Angiotensin II Analogues. Part II. Synthesis and incorporation of the sulfur-containing aromatic amino acids: L-(4′-SH)Phe,L-(4′-SO2NH2)Phe,L-(4′-SO)Phe and L-(4′-S-CH3)Phe

L -Phenylalanine has been treated with chlorosulfonic acid and the product was either hydrolyzed, ammonolyzed or reduced. The resulting sulfonic-acid and aminosulfonyl derivatives have been employed for peptide synthesis with Boc-protection of the N^α-position only. The reduction product L -(4′-SH)Phe has been protected by formation of asymmetric disulfides or with various thiol protecting groups (benzyl-, methyl- and acetamidomethyl groups, the latter being the most suitable for peptide synthesis). With these protected amino acids several analogues of angiotensin II have been synthesized by the solid-phase method. These analogues have been used for structure-activity relationship studies on three different bioassays.     

Synthesis of 2-isopropylidenehydrazinylthiazole and its subsequent annelation to the corresponding thiazolo[2,3-c]-s-triazole

An unequivocal synthesis of a new thiazolo[2,3-c]-s-triazole substituted at the C-5 position by a very useful methyl triphenylphosphonium salt has been achieved starting from the corresponding 2-isopropylidenehydrazinylthiazole and formic acid. Ring closure was found to be very easy without isolation of a formylhydrazino intermediate. The thiazole derivative was prepared from isopropylidenethiosemicarbazide and (3-chloro-2-oxo)propyltriphenylphosphonium chloride in a good yield.     

A new purification method for single-wall carbon nanotubes (SWNTs)

A new purification procedure is introduced, which uses the advantages of column chromatography and vacuum filtration. Potassium polyacrylate is used as stationary phase. This method is based on the idea that the size of the existing cavities in the polymer increases during a swelling process in distilled water. The cavities are big enough to entrap the nanoparticles, but allow for a free movement of nanotubes and bundles. Received: 6 March 2000 / Accepted: 7 March 2000 / Published online: 5 April 2000     

Reexamination of reduced pteridine cofactors behaviour by proton nuclear magnetic resonance spectroscopy and mass spectrometry

In aqueous solutions, the autoxidation by air of 2-amino-4-hydroxy-6,7-dimethyl-5,6,7,8-tetra-hydropteridine, a hydroxylase cofactor, leads to the corresponding 7,8-dihydro derivate. Oxidation by hydrogen peroxide and Horseradish peroxidase does not give a stable quinonoid form as previously claimed but affords two metabolic products. Kinetics of the two pathways and structures of the different final compounds were determined by ¹H nmr and mass spectrometry.     

Magnetic properties of a new BaO.Fe2O3.Na2O glass

Homogeneous BaO.Fe₂O₃.Na₂O glass containing 60% Fe₂O₃ is prepared by splat cooling technique. X-ray diffraction reveals the presence of a few small βNaFeO₂ crystallites in a glassy matrix. DTA studies show that βNaFeO₂ cristallizes first and BaFe₁₂O₁₉ next. In the temperature range 130K < T < 400K this glass shows Curie-Weiss behaviour with large negative Weiss constant. The magnetic susceptibility measurements below 130K exhibit a broad maximum near 90–110K. Mössbauer study reveals that the glass mainly consists of tetrahedral network of Fe³⁺O₄ and a hyperfine structure at low temperature; magnetic ordering temperature estimated is about (125 ± 5)K.     

Primary left atrial angiosarcoma: follow-up by magnetic resonance imaging

We report the case of a primary left atrial angiosarcoma followed by MRI over a period of 1 year. The tumor was lobulated, with an initial central hyperintensity on T1-weighted images which disappeared after radiotherapy. Compared with other imaging modalities, MRI offered the most accurate information about the location, extent, and outcome under treatment.     

A versatile approach to affinitychromic polythiophenes

The preparation of both postfunctionalizable and chromic poly[3-(N-succinimido-p-phenylcarboxylate(tetraethoxy)oxy)-4-methylthiophene] is reported. The N-hydroxysuccinimide ester side group can easily react with different amine-bearing molecules in the solid state to yield a library of new polythiophene derivatives. The resulting polymers can be dissolved in various solvents, and interactions between the side chains (ligands) and different analytes (targets) can be detected from modifications of both the side-chain and the backbone conformations resulting in important color changes (i.e., affinitychromism). This colorimetric polymeric transducer could therefore lead to highly valuable, versatile, and inexpensive tools for highthroughput screening and drug discovery.     

