The Experts below are selected from a list of 21 Experts worldwide ranked by ideXlab platform
Ueli Aebi - One of the best experts on this subject based on the ideXlab platform.
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towards the molecular architecture of the asymmetric unit membrane of the mammalian urinary bladder epithelium a closed twisted ribbon structure
Journal of Molecular Biology, 1995Co-Authors: Thomas Walz, Xue-ru Wu, Markus Häner, Christian Henn, Ueli Aebi, Andreas EngelAbstract:The asymmetric unit membrane (AUM) forms numerous plaques covering the apical surface of mammalian urinary bladder epithelium. These plaques contain four major integral membrane proteins called uroplakins Ia, Ib, II and III, which form particles arranged in a well-ordered hexagonal lattice with p6 symmetry and a lattice constant of 16.5 nm. Bovine AUM plaques negatively stained with anionic sodium silicotungstate revealed structural detail to 3.1 nm resolution. Correlation averaging resolved each particle into 12 stain-excluding domains arranged in two concentric rings (inner ring radius (rm) = 3.7 nm, outer ring radius (rout) = 6.6 nm), each with six domains which were rotated by roughly 30 degrees relative to each other. Negative staining with cationic Uranyl Formate increased the resolution to 2.2 nm and unveiled distinct connections between adjacent AUM particles. These connections may provide a molecular basis for the observed insolubility of the plaques in many detergents. Examination of the luminal face of freeze-dried/unidirectionally metal-shadowed AUM plaques established a left-handed vorticity of the 16 nm protein particles, whereas the cytoplasmic face exhibited no significant surface corrugations. Three-dimensional reconstruction from sodium silicotungstate-stained specimens revealed the AUM particles to be built of six "V-shaped" subunits anchored upright in the membrane. The mass density distribution within Uranyl Formate-stained AUM particles was similar except that the inner tip of each V was bridged to the outer tip of an adjacent V, so that the 16 nm AUM particle appeared as a continuous, "twisted ribbon" embracing a central cavity. Finally, mass measurements of unstained/freeze-dried plaques by scanning transmission electron microscopy yielded a total mass of 1,120 kDa per membrane-bound AUM particle. By imposing constraints on the possible uroplakin stoichiometries within AUM plaques, these data provide a first glimpse of the molecular architecture of the 16 nm particles constituting the plaques.
Song Gao - One of the best experts on this subject based on the ideXlab platform.
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c2h5 4n u2o4 hcoo 5 an ammonium Uranyl Formate framework showing para to ferro electric transition synthesis structures and properties
Inorganic Chemistry, 2014Co-Authors: Qianqian Zhu, Ran Shang, Sa Chen, Chunli Liu, Zheming Wang, Song GaoAbstract:We report an ammonium Uranyl Formate framework of formula [(C2H5)4N][U2O4(HCOO)5], prepared by using components of tetraethylammonium, Uranyl, and Formate. The compound possesses a layered structure of anionic Uranyl–Formate wavy sheets and intercalated (C2H5)4N+ cations. The sheet consists of pentagonal bipyramidal Uranyl cations connected by equatorial anti–anti and anti–syn HCOO– bridges, and it has a topology of 33·43·54 made of edge-sharing square and triangle grids. The high-temperature (HT) phase belongs to the chiral but nonpolar tetragonal space group P421m. In the structure, one HCOO– is 2-fold disordered, showing a flip motion between the two anti–syn orientations. On cooling, this flip motion slowed and finally froze, leading to a phase transition at ∼200 K. The low-temperature (LT) structure is monoclinic and polar in space group P21; the cations shift, and the layers slide. Especially, the concerted and net shifts of the ammonium cations toward the −b direction, with respect to the anionic ...
Takeshi Soga - One of the best experts on this subject based on the ideXlab platform.
