Studies on the Chemical and Photochemical Oxidation of Bacteriochlorophyll¹

Abstract

A simplified procedure is described for the preparation of crystalline bacteriochlorophyll from R. rubrum. The chemical dehydrogenation of bacteriochlorophyll with quinones is shown to give high yields of 2-desvinyl-2acetyl-chlorophyll a, whereas the photo-oxidation of bacteriochlorophyll results in a mixture of products of which 2-desvinyl-2acetyl-chlorophyll a is only a minor constituent. A number of interesting results have been observed spectrophotometrically during these oxidations under different reaction conditions. These observations are discussed and possible reaction mechanisms are outlined. The proton magnetic resonance spectrum of 2-desvinyl-2acetyl-chlorophyll a in deuteroacetone and the visible absorption spectra of this pigment and its magnesium-free derivative in acetone are reported. As expected, these spectra exhibit a marked resemblance to chlorophyll a and pheophytin a.