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141.
Gerhard Wendlberger Liljana Mladenova-Orlinova Walter Göhring Regina Scharf Erich Wünsch 《Monatshefte für Chemie / Chemical Monthly》1981,112(11):1297-1312
The synthesis of the tetratriacontapeptide amide corresponding to the revised primary structure of human big gastrin I is described. For this purpose the fragments were designed in view of the maximum use of those utilized in our previous synthesis of human big gastrin I according to the first sequence proposal. Consequently the key tripeptide-Pro-Pro-His- (sequence 7–9) was prepared in suitably protected form to be used as amino or carboxyl component for assembly of the segments 1–9 and 1–14, respectively. Final condensation of the latter nona- and tetradecapeptide derivatives with the C-terminal segments 10–34 and 15–34 via the azide and the dicyclohexylcarbodiimide/N-hydroxysuccinimide procedure, respectively, leads to crude fully protected human big gastrin I. Upon deprotection by exposure to trifluoroacetic acid in presence of ethanedithiol-(1,2) as scavanger, ion exchange chromatography and partition chromatography, the desired tetratriacontapeptide amide was isolated in satisfactory yield with a high degree of purity. The identical immunological behaviour of the synthetic material, if compared with that of natural human big gastrin I, represents ulterior strong evidence for the correctness of the newly proposed structure for this putative prohormonal form of the gastrins.
Kurzmitteilung:Wünsch E., Wendlberger G., Mladenova-Orlinova L., Göhring W., Jaeger E., Scharf R., Gregory R. A., Dockray G. J., Hoppe-Seyler's Z. Physiol. Chem.362, 179 (1981). 相似文献
142.
Walter Nielsch und Gerhard Böltz 《Fresenius' Journal of Analytical Chemistry》1954,143(3):168-172
Zusammenfassung Es wird gezeigt, daß die Bestimmung des Wismuts mit Thioharnstoff in bromwasserstoffsaurer Lösung auf photometrischem Wege mit dem Gerät ELKO II durchgeführt werden kann. Hierbei benutzt man zweckmäßig das Gerät mit der Glühlampe und Filter S 47 E oder den Quecksilberbrenner in Verbindung mit Filter Hg 436. Damit die Extinktion des gelbgefärbten Komplexes von der Thioharnstoffkonzentration unabhängig wird, muß die Lösung bei Benutzung des Filters S 45 E mindestens 10% Thiohamstoff, bei Benutzung des Filters Hg 436 mindestens 5% Thioharnstoff enthalten. Auch die Bromwasserstoffsäure übt einen Einfluß auf die Ausbildung der Extinktion aus. Wenn man die Messung mit dem Filter S 45 E durchführt und den Thioharnstoffgehalt mit 12% konstant hält, so darf die Bromwasserstoffkonzentration zwischen 1,2–9,2% betragen, um gleichbleibende Extinktionswerte zu erhalten. Benutzt man das Filter Hg 436 bei der gleichen Thioharnstoffkonzentration, so muß der Bromwasserstoffgehalt zwischen 3,0–7,5% liegen. Die Temperatur übt nur einen geringen Einfluß auf die Ausbildung des ThioharnstoffWismutkomplexes aus. Die Extinktion ist zeitunabhängig. Die Extinktionswerte ändern sich innerhalb 3 Std nach Zusammengeben der Reagenslösungen nicht. Das BEERsche Gesetz ist erfüllt. Das Verfahren besitzt erhebliche praktische Bedeutung, da sich sehr viele Metalllegierungen in denen Wismut zu bestimmen ist, mit Hilfe von Bromwasserstoffsäure und Brom sehr schnell lösen lassen. 相似文献
143.
The W(CO)5 and Fe(CO)4 complexes of the bicyclic phosphirane 3,5,6,6-tetraphenyl-1-phospha-2-thiabicyclo[3.1.0]hex-3-ene undergo a thermal 2-phenylphosphirane --> dihydrophosphaisoindole ring expansion, while the free phosphirane suffers both a [2 + 1] cycloreversion and a fragmentation yielding a butadienyl sulfide. 相似文献
144.
