Molecular composition and structural model of resinite in Fushun resinitic liptobiolith

The molecular framework of the resinite is composed of small molecules and macromolecule,mainly terpenoid derivatives. In this paper,the molecular composition of Fushun Paleogene resinite(amber) in resinitic liptobiolith was systematically studied by means of stepwise solvent extraction,ultimate analysis,13C NMR,FTIR,GC/MS and XPS. The evolution of small molecules and macromolecule structure between modern resin with fossil resin were discussed in detail. The results displayed that the small molecules in resinite were mainly composed of 1～2 aromatic hydrocarbons,esters and n-alkanes(C16～C30) with a small amount of monoterpenes and sesquiterpenes. The fatty acids in resinite mainly derived from the hydrolysis of esters,and fatty hydrocarbons were derived from the decarboxylation of resin acid. Aromatic hydrocarbons(alkyl benzene,alkyl naphthalene and their derivatives) mainly derived from the cross-linking reaction of coumaric acids with hydroxyl fatty acids or the disproportionation reaction of cyclic monoterpenes and sesquiterpenes. The mole fraction(Xb) of aromatic bridgehead carbon in aromatic carbon of the resinite was 0.18,and the content of aliphatic carbon(86.37%) was higher than that of aromatic carbon(13.63%). These results indicated that the structure of resinite was characterized by low aromaticity and long-branched chains. The macromolecular structure model of resinite was constructed using Materials Studio software. The macromolecular formula of the resinite was C96H152O8 with the relative molecular weight of 1 432. The macromolecule of resinite mainly contained cycloalkanes,terpenes(monoterpenes and sesquiterpenes),long-chain aliphatic compounds and alkylbenzene etc. The organic oxygen mainly presented in the form of different oxygen-containing functional groups(phenolic hydroxyl groups,ester group and carboxyl groups). These informations on the composition and evolution of small molecules in resinite has important theoretical significance for the understanding of its formation process,and the construction of its macromolecular structure model lays an important theoretical foundation for the study of its properties at the molecular scale.