Direct detection of the biradicals generated in the Norrish type II reaction

The biradicals generated in the Norrish type II reaction from the triplet manifold have been observed using laser flash photolysis techniques. The spectra and extinction coefficients closely resemble those of typical ketyl radicals. Typical lifetimes are in the 40–100 ns range depending on the solvent. Their interaction with oxygen is essentially diffusion controlled.     

Mechanism of the oxidation of cycloheptanone by chloramine-T

The oxidation kinetics of cycloheptanone by chloramine-T in alkaline media has been investigated. A mechanism involving the formation of an intermediate by the interaction between the enolic anion of cycloheptanone and chloramine-T in a slow step followed by its interaction with another molecule of chloramine-T in a fast step leading to products has been proposed. The scheme satisfactorily accords with the observed stoichiometry, negligible influence of ionic strength and a positive dielectric effect. Various rate parameters have been computed and 1.2-cycloheptanedione identified as the end product.With 2 Figures     

INTERACTION OF VIOLOGEN DYES WITH CHROMATOPHORES AND REACTION-CENTER PREPARATIONS FROM RHODOSPIRILLUM RUBRUM

Abstract —Various low-potential viologen dyes enhance light-induced absorption changes in the near-infrared region (ΔA870) in chromatophore preparations from Rhodospirillum rubrum in the presence of dichlorophenol indophenol and a high concentration of ascorbate (DCPIP + asc). An increase in ΔA870 was also observed in large reaction-center preparations from R. rubrum with viologens in the presence of ascorbate. Our results indicate that E'₀, of the primary electron acceptor X may be as low as -0.37 V, as suggested recently by P. A. Loach (1973, personal communication).     

PHYCOBILIPROTEINS: COMPARISON OF SOLUTION AND SINGLE CRYSTAL FLUORESCENCE FOR C-PHYCOCYANIN AND B-PHYCOERYTHRIN*

Abstract— Trimeric and hexameric solution forms of C-phycocyanin (CPC) from the cyanophyte Agme-nellum quadruplicatum have been isolated and their spectral properties compared to those obtained from single crystals. Although the absorbance peak of a suspension of small C-phycocyanin crystals is red-shifted only 7 nm relative to the solution forms, the single crystal fluorescence is red-shifted 60 nm relative to the solution forms. The crystal fluorescence spectrum exhibits a single peak at LD_max= 708 nm when excited at 514.5 or 530.9 nm and two peaks (LD_max= 661 and 708 nm) when excitation occurs at 568.2 nm. Fluorescence depolarization measurements indicate that extensive energy transfer could occur for both solution and crystal forms with the latter being dependent upon the relative orientation of the crystal with respect to the excitation dipole. Similar results were obtained with B-phycoerythrin (BPE) from the red alga Porphyridium cruentum where the single crystal fluorescence is red-shifted =50nm relative to the solution spectra with two peaks (LD_max= 583 and 617 nm) observed whose relative intensities are dependent on the excitation wavelength (LD_max– 514.5 and 530.9 nm). Single crystal fluorescent lifetimes exhibited considerable shortening relative to that observed for the solution forms. The implications of these results are discussed with respect to the possible relationships of the crystalline structures to the assembly forms present within phycobilisomes.     

Anwendung mikroanalytischer Methoden zur Lösung kunst- und kulturgeschichtlicher Probleme

Zusammenfassung Mit bekannten mikroanalytischen Arbeitsmethoden — Oberflächenreaktionen, Abstrichuntersuchungen mit dem Korundstäbchen, Schutzschichtreaktionen sowie dem Abdruckverfahren — lassen sich archaeometrische Probleme einer Lösung näherbringen. Die Art der Korrosion kupferhaltiger Oberflächen wurde diskutiert.

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Application of microanalytical methods to the solution of artistic- and cultural historical problems

Summary Archeometrical problems are brought closer to a solution by means of known microanalytical procedures-surface reactions, surface scraping studies with the corundum rod, protective layer reactions as well as the imprint method. A discussion of the corrosion of copper-bearing surfaces is included.

