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One Molecule (one + molecule)
Selected AbstractsChemInform Abstract: One-Pot Multicomponent Synthesis of Azaindoles and Pyrroles from One Molecule of a Silicon-Tethered Diyne and Three or Two Molecules of Organonitriles Mediated by Zirconocene.CHEMINFORM, Issue 11 2010Shaoguang Zhang 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: First Unsymmetrical Bisfullerene, C121: Evidence for the Presence of Both Homofullerene and Methanofullerene Cages in One Molecule.CHEMINFORM, Issue 22 2001Nita Dragoe 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] 1,3,4-Triphenyl-7-trifluoromethyl-1H -pyrazolo[3,4- b]quinoline at 293 and 100,KACTA CRYSTALLOGRAPHICA SECTION C, Issue 9 2010Szlachcic In the structure of the title compound, C29H18F3N3, belonging to the space group P65 (or P61), three symmetry-independent molecules are arranged in two chains, with two molecules alternating along the 32 axes, whereas the remaining molecule forms a chain along [0001] due to the 65 screw axis. The conformation of each of the molecules is stabilized by an intramolecular C,H...N hydrogen bond, with C...N distances in the range 2.964,(6),3.069,(5),Å at room temperature (293,K) and 2.943,(4),3.084,(4),Å at low temperature (100,K). One molecule has its ,CF3 group ordered even at 293,K, which can be explained only by considering its involvement in two weak intermolecular C,H...F interactions, with C...F distances in the range 3.084,(6),3.302,(5),Å at 293,K and 3.070,(3),3.196,(3),Å at 100,K, and also a C,F...N interaction, with a C...N distance of 3.823,(5),Å at 293,K and 3.722,(4),Å at 100,K. The trifluoromethyl groups in the two remaining molecules are disordered at 293,K, whereas at 100,K the continuous (dynamic) positional disorder of one of the ,CF3 groups (of the molecule forming the chain along [0001]) is totally eliminated while the ,CF3 group disorder remains for the third molecule. [source] Channel-forming solvates of 6-chloro-2,5-dihydroxypyridine and its solvent-free tautomer 6-chloro-5-hydroxy-2-pyridoneACTA CRYSTALLOGRAPHICA SECTION C, Issue 10 2009Sean R. Parkin On crystallization from CHCl3, CCl4, CH2ClCH2Cl and CHCl2CHCl2, 6-chloro-5-hydroxy-2-pyridone, C5H4ClNO2, (I), undergoes a tautomeric rearrangement to 6-chloro-2,5-dihydroxypyridine, (II). The resulting crystals, viz. 6-chloro-2,5-dihydroxypyridine chloroform 0.125-solvate, C5H4ClNO2·0.125CHCl3, (IIa), 6-chloro-2,5-dihydroxypyridine carbon tetrachloride 0.125-solvate, C5H4ClNO2.·0.125CCl4, (IIb), 6-chloro-2,5-dihydroxypyridine 1,2-dichloroethane solvate, C5H4ClNO2·C2H4Cl2, (IIc), and 6-chloro-2,5-dihydroxypyridine 1,1,2,2-tetrachloroethane solvate, C5H4ClNO2·C2H2Cl4, (IId), have I41/a symmetry, and incorporate extensively disordered solvent in channels that run the length of the c axis. Upon gentle heating to 378,K in vacuo, these crystals sublime to form solvent-free crystals with P21/n symmetry that are exclusively the pyridone tautomer, (I). In these sublimed pyridone crystals, inversion-related molecules form R22(8) dimers via pairs of N,H...O hydrogen bonds. The dimers are linked by O,H...O hydrogen bonds into R46(28) motifs, which join to form pleated sheets that stack along the a axis. In the channel-containing pyridine solvate crystals, viz. (IIa),(IId), two independent host molecules form an R22(8) dimer via a pair of O,H...N hydrogen bonds. One molecule is further linked by O,H...O hydrogen bonds to two 41 screw-related equivalents to form a helical motif parallel to the c axis. The other independent molecule is O,H...O hydrogen bonded to two related equivalents to form tetrameric R44(28) rings. The dimers are ,,, stacked with inversion-related dimers, which in turn stack the R44(28) rings along c to form continuous solvent-accessible channels. CHCl3, CCl4, CH2ClCH2Cl and CHCl2CHCl2 solvent molecules are able to occupy these channels but are disordered by virtue of the site symmetry within the channels. [source] Dimorphic forms of 3,6-dinitrodurene in a single space groupACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2009José Alberto Galicia Aguilar 3,6-Dinitrodurene (1,2,4,5-tetramethyl-3,6-dinitrobenzene), C10H12N2O4, has been crystallized in two polymorphic forms which may be distinguished by their colours in the solid state. Polymorph I gives clear colourless prismatic crystals, while polymorph II crystallizes in the dark and under an inert atmosphere as irregular purple blocks. Both forms belong to the space group C2/c, with both asymmetric units containing two half-molecules. One molecule is located on an inversion centre and the