The nature and fate of natural resins in the geosphere—VIII. NMR and Py–GC–MS characterization of soluble labdanoid polymers, isolated from Holocene class I resins

Abstract

Soluble polylabdanoids isolated by sequential solvent extraction have been characterized by liquid-state 13C- and 1H NMR and 13C- 1H HMQC (heteronuclear correlation) NMR spectroscopy in addition to solid-state NMR and Py–GC–MS techniques. Two Holocene resins originating from Santander, Colombia and Mombasa, Kenya were analyzed. Soluble polymers were isolated by extraction with a 1:1 (v/v) methylene chloride–methanol mixture following sequential extractions with methylene chloride and methanol. The molecular weight of polymer extracts was shown by GPC analyses to exceed that of non-polymeric occluded terpenoids. Py–GC–MS, solid-state 13C CP/MAS and 13C cross-polarization/depolarization NMR spectroscopy results indicated that chemical compositions of soluble polymers isolated from immature resins are highly representative of the structure of corresponding insoluble polymers, i.e. polylabdatrienes. These data provide evidence for cross-linking or cyclization of side-chain olefinic carbons during or shortly after polymerization. Generally, the characterization of soluble resin polymers by liquid-state NMR spectroscopy has proven to be an excellent means for investigating the maturation mechanism of polylabdanoid resinites, and has potential for furthering the application of Class I resinites as geothermal indicators.