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Vortrag anläßlich der Tagung Chemische Analysen — Kunst- und Kulturwissenschaften im Reiß-Museum in Mannheim, 19.–21. September 1974.     

A study of thermal decomposition of the solid-layered fluorocarbon,poly(carbon monofluoride)

Isothermal-thermogravimetric analyses were used to obtain kinetic data on the CF_x decomposition. Weight of samplevs. time curves were obtained for compounds having stoichiometries CF_0,61, CF_0.96, CF_1.08, and CF_1.12 for several different temperatures over the range 450–650° and in both a nitrogen atmosphere and in vacuum. A small percentage of fluorine in the atmosphere was shown to strongly inhibit thermal decomposition.These experimental results were fit to various theoretical models and it was found that a satisfactory fit was obtained by use of the Avrami equation, -In(1–)=(kt)ⁿ, where is the extent of reaction,k is an apparent rate constant, andn is an apparent reaction order. The valuen=2.0 was indicated which corresponds to planar growth of the decomposed phase.This information was combined with analytical data for the gaseous and solid products of decomposition to formulate a detailed mechanism.

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Zusammenfassung Isotherm-thermogravimetrische Analysen wurden durchgeführt um kinetische Daten über die Zersetzung von CF_x zu erhalten. Probengewicht-Zeit-Kurven wurden für Verbindungen mit stöchiometrischen Verhältnissen von CF_0.61, CF_0.96, CF_1.08 und CF_1.12 bei verschiedenen Temperaturen im Bereich von 450° bis 650°, in Stickstoff sowie im Vakuum aufgenommen. Ein geringer Prozentsatz an Fluor in der Atmosphäre wirkte stark inhibierend auf die thermische Zersetzung.Diese Versuchsergebnisse wurden verschiedenen theoretischen Modellen angepasst und es wurde gezeigt, dass mit Hilfe der Avrami-Gleichung -In (1–)=(kt)ⁿ eine befriedigende Anpassung möglich ist, wobei =Ausmaß der Reaktion, k=scheinbare Geschwindigkeitskonstante undn=scheinbare Reaktionsordnung ist. Der angedeutete Wertn=2.0 entspricht einer planaren Zunahme der zersetzten Phasen.Diese Information wurde mit analytischen Daten der gasförmungen und festen Zersetzungsprodukte kombiniert um einen Mechanismus in allen Einzelheiten zu formulieren.

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Résumé La TG isotherme a été utilisée pour obtenir des données cinétiques sur la décomposition de CF_x. Les courbes donnant le poids de l'échantillon en fonction du temps ont été energistrées à différentes températures, entre 450 et 650°, en atmosphère d'azote et sous vide, sur des composés de composition CF_0.61, CF_0.96 et CF_1.08. Un faible pourcentage de fluor dans l'atmosphèere s'est avéré inhiber considérablement la décomposition thermique.Ces résultats expérimentaux ont été confrontés à divers modèles mathématiques. On a trouvé un ajustement satisfaisant à l'aide de l'équation d'Avrami, -In (1–)=(kt)ⁿ, où es l'avancement de la réaction,k une constante de vitesse apparente etn un ordre de réaction apparent. La valeurn=2.0 correspond à une croissance dans le plan de la phase décomposée.Cette information a été combinée avec des données analytiques sur les produits de décomposition gazeux et solides, afin de formuler un mécanisme détaillé.

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- CF_x. — CF_0.61, CF_0.96, CF_1.08 F_1.12 450°–650°, , . . , -1(1–)= (kt)ⁿ, — , k — , n — . n=2, . , .

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Abstracted in part from the Ph. D. thesis of Peter Kamarchik, Jr. Rice University, Houston, Texas, May, 1976.

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This work was supported financially by the National Science Foundation, the U.S. Army Research Office (Durham), the National Aeronautics and Space Administration, and the Robert A. Welch Foundation. Liquid helium was provided under a grant from the Office of Naval Research.     

