57 research outputs found
Generation of torsional waves in a viscoelastic medium bounded by heterogeneous crustal layer and orthotropic substrate
No full textWrestling with Japanese Tribalism Emerging Collaborative Opportunities For India and Japan
Get PDFJapanese firms, with their strong technology base and high domestic factor costs, have the potential of teaming with India, with its more basic infrastructure and eight times the population. Japan's poorly-performing excess capital could fuel India's strongly-developing middle class and robust entrepreneurialism. Especially promising are collaborative information technology projects. What stands in the way of a greatly expanded relationship? Much of the blockage stems from Japan's insularism, an impetus here labeled tribalism. A hopeful dimension is that this tribalism can be clearly defined as archaic, recognized as detrimental, and then toned-down. Further points for development include an active campaign to encourage diversity in Japan, teaming up to provide alternatives to investment in neighboring China, and agitating for representation on the UN Security Council. India can help initiate all these processes, and can in turn benefit from a Japan reaching out for regional economic partnerships.homogeneity; tribalism; UN Security Council; partnership; immigration; trade; e-Japan strategy
Ultrahigh vacuum sample mount for x-ray photoelectron spectroscopy up to very high temperature (150-1400 K)
No full textSpectroscopic studies are rarely performed at very high temperature, especially when combined with light from a synchrotron source. Demanding conditions of maintaining ultrahigh vacuum (UHV) during heating, together with the typically brief access to beam time at multiuser synchrotron end stations, may contribute to some of the reasons for the difficulty of such experiments. Consequently, a large number of materials with interesting properties and industrial applications at high temperature remain unexplored. The authors describe here a simple portable sample mount assembly that can be easily utilized at a beamline, with potential utility for a variety of spectroscopic measurements requiring elevated temperatures and an UHV environment. In the specific application described here, the authors use a resistive cartridge heater interfaced with a standard manipulator previously designed for cooling by liquid nitrogen with an UHV chamber and a cylindrical mirror analyzer for x-ray photoemission spectroscopy (XPS) [also known as electron spectroscopy for chemical analysis (ESCA)] at the Synchrotron Radiation Center in Stoughton, WI. The heater cartridge required only modest power to reach target temperatures using an open-loop temperature control. Finally, the authors describe the measurements of XPS (ESCA) and total-electron yield x-ray absorption spectroscopy on nanopowders and on single crystals grown by them. They emphasize the simplicity of the setup, which they believe would be of interest to groups performing measurements at large facilities, where access and time are both limited. (C) 2011 American Vacuum Society. [DOI: 10.1116/1.3571528
Protein crystallographic studies to understand the reaction mechanism of enzymes: α-methylacyl-CoA racemase and argininosuccinate lyase
Get PDFAbstractEnzymes catalyze chemical changes in biological systems. Therefore, to understand the chemistry of living systems, it is important to understand the enzyme structure and the chemistry of the enzyme’s functional groups which are involved in catalysis. In this study, structure and function relationships of two enzymes, (1) α-methylacyl-CoA racemase from Mycobacterium tuberculosis (MCR) and (2) argininosuccinate lyase from Escherichia coli (eASL) have been studied using X-ray crystallography. The main focus of this study has been understanding the structure-function relationship of MCR. The eASL has been crystallized from a highly concentrated sample of purified recombinant α-methylacyl-CoA racemase in which it occurred as a minor impurity.The structure of eASL has been solved using molecular replacement at 2.44 Å resolution. The enzyme is a tetramer, but in this crystal form there is a dimer in the asymmetric unit. Each active site is constructed from loops of three different subunits. One of these catalytic loops, near residue Ser277 and Ser278, has been disordered in the previous structures of active lyases, but is very well ordered in this structure in one of the subunits due to the presence of two phosphate ions in the respective active site cavity. The positions of these phosphate ions indicate a plausible mode of binding of the succinate moiety of the substrate in the competent catalytic complex and therefore this structure has provided new information on the reaction mechanism of this class of enzymes.α-Methylacyl-CoA racemase (Amacr) catalyzes the racemization of α-methyl-branched CoA esters. An Amacr homologue from the eubacteria Mycobacterium tuberculosis, referred to as MCR, was taken as a model protein. MCR was purified, crystallized and the structure of unliganded protein was determined at 1.8 Å resolution using the MIRAS procedure. The structure shows that the enzyme is an interlocked dimer.To understand the reaction mechanism and the mode of substrate binding, several crystallographic binding studies were done using both wild type MCR and mutant H126A MCR crystals. In particular, the structures of the wild type MCR-complexes with (R, S)-ibuprofenoyl-CoA (1.85 Å), (R)-2-methylmyristoyl-CoA (1.6 Å) and (S)-2-methylmyristoyl-CoA (1.7 Å) were important in this respect. These crystal structures show that Asp156 and His126 are the two catalytic residues which are involved in proton donation and abstraction, respectively; when the (S)-enantiomeric substrate is bound in the active site and vice versa when the (R)-enantiomeric substrate is bound. The tight geometry of the active site also shows that His126 and Asp156 are involved in stabilizing the transition state. These crystal structures show that in the active site of MCR, there is one binding pocket for the CoA part and there are two different binding pockets (R-pocket and S-pocket) connected by a hydrophobic methionine rich surface for binding the fatty acyl part of the substrate. After substrate binding, proton abstraction takes place which produces a planar intermediate. Then, donation of a proton to the other side of the planar intermediate changes the configuration at the chiral center. During the stereochemical interconversion of the two enantiomers, the acyl group moves between R-pocket and S-pocket by sliding over the hydrophobic surface connecting these two pockets.Academic Dissertation to be presented with the assent of the Faculty of Science, University of Oulu, for public discussion in Kuusamonsali (Auditorium YB210), Linnanmaa, on June 6th, 2006, at 12 noonAbstract
Enzymes catalyze chemical changes in biological systems. Therefore, to understand the chemistry of living systems, it is important to understand the enzyme structure and the chemistry of the enzyme’s functional groups which are involved in catalysis. In this study, structure and function relationships of two enzymes, (1) α-methylacyl-CoA racemase from Mycobacterium tuberculosis (MCR) and (2) argininosuccinate lyase from Escherichia coli (eASL) have been studied using X-ray crystallography. The main focus of this study has been understanding the structure-function relationship of MCR. The eASL has been crystallized from a highly concentrated sample of purified recombinant α-methylacyl-CoA racemase in which it occurred as a minor impurity.
