G‐protein‐coupled receptors (GPCRs) are important targets for treating severe diseases. However why certain molecules act as activators whereas others, with similar structures, block GPCR activation, is poorly understood since the same molecule can activate one receptor subtype while blocking another closely related receptor. To shed light on these central questions, we used all‐atom, long‐time‐scale molecular dynamics simulations on the κ‐opioid and μ‐opioid receptors (κOR and μOR). We found that water molecules penetrating into the receptor interior mediate the activating versus blocking effects of a particular ligand–receptor interaction. Both the size and the flexibility of the bound ligand regulated water influx into the receptor. The solvent‐accessible inner surface area was found to be a parameter that can help predict the function of the bound ligand. 相似文献
Rare earth (RE)-doped chalcogenide glasses are an important promising material for active photonic devices, including mid-infrared (mid-IR) fiber lasers and amplifiers. Here we report on dysprosium ion (Dy3+)-doped GeAsGaSe chalcogenide glasses based on 10 atomic (at.) % Ga. A series of Dy3+-doped GeAsGaSe glasses, with increasing levels of Dy3+ dopant from 0 ppm to 2000 ppm added to the Ge16.5As9Ga10Se64.5 (at. %) base glass, is synthesized and characterized using: Fourier transform infrared spectrometry; X-ray diffraction (XRD); imaging and analysis using a high resolution transmission electron microscope, with selected area electron diffraction (HRTEM-SAED), and energy dispersive X-ray spectroscopy (HRTEM-EDX) and an environmental scanning electron microscope with energy dispersive X-ray spectroscopy (ESEM-EDX) and with secondary electron mapping. At the higher levels of Dy3+ doping, the glasses exhibit bulk crystallization; XRD, HRTEM-EDX and ESEM-EDX indicate the crystals are predominantly a modified, face centered cubic α-Ga2Se3, with some substitution of Ge. In addition, features on the bulk glass surface are shown to comprise Dy3+, sometimes accompanied by Si and [O] which, it is suggested, are due to contamination from the silica glass melting ampoule. 相似文献
We establish a supersymmetric version of the Golden-Thompson inequality.Supported in part by the Department of Energy under grant DE-FG02-88ER25065. 相似文献
The photochemistry of phenyl azide 1 and 13C-labeled phenyl azide 13C-1 incarcerated inside a hemicarcerand 4 was investigated. Low-temperature photolysis of hemicarceplex 41 and 413C-1 yields incarcerated 1-azacyclohepta-1,2,4,6-tetraene 42 and 413C-2 (18-50%), respectively, which were characterized by low-temperature FT-IR and 1H NMR and 13C NMR spectroscopy. After correction for the hemicarcerand-induced upfield shift, the 13C chemical shifts of incarcerated 13C-2 compare very well (Deltadelta = 3.5 ppm) with the GIAO chemical shift tensors calculated at the PBE1PBE/6-311G++(2d,2p) level. Incarcerated 2 has a lifetime of 32 min at 194.4 K and decomposes by ring contraction to singlet phenylnitrene 1PN. 1PN intersystem crosses to triplet phenylnitrene, which reacts with the surrounding host. From the time dependence of the characteristic ketenimine IR absorption of 2 at 1886 cm-1, the rate constant, kobs, for decay of 2 was measured between 198.3 and 174.3 K. Under the assumption that the intersystem-crossing rate constant kISC and the ring-expansion rate constant k1 in pentane (Gritsan, N. P.; Zhu, Z.; Hadad, C. M.; Platz, M. S. J. Am. Chem. Soc. 1999, 121, 1202) and in the inner phase are identical, the rate constant k' = 1011.0 +/- 0.7 x exp(-12.3 +/- 0.6 kcal/mol/RT) for the ring contraction of 2 was calculated. The activation energy compares very well with those calculated at the CASPT2N/6-311G(2d,p) (Karney, W. L.; Borden, W. T. J. Am. Chem. Soc. 1997, 119, 1378) and B3LYP/6-311+G(2d,p) (Tsao, M.-L.; Platz, M. S. J. Am. Chem. Soc. 2003, 125, 12014) level of theory. 相似文献
Thin films of aligned supramolecular architectures built from newly synthesized thiophene-substituted porphyrins have been processed from solution on surfaces. 相似文献
The preferences of a large number of na?ve listeners were elicited in response to a selection of multichannel audio items that had been degraded in quality by using band-limiting and down-mixing algorithms. Relationships were sought between these preference ratings and the quality judgements of experienced listeners in an attempt to determine whether one could be predicted from the other. Results suggest that a simple regression model can be used to do this with adequate results, but that a better prediction can be successfully based on experienced listener ratings of timbral and spatial fidelity. There is a difference between na?ve and experienced listeners in the weightings of the fidelities and their relationship to overall quality. 相似文献
We discuss global Laurent expansions for meromorphich-forms on a compact Riemann surface of genusg2. Our approach is motivated by Krichever and Novikov's work on string theory.Supported in part by the Department of Energy under Grant DE-FG02-88ER25065 相似文献
As is well-known, trace elements, especially metals, play an important role in the pathogenesis of many disorders. The topographic and quantitative elemental analysis of pathologically changed tissues may shed some new light on processes leading to the degeneration of cells in the case of selected diseases. An ideal and powerful tool for such purpose is the Synchrotron Microbeam X-ray Fluorescence technique. It enables the carrying out of investigations of the elemental composition of tissues even at the single cell level.
The tissue samples for histopathological investigations are routinely fixed and embedded in paraffin. The authors try to verify the usefulness of such prepared tissue sections for elemental analysis with the use of X-ray fluorescence microscopy. Studies were performed on rat brain samples. Changes in elemental composition caused by fixation in formalin or paraformaldehyde and embedding in paraffin were examined.
Measurements were carried out at the bending magnet beamline L of the Hamburger Synchrotronstrahlungslabor HASYLAB in Hamburg.
The decrease in mass per unit area of K, Br and the increase in P, S, Fe, Cu and Zn in the tissue were observed as a result of the fixation. For the samples embedded in paraffin, a lower level of most elements was observed. Additionally, for these samples, changes in the composition of some elements were not uniform for different analyzed areas of rat brain. 相似文献
We investigate the Kähler structure arising inn-component,N=2 supersymmetric quantum mechanics. We defineL2-cohomology groups of a modified
and relate them to the corresponding spaces of harmonic forms. We prove that the cohomology is concentrated in the middle dimension, and is isomorphic to the direct sum of the local rings of the singularities of the superpotential. In the physics language, this means that the number of ground states is equal to the absolute value of the index of the supercharge, and each ground state contains exactlyn fermions.Supported in part by the Department of Energy under Grant DE-F602-88ER25065 相似文献