The Croonian Lecture, 1970 The structural basis of muscular contraction

1971 ◽  
Vol 178 (1051) ◽  
pp. 131-149 ◽  
Keyword(s):  
Large Scale ◽  
Muscular Contraction ◽  
Important Change ◽  
Structural Basis ◽  
X Ray Diffraction ◽  
New Era ◽  
X Ray ◽  
Biology I ◽  
The Times ◽  
Polypeptide Chains

A previous occasion on which the Croonian lecture was directly concerned with the mechanism of muscular contraction was in 1945, when it was delivered by Professor W. T. Astbury. On that occasion he commented that it was a sign of the times that a physicist should be asked to give the Croonian lecture, and went on to say, and I quote: ‘We are at the dawn of a new era, the era of “molecular biology”, as I like to call it, and there is an urgency about the need for more intensive application of physics and chemistry, and specially structural analysis, to biological problems.’ These were very prophetic words, and, as a physicist just entering biology, I was much interested to read them, and to learn about his experiments. The basic experimental finding which Astbury reported (1947) was that there did not seem to be any important change in the wide angle X-ray diagram from muscle upon contraction; hence it followed that muscles did not contract by any process which simply involved the large-scale disorientation of originally well-ordered polypeptide chains, nor by an alteration in chain configuration in the well-ordered parts of the structure. Astbury suggested instead that there might be ‘specifically active foci’ which one could perhaps paraphrase as ‘larger structural units’ (i.e. larger than individual polypeptide chains) concerned in contraction, which might be studied in the electron microscope or by low angle X-ray diffraction.

Investigation of Residual Stress/Strain and Texture in a Large Dissimilar Metal Weld Using Synchrotron Radiation and Neutrons

2013 ◽  
Vol 772 ◽  
pp. 193-199 ◽  
Author(s):  
Carsten Ohms ◽  
Rene V. Martins
Keyword(s):  
Synchrotron Radiation ◽  
Neutron Diffraction ◽  
Residual Stresses ◽  
Large Scale ◽  
High Energy ◽  
X Ray Diffraction ◽  
Butt Weld ◽  
X Ray ◽  
Component Size ◽  
Thin Slice

Bi-metallic piping welds are frequently used in light water nuclear reactors to connect ferritic steel pressure vessel nozzles to austenitic stainless steel primary cooling piping systems. An important aspect for the integrity of such welds is the presence of residual stresses. Measurement of these residual stresses presents a considerable challenge because of the component size and because of the material heterogeneity in the weld regions. The specimen investigated here was a thin slice cut from a full-scale bi-metallic piping weld mock-up. A similar mock-up had previously been investigated by neutron diffraction within a European research project called ADIMEW. However, at that time, due to the wall thickness of the pipe, stress and spatial resolution of the measurements were severely restricted. One aim of the present investigations by high energy synchrotron radiation and neutrons used on this thin slice was to determine whether such measurements would render a valid representation of the axial strains and stresses in the uncut large-scale structure. The advantage of the small specimen was, apart from the easier manipulation, the fact that measurement times facilitated a high density of measurements across large parts of the test piece in a reasonable time. Furthermore, the recording of complete diffraction patterns within the accessible diffraction angle range by synchrotron X-ray diffraction permitted mapping the texture variations. The strain and stress results obtained are presented and compared for the neutron and synchrotron X-ray diffraction measurements. A strong variation of the texture pole orientations is observed in the weld regions which could be attributed to individual weld torch passes. The effect of specimen rocking on the scatter of the diffraction data in the butt weld region is assessed during the neutron diffraction measurements.

scholarly journals Structural basis for the alternating access mechanism of the cation diffusion facilitator YiiP

