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Peng Liu - One of the best experts on this subject based on the ideXlab platform.
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Purification, partial characterization, crystallization and structural determination of AHP-LAAO, a novel L-amino-acid oxidase with Cell apoptosis-inducing activity from Agkistrodon halys pallas venom.
Acta Crystallographica Section D Biological Crystallography, 2004Co-Authors: Hongmin Zhang, Liwen Niu, Maikun Teng, Yuzhen Wang, Qun Liu, Qingqiu Huang, Quan Hao, Yicheng Dong, Peng LiuAbstract:A snake-venom protein named AHP-LAAO has been purified from Agkistrodon halys pallas venom using four-stage chromatography. AHP-LAAO is a novel member of the snake-venom l-amino-acid oxidase family. Its amino-acid sequence shows high homology to other members of this family. For l-leucine, the values of kcat and KM are 31.1 s−1 and 0.25 mM, respectively. The molecular weight of AHP-LAAO is about 60.7 kDa as determined by MALDI–TOF mass spectrometry. AHP-LAAO can also induce apoptosis of cultured Hela Cells. Two sets of diffraction data with similar resolution limits (about 2.5 A) were collected independently at MacCHESS (Cornell High Energy Synchrotron Source, USA) and IHEP (Institute of High Energy Physics, Beijing, China). The crystals belong to space group I213, with Unit-Cell Parameter a = 169.31 A, corresponding to one molecule in the asymmetric Unit and a volume-to-weight ratio of 3.33 A3 Da−1. The final structural model is similar to that of l-amino-acid oxidase from Calloselasma rhodostoma venom.
Peter J Heaney - One of the best experts on this subject based on the ideXlab platform.
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synchrotron powder x ray diffraction study of the structure and dehydration behavior of palygorskite
American Mineralogist, 2007Co-Authors: Jeffrey E Post, Peter J HeaneyAbstract:Rietveld refinements using synchrotron powder X-ray diffraction data were used to study the crystal structure and dehydration behavior of pure monoclinic palygorskite samples from Korea and Alaska. The 300 and 100 K palygorskite structures in air compare well with previous models but provide additional details about zeolitic H2O sites and reveal that the Al atoms are ordered into the inner M2 octahedral sites and the Mg cations into the M3 sites at the edges of the tunnels. Real-time, temperature-resolved synchrotron powder X-ray diffraction data and Rietveld refinements were used to investigate the monoclinic palygorskite structure from 300 to 1400 K (in air). Rietveld refinements showed that most of the zeolitic H2O is lost by 425 K, accompanied by a decrease in the Unit-Cell volume of 1.3%, primarily owing to a decrease in the a Unit-Cell Parameter and an increase in the ? angle. The structurally bound H2O is lost in two stages, at temperature intervals of 475-540 and 580-725 K. Above 825 K in air a portion of the Korean sample transformed to a folded structure; the Alaskan sample folded at 575 K under vacuum. A structure model was refined for the folded structure. At 1015 K for the samplemore » heated in air, ?-quartz diffraction peaks appeared and increased in intensity as heating continued to the maximum temperature. Cristobalite formed above 1050 K, along with a small amount of clinoenstatite, and both phases persisted to the maximum temperature studied.« less
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synchrotron powder x ray diffraction study of the structure and dehydration behavior of sepiolite
American Mineralogist, 2007Co-Authors: Jeffrey E Post, David L Bish, Peter J HeaneyAbstract:Rietveld refinements using synchrotron powder X-ray diffraction data were used to study the crystal structure and dehydration behavior of pure monoclinic palygorskite samples from Korea and Alaska. The 300 and 100 K palygorskite structures in air compare well with previous models but provide additional details about zeolitic H2O sites and reveal that the Al atoms are ordered into the inner M2 octahedral sites and the Mg cations into the M3 sites at the edges of the tunnels. Real-time, temperature-resolved synchrotron powder X-ray diffraction data and Rietveld refinements were used to investigate the monoclinic palygorskite structure from 300 to 1400 K (in air). Rietveld refinements showed that most of the zeolitic H2O is lost by 425 K, accompanied by a decrease in the Unit-Cell volume of 1.3%, primarily owing to a decrease in the a Unit-Cell Parameter and an increase in the ? angle. The structurally bound H2O is lost in two stages, at temperature intervals of 475-540 and 580-725 K. Above 825 K in air a portion of the Korean sample transformed to a folded structure; the Alaskan sample folded at 575 K under vacuum. A structure model was refined for the folded structure. At 1015 K for the samplemore » heated in air, ?-quartz diffraction peaks appeared and increased in intensity as heating continued to the maximum temperature. Cristobalite formed above 1050 K, along with a small amount of clinoenstatite, and both phases persisted to the maximum temperature studied.« less
Andrei V. Shevelkov - One of the best experts on this subject based on the ideXlab platform.
