Study On The Interactions Between Model Humic Subunits And Polycycilc Aromatic Hydrocarbons

The natural humic acids(HAs)have important impact on the nature of polycyclic aromatic hydrocarbons(PAHs)and can change its ecological effect,so the interaction between PAHs and HAs aroused widely attention.However,the complexity of the HAs' structure brings the difficulty to the research.In this thesis,some compounds,which include aromatic carboxylic acids(benzoic acid,o-hydroxybenzoic acid,p-hydroxybenzoic acid),fatty acids(3-phenylpropionic acid),N-heterocyclic ring substance(o-phenanthroline), and the substance of fatty acid and N-heterocyclic ring coexistence(folic acid),were selected as the model humic subunits to represent certain part characteristic of HAs.The interaction modes between anthracene,which is one of the typical PAHs,and the model humic subunits were determined using UV difference spectrum and IR spectrum.The stochiometric ratio and association constants were determined using fluorescence quenching method. According to the experiment results,a preliminary discussion on the interaction between anthracene and the special construction of natural HAs was also doneThe aromatic carboxylic acid is the main acidic functional group of HAs.The experiment results showed that there was strong specific intermolecular interaction existed between the aromatic carboxylic acids and PAHs,and the bonding mode has structure and solution acidity dependency.π-H hydrogen bond was in the interaction process between proton of aromatic carboxylic acid and anthracene,but it was easily affected by the solution acidity and the relative location of the acid functional group and other substituted group.When pH＞pK_a, theπ-H hydrogen bond was destroyed by decomposing of carboxylic proton,and theπ-πelectron donor-acceptor interaction became the main association mode.If a hydroxyl group was coexisted with carboxylic acid on one aromatic ring,its effect was different according to their relative locations.When the hydroxyl group was located on the ortho-place of carboxyl, the bonding mode remained unchanged,but the intensity became weaken.When hydroxyl was located on the para-place of carboxyl,the bonding mode was always theπ-πinteraction and the intensity obviously enhanced no matter solution acidity,because the special D-π-A structure ofp-hydroxybenzoic acid made it easily to form the planar multi-molecule polymer that could interact with PAHs.The experiment results also showed thatπ-πelectron donor-acceptor interaction played a role in association of N-heterocyclic ring substance with anthracene,and the bonding intensity was increased with acidity enhanced because of the protonization of N atom.When fatty acid and N-heterocyclic ring coexisted in solution,fatty acid could act as the main proton donor for the protonization of N atom,as the flexibility and deformability of the single bond made the carboxyl proton to approach N atom.