Spiers memorial lecture dynamics of surface reactions

The dynamics of electrode processes is discussed in the framework of the general hierarchy of dynamic processes underlying interface reactions. On the quantum level, the energy transfer between the various degrees of freedom of a reacting system may now be studied by ultrafast (femtosecond) laser techniques. On the atomic level the mechanism of surface reactions may be investigated by STM and spectroscopic methods. Frequently a surface reaction will affect the structure of the substrate on the mesoscopic scale. The kinetics of such phase transformations proceeds either by a nucleation and growth mechanism or by spinodal decomposition. The latter can be studied in electrodissolution by combining STM with very short potential pulses. In this context, a novel technique for electrochemical micromachining is presented. Finally, some aspects of nonlinear kinetics on the macroscopic level associated with spatio-temporal pattern formation are briefly discussed.     

Die Abstimmung chromatographischer Flie?mittel auf Aluminiumoxide eingestellter Aktivit?t

Zusammenfassung Aluminiumoxid, das mit Wasser vorbelegt ist, gibt an organische Lösungsmittel einen Teil davon ab und ändert dadurch seine Aktivität. In einer chromatographischen Trennsäule können sich hieraus ernste Störungen ergeben. Man vermeidet sie durch die Anwendung von Fließ-mitteln mit passendem Wasserzusatz. Auf die Trocknung von Pyridin an aktivem Aluminiumoxid wird kurz eingegangen.

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Summary Aluminium oxide containing a certain amount of water transfers it in part to organic solvents, thus changing its activity. Serious interferences in chromatographic column separations can arise from that fact. They can be prevented by use of solvents with adjusted water content. The use of active aluminium oxide for desiccation of pyridine is described shortly.

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Ein Teil der Ergebnisse wurde bereits in verschiedenen Vorträgen mitgeteilt.

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Roscher, G.: Diss. Univ. Erlangen 1960.     

Voltammetrische Bestimmung von Coffein in Kaffee,Tee und coffeinhaltigen Getränken

Zusammenfassung Zur Bestimmung von Coffein in Erfrischungsgetränken (Cola), Kaffee und Tee wird die Differential-Pulsvoltammetrie verwendet. Bei dieser Methode wird Coffein bei pH 1,2 an einer glasartigen Kohlenstoffelektrode oxydiert und quantitativ bestimmt. Die voltammetrisch ermittelten Analysenergebnisse werden mit den Resultaten der Flüssigkeistchromatographie verglichen. Um einen weiteren Einblick in den Reaktionsverlauf zu erhalten, wurde Coffein anodisch bei pH 1,2, 2,3 und pH 6 oxydiert. Die Reaktionsprodukte wurden kathodisch durch Differential-Pulspolarographie identifiziert.

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Voltammetric determination of caffeine in coffee, tea, and soft drinks

Summary Differential pulse voltammetry is used for the determination of caffeine in soft drinks, coffee, and tea. In this method caffeine is oxidised at a glassy carbon electrode at pH 1.2 and determined quantitatively. The voltammetric results are compared with those found by HPLC. To elucidate the mechanism of the electrode processes the reaction products were produced by anodic oxidation of caffeine at pH 1.2, 2.3 und pH 6 and then identified by cathodic differential pulse polarography.

     

Position dependent heavy atom effect in physical triplet quenching by electron donors

The radical yields and rate constants in the quenching reaction of thionine triplet with the complete series of monohalogen substituted anilines as electron donors were determined by flash spectroscopy. Whereas the quenching rate constants show little and unsystematic variation, the radical yields decrease with increasing spin—orbit coupling constant of the halogen substituent. This effect is very sensitive to the position of the halogen in the donor. The results are explained in terms of a heavy atom effect on the intersystem crossing rate constant in a triplet exciplex.     

Analyse von Rutil-Anatas-Gemischen mittels diffuser Reflexionsmessungen

Zusammenfassung Pulvergemische von zwei verschiedenen Modifikationen eines Stoffes oder von zwei Pigmenten lassen sich mit Hilfe diffuser Reflexionsmessungen quantitativ analysieren, wenn die Reflexionsspektren sich in einem zugänglichen Spektralgebiet genügend stark unterscheiden. Die Methode wird am Beispiel der Titandioxyde Rutil und Anatas im einzelnen beschrieben.

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Summary Mixtures of two modifications of solid powdered material can be quantitatively analyzed by diffuse reflectance measurements, if the reflectance spectra are sufficiently different in some wavelength range. The method is described with the example of the titanium dioxides rutile and anatase.

     

Zur Kenntnis schichtförmiger Si-Verbindungen des Typs (SiX) n

Zusammenfassung Die Reaktion zwischen CaSi₂ und JCl liefert in einer Festkörperreaktion unter Aufspaltung des Schichtgitters ein stöchiometrisch und strukturell definiertes (SiCl) _n . Eigenschaften und Hydrolyse der Verbindung werden besprochen. Solvolyse mit Alkoholen führt zu entsprechenden Alkoxyderivaten, die Umsetzung mit Lithiummethyl zur methylierten Verbindung.Mit 2 Abbildungen4. Mitt.:E. Hengge undH. Grupe, Chem. Ber.97, 1783 (1964).     

Eine neue photometrische bestimmung für nickel mit aethylendiamintetraessigsäure

It is possible to determine very high concentrations of nickel photometrically by means of ethylenediaminetetra-acetic acid, by working at a pH between 4.55 and 6.82. The absorption curves obtained for this complex are very reproducible; for these measurements an Elko II apparatus with filter S57E is used. High concentrations of ammoniacal salts hinder the measurement. The formation of the complex is not influenced by the anion of the compound of nickel used. The Lambert-Beer law is followed for strengths of nickel of 40 — 5000 mg/100 ml. This procedure is convenient for alloys rich in nickel.     

Matrix-isolation-FTIR spectroscopy with an integrating sphere

The use of an integrating sphere for the measurement of absorption spectra of thin films is described. The thin film (for example a rare gas matrix) is grown directly on the inside surface of the sphere. Multiple reflections inside the integrating sphere lead to significant enhancement of weak absorptions of the film, increasing the sensitivity of such measurements.     

A 3D QSAR study on a set of dopamine D4 receptor antagonists

The molecular alignments obtained from a previously reported pharmacophore model have been employed in a three-dimensional quantitative structure-activity relationship (3D QSAR) study, to obtain a more detailed insight into the structure-activity relationships for D(2) and D(4) receptor antagonists. The frequently applied CoMFA method and the related CoMSIA method were used. Statistically significant models have been derived with these two methods, based on a set of 32 structurally diverse D(2) and D(4) receptor antagonists. The CoMSIA and the CoMFA methods produced equally good models expressed in terms of q(2) values. The predictive power of the derived models were demonstrated to be high. Graphical interpretation of the results, provided by the CoMSIA method, brings to light important structural features of the compounds related to either low- or high-affinity D(2) or D(4) antagonism. The results of the 3D QSAR studies indicate that bulky N-substituents decrease D(2) binding, whereas D(4) binding is enhanced. Electrostatically favorable and unfavorable regions exclusive to D(2) receptor binding were identified. Likewise, certain hydrogen-bond acceptors can be used to lower D(2) affinity. These observations may be exploited for the design of novel dopamine D(4) selective antagonists.