Rubén Ocampo

A novel chlorophyll c related petroporphyrin in oil shale

Abstract A novel C 31 nickel petroporphyrin skeleton, 15,17-(15 2 -methyl)ethano-3,8-diethyl-2,7,12,18-tetramethylporphyrin 3, related to chlorophyll c, has been isolated from the Messel oil shale, and it structure determined by selective decoupling and nuclear Overhauser effect studies.

Porphyrins from Messel oil shale (Eocene, Germany): Structure elucidation, geochemical and biological significance, and distribution as a function of depth

Abstract The extraction and isolation procedures of twenty nickel porphyrins (seven alkylporphyrins, thirteen carboxylic acids) from lacustrine Messel shale (Eocene, Germany), as well as the unequivocal structural assignments (obtained using 200 and 400 MHz nuclear magnetic resonance (NMR), nuclear Overhauser effect, mass spectrometry and total or partial synthesis of six reference compounds) are described. Ten porphyrins could be specifically correlated with biological precursors: algal chlorophyll c (4), bacteriochlorophylls d (3) and heme (3), while the remaining ones may arise from several chlorophylls. The structures of these fossil pigments mostly confirm the classical “Treibs scheme,” including the origin of some porphyrins from nonchlorophyll sources. They also show that, even in a very immature sediment, deep modifications occur, including, in particular, extensive degradation of chlorophyll E ring. The composition of the porphyrin fractions of Messel oil shale was also studied as a function of depth. A porphyrin acids/alkylporphyrins ratio varying from 0.35 to 24.8 demonstrated that the apparent homogeneity of the shale is not reflected on the molecular scale. This was confirmed when the abundance of the twenty individual porphyrins of known structure was measured along the core. Significant correlations between individual porphyrins were found: fossils of bacteriochlorophylls d , homolog pairs of porphyrins (3-H/3-ethyl), etc.

Evidence for porphyrins bound, via ester bonds, to the Messel oil shale kerogen by selective chemical degradation experiments

Abstract High amounts of nickel mono- and di-acid porphyrins were released from Messel oil shale kerogen (Eocene, Germany) by selective chemical degradation (acid and base hydrolysis). The released porphyrin fractions were quantified (UV-vis) and their constituents isolated and characterized at the molecular level (UV-vis, MS, NMR). The mono-acid porphyrin fraction released contained four compounds of similar abundance which arise from an obvious chlorophyll or bacteriochlorophyll precursor. The di-acid porphyrin fraction was, however, dominated by far by one compound, mesoporphyrin IX, which must have originated from heme-like precursors (heme, cytochromes, etc.). These results show unambigously that the released mono- and di-acid porphyrins were linked to the macromolecular kerogen network via ester bonds and suggest that precursor heme-like pigments could be selectively and/or more readily incorporated into the macromolecular kerogen network than precursor chlorophylls and bacteriochlorophylls.

Molecular fossils of chlorophyll c of the 17-nor-DPEP series. Structure determination, synthesis, geochemical significance

Two porphyrins 1 and 2, having totally (1) or partially (2) lost the C-17 substituent, have been isolated from two Moroccan oil shales of Cretaceous age. An origin from chlorophyll c, which possesses a 17-acrylic side-chain, can explain this transformation. A synthesis of 1 from chlorophyll (a + b) is described. Porphyrin 1 is widely distributed in sediments and its relative abundance with regard to other molecular fossils of chlorophyll c is discussed briefly.

Isolation and structure determination of the unstable 132, 173-Cyclopheophorbide a enol from recent sediments

Abstract We observed that the unstable 132, 173-cyclopheophorbide a enol is one of the most abundant pigments in recent sediments (Black Sea, Mediterranean Sea, Peru margin) and here we report its isolation and structure determination (high-performance liquid chromatography, ultraviolet-visible spectrometry, mass spectrometry, and nuclear magnetic resonance). This enol has been considered as the precusor of sedimentary chlorins and porphyrins bearing either a seven + five- or a seven-membered ring system. Analysis of sediment trap samples collected from the Peru Upwelling area revealed relatively high concentrations of 132, 173-cyclopheophorbide a enol in trap samples containing high concentrations of metabolically derived carotenoid transformation products. The abundance of 132, 173-cyclopheophorbide a enol in sediment trap samples and recent sediments suggests that formation of an exocyclic seven-membered ring is a major diagenetic pathway for chlorophylls. Biologically mediated transformations of chlorophylls can therefore yield products not included in the classical Triebs degradation scheme for cyclic tetrapyrroles.

Occurrence of bacteriopetroporphyrins in oil shale

The structure of the higher homologues (C34–C36) of porphyrin acids of the Messel oil shale, elucidated by nuclear Overhauser effect studies in the case of the C35 compound, reflect their origin from photosynthetic bacteria.

Identification of polar porphyrins in oil shale

Several porphyrin acids [(1)–(6); C30–C33] have been isolated from the Messel oil shale and identified by nuclear Overhauser effect studied and synthesis; they imply the existence of several diagenetic pathways leading from the chlorophylls to the alkylpetroporphyrins.

Identification of a novel C33 DPEP petroporphyrin from boscan crude oil : evidence for geochemical reduction of carboxylic acids.

Abstract The isolation and structural determination (n.m.r., n.O.e., synthesis) of a C 33 member of the DPEP series from Boscan crude oil indicates that total reduction of the propionic side-chain of a precursor chlorophyll may occur during, the processes leading to oil formation.

Study of the porphyrins released from the Messel oil shale kerogen by hydrous pyrolysis experiments

Eight samples of pre-extracted Messel oil shale have been submitted to hydrous pyrolysis at different temperatures between 225°C and 350°C. The porphyrins released were evaluated, fourteen isolated, and seven of them characterized (from the sample heated at 250°C) by comparison with geological and/or synthetic standards (UV-visible, HPLC, MS and NMR). We followed the thermal release of porphyrins by HPLC and MS to examine changes in the distributions and, to get a better idea of the porphyrins bound to the macromolecular kerogen network of the Messel shale. The structures of the released porphyrins indicate that dealkylation reactions occur during the thermal stress. The presence of acid porphyrins, in the case of the lowest temperature experiments (225°C and 250°C), suggests that at least part of the released alkyl porphyrins are formed by the decarboxylation of acid porphyrins present in the kerogen. Etioporphyrins are more abundant and they are released later (at higher temperature) than DPEPs. This observation may indicate that ETIOs are more strongly attached to the macromolecular network than DPEPs. The results obtained seem to indicate that, during these maturation experiments, the DPEPs are destroyed by the thermal stress rather than being transformed into ETIOs.

Identification of long-chain tricyclic terpene hydrocarbons (C21–C30) in geological samples

The structure of a series of long-chain tricyclic terpene hydrocarbons occurring in sediments and petroleums has been confirmed by synthesis of the C21–C30 members; these compounds could result from a yet unknown cyclisation of polyprenols in micro-organisms.