Beitrag zur direkten Sauerstoffbestimmung in organischen Verbindungen

Zusammenfassung Es wird über zehnjährige Erfahrungen mit der maßanalytischen Mikrobestimmung des Sauerstoffes nachUnterzaucher berichtet. Silikon-schlauchverbindungen dürfen nicht verwendet werden, da sie gasdurchlässig sind. Die Gesamtanalysenzeit kann durch Verwendung eines Klappbrenners auf 15 Minuten verkürzt werden. Die Möglichkeit, das vonEmich im Prinzip vorgeschlagene CO₂-Multiplikationsverfahren anzuwenden, wurde überprüft. Zur Endbestimmung wird für Routine-analysen dem jodometrischen Verfahren wegen seiner Schnelligkeit und Empfindlichkeit der Vorzug gegeben.

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Summary A report is given of 10 years of experiences with the volumetric micro determination of oxygen by theUnterzaucher procedure. Silicone tube connections must not be used since they are permeable to gases. The total analysis time can be shortened to 15 minutes by using a shutter burner. A study was made of the possibility of using the multiplication procedure that in principle was recommended byEmich. For routine analyses, it was found preferable to employ the iodometric method for the final measurement because of its rapidity and sensitivity.

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Résumé On donne un compte rendu sur des expériences effectuées depuis une dizaine d'années sur le microdosage volumétrique de l'oxygène d'aprèsUnterzaucher. Il ne faut pas employer pour ces expériences de tubes siliconés car ils sont perméables aux gaz. La durée totale d'une analyse peut être ramenée à 15 minutes en employant un brûleur à charnière. On a examiné la possibilité d'appliquer le procédé de multiplication de CO₂ préconisé dans le principe parEmich. Pour la détermination du point équivalent dans les analyses en série, on donne la préférence au procédé iodométrique en raison de sa rapidité et de sa sensibilité.

     

An Efficient Strategy to Orthogonally Protected (R)- and (S)-alpha-Methyl(alkyl)serine-Containing Peptides via a Novel Azlactone/Oxazoline Interconversion Reaction

A novel strategy for the synthesis of (R)- and (S)-alpha-methyl(alkyl)serine-containing peptides is presented. Using (S)-phenylalanine cyclohexylamide 6 as chiral auxiliary, the optically pure azlactones (R)- and (S)-2 were synthesized via a novel azlactone/oxazoline interconversion reaction (Figures 3 and 6). These azlactones constitute fully protected and activated synthetic equivalents of (R)- and (S)-alpha-methylserine and can be directly incorporated into peptides without further protective group manipulations. Like other alpha,alpha-dialkylated glycines, optically pure alpha-alkylserines can be used to stabilize beta-turn and alpha-helical conformations in short peptides.     

Cobalt Chalcogenide Clusters. Synthesis,Characterization and DFT Calculations of [Co4Se2(CO)10] and [Co4Te2(CO)11]. Crystal Structure of [Co8Se4(CO)16(μ‐dppa)2]

The reactions of [Co₂(CO)₈] with E(SiMe₃)₂ (E = Se, Te) in CH₂Cl₂ result in the formation of the compounds [Co₄Se₂(CO)₁₀]> ( 1 ) and [Co₄Te₂(CO)₁₁] ( 2 ), respectively. Both cluster complexes have similar molecular structures in which the cobalt atoms form four‐membered rings with μ₄‐bridging chalcogen atoms (Se and Te) above and below the plane of the metal atoms and the carbonyl ligands as either terminal or μ₂‐bridging ligands. DFT‐calculations for both compounds have been carried out in order to obtain some more information about their electronic distribution. In the presence of the phosphine Ph₂PC≡CPPh₂ (dppa), the reaction of [Co₂(CO)₈] with Se(SiMe₃)₂ leads to the formation of [Co₈Se₄(CO)₁₆(μ‐dppa)₂] ( 3 ). During the reaction two molecules of [Co₂(CO)₈] have been added to the acetylene groups of the dppa ligands, whilst the remaining cobalt atoms coordinate to the phosphorus atoms of the phosphine. In this compounds the selenium atoms act as μ₃‐ligands, bridging the metal atoms bonded to the phosphorus with those bonded to the acetylene groups.     

Shake-up and multiplet structure of ESCA satellites of Cu compounds

The ESCA inner shell spectra of Cu compounds are investigated theoretically. It is shown that the large satellites appearing for Cu(II) compounds correspond to shake-up states which are close to the configuration p⁵d⁹ and have the characteristic multiplet splitting of this configuration.     

A multi-angle magnetic spectrograph for nuclear reaction studies

A multi-angle magnetic spectrograph for recording spectra of charged particles emitted in nuclear reactions has been built. The apparatus and the beam transport system are described and their parameters are discussed.     

Elastic scattering of α-particles on10B forEα = 5?50 MeV

Experimental data of the elastic scattering of-particles on¹⁰B forE = 30–50.6 MeV are presented. They are analysed together with the data of a previous measurement forE = 5–30 MeV in the frame of the optical model including spin-orbit coupling. The interaction radii of the-¹⁰B-systems are determined with the Inopin-Ericson model forE = 5–50 MeV. The mean free path of-particles in¹⁰B is calculated.