Spin Density Distribution in 2,4,6-Triphenylphenoxyl

The distribution of the unpaired electron over the oxygen and the 24 carbon atoms in the free 2,4,6-triphenylphenoxy radical was determined by electron spin resonance spectroscopy and quantum-mechanical approximation methods. The hyperfine splitting was evaluated with the aid of the spectra of triphenylphenoxyls deuterated in some or all of the substituent phenyl groups. The results of the quantum-mechanical approximations were checked by recording the ESR spectra of triphenylphenoxyls labeled with ¹³C in positions 1,2,3, or 4 of the central ring. The spin density distribution permits a first discussion of the ¹⁷O-coupling constants of correspondingly labeled triphenylphenoxyl and other organic free radicals.     

Solution conformation by NMR and molecular modeling of three sulfide-free somatostatin octapeptide analogs compared to angiopeptin

Summary The conformation in dimethylsulfoxide of the somatostatin derivative angiopeptin and of three disulfide-free analogs was estimated by two-dimensional nuclear magnetic resonance spectroscopy at room temperature. The resulting 3D molecular graphics were compared and shown to reflect the observed differences in the inhibition of restenosis after rat aorta balloon injury by these octapeptide inhibitors. Angiopeptin and its active analog 2 displayed a relatively rigid conformation of the cyclic hexapeptide backbone due to the presence of two well-defined hydrogen bonds, further stabilized by a third hydrogen bond outside the ring. No such constraints were detected for the two biologically inactive analogs, which, compared to 2, had a two-atom longer or shorter hexapeptide ring. The well-defined structure of compound 2 may serve as an improved pharmacophore for this new class of drugs.     

High-performance liquid chromatographic quantitation of cyclooxygenase and lipoxygenase metabolites of arachidonic acid from rat polymorphonuclear leukocytes

10-Ethyl-10-deaza-aminopterin (10-EdAM) is a novel folic acid antimetabolite currently being tested in phase II clinical trials. We have developed an isocratic high-performance liquid chromatographic method for the quantification of 10-EdAM and metabolites in plasma. Solid-phase extraction was used for sample clean-up. Adequate accuracy was obtained without the use of an internal standard. Fluorometric detection with excitation at 243 nm and emission at 488 nm was used for accurate quantification of samples containing small amounts of drug or metabolites (2.0-4.0 nM, depending on the compound). Ultraviolet detection at 350 nm was only applicable for the analysis of plasma concentrations of 10-EdAM exceeding 50 nM. The usefulness of the assay was demonstrated by the results obtained in a pharmacokinetic study. The assay could separate the parent compound from seven identified and two unknown products.     

Einige systematische Fehlerquellen bei der Bestimmung von Elementen im ng- und pg-Bereich mit der Atomabsorptionsspektrometrie mit flammenloser Anregung im Graphitofen

Zusammenfassung Es wird versucht, an Hand ausgewählter Elemente (Fe, Co, Ni, Ag und Cd) schwerwiegende systematische Fehler bei der Bestimmung durch flammenlose Atomabsorptionsspektrometrie aufzuzeigen und deren Ursache zu diskutieren. Neben den Parametern des Temperaturprogramms und des Schutzgasstroms ist die Art und Struktur des Graphits, sowie dessen Reaktivität von entscheidendem Einfluß auf Empfindlichkeit und Nachweisvermögen des Verfahrens. Depressionen bei der Verwendung stark saurer Analysenlösungen werden bestätigt und es wird versucht, diese im Zusammenhang mit der Reaktivität von Graphit zu erklären.An einem vereinfachten Modell wird der Einfluß organischer Lösungsmittel bzw. organischer Lösungen von Komplexbildnern wie Dithizon, NH₄-DDTC und APDC auf die Atomisierung untersucht. Es wird diskutiert, ob die dabei registrierten Depressionen Verluste sind, die durch die Bildung flüchtiger metallorganischer Verbindungen bereits bei Temperaturen ab 500° C entstehen. Besonders schwerwiegend sind diese Verlustreaktionen bei Anwesenheit halogenierter Kohlenwasserstoffe, wie an Hand der Reaktionen von Fe, Cd, Co, Ni und Ag mit Chloroform gezeigt werden kann.