The structure of eASL has been solved using molecular replacement at 2.44 Å resolution. The enzyme is a tetramer, but in this crystal form there is a dimer in the asymmetric unit. Each active site is constructed from loops of three different subunits. One of these catalytic loops, near residue Ser277 and Ser278, has been disordered in the previous structures of active lyases, but is very well ordered in this structure in one of the subunits due to the presence of two phosphate ions in the respective active site cavity. The positions of these phosphate ions indicate a plausible mode of binding of the succinate moiety of the substrate in the competent catalytic complex and therefore this structure has provided new information on the reaction mechanism of this class of enzymes.
α-Methylacyl-CoA racemase (Amacr) catalyzes the racemization of α-methyl-branched CoA esters. An Amacr homologue from the eubacteria Mycobacterium tuberculosis, referred to as MCR, was taken as a model protein. MCR was purified, crystallized and the structure of unliganded protein was determined at 1.8 Å resolution using the MIRAS procedure. The structure shows that the enzyme is an interlocked dimer.
To understand the reaction mechanism and the mode of substrate binding, several crystallographic binding studies were done using both wild type MCR and mutant H126A MCR crystals. In particular, the structures of the wild type MCR-complexes with (R, S)-ibuprofenoyl-CoA (1.85 Å), (R)-2-methylmyristoyl-CoA (1.6 Å) and (S)-2-methylmyristoyl-CoA (1.7 Å) were important in this respect. These crystal structures show that Asp156 and His126 are the two catalytic residues which are involved in proton donation and abstraction, respectively; when the (S)-enantiomeric substrate is bound in the active site and vice versa when the (R)-enantiomeric substrate is bound. The tight geometry of the active site also shows that His126 and Asp156 are involved in stabilizing the transition state. These crystal structures show that in the active site of MCR, there is one binding pocket for the CoA part and there are two different binding pockets (R-pocket and S-pocket) connected by a hydrophobic methionine rich surface for binding the fatty acyl part of the substrate. After substrate binding, proton abstraction takes place which produces a planar intermediate. Then, donation of a proton to the other side of the planar intermediate changes the configuration at the chiral center. During the stereochemical interconversion of the two enantiomers, the acyl group moves between R-pocket and S-pocket by sliding over the hydrophobic surface connecting these two pockets
Pushing the VHE Frontier: LST-1’s Inaugural Detection of the Distant Quasar OP 313
Get PDFIn December 2023, the Flat Spectrum Radio Quasar OP 313 experienced an extraordinary very-high-energy (VHE, E > 100 GeV) gamma-ray flare, reaching an integral flux of 0.3 Crab Units above 100 GeV. This event marked the first VHE detection of OP 313 by the first Large-Sized Telescope (LST-1) at the Northern site of the Cherenkov Telescope Array Observatory, delivering its inaugural scientific result and establishing OP 313 as the most distant blazar detected in this energy regime (z = 0.997). Coordinated observations with LST-1, the MAGIC telescopes, and Fermi-LAT enabled us to capture the detailed spectral and temporal evolution of the flare, which we compared with a low-emission state observed in January 2024. A complementary multi-wavelength campaign — from radio through X-rays — enabled us to construct and model the broad-band spectral energy distribution within a two-zone leptonic framework. In this scenario, synchrotron and external Compton processes, involving seed photons from the dusty torus and broad-line region, account for the observed emission, although several combinations of photon fields remain plausible. Furthermore, the broad energy coverage provided by our observations allowed us to probe the attenuation of VHE gamma-rays by the Extragalactic Background Light, yielding competitive upper limits on its intensity. This work not only demonstrates the breakthrough capabilities of LST-1 in VHE gamma-ray astronomy but also provides fresh insights into the complex radiative mechanisms of high-redshift blazars, paving the way for future studies of extreme extragalactic sources.LASTR
Protein crystallographic studies to understand the reaction mechanism of enzymes:α-methylacyl-CoA racemase and argininosuccinate lyase
No full textAbstract
Enzymes catalyze chemical changes in biological systems. Therefore, to understand the chemistry of living systems, it is important to understand the enzyme structure and the chemistry of the enzyme’s functional groups which are involved in catalysis. In this study, structure and function relationships of two enzymes, (1) α-methylacyl-CoA racemase from Mycobacterium tuberculosis (MCR) and (2) argininosuccinate lyase from Escherichia coli (eASL) have been studied using X-ray crystallography. The main focus of this study has been understanding the structure-function relationship of MCR. The eASL has been crystallized from a highly concentrated sample of purified recombinant α-methylacyl-CoA racemase in which it occurred as a minor impurity.
