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51.
We study theoretically the gain for a linear-cavity (Fabry-Perot) FIR laser pumped by a travelling-wave infrared beam. Arbitrary field intensities and pressure and Doppler broadenings are considered. The simultaneous presence inside the laser cavity of the forward and backward generated waves produces strong competition and coupling effects between these waves which are interpreted in terms of Lamb-dip and multiphoton processes. These effects determine the main differences in the amplifying behaviour between the bi-directional (linear) and uni-directional (ring) laser configurations. 相似文献
52.
Zoltan Dekan Thomas Kremsmayr Peter Keov Mathilde Godin Ngari Teakle Leopold Dürrauer Huang Xiang Dalia Gharib Christian Bergmayr Roland Hellinger Marina Gay Marta Vilaseca Dennis Kurzbach Fernando Albericio Paul F. Alewood Christian W. Gruber Markus Muttenthaler 《Chemical science》2021,12(11):4057
Vasopressin (VP) and oxytocin (OT) are cyclic neuropeptides that regulate fundamental physiological functions via four G protein-coupled receptors, V1aR, V1bR, V2R, and OTR. Ligand development remains challenging for these receptors due to complex structure–activity relationships. Here, we investigated dimerization as a strategy for developing ligands with novel pharmacology. We regioselectively synthesised and systematically studied parallel, antiparallel and N- to C-terminal cyclized homo- and heterodimer constructs of VP, OT and dVDAVP (1-deamino-4-valine-8-d-arginine-VP). All disulfide-linked dimers, except for the head-to-tail cyclized constructs, retained nanomolar potency despite the structural implications of dimerization. Our results support a single chain interaction for receptor activation. Dimer orientation had little impact on activity, except for the dVDAVP homodimers, where an antagonist to agonist switch was observed at the V1aR. This study provides novel insights into the structural requirements of VP/OT receptor activation and spotlights dimerization as a strategy to modulate pharmacology, a concept also frequently observed in nature.Structural and pharmacological study of parallel, antiparallel and N- to C-terminal cyclized homo- and heterodimers of vasopressin and oxytocin. This study spotlights dimerization as a strategy to modulate the pharmacology of neuropeptides. 相似文献
53.
Heterotrimetallic complexes with a Pt---Hg---Pt arrangement are formed by reaction of zerovalent platinum complexes with [(PPh3)2RPt---HgR]; X-ray diffraction has established the structure of [(PPh3)2(2,4,6-C6H2Cl3)Pt]2Hg. 相似文献
54.
Steven M. Allin Liam J. Duffy Vickie McKee Michael J. McKenzie Oriol Bassas Joan Bosch 《Tetrahedron letters》2006,47(32):5713-5716
We report new and complementary routes for the highly stereoselective construction of functionalized benzoquinolizidine targets from readily available, non-racemic chiral templates. The methods developed allow us to predetermine relative product stereochemistries by judicious choice of substrate sub-structure, and provide ready access to alternative stereoisomers. 相似文献
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Oriol Vallcorba Sonia Latorre Xavier Alcob Carles Miravitlles Jordi Rius 《Acta Crystallographica. Section C, Structural Chemistry》2011,67(11):o425-o427
The title compound, C21H14N4O2S, belongs to a family of molecules possessing nonlinear optical properties in solution. Its structure has been solved from laboratory X‐ray powder diffraction data using a new direct‐space structure solution method, where the atomic coordinates are directly used as parameters and the molecular geometry is described by restraints. The molecular packing is controlled by two systems of π–π interactions and one weak edge‐to‐face interaction. 相似文献
58.
Dr. Oriol Arteaga Dr. Adolf Canillas Dr. Joaquim Crusats Dr. Zoubir El‐Hachemi Prof. Joan Llorens Eduardo Sacristan Prof. Dr. Josep M. Ribo 《Chemphyschem》2010,11(16):3511-3516
Hydrodynamic forces in stirred solutions induce chirality in some supramolecular species of J‐aggregates, as detected at the level of the electronic transition. However, the mechanism that explains the phenomenon remains to be elucidated, although the basic effect of hydrodynamic gradients of the shear rate is most probably the folding or bending of the nanoparticles in solution. Herein, we demonstrate a correlation between chiral flows in different regions of circular and square stirred cuvettes and the emergence of true circular dichroism (CD). The results show that chaotic flows lead to a racemic mixture of chiral shaped supramolecular species, and vortical flows to scalemic mixtures. In a magnetically stirred flask the descending and ascending flows are of different chiral sign and the CD reading depends on the weighting of these two flows of inverse chiral sign. The effect of the gradient of shear rates of the flows leading to chiral shape objects depends on the shape of the cuvette, which suggests that the flask shape and the controlled addition of reagents in defined regions of the stirred solutions may exert a control in self‐assembly processes. 相似文献
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R. Belhassen S. Boufi F. Vilaseca J. P. López J. A. Méndez E. Franco M. A. Pèlach P. Mutjé 《先进技术聚合物》2009,20(12):1068-1075
Biocomposite materials based on Alfa cellulose fibers (esparto grass plant) as reinforcing element and starch‐based biopolymer matrix were prepared and characterized in terms of mechanical performance, thermal properties, and water absorbance behavior. The fibers and the matrix were first mixed in the melted state under mechanical shearing using a plastograph and the obtained composites were molded by injection process. The tensile mechanical analysis showed a linear increase of the composite flexural and tensile modulus upon increasing the fiber content, together with a sharp decrease of the elongation at break. The fibers′ incorporation into the biopolymer matrix brings about an enhancement in the mechanical strength and the impact strength of the composite. Dynamic mechanical thermal analysis (DMTA) investigation showed two relaxations occurring at about ?30 and 35°C. The addition of Alfa fibers enhanced the storage modulus E′ before and after Tα, which is consistent with the reinforcing effect of Alfa cellulose fibers. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献