A fluorescence quenching method was used to determine the equilibrium binding constants for the association of acridine, acridine orange, and acridine yellow G to humic acid. The fluorescence of each polycyclic aromatic nitrogen heterocycle (PANH) was monitored as aliquots of humic acid were added, and a Stern-Volmer plot was produced.  A van't Hoff plot generated from the equilibrium binding constants as a function of temperature for a given PANH resulted in a linear plot.  Calculation of the ?Hbinding, ?Gbinding, and ?Sbinding for each PANH leads to the conclusion that the equilibrium binding constant, and ?Gbinding, appear to be good predictors of bioavailability.  Acridine yellow G is the least bioavailable of the three PANHs studied because of its strong ?Hbinding = -29.8 kJ/mol which leads to ?Gbinding = -0.71 kJ/mol.  Thermodynamic values and equilibrium binding constants for all three compounds are reported.

Examination of the binding of PANHs to humic acid using fluorescence quenching

244th National Meeting (2012)

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