Determination of Henry's law constant by automated Head space-Gas chromatography

Summary A method for determining the Henry constant of aqueous solutions by automated Head space-Gas chromatography (HSGC) is described. Acetone, 2,6-dichlorobenzonitrile, 2-nitrophenol, pyridine, trichloroethene and toluene were used as test substances. The temperature dependence of the Henry constant proved to be linear in the Arrhenius diagram (log H/T ^–1) in all cases. The ionic strength influences H as should be expected from the well-known salting-out effects. Detergent (cetyl-trimethylammonium bromide) is without influence below the critical micelle concentration (CMC); above the CMC it decreases the Henry constant. The effect of pH upon H follows exactly the rules of dissociation; hence it is possible to use the measurement of H for a determination of pKa-values and vice versa. With 2-nitrophenol and trichloroethene the water solubilities at various temperatures were evaluated and from these and the corresponding vapour pressure, the Henry constants were calculated. The slopes of the log H/T ^–1 plots are identical to those from the H-values as measured by HSGC. The applicability of the method ranges from (dimension-less) values for H from 10^–4 to 10^–1.

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Bestimmung der Henry-Konstanten durch automatische Dampfraumanalyse.Bestimmung gelöster Gase

Zusammenfassung Ein Verfahren zur Bestimmung der Henry-Konstanten wässriger Lösungen mit Hilfe der automatischen Dampfraumanalyse wird beschrieben. Als Testsubstanzen kamen zur Anwendung Aceton, 2,6-Dichlorbenzonitril, 2-Nitrophenol, Pyridin, Trichlorethen und Toluol. Die Temperaturabhängigkeit der Henry-Konstanten H im log H/T ^–1-Diagramm ist linear. Eine Steigerung der Ionenstärke führt zur Erhöhung der Henry-Konstanten, wie nach dem bekannten Aussalzeffekt zu erwarten. Cetyltrime-thylammoniumbromid in Konzentrationen unterhalb der kritischen Micellbildungskonzentration (CMC) ist ohne Einfluß, oberhalb der CMC tritt eine Erniedrigung der Henry-Konstanten ein. Der Einfluß des pH entspricht exakt dem Dissoziationsverhalten der Testsubstanz, so daß über eine Messung der Henry-Konstanten die Ermittlung des pKa-Werts möglich ist und umgekehrt aus dem pKa-Wert die Henry-Konstante berechnet werden kann.Aus den Wasserlöslichkeiten und Dampfdrucken von 2-Nitrophenol und Trichlorethen wurden die Henry-Konstanten berechnet; die Neigungen dieser log H/T ^–1 Geraden sind identisch mit denen der gemessenen Werte. Die Methode ist anwendbar auf Henry-Konstanten (als dimensionslose Größe) im Bereich von 10^–4 bis 10 ^–1.

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We thank for financial support by the Umweltbundesamt, Berlin.     

Stochastic motion of Sine-Gordon-solitons and the spin-correlation function of CsNiF3

The interaction of solitons and magnons (linear modes) of the Sine-Gordon equation is studied. The phase shift of the magnon in presence of a soliton gives rise to a shift of the position of the soliton, if magnon wave packets are considered. This leads to a stochastic part of the soliton motion in a gas of thermally activated magnons yielding an effective velocity and a diffusion constant. The influence of this effect on the solitonic part of the correlation function is discussed and compared with the recent experiment by Steiner and Kjems.     

RPA for the linewidth of the van der Pol Oscillator

The linewidth of then component van der Pol Oxcillator is calculated in random phase approximation. Forn=2 this model describes a single mode laser. This approximation is asymptotically correct for weak and strong pumping and also in the largen limit for all pumping. The result is in good agreement with numerical results forn=2 in the whole range including the threshold. The corresponding vertex renormalized approximation on the other hand yields poor agreement and the wrong asymptotic value in the limit of strong pumping. The reason for this failure is discussed.     

Stereoselectivity in reactions of metal complexes. V. Synthesis of mixed-ligand cobalt(III) complexes with (S)-aspartic-N-monoacetic acid and different amino-acids

The synthesis of mixed-ligand cobalt(III) complexes with (S)-aspartic-N-monoacetic acid ((S)-AMA) and different amino-acids Na[Co((S)-AMA)(AA)] (AA = gly, (R)- and (S)-ala, val, phe, ser and leu) leads to a mixture of cis-N- and trans-N-isomers. These isomers are formed stereospecifically. VIS., CD.- and NMR.-spectra are reported and a proposal is given for the absolute configuration of all the compounds isolated.     

7-Methylguanine nucleotides and their structural analogues; protolytic equilibria, complexing with magnesium (II) ion and kinetics for alkaline opening of the imidazole ring

First-order rate constants for the alkaline opening of the imidazole ring of several 7-methylguanine nucleotides and their structural analogues were determined. The results obtained suggested that intramolecular interaction between the negatively charged 5'-phosphate group and the positively charged imidazole ring markedly retard the attack of hydroxide ion on the C8 atom of the 7-methylguanine ring. In contrast, hardly any influence on the acidities of the interacting base and phosphate moieties was detectable. No effect on the complexing of the phosphate group with magnesium(II) ion could be detected.     

Wasseruntersuchung

Ohne Zusammenfassung