2018 ◽  
Vol 115 (12) ◽  
pp. 3042-3047 ◽  
Author(s):  
Maria Luisa Lopez-Redondo ◽  
Nicolas Coudray ◽  
Zhening Zhang ◽  
John Alexopoulos ◽  
David L. Stokes
Keyword(s):  
Large Scale ◽  
Structural Basis ◽  
Membrane Domains ◽  
Cation Diffusion ◽  
Cation Diffusion Facilitator ◽  
X Ray ◽  
Bacterial Membranes ◽  
Helix Bundle ◽  
Four Helix Bundle ◽  
Alternating Access

YiiP is a dimeric antiporter from the cation diffusion facilitator family that uses the proton motive force to transport Zn2+ across bacterial membranes. Previous work defined the atomic structure of an outward-facing conformation, the location of several Zn2+ binding sites, and hydrophobic residues that appear to control access to the transport sites from the cytoplasm. A low-resolution cryo-EM structure revealed changes within the membrane domain that were associated with the alternating access mechanism for transport. In the current work, the resolution of this cryo-EM structure has been extended to 4.1 Å. Comparison with the X-ray structure defines the differences between inward-facing and outward-facing conformations at an atomic level. These differences include rocking and twisting of a four-helix bundle that harbors the Zn2+ transport site and controls its accessibility within each monomer. As previously noted, membrane domains are closely associated in the dimeric structure from cryo-EM but dramatically splayed apart in the X-ray structure. Cysteine crosslinking was used to constrain these membrane domains and to show that this large-scale splaying was not necessary for transport activity. Furthermore, dimer stability was not compromised by mutagenesis of elements in the cytoplasmic domain, suggesting that the extensive interface between membrane domains is a strong determinant of dimerization. As with other secondary transporters, this interface could provide a stable scaffold for movements of the four-helix bundle that confers alternating access of these ions to opposite sides of the membrane.

scholarly journals Structure of undecaprenyl pyrophosphate synthase from Acinetobacter baumannii

2018 ◽  
Vol 74 (12) ◽  
pp. 765-769 ◽  
Author(s):  
Tzu-Ping Ko ◽  
Chi-Hung Huang ◽  
Shu-Jung Lai ◽  
Yeh Chen
Keyword(s):  
Acinetobacter Baumannii ◽  
Active Site ◽  
Multidrug Resistant ◽  
Structural Basis ◽  
X Ray Diffraction ◽  
X Ray ◽  
Peptidoglycan Synthesis ◽  
C Terminus ◽  
Dimeric Protein ◽  
Β Sheet

Undecaprenyl pyrophosphate (UPP) is an important carrier of the oligosaccharide component in peptidoglycan synthesis. Inhibition of UPP synthase (UPPS) may be an effective strategy in combating the pathogen Acinetobacter baumannii, which has evolved to be multidrug-resistant. Here, A. baumannii UPPS (AbUPPS) was cloned, expressed, purified and crystallized, and its structure was determined by X-ray diffraction. Each chain of the dimeric protein folds into a central β-sheet with several surrounding α-helices, including one at the C-terminus. In the active site, two molecules of citrate interact with the side chains of the catalytic aspartate and serine. These observations may provide a structural basis for inhibitor design against AbUPPS.

In-Situ Diffraction Studies of Gas Storage Materials on a Laboratory X-Ray System

2013 ◽  
Vol 1544 ◽  
Author(s):  
Marco Sommariva ◽  
Harald van Weeren ◽  
Olga Narygina ◽  
Jan-André Gertenbach ◽  
Christian Resch ◽  
...  
Keyword(s):  
Large Scale ◽  
Fossil Fuels ◽  
Reaction Chamber ◽  
Hydrogen Gas ◽  
Gas Pressure ◽  
X Ray Diffraction ◽  
X Ray ◽  
Structural Modifications ◽  
Model Studies

