MEASUREMENT OF THE TEMPERATURE DEPENDENCE OF THE FLUORESCENCE QUANTUM YIELD OF ORGANIC MOLECULES IN SOLUTION

A DETAILED investigation of the temperature dependence of the fluorescence quantum yield φ_f can yield–directly or indirectly–significant information about behavior of excited states of organic molecules, such as the temperature effect on radiationless transitions and on photochemical reactivity. Variation of the temperature changes the viscosity of the solvent and, in conjunction with measurements of φ_f( T ), allows investigations of diffusion-controlled processes. For example, energy transfer and quenching processes as well as excimer or exciplex formation fall into this category. Recent review articles by Weller (1962) and Birks (1970) deal with this topic. Moreover, Huber and Mantulin (1972) have suggested that restraints placed upon geometric modifications of the excited molecule by temperature-induced changes in the solvent cage (variation of site structure) are reflected in a varying φ_f.
The purpose of this note is to describe and verify a simple procedure, accurate to about ± 5%, for measuring the relative fluorescence quantum yield as a function of temperature. A quantum yield study of 9,10-diphenylanthracene between room temperature and 77°K is employed to demonstrate the capabilities of this method. In addition, we consider an example of diffusion-controlled quenching by oxygen measured over a wide temperature range.     

Chlorination of α-sulfonyl carbanions with hexachloroethane: A novel preparation of α-halosulfones

The cyclic sulfones1,2, and3 are lithiated in benzene with n-butyllithium. Lithiation is demonstrated to lead to α-mono, α,α′-di and/or α,α-di and α,α,α′ trimetallation. The lithiated sulfones are chlorinated with hexachloroethane (HCE). Some mechanistic aspects of the reaction of the lithiosulfones with vicinal dihalides are discussed.     

Neuere Ergebnisse zur Anwendung der Gras-Chromatographie

Zusammenfassung Es wird über die allgemeine Entwicklung der Gaschromatographie (GC) berichtet, soweit sie deren Anwendung beeinflussen kann. Neuere Ergebnisse zur Trennsäulenherstellung (Trennflüssigkeit, Trägermaterial und Zusätze) und zur Anwendung von Korrekturfaktoren bei der quantitativen GC werden gestreift. Eine neue Säulenkennzahl, die Trennzahl wird zur Diskussion gestellt. Sie ersetzt die Trennstufenzahl beim Vergleich von isotherm und nichtiostherm betriebenen gefüllten Trennsäulen und Trenncapillaren. Der Bericht schließt mit Hinweisen auf die Tief temperatur-GC, die Anwendung hochflüchtiger Trennflüssigkeiten auch bei Bestimmung physikalisch-chemischer Daten und die Ausweitung der GC auf Gebiete der anorganischen Chemie.Auszugsweise vorgetragen zum Arbeitstreffen GC in der Technischen Hoch. schule Karlsruhe, Oktober 1961.     

Dark induction of haem oxygenase messenger RNA by haematoporphyrin derivative and zinc phthalocyanine; agents for photodynamic therapy.

Haematoporphyrin derivative is one of the main drugs currently used in clinical trials involving photodynamic therapy of cancer, and zinc phthalocyanine is being considered as one of several possible alternatives. We show that incubation of cultured human fibroblasts populations with either of the two drugs will lead to a sharp increase in the accumulation of the messenger RNA corresponding to haem oxygenase. Only cells incubated with haematoporphyrin derivative show additional enhancement of expression of this specific gene on exposure to red light. Since haem oxygenase induction appears to be a specific stress response that may be involved in cellular defence, such observations should be confirmed under conditions which would allow the clinical implications to be fully evaluated.     

Studies of phosphazenes. Aminolysis reactions of pentachloro(2′, 2′, 2′-triphenyl-phosphazen-1′-yl) cyclotriphosphazene,N3P3Cl5(NPPh3)

The reactions of pentachloro(2′, 2′, 2′-triphenylphosphazen-1′-yl)cyclotriphosphazene, N₃P₃Cl₅(NPPh₃), with primary and secondary amines have been investigated using diethyl ether, methyl cyanid or benzene as the solvent. The structures of the products obtained, N₃P₃Cl_5minus;nR_n(NPPh₃) [n = 1, R = NHMe, NHBu^t, NMe₂, NC₅H₁₀, NEt₂; n = 2, R = NMe₂, NC₅H₁₀, NEt₂; n = 3, R = NMe₂, NHBu^t; n = 5, R = NMe₂] are elucidated by ¹H and ³¹P NMR spectroscopy. The ? NPPh₃ substituent exerts a pronounced geminal directing influence on incoming secondary amino nucleophiles; compounds containing a ≡ PCl(NPPh₃) group are not formed at the bis and subsequent stages of chlorine replacement. The reactions that involve primary amines follow the pattern established for the analogous reactions of hexachlorocyclotriphosphazene. The effect of solvent and possible mechanism(s) are discussed.     