other lies on a twofold axis. The polymorphism arises from different orientations of the twofold axis: in form I, this axis passes through the mid-points of two C,C bonds of the benzene ring and, as a consequence, all atoms in the asymmetric unit are in general positions. In form II, the N atoms of the nitro groups and the Cipso atoms are located on the binary axis. Comparing phases I and II, slightly different conformations are observed for the nitro substituents, while the stacking structures are very similar. [source] Octasubstituted biphenylenes: is there a favoured conformation?ACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2007Peter J. Steel Octakis(pyrazol-1-ylmethyl)biphenylene ethanol solvate, C44H40N16·C2H6O, has two independent centrosymmetric molecules, one of which is hydrogen bonded to the solvent molecule. One molecule adopts an arrangement with three arms up and one down in each benzene ring, whilst the other molecule has a conformation with two adjacent arms on the same side of the ring. In neither case is the expected fully alternating form observed. [source] Crystallization of the flexible nuclear import receptor importin-, in the unliganded stateACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 6 2009Noelia Roman The transport of macromolecules across the nuclear envelope is an essential eukaryotic process that enables proteins such as transcription factors, polymerases and histones to gain access to the genetic material contained within the nucleus. Importin-, plays a central role in the nucleocytoplasmic transport process, mediating nuclear import through a range of interactions with cytoplasmic, nuclear and nuclear pore proteins such as importin-,, Ran, nucleoporins and various cargo molecules. The unliganded form of the full-length yeast importin-, has been expressed and crystallized. The crystals were obtained by vapour diffusion at pH 6.5 and 290,K. The crystals belonged to space group P21 (unit-cell parameters a = 58.17, b = 127.25, c = 68.52,Å, , = 102.23). One molecule is expected in the asymmetric unit. The crystals diffracted to 2.4,Å resolution using a laboratory X-ray source and were suitable for crystal structure determination. [source] Crystallization and preliminary crystallographic analysis of thermophilic cellulase from Fervidobacterium nodosum Rt17-B1ACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 3 2009Baisong Zheng FnCel5A, a thermostable endoglucanase, is a member of glycohydrolase family 5 which catalyzes the hydrolysis of cellulose to glucose in the thermophilic bacterium Fervidobacterium nodosum Rt17-B1. FnCel5A is particularly interesting because of its high thermostability (Topt = 353,K, half-life 48,h) and its high specific activity towards carboxymethylcellulose. These properties make FnCel5A an attractive target for protein engineering to improve cellulase activity. In order to resolve the crystal structure of FnCel5A and to gain a better understanding of its biological function, recombinant FnCel5A was expressed, purified and crystallized at 291,K using NaH2PO4/KH2PO4 as a precipitant. A 2.4,Å resolution native data set was collected from a single flash-cooled crystal (100,K) using 20%(v/v) glycerol as a cryoprotectant. These crystals belonged to space group P21212, with unit-cell parameters a = 53.5, b = 81.7, c = 85.2,Å, , = , = , = 90°. One molecule is assumed to be present per asymmetric unit, which gives a Matthews coefficient of 2.5,Å3,Da,1. A data set was also collected to 1.7,Å resolution from a selenomethionyl derivative; it belonged to space group P212121 with the same unit-cell parameters as the native crystals. [source] Natural polyphenols as chain-breaking antioxidants during methyl linoleate peroxidationEUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 8 2010Ivan Tichonov Abstract A technique based on monitoring oxygen consumption was applied to study 11 natural and model polyphenols (PP, QH2) as well as four typical monophenolics as a chain-breaking antioxidant during the controlled chain oxidation of methyl linoleate (ML) in bulk at 37°C. The antioxidant activities of QH2 were characterized by two parameters: the rate constant k1 for reaction of QH2 with the peroxy radical : (i) QH2,+,,,,,+,LOOH and the stoichiometric factor of inhibition, f, which shows how many kinetic chains may be terminated by one molecule of QH2. The rate constant k1 were reduced significantly by factor of 4 ,28 as compared to these determined during the oxidation of styrene in bulk; the effect was typically more pronounced for catechol derivatives than for pyrogallol derivatives. At the