A STUDY OF LIGNIN FORMATION AT THE MOLECULAR-LEVEL BY SCANNING-TUNNELING-MICROSCOPY

A scanning tunneling microscope (SIM) was used to observe the temporal formation and organization of dehydrogenative polymer (DHP) synthesiz ed from coniferyl alcohol. The images obtained elucidate this structur e for the first time. The structure of DHP, as seen from STM images, s hows long-range order. It appears that DHP consists of building units or modules assembled into larger assemblies called supermodules. Super modules are interconnected into the overall lattice-like polymer struc ture with or without spherical regions. One module consists of about 2 0 monomers, while the supermodule contains about 500 monomers. Calcula ted molecular weights for modules and supermodules agree with DHP mole cular weight distribution peaks. Samples prepared at two different pH values, 6.4 and 7.6, have the same characteristics. The results presen ted demonstrate that the process of lignification, even in in vitro co nditions, is highly ordered, and as such contribute to our understandi ng of the structure of lignin, a significant constitutive and function al element of cell walls.