Spectroscopic and electrochemical characterization of chlorophyll a in different water + organic solvent mixtures

Abstract

Triangular-sweep adsorption voltammetry and absorption and fluorescence spectroscopy are employed in the study of chlorophyll a hydration and aggregation in binary mixtures of water with acetone, dimethylformamide (DMF) and acetonitrile (ACN). From the variation of the relative intensities and positions of the polarographic and spectroscopic peaks with the composition of the solvent, it is concluded that the organic solvates of Chl a are completely converted to Chl a · 2 H 2O at a water molc fraction x H2O > 0.66. A further shift in the equilibrium towards the dimerization of Chl a · 2 H 2O is observed at x H2O > 0.75. The lower water content and Chl a concentration required for aggregation in DMF and ACN compared with that required in acetone is discussed in terms of the bulk properties of the binary solvent mixtures.