scholarly journals Modeling of the Resonant X-ray Response of a Chiral Cubic Phase

Crystals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 214
Author(s):  
Timon Grabovac ◽  
Ewa Gorecka ◽  
Damian Pociecha ◽  
Nataša Vaupotič
Keyword(s):  
Absorption Edge ◽  
Unit Cell ◽  
Resonant Peak ◽  
Cubic Phase ◽  
Tensor Form ◽  
Resonant Enhancement ◽  
X Ray ◽  
X Ray Scattering ◽  
Thermotropic Liquid Crystals ◽  
Carbon Absorption

The structure of a continuous-grid chiral cubic phase made of achiral constituent molecules is a hot topic in the field of thermotropic liquid crystals. Several structural models have been proposed so far. Resonant X-ray scattering (RXS), which gives information on the molecular orientation in the unit cell, could be applied to select the most appropriate model. We modeled the RXS response for the recently proposed chiral cubic phase structure with an all-hexagon chiral continuous grid. A tensor form factor of a unit cell is constructed, which enables calculation of intensities of peaks for all Miller indices. We find that all the symmetry allowed peaks are resonantly enhanced, and their intensity is much stronger than the intensity of the symmetry forbidden (resonant) peaks. In particular, we predict that a strong resonant enhancement of the symmetry allowed peaks (011) and (002), not observed in a nonresonant scattering, could be observed by RXS at the carbon absorption edge. By RXS at the sulfur absorption edge, one might observe a resonant peak (113) and resonantly enhanced peak (233), and resonant enhancement of all the peaks that are observed in a nonresonant scattering, which probably hide the rest of the predicted resonant peaks.

scholarly journals Exploring the in meso crystallization mechanism by characterizing the lipid mesophase microenvironment during the growth of single transmembrane α-helical peptide crystals

2016 ◽  
Vol 374 (2072) ◽  
pp. 20150125 ◽  
Author(s):  
Leonie van 't Hag ◽  
Konstantin Knoblich ◽  
Shane A. Seabrook ◽  
Nigel M. Kirby ◽  
Stephen T. Mudie ◽  
...  
Keyword(s):  
Crystal Growth ◽  
Self Assembly ◽  
Lamellar Phase ◽  
Cubic Phase ◽  
Supporting Evidence ◽  
X Ray ◽  
X Ray Scattering ◽  
Standard Procedures ◽  
Helical Peptide ◽  
Saxs Analysis

The proposed mechanism for in meso crystallization of transmembrane proteins suggests that a protein or peptide is initially uniformly dispersed in the lipid self-assembly cubic phase but that crystals grow from a local lamellar phase, which acts as a conduit between the crystal and the bulk cubic phase. However, there is very limited experimental evidence for this theory. We have developed protocols to investigate the lipid mesophase microenvironment during crystal growth using standard procedures readily available in crystallography laboratories. This technique was used to characterize the microenvironment during crystal growth of the DAP12-TM peptide using synchrotron small angle X-ray scattering (SAXS) with a micro-sized X-ray beam. Crystal growth was found to occur from the gyroid cubic mesophase. For one in four crystals, a highly oriented local lamellar phase was observed, providing supporting evidence for the proposed mechanism for in meso crystallization. A new observation of this study was that we can differentiate diffraction peaks from crystals grown in meso , from peaks originating from the surrounding lipid matrix, potentially opening up the possibility of high-throughput SAXS analysis of in meso grown crystals. This article is part of the themed issue ‘Soft interfacial materials: from fundamentals to formulation’.

scholarly journals Combining solution wide-angle X-ray scattering and crystallography: determination of molecular envelope and heavy-atom sites

2009 ◽  
Vol 42 (2) ◽  
pp. 259-264 ◽  
Author(s):  
Xinguo Hong ◽  
Quan Hao
Keyword(s):  
Structure Determination ◽  
Heavy Atom ◽  
Unit Cell ◽  
Wide Angle ◽  
X Ray ◽  
X Ray Scattering ◽  
Molecular Envelope ◽  
Waxs Data ◽  
Ray Scattering

