3-DIMENSIONAL, MOLECULAR-STRUCTURES OF HUMIC ACIDS AND THEIR INTERACTIONS WITH WATER AND DISSOLVED CONTAMINANTS

A novel three-dimensional structural concept for humic acids (HAs) in soils and water was developed which was based on comprehensive investi gations combining geochemical, wet-chemical, biochemical, spectroscopi c, agricultural and ecological data with analytical pyrolysis. Direct, temperature-programmed pyrolysis in the ion-source of the mass spectr ometer combined with soft ionization in very high electric fields (Py- FIMS) and Curie-point pyrolysis-gas chromatography/mass spectrometry ( Py-GC-MS) were the principal analytical methods for the proposed humic acid monomer. Emphasis was put on molecular modeling and geometry opt imization of humic complexes with biological and anthropogenic substan ces using modern PC software (HyperChem) in order to determine low ene rgy conformations, space requirements, voids, as well as inter- and in tramolecular hydrogen bonds. Initial simulations of molecular model st ructures of humic acids for trapping and binding of water molecules an d humic-contaminant complexes with pentachlorophenol dissolved in wate r are illustrated. Molecular mechanics calculations are reported (a) t o visualize interactions between humic acid and water as well as humic acid and contaminant; (b) to describe the nanochemistry (e.g. bond di stances, angles, torsions, bends, van der Waals forces and inter- and intramolecular hydrogen bonds) of humic acids and their complexes in v acuum and in aqueous solution; and (c) to introduce experiments using periodic boxes containing water molecules with dissolved humic-contami nant complexes.