same time, f for QH2 was found to be close to two independent of the number of active OH groups, similar to that determined earlier during the inhibited oxidation of styrene. The formation of H bond between OH group of QH2 and carboxyl group of ML is suggested as a reason for reducing effect of ML on k1. Practical applications: This work reports rate constants for the reaction of lipid peroxyl radical with phenolics and stoichiometric coefficient of inhibition, which characterize the antioxidant activity (AOA) of 15 natural and model PP, QH2 during the controlled peroxidation of ML. The reactivity of PP, QH2 during the oxidation of ML is routinely lower than the reactivity during the oxidation of non-polar model hydrocarbons. This information may be useful to estimate the AOA of natural PP, QH2 in real systems of practical significance including plant oils, fats, food-stuffs, biological objects, and similar. [source] Physical characterization of plakophilin 1 reconstituted with and without zincFEBS JOURNAL, Issue 14 2000Ilse Hofmann Plakophilin 1 (PKP1) belongs to the arm -repeat protein family which is characterized by the presence of a conserved 42-amino-acid motif. Despite individual members of the family containing a similar type of structural domain, they exhibit diverse cellular functions. PKP1 is ubiquitously expressed in human tissues and, depending on the type of cell, found prominently in the karyoplasm and/or in desmosomes. In surface plasmon resonance detection experiments, we noticed that PKP1 specifically bound zinc but not calcium or magnesium. Therefore we have used circular dichroism spectroscopy, limited proteolysis, analytical ultracentrifugation, electron microscopy and dynamic light scattering to establish the physical properties of recombinant PKP1 depending on the presence or absence of zinc. The , helix content of PKP1 was considerably higher when reconstituted with zinc than without. By atomic absorption spectroscopy 7.3 atoms zinc were shown to be tightly associated with one molecule of wild-type PKP1. The zinc-reconstituted protein formed globular particles of 21.9 ± 8.4 nm diameter, as measured by electron microscopy after glycerol spraying/rotary metal shadowing. In parallel, the average sedimentation coefficient (s20,w) for zinc-containing PKP1 was 41S and its diffusion coefficient, as obtained by dynamic light scattering, 1.48 × 10,7 cm2·s,1. The molecular mass of 2.44 × 106 obtained from s and D yields an average stoichiometry of 30 for the PKP1 oligomer. In contrast, PKP1, reconstituted without zinc, contained no significant amount of zinc, sedimented with 4.6S, and was present in monomeric form as determined by sedimentation equilibrium centrifugation. [source] The chain-breaking antioxidant activity of phenolic compounds with different numbers of O-H groups as determined during the oxidation of styreneINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 2 2009Ivan Tikhonov The technique based on monitoring oxygen consumption was applied to test 18 polyphenols (PP) and model phenolics as a chain-breaking antioxidant during the oxidation of styrene initiated by 2,2,-azobis(2,4-dimethylvaleronitril) at 37°C. The chain-breaking capability of PP was characterized by two parameters: the rate constant k1 for the reaction of antioxidants with the peroxy radical produced from styrene and the stoichiometric coefficient of inhibition, f, which shows how many kinetic chains are terminated by one molecule of PP. Rate constants k1 × 105 (in M,1 s,1) were found to be 10 (catechol), 27 (pyrogallol), 34 (3,6-di-tert-Bu-catechol), 4.3 (protocatechic acid), 12 (gallic acid), 15 (caffeic acid), <0.01 (chrysin), 1.3 (kaempferol), 19 (quercetin), 5.3 (baicalein), 16 (epicatechin), 32 (epigallocatechin), 9.0 (dihydroquercetin), 3.3 (resveratrol), and 16 (nordihydroguaiaretic acid). The value of k1 increases when going from one to two and three adjacent O-H groups in a benzene ring (catechol and pyrogallol derivatives, respectively). At the same time, two O-H groups in metaposition in a A-ring of flavonoids actually do not participate in the inhibition. For the majority of PP, f is near to 2 independent of the number of OH groups. The correlation of k1 with the structure of PP and the OH bond dissociation enthalpy has been discussed. