Molecular size of humic substances. Supramolecular associations versus macromolecular polymers (Reprinted from Advances in Environmental Research, vol 3, pg 508-521, 2000)

摘要

This work illustrates recent experiments conducted by low-and high-pressure size exclusion chromatography (HPSEC) on humic substances of different origin and molecular structure. Solutions of humic substances were either injected as such into the HPSEC system that operated with eluents which differed in composition but were constant in ionic strength, or were previously modified with mineral and organic acids and then eluted in the HPSEC operating with a constant solution. The findings indicate that humic substances behave as associations of relatively small molecules rather than as macromolecular polymers. The weak association of humic molecules into supramolecular structures is stabilized by weak hydrophobic forces. Interactions with mineral and organic acids of different degrees of aliphaticity may reversibly disrupt the supramolecular association and separate smaller sub-units. The recognition that soil humus possesses supramolecular rather than polymeric properties is of importance in further understanding the function and reactivity of soil organic matter in the environment. [References: 57]