The interfacial factor in the heat‐induced conversion of chlorophyll to pheophytin in green leaves

The rates of the conversion of chlorophyll to pheophytin in the green leaves of common vegetables and other plants at different temperatures in buffered electrolyte systems were studied. Kinetic measurements showed that the conversion only occurred above a threshold temperature of 50–60 °C and was most probably a pseudo‐first order reaction. Rates were found to be proportional to √[H + ]. The dependence of the rate of conversion upon species, temperature and electrolyte type can be explained on the basis of a heat‐induced metamorphosis of the chloroplasts to a smectic mesophase which occludes the chlorophyll. The rate of the reaction then depends on the transfer of hydronium ions across the interface and can be largely controlled by modifying the interfacial potential.