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synthesis structure and transport properties of type i derived clathrate ge46 xpxse8 y x 15 4 1 y 0 2 65 with diverse host guest bonding
Inorganic Chemistry, 2013Co-Authors: Maria A Kirsanova, Andrei V Olenev, Artem M Abakumov, Takao Mori, Satofumi Maruyama, Maria Matveeva, Dmitry Batuk, Andrei V Gerasimenko, Yuri Grin, Andrei V. ShevelkovAbstract:A first clathrate compound with selenium guest atoms, [Ge46–xPx]Se8–y□y (x = 15.4(1); y = 0–2.65; □ denotes a vacancy), was synthesized as a single-phase and structurally characterized. It crystallizes in the space group Fm3 with the Unit Cell Parameter a varying from 20.310(2) to 20.406(2) A and corresponding to a 2 × 2 × 2 superCell of a usual clathrate-I structure. The superstructure is formed due to the symmetrical arrangement of the three-bonded framework atoms appearing as a result of the framework transformation of the parent clathrate-I structure. Selenium guest atoms occupy two types of polyhedral cages inside the positively charged framework; all selenium atoms in the larger cages form a single covalent bond with the framework atoms, relating the title compounds to a scanty family of semiclathrates. According to the measurements of electrical resistivity and Seebeck coefficient, [Ge46–xPx]Se8–y□y is an n-type semiconductor with Eg = 0.41 eV for x = 15.4(1) and y = 0; it demonstrates the maximal...
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homo and heterovalent substitutions in the new clathrates i si30p16te8 xsex and si30 xp16 xte8 xbrx synthesis crystal structure and thermoelectric properties
Inorganic Chemistry, 2012Co-Authors: Nikolay S Abramchuk, Andrei V Olenev, Wilder Carrillocabrera, Igor Veremchuk, N Oeschler, Y Prots, Ulrich Burkhardt, Evgeny V Dikarev, Y Grin, Andrei V. ShevelkovAbstract:The new cationic clathrates I Si30P16Te8–xSex and Si30+xP16–xTe8–xBrx were synthesized by the standard ampule technique. The Si30P16Te8–xSex (x = 0–2.3) clathrates crystallize in the cubic space group Pm3n with the Unit Cell Parameter a ranging from 9.9382(2) to 9.9696(1) A. In the case of the Si30+xP16–xTe8–xBrx (x = 1–6.4) clathrates, the lattice Parameter varies from 9.9720(8) to 10.0405(1) A; at lower Si/P ratios (x = 1–3) the ordering of bromine atoms induces the splitting of the guest positions and causes the transformation from the space group Pm3n to Pm3. Irrespective of the structure peculiarities, the normal temperature motion of the guest atoms inside the oversized cages of the framework is observed. The title clathrates possess very low thermal expansion coefficients ranging from 6.6 × 10–6 to 1.0 × 10–5 K–1 in the temperature range of 298–1100 K. The characteristic Debye temperature is about 490 K. Measurements of the electrical resistivity and thermopower showed typical behavior of p-type...
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semiclathrates of the ge p te system synthesis and crystal structures
Chemistry: A European Journal, 2011Co-Authors: Maria A Kirsanova, L N Reshetova, Andrei V Olenev, Artem M Abakumov, Andrei V. ShevelkovAbstract:Novel compounds (Ge46xPx)Tey (13.9 x 15.6, 5.92 y 7.75) with clathrate-like structures have been prepared and structurally charac- terized. They crystallize in the space group Fm3 ¯ with the Unit Cell Parameter changing from 20.544(2) to 20.698(2) � (Z = 8) on going from x = 13.9 to x = 15.6. Their crystal structure is com- posed of a covalently bonded GeP framework that hosts tellurium atoms in the guest positions and can be viewed as a peculiar variant of the type I clathrate superstructure. In con- trast to the conventional type I clath- rates, (Ge46xPx)Tey contain tricoordi- nated (3b) atoms and no vacancies in the framework positions. As a conse- quence of the transformation of the framework, the majority of the guest tellurium atoms form a single covalent bond with the host framework and thus the title compounds are the first repre- sentative of semiclathrates with cova- lent bonding. A comparison is made with silicon clathrates and the evolu- tion of the crystal structure upon changing the tellurium content is dis- cussed.
