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Structure Investigation (structure + investigation)
Selected AbstractsStructure Investigation of Bridgehead Aziridine: Synthesis, Theoretical, and Crystallographic Study of 2,4,6-Triphenyl-1,3-diazabicyclo[3.1.0]hex-3-eneHELVETICA CHIMICA ACTA, Issue 2 2006Giuseppe Bruno Abstract A one-pot three-component procedure to efficiently create the 1,3-diazabicyclo[3.1.0]hex-3-ene system is reported. The molecular structure of 2,4,6-triphenyl-1,3-diazabicyclo[3.1.0]hex-3-ene (3) was studied by X-ray diffraction and compared to ab initio and density-functional-theory (DFT) calculations restricted to the core moiety. Geometry optimizations for structural isomers and tautomeric forms of this aziridine fragment, taken as simplified models, were carried out at high calculation levels. Moreover, the same methods were utilized to evaluate the proton affinity of two crucial aziridine tautomers. [source] LaSeTe2 , Temperature Dependent Structure Investigation and Electron Holography on a Charge-Density-Wave-Hosting Compound.CHEMINFORM, Issue 8 2004Thomas Doert Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: Single Crystal Structure Investigation of Twinned NaKSi2O5 , A Novel Single Layer Silicate.CHEMINFORM, Issue 50 2001Srdjan Rakic Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Single-Crystal Structure Investigation of NdNi and NdNi5.CHEMINFORM, Issue 3 2001Lingmin Zeng Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Synthesis and Structure Investigations of Potential Sedative and Anticonvulsant Hydroxy- and Acetoxy-N-(3-oxobutyl)-pyrido[2,3-d]pyridazinones.CHEMINFORM, Issue 1 2003Edith Goessnitzer Abstract For Abstract see ChemInform Abstract in Full Text. [source] Structure investigation of Maltacine C1a, C1b, C2a and C2b,cyclic peptide lactones of the Maltacine complex from Bacillus subtilisJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 10 2005Gunnar Hagelin Abstract A new complex of cyclic peptide lactone antibiotics from Bacillus subtilis, which we named Maltacines, has recently been described. The structure elucidation of four of them is reported in this paper. The amino acid sequences and structures of the peptides were found by MSn of the ring-opened linear peptides, which gave uninterrupted sequences of Bn and Y,n ions. The identities of three unknown residues in the sequences were solved by a combination of derivatisation with phenylisothiocyanate (PITC), high-resolution mass spectrometry and H/D exchange. The nature and position of the cyclic structure was disclosed by a chemo-selective ring opening with Na18OH and was found to be a lactone formed between a hydroxyl of residue number 4 and the C -terminal amino acid number 12. For verification of the structure of the B2+ ion, peptides with different combinations of P/Q and P/K at the N -terminus were synthesised. The structure of the four peptides were found to be: C1a and C2a: cyclo-4,12(P-Q-Y-Adip-V-E-T-Y-Orn-103-Y-I-OH) and C1b/C2b: cyclo-4,12(P-Q-Y-Adip-V-E-T-Y-K-103-Y-I-OH). Adip = aminodihydroxy pentanoic acid. Copyright © 2005 John Wiley & Sons, Ltd. [source] Structure investigation of Maltacine D1a, D1b and D1c,cyclic peptide lactones of the Maltacine complex from Bacillus subtilisJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 10 2005Gunnar Hagelin Abstract A new complex of cyclic peptide lactone antibiotics from Bacillus subtilis, which we named Maltacines has recently been described. The structure elucidation of three of them is reported in this paper. The amino acid sequences and structures of the peptides were found by MSn of the ring-opened linear peptides that gave uninterrupted sequences of Bn and Y,n ions. The identities of four unknown residues in the sequences were solved by a combination of derivatisation with phenylisothiocyanate (PITC), high-resolution mass spectrometry and H/D exchange. The nature and position of the cyclic structure was disclosed by a chemo-selective ring opening with Na18OH and was found to be a lactone formed between a hydroxyl of residue number 4 and the C -terminal amino acid number 12. For verification of the structure of the B2+ ion, peptides with different combinations of P/Q and P/K at the N -terminus were synthesized. The structures of the four peptides is tentatively suggested to be: D1a: cyclo(4,12)-P-Q-Y-Adip-A-E-T-Y-Orn-HGly-Y-I-OH, D1b: cyclo(4,12)-P-Q-Y-Adip-A-E-T-Y-Orn-S-Y-I-OH and D1c: cyclo(4,12)-P-Q-Y-Adip-A-E-T-Y-K-S-Y-I-OH. Adip = aminodihydroxy pentanoic acid and HGly = hydroxyglycine. Copyright © 2005 John Wiley & Sons, Ltd. [source] Synthesis and crystal structure investigation of pyridine-2-(3,-mercaptopropanoic acid)- N -oxideCRYSTAL RESEARCH AND TECHNOLOGY, Issue 10 2007R. Ramasubramanian