One-dimensional and two-dimensional NMR studies of atrazine and simple organic compounds sorbed by humic acid micelles.

摘要

This thesis addresses the following research questions: (1) how does the herbicide atrazine bound to humic macromolecules; (2) are synthetic surfactants, like sodium dodecyl sulfate (SDS), a good representation of humic micelles; (3) what is the structure and conformation of humic macromolecules ; and (4) how do simple organic molecules bind to humic macromolecules?; Using hydrophilic and hydrophobic paramagnetic probes, we did a nuclear magnetic resonance study that shows atrazine solubilized by concentrated humic acid solutions occupies a domain accessible only to neutral hydrophobic probe and, hence, confirms the existence of hydrophobic domains, located at the interior of humic macromolecular aggregates.; Though micellar solutions of both the synthetic surfactant SDS and humic acids solubilize atrazine, the behavior of atrazine in humic micellar solutions differs markedly from SDS micellar solutions in the following ways: (1) amazine forms dimers in SDS micelles but not in humic micelles; (2) atrazine molecules are anchored to the hydrophobic domain of humic acids through hydrogen-bonding; (3) only polar organic solvents capable of hydrogen-bonding can break the bonds binding atrazine to humic acid molecules.; Two-dimensional homonuclear 1H nuclear Overhauser effect spectroscopy (NOESY) of humic acid solutions reveals pH-dependent changes in humic acid conformation in aqueous solution. The lack of cross-peaks spanning aliphatic structures in the pH 13 NOESY spectrum supports a chain-like primary structure for humic structures. As pH decreased, aliphatic structures fold together, indicating humic aliphatic domains are flexible whereas humic aromatic domains are rigid because they do not fold. Humic aromatic domains seem not interact with aliphatic domains.; Two-dimensional NOESY of humic acid solutions also reveals the partitioning of simple organic molecules into aliphatic rich domains and unusual folding of linear aliphatic compounds in humic acid micelles as follows: (1) organic solutes do not partition into humic aromatic domains; (2) hydrogen-bonding shifts the partitioning to oxygen-substituted aliphatic domains; and (3) 1-octanol and 2-octanone are folded in humic acid micelles, suggesting cage-like structures form within humic aliphatic phatic domains.