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Structural Investigations (structural + investigation)
Selected AbstractsMagnetic and Structural Investigation of ZnSe Semiconductor Nanoparticles Doped With Isolated and Core-Concentrated Mn2+ IonsADVANCED FUNCTIONAL MATERIALS, Issue 15 2009Christina Graf X-Ray magnetic circular dichroism (XMCD) experiments on diluted magnetic semiconductor nanocrystals (2,7,nm) are reported in order to study their local electronic structure and magnetic properties. ZnSe nanoparticles containing either single manganese ions (Mn2+) distributed in the lattice of the entire particle or a MnSe core in the center are prepared using high temperature approaches. The Mn2+ concentration is varied between less than one to several tens of manganese ions per nanocrystal. For all samples it is shown that the Mn2+ is exclusively present in the bulk of ZnSe nanoparticles with no evidence for oxidation to higher Mn-oxidation states. The magnetic ions are highly polarized inside the nanocrystals reaching about 80% of the theoretical value of a pure d5 state under identical conditions for the case of isolated manganese ions. Nanocrystals with a MnSe core ZnSe shell structure reach <50% of this value. Thus, their polarization is significantly more hindered, which is due to the significantly enhanced Mn,Mn interactions and a more distorted crystalline lattice. In contrast, no coupling between the manganese centers is observed in the nanoparticles doped samples with low concentrations of Mn2+, indicating that these ions are isolated in the bulk of the nanoparticles. [source] A Structural Investigation of Third-Currency Shocks to Bilateral Exchange Rates,INTERNATIONAL FINANCE, Issue 1 2008Martin Melecky An exchange rate between two currencies can be materially affected by shocks emerging from a third country. A US demand shock, for example, can affect the exchange rate between the euro and the yen. Because positive US demand shocks have a greater positive impact on Japanese interest rates than on euro area rates, the yen appreciates against the euro in response. Using quarterly data on the United States, the euro area and Japan from 1981 to 2006, this paper shows that the third-currency effects are significant even when exchange rates evolve according to uncovered interest parity. This is because interest rates are typically set in response to output and inflation, which are in turn influenced by other exchange rates. More importantly, third-currency effects are also transmitted to the actual exchange rate through the expected future exchange rate, which is, in a multi-country set-up, influenced by third-countries' fundamentals and shocks. Third-currency effects have a stronger impact on the currency of a relatively more open economy. The analysis implies that small open economies should avoid strict forms of bilateral exchange rate targeting, since higher trade and financial openness work as a force intrinsically amplifying currency fluctuations. [source] Preparation and Structural Investigation of CuCl2 Graphite Intercalation CompoundsACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 5 2008BIN Xiaopei Abstract Superfine graphite powder was prepared by ball-milling exfoliated graphite containing anhydrous CuCI2 in planetary ball milling systems. Nano-scale CuCl2 graphite intercalation compounds were synthesized by heating a mixture of anhydrous CuCl2 and graphite nanosheets. Scanning electron microscopy, energy-dispersive X-ray spectroscopy and high-resolution transmission electron microscopy were performed to characterize the microstructures of stage-1 nano-scale CuCI2 graphite intercalation compounds. The structure and components of the domain wall and core in the nano-scale CuCl2 graphite intercalation compounds are described. The results show that the content of CuCl2 in the mixture plays a crucial role in the size of the nano-scale CuCl2 graphite intercalation compound. [source] Structural Investigation of the Binding of 5-Substituted Swainsonine Analogues to Golgi ,-Mannosidase IICHEMBIOCHEM, Issue 5 2010Douglas A. Kuntz Dr. Abstract Golgi ,-mannosidase II (GMII) is a key enzyme in the N-glycosylation pathway and is a potential target for cancer chemotherapy. The natural product swainsonine is a potent inhibitor of GMII. In this paper we characterize the binding of 5,-substituted swainsonine analogues to the soluble