Investigation of silica-lignin interaction. Application of AFM and fluorescence techniques

Abstract

In this study, we investigated, in an in vitro system, the interaction of SiO2 (as a complex with NH4OH) with the peroxidase-catalyzed polymerization of lignin monomer into lignin model compound DHP, imitating conditions of the last step of lignin formation in the cell walls. The structure of obtained polymer was monitored using fluorescent spectroscopy and AFM 30 minutes after the start of synthesis. We studied effect of two different Si concentrations, 0.6 mM and 6 mM. Analysis of the DHP fluorescent spectra, and the application of mathematical decomposition clearly shows that structure of lignin model compound depends on Si concentration in the reaction mixture. The amount of Si affects the distribution of electrons in the DHP polymer. When silicon is present at a concentration of 6 mM, the position of the longest-wavelength APD band shifts towards shorter wavelengths compared to the position of the APD band for 0.6 mM Si. This indicates that during polymer synthesis, higher concentration of silicon may inhibit the formation of pi-electronic structures, which are responsible for electron delocalization. AFM images also show differences in the size and regularity of DHP globules.