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Some sources of systematic errors in the determination of elements in the ng- and pg-range by atomic absorption spectrometry with flameless excitation in the graphite oven

With selected elements (Fe, Co, Ni, Ag and Cd), the serious systematic errors inherent in flameless atomic absorption spectrometry are demonstrated and their origins are discussed. Besides the parameters of the temperature program and the inert gas stream, the type and structure of the graphite, as well as its reactivity have a decisive influence on the sensitivities and limits of detection of the technique. Depression of the signal is observed with the use of strongly acid solutions and it has been attempted to explain this in connection with the reactivity of the graphite.The influence of organic solvents and organic solutions of complexes with dithizone, NH₄-DDTC and APDC on the atomization have been investigated with simplified examples. It can be presumed that the resulting depression of the signal is due to losses by the formation of volatile metal-organic compounds at temperatures above 500° C. Particularly large are the losses in the presence of hydrocarbon halides as can be demonstrated by the reaction of Fe, Cd, Co, Ni, and Ag with chloroform.

     

Experimental upper limits for hadronic and axion decays of the γ(1S)

A search for the decays γ→ρπ, γ→J/ψX and γ→γa (whereX is undetermined and a is an axion) has been completed using the LENA detector at the DORIS storage ring. No evidence for any of these processes was found. For these decay modes we set branching fraction upper limits (90% C.L.) of 2.1×10^?3, 2.0×10^?2 and 9.1×10^?4, respectively.     

Über Eisen(III)-Komplexe mit Phenolen. IV. Säurekonstanten einiger Polyphenole

The apparent acid constants of some polyphenols and of derivates from salycilic acid are determined by potentiometry using glass or hydrogen electrodes and by UV spectrophotometry on comparable conditions respectively. Anaerobic manipulations were strictly used to avoid autoxidation. The results can be interpreted qualitatively, if the possibility of the formation of intramolecular hydrogen bridges is considered besides the effects of substituting groups.     

Structural and magnetic properties of Ni2MnIn Heusler thin films grown on modulation-doped InAs heterostructures with metamorphic buffer

This paper reports on the morphological, structural, magnetic, and magneto-optic properties of Ni₂MnIn Heusler films grown on InAs-high electron-mobility transistor structures (HEMT) with metamorphic buffers for spintronic applications. Similar to our previous results on the Ni₂MnIn/InAs (001) system, the Heusler layer is found to have a (110) orientation relative to the (001) InAs-HEMT surface. We observe almost equal spin-polarizations for Heusler films on (001) InAs-HEMT as well as on (001) InAs. In addition, we find further support for interfacial intermixing previously reported for the Ni₂MnIn/InAs (001) system. On the other hand, the Heusler/InAs-HEMT system shows distinct morphologic, structural, and magnetic properties as compared to the Ni₂MnIn/InAs (001) system. In particular, more rapid and complex plastic deformation effects resulting in a high surface density of pin-holes in the Heusler films are found. We report on complex mutual deformation effects between the Heusler films and the underlying InAs-HEMT structure. Furthermore, a hysteresis loop squareness close to 1 for a 50 nm Heusler film on InAs-HEMT is observed. We tentatively associate these phenomena with the higher mismatch strain of the Ni₂MnIn/InAs-HEMT system compared to Ni₂MnIn films grown on (001) InAs.     

[Bis(tetrahydrofuran–O)–bis(1,3–dialkyl–2–diphenylphosphanyl–1,3–diazaallyl)calcium] – Synthesis and Crystal Structures of Calcium Bis[phospha(III)guanidinates] and Investigations of Catalytic Activity

The reaction of [(thf)₄Ca(PPh₂)₂] ( 1 ) with diisopropyl– and dicyclohexylcarbodiimides yields the phospha(III)guanidinates [(thf)₂Ca{RNC(PPh₂)NR}₂] with R = isopropyl ( 2 ) and cyclohexyl ( 3 ). The metathesis reaction of K{RNC(PPh₂)NR} with anhydrous CaI₂ also allows the synthesis of these phospha(III)guanidinate complexes 2 and 3 . For 2 a cis arrangement is observed whereas 3 crystallizes as trans isomer. The phospha(III)guanidinates act as bidentate chelate bases with an average Ca–N distance of 242.5 pm. The C–P bond length between the PPh₂ fragment and the 1,3–diazaallyl unit is with values above 190 pm very large. The complexes 2 and 3 show a moderate catalytic activity in hydrophosphanylation reactions of dialkylcarbodiimides with diphenylphosphane.