confirm that the TCNQ moieties are partially charged in the solid state. EPR, magnetic susceptibility, and electrical conductivity measurements are all consistent with (n-Bu(4)N)(2)(TCNQ)(5) behaving as a quasi-one-dimensional organic semiconductor. 相似文献
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The structural and electronic transport properties of La1−x
Ce
x
MnO3 (x=0.0–1.0) have been studied. All the samples exhibit orthorhombic crystal symmetry and the unit cell volume decreases with
Ce doping. They also make a metal-insulator transition (MIT) and transition temperature increases with increase in Ce concentration
up to 50% doping. The system La0.5Ce0.5MnO3 also exhibits MIT instead of charge-ordered state as observed in the hole doped systems of the same composition. 相似文献
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Saulius Mickevičius Darius Germanas Ramutis K. Kalinauskas 《Central European Journal of Physics》2012,10(2):421-428
We present a new independent scheme of SO(3) group transformations suitable for the N particle system, composed of N − 1 and 1 particle subsystems, where N − 1 particles have their own intrinsic clusterization. The simple expressions for corresponding four-particle harmonic-oscillator
transformation brackets are presented, as well as their simplifications for the special values of mass ratio parameters d = 0, d → ∞ and d
1 = 0, d
1 → ∞. 相似文献
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Jérôme JP. Leon 《Letters in Mathematical Physics》1981,5(1):75-80
We establish a transformation which connects the potentials of the one-dimensional Dirac and Klein-Gordon operators. This transformation links the solutions of the nonlinear evolution equations solvable by means of the two inverse spectral transforms which use the Dirac and Klein-Gordon direct and inverse spectral problems. 相似文献
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Jian Peng Bao Zhang Weibo Hua Yaru Liang Wang Zhang Yumeng Du Germanas Peleckis Sylvio Indris Qinfen Gu Zhenxiang Cheng Jiazhao Wang Huakun Liu Shixue Dou Shulei Chou 《Angewandte Chemie (International ed. in English)》2023,62(6):e202215865
Sodium-ion batteries (SIBs) with fast-charge capability and long lifespan could be applied in various sustainable energy storage systems, from personal devices to grid storage. Inspired by the disordered Rubik's cube, here, we report that the high-entropy (HE) concept can lead to a very substantial improvement in the sodium storage properties of hexacyanoferrate (HCF). An example of HE-HCF has been synthesized as a proof of concept, which has achieved impressive cycling stability over 50 000 cycles and an outstanding fast-charging capability up to 75 C. Remarkable air stability and all-climate performance are observed. Its quasi-zero-strain reaction mechanism and high sodium diffusion coefficient have been measured and analyzed by multiple in situ techniques and density functional theory calculations. This strategy provides new insights into the development of advanced electrodes and provides the opportunity to tune electrochemical performance by tailoring the atomic composition. 相似文献