Fluorine-19 nuclear magnetic resonance study of atrazine in humic and sodium dodecyl sulfate micelles swollen by polar and nonpolar solvents

Though sodium dodecyl sulfate (SDS) and humic micellar solutions both solubilize atrazine, the behavior of atrazine in humic micellar solutions differs markedly from SDS micellar solutions, in both the capacity to absorb solvents and the effect of these solvents on the chemical shift of atrazine within the solvent-swollen micelles. From this we conclude humic hydrophobic domains differ substantially from the SDS micellar core and the latter is not a suitable model for the former. Several lines of evidence, ranging from dimerization to partitioning between two-phase (solvent and micellar solution) systems, suggest atrazine forms strong, probably cooperative, hydrogen bonds when absorbed within humic hydrophobic domains. Polar hydrogen-bond donor or acceptor solvents can dissociate atrazine from humic molecules above a critical threshold, but nonpolar aprotic solvents seem unable to overcome the strong interactions that bind atrazine to humic molecules. Finally, humic micellar solutions exhibit a remarkable capacity to absorb organic solvents and most likely form stable microemulsions.