ON THE MECHANISM OF PHOTOSENSITIZING ACTION OF CHLOROPHYLL

Abstract— The paper presents ideas according to which the primary photochemical reaction of chlorophyll and its analogs can be either photooxidation or photoreduction of the pigment sensitizer depending on the reaction conditions. The factors determining the course of the process of photosensitization comprise the nature and state of the pigment and participating reagents, the nature and reaction of the medium, concentration of the oxidant and reductant, their ability to form complexes with the pigment, etc.
The paper presents the results of simple kinetic investigations in which, by means of changing pH of the medium, conditions were created favouring either the primary photo-oxidation or the primary photoreduction of the pigment-sensitizer. These results, as well as the data of experiments on the changes in reagents' concentration show the reality of the above mentioned concepts.
Considerations are presented on the possibility of photochemical interaction of two chlorophyll molecules in vivo during the photosensitization of photosynthesis.