Anordnung und Orientierung kationischer Tenside auf ebenen Silicatoberflächen

Zusammenfassung Die n-Alkylammoniumderivate der glimmerartigen Schichtsilicate können als Modellsubstanzen für die Anordnung kationischer Tenside an Festkörpergrenzflächen herangezogen werden. Im ersten Teil der Arbeit wird die Darstellung durch Kationenaustausch aus den natürlichen Schichtsilicaten beschrieben. Es wird ausführlich auf die Fehlerquellen hingewiesen, die reproduzierbare Messungen erschweren.

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Summary The n-alkylammonium derivatives of mica-type layer silicates are suitable models for studies about the arrangement of cationic tensides at solid interfaces. Part I of the paper deals with the preparation of these compounds by a simple cation exchange reaction. Sources for errors in obtaining reproducible data are discussed in detail.

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Mit 1 Abbildung in 3 Einzeldarstellungen und 3 Tabellen     

Evaluation of methods to measure differential 15N labeling of soil and root N pools for studies of root exudation

To study patterns of root exudation, the effectiveness of different techniques for in situ 15N labeling of Brassica napus, Centaurea jacea and Lolium perenne with ammonium nitrate was tested. Stem infiltration was found to effectively label plants with thicker stems, whereas, for grass species, cutting and immersing the leaf tips into 15N solution proved to be most effective. A microdiffusion technique to isolate ammonium, combined with conventional cation-exchange chromatography to separate nitrate from amino-N compounds thereafter, was found suitable for separation of the N fractions of plant and soil extracts for 15N determination. All three species were then cultivated in nutrient solution and labeled with 15NH4 15NO3 by stem feeding for 42 hours. Kinetics of 15N labeling of bulk roots and shoots as well as hot water extractable material were assessed, and up to 1.1 at% 15N excess (APE) was found in nutrient solutions. The main amino acids exuded by L. perenne were glycine, serine, alanine and aspartic acid. To assess the suitability of this set of methods to study root exudation in field settings, L. perenne was grown without fertiliser addition in pots containing low-nutrient soil. Plants were 15N labeled via tip immersion and 15N and N concentrations were analysed in shoots, roots and soils during a 48-h interval. Shoots reached 1.25 APE, roots and soil 0.10 and 0.005 APE, respectively. Between 4% (48 h) and 6% (24 h) of total plant 15N was exuded by roots into the soil. In roots amino acids comprised the largest proportion of the soluble 15N pool, whereas soil 15N levels were similar for amino acids and ammonium, exceeding those of nitrate. Mechanisms for the shift within N fractions from roots to soils are briefly discussed.     

Ab initio SCF Calculation of the Fluoronium Ion: Geometry,electronic structure and vibrational constants

An ab initio SCF calculation of 42 points of the energy hypersurface of the fluoronium ion is presented using a contracted F(5s/3p), H(2s) gaussian basis set. In its equilibrium structure a bond length of 1.812 a.u. and a HFH bond angle of 127.2° are predicted. The calculated vibrational frequencies for H₂F⁺, HDF⁺, and D₂F⁺ are in good agreement with the experimental data.     

Die Struktur des Paucins

Zusammenfassung Beim Abbau von Paucin wird Brenzcatechin, Kaffeesäure und Putrescin erhalten. Daraus und aus spektroskopischen Befunden ergibt sich für das Paucin die Strukturformel3.

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The structure of Paucine

Paucine can be degradated to catechol, caffeic acid and putrescine. This together with spectroscopic data allows us to deduce formula3 for paucine.

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Mit 6 Abbildungen

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Meinem Lehrer, Prof. Dr.H. Bretschneider, zum 65. Geburtstag gewidmet.     

Densest packings of eleven congruent circles in a circle

In 1969 Pirl provided the densest packings ofn equal circles in a circle forn 10. We will prove the optimality for the packings that were conjectured forn=11. The proof is based on elementary combinatorial and analytical techniques.     

The nature of the C-defects in nickel and their rôle in the interpretation of radiation damage in metals

In previous Perturbed-Angular-Correlation (PAC) studies of the - emission of ¹¹¹In probe nuclei in cold-worked or particle-irradiated nickel, it has been found that thermal annealing in the temperature regime of recovery stage III leads to the formation of so-called C-defects (Cubic defects). This is indicated by the occurrence of a new frequency of about 80 Mrad/s, in addition to the frequency (200 Mrad/s) that is due to ¹¹¹In on substitutional sites. Obviously, the C-defects are complexes consisting of ¹¹¹In and the intrinsic point-defect species that migrates freely in recovery stage III. Therefore, they have played an important rôle in the long-standing controversy on whether the recovery-stage-III defects are vacancies (one-interstitial model) or self-interstitials (two-interstitial model). The present paper reports on a novel experimental effort to reveal the nature of the C-defects by combining PAC studies on nickel samples differently pretreated in a systematic way, investigations of the Extended X-ray Absorption Fine Structure (EXAFS) on In-doped nickel, and measurements of the decay rate of ¹¹¹In nuclei in the Electron-Capture-Induced Decay (ECID). On the basis of the results of these experiments it is concluded that the defects trapped by substitutional ¹¹¹In atoms (In_s) in recovery stage III are self-interstitials (I), as expected according to the two-interstitial model. Moreover, there is evidence that the C-defects are In interstitials on tetrahedral sites (In_i) that form exclusively in the vicinity of the specimen surface from In_s – I pairs via the reaction In_s+I In_i.