The First Experimental Demonstration of Benzoporphyrin Formation from Sedimentary Porphyrins

Abstract

Etioporphyrin, one of the most common sedimentary porphyrins, was heated at 300 to 450 °C to investigate the diagenetic formation of benzoporphyrins. Chromic acid oxidation of the resulting products afforded maleimides, as well as phthalimides, indicating the formation of benzopyrrole units in the substrate. Isomer ratios of dimethylphthalimides formed during heating were in accordance with those obtained by chromic acid oxidation of the Cretaceous/Tertiary sediments at Rumoi, Hokkaido, which suggests that alkylporphyrins could be transformed into benzoporphyrins in sediments.

Maleimide index: a paleo-redox index based on fragmented fossil-chlorophylls obtained by chromic acid oxidation

“…It is known that the side chains of the porphyrins and their related substances present in sedimentary rocks are altered by geothermal pyrolysis. 17,19–21 Thus, to examine the changes in the side chains of the bacteriochlorophylls, we performed heating experiments using two model porphyrins, 1 and 2 (Chart 2), which were prepared as described in our previous study. 21,22 We designed these model porphyrins based on simple structures to clarify the changes taking place in the pyrrole B-ring pyrroles of the bacteriochlorophylls.…”

“…Porphyrins and their related substances are commonly found in sedimentary rocks, crude oils, and recent sediments. 1–21 These compounds are considered to be degradation products of the chlorophylls possessed by photosynthetic organisms that lived in the past. 1–22…”

“…1–21 These compounds are considered to be degradation products of the chlorophylls possessed by photosynthetic organisms that lived in the past. 1–22…”

“…1–5 Since each photoautotroph possesses a different type of chlorophyll, 23 determination of the source chlorophyll from analysis of the porphyrin in geological samples can lead to an estimation of past photosynthetic organism distributions. 1–21 The information related to dominant photosynthetic organisms has been previously employed for paleoenvironmental reconstructions, since the paleoenvironment can be estimated from such habitat characteristics. 6–10…”

“…The majority of porphyrins present in sedimentary rocks are trapped within an insoluble and amorphous polymer known as kerogen, 13–22 and so their extraction with common solvents is challenging. To address this issue, the analysis of maleimides (1 H -pyrrole-2,5-diones, Mis) derived from the pyrrole skeletons of porphyrins, is promising, since these soluble compounds can be easily extracted and analyzed by gas chromatography-mass spectrometry (GC-MS).…”