Caged compounds light source

The time resolution of the photochemical release of caged substrates depends on two factors the energy/time profile of the light source used for photolysis and the effective rate of liberation of active substrate. It should be remembered that the time scale of the potential application of a kinetic technique depends critically on the accuracy of the determination of zero time. Some practical details of the investigation of different parameters are illustrated below. Suffice it to say for the moment that the range of compounds presently available for different systems have time constants from 10 ms to 10 ps for the liberation of phosphates and amino derivatives (neurotransmitters). 

The principles of design and interpretation of kinetic investigations with photolabile precursors can be best illustrated by some of the many uses of npe-ATP. The important parameters to be determined with each compound are the absorption spectrum, quantum yield, rate of appearance of active substrate, the possible binding (competitive inhibition) of the caged compound and the effects of any photoproducts. Additional to these compound specific parameters, instrumentation parameters have to be considered. These are concerned with the light source for photolysis and with the detection equipment. The latter can either monitor the photolytic reaction of the caged compound or the physiological process stimulated by... 

In addition to iodonium, sulfonium and selenonium compounds, onium salts of bromine, chlorine, arsenic, and phosphoras are also stable and can act as sources of cation radicals as well as Bronsted acids, when irradiated with light. Performance of diaryl chloronium and diaryl bromonium salts was studied by Nickers and Abu. Also, aryl ammonium and aryl phosphonium, and an alkyl aryl sulfonium salt were investigated. It appears that the general behavior of these materials is similar to diphenyl iodonium and triphenyl sulfonium salts. These are formations of singlet and triplet states followed by cleavages of the carbon-onium atom bonds and in-cage and out of cage-escape reactivity. The anions of choice appear to be boron tetrafluoride, phosphorus hexafluoride, arsenic hexafluoride, and antimony hexafluoride. 

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