Freeze-thaw cycles were used to produce morphologically dissimilar hum
ic acid fractions that showed evidence of possessing distinctly differ
ent molecular features. The kinetics of fluorescence enhancement produ
ced by the addition of Sm3+ ions to pyrene/humic acid solutions indica
ted that the ability to form pseudomicellar domains was vastly differe
nt among the fractions. C-13 NMR spectra bore out the suggestion that
the tendency of humic acid fractions to undergo intramolecular coiling
is related to their aliphatic content. Published by Elsevier Science
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