title: Molecular structures and associations of humic substances in the terrestrial environment.
abstract: Here we show, for the first time, evidence of the primary molecular structures in humic substances (HS), the most abundant naturally occurring organic molecules on Earth, and their associations as mixtures in terrestrial systems. Multi-dimensional nuclear magnetic resonance (NMR) experiments show us that the major molecular structural components in the mixtures operationally defined as HS are aliphatic acids, ethers, esters and alcohols; aromatic lignin derived fragments; polysaccharides and polypeptides. By means of diffusion ordered spectroscopy, distinct diffusion coefficients consistent with relatively low molecular weight molecules were observed for all the components in the mixtures, and saccharides were the largest single class of component present. Liquid chromatography NMR confirmed that HS components can be easily separated and nuclear Overhauser effect (NOE) enhancements support the finding that the components are of relatively low molecular weight <approximately 2,000 Da. The widely recognized properties of HS, i.e., characteristics indicative of crosslinked, macromolecular networks, can now be explained as aggregation of mixtures, most likely instigated by complexation with metal cations.
authors.affiliation: Department of Chemistry, Ohio State University, Columbus 43210, USA. asimpson@chemistry.ohio-state.edu
authors.forename: André J
authors.initials: AJ
authors.lastname: Simpson
authors.forename: William L
authors.initials: WL
authors.lastname: Kingery
authors.forename: Michael H B
authors.initials: MH
authors.lastname: Hayes
authors.forename: Manfred
authors.initials: M
authors.lastname: Spraul
authors.forename: Eberhard
authors.initials: E
authors.lastname: Humpfer
authors.forename: Peter
authors.initials: P
authors.lastname: Dvortsak
authors.forename: Rainer
authors.initials: R
authors.lastname: Kerssebaum
authors.forename: Markus
authors.initials: M
authors.lastname: Godejohann
authors.forename: Martin
authors.initials: M
authors.lastname: Hofmann
mesh_terms: D000818:Animals; D001419:Bacteria / Q000378:metabolism; D017753:Ecosystem; D005658:Fungi / Q000378:metabolism; D006812:Humic Substances / Q000378:metabolism*; D010944:Plants / Q000378:metabolism*
chemical_list: D006812:Humic Substances