Formation of insoluble, nonhydrolyzable, sulfur-rich macromolecules via incorporation of inorganic sulfur species into algal carbohydrates

The process of sulfur incorporation into organic matter was simulated in th e laboratory by sulfurization of cell material of the prymnesiophyte alga P haeocystis in sea water with inorganic polysulfides at 50 degrees C. Flash pyrolysis of the residue, obtained after extraction and several hydrolysis steps, yielded mainly C-1-C-4 alkylbenzenes and C-1-C-4 alkylphenols and, i n contrast to control and blank experiments, relatively high amounts of C-0 -C-4 alkylthiophenes. The distribution of the thiophenes is very similar to that in pyrolysates of type II-S kerogens. The formation of high-molecular -weight sulfur-rich macromolecules co-occurs with a marked drop in the cont ent of hydrolyzable carbohydrates. This indicates that sulfurization result s in the preservation of algal carbohydrate carbon in a macromolecular stru cture composed of (poly) sulfidic cross-linked carbohydrate skeletons, whic h upon pyrolysis yields alkylthiophenes. Sulfurization of glucose under sim ilar conditions resulted in the formation of a nonhydrolyzable, solid mater ial, which yielded high amounts of organic sulfur compounds upon pyrolysis, mainly short-chain alkylthiophenes, although with a different distribution than that in the pyrolysate of the sulfurized algal material. The carbon n umbers of these organic sulfur compounds extend beyond six, indicating that the length of the carbon skeleton of the pyrolysis products is not limited by the length of the carbon skeleton of the substrate. These results sugge st that the sulfurization of carbohydrates may be an important pathway in t he preservation of organic matter in euxinic depositional environments. Cop yright (C) 2000 Elsevier Science Ltd.