13C-NMR structural features of soil humic acids and their methylated, hydrolyzed and extracted derivatives

Abstract

13C-NMR spectra of aqueous solutions of three humic acids (1 Typic Chromoxerert (HA-V), 1 Humic Haplorthod (HA-P), and 1 Inceptisol (HA-D)) are presented. The influence of chemical modifications (hydrolysis with 6N HCl, diazomethane methylation, and organic solvent extraction) of the humic substances and their spectra is studied. The spectra of the various humic substances show significant differences. Methylation of the compounds introduces changes in the aromatic and aliphatic (sp3) region of the spectra. Acid hydrolysis removes residual carbohydrates and amino acid signals from the spectra, whereas solvent extraction has the most pronounced influence upon the aliphatic high field region of the spectra, and shows also, that a significant amount of the paraffinic carbons is bound covalently to the aromatic nuclei of the compounds.