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141.
McColl IH Blanch EW Gill AC Rhie AG Ritchie MA Hecht L Nielsen K Barron LD 《Journal of the American Chemical Society》2003,125(33):10019-10026
The vibrational Raman optical activity (ROA) spectrum of a polypeptide in a model beta-sheet conformation, that of poly(l-lysine), was measured for the first time, and the alpha-helix --> beta-sheet transition monitored as a function of temperature in H(2)O and D(2)O. Although no significant population of a disordered backbone state was detected at intermediate temperatures, some side chain bands not present in either the alpha-helix or beta-sheet state were observed. The observation of ROA bands in the extended amide III region assigned to beta-turns suggests that, under our experimental conditions, beta-sheet poly(L-lysine) contains up-and-down antiparallel beta-sheets based on the hairpin motif. The ROA spectrum of beta-sheet poly(L-lysine) was compared with ROA data on a number of native proteins containing different types of beta-sheet. Amide I and amide II ROA band patterns observed in beta-sheet poly(L-lysine) are different from those observed in typical beta-sheet proteins and may be characteristic of an extended flat multistranded beta-sheet, which is unlike the more irregular and twisted beta-sheet found in most proteins. However, a reduced isoform of the truncated ovine prion protein PrP(94-233) that is rich in beta-sheet shows amide I and amide II ROA bands similar to those of beta-sheet poly(L-lysine), which suggests that the C-terminal domain of the prion protein is able to support unusually flat beta-sheets. A principal component analysis (PCA) that identifies protein structural types from ROA band patterns provides a useful representation of the structural relationships among the polypeptide and protein states considered in the study. 相似文献
142.
Svihla C. Kurt Dronawat Sundeep N. Hanley Thomas R. 《Applied biochemistry and biotechnology》1995,(1):355-366
It can be difficult to obtain reliable rheological data for filamentous fermentation broths using conventional instruments.
One common approach is to measure the torque drawn by an impeller rotating in the suspension (1–7). Many previous workers have assumed that the applicable shear rate in such a device is related to the impeller speed by
a fluid-independent constant determined by calibration with Newtonian and non-Newtonian fluids (1–9). The rheology ofAspergillus niger broths have been characterized using the impeller viscometer approach. The changes in the broth rheology were measured, and
used to interpret the growth of biomass and the evolution of the microorganism morphology. 相似文献
143.
[reaction: see text] Rhodium-catalyzed oxygen transfer was used to generate benzyl 2-silyl-2-oxoacetates in good yields. The hydrogenation of these compounds led to chiral alpha-silyl-substituted alpha-hydroxyacetic acids. Resolution by means of HPLC using a chiral stationary phase afforded an enantiomerically pure representative of this class of compounds, which was successfully applied as a chiral ligand in an asymmetric aldol-type reaction. 相似文献
144.
Synthesis and Crystal Structure of [ReNCl(NPPh2C6H4)]2 · [Ph3PNH2]Cl · CH3CN, a Rhenium Organic Nitrido Phosphoraneiminato Complex The title compound is synthesized by the reaction of ReNCl4 with Me3SiNPPh3 in boiling acetonitrile, forming colourless crystals, which are characterized by an X-ray structure determination. Space group P1 , Z = 2, 4 037 observed unique reflections, R = 0.043. Lattice dimensions at 19°C: a = 1 005.5; b = 1 695.2; c = 1 744.7 pm, α = 105.86°; β = 101.49°; γ = 104.45°. The structure consists of dimeric molecules [ReNCl(NPPh2C6H4)]2, triphenylphosphorane ammoniumchloride and included acetonitrile molecules. In the nitrido phosphoraneiminato complex the rhenium atoms are μ2-bridged via the N-Atoms of the phosphoraneiminato ligands. Because of this bridging and a Re? Re bond, one terminal nitrido ligand, one terminal chloro ligand, and a Re? C bond of an -C-atom of one phenylene group of Re-atoms attain co-ordination number six. 相似文献
145.
Synthesis and Crystal Structure of [Se3N2Cl]+GaCl4? [Se3N2Cl]+GaCl4? has been prepared by the reduction of [Se2NCl2]+GaC14? with SbPh3 in CH2Cl2 solution, forming red crystals, which were characterized by an X-ray structure determination. Space group P21/n, Z = 4, 1640 observed unique reflections, R = 0.050. Lattice dimensions at ? 80 °C: a = 929.4(1), b= 1078.8(1), c = 1135.7(1) pm, β = 92.026(9)°. The cations from nearly planar Se3N2 five membered rings with Se? N bond lengths from 170 to 176pm and a Se? Se bond of 242.2 pm. One of the selenium atoms is bonded to the chlorine atom. 相似文献
146.
