镍电极开路电位测定微量硼氢根离子

实验采用循环伏安法，用镍电极代替铂铑等贵金属电极测定了碱性体系中不同硼氢根离子浓度下的开路电位，得出了研究电极的开路电位（-0．355～-0．280vs.SCE／V）与微量硼氢根离子浓度的对应关系，并用于监测电解偏硼酸钠制备硼氢化钠体系中微量硼氢根离子，同时计算了该方法的误差。结果表明，测量结果的相对标准偏差为2．2％；回收率为98．4％。该法简单、快速，可测定10^-5～10^-3mol／L范围的硼氢根离子浓度。     

Atomabsorptions-Flammenphotometrie im Einstrahlverfahren mit Kompensation der von Flamme und Hintergrundstrahler verursachten Schwankungen

Zusammenfassung Es wird gezeigt, daß auch im Einstrahlverfahren sogar extrem starke Schwankungen der Betriebsparameter der Flamme (Brenngas- und Preßluftdruck, Probendurchsatz) aus dem Meßergebnis weitgehend eliminiert werden können, wenn hinreichend oft Zwischeneichungen vorgenommen werden. Auf die gleiche Weise kann man selbstverständlich auch zeitliche Änderungen der Emission des Hintergrundstrahlers ausschalten. Für die Voruntersuchungen wurde ein aus handelsüblichen Bauteilen zusammengestelltes Gerät benutzt, welches mehr als 15 Zwischeneichungen pro Minute zuläßt. Dabei zeigte sich unter anderem, daß eine Änderung des Probendurchsatzes um den Faktor 10 (innerhalb 1 min) eine Änderung des Extinktionswertes der Probe um den Faktor 4 (also 400%) zur Folge hat. Dagegen beträgt in dieser Meßreihe die größte beobachtete Abweichung einer Einzelmessung des Extinktionsverhältnisses Analysenlösung/Eichlösung vom Mittelwert nur 22%. Abschließend wird ein in der Entwicklung befindliches und weitgehend automatisiertes Gerät vorgeschlagen, welches wesentlich bessere Ergebnisse erwarten läßt.

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Summary It is shown that even for atomic-absorption analyses with a single-beam instrument, the values measured will be essentially independent on large fluctuations in the operating conditions of the flame (gas pressures and sample flow rate), if the standard measurement made after every sample measurement is repeated often enough. Naturally, with the same technique the variation of emission from the discharge lamp will also not affect the analytical results. For the first experiments an instrument composed of commercially available components was used. It allowed the sample solution and standard solution to be alternately aspirated more than 15 times per minute. It was observed that the extinction value for the sample solution changed by a factor of 4 (that is 400%) when the sample flow rate changed by a factor of 10 (within a minute). On the other hand, in this series of measurements the gratest deviation observed between a single value for the ratio of sample solution extinction/standard solution extinction and the average value amounted to only 22%. Finally, an essentially automatic instrument being developed is proposed. With this instrument considerably better results can be expected.

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Herrn Prof. Dr. R. Herrmann möchte ich auch an dieser Stelle meinen Dank aussprechen für sein reges Interesse am Fortgang der Arbeit und für die kritische Durchsicht des Manuskriptes. Fräulein B. Gutsche danke ich für die Mitarbeit bei der Durchführung und Auswertung der Messungen.     

Interaction of porphyrins with a dendrimer template: self-aggregation controlled by pH

The interaction between self-aggregated porphyrins such as 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) and 5,10,15,20-tetrakis(4-phosphonatophenyl)porphyrin (TPPP), and a generation 5 (G5) PAMAM dendrimer template is governed by minute differences of porphyrin acido-basic properties. While at neutral pH both monomeric TPPS and TPPP form complexes with G5, decreasing pH did not lead to porphyrin ring protonation (pK(a) approximately 5) but rather to the preferential formation of H-aggregates (probably H-dimers), most likely due to protonation of the G5. Upon further acidification of the solution, this face-to-face orientation of the porphyrin units is being converted to edge-to-edge aligned J-aggregates with a tightly defined structure. This process starts by protonation of the porphyrin ring at pH below 2.3 and 2.8 for TPPS and TPPP, respectively. The AFM imaging of porphyrin/G5 nanostructures obtained at pH 0.7 shows the formation of long nanorods of TPPS with partially aggregated G5 and small aggregates of TPPP connected to individual G5 molecules.     

First organophosphorus radical-mediated cyclisations to afford medium-sized rings: eight-membered lactones and seven- and eight-membered lactams

The phosphorus based radical precursors N-ethylpiperidine hypophosphite (EPHP) and diethylphosphine oxide (DEPO) are efficient reagents for carrying out the formation of seven- and eight-membered rings. Esters and amides were successfully converted into the corresponding eight-membered lactones and seven- and eight-membered lactams in good to excellent yields.     

Beta-delayed two-proton decay of39Ti

The beta-delayed two-proton decay of theT _z =–5/2 nuclide³⁹Ti has been observed. The³⁹Sc isobaric analog state has been calculated to lie at 8.82 MeV using the measured two-proton sum energy of 4750±40 keV for its decay to the³⁷K ground state. Combining this excitation energy with a Coulomb displacement energy calculation has lowered the energy available for ground state two-proton emission of³⁹Ti from 760 to 530 keV.This work was supported by Director, Office of Energy Research, Division of Nuclear Physics of the Office of High Energy and Nuclear Physics of the U.S. Depeartment of Energy under Contracts DE-AC03-76SF00098 with Lawrence Berkeley Laboratory, DE-AC02-76CH00016 with Brookhaven National Laboratory and DE-AC06-76RL0 1830 with Pacific Northwest Laboratories.     

Dynamical and thermal aspects of relativistic heavy-ion collisions

Within a covariant BUU-approach we simulate heavyion collisions at various bombarding energies from 400 MeV/u to 1 GeV/u. We evaluate locally the energymomentum tensorT ^v (x), and extract pressures, energydensities and temperatures. The connection of these thermodynamical quantities to experimental observables and their sensitivity to the equation of state is discussed. Furthermore, we investigate the question of local equilibration and evaluate the entropy produced in these reactions.Dedicated to Prof. Dr. P. Kienle on the occasion of his 60th birthday. Work supported by BMFT and GSI Darmstadt     

Endogenous growth of the population of reverse micelles

The coupling reaction between cetylbromide (CB) and trimethylamine (TMA) to yield the surfactant cetyltrimethylammonium bromide (CTAB) is studied in the system chloroform/isooctane (2/1,v/v)/water in which CTAB forms reverse micelles. This system affords an endogenous micelle population growth, i.e., an increase of the concentration of the micelles due to appearance of the surfactant in situ. The reaction is studied in the presence of preexisting CTAB reverse micelles. The rate of CTAB formation is measured by NMR spectroscopy, and the endogenous micelle population growth is directly monitored by time-resolved fluorescence quenching analysis. Under our experimental conditions, a 100% yield of the chemical reaction brings about a fourfold increase in the population of the reverse micelles. Since the water concentration is constant during chemical reaction, the newly formed water pools are formed at the expense of the initial ones, which brings about a decrease of the average water pool radius during micellar growth. The implication of the endogenous micelle population growth as a model for biological systems is briefly discussed.