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Svetlana V Antonyuk - One of the best experts on this subject based on the ideXlab platform.
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sub atomic resolution x ray crystallography and neutron crystallography promise challenges and potential
IUCrJ, 2015Co-Authors: M P Blakeley, Samar S Hasnain, Svetlana V AntonyukAbstract:The International Year of Crystallography saw the number of macromolecular structures deposited in the Protein Data Bank cross the 100000 mark, with more than 90000 of these provided by X-ray crystallography. The number of X-ray structures determined to sub-atomic resolution (i.e. ≤1 A) has passed 600 and this is likely to continue to grow rapidly with diffraction-limited synchrotron Radiation sources such as MAX-IV (Sweden) and Sirius (Brazil) under construction. A dozen X-ray structures have been deposited to ultra-high resolution (i.e. ≤0.7 A), for which precise electron density can be exploited to obtain charge density and provide information on the bonding character of catalytic or electron transfer sites. Although the development of neutron macromolecular crystallography over the years has been far less pronounced, and its application much less widespread, the availability of new and improved instrumentation, combined with dedicated deuteration facilities, are beginning to transform the field. Of the 83 macromolecular structures deposited with neutron diffraction data, more than half (49/83, 59%) were released since 2010. Sub-mm3 crystals are now regularly being used for data collection, structures have been determined to atomic resolution for a few small proteins, and much larger unit-cell systems (cell edges >100 A) are being successfully studied. While some details relating to H-atom positions are tractable with X-ray crystallography at sub-atomic resolution, the mobility of certain H atoms precludes them from being located. In addition, highly polarized H atoms and protons (H+) remain invisible with X-rays. Moreover, the majority of X-ray structures are determined from cryo-cooled crystals at 100 K, and, although Radiation damage can be strongly controlled, especially since the advent of shutterless fast detectors, and by using limited doses and crystal translation at micro-focus Beams, Radiation damage can still take place. Neutron crystallography therefore remains the only approach where diffraction data can be collected at room temperature without Radiation damage issues and the only approach to locate mobile or highly polarized H atoms and protons. Here a review of the current status of sub-atomic X-ray and neutron macromolecular crystallography is given and future prospects for combined approaches are outlined. New results from two metalloproteins, copper nitrite reductase and cytochrome c′, are also included, which illustrate the type of information that can be obtained from sub-atomic-resolution (∼0.8 A) X-ray structures, while also highlighting the need for complementary neutron studies that can provide details of H atoms not provided by X-ray crystallography.
M P Blakeley - One of the best experts on this subject based on the ideXlab platform.
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sub atomic resolution x ray crystallography and neutron crystallography promise challenges and potential
IUCrJ, 2015Co-Authors: M P Blakeley, Samar S Hasnain, Svetlana V AntonyukAbstract:The International Year of Crystallography saw the number of macromolecular structures deposited in the Protein Data Bank cross the 100000 mark, with more than 90000 of these provided by X-ray crystallography. The number of X-ray structures determined to sub-atomic resolution (i.e. ≤1 A) has passed 600 and this is likely to continue to grow rapidly with diffraction-limited synchrotron Radiation sources such as MAX-IV (Sweden) and Sirius (Brazil) under construction. A dozen X-ray structures have been deposited to ultra-high resolution (i.e. ≤0.7 A), for which precise electron density can be exploited to obtain charge density and provide information on the bonding character of catalytic or electron transfer sites. Although the development of neutron macromolecular crystallography over the years has been far less pronounced, and its application much less widespread, the availability of new and improved instrumentation, combined with dedicated deuteration facilities, are beginning to transform the field. Of the 83 macromolecular structures deposited with neutron diffraction data, more than half (49/83, 59%) were released since 2010. Sub-mm3 crystals are now regularly being used for data collection, structures have been determined to atomic resolution for a few small proteins, and much larger unit-cell systems (cell edges >100 A) are being successfully studied. While some details relating to H-atom positions are tractable with X-ray crystallography at sub-atomic resolution, the mobility of certain H atoms precludes them from being located. In addition, highly polarized H atoms and protons (H+) remain invisible with X-rays. Moreover, the majority of X-ray structures are determined from cryo-cooled crystals at 100 K, and, although Radiation damage can be strongly controlled, especially since the advent of shutterless fast detectors, and by using limited doses and crystal translation at micro-focus Beams, Radiation damage can still take place. Neutron crystallography therefore remains the only approach where diffraction data can be collected at room temperature without Radiation damage issues and the only approach to locate mobile or highly polarized H atoms and protons. Here a review of the current status of sub-atomic X-ray and neutron macromolecular crystallography is given and future prospects for combined approaches are outlined. New results from two metalloproteins, copper nitrite reductase and cytochrome c′, are also included, which illustrate the type of information that can be obtained from sub-atomic-resolution (∼0.8 A) X-ray structures, while also highlighting the need for complementary neutron studies that can provide details of H atoms not provided by X-ray crystallography.
Samar S Hasnain - One of the best experts on this subject based on the ideXlab platform.
