STRUCTURAL COMPARISON OF NICKEL, VANADYL, COPPER, AND FREE BASE PORPHYRINS FROM OULAD ABDOUN OIL-SHALE (MAASTRICHTIAN, MOROCCO)

Twenty-eight individual alkylporphyrins have been identified complexed by nickel, vanadyl, or copper in the Moroccan bituminous marl of Ouland Abdoun. A structural comparison of the composition of the nickel and vanadyl porphyrin fractions has shown substantial differences. The nickel porphyrins are strongly enriched in a whole variety of yet unidentified “etio” compounds, in cycloheptano components, and in rearranged products derived from algal chlorophyll c. The vanadyl fraction is enriched in 17-nor-DPEP (DPEP = deoxophylloerythioetioporphyrin), presumably also derived from chlorophyll c, relative to classical C32-DPEP, which is major in the nickel fraction. A free base porphyrin fraction has been tentatively characterized and seems to be restricted to a mixture of “etioporphyrins”. The reasons for these differences are still unelucidated; they may arise from a selective availability of metals at various stages of sedimentation or from a structure-dependent selectivity in metal insertion. © 1990, American Chemical Society. All rights reserved.