Model systems for photosynthesis - III. Primary photoprocesses of chloroplast pigments in monomolecular arrays on solid surfaces

Abstract
By means of the Langmuir-Blodgett technique, monomolecular layers containing chloroplast pigments and lipids have been prepared and transferred from a water surface to solid substrates for spectroscopic study. The absorption spectra of such monolayers of pure chlorophyll a and b have been characterized on several different surfaces. Phytol and M$^{2+}-1\colon 1$ stearate-oleate have been used as inert, transparent layer diluents for the chlorophylls to enable the effect of pigment concentration on the absorption and fluorescence spectra to be studied. Self-quenching of the fluorescence of both chlorophylls has been observed and the chromophore separation at the half-quenching concentration is compared with similar data for monolayers on the surface of water, as well as solid and solution systems. Energy transfer between chlorophyll b and a within a monolayer has also been investigated, and found to involve essentially irreversible transfer of excitation energy from b to a. Experiments involving the quenching of chlorophyll fluorescence by quinones in the monolayer leads to the conclusion that the efficiency of quinone quenching is not enhanced at high chlorophyll concentrations. The monolayer properties of the photosynthetically important quinone, plastoquinone A, were investigated, and it was found to form very unstable layers, unsuitable in the present work.

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