E.W. Tegelaar

A reappraisal of kerogen formation

Abstract Comparative microscopical and chemical studies of recognizable entities in kerogen and their extant counterparts suggest a new and simple mechanism of kerogen formation which clarifies the interrelationships between extant biomass, kerogen, and fossil fuels.

Analysis of modern and fossil plant cuticles by Curie point Py-GC and Curie point Py-GC-MS: recognition of a new, highly aliphatic and resistant biopolymer

Abstract This paper investigates to what extent the chemical constituents of plant cuticles (waxes and cutin) can survive diagenesis. Recent and fossil plant cuticles were analyzed by means of Curie point pyrolysis-gas chromatography and Curie point pyrolysis-gas chromatography-mass spectrometry. Recent cuticles were analyzed without treatment, after solvent extraction and after cutin depolymerization. Extensive series of straight-chain alkanes, alk-1-enes and α,ω)-alkadienes dominate the pyrolysates, especially after removal of the wax and cutin. 13 C-NMR spectroscopy of the residue after removal of the cutin confirmed the presence of a new, highly aliphatic biopolymer and a polysaccharide fraction. The abundance of straight-chain alkanes, alk-1-enes and α,ω-alkadienes in the fossil plant cuticles indicates the chemical resistence of the biopolymer to diagenesis and may explain the occurrence of straight-chain aliphatic moieties in organic-matter-rich sediments and coals as revealed by “C-NMR spectroscopy and flash pyrolysis methods. The highly aliphatic biopolymer may function as an important oil precursor.

A new non-saponifiable highly aliphatic and resistant biopolymer in plant cuticles

Analysis of present-day plant cuticles by flash pyrolysis methods revealed the presence of a previously unknown, non-saponifiable highly aliphatic biopolymer. Its occurrence in fossil plant cuticles suggests a high chemical resistance towards diagenesis and offers a clue to the unraveling of the chemical nature of the coal maceral cutinite. p lant cuticles are thin, continuous extracellular layers which cover the outer surface of the aerial parts of plants. Their occurrence is ubiquitous and their role as contributors to the organic matter in sediments and coals may be very important. It is generally agreed that the chief chemical components of plant cuticles are lipids, the insoluble high-molecular-weight polyester cutins that form the structural framework of the membrane with soluble waxes embedded within it and secreted onto its surface. However, analysis of recent and fossil plant cuticles by flash pyrolysis techniques has revealed the existence of a previously unknown, non-saponifiable highly aliphatic and chemically resistant biopolymer. This biopolymer represents a significant proportion of the biomass of some present-day and several fossil plant cuticles. To verify the possibility that the maceral cutinite of coals originates from plant cuticles, we have recently investigated a number of fossilized cuticles. Because the organic matter in these cuticles is present almost exclusively in the polymeric state, Curie-point pyrolysis coupled with gas chromatography (Py-GC) and mass spectrometry (Py-GCMS) were chosen as the primary methods of analysis. Such techniques have already been shown to be extremely useful in the identification and structurai elucidation of a wide range of natural and synthetic polymeric materials.

Chemical characterization of the periderm tissue of some angiosperm species: recognition of an insoluble, non-hydrolyzable, aliphatic biomacromolecule (Suberan)

Abstract In order to establish the chemical relationship between the liptinitic maceral suberinite and its recent counterpart, an inventory of the constituents of isolated outer bark tissue (periderm) of five extant angiosperm species was made. Samples were analyzed by means of chemical degradation methods in combination with Curie-point pyrolysis-gas chromatography-mass spectrometry and gas chromatrography-mass spectrometry. It was demonstrated that the periderm of the species investigated consisted of complex mixtures of lipids and biomacromolecules which include the biopolyester suberin, tannins, polysaccharides, lignin, and a hitherto unknown insoluble, non-hydrolyzable highly aliphatic biomacromolecule, named suberan. The liptinitic nature of the maceral suberinite can probably be explained by assuming selective preservation and consequent selective enrichment of suberan during the processes of diagenesis. The lignin present in the periderm of extant angiosperms is of a distinctively different monomeric composition from that of the corresponding wood with a marked guaiacyl over syringyl predominance. The presence of different physiological functions within the plant is offered as explanation for this divergence.

Possible origin of aliphatic moieties in humic substances

Abstract Various hypotheses have been put forward concerning the origin of aliphatic moieties in humic substances. In this paper we consider the possibility of a direct contribution of various classes of aliphatic moieties, occurring in extant organisms, to humic substances. On the basis of their resistance against chemical and biological degradation, it is speculated that recently discovered insoluble, non-hydrolyzable aliphatic biopolymers in algal cell walls and the protective layers of higher terrestrial plants are, via a mechanism of selective preservation, major precursors of aliphatic moieties in humic substances.

Scope and limitations of several pyrolysis methods in the structural elucidation of a macromolecular plant constituent in the leaf cuticle of Agave americana L.

