Analysis of polymeric extractives of Western Juniper (Juniperus occidentalis) heartwood

Abstract

Extractives of Western Juniper (Juniperus occidentalis) have been isolated and separated by chromatographic means. Since this species is durable, bioactivity of several fractions has been determined. The bioactivity has been determined by the brine shrimp lethal bioassay. Less polar compounds with a low molecular weight average possess a high toxicity therefore contribute to the overall durability of this species. More polar fractions with higher molecular weight averages are non-toxic. The polymeric material with Mw = 13,550 g/mole, termed phlobaphene, has been purified. The analyses of western juniper phlobaphene by Fourier Transformed Infrared spectroscopy and 2D HMBC NMR (two dimensional Heteronuclear Multiple Bond Correlation) show that this is a heterogeneous polymeric material which reveals three long-range correlations. A long range labelled carbonyl correlation at around δ = 6.00 ppm corresponding to α-proton of β-O-4 type ether structures which is comparable to similar correlations found in lignins. The two other long-range correlations at around δ = 5.00 ppm and δ = 5.30 ppm are not assignable to any lignin-like structure. The 2D HMBC experiment can be used as an improved quantitative NMR technique for the assessment of labelled lignins and phlobaphenes. The ¹³C NMR has a potential applicability as an improved technique for quantitative analyses of labelled lignins.