Fractal analysis of STM images of lignin polymer obtained by in vitro synthesis

Lignin, the structural polymer of the plant cell walls, is produced by free radical polymerization of phenolic alcohols, catalyzed by different peroxi dases. The mechanism and the structural organization of lignin in the cell have not been completely understood. In this study we applied fractal analy sis to images of lignin polymer obtained using scanning tunneling microscop e. The analysis showed the regularity of the polymer at different levels of organization. According to the results obtained, at the 95% confidence lev el, there is no significant difference in the fractal dimension between ima ges representing different organizational levels of lignin. In other words, lignin produced in in vitro conditions has fractal structural organization and, consequently the polymer can be expected to be regular in in vivo con ditions. The value of the fractal dimension 1.929 +/- 0.021 is in good agre ement with the theoretically predicted value for polyaddition and polyconde nsation mechanism of polymerization. The mechanism of in vivo lignin synthe sis is discussed in terms of various experimental and theoretical evidences . In this paper, we could show that fractal analysis of the lignin polymer is a useful complementary approach to the experimental data collection in s tructural and phenomenological studies.