Huen Lee - One of the best experts on this subject based on the ideXlab platform.
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spectroscopic identification of the mixed hydrogen and carbon dioxide clathrate hydrate
Journal of the American Chemical Society, 2005Co-Authors: Doyoun Kim, Huen LeeAbstract:In this contribution, we first found the novel clathrate hydrate containing two gaseous guests of hydrogen and carbon dioxide by spectroscopic analysis. X-ray powder diffraction and NMR spectroscopy were used to identify structure and guest distribution of the mixed H2 + CO2 hydrate. X-ray diffraction result confirmed that the Unit Cell Parameter was 11.8602 ± 0.0010 A, and the formed hydrate was identified as structure I hydrate. 1H magic angle spinning (MAS) NMR and 13C cross-polarization (CP) NMR spectroscopy were used to examine the distribution of hydrogen and carbon dioxide molecules in the cages of structure I, respectively. These NMR spectra showed that carbon dioxide molecules occupied both small 512 cages and large 51262 cages, and hydrogen molecules only were occluded in small 512 cages of structure I. The new finding of the mixed hydrogen hydrate is expected to contribute toward the development of hydrogen production technology and, particularly, inclusion chemistry.
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structure and guest distribution of the mixed carbon dioxide and nitrogen hydrates as revealed by x ray diffraction and 13c nmr spectroscopy
Journal of Physical Chemistry B, 2004Co-Authors: Yutaek Seo And, Huen LeeAbstract:In this contribution, X-ray diffraction and 13C NMR spectroscopy were used to identify structure and guest distribution of the mixed N2 + CO2 hydrates. X-ray diffraction results of the mixed N2 + CO2 hydrates confirmed that the Unit Cell Parameter was ∼11.8 A over the gas mixture composition range of 3−20 mol % CO2 and the formed hydrates were identified as structure I. When the composition of the gas mixture was reduced to 1 mol % CO2, the structure of the mixed hydrate was transformed to structure II showing the Unit Cell Parameter of 17.26(2) A. 13C cross-polarization (CP) NMR spectroscopy was used to examine the distribution of carbon dioxide molecules in small 512 and large 51262 cages of structure I. From NMR spectra of the mixed N2 + CO2 hydrate formed from gas mixture of 20 and 10 mol % CO2, powder patterns having chemical shift anisotropy of −54.5 and −53.8 ppm were observed, respectively. There was no clear isotropic line indicating carbon dioxide molecules in the small 512 cages of structure I....
U Bismayer - One of the best experts on this subject based on the ideXlab platform.
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high temperature structural transformations in the relaxor ferroelectrics pbsc0 5 ta0 5 o3 and pb0 78 ba0 22 sc0 5 ta0 5 o3
Physical Review B, 2008Co-Authors: B Mihailova, Bernd J Maier, C Paulmann, Thomas Malcherek, J Ihringer, M Gospodinov, Rainer Stosch, B Guttler, U BismayerAbstract:Temperature-driven structural transformations in Pb-based perovskite-type relaxors are studied by using polarized Raman spectroscopy, high-resolution powder, and synchrotron single-crystal x-ray diffraction applied to PbSc0.5 Ta0.5 O3 (PST) and Pb0.78 Ba0.22 Sc0.5 Ta0.5 O3 (PBST). The two compounds were chosen as model systems because PST is a relaxor that exhibits ferroelectric long-range order on cooling, whereas PBST shows canonical relaxor behavior. The temperature evolution of phonon anomalies and the pseudocubic Unit-Cell Parameter for both PST and PBST reveals the existence of a characteristic temperature T between the Burns temperature TB and the temperature of the dielectric-permittivity maximum Tm. T is associated with the coupling of initially nucleated small polar clusters and their aggregation into larger polar clusters. The temperature range between TB and T is characterized by a coupling between adjacent off-centered BO6 octahedra to form initial polar clusters, while the range between T and Tm is characterized by a coupling between off-centered B cations from adjacent polar clusters. Off-centered Pb atoms exist even above the Burns temperature and their length of coherence governs the coupling between polar regions comprising B -cation off-center shifts and, consequently, directs the formation of the ferroelectric state to a normal, long-range ordered or nonergodic relaxor state.
