The Photo–oxidation of a Chlorophyll ‘Preparation

Examination has been made of the photo–oxidation in white light of a chlorophyll preparation on various solids by the direct measurement of oxygen pressure decrease. Rates were very low on glass, zinc oxide, aluminium oxide, thallous phosphate, and ferric phosphate, but were some ten times more rapid on thallous bromide and thallous iodide. No change in rate with thallous bromide preparations was observed in the presence of water vapour and carbon dioxide. The quantum efficiency on glass was of the order of 10˜8 for blue light. The oxygen: chlorophyll and the oxygen: carotene molecular ratios of the final photoproduct were almost exactly unity. The final stable product is regarded as a hydroperoxide: partial reversibility of the oxidation was observed by simple pressure reduction. In general, the course of the oxidation resembles that of some other organic molecule oxidations, being characterised by an induction period, by a constant–rate portion, and by a subsequent rate of oxidation slowly decreasing to zero.