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 92,100, 2009 [source] Structure,function studies of glutamate synthases: A class of self-regulated iron-sulfur flavoenzymes essential for nitrogen assimilationIUBMB LIFE, Issue 5 2008Maria Antonietta Vanoni Abstract Glutamate synthases play with glutamine synthetase an essential role in nitrogen assimilation processes in microorganisms, plants, and lower animals by catalyzing the net synthesis of one molecule of L -glutamate from L -glutamine and 2-oxoglutarate. They exhibit a modular architecture with a common subunit or region, which is responsible for the L -glutamine-dependent glutamate synthesis from 2-oxoglutarate. Here, a PurF- (Type II- or Ntn-) type amidotransferase domain is coupled to the synthase domain, a (,/,)8 barrel containing FMN and one [3Fe-4S]0,+1 cluster, through a ,30 Å-long intramolecular tunnel for the transfer of ammonia between the sites. In bacterial and eukaryotic GltS, reducing equivalents are provided by reduced pyridine nucleotides thanks to the stable association with a second subunit or region, which acts as a FAD-dependent NAD(P)H oxidoreductase and is responsible for the formation of the two low potential [4Fe-4S]+1,+2 clusters of the enzyme. In photosynthetic cells, reduced ferredoxin is the physiological reductant. This review focus on the mechanism of cross-activation of the synthase and glutaminase reactions in response to the bound substrates and the redox state of the enzyme cofactors, as well as on recent information on the structure of the ,, protomer of the NADPH-dependent enzyme, which sheds light on the intramolecular electron transfer pathway between the flavin cofactors. © 2008 IUBMB IUBMB Life, 60(5): 287,300, 2008 [source] Biginelli-like three component reaction: Synthesis of some new ethyl 6-ethoxycarbonylmethyl-4-aryl-2-oxo-1,2,3,4-tetrahydropyrimidine-5-carboxylate derivativesJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 2 2007Javad Azizian In the context of our high-throughput organic synthesis program, we have studied the reactivity of special ,-keto esters toward the Biginelli reaction. We have found that a diethyl-3-oxoglutarate reacts with one molecule of urea and one molecule of aldehyde under solvent-free conditions to give a new family of 3,4-dihydropyrimidin-2(1H)-ones in good yields. [source] Exothermic thermal reaction of dopamine with 3,5-dinitrobenzoic acidJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 11 2003Yoshikatsu Ito Abstract Pyrolysis of the crystalline 1,:,1 molecular complex DA,dnba, which was prepared from cocrystallization of dopamine (DA) and 3,5-dinitrobenzoic acid (dnba), was studied. This cocrystal decomposed violently at the melting-point, leading to the formation of a black solid along with a tiny amount of 3-amino-5-nitrobenzoic acid (1). The pyrolysis reaction was followed by differential scanning calorimetry (DSC) and one large exothermic peak was observed at the decomposition temperature. In view of the DSC patterns for cocrystal DA,dnba and other compounds, it seems that both a catechol moiety and an amino group of DA in addition to a strong electron acceptor such as dnba are required for the appearance of the exothermic peak. On the basis of (a) elemental analysis of the black solid and (b) other pyrolysis experiments for cocrystals PA,dnba (PA: ,-phenylethylamine), BA,dnba (BA: benzylamine), DMDA,dnba (DMDA: O,O,-dimethyldopamine) and DHBA,dnba (DHBA: 3,4-dihydroxybenzylamine), it is assumed that the black solid was formed mainly through elimination of more than one molecule of water from one molecule of DA,dnba. Copyright © 2003 John Wiley & Sons, Ltd. [source] Phase behavior and photo-responsive studies of photoactive liquid crystalline hyperbranched polyethers containing benzylidene moietyJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 11 2009V. Srinivasa Rao Abstract Two sets of hyperbranched polyether epoxies were synthesized to study the effect of substituent, rigidity, and nature of photoactive unit on the thermal and photoresponsive properties. Each set was comprised of one molecule with an acyclic moiety in the repeating unit, and two molecules with a cyclic moiety of varying rigidity (cycle size) in the repeating unit. Two substituents on aromatic rings in the repeating unit were present in one set, and other set was without a substituent. The mesogenic and photoresponsive properties were studied and correlated to the varied structural parameters. The effects of varied molecular structural parameters on phase behavior and photoresponsive properties were very prominent. Out of six monomeric diols, only four have exhibited liquid crystalline phase while the polymers corresponding to all monomeric diols revealed mesophase. The findings in photoresponsive properties were further supported by molecular modeling studies. The changes in refractive index, photoviscosity, and fluorescence intensity with irradiation time substantiated the spectral pattern observed in UV-Vis spectroscopy. