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81.
Prof. Dr. Roger Blachnik Ulrike Peukert Anette Czediwoda B. Engelen K. Boldt 《无机化学与普通化学杂志》1995,621(10):1637-1643
The Molecular Composition of Solidified Phosphorus-Sulfur Melts and the Crystal Structure of β-P4S6 Phosphorus sulfur melts were annealed for one week at 673 K and then quenched in ice water. The solids were dissolved in CS2 and the concentrations of phosphorus sulfides were determined by 31P NMR spectroscopy. Samples containing between 44 and 70 mol% sulfur dissolved completely in CS2. Between 0 and 42 mol% remains an insoluble residue of red phosphorus. Above 72 mol% it consisted of sulfur chains linked by phosphorus atoms. The solutions contained mainly the congruently melting compounds P4S3, P4S7, and P4S10 having maximum concentrations at their stoichiometric compositions. Other compounds P4Sn (n = 4–9) which decompose on heating, according to the phase diagram, were also found in surprisingly high concentrations. One of these was β-P4S6 which crystallizes in the monoclinic space group P21/c with the lattice parameters a = 702.4(2), b = 1 205.6(2), c = 1 148.9(6) pm and β = 103.4(2)°. Reaction of white phosphorus with sulfur was also investigated. In contrast to the results of previous authors, who described the system P4–S8 below 373 K as eutectic, we found that the elements reacted below this temperature. 相似文献
82.
Rognan D Stryhn A Fugger L Lyngbaek S Engberg J Andersen PS Buus S 《Journal of computer-aided molecular design》2000,14(1):53-69
A three-dimensional model of the complex between an Influenza Hemagglutinin peptide, Ha255–262, and its restricting element, the mouse major histocompatibility complex (MHC) class I molecule, Kk, was built by homology modeling and subsequently refined by simulated annealing and restrained molecular dynamics. Next, three-dimensional models of two different T cell receptors (TCRs) both specific for the Ha255–262/Kk complex were generated based on previously published TCR X-ray structures. Finally, guided by the recently published X-ray structures of ternary TCR/peptide/MHC-I complexes, the TCR models were successfully docked into the Ha255–262/Kk model. We have previously used a systematic and exhaustive panel of 144 single amino acid substituted analogs to analyze both MHC binding and T cell recognition of the parental viral peptide. This large body of experimental data was used to evaluate the models. They were found to account well for the experimentally obtained data, lending considerable support to the proposed models and suggesting a universal docking mode for TCRs to MHC-peptide complexes. Such models may also be useful in guiding future rational experimentation. 相似文献
83.
Frank Podebrad Martin Heil Anette Scharrer Sabine Feldmer Oliver Schulte-Mter Armin Mosandl Adrian C. Sewell Hans J. Bhles 《Journal of separation science》1999,22(11):604-608
Methylcitric acid (2-hydroxybutane-1,2,3-tricarboxylic acid–MCA) is a structural analogue of citric acid, but due to an additional methyl group it is a chiral molecule with two stereogenic centers and thus four stereoisomers are conceivable. MCA occurs naturally as prominent metabolite in body fluids of patients with inherited metabolic diseases such as propionic acidemia, methylmalonic aciduria, or holocarboxylase synthetase deficiency. Therefore methylcitric acid is considered to be an important diagnostic marker for these diseases. MCA is most likely produced from accumulated propionyl-CoA in these diseases by the enzyme si-citrate synthase from the citric acid cycle; however, there are other enzymes known which could catalyze the same reaction with different stereoselectivity, such as re-citrate synthase or the more specific enzyme methylcitrate synthase, found in microorganisms. Almost all methods dealing with MCA in the literature are non-enantioselective. For that reason there is no information about occurrence of MCA enantiomers in healthy people, patients with propionic acidemia, methylmalonic aciduria, or holocarboxylase synthetase deficiency and about value of enantiomeric distribution for diagnosis and long-term treatment. The enantioselective analysis of MCA as corresponding trimethyl ester was achieved by enantioselective multidimensional gas chromatography coupled with mass spectrometry using heptakis-(2,3-di-O-methyl-6-O-tert-butyl-dimethylsilyl)-β-cyclodextrin as chiral stationary phase. The described method allows a reliable screening of MCA in complex matrices like urine without time consuming sample preparation and with mass selective detection. During this investigation urine samples from various patients and healthy controls were analyzed. As concluded, MCA is a good diagnostic marker and can be easily measured by the method presented. Only the two stereoisomers (2S,3R) and (2S,3S) were detectable in patients and healthy controls. The varying ratios of these stereoisomers cannot presently be correlated with the health status of patients, although there are some indications that this might be possible. However, the quantitative levels of MCA, determined as the ratio of MCA absolute peak area divided by 1,000 to the creatinine contents of urine samples in this investigation, showed a dependence on the state of health and MCA would thus also be a possible marker for long-term treatment. Such a substance is of major interest nowadays since there are different studies searching for such a long-term marker in propionic acidemia or methylmalonic aciduria. 相似文献
84.
85.
Anette Beck‐Sickinger Peter R. Schreiner Joachim Spatz 《Nachrichten aus der Chemie》2002,50(6):692-693
86.
87.
Joachim Mohn Benjamin Wolf Sakae Toyoda Cheng‐Ting Lin Mao‐Chang Liang Nicolas Brüggemann Holger Wissel Amy E. Steiker Jens Dyckmans Lars Szwec Nathaniel E. Ostrom Karen L. Casciotti Matthew Forbes Anette Giesemann Reinhard Well Richard R. Doucett Chris T. Yarnes Anna R. Ridley Jan Kaiser Naohiro Yoshida 《Rapid communications in mass spectrometry : RCM》2014,28(18):1995-2007
88.
Influence of Lumbricus terrestris and Folsomia candida on N2O formation pathways in two different soils – with particular focus on N2 emissions
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89.
90.
Unwinding of the C‐Terminal Residues of Neuropeptide Y is critical for Y2 Receptor Binding and Activation
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Anette Kaiser Paul Müller Tristan Zellmann Dr. Holger A. Scheidt Dr. Lars Thomas Mathias Bosse Dr. Rene Meier Prof. Dr. Jens Meiler Prof. Dr. Daniel Huster Prof. Dr. Annette G. Beck‐Sickinger Dr. Peter Schmidt 《Angewandte Chemie (International ed. in English)》2015,54(25):7446-7449
Despite recent breakthroughs in the structural characterization of G‐protein‐coupled receptors (GPCRs), there is only sparse data on how GPCRs recognize larger peptide ligands. NMR spectroscopy, molecular modeling, and double‐cycle mutagenesis studies were integrated to obtain a structural model of the peptide hormone neuropeptide Y (NPY) bound to its human G‐protein‐coupled Y2 receptor (Y2R). Solid‐state NMR measurements of specific isotope‐labeled NPY in complex with in vitro folded Y2R reconstituted into phospholipid bicelles provided the bioactive structure of the peptide. Guided by solution NMR experiments, it could be shown that the ligand is tethered to the second extracellular loop by hydrophobic contacts. The C‐terminal α‐helix of NPY, which is formed in a membrane environment in the absence of the receptor, is unwound starting at T32 to provide optimal contacts in a deep binding pocket within the transmembrane bundle of the Y2R. 相似文献