Solving the phase problem remains central to crystallographic structure determination. A six-dimensional search method of molecular replacement (FSEARCH) can be used to locate a low-resolution molecular envelope determined from small-angle X-ray scattering (SAXS) within the crystallographic unit cell. This method has now been applied using the higher-resolution envelope provided by combining SAXS and WAXS (wide-angle X-ray scattering) data. The method was tested on horse hemoglobin, using the most probable model selected from a set of a dozen bead models constructed from SAXS/WAXS data using the programGASBORat 5 Å resolution (qmax= 1.25 Å−1) to phase a set of single-crystal diffraction data. It was found that inclusion of WAXS data is essential for correctly locating the molecular envelope in the crystal unit cell, as well as for locating heavy-atom sites. An anomalous difference map was calculated using phases out to 8 Å resolution from the correctly positioned envelope; four distinct peaks at the 3.2σ level were identified, which agree well with the four iron sites of the known structure (Protein Data Bank code 1ns9). In contrast, no peaks could be found close to the iron sites if the molecular envelope was constructed using the data from SAXS alone (qmax= 0.25 Å−1). The initial phases can be used as a starting point for a variety of phase-extension techniques, successful application of which will result in complete phasing of a crystallographic data set and determination of the internal structure of a macromolecule to atomic resolution. It is anticipated that the combination ofFSEARCHand WAXS techniques will facilitate the initial structure determination of proteins and provide a good foundation for further structure refinement.

scholarly journals Phase Transition in Di-oleoylphosphatidylglycerol/Monoolein Membranes due to Interactions of Positively Charged Peptides at their Lipid Membrane-Interface

1970 ◽  
Vol 45 (3) ◽  
pp. 219-224
Author(s):  
Shah Md Masum ◽  
Masahito Yamazaki
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Small Angle ◽  
Lipid Membrane ◽  
Cubic Phase ◽  
Membrane Interface ◽  
X Ray ◽  
X Ray Scattering ◽  
Charged Peptides ◽  
Positively Charged

To elucidate the factors that induce phase transitions in biomembranes due to interactions of proteins/peptides at the lipid membrane-interface, the effects of positively charged peptides on the cubic phase (Q229) of Dioleoylphosphatidylglycerol (DOPG)/Monoolein (MO) membranes were investigated. Small angle X-ray Scattering (SAXS) results revealed that 12 mol% DOPG/88 mol % MO membranes in excess water at 25°C is body centered cubic phase of crystallographic space group Im3m (Q229). In presence of peptide LLKKK, the lattices constant of Q229 phase was gradually decreased with an increase of peptide concentration and a phase transition from cubic (Q229) to cubic (Q224) phase occurred at R=0.080; (R= molar ratio of peptide to lipid). On the other hand the designed peptide WLFLLKKK and antimicrobial peptide Magainin-2 induced lamellar phase (Lα) in the same mixture membranes. These results indicate that the interactions of the these peptides with this mixture membrane are different: LLKKK induces electrostatic attractive interactions and that of WLFLLKKKK and Magainin-2 bound with the lipid membranes induce electrostatic repulsive interaction at the membrane-interface, might be the major factor inducing different phase transitions in 12 mol% DOPG/88mol% MO mixture membranes. Key words: Antimicrobial peptide Magain-2; Dioleoylphosphatidylglycerol; Monoolein; Cubic phases; Small angle X-ray Scattering DOI: 10.3329/bjsir.v45i3.6530Bangladesh J. Sci. Ind. Res. 45(3), 219-224, 2010

The Structure of Amorphous Platinum Disulfide as Studied by Anomalous X-ray Scattering

1994 ◽  
Vol 49 (11) ◽  
pp. 1031-1036 ◽  
Author(s):  
Masatoshi Saito ◽  
Makoto Wakeshima ◽  
Nobuaki Sato ◽  
Takeo Fujino ◽  
Yoshio Waseda ◽  
...  
Keyword(s):  
Variational Method ◽  
Least Squares ◽  
Absorption Edge ◽  
Structural Unit ◽  
Precipitation Process ◽  
Interference Function ◽  
X Ray ◽  
Atomic Arrangement ◽  
X Ray Scattering ◽  
Ray Scattering

Abstract Anomalous X-ray scattering (AXS) has been applied to study the structure of amorphous plati­ num disulfide, Pt1-xS2, prepared by the precipitation process. The local atomic arrangement in amorphous Pt1-xS2 was determined by the least-squares variational method so as to reproduce the experimental differential interference function at the Pt Lm absorption edge by the AXS method as well as the ordinary interference function by Mo K α. The structural unit in amorphous Pt1-xS2 is found to be a PtS6 octahedron, similar to that in crystalline PtS2. These octahedra share both their corners and edges, while only edge-sharing linkages occur in crystalline PtS2

Small-Angle Neutron and X-ray Scattering from Amphiphilic Stimuli-Responsive Diamond-Type Bicontinuous Cubic Phase