ABSTRACTThe sorption processes for hydrogen and carbon dioxide are of considerable, and growing interest, particularly due to their relevance to a society that seeks to replace fossil fuels with a more sustainable energy source. X-ray diffraction allows a unique perspective for studying structural modifications and reaction mechanisms that occur when gas and solid interact. The fundamental challenge associated with such a study is that experiments are conducted while the solid sample is held under a gas pressure. To date in-situ high gas pressure studies of this nature have typically been undertaken at large-scale facilities such as synchrotrons or on dedicated laboratory instruments. Here we report high-pressure XRD studies carried out on a multi-purpose diffractometer. To demonstrate the suitability of the equipment, two model studies were carried out, firstly the reversible hydrogen cycling over LaNi5, and secondly the structural change that occurs during the decomposition of ammonia borane that results in the generation of hydrogen gas in the reaction chamber. The results have been finally compared to the literature. The study has been made possible by the combination of rapid X-ray detectors with a reaction chamber capable of withstanding gas pressures up to 100 bar and temperatures up to 900 °C.

Large-scale and facile fabrication of PbSe nanostructures by selenization of a Pb sheet

2015 ◽  
Vol 08 (05) ◽  
pp. 1550063 ◽  
Author(s):  
Sara Hoomi ◽  
Ramin Yousefi ◽  
Farid Jamali-Sheini ◽  
Abdolhossein Sáaedi ◽  
Mohsen Cheraghizade ◽  
...  
Keyword(s):  
Large Scale ◽  
Chemical Vapor ◽  
Infrared Region ◽  
Photoelectron Spectra ◽  
X Ray Diffraction ◽  
X Ray ◽  
Facile Fabrication ◽  
Higher Temperature ◽  
Set Up ◽  
Lower Temperature

PbSe nanostructures were synthesized by selenization of lead sheets in a chemical vapor deposition (CVD) set-up under a selenium ambiance. The lead sheets were placed in the different temperature zones, between 300°C and 450°C. Field emission scanning electron microscope (FESEM) images showed that, PbSe nanostructures grown on the lead sheets with different morphologies. PbSe nanostructures with flakes shape were grown on the lead sheets that were placed in the lower temperature, while PbSe nanocubes and nanorods, which were grown on the nanocubes, were grown on the lead sheets in the higher temperature. The phase and composition of the product were identified by X-ray diffraction (XRD) pattern and X-ray photoelectron spectra (XPS). The XRD and XPS results showed that, the PbSe phase was started to form after 350°C and completed at 450°C. However, the XPS results showed that the Se concentration was different in the samples. In addition, Raman measurements confirmed the XRD and XPS results and indicated three Raman active modes, which belonged to PbSe phase for the nanostructures. The optical properties of the products were characterized by UV–Vis. The optical characterization results showed a band gap for the PbSe nanostructures in the infrared region.

scholarly journals In Situ Observation of Stress Accumulation during Sub-Merged Arc Welding

2014 ◽  
Vol 996 ◽  
pp. 417-423 ◽  
Author(s):  
Arne Kromm ◽  
Thomas Kannengiesser
Keyword(s):  
Arc Welding ◽  
Large Scale ◽  
X Ray Diffraction ◽  
X Ray ◽  
Residual Stress State ◽  
Testing Facility ◽  
Large Scale Testing ◽  
The Impact ◽  
Stress Accumulation

Results obtained from laboratory tests mostly need to be verified under fabrication conditions in order to incorporate design specifics (joint configuration and restraint), which effect the residual stress state considerably. For this purpose, multi-pass sub merged arc welding was performed in a special large-scale testing facility. The impact of varying interpass temperatures could be proven in-situ by means of a pronounced stress accumulation during welding and subsequent heat treatment accompanied by stress determination using X-ray diffraction.