catalytic domain of Drosophila GMII by X-ray crystallography. These inhibitors enjoy an advantage over previously reported GMII inhibitors in that they did not significantly decrease the inhibitory potential of the swainsonine head-group. The phenyl groups of these analogues occupy a portion of the binding site not previously seen to be populated with either substrate analogues or other inhibitors and they form novel hydrophobic interactions. They displace a well-organized water cluster, but the presence of a C(10) carbonyl allows the reestablishment of important hydrogen bonds. Already approximately tenfold more active against the Golgi enzyme than the lysosomal enzyme, these inhibitors offer the potential of being extended into the N-acetylglucosamine binding site of GMII for the creation of even more potent and selective GMII inhibitors. [source] Structural Investigation of the HIV-1 Envelope Glycoprotein gp160 Cleavage Site 3: Role of Site-Specific Mutations,CHEMBIOCHEM, Issue 12 2004Lucia Falcigno Dr. Abstract Proteolytic processing of HIV gp160 to produce gp120 and gp41 is performed by PC enzymes. This process is a prerequisite for the virus infectivity, since both gp120 and gp41 participate in the virus HIV-1 entry mechanism. The structure of the gp120/gp41 junction remains to be elucidated, and the structural features required for molecular recognition between HIV-1 gp160 and proteolytic enzymes have not been clarified. Furin is the best PC candidate for the gp160 proteolytic processing known to date. In previous studies on model peptides, we have shown the relevance of an N-terminal helix for the proper recognition of the gp160 processing site by furin. Here we analyze the effect of point mutations in peptides lacking a regular N-terminal helix. To this end, we present the structure,activity characterization of three peptide analogues of the HIV gp160 processing site that all present mutations in proline at positions P3 and/or P2,, while sharing the same N-terminal sequence, containing helix-breaking D -amino acids. Conformational analysis of the peptides was carried out in solution by NMR techniques, and furin's efficiency in cleaving them was measured. Structural findings are presented and discussed in relation to the different exhibited activity. [source] Structural Investigation of a High-Affinity MnII Binding Site in the Hammerhead Ribozyme by EPR Spectroscopy and DFT Calculations.CHEMBIOCHEM, Issue 10 2003Effects of Neomycin B on Metal-Ion Binding Abstract Electron paramagnetic resonance spectroscopy and density functional theory methods were used to study the structure of a single, high-affinity MnIIbinding site in the hammerhead ribozyme. This binding site exhibits a dissociation constant Kdof 4.4 ,M in buffer solutions containing 1,M NaCl, as shown by titrations monitored by continuous wave (cw) EPR. A combination of electron spin echo envelope modulation (ESEEM) and hyperfine sublevel correlation (HYSCORE) experiments revealed that the paramagnetic manganese(II) ion in this binding site is coupled to a single nitrogen atom with a quadrupole coupling constant,of 0.7 MHz, an asymmetry parameter,of 0.4, and an isotropic hyperfine coupling constant of Aiso(14N)=2.3 MHz. All three EPR parameters are sensitive to the arrangement of the MnIIligand sphere and can therefore be used to determine the structure of the binding site. A possible location for this binding site may be at the G10.1, A9 site found to be occupied by MnIIin crystals (MacKay et al., Nature 1994, 372, 68 and Scott et al., Science 1996, 274, 2065). To determine whether the structure of the binding site is the same in frozen solution, we performed DFT calculations for the EPR parameters, based on the structure of the MnIIsite in the crystal. Computations with the BHPW91 density function in combination with a 9s7p4d basis set for the manganese(II) center and the Iglo-II basis set for all other atoms yielded values of,(14N)=+0.80 MHz, ,=0.324, and Aiso(14N)=+2.7 MHz, in excellent agreement with the experimentally obtained EPR parameters, which suggests that the binding site found in the crystal and in frozen solution are the same. In addition, we demonstrated by EPR that MnIIis released from this site upon binding of the aminoglycoside antibiotic neomycin B (Kd=1.2 ,M) to the hammerhead ribozyme. Neomycin B has previously been shown to inhibit the catalytic activity