Three-dimensional fluorescence analysis of chernozem humic acids and their electrophoretic fractions

摘要

Polyacrylamide gel electrophoresis in combination with size-exclusion chromatography (SEC-PAGE) has been used to obtain stable electrophoretic fractions of different molecular size (MS) from chernozem humic acids (HAs). Three-dimensional fluorescence charts of chernozem HAs and their fractions have been obtained for the first time, and all fluorescence excitation-emission maxima have been identified in the excitation wavelength range of 250-500 nm. It has been found that fractionation by the SEC-PAGE method results in a nonuniform distribution of protein- and humin-like fluorescence of the original HA preparation among the electrophoretic fractions. The electrophoretic fractions of the highest and medium MSs have only the main protein-like fluorescence maximum and traces of humin-like fluorescence. In the electrophoretic fraction of the lowest MS, the intensity of protein-like fluorescence is low, but the major part of humin-like fluorescence is localized there. Relationships between the intensity of protein-like fluorescence and the weight distribution of amino acids have been revealed, as well as between the degree of aromaticity and the intensity of humin-like fluorescence in electrophoretic fractions of different MSs. The obtained relationships can be useful in the interpretation of the spatial structural organization and ecological functions of soil HAs.