The Spontaneous Change of Ferriprotoporphyrin in Alkaline Solution

Abstract

THERE are repeated suggestions in the literature that ferriprotoporphyrin in alkaline solution is unstable. Haurowitz¹ observed a decreased diffusion rate with time, and Shack and Clark² noted changes in the visible spectrum. Both these observations were interpreted as resulting from an increase in particle size. Rosenfeld and Surgenor³ found that ferriprotoporphyrin could be separated from the alkaline conversion product by differences in solubility in the two-phase system, n-butanol and pH 9.6 bicarbonate buffer. In spite of these and other observations, the nature of the reaction remains unknown. In this communication we present spectrophotometric evidence that a chemical change occurs in ferriprotoporphyrin on standing in an aerated alkaline solution, and that the change is probably a modification of the vinyl side-chains.