Gerhard Schulze Edzard Han Wolfgang Frenzel 《Fresenius' Journal of Analytical Chemistry》1989,332(8):844-848
Summary The interferences caused by inorganic ions, organic anions and Triton X-100 in the determination of lead by flow injection potentiometric and voltammetric stripping analysis at a mercury film electrode were investigated. The experiments were performed in the concentration range of 1–10 mg/l Pb2+. For both methods linear calibration plots were obtained in the presence of an excess of nitrate, chloride, perchlorate and sulphate. Iodide strongly interferes due to mercury complexation.Metal ion interference caused by formation of irreversible amalgams (as in the case of codeposition of Ni, Co, Fe and Cr) is avoided by proper choice of deposition potential. No effect of water soluble reduced species, i.e. Fe(II) and Cr(II), on the stripping signals was observed. The presence of acetate, citrate and tartrate does not limit the determination of lead by potentiometric stripping analysis (PSA) but has a marked effect on anodic stripping voltammetric (ASV) signals. No influence of Triton X-100 on the determination of lead by PSA was found. In ASV 10–3% Triton X-100 diminished the peak current by 15%.
Herrn Prof. Dr. Rolf Neeb aus Anlaß seines 60. Geburtstags gewidmet 相似文献
Herrn Prof. Dr. Rolf Neeb aus Anlaß seines 60. Geburtstags gewidmet 相似文献
145.
Oskar Friedrich Olaj Gerhard Zifferer Herbert Rhemann 《Monatshefte für Chemie / Chemical Monthly》1985,116(12):1395-1412
A formalism has been worked out which allows to transform any non-punctiform segment-segment potential of isolated polymer segments ε of fairly short-ranged character into the pair-potentialU operating between linear polymer chains with a certain reference to the arguments as they have been originally put forward byFlory andKrigbaum. Although no restrictions are made in the derivation as to the repulsive or attractive contribution of the segment-segment potential ε because of some known general deficiencies of theFlory-Krigbaum treatment for exclusively repulsive interaction, the resulting equations are primarily intended to describe the thermodynamic situation at and close to the θ-point where repulsion and attraction—though working at different ranges of segment separation—cancel. As the equation derived is somewhat complicated two different approximate forms have been developed: The first one is based on aTaylor series expansion retaining terms up to the fourth order which allows to characterizeU by the second and the fourth moment of the pair segment-segment distribution function, β and γ (β being the so-called binary cluster integral of segment-segment interaction, which is considered to be zero for θ-conditions). In this caseU may be represented by an expression of the general form $$U/kT = A(1 - BR^2 )\exp \{ - bR^2 \} .$$ The second method is based on a separate integration over the repulsive and attractive ranges of ε giving the repulsive (U +) and the attractive (U ?) part ofU finally after some approximations leading to an equation of the general form $$U/kT = (U_ + + U_ - )/kT = A_1 \exp \{ - b_1 R^2 \} - A_2 \exp \{ - b_2 R^2 \} .$$ In both cases the knowledge of the exact form of ε is dispensable, only β and γ—or for the second case their repulsive (β+ and γ+) and attractive (β? and γ?) parts have to be known. It is shown that the approximations are in excellent accordance with the exact form so that they may be conveniently used to describe pair potentials of polymer chains and to analyze pair potentials of segment-segment interactions under the limitations and conditions indicated. 相似文献
146.
Investigation of sulfur release in ETV-ICP-AES and its application for the determination of sulfates 总被引:3,自引:0,他引:3
Antje Mroczek Gerhard Werner R. Wennrich Werner Schr?n 《Fresenius' Journal of Analytical Chemistry》1998,361(1):34-42
Electrothermal vaporization inductively coupled plasma atomic emission spectrometry was applied to the determination of sulfur
species in aqueous solutions. The sensitivity for sulfur as sulfate was found to be depending on the cations in the sample.
For understanding this phenomenon the thermal behavior of sulfuric acid, ammonium sulfate and the sulfates of sodium, zinc,
magnesium and silver was studied. There were significant differences in the thermal release of sulfur from these sulfates.
To explain these phenomena different reaction mechanisms were calculated using thermodynamic data. Pd(NO3)2 and Ge in KOH were successfully applied as modifiers for the stabilization of the sulfates during the thermal pre-treatment
step and to establish a uniform thermal behavior of different sulfates. The stabilization of sulfur using Ge and Pd as modifiers
is based on the reduction of the sulfates in presence of carbon, resulting in the formation of GeS and PdS, respectively.
This explanation has been supported by comparing the experimental results with thermodynamic calculations considering different
reactions for the thermal decomposition of the sulfates. Applying Ge (in KOH) as modifier the absolute detection limit was
300 pg sulfur (e.g. LOD 30 ng mL–1). The significant influence of phosphates on the determination of sulfur could be essentially reduced by Pd as modifier.