of this ribozyme (Uhlenbeck et al., Biochemistry 1995, 34, 11,186). [source] ChemInform Abstract: Strontium,Copper Selenite,Chlorides: Synthesis and Structural Investigation.CHEMINFORM, Issue 48 2009Peter S. Berdonosov Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 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: Structural Investigation of Tetraperoxo Complexes of Mo(VI) and W(VI) , X-Ray and Theoretical Studies.CHEMINFORM, Issue 28 2009M. Grzywa Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 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: Structural Investigation of Eu2+ Emissions from Alkaline Earth Zirconium Phosphate.CHEMINFORM, Issue 27 2009Masaaki Hirayama Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 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: Crystal Growth and Structural Investigation of A2BReO6 (A: Sr, Ba; B: Li, Na).CHEMINFORM, Issue 5 2009M. Bharathy Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 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: Structural Investigation of the Alluaudite-Like Mixed-Valence Iron Phosphate: Na1.25Mg1.10Fe1.90 (PO4)3.CHEMINFORM, Issue 14 2008M. Hidouri Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 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] Improved Preparation and Structural Investigation of 4-Aryl-4-oxo-2-hydroxy-2-butenoic Acids and Methyl Esters.CHEMINFORM, Issue 47 2004Cedric Maurin Abstract For Abstract see ChemInform Abstract in Full Text. [source] Structural Investigation of Ternary LnIr3B2 Compounds (Ln: Ce and Pr).CHEMINFORM, Issue 48 2003O. Sologub Abstract For Abstract see ChemInform Abstract in Full Text. [source] Structural Investigations of Two New Ternary Magnesium,Niobium Hydrides, Mg6.5NbH,14 and MgNb2H,4.CHEMINFORM, Issue 36 2006Toyoto Sato Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Nanosized Ball Joints Constructed from C60 and Tribenzotriquinacene Sockets: Synthesis, Component Self-Assembly and Structural InvestigationsCHEMISTRY - A EUROPEAN JOURNAL, Issue 35 2007Björn Bredenkötter Dr. Abstract The formation of supramolecular host,guest complexes of fullerene (C60) and two novel tribenzotriquinacene based hosts (5,a and 5,b) was investigated in solution and in the solid state. Stability constants for 1:1 and 2:1 complexes were obtained from spectroscopic (UV/Vis, 1H,NMR) titration experiments. Association constants of K1=(2908±360),L,mol,1 and K2=(2076±300),L,mol,1 for C60/5,a, and K1=(5608±220),L,mol,1 and K2=(673±160),L,mol,1 for C60/5,b were obtained. Single crystal X-ray structural analysis of compound C60,5,b,3,toluene revealed that a molecule of C60 was located at short van der Waals contact distances in the open pre-organised cavity of the rigid host. The supramolecular complex created resembles an engineered nanosized ball joint and represents the first member for a future nanomechanics construction kit. [source] Water as a Building Block in Solid-State Acetonitrile,Pyrogallol[4]arene Assemblies: Structural InvestigationsCHEMISTRY - A EUROPEAN JOURNAL, Issue 29 2007Scott Abstract Under various conditions, water molecules dramatically affect a number of solid-state C -alkylpyrogallol[4]arene assemblies. In the absence of water, hydrogen-bonded hexameric capsules are formed for the C -butyl, pentyl, hexyl, and heptyl pyrogallol[4]arenes. Introduction of water to acetonitrile solutions containing C -propyl,C -octylpyrogallol[4]arenes resulted in the formation of markedly different bilayer structures and the structural identification of two new dimer-type motifs. [source] Structural investigation of GeSb6Te10 and GeBi6Te10 intermetallic compounds in the chalcogenide homologous seriesACTA CRYSTALLOGRAPHICA SECTION B, Issue 4 2010Toshiyuki Matsunaga The crystal structures of GeSb6Te10 and GeBi6Te10 were scrutinized using an X-ray powder diffraction method, which revealed that these compounds crystallize in trigonally distorted cubic close-packed structures with a 51-layer period (). Each layer consists of a triangular atomic net; Te atoms occupy their own specific layers, whereas Ge, Sb and Bi atoms are located in the other layers. In these pseudobinary compounds, random atomic occupations of Ge and Sb/Bi are observed and the layers form two kinds of elemental structural blocks by their successive stacking along the c axis. These compounds can be presumed to be isostructural. It is known that