Nuclear magnetic resonance spectroscopy of humic materials

Abstract

ALTHOUGH humic substances are some of the most important naturally occurring macromolecules in both soil and aqueous environments, their structures are still unknown. Our understanding of the components which comprise humic mixtures has been confined to the analysis of only minor portions (5–10%) of the total humic entity. It is, however, the whole humic aggregate, most of which is structurally unknown, which plays an active nutritional or transport role in nature. When the major fraction of humic matter, the alkali soluble substances, are studied, only poorly defined spectra have been obtained. Infrared, ¹H-NMR and ¹³C-NMR spectroscopic techniques have yielded unresolved spectra in which little detail can be distinguished^1–5. We report here that, using large magnetic fields and very high frequency (270 MHz) Fourier transform ¹H-NMR instrumentation, we have found that a wealth of detail can be obtained on the structure of humic solutions. A convolution difference method⁶ allows discrete signals to be detected above the general broad band absorptions in much the same way as important structural and dynamic information concerning proteins has been gathered.