Thermodynamic Study on Release of Thiamine Disulfide (TDS) from TDS-Higher Fatty Acids Complexes. : I. Effect of Even-Numbered Fatty Acids

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The rates of release of thiamine disulfide (TDS) from higher fatty acid-TDS complexes were determined in a JP XI dissolution test apparatus in JP XI disintegration test medium No. 1 (pH 1.2) at various temperatures, and the thermodynamic quantities for the release of TDS from the complexes were estimated. The concentration of TDS was determined spectrophotometrically.The rate of release of TDS from the complexes decreased with increasing carbon number in the fatty acid and increased at higher temperature. The values of free energy change ΔG, entropy change ΔS, and enthalpy change ΔH for the release of TDS from the complexes were all positive. The release of TDS from the complex was found to be an enthalpically controlled reaction.The release of TDS from octadecanoic acid-TDS complex, (SA)_6(TDS), was found to be most disadvantageous from the enthalpic viewpoint and most advantageous from the entropic viewpoint as compared with the complexes formed with hexadecanoic acid and tetradecanoic acid. Furthermore, the largest value of activation energy for the release of TDS from (SA)_6(TDS) was found to correspond to the largest positive value of free energy change for the release of TDS.
1989-10-25