title: Characterization of noncovalent interactions between 6-propionyl-2-dimethylaminonaphthalene (PRODAN) and dissolved fulvic and humic acids.
abstract: Noncovalent interactions between the fluorescent probe 6-propionyl-2-dimethylaminonaphthalene (PRODAN) and dissolved Norman Landfill leachate fulvic acid, Suwannee River fulvic acid, Suwannee River humic acid, and Leonardite humic acid were examined as a function of pH, fulvic and humic acid (FA and HA) concentration, and solvent polarity using steady-state fluorescence spectroscopy. Static quenching processes, as indicated by linear Stern-Volmer plots and high K(d) values, were positively correlated with the % aromaticity of the FA and HAs, as well as with solution pH. Results illustrate that for FA molecules with relatively low % aromaticity values, solvophobic interactions between PRODAN and FA are the primary interaction mode. For HA molecules with higher % aromaticity, PRODAN engages in both solvophobic interactions and pi-pi interactions, in particular electron donor-acceptor interactions, via condensed aromatic, electron-accepting moieties inherent within HA molecules. Experiments modifying solvent polarity demonstrated that protonation of carboxylic acid functional groups at low pH ( approximately 4) increased the hydrophobicity of the dissolved FA and HA molecules, thereby enhancing noncovalent interactions with PRODAN through increased solvophobic forces.
authors.affiliation: School of Civil Engineering and Environmental Science, College of Engineering, The University of Oklahoma, Norman 73019, USA.
authors.forename: Praveen
authors.initials: P
authors.lastname: Gadad
authors.forename: Hongxia
authors.initials: H
authors.lastname: Lei
authors.forename: Mark A
authors.initials: MA
authors.lastname: Nanny
mesh_terms: D015081:2-Naphthylamine / Q000031:analogs & derivatives* / Q000737:chemistry; D001578:Benzopyrans / Q000737:chemistry*; D006812:Humic Substances; D012995:Solubility; D013050:Spectrometry, Fluorescence
chemical_list: D001578:Benzopyrans; D006812:Humic Substances; C038517:prodan; D015081:2-Naphthylamine; C005023:fulvic acid