The structure of eASL has been solved using molecular replacement at 2.44 Å resolution. The enzyme is a tetramer, but in this crystal form there is a dimer in the asymmetric unit. Each active site is constructed from loops of three different subunits. One of these catalytic loops, near residue Ser277 and Ser278, has been disordered in the previous structures of active lyases, but is very well ordered in this structure in one of the subunits due to the presence of two phosphate ions in the respective active site cavity. The positions of these phosphate ions indicate a plausible mode of binding of the succinate moiety of the substrate in the competent catalytic complex and therefore this structure has provided new information on the reaction mechanism of this class of enzymes.
α-Methylacyl-CoA racemase (Amacr) catalyzes the racemization of α-methyl-branched CoA esters. An Amacr homologue from the eubacteria Mycobacterium tuberculosis, referred to as MCR, was taken as a model protein. MCR was purified, crystallized and the structure of unliganded protein was determined at 1.8 Å resolution using the MIRAS procedure. The structure shows that the enzyme is an interlocked dimer.
To understand the reaction mechanism and the mode of substrate binding, several crystallographic binding studies were done using both wild type MCR and mutant H126A MCR crystals. In particular, the structures of the wild type MCR-complexes with (R, S)-ibuprofenoyl-CoA (1.85 Å), (R)-2-methylmyristoyl-CoA (1.6 Å) and (S)-2-methylmyristoyl-CoA (1.7 Å) were important in this respect. These crystal structures show that Asp156 and His126 are the two catalytic residues which are involved in proton donation and abstraction, respectively; when the (S)-enantiomeric substrate is bound in the active site and vice versa when the (R)-enantiomeric substrate is bound. The tight geometry of the active site also shows that His126 and Asp156 are involved in stabilizing the transition state. These crystal structures show that in the active site of MCR, there is one binding pocket for the CoA part and there are two different binding pockets (R-pocket and S-pocket) connected by a hydrophobic methionine rich surface for binding the fatty acyl part of the substrate. After substrate binding, proton abstraction takes place which produces a planar intermediate. Then, donation of a proton to the other side of the planar intermediate changes the configuration at the chiral center. During the stereochemical interconversion of the two enantiomers, the acyl group moves between R-pocket and S-pocket by sliding over the hydrophobic surface connecting these two pockets
Long-term irrigation with zinc smelter effluent affects important soil properties and heavy metal content in food crops and soil in Rajasthan, India
No full text
Floating Zone Growth of Bulk Single Crystals of Complex Oxides
No full textABSTRACTIn this MRS Proceedings paper, we present a review of the floating zone growth process, and describe growth techniques as relevant to four selected families of current or continued interest in the area of condensed matter physics of highly correlated electron systems: Cuprate oxides (Bi2Sr2CaCu2Oy), Ruthenate oxides (Sr2RuO4), Manganite oxides (La1-xSrxMnO3, La2–2xSr1+2xMn2O7, (RE) MnO3 (RE=Rare Earth)) and Ferrite oxides (BiFeO3). We also discuss our experiences with factors that tend to contribute to poor crystal growth, as relevant to experiments to probe correlated-electron physics in such crystals.</jats:p
Phosphorus-supported multidentate coumarin-containing fluorescence sensors for Cu<SUP>2+</SUP>
No full textPhosphorus hydrazides PhP(O)[N(Me)NH2]2, (S)P[N(Me)NH2]3, and N3P3[N(Me)NH2]6 were condensed with 7-diethylaminocoumarin-3-aldehyde (RCHO) to afford the corresponding hydrazones PhP(O)[N(Me)NCHR]2 (1), (S)P[N(Me)=NCHR]3 (2), and N3P3[N(Me)N=CHR]6 (3). The structural characterization of 1-3 was carried out by their HRMS, 1H and 31P{1H} NMR spectra. The molecular structure of 2 was established by a single-crystal X-ray analysis. Interaction of 1 and 2 with various transition metal ions revealed substantial fluorescence enhancement upon interaction with Cu2+ enabling a selective detection mechanism for this metal ion. However, such a fluorescence enhancement was not observed in the case of 3. A 1:1 complex [2·Zn][ClO4]2·4CH2Cl2 was isolated in the reaction of 2 with Zn(ClO4)2·6H2O. The molecular structure of this complex revealed that the ZnII is encapsulated by the ligand utilizing a 3N, 3O coordination set
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