Abstract Pyridine-2-(3,-mercaptopropanoic acid)- N -oxide (I), is a higher homologue of 1-oxopyridinium-2-thioacetic acid (II) [1]. It crystallizes in monoclinic space group P21 with a = 9.2168(2) Å, b = 4.1423(2) Å, c = 11.3904(4) Å, , = 98.65(2)°, V = 429.93(3) Å3 and Z = 2. The least-squares refinement gave residual index R = 0.024 for 1070 observed reflections. The introduction of an additional methylene group in (II) causes a flip in the carboxylic acid group of (I) that facilitates the molecules to align infinite antiparallel chains through strong C,H···O interactions. The molecules are interlinked by O,H···O hydrogen bonding across the chains and forming an infinite screw chain along y-direction. The molecular packing is stabilized by O,H···O and C,H···O hydrogen bonding and ,-, electron interactions. This is an important facet of the crystal packing. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Organic cyclic difluoramino-nitramines: infrared and Raman spectroscopy of 3,3,7,7-tetrakis(difluoramino)octahydro 1,5-dinitro-1,5-diazocine (HNFX)JOURNAL OF RAMAN SPECTROSCOPY, Issue 8 2009Philippe F. Weck Abstract We present the first vibrational structure investigation of 3,3,7,7-tetrakis(difluoramino)octahydro-1,5-dinitro- 1,5-diazocine (HNFX),and, more generally, of a member of the new class of gem -bis(difluoramino)-substituted heterocyclic nitramine energetic materials,using combined theoretical and experimental approaches. Optimized molecular structure and vibrational spectra of the Ci, symmetry conformer constituting the HNFX crystal were computed using density functional theory methods. Fourier transform infrared and Raman spectra of HNFX crystalline samples were also collected at ambient temperature and pressure. The average deviation of calculated structural parameters from X-ray diffraction data is ,1% at the B3LYP/6-311 + + G(d,p) level of theory, suggesting the absence of significant molecular distortion induced by the crystal field. Very good agreement was found between simulated and measured spectra, allowing reliable assignment of the fundamental normal modes of vibration of the HNFX crystal. Detailed analysis of the normal modes of the C,(NF2)2 and N,NO2 moieties was performed due to their critical importance in the initial steps of the molecular homolytic fragmentation process. Copyright © 2009 John Wiley & Sons, Ltd. [source] Local structure investigation of the active site of the imidazolonepropionase from Bacillus subtilis by XANES spectroscopy and ab initio calculationsJOURNAL OF SYNCHROTRON RADIATION, Issue 2 2008Feifei Yang Imidazolonepropionase is an important enzyme that plays a crucial role in the degradation of the histidine in mammals and bacteria. In this contribution a detailed structural investigation is presented of the imidazolonepropionase from Bacillus subtilis at the zinc site by X-ray absorption near-edge structure (XANES) spectroscopy combining experimental data with ab initio calculation in the framework of the multiple-scattering theory. The resolved local structure leads to a modification of the data set in the Protein Data Bank (PDB) (PDB code 2BB0). Actually, data suggest that the carboxyl of the Asp324 moves far away from the zinc ion at the center, while the water molecule and the nearest-neighbor histidines move towards it. This new conformation and the occurrence of a short water-to-zinc bond length support the nucleophilic attack catalytic mechanism proposed for this enzyme. [source] Incommensurate structure of Ca2Al2O5 at high temperatures , structure investigation and Raman spectroscopyACTA CRYSTALLOGRAPHICA SECTION B, Issue 4 2008Biljana Lazic A high-temperature X-ray diffraction study revealed that brownmillerite-type Ca2Al2O5 transforms to an incommensurately modulated structure at elevated temperatures. Single crystals of Ca2Al2O5 were synthesized in an end-loaded piston cylinder press at 2.5,GPa and 1273,K. The diffraction pattern observed at 1090,(10),K by in situ single-crystal diffraction experiments can be indexed by an I -centred orthorhombic cell and a modulation wavevector of q = 0.595,(1)c*. A (3,+,1)-dimensional model in superspace group Imma(00,)s00 was used to refine the modulated structure. The structure is assembled from two building units: (i) layers of corner-sharing [AlO6] octahedra, stacked along b alternate with (ii) layers of zweier single chains of [AlO4] tetrahedra running along a. The modulated structure arises from an aperiodic sequence of two different configurations of the chains within the tetrahedral layers. The modulated high-temperature phase of Ca2Al2O5 is isotypic to the modulated high-temperature modification of Ca2Fe2O5. A large hysteresis was found in the phase-transition temperature. On heating, the