Two-dimensional separations and behaviour of alkaloids of various polarities on unmodified silica gel in polar and very polar neutral or acidic mobile phases

Summary New separation procedures for alkaloids of similar polarity and structure or of very different polarity and structure, based upon two-dimensional thin-layer chromatography on unmodified silica gel under mild conditions are described. Separation factors and separation mechanisms based on the structure of the bases and mobile phase composition are discussed for some examples of very efficient procedures.Proportions in solvent mixtures are v/v except where otherwise indicated.     

Chlorine nitrate photolysis by a new technique: very low pressure photolysis

Very low pressure photolysis (VLPØ) of chlorine nitrate was performed in a quartz Knudsen cell. The light source was a 2500 W high-pressure xenon lamp, and a modulated molecular-beam mass spectrometer was used to monitor the concentration of ClONO₂ and photolysis products. Because of the low pressures used (? 10^?3 torr) and the short residence time in the cell (≈1 s), secondary reactions were unimportant and the primary products could be directly identified. The primary photolysis products (λ ≈ 2700 Å) are atomic chlorine and NO₃ free radical. Chlorine atoms were identified both by the appearance of Cl₂ (wall recombination product; the walls were not poisoned) and by HCl produced when C₂H₆ was added to the cell. Nitrate free radical was directly identified as a mass peak at m/e = 62, as well as by chemical titration with nitric oxide: NO₃ + NO → 2NO₂. It was verified by direct tests that the peak at m/e = 62 did not arise from possible HNO₃ contamination or from N₂O₅, a possible secondary product. This titration reaction was used to measure quantitatively a lower limit to the primary quantum yield, φ ? 0.5 ± 0.3. This represents a lower limit because of the unknown extent of the secondary photolysis of NO₃ under our conditions. We believe this to be the first observation using mass spectrometry of the NO₃ free radical. The quantum yield for atomic chlorine is φ = 1.0 ± 0.2. N₂O was used to test for O(¹D) according to the reaction, O(¹D) + N₂O → products; none was observed. Triplet oxygen, O(³P) was observed to the extent of ≈ 10% by the reaction O(³P) + NO₂ → NO + O₂, but this yield can also be due to the photolysis of NO₃ free radical produced in the primary step. We conclude that the predominant reaction pathway is

.     

Spectra and structure of organogermanes: Part XX. Infrared and Raman spectra of (CH3)3GeNCO and (CH3)3GeNCS

The infrared and Raman spectra of gaseous and solid (CH₃)₃ GeNCO and solid (CH₃)₃GeNCS have been recorded over the frequency range 20–4000 cm^?1 . The Raman spectra of the liquids have also been recorded. Assignments of the normal modes have been made on the bases of band types, Raman depolarization values, and characteristic frequencies. Spectral data indicate that (CH₃)₃ GeNCO is non-linear in all phases and that (CH₃)₃GeNCS has a linear or quasi-linear heavy atom skeleton in the fluid phases.     

Hormone-receptor interactions. Carboranylalanine (Car) as a phenylalanine analogue: reactions with chymotrypsin.

In order to test the effects of the replacement of phenylalanine by carboranylalanine (Car) in biological ligand-acceptor interactions, Z · Ala-Ala-Car · OH (1) and Ac · Car · OEt (2) were synthesized and their reactions with chymotrypsin studied. The two compounds proved to be good inhibitors with K(i) values of 3 · 10^?4M (1) and 8.6 · 10⁴M (2) ; the K(i) of Z · Ala-Ala-Phe · OH (1a) is 1 · 10^?3M . The inhibition constants were determined by a new photolytic technique, inhibition of photoaffinity labelling by Z · Ala-Ala-Phe(pN₃) · OH. Ac · Car · OEt is not hydrolysed by chymotrypsin. The findings indicate that the carboranyl group can interact with the ‘phenyl recognition site’ of the enzyme to produce the binding that is characteristic of aromatic amino acid residues. However, some kind of distortion in the region of the ‘mechanistic site’ must be postulated in order to account for the failure of hydrolysis. Some possible effects of the replacement of aromatic amino acids by Car in peptide hormones on hormone-receptor interactions are discussed.