Absorption spectra of chlorophyll a in aqueous carbitol solvents

Abstract

The absorption spectrum of chlorophyll a in aqueous methyl and butyl carbitol has been measured. The red-absorption maximum of chlorophyll dissolved in methyl carbitol (665 mμ) shifts to the red as the solvent is made increasingly aqueous (672 mμ in 30% methyl carbitol). Concurrently, the extinction coefficient decreases and fluorescence is lost. It has also been shown that only the non-fluorescent form of chlorophyll can form a colloid absorbing at 685 mμ in the presence of 6% dioxane. Butyl carbitol is more effective than methyl carbitol in keeping chlorophyll in a fluorescent form at high water concentrations, some fluorescence persisting when the solvent is 70–80% aqueous. Dioxane colloids prepared in 10% butyl carbitol exhibit an absorption maximum at 690 mμ, with a subsidiary maximum at 695 mμ. The 695-mμ absorption is considerably strengthened on standing. Thus, in these two solvent systems it is possible to prepare colloidal states of chlorophyll absorbing maximally at 672, 685, 690, and 695 mμ.