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2774,2786, 2009 [source] Intermolecular H-bond in propan-2-ol and its solutions with acetonitrileJOURNAL OF RAMAN SPECTROSCOPY, Issue 12 2007F. H. Tukhvatullin Abstract Formation of propan-2-ol,acetonitrile dimers is manifested in the Raman spectra as an appearance of a band of aggregates in the high-wavenumber side of the CN vibrational band of liquid acetonitrile (,2 cm,1). The intensity of the band of aggregates changes with a change in the concentration of the mixture (1,0.05 mole fraction). For propan-2-ol we carried out nonempirical calculations of a structure of isolated dimer aggregates. The formation of an intramolecular H-bond between the H and the O atom of the \newbox\osprulebox \newdimen\osprulewd \def\osprule#1#2{ \global\setbox\osprulebox=\hbox{#1} \osprulewd=\wd\osprulebox\advance\osprulewd by -8pt \raise0.5pc\hbox{$\matrix{\hskip-1pt\lower6.5pt\hbox{\vrule height #2pt}\lower4.5pt\hbox to \osprulewd{\hrulefill}\lower6.5pt\hbox{\vrule height #2pt}\cr \noalign{\vskip-1pt} \hbox{#1}\cr}$} } $\osprule{{\rm HCO}}{2.5} \hbox{H}$ group of length 2.045 Å is possible in the monomer molecule. The CH3 groups of alcohol are not equivalent. In the dimer formation, intramolecular H-bond in the \newbox\osprulebox \newdimen\osprulewd \def\osprule#1#2{ \global\setbox\osprulebox=\hbox{#1} \osprulewd=\wd\osprulebox\advance\osprulewd by -8pt \raise0.5pc\hbox{$\matrix{\hskip-1pt\lower6.5pt\hbox{\vrule height #2pt}\lower4.5pt\hbox to \osprulewd{\hrulefill}\lower6.5pt\hbox{\vrule height #2pt}\cr \noalign{\vskip-1pt} \hbox{#1}\cr}$} } $\osprule{{\rm HCO}}{2.5} \hbox{H}$ group is preserved. An intermolecular H-bond of length 2.045 Å and energy 15 kJ/mole is formed between the H atom of one molecule and the O atom of another molecule of the OH. The length and energy of the H-bond for the propan-2-ol,acetonitrile dimer formations calculate to 2.27 Å and 12.9 kJ/mole, respectively. The H-bond is formed by ,-electrons of nitrogen. The experimental data and the results of calculations are in good agreement. Copyright © 2007 John Wiley & Sons, Ltd. [source] Effect of Surface-Active Substances on the Rheological Properties of Silicon Carbide Suspensions in ParaffinJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2000Reinhard Lenk In this paper, the possibility of stabilization of SiC suspensions in paraffin (hot-molding slips) was investigated from the colloid science point of view. By considering the surface properties of finely dispersed silicon carbide, surface-active agents (fatty amine and alkylsuccinimide) which are suitable for surface modification by chemical adsorption on SiC were selected. Adsorption of fatty amines and alkylsuccinimide was carried out in model experiments in chloroform. Increasing the length of the carbon,hydrogen chain caused the adsorption to decrease, and the adsorption area of one molecule in the saturated adsorption layer to increase. The stabilizing effect of surface-active agents resulted in improved flow behavior of hot-molding slips. The efficiency of surface-active agents increased with increased adsorption layer thickness. In highly concentrated SiC hot-molding slips, a combination of alkylsuccinimide and fatty amine proved to be very efficient. This synergistic effect of long- and short-chained surface-active agents is discussed in terms of an adsorption layer model. [source] Lipofuscin and Macular DegenerationNUTRITION REVIEWS, Issue 10 2003George Wolf DPhil The accumulation of the autofluorescent pigment lipofuscin in the retina that occurs with aging has been explained as a side effect of the visual cycle. It occurs when two molecules of all- trans -retinal condense with one molecule of phosphatidylethanolamine in the discs of the rod outer segments, and is followed by uptake into retinal pigment epithelium (RPE) and conversion to the stable A2E, a pyridinium bisretinoid that is toxic to RPE cells. The accumulation of A2E, the major component of lipofuscin causes RPE cell apoptosis, thereby explaining age-related macular degeneration and macular degeneration characteristic of Stargardt disease. The drug isotretinoin (13- cis - retinoic acid) prevents accumulation of A2E in mice by slowing down the visual cycle and might therefore be used to prevent macular degeneration. [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] Ligand binding to the inhibitory and stimulatory GTP cyclohydrolase I/GTP cyclohydrolase I feedback regulatory protein complexesPROTEIN SCIENCE, Issue 4 2001Toshie