Comparison of one-dimensional models and a 1-D/2-D model for closed-loop thermosyphons with vertical heat transfer sections

The results of a comparison between traditional one-dimensional (1-D) models and a 1-D/2-D model for closed-loop thermosyphons with vertical heat transfer sections are reported in this paper. Attention is limited to problems in which the flow is laminar. For cases where heat losses from the insulated portions of the loop are negligible,St _m=o, it is shown that traditional 1-D models can significantly overpredict the average fluid velocity in the loop for high power inputs (highGr _m). Local results of two-dimensional numerical simulations in the heated and cooled sections reveal that this discrepancy arises because the 1-D models do not account for mixed-convection effects which distort the velocity and temperature profiles from their fully developed forced convection shapes. Furthermore, for cases whereSt _m o, predictions of heat losses (or gains) produced by the 1-D models are handicapped by inaccuracies in the corresponding temperature predictions inside the loop.

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Vergleich eindimensionaler Modelle mit einem 1-D/2-D Modell zur Berechnung geschlossener Thermosiphonkreisläufe mit vertikalen Wärmeübergangsabschnitten

Zusammenfassung In dieser Arbeit werden die Ergebnisse eines Vergleichs zwischen traditionellen eindimensionalen (1-D) Modellen und einem 1-D/2-D Modell zur Berechnung geschlossener Thermosiphonkreisläufe mit vertikalen Wärmeübergangsabschnitten mitgeteilt. Die Untersuchung beschränkt sich auf reine Laminarströmungen. In Fällen, wo die Wärmeverluste an den isolierten Abschnitten des Kreislaufs vernachlässigt werden können (St _m=o), zeigt sich, daß traditionelle 1-D Modelle die mittlere Strömungsgeschwindigkeit im Kreislauf bei hohem Leistungseintrag (Gr _m hoch) signifikant überbewerten. Örtliche Ergebnisse zweidimensionaler Simultationsrechnungen für die beheizten bzw. gekühlten Abschnitte zeigen, daß diese Widersprüche im Unvermögen der 1-D Modelle begründet liegen, Mischkonvektionseffekte berücksichtigen zu können. Diese deformieren die reiner Zwangskonvektion in ädaquate Form der Geschwindigkeits- und Temperaturfelder. Ferner leidet im FalleSt _m o die Berechnung von Wärmeverlusten oder -gewinnen nach den 1-D Modellen unter der ungenauen Kenntnis der Temperaturverteilung im Inneren des Kreislaufs.

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Nomenclature f Fanningfriction factor [= _w/(V ²)/2] - g acceleration due to gravity - Gr _q Grashof number - Gr _m modified Grashof number - L total length of the closedloop - P _w power input - Pr Prandtl number [=C _p/k] - q heat flux - R radius of curvature of the 180° bends, Fig. 1 - Re Reynolds number - Re _ref reference Reynolds number - r _i internal radius of the pipe [=D/2] - St _m modified Stanton number - T area-weighted mean cross-sectional temperature - T _a ambient temperature - T _b bulk temperature - T _w mean wall temperature in the cooled section - U overall heat loss coefficient (W/m–°C) - V average velocity in the loop - V nondimensional average velocity [=V/V _ref] - V _ref reference velocity - X parameter used in Eq. (3) - volumetric thermal expansion - z height difference between the middle of the heated and cooled sections, Fig. 1 - length parameter - dimensionless ambient temperature - modified heat loss coefficient This research was financially supported by the Natural Sciences and Engineering Research Council of Canada, in the form of a Post-Graduate Scholarship granted to M. A. Bernier and through individual operating grants awarded to Prof. B. R. Baliga.     

Synthesis of 6-phenyl and 6-styrylthiazolo[3,2-b] [1,2,4]triazoles

Thiazole rings have been often encountered in the structure of antibiotic or antitumor drugs. An easy synthesis of them has revealed itself necessary in order to elucidate the mechanism of action of these naturally occurring substances. A method of preparation of conjugated b-ethylenic thiazole[3,2-b] [1,2,4]triazoles by heating a 3-thio substituted [1,2,4]triazole in the presence of polyphosphoric acid is reported here, giving the expected product in a 60% yield.