Solid state characterization of α-tocopherol in inclusion complexes with cyclodextrins.

The alternative for a pure soluble, sensible for physical and chemical conditions oil form of α-tocopherol (α-T) is its complexation with cyclodextrins. A different influence of cyclodextrins on the included substance demands a stability investigation of the substance enclosed in a host-guest complex. Hence, the thermal stability of α-T in inclusion complexes (InCs) with cyclodextrins (CDs) was studied. The inclusion complexes were obtained by two different methods: a lyophilization and a kneading method, and their formation was examined by IR spectroscopy, differential scanning calorimetry and 1H-NMR spectroscopy. The inclusion complexes were subjected to the test of accelerated aging at 323 K, 333 K, 338 and 343 K, for comparison α-T as a substance and physical mixtures (PhM) of α-T with CDs were used. Changes in α-T concentration during the experiment were followed by HPLC method and next, the products of thermal decomposition were studied by LC-ESI-MS/MS method. The reaction of α-T decomposition in inclusion complexes with CDs was found to be of the first order. The same order of a decomposition reaction was observed in a sample of α-T as a substance. It seems that cyclodextrins protect α-T against thermal decomposition, moreover, the protective effect of natural β-cyclodextrin (β-CD) appears to be greater than that of 2-hydroxypropyl-β-cyclodextrin (2-HP-β-CD). However, the CDs do not influence the type of a formed product of decomposition. This product, i.e., the dimer of α-T (m/z 859 Da), was found in all tested samples. The protective effect of CDs and transformation from the liquid state to the solid state of α-T can be used to create a new pharmaceutical form--tablets with α-T.