2007 ◽  
Vol 129 (44) ◽  
pp. 13474-13479 ◽  
Author(s):  
Borislav Angelov ◽  
Angelina Angelova ◽  
Vasil M. Garamus ◽  
Geneviève Lebas ◽  
Sylviane Lesieur ◽  
...  
Keyword(s):  
Small Angle ◽  
Cubic Phase ◽  
Stimuli Responsive ◽  
X Ray ◽  
X Ray Scattering ◽  
Bicontinuous Cubic ◽  
Diamond Type ◽  
Ray Scattering

scholarly journals Isoprenoid-chained lipid EROCOC17+4: a new matrix for membrane protein crystallization and a crystal delivery medium in serial femtosecond crystallography

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Kentaro Ihara ◽  
Masakatsu Hato ◽  
Takanori Nakane ◽  
Keitaro Yamashita ◽  
Tomomi Kimura-Someya ◽  
...  
Keyword(s):  
Protein Crystallization ◽  
Water System ◽  
Cubic Phase ◽  
Marked Contrast ◽  
X Ray ◽  
X Ray Scattering ◽  
Membrane Protein Crystallization ◽  
Almost All ◽  
Serial Femtosecond Crystallography ◽  
Delivery Medium

Abstract In meso crystallization of membrane proteins relies on the use of lipids capable of forming a lipidic cubic phase (LCP). However, almost all previous crystallization trials have used monoacylglycerols, with 1-(cis-9-octadecanoyl)-rac-glycerol (MO) being the most widely used lipid. We now report that EROCOC17+4 mixed with 10% (w/w) cholesterol (Fig. 1) serves as a new matrix for crystallization and a crystal delivery medium in the serial femtosecond crystallography of Adenosine A2A receptor (A2AR). The structures of EROCOC17+4-matrix grown A2AR crystals were determined at 2.0 Å resolution by serial synchrotron rotation crystallography at a cryogenic temperature, and at 1.8 Å by LCP-serial femtosecond crystallography, using an X-ray free-electron laser at 4 and 20 °C sample temperatures, and are comparable to the structure of the MO-matrix grown A2AR crystal (PDB ID: 4EIY). Moreover, X-ray scattering measurements indicated that the EROCOC17+4/water system did not form the crystalline LC phase at least down to − 20 °C, in marked contrast to the equilibrium MO/water system, which transforms into the crystalline LC phase below about 17 °C. As the LC phase formation within the LCP-matrix causes difficulties in protein crystallography experiments in meso, this feature of EROCOC17+4 will expand the utility of the in meso method.

X-ray Structural Study of Ferromagnetic Vitreous 0.5 La0.7Sr0.3MnO30.5B2O3

1989 ◽  
Vol 44 (8) ◽  
pp. 723-725 ◽  
Author(s):  
E. Matsubara ◽  
Y. Waseda ◽  
K. Inomata ◽  
S. Hashimoto
Keyword(s):  
Magnetic Properties ◽  
Characteristic Feature ◽  
Absorption Edge ◽  
Random Network ◽  
Oxide Glass ◽  
X Ray Diffraction ◽  
Diffraction Profile ◽  
X Ray ◽  
X Ray Scattering ◽  
Distinctive Structure

Abstract The ordinary x-ray diffraction profile and the anomalous x-ray scattering profiles at Sr K-absorption edge were measured in a ferromagnetic oxide glass of 0.5La0.7Sr0.3MnO30.5B2O3. The result indicates the characteristic feature of coexistence of a highly ordered perovskite La0.7Sr0.3MnO3-like region and a random network structure consisting of BO3 triangles. It is expected that the characteristic magnetic properties of this sample are attributed to this distinctive structure.

scholarly journals High-energy-resolution diced spherical quartz analyzers for resonant inelastic X-ray scattering

2018 ◽  
Vol 25 (2) ◽  
pp. 373-377 ◽  
Author(s):  
Ayman H. Said ◽  
Thomas Gog ◽  
Michael Wieczorek ◽  
XianRong Huang ◽  
Diego Casa ◽  
...  
Keyword(s):  
Energy Resolution ◽  
Absorption Edge ◽  
High Energy ◽  
Fabrication Process ◽  
High Energy Resolution ◽  
Magnetic Excitations ◽  
X Ray ◽  
X Ray Scattering ◽  
Ray Scattering

A novel diced spherical quartz analyzer for use in resonant inelastic X-ray scattering (RIXS) is introduced, achieving an unprecedented energy resolution of 10.53 meV at the IrL3absorption edge (11.215 keV). In this work the fabrication process and the characterization of the analyzer are presented, and an example of a RIXS spectrum of magnetic excitations in a Sr3Ir2O7sample is shown.

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