Studies of Colloidal Chlorophyll in Aqueous Dioxane

The preparation and properties of a colloidal state of pure chlorophyll a in aqueous dioxane are described. The red absorption maximum is at 685+/- 1 mmu, depending on buffer concentration. The typical 672 mmu colloid (obtained by diluting an acetone solution with water) can be converted directly to the 685 mmu colloid by the addition of 1 M dioxane. The 672 --> 685 mmu conversion is irreversible and is second order with respect to both 672 colloid and dioxane. It is shown that the formation of the 685 mmu colloid of chlorophyll a requires the Mg atom; no dioxane species is obtained with pheophytin or ethyl pheophorbide. Furthermore, of the transition metal salts of chlorophyll, Cu, Co, Ni, and Zn, only the Zn salt interacts with dioxane.