Examination has bean made of the ohotooxidation, in visible light, of chlorophyll preparations, deposited on various solids, by means of the
direct measurement of oxygen pressure decrease.
Rates of oxidation were very low on glass,
zinc oxide, aluminium oxide, ferric oxide, and on
talc, but were some five to ten times more rapid on
thallous bromide and thallous iodide. The maximum
quantum efficiency on glass in light of wave length
4358 A.U. was of the order 10⁻², increasing slightly
with decreasing film thickness.
Chromatographic and solvent partition
separation methods applied to two chlorophyll
preparations enabled two main fractions to be examin¬
ed, a yellow carotene fraction and the green chloro¬
phyll fraction. Cn thallous bromide, the oxygen
to carotene and the oxygen to chlorophyll molar
ratios in oxidation were unity. The chlorophyll
fraction of a second sample showed an apparent oxygen
to chlorophyll molar ratio of approximately two.
Oxidations were partly reversible by simple pressure
reduction. For one chlorophyll preparation, a limit
of oxygen pressure of approximately 0.1mm. was
established, below which no oxidation occurred.
A possible mechanism has been discussed
in relation to the experimental results and to the
general nature of such preparations.