the chemical formula of the chalcogenide compounds with the homologous structures found in these pseudobinary systems can be written as (GeTe)n(Sb2Te3)m or (GeTe)n(Bi2Te3)m (n, m: integer); the GeSb6Te10 and GeBi6Te10 investigated in this study, which correspond to the case in which n = 1 and m = 3, naturally have 3,×,l = 51-layer structures according to a formation rule l = 2n + 5m commonly found in the compounds of these chalcogenide systems (l represents the number of layers in the basic structural unit). Calculations based on the density functional theory revealed that these materials are compound semiconductors with very narrow band gaps. [source] Designing Ionic Liquids: 1-Butyl-3-Methylimidazolium Cations with Substituted Tetraphenylborate CounterionsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 15 2003Joep van den Broeke Abstract The hydrophobic, low melting, 1-butyl-3-methylimidazolium (BMIm) salts [BMIm][BPh4] (1), [BMIm][B(C6H4Me-4)4] (2), [BMIm][B{C6H4(CF3)-4}4] (3), [BMIm][B{C6H3(CF3)2 -3,5}4] (4), [BMIm][B{C6H4(C6F13)-4}4] (5), [BMIm][B{C6H4(SiMe3)-4}4] (6), [BMIm][B(C6H4{SiMe2(CH2CH2CF3)}-4)4] (7), [BMIm][B{C6H4(SiMe2C8H17}-4}4] (8) and [BMIm][B(C6H4{SiMe2(CH2CH2C6F13)}-4)4] (9) have been prepared. Systematic variation of the substituents on the tetraphenylborate anion allowed an assessment of their influence on the physical properties of the imidazolium salts. Structural investigations using NMR and IR spectroscopy, combined with single crystal X-ray structure determinations for 2, 3, 5 and 6, revealed hydrogen-bonding interactions between the imidazolium ring protons and the borate anion, both in the solid state and in solution. These interactions are weakened upon the introduction of electron-withdrawing substituents in the anion and follow the order 3,5-(CF3)2 < ,C6F13 < ,CF3 < ,SiMe2CH2CH2C6F13 < ,SiMe2CH2CH2CF3 < ,H < ,Me < ,SiMe3. The melting points of the salts depend primarily on the bulk of the lipophilic substituents, and decrease with increasing size. Bulky lipophilic substituents dramatically enhance the solubility of the imidazolium borates 8 and 9 in hexane and reduce their relative polarity. These unique properties make imidazolium borates 8 and 9 interesting as amphiphilic ionic liquids with low polarity. Attempts to crystallise 7 resulted in decomposition. A single-crystal X-ray structure determination of the product, isolated in 6% yield, showed that a carbene,tris[4-{dimethyl(3,3,3-trifluoropropyl)silyl}phenyl]borane adduct was formed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Structural investigations of polypropylene glycol (PPG) and isophorone diisocyanate (IPDI)-based polyurethane prepolymer by 1D and 2D NMR spectroscopyJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 6 2005A. Prabhakar Abstract Polyurethane prepolymers are widely used in reactive hot melt adhesives and moisture cured coatings. NCO-terminated polyurethane of polypropylene glycol (PPG)-1000 and isophoron diisocyanate (IPDI) with an NCO/OH ratio of 1.2:1 were prepared without any catalyst or solvent. 1D and 2D NMR spectroscopy was used for the structural investigation of the synthesized prepolymer. 1H NMR spectra and dibutylamine back-titration were used to monitor the reaction of isocyanate groups with the hydroxyl function of PPG and to allow a good description of the evaluation of the urethane groups. The data on percentage conversion were crosschecked with 13C NMR spectroscopy in the urethane zone for the methanol endcapped prepolymer. The observations show a higher reactivity of the secondary NCO group than of the primary group. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1196,1209, 2005 [source] Scaleable synthesis route for silicon nanocrystal assembliesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2007S. Limaye Abstract We report on a scaleable synthesis route for highly luminescent silicon nanocrystal assemblies and demonstrate that their emission properties are identical to those known for other systems containing silicon nanocrystals. Structural investigations confirmed that chemically porosified metallurgical grade silicon powder consists of silicon nanocrystal assemblies having nanometer sizes characterized by very high total internal surface area. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Structural investigations of isomeric oxidised forms of hyperforin by HPLC-NMR and HPLC-MSnPHYTOCHEMICAL ANALYSIS, Issue 5 2003J.