Probing cellulose structures with vibrational spectroscopy

This paper reviews principles, data interpretations, and applications of vibrational spectroscopic methods used for analysis of cellulose in the isolated state and in plant cell walls or lignocellulose biomass. The paper begins with reviewing the crystalline structures of crystalline cellulose polymorphs and the principles of three different vibrational spectroscopy methods-infrared (IR), Raman, and sum frequency generation (SFG)-complemented with density functional theory calculations. Then, it discusses the vibrational modes of crystalline celluloses, how the chain orientation in crystalline domain is analyzed in each method, and how the concentration and spatial distribution of crystalline cellulose domains interspersed in amorphous matrices are manifested or analyzed differently in these three methods. Lastly, the paper discusses examples of analyzing crystalline cellulose in plant cell walls or lignocellulose biomass with IR, Raman, and SFG including spectroscopic imaging. One review cannot cover all vibrational spectroscopy literatures on cellulose; this review aims at providing tutorial information, using selected literatures and experimental data, needed to interpret nano-, meso-, and micro-scale structures of cellulose in plant cell walls and lignocellulose biomass. [GRAPHICS] .