Yoneyama BH4, 6R - l - erythro -5,6,7,8-tetrahydrobiopterin; GFRP, GTP cyclohydrolase I feedback regulatory protein Abstract GTP cyclohydrolase I feedback regulatory protein (GFRP) mediates feedback inhibition of GTP cyclohydrolase I activity by 6R - l - erythro -5,6,7,8-tetrahydrobiopterin (BH4), which is an essential cofactor for key enzymes producing catecholamines, serotonin, and nitric oxide as well as phenylalanine hydroxylase. GFRP also mediates feed-forward stimulation of GTP cyclohydrolase I activity by phenylalanine at subsaturating GTP levels. These ligands, BH4 and phenylalanine, induce complex formation between one molecule of GTP cyclohydrolase I and two molecules of GFRP. Here, we report the analysis of ligand binding using the gel filtration method of Hummel and Dreyer. BH4 binds to the GTP cyclohydrolase I/GFRP complex with a Kd of 4 ,M, and phenylalanine binds to the protein complex with a Kd of 94 ,M. The binding of BH4 is enhanced by dGTP. The binding stoichiometrics of BH4 and phenylalanine were estimated to be 10 molecules of each per protein complex, in other words, one molecule per subunit of protein, because GTP cyclohydrolase I is a decamer and GFRP is a pentamer. These findings were corroborated by data from equilibrium dialysis experiments. Regarding ligand binding to free proteins, BH4 binds weakly to GTP cyclohydrolase I but not to GFRP, and phenylalanine binds weakly to GFRP but not to GTP cyclohydrolase I. These results suggest that the overall structure of the protein complex contributes to binding of BH4 and phenylalanine but also that each binding site of BH4 and phenylalanine may be primarily composed of residues of GTP cyclohydrolase I and GFRP, respectively. [source] Cleaved antitrypsin polymers at atomic resolutionPROTEIN SCIENCE, Issue 2 2000Michelle A. Dunstone Abstract ,1 -Antitrypsin deficiency, which can lead to both emphysema and liver disease, is a result of the accumulation of ,1 antitrypsin polymers within the hepatocyte. A wealth of biochemical and biophysical data suggests that ,1 -antitrypsin polymers form via insertion of residues from the reactive center loop of one molecule into the ,-sheet of another. However, this long-standing hypothesis has not been confirmed by direct structural evidence. Here, we describe the first crystallographic evidence of a ,-strand linked polymer form of ,1 -antitrypsin: the crystal structure of a cleaved ,1 -antitrypsin polymer. [source] Computer-assisted interpretation of atmospheric pressure chemical ionization mass spectra of triacylglycerolsRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 23 2006Josef Cva Current lipidomics approaches require simple and rapid algorithms enabling the interpretation of mass spectra of lipids. Most lipids are complex mixtures of related components in which the composition of the aliphatic fatty acid chains varies from one molecule to the next. Triacylglycerols (TAGs) are an example of such a lipid class. Fatty acid chains are the only parts of the molecule to change from one species to another. Fatty acids, and consequently also TAGs, can be characterized by two parameters; the number of carbon atoms and the number of double bonds. All calculations reflecting relations among ions in the spectra can be easily made using these parameters. An algorithm for the automated interpretation of TAGs from atmospheric pressure chemical ionization mass spectra (TriglyAPCI) is presented in this paper. The algorithm first identifies diacylglycerol fragments and molecular adducts. In the next step, relations among the ions are searched and possible TAG structures are suggested. Individual features of the algorithm are described in detail and the software performance is demonstrated for the liquid chromatography/mass spectrometric (LC/MS) analysis of TAGs isolated from the termite Prorhinotermes canalifrons. Copyright © 2006 John Wiley & Sons, Ltd. [source] Planar packing of tetrachlorodicyanobenzenes.ACTA CRYSTALLOGRAPHICA SECTION B, Issue 1 2009Equimolar mixtures of ortho - and meta -, or ortho - and para -, or meta - and para -tetrachlorodicyanobenzene, C6Cl4(CN)2, form structures with disordered layers containing both kinds of molecules in rhombohedral or pseudo-rhombohedral cells. These structures are similar to the structure of the rhombohedral form of the meta isomer. The guiding force appears to be an intermolecular synthon, in which a nitrile group in one molecule interacts with Cl atoms in two adjacent molecules with N...Cl distances of approximately 3.1,Å. [source] Crystal packing in vicinal diols CnHm(OH)2ACTA CRYSTALLOGRAPHICA SECTION