-L. Wolfender Abstract The prenylated phloroglucinol hyperforin, thought to be an essential component for the anti-depressant activity of St. John's Wort (Hypericum perforatum), is unstable. The facile oxidative degradation of hyperforin poses serious problems for standardisation, and may also dramatically affect the pharmacological activity of the extracts. Hyperforin was dissolved in hexane and stored at room temperature for 3 days and yielded various closely related degradation products which, although dif,cult to isolate on the preparative scale, have been analysed by on-,ow and stop-,ow HPLC-NMR and HPLC-MS/MS. From on-line spectroscopic data, and with the aid of complementary in-mixture standard NMR two-dimensional correlation experiments, the different oxidised forms of hyperforin were found to be phloroglucinol derivatives in which a hydroxy-dihydrofuran ring is formed involving the enol OH at C-7 or C-9 (tautomeric form) and the prenyl chain at C-8 of the core nucleus of hyperforin. The strategy followed for the on-line identi,cation of these constituents is discussed. Copyright © 2003 John Wiley & Sons, Ltd. [source] Structural investigations of phosphorus,nitrogen compounds.ACTA CRYSTALLOGRAPHICA SECTION B, Issue 3-2 2002A systematic study is presented on the products of aminolysis of N3P3Cl6 (1) and N3P3Ph2Cl4 (4) with dibenzylamine. Two series of mono- and disubstituted derivatives of compounds (1) and (4), namely N3P3Cl5[N(CH2Ph)2] (2) and N3P3Cl4[N(CH2Ph)2]2 (3) and N3P3Ph2Cl3[N(CH2Ph)2] (5) and N3P3Ph2Cl2[N(CH2Ph)2]2 (6) [where (2), (3), (5) and (6) are new structures], are investigated in order to determine whether steric or electronic effects prevail in the formation of dibenzylamino-substituted cyclophosphazenes. The influence of an electron-releasing group (i.e. phenyl) on the stereochemistry and degree of substitution of the product is analysed by comparison of the above two series. The difference in unsymmetrically substituted endocyclic P,N bond lengths, ,, is used as a measure of the degree of the electronic contribution, in combination with basicity constants, to quantify the degree of the electron-releasing capacity of the R group. In order to compare geminal versus non-geminal substitution, a difunctional secondary amine was used to form the compound N3P3Cl4[NMe(CH2)3NMe] (7) (a reinvestigation) for inclusion in this study. It is shown that electron-releasing groups have a greater effect on the lengthening of P,Cl bonds as opposed to endocyclic P,N bonds and that this effect is greater in the non-geminal PRCl case than for geminal PCl2. However, steric effects are shown to be dominant in the reactions of dibenzylamine with N3P3 derivatives, with a disposition to a trans stereochemistry in bisdibenzylamino derivatives. [source] Purification, crystallization and preliminary X-ray diffraction studies on avian haemoglobin from pigeon (Columba livia)ACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 2 2009Pon. Sathya Moorthy Haemoglobin is a physiologically significant metalloprotein that is involved in the exchange of gases for sustaining life. The respiratory system of birds is unique and complex compared with that of mammals. Many investigations of avian haemoglobins have revealed the presence of inositol pentaphosphate (IP5), a principal allosteric effector that is involved in regulation of their function. Structural investigations of avian haemoglobins are presently not adequate to explain their function. Efforts have been made in this direction in order to understand the oxygen-binding affinity involved in adapting to hypoxia in avian haemoglobins. Fresh whole blood was collected from pigeon (Columba livia) and purified using a DEAE cellulose anion-exchange chromatographic column. Crystallization of pigeon haemoglobin was accomplished using the hanging-drop vapour-diffusion method using PEG 3350 as a precipitant in 50,mM sodium acetate buffer pH 5.5 with 1,M NaCl. Data collection was carried out using a MAR345 image-plate detector system. The crystals diffracted to 2,Å resolution. Pigeon haemoglobin crystallizes in a triclinic space group, with two whole biological molecules in the asymmetric unit and with unit-cell parameters a = 55.005, b = 65.528, c = 104.370,Å, , = 78.742, , = 89.819, , = 65.320°. [source] Evaluation of Thin Film Titanium Nitride Electrodes for