Resistant biomacromolecules as major contributors to kerogen JAN W. DE LEEUW1, PIM F. VAN BERGEN1, BEN G. K. VAN AARSSEN1, JEAN-PIERRE L. A. GATELLIER1, JAAP S. SINNINGHE DAMSTE 1 a nd MARGARET E. COLLINSON 2 1 Organic Geochemistry U n i t ,Faculty o f Chemical Technology and M aterials Science, D elft University o f Tech De Vries van Heystplantsoen 2, 2628 R Z Delft, The Netherlands 2 Biosphere Sciences Division, King’s College London, Kensington Campus, Campden H ill Road, London W 8 7A H , U.K. SUMMARY Current research concerning the chemical characterization of organic macromolecules present in well- preserved fossilized materials with known morphologies revealed by (electron) microscopic studies results in the recognition of unknown, resistant biomacromolecules in a variety of organisms. It is shown that highly aliphatic, non-saponifiable biomacromolecules in cell walls of algae (algaenans) have unique structures, probably as a result of different biosynthetic pathways and that they consist of «-alkyl-, isoprenoid and tricyclic alkyl units. It is also becoming clear that algaenans are structurally different from the highly aliphatic, non-saponifiable biomacromolecules occurring in plant cuticles (cutans), periderm tissue (suberans), some sporopollenins and in tegmens of seeds of water plants. All these types of aliphatic biomacromolecules are highly resistant and therefore selectively preserved in the geosphere. In particular, Type I and II kerogens consist mainly, in some cases exclusively, of these aliphatic biomacromolecules. Polysesquiterpenoids and polyditerpenoids occur in fresh and fossil angiosperm and gymnosperm resins respectively and also show resistant behaviour in the geosphere. Some waxy crude oils contain large amounts of compounds derived from these substances after thermal cracking. A completely new polyphenol type of biomacromolecule was encountered in several fossilized outer walls of seeds (testae) of water plants. Preliminary results indicate that this phenolic biomacromolecule is an alternative source of phenolic moieties in lignites and coals. The significance of lignin as a source of phenolic moieties in subsurface organic matter (e.g. vitrinites) is probably overestimated. 1. I N T R O D U C T I O N The organic matter present in the subsurface of the Earth consists of two operationally defined fractions, the bitumen soluble in common organic solvents and the kerogen, which is insoluble in such solvents. The far greater part of the sedimentary organic matter (. ca . 95 %) consists of kerogen, even if oil accumulations are taken into consideration. Over the last fifty years or so research efforts on the molecular level mainly concentrated on the structural elucidation of low molecular mass ( l m m ) compounds present in crude oils and bitumens from sediments. The results of these studies have tremendously improved our knowledge of palaeo-environments and diagenetical pathways, and are applied in oil exploration. It has to be realized that in this way only a few percent of the organic matter in the subsurface has been analysed, simply because of the fact that soluble l mm organic compounds can be analysed relatively easily by means of standard methods such as gas chromatography—mass spectro- metry ( g c —ms ). Consequently, our view of the mol- ecular composition of organic matter in the geosphere has been very limited and probably also highly biased. During the last decade several analytical methods and techniques have become available to organic geo- chemists and other natural product chemists to characterize on a molecular level high molecular mass ( h m m ) insoluble organic substances such as kerogen and a variety of biomacromolecules. In most cases these analyses are indirect in that a ‘ demacro- molecularization ’ step is performed before building blocks are identified by classical techniques. Demacro- molecularization by specific chemical reactions (chemolysis) and flash-pyrolysis in combination with appropriate derivatizations, chromatographic separa- tions and mass spectrometry are good examples of such an approach. Solid-state 13C nuclear magnetic res - onance ( n m r ) and Fourier transform infrared ( f t —ir ) spectroscopy are also useful tools, although the res- olution of these methods is limited and information is obtained at only the functional group level. As a result of the availability of these new method- ologies and their application to investigate kerogens and unrecognized biomacromolecules, an alternative mechanism for the formation of kerogen has recently Phil. Trans. R. Soc. Lond. B (1991) 333, 329-337 Printed in Great Britain 329 Downloaded from https://royalsocietypublishing.org/ on 28 January 2022