Received: 11 November 1997 / Revised: 14 January 1998 / Accepted: 18 January 1998 相似文献
147.
Oliver Mechnich Gerhard Messier Horst Kessler Michael Bernd Bernhard Kutscher 《Helvetica chimica acta》1997,80(5):1338-1354
The conformational analysis of naturally occurring cytostatic cyclic heptapeptides axinastatin 2, 3, and 4 was carried out by two-dimensional NMR spectroscopy in combination with distance-geometry (DG) and molecular-dynamics (MD) calculations in explicit solvents. The synthesized secondary metabolites were examined in (D6)DMSO. Axinastatin 2 was also investigated in CD3OH. In all structures, Pro2 is in the i + 1 position of a βI turn and Pro6 occupies the i + 2 position of a βVIa turn about the cis amide bond between residue 5 and Pro6. In all peptides, a bifurcated H-bond occurs between residue 4 CO and the amide protons of residue 1 and 7. For axinastatin 2 and 3, an Asn Ig turn was found about Asn1 and Pro2. We compared these structures with conformations of cyclic heptapeptides obtained by X-ray and NMR studies. A β-bulge motif with two β turns and one bifurcated H-bond is found as the dominating backbone conformation of cyclic all-L-heptapeptides. Axinastatin 2, 3, and 4 can be characterized by six trans and one cis amide bond resulting in a β/βVI(a)-turn motif, a conformation found for many cyclic heptapeptides. Detailed biological tests of the synthetic compounds in different human cancer cell lines indicates these axinastatins to be inactive or of low activity. 相似文献
148.
Muñoz-Espí R Qi Y Lieberwirth I Gómez CM Wegner G 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,12(1):118-129
Polystyrene latex particles modified at the surface with different hydrophilic functional groups were prepared by miniemulsion polymerization and used as controlling agents in the crystallization of zinc oxide from aqueous medium. The effects of the chemical nature of the surface functionalization and the latex concentration on the crystal growth, morphology, and crystalline structure of the resulting zinc oxide were analyzed. Micro- and submicrosized crystals with a broad variety of morphologies depending on the functionalization were obtained. Among the different latexes studied, the acrylic-acid-derived particles were shown to be a convenient system for further quantitative investigations. In this case, as the additive concentration increases, the length-to-width ratio (aspect ratio) of the crystals decreases systematically. Preferential adsorption of the latex particles onto the fast-growing faces {001} of ZnO is assumed to follow a Langmuir-type isotherm, and interaction of the adsorbed particles with the growth centers will reduce the growth rate in [001]. This leads to a quantitative relationship linking the aspect ratio to the latex concentration at constant diameter and surface chemistry of the latex. The dependence of the aspect ratio on charge density of the latex can also be modeled by an algorithm in which attractive forces between the latex particle and the ZnO surface are balanced against repulsive forces of an osmotic nature. The latter are associated with the confined volume between the crystal and latex particle surfaces. 相似文献
149.
Heinz Berner Gerhard Schulz Gernot Fischer Hellmuth Reinshagen 《Monatshefte für Chemie / Chemical Monthly》1978,109(3):557-566
In order to obtain a better partition of a prodigiosin derivative in biological media, two hydroxy groups were introduced into theansa-part of the molecule. The synthesis of the title compound is described in detail. 相似文献
150.
Chroma to graphic Separation and Identification of Diastereomeric Carotinoids with Distant Chiral Centers The high-performance liquid chromatographic separation of diastereomeric C40-carotinoids is described possessing chiral centers which are separated by 18 C-atoms (nonaene system). The method is applied to the separation of the two diastereomers of 6,6′-dihydrorhodoxanthin 1a and 1b (ε,ε-carotene-3,3′-dione) and the six diastereomers of tunaxanlhin (ε,ε-carotene-3,3′-diol; 2a–2f ). Conditions for the separation of lutein [(3R, 3′R, 6′R)-β,ε-carotene-3.3′-diol, 3a ], 3′-epi-lutein [(3R,3′S,6′R)-β, ε-carotene-3,3′-diol, 3b ] and its 13′-cis- ( 3c ) and 13-cis-stereo-isomers( 3d ) are also reported. Identification of the different chromatographic fractions was possible by use of authentic synthetic samples or by 1H-NMR. spectroscopy. 相似文献