P. De Mayo

Biphasic photochemistry: time-resolved spectra of adsorbed hydrocarbons

Abstract Time-resolved fluorescence spectra were measured for pyrene and naphthalene adsorbed on a silica gel surface using the time-correlated photon-counting technique Excimer-Iike emission was observed within an excitation lamp duration of a few nanoseconds with both pyrene and naphthalene. It is suggested, from the excitation spectra, that ground state complexes of the adsorbates are responsible for the formation of the excimer-like emission.

Thione photochemistry: Fluorescence from higher excited states

Abstract A number of aralkyl thiones have been prepared all of which exhibit fluorescence from the higher singlet, S 2 , with the high quantum yield Φ F ≈ 5 × 10 −3 .

The absolute stereostructure of copaene

Abstract Authentic copaene has been isolated from two sources. The cadinane carbon skeleton and the position of the double bond has been confirmed. By a series of steps involving aromatisation of one ring, and by another sequence resulting in the isolation of a cyclobutanone, copaene has been shown to contain cyclobutane ring. The structure deduced, together with the conversion of copaene to (−)-cadinene dihydrochloride permits the allocation of the absolute stereostructure (VI) to this sesquiterpene.

Mould metabolites—IV : The isolation and constitution of some ergot pigments☆

Abstract The mixture of ergot pigments from a Portuguese ergot drug has been separated. Aside from ergoflavin five other pigments have been characterized and structural proposals for four of these made.

Surface photochemistry: The effect of surface modification on the singlet quenching of pyrene adsorbed on silica gel by 2-bromonaphthalene

Abstract Variation in the heat treatment of silica gel, and thus its degree of hydration, prior to the adsorption of pyrene and the quencher 2-bromonaphthalene (BN) onto the surface, influences the rate of quenching of pyrene fluorescence. The quenching rate is slow with dry silica gel whereas on dry silica gel treated with additives such as water or 1-decanol the rate is greater. Heat treatment causes changes in the number, nature and disposition of silanol groups on the gel surface, thereby influencing the mobilities of pyrene and BN and their diffusional quenching rates and the contribution to the total emission and ground state “dimers”.

BIPHASIC PHOTOCHEMISTRY: PHOTOCHEMICAL REGIOSPECIFICITY AND CRITICAL MICELLE CONCENTRATION DETERMINATION

Abstract— The irradiation of 3‐n‐butylcyclopentenone has been shown to give cyclobutane dimers, the ratio of head‐to‐head and head‐to‐tail isomers being solvent dependent. It is now shown that in aqueous medium this ratio is dependent on surfactant concentration both for charged and uncharged species. A very abrupt change in regiospecificity occurs at the critical micelle concentration, and c.m.c. values are obtained in which there is no ambiguity from extrapolation and which are in excellent agreement with values in the literature. This technique represents a new method for c.m.c. determination.

The biogenesis of helminthosporal

Die Biogenese des Pilzstoffes Helminthosporal wurde untersucht, indem der Pilz bei Anwesenheit von Mevalonsäure, mit C2 mit Kohlenstoff-14 markiert, gezüchtet wurde. Es wird gezeigt, dass das Dialdehyd aus einem tricyclischen Vorläufer durch oxidative Spaltung entsteht.

Photosensitized oxidation of acetylenes

Abstract The sensitized (electron transfer) photo-oxidation of acetylenes to yield benzils is described and the mechanism is discussed.

BIPHASIC PHOTOCHEMISTRY: THE FIRST ACTINOMETRIC REACTION ON A SOLID SUPPORT

Abstract— An apparatus is described and an actinometric standard proposed (the intramolecular cycloaddition of the tricyclic dienedione 1) for the determination of quantum yields of reaction of substances adsorbed on silica gel.

Mould metabolites—V : The constitution of ergoxanthin

Abstract Ergoxanthin has been shown to have the gross structure of a lactonized seco-ergochrysin (IV).