Head-to-head linked isoprenoids in Miocene coal lithotypes

Aliphatic fractions of chloroform bitumens from homogeneous (humovitrain, xylain and liptain) and heterogeneous (humoclarain) lithotypes of lignite Maritza-Iztok as well as products of their mild reduction with NaH were studied for acyclic isoprenoid biomarkers. Mass spectral data revealed the presence of regular C19–C33 isoprenoids without pristane/phytane dominance, one “tail-to-tail” isoprenoid, C30, squalane, in all samples under study. High molecular weight “head-to-head” isoprenoids, C38–C40, with slight preponderance of coupled pristyl- and phytyl units were registered in humovitrain and humoclarain samples after NaH treatment. These irregular isoprenoids are indicators for strictly anaerobic methanogens present in paleodepositional environment. Mild reductive treatment with NaH is a promising approach to rupture ether linkage in coal structure and give us one more possibility to loose isoprenoid moieties.