Electroanalytical ApplicationsELECTROANALYSIS, Issue 10 2007Carolina Nunes, Kirchner Abstract Titanium nitride is a hard and inert conducting material that has yet not been widely used as electrode material for electroanalytical applications although there are highly developed protocols available to produce well adherent micro and nanostructured electrodes. In this paper the possibilities of using titanium nitride thin films for electroanalytical applications is investigated. Scanning electrochemical microscope (SECM) was used for analysis of the redox kinetics of a selected fast redox couple at thin films of titanium nitride (TiN) in different thicknesses. The investigation was carried out by approaching an amperometric ultramicroelectrode (UME) to the TiN film while the soluble redox couple (ferrocenemethanol/ferrociniummethanol) served as mediator in a SECM configuration. The substrate was biased at a potential so that it rereduces the species being produced at the UME, thus controlling the feedback effect. Normalized current,distance curves were fitted to the theoretical model in order to find the apparent heterogeneous standard rate constant (k°) at the sample. The data are further supported by structural investigation of the TiN films using scanning force microscopy and X-ray photoelectron spectroscopy. It was found that the kinetics are little influenced by prolonged storage in air. The heterogeneous standard rate constants in 2,mM ferrocenemethanol were (0.73±0.05)×10,3,cm s,1 for 20,nm TiN thin layer, (1.5±0.2)×10,3,cm s,1 for 100,nm TiN thin layer and (1.3±0.2)×10,3,cm s,1 for 300,nm TiN thin layer after prolonged storage in air. Oxidative surface treatment (in order to remove organic adsorbates) decreased the kinetics in agreement with a thicker oxide layer on the material. The results suggest that their direct use for amperometric detection of reversible redox systems in particular at miniaturized configurations may be advantageous. [source] Correlative 3D Microscopy: CLSM and FIB/SEM TomographyIMAGING & MICROSCOPY (ELECTRONIC), Issue 3 2008A Study of Cellular Entry of Vaccinia Virus Abstract Subcellular structural investigation on single cells or tissue samples requires the coupling of optimal structural preservation with detailed imaging at the light and electron microscopic level. To apply light microscopy (FLM, CLSM) and electron microscopy (SEM, FIB/SEM, TEM) imaging modes to the identical sample area has become available with the establishment of chemical preparation, or freeze-substitution protocols after high pressure freezing, adapted to retain fluorophores. One and the same structure can now be investigated at mm to nm range in 2D and 3D in a multimodal set-up [1, 2]. In combination with live cell imaging prior to immobilisation, this approach becomes a powerful tool in life science, e.g. in the development of new anti-viral strategies, as this requires detailed information on the replication cycle of viruses and their interaction with their host cells. [source] Structural investigations of polypropylene glycol (PPG) and isophorone diisocyanate (IPDI)-based polyurethane prepolymer by 1D and 2D NMR spectroscopyJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 6 2005A. Prabhakar Abstract Polyurethane prepolymers are widely used in reactive hot melt adhesives and moisture cured coatings. NCO-terminated polyurethane of polypropylene glycol (PPG)-1000 and isophoron diisocyanate (IPDI) with an NCO/OH ratio of 1.2:1 were prepared without any catalyst or solvent. 1D and 2D NMR spectroscopy was used for the structural investigation of the synthesized prepolymer. 1H NMR spectra and dibutylamine back-titration were used to monitor the reaction of isocyanate groups with the hydroxyl function of PPG and to allow a good description of the evaluation of the urethane groups. The data on percentage conversion were crosschecked with 13C NMR spectroscopy in the urethane zone for the methanol endcapped prepolymer. The observations show a higher reactivity of the secondary NCO group than of the primary group. