ACTIVATION THERMODYNAMIC QUANTITIES FOR THE RELEASE OF 3-AMINOPYRIDINE (3AP) FROM FATTY ACID-3AP EQUIMOLAR COMPLEXES

The rates of release of 3-aminopyridine (3AP) from fatty acid (FA)-3AP complexes, FA-3AP, were determined at various temperatures, and the t hermodynamic quantities of the release of 3AP were estimated. The resu lts were compared with previous results obtained for FA-nicotinamide ( NAA) complexes, FA-NAA. The values of activation enthalpy (DELTAH(not- equal)) and activation entropy (DELTAS(not-equal)) for the release of 3AP from FA-3AP were positive and negative, respectively, indicating t hat the release of 3AP is disadvantageous from not only enthalpic but also entropic viewpoints. The plots of DELTAH(not-equal) against the c arbon number (n) in the constituent FA showed a zig-zag line with an u pward convex at odd-numbered positions and the plots of the absolute v alues of \-DELTAS(not-equal)\ showed a zig-zag line with a downward co nvex at odd-numbered positions, though the positive value of DELTAH(no t-equal) increased and the negative ralue of DELTAS(not-equal) decreas ed with an increasing n for either even-numbered or odd-numbered FA. I t was found that the release of 3AP from FA-3AP formed with odd-number ed FA is more disadvantageous enthalpically but more advantageous entr opically as compared with that from FA-3AP formed with even-numbered F A. Furthermore, it is suggested that FA-3AP is formed by at least van der Waals forces and hydrophobic interactions. It was found that FA-3A P has similar physicochemical properties to FA-NAA and that the variat ion in physico-chemical properties of FA-3AP owing to the difference i n n is smaller than that of FA-NAA. This is considered to be due to th e fact that the packing of 3AP into the FA host cavity is looser than that of NAA.