Photochemical reactions of azidocoumarins.

Photochemical reactions of 6-azidocoumarin and 7-azido-4-methylcoumarin in the presence of secondary amines have been investigated for their potential applications in photoaffinity labeling. It was found that the singlet nitrene generated from 6-azidocoumarin isomerized to a dehydroazepine intermediate that reacted with an amine to yield two isomeric adducts. Photolysis of 7-azido-4-methylcoumarin, in contrast, gave a triplet nitrene that abstracted hydrogen atoms from secondary amine molecules to form 7-amino-4-methylcoumarin as the major product. The difference in the intersystem crossing rate between the two compounds originates from the azido position relative to the carbonyl group. Because of its ability to form a covalent linkage with a nucleophile, 6-azidocoumarin is deemed to have a greater potential as a photoaffinity label than 7-azido-4-methylcoumarin.

Nucleation on photoexcited molecules.

On irradiation with light of suitable wavelength and intensity, certain organic compounds, even at very low concentrations, cause very efficient nucleation of supersaturated vapors. A mechanism is suggested to account for this phenomenon. Nuclei containing only a few photoexcited molecules are responsible for the nucleation.

Kinetics of the decomposition of hydrogen peroxide catalyzed by ferric ethylenediaminetetraacetate complex.

Added substrates, acetone and t-butyl alcohol, strongly retard the decomposition of H(2)O(2) brought about by ferric ethylenediaminetetraacetate (EDTA) at pH 8-9.5. Their relative effectiveness and the kinetic form of the retardation are consistent with their interruption of a hydroxyl radical chain that is propagated by HO. attack both upon H(2)O(2) and on complexed and uncomplexed EDTA. Similar retardation is observed with decompositions catalyzed by ferric nitrilotriacetate and hemin, and it is proposed that such redox chains may be quite a general path for transition metal ion catalysis of H(2)O(2) decomposition.