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1196,1209, 2005 [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] Residues Asp164 and Glu165 at the substrate entryway function potently in substrate orientation of alanine racemase from E. coli: Enzymatic characterization with crystal structure analysisPROTEIN SCIENCE, Issue 6 2008Dalei Wu Abstract Alanine racemase (Alr) is an important enzyme that catalyzes the interconversion of L-alanine and D-alanine, an essential building block in the peptidoglycan biosynthesis. For the small size of the Alr active site, its conserved substrate entryway has been proposed as a potential choice for drug design. In this work, we fully analyzed the crystal structures of the native, the D-cycloserine-bound, and four mutants (P219A, E221A, E221K, and E221P) of biosynthetic Alr from Escherichia coli (EcAlr) and studied the potential roles in substrate orientation for the key residues involved in the substrate entryway in conjunction with the enzymatic assays. Structurally, it was discovered that EcAlr is similar to the Pseudomonas aeruginosa catabolic Alr in both overall and active site geometries. Mutation of the conserved negatively charged residue aspartate 164 or glutamate 165 at the substrate entryway could obviously reduce the binding affinity of enzyme against the substrate and decrease the turnover numbers in both D- to L-Ala and L- to D-Ala directions, especially when mutated to lysine with the opposite charge. However, mutation of Pro219 or Glu221 had only negligible or a small influence on the enzymatic activity. Together with the enzymatic and structural investigation results, we thus proposed that the negatively charged residues Asp164 and Glu165 around the substrate entryway play an important role in substrate orientation with cooperation of the positively charged Arg280 and Arg300 on the opposite monomer. Our findings are expected to provide some useful structural information for inhibitor design targeting the substrate entryway of Alr. [source] Long-range allosteric transitions in carbamoyl phosphate synthetasePROTEIN SCIENCE, Issue 9 2004James B. Thoden Abstract Carbamoyl phosphate synthetase plays a key role in both pyrimidine and arginine biosynthesis by catalyzing the production of carbamoyl phosphate from one molecule of bicarbonate, two molecules of MgATP, and one molecule of glutamine. The enzyme from Escherichia coli consists of two polypeptide chains referred to as the small and large subunits, which contain a total of three separate active sites that are connected by an intramolecular tunnel. The small subunit harbors one of these active sites and is responsible for the hydrolysis of glutamine to glutamate and ammonia. The large subunit binds the two required molecules of MgATP and is involved in assembling the final product. Compounds such as L-ornithine, UMP, and IMP allosterically regulate the enzyme. Here, we report the three-dimensional structure of a site-directed mutant protein of carbamoyl phosphate synthetase from E. coli, where Cys 248 in the small subunit was changed to an aspartate. This residue was targeted for a structural investigation because previous studies demonstrated that the partial glutaminase activity of the C248D mutant protein was increased 40-fold relative to the wild-type enzyme, whereas the formation of carbamoyl phosphate using glutamine as a nitrogen source was completely abolished. Remarkably, although Cys 248 in the small subunit is located at ,100 Å from the allosteric binding pocket in the large subunit, the electron density map clearly revealed the presence of UMP, although this ligand was never included in the purification or crystallization schemes. The manner in which UMP binds to carbamoyl phosphate synthetase is described. [source] Disorder in Ag7GeSe5I, a superionic conductor: temperature-dependent anharmonic structural studyACTA CRYSTALLOGRAPHICA SECTION B, Issue 1 2008Stéphanie Albert A temperature-dependent structural investigation of the substituted argyrodite Ag7GeSe5I has been carried out on a single crystal from 15 to 475,K, in steps of 50,K, and correlated to its conductivity properties. The argyrodite crystallizes in a cubic cell with the space group. The crystal structure exhibits high static and dynamic disorder which has been efficiently accounted for using a combination of (i) Gram,Charlier development of the Debye,Waller factors for iodine and silver, and (ii) a split-atom model for Ag+ ions. An increased delocalization of the mobile d10 Ag+ cations with temperature has been clearly shown by the inspection of the joint probability-density functions; the corresponding diffusion pathways have been determined. [source] | |||||||||||||||||||||||||||||||||||||