Abstract Cuticles of Agave americana contain a substantial amount of an insoluble, non-hydrolyzable macromolecular substance of a highly aliphatic nature. Based on Fourier transform infrared (FTIR) and 13 C cross-polarization magic angle spinning NMR spectroscopy it was established that the isolated macromolecular substance consists of a polysaccharide and polymethylene moiety in an estimated ratio of 60:40 by weight. After treatment with acid this ratio changed to 37: 63. The isolates obtained before and after the acid treatment were subjected to Curie-point pyrolysis-gas chromatography with flame ionization detection, Curie-point pyrolysis-gas chromatography/mass spectrometry, Off-line pyrolysis in combination with gas chromatography and gas chromatography/mass spectrometry, desorption chemical ionisation mass spectrometry, time/temperature-resolved pyrolysis-field ionization mass spectrometry and heating experiments in a closed system in order to elucidate the molecular structure. Each of the methods applied has its own specifications with respect to pyrolysis conditions and response factors of different classes of pyrolysis products. The data obtained are highly complementary and, in combination with FTIR and 13 C NMR, several new features of the insoluble, non-hydrolyzable aliphatic biopolymer were revealed.

Aliphatic components of forest soil organic matter as determined by solid-state 13C NMR and analytical pyrolysis

Forest soil organic matter contains a refractory alkyl-carbon component of unknown structure and composition. Soil samples obtained from different types of forest humus and from litter-bag experiments were examined by the complementary techniques of solid-state 13C NMR and analytical pyrolysis to determine the structural composition of the unknown alkyl carbon. The NMR techniques of cross polarization magic angle spinning and dipolar dephasing provide quantitative data on the average structural composition, whereas the pyrolysis method provides detailed molecular information. The data suggest that the unknown alkyl-carbon structures in fresh forest litter are composed of the plant polyester cutin and another aliphatic biopolymer. These components correspond to a mobile and a more rigid fraction of aliphatic carbon as determined by dipolar dephasing 13C NMR spectroscopy. With increasing humification in the forest soils the percentage of rigid carbon increases. This could be indicative of a selective preservation of rigid carbon moieties derived from plants or soil microorganisms. The molecular structure of the aliphatic moieties was further investigated with Curie-point pyrolysis-gas chromatography (-mass spectrometry). The results indicate that aliphatic biomacromolecules of plant or microbial origin are present in very small quantities in these soil samples. They are not selectively preserved during decomposition. It is concluded that the rigid carbon moieties result from an increase in cross linking during the humification process.

Bias of the paleobotanical record as a consequence of variations in the chemical composition of higher vascular plant cuticles

The impact of the variations in the chemical composition of higher vascular plant cuticles on their fossil record is usually not considered in paleobotanical and, more particularly, taphonomic studies. Here we address the subject with reference to the chemical characterization of insoluble cuticular matrices of a large variety of recent and fossil cuticles. The cuticles were analyzed using Curie-point pyrolysis-gas chromatographic techniques. Cuticular matrices of extant higher plants consist either of the biopolyester cutin, the insoluble, non-hydrolyzable polymethylenic biopolymer cutan, or a mixture of both biopolymers. In fossil cuticles an additional cuticular matrix type consisting of cutan and cutin-derived material is recognized. On the basis of the variations in their chemical composition and the different behavior of the cuticular constituents (viz., cutin and cutan) during diagenesis, it is concluded that the paleobotanical record of cuticles will be biased toward taxa originally having a significant amount of cutan in their cuticular matrix.

Some mechanisms of flash pyrolysis of naturally occurring higher plant polyesters

Abstract The structurally well-defined cutin of Lycopersicon esculentum (Tomato) fruit has been used to examine the major mechanisms of pyrolysis of this class of natural lipid polyester. On the basis of the products identified by Curie-point pyrolysis-gas chromatography/mass spectrometry it was concluded that the main pyrolytic mechanisms are six-membered ring rearrangement reactions triggered by the ester function. The generation of products produced by cleavage of one bond in the polymer is highly favoured when compared to those which can be volatilized only after the cleavage of two or more bonds.

Characterization of Estonian Kukersite by spectroscopy and pyrolysis: Evidence for abundant alkyl phenolic moieties in an Ordovician, marine, type II/I kerogen

Abstract The kerogen of a sample of Estonian Kukersite (Ordovician) was examined by spectroscopic (solid state 13C NMR, FTIR) and pyrolytic (“off-line”, flash) methods. This revealed an important contribution of long, linear alkyl chains in Kukersite kerogen. The hydrocarbons formed upon pyrolysis are dominated by n-alkanes and n-alk-1-enes and probably reflect a major contribution of selectivity preserved, highly aliphatic, resistant biomacromolecules from the outer cell walls of Gloeocapsomorpha prisca. This is consistent with the abundant presence of this fossilized organism in Kukersite kerogen. In addition high amounts of phenolic compounds were identified in the pyrolysates. Series of non-methylated, mono-, di- and trimethylated 3-n-alkylphenols, 5-n-alkyl-1,3-benzenediols and n-alkylhydroxybenzofurans were identified. All series of phenolic compounds contain long (up to C19), linear alkyl side-chains. Kukersite kerogen is, therefore, an aliphatic type II/I kerogen, despite the abundance of free phenolic moieties. This study shows that phenol-derived moieties are not necessarily associated with higher plant-derived organic matter. The flash pyrolysate of Kukersite kerogen was also compared with that of the kerogen of the Guttenberg Oil Rock (Ordovician) which is also composed of accumulations of fossilized G. prisca. Similarities in the distributions of hydrocarbons and sulphur compounds were noted, especially for the C1–C6 alkylbenzene and alkylthiophene distributions. However, no phenolic compounds were detected in the flash pyrolysate of the Guttenberg kerogen. Possible explanations for the observed similarities and differences are discussed.