Encapsulation of proteinaceous materials in macromolecular organic matter as a mechanism for environmental preservation.

摘要

In this study, the nature and extend of preservation of organic nitrogen during diagenesis in various terrestrial and aquatic environments were evaluated by various analytical techniques, including solid-state NMR (13C and 15N), pyrolysis GC-MS, and TMAH thermochemolysis GC-MS. The results of this study show that while most proteins are degraded during diagenesis, a small portion of the total proteinaceous nitrogen pool is retained within biologically refractory organic components of sedimentary deposits and in refractory natural biopolymers. These preserved proteinaceous materials constitute the major components of the refractory organic nitrogen in the aquatic and terrestrial samples analyzed in this study.; To explore the possible preservation mechanism of the refractory organic nitrogen, chemical structures of the preserved natural biopolymers, i.e. algaenan from B. braunii and Coorongite, were first investigated. The following structural characteristics of these two natural biopolymers were revealed: (1) long paraffinic carbon chains are major structural components in both of these two biopolymers, (2) ether and ester linkages are the major crosslinking bridges that intermolecularly connect the paraffinic carbon chains into a highly aliphatic, insoluble, and chemically resistant three-dimensional network, (3) relative to the B. braunii algaenan, the Coorongite has a more crosslinked structure which implies a more extensive degradation.; An encapsulation hypothesis postulating that the preservation of organic nitrogen, such as proteinaceous nitrogen, is achieved by a physical encapsulation of these labile organic nitrogenous materials in the interior domains of macromolecular refractory organic materials was proposed. Physical encapsulation processes that protect proteinaceous materials from degradation were simulated in the laboratory using a humic acid and Coorongite as encapsulating media. Chemical attack on these labile organic nitrogenous materials was prevented by steric hindrance from the macromolecular network surrounding the encapsulated labile organic nitrogenous materials.; A more definitive evaluation of the dominant preservation mechanism in the specific degradation of B. braunii algae was achieved by a 2D solid-state 13C-15N double cross polarization MAS NMR experiment. The results clearly show that the proteinaceous materials in each algal pool maintained their original structural integrity during the degradation and a depolymerization-recondensation process did not occur.