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the resonance raman effect of Uranyl Formate in dimethyl sulfoxide
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2000Co-Authors: Takeshi SogaAbstract:The resonance Raman scattering spectra of Uranyl Formate (UO(2)(HCOO)(2)) in dimethyl sulfoxide ((CH(3))(2)SO, DMSO) have been measured under laser excitation of the Uranyl ion in resonance with the 1Sigma(g)(+)-->(1)Phi(g) Laport forbidden f-f electronic transitions (ranging from 510 to 450 nm) by using ten output lines with wavelength ranging from 528.7 to 454.5 nm of the argon-ion laser at room temperature. The observed resonance excitation profile resembles the vibronic structure of the electronic absorption spectrum (ABS) but does not completely superimpose on it. Such a discrepancy is quantitatively explained by the interference effect, which occurs noticeably in the UO(2)L(2) (L=NO(3), CH(3)COO, Cl or HCOO)-DMSO system. Transform theory that makes use of the electronic ABS of the resonant electronic state has been applied to predict the Raman excitation profile (REP) of the Uranyl totally symmetric stretching vibrational mode. Comparing the experimental REP with the transform theory prediction, it is found that the resonance Raman intensities of this stretching mode depend mainly on the vibronic interaction (non-Condon effect) in excited electronic states. Reliable value of the nuclear displacement on going the 1Sigma(g)(+)-->(1)Phi(g) electronic transition and the amount of charge transferred from the ligand to uranium of Uranyl ion both in the ground and excited states are obtained. Elongation of the U-O equilibrium bond length due to the electronic transition is related to the magnitude of the change in the excitation profile, and has linear relation to the change in the amount of charge transferred from the ligand to uranium of Uranyl ion in UO(2)L(2) type Uranyl compounds in DMSO.
Michael Stipdonk - One of the best experts on this subject based on the ideXlab platform.
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Gas Phase Reactions of Ions Derived from Anionic Uranyl Formate and Uranyl Acetate Complexes
Journal of The American Society for Mass Spectrometry, 2016Co-Authors: Evan Perez, Cassandra Hanley, Stephen Koehler, Jordan Pestok, Nevo Polonsky, Michael StipdonkAbstract:The speciation and reactivity of uranium are topics of sustained interest because of their importance to the development of nuclear fuel processing methods, and a more complete understanding of the factors that govern the mobility and fate of the element in the environment. Tandem mass spectrometry can be used to examine the intrinsic reactivity (i.e., free from influence of solvent and other condensed phase effects) of a wide range of metal ion complexes in a species-specific fashion. Here, electrospray ionization, collision-induced dissociation, and gas-phase ion-molecule reactions were used to create and characterize ions derived from precursors composed of Uranyl cation (U^VIO_2 ^2+) coordinated by Formate or acetate ligands. Anionic complexes containing U^VIO_2 ^2+ and Formate ligands fragment by decarboxylation and elimination of CH_2=O, ultimately to produce an oxo-hydride species [U^VIO_2(O)(H)]^-. Cationic species ultimately dissociate to make [U^VIO_2(OH)]^+. Anionic complexes containing acetate ligands exhibit an initial loss of acetyloxyl radical, CH_3CO_2•, with associated reduction of Uranyl to U^VO_2 ^+. Subsequent CID steps cause elimination of CO_2 and CH_4, ultimately to produce [U^VO_2(O)]^–. Loss of CH_4 occurs by an intra-complex H^+ transfer process that leaves U^VO_2 ^+ coordinated by acetate and acetate enolate ligands. A subsequent dissociation step causes elimination of CH_2=C=O to leave [U^VO_2(O)]^–. Elimination of CH_4 is also observed as a result of hydrolysis caused by ion-molecule reaction with H_2O. The reactions of other anionic species with gas-phase H_2O create hydroxyl products, presumably through the elimination of H_2. Graphical Abstract ᅟ
Matthias Mörgelin - One of the best experts on this subject based on the ideXlab platform.
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Negative Staining and Transmission Electron Microscopy of Bacterial Surface Structures
Methods of Molecular Biology, 2016Co-Authors: Matthias MörgelinAbstract:Negative staining is an essential and versatile staining technique in transmission electron microscopy that can be employed for visualizing bacterial cell morphology, size, and surface architecture at high resolution. Bacteria are usually transferred by passive electrostatic adsorption from suspensions in physiological saline onto suitable hydrophilic support films on electron microscopic grids. There they are contrasted, or "stained," by heavy metal ions in solution such as tungsten, Uranyl, molybdate, or vanadate compounds. Here, I describe how to visualize the interaction between the bacterial M1 protein and complement factors C1q and C3 on the surface of group A streptococcus by negative staining with Uranyl Formate on carbon support films. The methodology should be generally applicable to the study of a large number of other bacteria-protein interactions.