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sub atomic resolution x ray crystallography and neutron crystallography promise challenges and potential
IUCrJ, 2015Co-Authors: M P Blakeley, Samar S Hasnain, Svetlana V AntonyukAbstract:The International Year of Crystallography saw the number of macromolecular structures deposited in the Protein Data Bank cross the 100000 mark, with more than 90000 of these provided by X-ray crystallography. The number of X-ray structures determined to sub-atomic resolution (i.e. ≤1 A) has passed 600 and this is likely to continue to grow rapidly with diffraction-limited synchrotron Radiation sources such as MAX-IV (Sweden) and Sirius (Brazil) under construction. A dozen X-ray structures have been deposited to ultra-high resolution (i.e. ≤0.7 A), for which precise electron density can be exploited to obtain charge density and provide information on the bonding character of catalytic or electron transfer sites. Although the development of neutron macromolecular crystallography over the years has been far less pronounced, and its application much less widespread, the availability of new and improved instrumentation, combined with dedicated deuteration facilities, are beginning to transform the field. Of the 83 macromolecular structures deposited with neutron diffraction data, more than half (49/83, 59%) were released since 2010. Sub-mm3 crystals are now regularly being used for data collection, structures have been determined to atomic resolution for a few small proteins, and much larger unit-cell systems (cell edges >100 A) are being successfully studied. While some details relating to H-atom positions are tractable with X-ray crystallography at sub-atomic resolution, the mobility of certain H atoms precludes them from being located. In addition, highly polarized H atoms and protons (H+) remain invisible with X-rays. Moreover, the majority of X-ray structures are determined from cryo-cooled crystals at 100 K, and, although Radiation damage can be strongly controlled, especially since the advent of shutterless fast detectors, and by using limited doses and crystal translation at micro-focus Beams, Radiation damage can still take place. Neutron crystallography therefore remains the only approach where diffraction data can be collected at room temperature without Radiation damage issues and the only approach to locate mobile or highly polarized H atoms and protons. Here a review of the current status of sub-atomic X-ray and neutron macromolecular crystallography is given and future prospects for combined approaches are outlined. New results from two metalloproteins, copper nitrite reductase and cytochrome c′, are also included, which illustrate the type of information that can be obtained from sub-atomic-resolution (∼0.8 A) X-ray structures, while also highlighting the need for complementary neutron studies that can provide details of H atoms not provided by X-ray crystallography.
A. H. Grigoryan - One of the best experts on this subject based on the ideXlab platform.
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Resonance properties of low-energy electron Beams Radiation in a two-layer waveguide
Journal of Contemporary Physics (Armenian Academy of Sciences), 2013Co-Authors: A. H. GrigoryanAbstract:We obtain an approximating formula for the low-energy impedance of a two-layer cylindrical waveguide, which allows constructing explicit expressions for the space-time functions that characterize the Radiation of a charged particle in a waveguide. The general laws of the evolution of impedance and wake potentials with increasing particle energy and with the change of geometric and electrodynamical parameters of the waveguide are obtained. The settings of waveguides convenient for experimental research and having resonance properties at energies of about 20 MeV are revealed.
Pehr A Lind - One of the best experts on this subject based on the ideXlab platform.
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myocardial perfusion changes in patients irradiated for left sided breast cancer and correlation with coronary artery distribution
International Journal of Radiation Oncology Biology Physics, 2001Co-Authors: Pehr A Lind, Robert Pagnanelli, Lawrence B Marks, Salvador Borgesneto, S Zhou, K Light, Patricia H HardenberghAbstract:Abstract Purpose: To evaluate postRadiation regional heart perfusion changes with single photon emission tomography (SPECT) myocardial perfusion imaging in 69 patients treated with tangential photon Beams Radiation therapy (RT) for left-sided breast cancer. To correlate SPECT changes with percent irradiated left ventricle (LV) volume and risk factors for coronary artery disease (CAD). Methods and Materials: Rest SPECT of the LV was acquired pre-RT and at 6-month intervals post-RT. The extent of defects (%) with a severity > 1.5 standard deviations below the mean was quantitatively analyzed for the distributions of the left anterior descending (LAD) artery, left circumflex (LCX) artery, and right coronary artery (RCA) based on computer assisted polar map reconstruction (i.e., bull's-eye-view). Changes in perfusion were correlated with percent irradiated LV receiving > 25 Gy (range 0–32%). Data on patient- and treatment-related factors were collected prospectively (e.g., cardiac premorbidity, risk factors for CAD, chemotherapy, and hormonal treatment). Results: In the LAD distribution, there were increased perfusion defects at 6 months (median 11%; interquartile range 2–23) compared with baseline (median 5%; interquartile range 1–14) ( p p p = 0.005), and pre-RT hypercholesterolemia ( p = 0.006). The SPECT defects in the LAD distribution at 12 and 18 months were not statistically different from those at 6 months. The perfusion defects in the LAD distribution were limited essentially to the regions of irradiated myocardium. Conclusion: Tangential photon beam RT in patients with left-sided breast cancer was associated with short-term SPECT defects in the vascular distribution corresponding to the Radiation portals. Factors related to the extent of perfusion defects included the percent irradiated LV, hormonal treatment, and pre-RT hypercholesterolemia.