A new technique for the identification of chloride ions by the formation of chromyl chloride

Summary A new technique is described for the identification of the chloride ion through the formation of chromyl chloride, based on the extraction of the latter with carbon tetrachloride. The identification limit is 2g of chloride. It is possible to carry out the test in the presence of many other anions, including fluoride, which cannot be present when the traditional distillation technique is employed.

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Zusammenfassung Vorgeschlagen wird eine neue Technik zum Chloridnachweis durch Bildung von Chromylchlorid. Dieser Nachweis beruht auf der Extraktion des Chromylchlorids mit Tetrachlorkohlenstoff. Die Nachweisgrenze liegt bei 2g Chlorid, wobei die Möglichkeit besteht, den Test auch in Gegenwart von Fluorid durchzuführen, das bei Anwendung der üblichen Destillationsmethoden nicht anwesend sein darf.

     

Darstellung und Reaktionen des 3-Ethinyl-2,4-diformyl-pentandials

Preparation and physical and chemical properties of 3-ethinyl-2,4-diformyl-pentandial (3 a) and its salts are described.3 a contains 2 malonaldehyde groups. Starting from3 a, 4H-pyranes, 4H-dihydropyridines, dipyrazoles, diisoxazoles, bisdiazepines and vinamidine derivates are obtained.

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Mit 1 Abbildung     

Zur Umsetzung des 3,4,5,6-Tetrahydro-6-hydroxy-4,4,6-trimethyl-1,3-thiazin-2-thions mit sekundären Aminen

Tetrahydro-6-hydroxy-trimethyl-1,3-thiazine-2-thione (1) reacts with secondary amines via the dialkylammonium-3-oxoalkyldithiocarbamate3, either via isothiocyanates6 to 4-dialkylaminodihydro-2(1H)-pyridinethiones7 or to dialkylammonium dithiocarbamates (13), depending on the amine used and the reaction conditions. Subsequently, 6-dialkylaminotetrahydro-1,3-thiazine-2-thiones11 or tetrahydro-6-mercapto-1,3-thiazine-2-thione10 are formed. On being heated to reflux,11 reacts to pyridinethione7 and 4-dialkylaminodihydrothiopyranthione19. With secondary amines only13 is formed from tetrahydro-6-hydroxytetramethyl-1,3-thiazine-2-thione20. The reaction of dihydrotrimethyl-1,3-thiazine-2-thione21 with secondary amines leads to N,N-dialkylthioureas16 or dialkylammonium thiocyanates17 and with dialkylformamides 4-dialkylaminodihydropyridinethiones7 are formed. Dihydrotetramethyl-1,3-thiazine-2-thione24 reacts neither with secondary amines nor with dialkylformamides.     

Beiträge zur Chemie der Pyrrolpigmente, 19. Mitt.: Die elektrochemische Oxidation von Pyrromethenonen und Pyrromethenen (Gallenpigment-Partialstrukturen)

The electrochemical oxidation of arylmethylene-pyrrolinones, pyrromethenones and pyrromethenes as representative bile pigment partial structure models was investigated by means of a rotating disc platinum electrode using acetonitrile as the solvent. Two different oxidation reactions were found. The first reaction being a reversible one-electron oxidation with compounds of the arylmethylene-pyrrolinone series and pyrromethenones which are unsubstituted in position 5 of the pyrrole ring. A two step reaction (the first one reversible, the second irreversible) on the other hand was found to be typical for pyrromethenones bearing a methyl group in this position.Through protonation the first step is at a higher potential, whereas the second one is lowered and becomes reversible. The resulting oxidation pattern can be interpreted analogous to the oxidation of hydroquinones in aprotic solvents.The geometrical isomers of a pyrromethenone were oxidized at appr. the same potential, but there is a strong dependence of the potential of the first oxidation step on the substitution: a higher degree of alkylation favours oxidation by lowering the oxidation potential.

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Mit 1 Abbildung