transition occurs at ca 1075,(10),K; on cooling, satellite reflections can be observed down to 975,(10),K. The characterization of Ca2Al2O5 is completed by Raman spectroscopy, including a partial interpretation of the spectra. [source] Cis ,-viniferin: A New Antifungal Resveratrol Dehydrodimer from Cyphostemma crotalarioides RootsJOURNAL OF PHYTOPATHOLOGY, Issue 1 2000A. E. A. Bala Abstract Six antifungal constituents were isolated from the roots of Cyphostemma crotalarioides (Vitaceae): a new product, Cis - , -viniferin 3, along with five known compounds: trans -resveratrol I and its oligomers: trans , -viniferin 2, gnetin C 4, pallidol 5 and gnetin E 6. It is the first time such compounds have been reported in this plant species. The roots tissues were found to be rich in other resveratrol oligomers, however, the available amounts of the other purified products did not allow structure investigations. No fungicidal activity was detected in the leaves of this plant. Zusammenfassung Cis - , -Viniferin: Ein neues antifungal wirkendes Resveratrol-Dehydrodimer aus den Wurzeln von Cyphostemma crotalarioides Aus den Wurzeln von Cyphostemma crotalarioides (Vita-ceae) wurden sechs antifungal wirkende Bestandteile isoliert: ein neues Produkt, cis - , -Viniferin 3, neben fünf bekannten Verbindungen: trans -Resveratrol 1 und seine Oligomete: trans - , -Viniferin 2, Gnetin C 4, Pallidol 5 und Gnetin E 6. Dies ist der erste Bericht über das Aufreten solcher Verbindungen in dieser Pflanzenart. Die Wurzel-gewebe waren reich an weiteren Resveratrol-Oligomeren. doch die Ausbeuten der anderen gereinigten Substanzen erlaubten keine Strukturbestimmungen. In den Bláttern dieser Pflanze wurde keine fungizide Aktivität festgestellt. [source] Enacting reform-based science materials: The range of teacher enactments in reform classrooms,,JOURNAL OF RESEARCH IN SCIENCE TEACHING, Issue 3 2005Rebecca M. Schneider To promote large-scale science education reform, developers must create innovations that teachers can use to learn and enact new practices. As part of an urban systemic reform effort, science materials were designed to reflect desired reforms and to support teacher thinking by addressing necessary content, pedagogy, and pedagogical content knowledge for teachers. The goal of this research was to describe teachers' enactments in comparison to reform as instantiated in the materials. Four middle school teachers' initial enactment of an inquiry-based science unit on force and motion were analyzed. Findings indicate two teachers' enactments were consistent with intentions and two teachers' enactments were not. However, enactment ratings for the first two were less reflective of curriculum intent when challenges were greatest, such as when teachers attempted to present challenging science ideas, respond to students' ideas, structure investigations, guide small-group discussions, or make adaptations. Overall, findings suggest that purposefully using materials with detailed lesson descriptions and specific, consistent supports for teacher thinking can help teachers with enactment. However, materials alone are not sufficient; reform efforts must include professional development and efforts to create systemic change in context and policy to support teacher learning and classroom enactment. © 2005 Wiley Periodicals, Inc. J Res Sci Teach 42: 283,312, 2005 [source] X-ray diffraction analysis of a human tRNAGly acceptor-stem microhelix isoacceptor at 1.18,Å resolutionACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 1 2009André Eichert Interest has been focused on comparative X-ray structure analyses of different tRNAGly acceptor-stem helices. tRNAGly/glycyl-tRNA synthetase belongs to the so-called class II system, in which the tRNA identity elements consist of simple and unique determinants that are located in the tRNA acceptor stem and the discriminator base. Comparative structure investigations of tRNAGly microhelices provide insight into the role of tRNA identity elements. Predominant differences in the structures of glycyl-tRNA synthetases and in the tRNA identity elements between prokaryotes and eukaryotes point to divergence during the evolutionary process. Here, the crystallization and high-resolution X-ray diffraction analysis of a human tRNAGly acceptor-stem microhelix with sequence 5,-G1C2A3U4U5G6G7 -3,, 5,-C66C67A68A69U70G71C72 -3, is reported. The crystals belonged to the monoclinic space group C2, with unit-cell parameters a = 37.32, b = 37.61, c = 30.47,Å, , = 112.60° and one molecule per asymmetric unit. A data set was collected using synchrotron radiation and data were processed within the resolution range 50.0,1.18,Å. The structure was solved by molecular replacement. [source] | ||||||||||