Interaction between Chlorophyll a and Vitamin K1 in Monomolecular Films

Abstract

As part of a continuing study of monolayers containing molecules involved in photosynthesis, we have examined mixed films containing chlorophyll a and vitamin K₁ (2‐methyl‐3‐phytyl‐1,4‐naphthoquinone). This quinone quenches the fluorescence of chlorophyll, both in monolayers highly diluted with oleyl alcohol and in those composed solely of pigment and vitamin K₁. Mixed chlorophyll—vitamin K₁ monolayers show deviations from ideal behavior, but the excess free energy of mixing, estimated from the pressure‐area characteristics, is small (∼0.1 kcal/mole). Fluorescence measurements on diluted films can be interpreted in terms of collisional quenching. In concentrated films, where the lifetime of the excited state is greatly reduced and energy migration among pigment molecules is rapid, only qualitative interpretation is possible. Under these conditions, the effectiveness of each vitamin K₁ molecule in quenching excitations which arrive on neighboring chlorophyll molecules appears to be reduced, but sharing of energy among pigment molecules leads to an efficient reduction in fluorescence yield.