Fractal analysis of STM images of photochemical polymer of coniferyl alcohol.

Fractal analysis was applied to images of photochemical lignin polymer obtained using scanning tunneling microscope. We studied the polymer obtained in vitro by ionic mechanism through UV radiation--induced polymerization. The analysis showed the regularity of the lignin-like polymer at different levels of organization. At the 95% confidence level, there was no significant difference in the fractal dimension between images representing different organizational levels of photochemical lignin. That means that lignin produced in in vitro conditions by photochemical mechanism of synthesis, has a fractal structural organization. The obtained values of the fractal dimension are in good agreement with the theoretically predicted value for the polyaddition and polycondensation mechanism of polymerization, known as the bulk model.

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 peroxidases. The mechanism and the structural organization of lignin in the cell have not been completely understood. In this study we applied fractal analysis to images of lignin polymer obtained using scanning tunneling microscope. The analysis showed the regularity of the polymer at different levels of organization. According to the results obtained, at the 95% confidence level, there is no significant difference in the fractal dimension between images 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 conditions. The value of the fractal dimension 1.929 +/- 0.021 is in good agreement with the theoretically predicted value for polyaddition and polycondensation mechanism of polymerization. The mechanism of in vivo lignin synthesis 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 structural and phenomenological studies.

A study of lignin formation at the molecular level by scanning tunneling microscopy.

A scanning tunneling microscope (STM) was used to observe the temporal formation and organization of dehydrogenative polymer (DHP) synthesized from coniferyl alcohol. The images obtained elucidate this structure for the first time. The structure of DHP, as seen from STM images, shows long-range order. It appears that DHP consists of building units or modules assembled into larger assemblies called supermodules. Supermodules are interconnected into the overall lattice-like polymer structure with or without spherical regions. One module consists of about 20 monomers, while the supermodule contains about 500 monomers. Calculated molecular weights for modules and supermodules agree with DHP molecular weight distribution peaks. Samples prepared at two different pH values, 6.4 and 7.6, have the same characteristics. The results presented demonstrate that the process of lignification, even in in vitro conditions, is highly ordered, and as such contribute to our understanding of the structure of lignin, a significant constitutive and functional element of cell walls.

Adrenocorticotropin binding activity of B16/C3 melanoma cells.

The binding of adrenocorticotropic hormone (ACTH) to B16/C3 murine melanoma cells was found to be specific and saturable. The binding capacity of the cells changed as a function of the age of the culture. Scatchard analysis revealed one class of high-affinity ACTH binding sites. The specificity of ACTH binding to the cells was tested by displacement experiments with human leukocyte interferon (alpha-IFN) and alpha-melanocyte stimulating hormone (alpha-MSH) as the competitors. Structure-activity relationship of ACTH, alpha-MSH and alpha-IFN was discussed.