Polarized infrared microspectroscopy of single spruce fibers: hydrogen bonding in wood polymers.

We studied wood polymers in their native composite structure using mechanically isolated single spruce (Picea abies [L.] Karst.) fibers. Dichroic infrared spectra of fibers placed in a custom-built microfluidic cuvette were acquired in air, in liquid (heavy) water, and in liquid dimethylacetamide using a novel combination of synchrotron-based Fourier transform infrared microspectroscopy with polarization modulation. Differences were observed in the O-H stretching frequency region of the spruce spectra upon changing the ambient conditions. Analysis of these spectral variations provides information on hydrogen bonding, orientation, and accessibility of structural units of the wood polymers in the spruce cell walls. Our in situ approach contributes to a further understanding of the structural details of wood polymers in their native setting.