Characterizing the chemistry of artificially degraded Scots pine wood serving as a model of naturally degraded waterlogged wood using1H–13C HSQC NMR

Abstract

Chemically and biologically degraded Scots pine wood was prepared as a model material for the research on new conservation agents for waterlogged archeological wood. In this study, the model wood was characterized using a 2D¹H–¹³C solution-state NMR technique without derivatization, isolation, or extraction to assess the effect of applied degradation processes on its chemical composition and structure. The results clearly show how the two artificially degraded model wood types are chemically different. Biological decay by the brown-rot fungus Coniophora puteana caused degradation of wood polysaccharides, with heavy depletion in arabinan, mannan, and galactan, along with an increase in the cellulose's reducing ends (i.e., lowering the degree of polymerization) and partial deacetylation of mannan. The fungus cleaved roughly one-fifth of the β-aryl ethers in lignin, leading to a broadening effect on the lignin aromatic unit contours; other lignin sidechains were left untouched. Chemical degradation by NaOH hydrolysis resulted in a depletion in mannan, galactan, and glucan, as well as efficient deacetylation of mannan. It also decreased lignin content, causing changes in its structure; minor β-aryl ether cleavage along with substantial phenylcoumaran cleavage were evident. Detailed knowledge about the chemical composition and structure of artificially degraded model pine wood obtained in this research is necessary to understand the reactivity of these wood types with chemicals used for their conservation. This research will help explain the differences in the stabilization effectiveness observed between these wood types treated during conservation and understand the stabilization mechanisms, thus contributing to developing new, more effective conservation agents for wooden artifacts of Cultural Heritage.