Variables Involved in the Planting of Rice in the Rice Husk

2012 ◽  
Vol 517 ◽  
pp. 430-436
Author(s):  
J.L. Akasaki ◽  
E.J. Silva ◽  
L.C. Sousa ◽  
J.L.P. Melges ◽  
M.M. Tashima ◽  
...  
Keyword(s):  
Rice Husk ◽  
Large Scale ◽  
Rice Husk Ash ◽  
Scale Production ◽  
X Ray Diffraction ◽  
X Ray ◽  
Large Scale Production ◽  
Pozzolanic Materials ◽  
Different Strains ◽  
Different Origins

Rice production in Brazil in 2010 was approximately 12,2 million tons, and to reach that amount several planting techniques were used with different strains of rice in different rice-growing areas. Since Rice Husk Ash (RHA) is the pozzolan of vegetable origin most studied by researchers working in the area of pozzolanic materials, the present paper evaluates the influence that the form of planting, the climate, the soil, the strain of rice and the origin/amount of nitrogen-based fertilizers used in rice cultivation has on the chemical composition and crystallographic properties of RHA. The results obtained in this paper, confirm the importance of carrying out routine chemical analysis and X-Ray diffraction to maintain the quality control of the CCAs produced, because in situations of large-scale production, husks of different origins may be used.

Uniform Cerium-Based Coordination Polymer Microspheres: Preparation and Upconversion Emission

2016 ◽  
Vol 16 (4) ◽  
pp. 3705-3709 ◽  
Author(s):  
Zhi-Wen Nie ◽  
Cheng-Hui Zeng ◽  
Gang Xie ◽  
Sheng-Liang Zhong
Keyword(s):  
Electron Microscopy ◽  
Coordination Polymer ◽  
Large Scale ◽  
Upconversion Emission ◽  
X Ray Diffraction ◽  
X Ray ◽  
Band Emission ◽  
Transmission Electron ◽  
Light Excitation ◽  
Luminescent Spectra

Homogeneously doped Yb3+ and Er3+ cerium-based coordination polymer (CP) microspheres have been successfully synthesized on a large scale through a simple solvothermal route with 2, 5-pyridinedicarboxylic acid (2, 5-H2PDC) as the organic linker. CeO2:Yb3+, Er3+ porous microspheres were obtained by annealing the corresponding CP microspheres at 600 °C for 4 h under atmospheric pressure. These as-prepared products were characterized by Powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), energy-dispersion X-ray (EDX) spectroscopy, Thermogravimetric (TG) and derivative thermogravimetric (DTG) analysis. The room temperature upconversion luminescent spectra of the as-prepared microspheres were carried out by 980 nm NIR light excitation. Interestingly, Yb3+ and Er3+ codoped CP microspheres give a single-band emission centered at 673 nm, while the CeO2:Yb3+, Er3+ microspheres give emission in green and red region, with red being the dominant emission. The emission intensity of the CeO2:Yb3+, Er3+ microspheres were much stronger than that of the Yb3+ and Er3+ codoped CP microspheres.

SYNTHESIS OF In2O3 NANOWIRES ENHANCED BY ANODIC ALUMINA MEMBRANE

2006 ◽  
Vol 05 (04n05) ◽  
pp. 479-485
Author(s):  
C. W. LAI ◽  
X. Y. ZHANG ◽  
H. C. ONG ◽  
J. Y. DAI ◽  
H. L. W. CHAN
Keyword(s):  
Electron Microscopy ◽  
Large Scale ◽  
Anodic Alumina ◽  
X Ray Diffraction ◽  
Alumina Membrane ◽  
Thermal Evaporation Method ◽  
Single Crystalline ◽  
X Ray ◽  
Alumina Membranes ◽  
Transmission Electron

Large-scale single crystalline In 2 O 3 nanowires were successfully synthesized on anodic alumina membranes by a simple thermal evaporation method at 570°C. X-ray diffraction, transmission electron microscopy, and scanning electron microscopy studies revealed the formation of single crystalline In 2 O 3 nanowires with diameters of 50–100 nm and lengths of up to a few hundreds of micrometers. Cathodeluminescence study revealed existence of oxygen vacancies evidenced by a strong and broad emission at 470 nm with a shoulder at 400 nm. The growth mechanism of the nanostructures is also discussed.

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