B, Issue 6 2002Carolyn Pratt Brock The O,H,O bonds in vic -diols CnHm(OH)2 have been studied using data retrieved from the Cambridge Structural Database. About half of these diols form complete, or almost complete, sets of intermolecular O,H,O bonds (i.e. two satisfied donors per molecule). For this half of the structures the frequencies of high-symmetry space groups and of structures with Z,,>,1 (more than one molecule in the asymmetric unit) are substantially elevated. The most common motif among fully bonded structures is an dimer, which can be linked in a variety of ways to form one-, two- or even three-dimensional patterns. Most of the other half of the vic -diols form simple O,H,O chains in which each OH group participates in only one intermolecular hydrogen bond. The space-group frequencies for this second group of structures are unexceptional. The most important factor determining the extent of O,H,O bond formation is the degree of substitution of the vic -diol. The spatial segregation of OH groups that is necessary for the formation of O,H,O bonds is found to make the dense filling of space more difficult because the intermolecular spacings that are appropriate for the O,H,O bonds may be inappropriate for the rest of the molecule. [source] Powder X-ray studies of meso -hexamethyl propylene amine oxime (meso -HMPAO) in two different phasesACTA CRYSTALLOGRAPHICA SECTION C, Issue 9 2010Mahmoud Al-Ktaifani Two different forms of meso -3,3,-[2,2-dimethylpropane-1,3-diylbis(azanediyl)]dibutan-2-one dioxime, commonly called meso -hexamethyl propylene amine oxime (HMPAO), C13H28N4O2, designated , and ,, were isolated by fractional crystallization and their crystal structures were determined by powder X-ray diffraction using the direct-space method with the parallel tempering algorithm. The , form was first crystallized from acetonitrile solution, while the , form was obtained by recrystallization of the , phase from diethyl ether. The , form crystallizes in the triclinic system (space group P), with one molecule in the asymmetric unit, while the crystal of the , form is monoclinic (space group P21/n), with one molecule in the asymmetric unit. In both phases, the molecules have similar conformations and RS/EE geometric isomerism. The crystal packing of the two phases is dominated by intermolecular hydrogen-bonding interactions between the two O,H oxime groups of an individual molecule and the amine N atoms of two different adjacent molecules, which lead to segregation of extended poly(meso -HMPAO) one-dimensional chains along the c direction. The structures of the two phases are primarily different due to the different orientations of the molecules in the chains. [source] Ezetimibe anhydrate, determined from laboratory powder diffraction dataACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2010Jürgen Brüning Ezetimibe {systematic name: (3R,4S)-1-(4-fluorophenyl)-3-[(3S)-3-(4-fluorophenyl)-3-hydroxypropyl]-4-(4-hydroxyphenyl)azetidin-2-one}, C24H21F2NO3, is used to lower cholesterol levels by inhibiting cholesterol resorption in the human intestine. The crystal structure of ezetimibe anhydrate was solved from laboratory powder diffraction data by means of real-space methods using the program DASH [David et al. (2006). J. Appl. Cryst.39, 910,915]. Subsequent Rietveld refinement with TOPAS Academic [Coelho (2007). TOPAS Academic User Manual. Version 4.1. Coelho Software, Brisbane, Australia] led to a final Rwp value of 8.19% at 1.75,Å resolution. The compound crystallizes in the space group P212121 with one molecule in the asymmetric unit. The molecules are closely packed and two intermolecular hydrogen bonds form an extended hydrogen-bond architecture. [source] Structural comparison of three N -(4-halogenophenyl)- N,-[1-(2-pyridyl)ethylidene]hydrazine hydrochloridesACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2010Julia Heilmann-Brohl 2-{1-[(4-Chloroanilino)methylidene]ethyl}pyridinium chloride methanol solvate, C13H13ClN3+·Cl,·CH3OH, (I), crystallizes as discrete cations and anions, with one molecule of methanol as solvent in the asymmetric unit. The N,C,C,N torsion angle in the cation indicates a cis conformation. The cations are located parallel to the (02) plane and are connected through hydrogen bonds by a methanol solvent molecule and a chloride anion, forming zigzag chains in the direction of the b axis. The crystal structure of 2-{1-[(4-fluoroanilino)methylidene]ethyl}pyridinium chloride, C13H13FN3+·Cl,, (II), contains just one anion and one cation in the asymmetric unit but no solvent. In contrast with (I), the N,C,C,N torsion angle in the cation corresponds with a trans conformation. The cations are located parallel to the (100) plane and are connected by hydrogen bonds to the chloride anions, forming zigzag chains in the direction of the b axis. In addition, the crystal packing is stabilized by weak ,,, interactions between the pyridinium and benzene rings. The crystal of (II) is a nonmerohedral monoclinic twin which emulates an orthorhombic diffraction pattern. Twinning occurs via a twofold rotation about the c axis and the fractional contribution of the minor twin component refined to 0.324,(3). 