ABSTRACT
All important hypotheses regarding humification are based on the concept of formation of molecules of humic substances by partial transformation of naturally occurring biomolecules or interaction of their structural units. From this viewpoint the inolecules of humic substances may be considered a combination of original or partially transformed biomolecules and their fragments, which provides a starting point for the search for their structural components. A rational selection of structural units must be based on the absolute yield of the products, the possibility of their secondary modification during destruction of humic substances and sources of possible incidental admixtures. Functional groups occupy a special place among the structural units of humic substances. They also enable us to evaluate the actual reactive capacity of HA, HMA and FA. Glebko examined the polyelectrolytic nature of HA for which a change in the apparent dissociation constant is quite possible with increasing substitution of protons in individual groups.
