Synthesis,thermal reactivity and structure of 1,2-bis(4-hydroxy-3-methoxyphenylethynyl)benzene

The crystal structure of the new enediyne 3 was determined by X-ray diffraction. 3 crystallizes in the orthorhombic space group Pbca (No. 61) with a = 12.7148(9) Å, b = 7.4872(8) Å, c = 38.890(4) Å, = = = 90 and Z = 8. The three-dimensional structure is characterized by an 8-membered cyclic array linking four molecules of 3 by hydrogen bonding between phenolic and methoxy groups. Furthermore, stabilization by –-stacking and CH s interactions is present. The important cd distance (between the two terminal acetylene carbons of the enediyne) which is relevant for the Bergman cyclization, was determined to 401 pm, being in good agreement with the high cyclization barrier ( G = 147.9 kJ mol^–1 at 220C) that was determined by differential scanning calorimetry (DSC).     

The reactions of 12C with 12C AT 293 MeV

Energy spectra, angular distributions, and elemental yield distributions have been measured for products Z = 1?9 produced in the reactions of ¹²C on ¹²C. A total reaction cross section 1170_?100⁺¹⁷⁰ mb was determined from the measured elemental cross sections and the principle of charge conservation. This total reaction cross section is about 250 mb less than the geometric cross section and agrees with the Glauber-model calculations of DeVries and Peng. The experimental energy spectra, angular distributions, and yield distributions were compared with those from model calculations for the statistical decay of the products of fusion and of incomplete fusion reactions. For both types of calculations, a modified version of the code LILITA was used. By comparing the data to model calculations, an upper limit of 75 mb for the fusion cross section was determined. That limit corresponds to an upper limit of L_crit for fusion of 10? in the sharp-cutoff approximation. The dominant reaction mechanisms appear to be incomplete fusion processes.     

Über Inclusions-Chromatographie und ein neues Retentionsprinzip für benzolderivate

Zusammenfassung Cellulose läßt sich in der Weise acetylieren, daß die Konformation und die gegenseitige Anordnung der Kohlehydratbänder in ihren kristallinen Bereichen erhalten bleibt. In gequollenem Zustand includiert diese mikrokristalline Acetylcellulose organische Moleküle der verschiedensten Art stoffspezifisch und es lassen sich daran chromatographische Trennungen durchführen. Chirale Verbindungen werden dabei teilweise, in einigen Fällen vollständig in die Antipoden gespalten. Diese Fähigkeiten verschwinden weitgehend, wenn das Material aus organischen Lösungen umgefällt wird. Eine besonders hohe Affinität zu der mikrokristallinen Acetylcellulose hat der Benzolkern, wenn mindestens 3 benachbarte Stellen nicht substituiert sind. Die Haftfestigkeit wird viel stärker durch sterische Faktoren als durch die chemische Natur der Substituenten beeinflußt. Insbesondere lassen sich o-Disubstitutionsprodukte des Benzols präparativ von den m- und p-Isomeren trennen. Da die neue Methode besonders gut auf Kohlenwasserstoffe und andere unpolare Moleküle anspricht, ergänzt sie die Gas-Chromatographie bei der Trennung und Reinigung labiler Verbindungen.

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Inclusion chromatography and a new retention mechanism for benzene derivatives

Summary Cellulose can be acetylated so that the conformation and the mutual arrangement of the carbohydrate chains within their crystalline regions is maintained. This microcrystalline acetyl cellulose in its swollen state is capable of specifically occluding a wide range of different molecules, and it can be used for chromatographic separations. Chiral compounds are partially, and in some cases completely, resolved into their antipodes. This ability, however, vanishes almost completely if the material is re-precipitated from organic solvents. The benzene ring shows a particularly high affinity for the microcrystalline acetyl cellulose when at least 3 adjacent positions are unsubstituted. The strength of sorption is more strongly influenced by steric factors than it is by the chemical nature of the substituents. Hence, the o-disubstituted benzene derivatives in particular can be separated on a preparative scale from the m- and p-isomers. Since the new method works best with hydrocarbons and other nonpolar molecules, it may be useful as a complementary technique to gas chromatography for the separation and purification of unstable compounds.

     

Stability-indicating assay for mecillinam using high-pressure liquid chromatography

A high-pressure liquid chromatographic method has been developed for use as a stability-indicating assay for mecillinam. Seven related compounds and at least one unknown degradation product are well separated and easily determined. The accuracy of the method is in good agreement with the published UV assay and the precision of a series of seven replicate determinations is +/- 1.0% R.S.D.     

Stability-indicating assay for pivmecillinam hydrochloride and pivmecillinam hydrochloride capsules.

A high-pressure liquid chromatographic assay has been developed for pivmecillinam hydrochloride and pivmecillinam hydrochloride capsules. The method separates five reported degradation products and a number of esterified, related compounds. The accuracy of this method is comparable to the published ultraviolet assay and the relative standard deviation of a series of six replicate assays was better than +/- 0.7%.     

Magnetic-field-induced band-structure change in CeBiPt

We report on a field-induced change of the electronic band structure of CeBiPt as evidenced by electrical-transport measurements in pulsed magnetic fields. Above approximately 25 T, the charge-carrier concentration increases nearly 30% with a concomitant disappearance of the Shubnikov-de Haas signal. These features are intimately related to the Ce 4f electrons since for the non-4f compound LaBiPt the Fermi surface remains unaffected. Electronic band-structure calculations point to a 4f-polarization-induced change of the Fermi-surface topology.     

An automated method for the simultaneous determination of salicylic acid and salicylazoiminopyridine in commercial salicylazosulphapyridine.

A technique for estimating nanogram quantities of mercury in sediment samples is described. Samples are heated at 870°C in an oxygen atmosphere, and the released mercury is collected on a gold-coated glass bead trap. The trap is then heated to 500°C in a helium stream; mercury is swept through a d.c. discharge cell and measured by emission spectrometry. Recoveries of mercury added to sediment samples were quantitative. Comparison of five separate samples by the proposed method and by a conventional cold-vapor atomic absorption technique showed similar results. The proposed method gives linear calibration plots up to 1700 ng Hg; the detection limit is 10 ng Hg, so that the sensitivity is 0.005 ppm for a 2.0-g sample.     

One and Two Photon Excitation of Radiofrequency Trapped Ca

Radiofrequency （rf） trapped ions are versatile candidates for a large panel of applications ranging from quantum information to the creation of cold molecules. Sample size can range from a single to 10^6 ions, and the internal and external energy states of the atoms can be controlled with high precision. In the experiment, we focus on different protocols related to frequency metrology using rf trapped Ca.     

Single-transverse-spin asymmetries of identified charged hadrons in polarized pp collisions at sqrt[s]=62.4 GeV

The first measurements of xF-dependent single-spin asymmetries of identified charged hadrons, pi+/-, K+/-, and protons, from transversely polarized proton-proton collisions at 62.4 GeV at RHIC are presented. Large asymmetries are seen in the pion and kaon channels. The asymmetries in inclusive pi+ production, AN(pi+), increase with xF from 0 to approximately 0.25 and AN(pi-) decrease from 0 to approximately -0.4. Observed asymmetries for K- unexpectedly show positive values similar to those for K+, increasing with xF, whereas proton asymmetries are consistent with zero over the measured kinematic range. Comparisons of the data with predictions of QCD-based models are presented.