2-{1-[(4-Fluoroanilino)methylidene]ethyl}pyridinium chloride methanol disolvate, C13H13FN3+·Cl,·2CH3OH, (III), is a pseudopolymorph of (II). It crystallizes with two anions, two cations and four molecules of methanol in the asymmetric unit. Two symmetry-equivalent cations are connected by hydrogen bonds to a chloride anion and a methanol solvent molecule, forming a centrosymmetric dimer. A further methanol molecule is hydrogen bonded to each chloride anion. These aggregates are connected by C,H...O contacts to form infinite chains. It is remarkable that the geometric structures of two compounds having two different formula units in their asymmetric units are essentially the same. [source] p -Phenylenediamine and its dihydrate: two-dimensional isomorphism and mechanism of the dehydration process, and N,H...N and N,H..., interactionsACTA CRYSTALLOGRAPHICA SECTION C, Issue 3 2010Agnieszka Czapik p -Phenylenediamine can be obtained as the dihydrate, C6H8N2·2H2O, (I), and in its anhydrous form, C6H8N2, (II). The asymmetric unit of (I) contains one half of the p -phenylenediamine molecule lying about an inversion centre and two halves of water molecules, one lying on a mirror plane and the other lying across a mirror plane. In (II), the asymmetric unit consists of one molecule in a general position and two half molecules located around inversion centres. In both structures, the p -phenylenediamine molecules are arranged in layers stabilized by N,H..., interactions. The diamine layers in (I) are isostructural with half of the layers in (II). On dehydration, crystals of (I) transform to (II). Comparison of their crystal structures suggests the most plausible mechanism of the transformation process which requires, in addition to translational motion of the diamine molecules, in-plane rotation of every fourth p -phenylenediamine molecule by ca 60°. A search of the Cambridge Structural Database shows that the formation of hydrates by aromatic amines should be considered exceptional. [source] 3-Oxoandrosta-4,6-dien-17,-yl 2-methyl-1H -imidazole-1-carboxylate and 3-oxo-5,-androst-17,-yl 2-methyl-1H -imidazole-1-carboxylate: C,H..., and ,,, intermolecular interactionsACTA CRYSTALLOGRAPHICA SECTION C, Issue 3 2009Manuela Ramos Silva The title compounds, C24H30N2O3, (I), and C24H34N2O3, (II), both contain an androstane backbone and a 2-methylimidazole-1-carboxylate moiety at the 17-position. Compound (I) contains two symmetry-independent molecules (denoted 1 and 2), while compound (II) contains just one molecule in the asymmetric unit. The C,C,O,C torsion angle that reflects the twisting of the 2-methylimidazole-1-carboxylate moiety from the mean steroid plane is 143.1,(2)° for molecule 1 of (I), 73.1,(3)° for molecule 2 of (I) and 86.63,(17)° for (II). The significance of this study lies in its observation of significant differences in both molecular conformation and supramolecular aggregation between the molecules of the title compounds. The solid-state conformations compared with those obtained theoretically from ab initio methods for the isolated molecules show large differences, especially in the orientation of the methylimidazole substituent. [source] A fluoresceinophane: 19,4,16-trioxa-1(2,10)-anthracena-2(1,2)-benzenacyclohexadecaphane-17,3(19H)-dioneACTA CRYSTALLOGRAPHICA SECTION C, Issue 6 2007Stéphane Dufresne A novel macrocycle containing fluorescein, the highly fluorescent title compound, C31H32O5, has a xanthene core and a benzyl unit that are planar. The latter is rotated by 72.99,(3)° from the xanthene mean plane. The C11 alkyl tether and the xanthene group adopt a cage-like structure and the xanthene adopts a quinoid-type configuration. The compound crystallizes as a racemic mixture with one molecule of each isomer per unit cell. Even though the planes described by the xanthene and the benzene rings of different molecules are separated by 3.341,(4) and 3.73,(1),Å, respectively, there is insufficient overlap between the aryl units to promote ,-stacking. [source] | |||||||||||||||||||||||||||||||