(PPh4)2[MoN(N3)3Cl]2; Synthesis, IR Spectrum, and Crystal Structure The title compound is formed in the reaction of molybdenum (II) benzoate with trimethylsilyl azide and PPh4Cl in dichloro methane forming dark red single crystals. A PPh3Me⊕ salt of the ion [MoN(N3)3Cl]22? is obtained from (PPh3Me)2MoNCl4] treated with silver azide in CH2Cl2 suspension. The solvent CH2Cl2 participates in both reactions as oxidizing agent. (PPh4)2[MoN(N3)3Cl2 is characterized by a structural analysis based upon X-ray data: space group P1 , Z = 1, a = 1050.7 pm; b = 1185.4 pm; c = 1190.8 pm; α = 98.90°; β = 106.87°; γ = 103.97° (4505 independent, observed reflexions, R = 0.039). The compound consists of PPh4⊕ cations and centrosymmetric anions [MoN(N3)3Cl22? in which the molybdenum atoms are bridged by the Nα atoms of two azide groups; the resulting Mo? N bond lengths are 208 pm and 260 pm. In trans position to the long Mo? N bond the terminal nitrido ligand is situated, the Mo?N distance of 164 pm corresponds to a triple bond. Two terminal azido ligands and the chloro ligand are filling up the coordination sphere of the molybdenum atoms to a coordination number of six. The i.r. spectrum is reported and assigned. 相似文献
147.
Diiodoacetylene Complexes of Tungsten(IV). Crystal Structure of PPh4[WCl5(C2I2)] · 0.5 CH2Cl2 Tungsten hexachloride and diiodoacetylene react in CCl4 solution forming [WCl4(I? C?C? I)]2 which has a dimer structure with chloro bridges. In CH2Cl2, it reacts with PPh4Cl yielding PPh4[WCl5(I? C?C? I)] · 0.5 CH2Cl2. In both compounds the C2I2 ligands attain a marked increase in thermal stability by their side-one coordination to the tungsten atoms. The crystal structure of the PPh4⊕ salt was determined with X-ray diffraction data (3879 observed reflexions, R = 0.050). PPh4[WCl5(C2I2)] · 0.5 CH2Cl2 crystallizes in the space group P21/n with 8 formula units per unit cell. The lattice constants are a = 1723.0, b = 1681.2, c = 2214.6 pm and β = 94.38°. There are two crystallographically independent [WCl5(C2I2)]? ions which differ only slightly from one another. The C2I2 ligand has a staggered arrangement relative to the W? Cl groups, with C? C bond lengths of 127 pm. The infrared spectra are discussed. 相似文献
148.
Ligia Bicudo de Almeida Marilene De Vuono Camargo Penteado George Britton Peter Uebelhart Murat Acemoglu Conrad Hans Eugster 《Helvetica chimica acta》1988,71(1):31-32
The 5,6:5′,6′-diepoxy-5,6:5′,6;-tetrahydro-β,β-carotene, isolated from tubers of a white-fleshed variety of sweet potato (Ipomoea batatas LAM .) has been assigned the (5R,6S,5′R,6′S)-chirality on the basis of its HPLC, UV/VIS, and CD data. 相似文献
149.
Matthias Treu Christian Hametner Johannes Frohlich Ulrich Jordis Kurt Mereiter 《Journal of heterocyclic chemistry》2002,39(6):1283-1288
The synthesis of a novel unnatural carbocyclic analog of the acetylcholine esterase inhibitor galanthamine with a K3[Fe(CN)6] promoted oxidative tandem cyclization as the key step is reported. 相似文献
150.
Murat Acemoglu Roland Prewo Jost Hans Bieri Conrad Hans Eugster 《Helvetica chimica acta》1984,67(1):175-183
Synthesis and X-Ray Structure of (6′RS,8′RS,2E)- and (6′RS,8′SR,2E)-3-Methyl-3-(2′,2′,6′-trimethyl-7′-oxabicyclo[4.3.0]non-9′-en-8′-yl)-2-propenal ([(5RS,8RS)- and (5RS,8SR)-5,8-Epoxy-5,8-dihydro-ionylidene]acetaldehyde) To check our previous spectroscopic assignments of the structures of trans- and cis-substituted furanoid end groups of carotenoid-5,8-epoxides, we now have synthesized the title compounds. An X-ray structure determination of a single crystal of the trans-isomer (±)- -10A is in agreement with the 1 H-NMR spectroscopic arguments: isomers with Δδ (H? C(7), H? C(8)) = 0.15–0.22 ppm and J > 1.4 for H? C(7) belong to the cis-series; Δδ in trans-compounds is < 0.07 ppm, and H? C(7) appears as a broad singulett. 相似文献