Release kinetics of nicotinamide from fatty acid-nicotinamide equimolar complexes. II. Activation thermodynamic quantities

Article abstract of DOI:10.1248/cpb.39.3114

The rates of release of nicotinamide (NAA) from fatty acid (FA)-NAA complexes, FA-NAA, were determined at various temperatures, and the thermodynamic quantities for the release of NAA were estimated. The results were compared with the previous results obtained for FA-thiamine disulfide (TDS) complexes, (FA)₆(TDS). The values of activation enthalpy (Δ H(≠)) and activation entropy (Δ S(≠)) for the release of NAA from FA-NAA were positive and negative, respectively, indicating that the release of NAA is disadvantageous from not only enthalpic but also entropic viewpoints. The plots of ΔH(≠) against the carbon number (n) in the constituent FA showed a zig-zag line with an upward convex at an odd-numbered position and the polts of the absolute values of -ΔS(≠) showed a zig-zag line with a downward convex at an odd-numbered position, though the positive value of ΔH(≠) increases and the negative value of Δ S(≠) decreases with an increasing n for either even-numbered or odd-numbered FA. It was found that the release of NAA from FA-NAA formed with odd-numbered FA is more disadvantageous enthalpically but more advantageous entropically as compared with that from FA-NAA formed with even-numbered FA. This phenomenon was similar to that observed for (FA)₆(TDS). Furthermore, it is suggested that FA-NAA is formed at least by van der Waals forces and hydrophobic interactions and that van der Waals forces are dominant for the formation of FA-NAA formed with odd-numbered FA and that hydrophobic interactions are dominant for the formation of FA-NAA formed with even-numbered FA.

Full text of DOI:10.1248/cpb.39.3114

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