Accessibility of hydroxyl groups of brown-rot degraded spruce wood to heavy water

The accessibility of alcoholic and phenolic hydroxyl (O-H) groups in non-degraded and brown-rot degraded spruce wood (Piceas abies L. Karst.) was investigated with Fourier transform near infrared (FT-NIR) transmission spectroscopy in combination with deuterium exchange with heavy water (D2O). In the presence of excess D2O, accessible O-H groups were converted into O-D groups and characteristic O-H first overtone bands disappeared in the FT-NIR spectra. Hydroxyl groups of cellulose I-alpha were more accessible than those of cellulose I-beta. O-H groups of wood degraded by brown-rot fungi showed much lower overall accessibility, and free O-H groups from amorphous matrix polysaccharides, preferentially those located in primary and outer secondary cell walls and middle lamellae were least accessible, whereas H-bonded O-H groups associated with cellulose microfibrils showed residual accessibility in brown-rotted wood of incipient, early and pronounced degradation stages.