Chemical structure of algaenans from the fresh water algae Tetraedron minimum, Scenedesmus communis and Pediastrum boryanum

The cell wails of the fresh water green microalgae Tetraedron minimum, Scenedesmus communis and Pediastrum boryanum are composed of highly resistant, non-hydrolyzable aliphatic biopolymers as revealed by C-13-NMR, FTIR and thermal and chemical degradations. The biopolymers are composed of long-chain even-carbon-numbered omega(9)-unsarurated omega-hydroxy fatty acid monomers varying in chain length from 30 to 34 carbon atoms. These monomers are intermolecularly ester linked to form linear chains in which the unsaturations act as the starting position of ether cross-linking. S. communis biosynthesises a more densely cross-linked algaenan than T. minimum and P. boryanum. The monomers of T. minimum have, on average, larger chain lengths than those of P. boryanum and S. communis. The polyether nature of these algaenans makes them highly resistant against degradation, so that they are selectively preserved in the sedimentary record. Therefore, these algaenans probably are important precursors for Type I kerogens. (C) 1998 Elsevier Science Ltd. All rights reserved.