Study of ascorbic acid interaction with hydroxypropyl-β-cyclodextrin and triethanolamine, separately and in combination

Complexation between ascorbic acid, hydroxypropyl-beta-cyclodextrin (HP-beta-CD) and triethanolamine (TEA), separately and in combination, was studied in solution and solid state. The freeze-drying method was used to prepare solid complexes, while physical mixtures being obtained by simple blending. These complexes were characterized in the solid state using differential scanning calorimetry (DSC) and infrared spectroscopy (IR). Nuclear magnetic resonance spectroscopy (H-1 and C-13 NMR) was used in aqueous solutions to obtain information about the mode of interaction. The degradation rate of each complex in solution was determined, and the stability constant of the complexes and the degradation rate of the ascorbic acid within the complexes were obtained. NMR studies provided clear evidence of partial inclusion into the HP-beta-CD cavity, but the stability constant value was very small indicating a weak host-guest interaction. The influence of complexation on the degradation rate of ascorbic acid was evaluated, and the data obtained showed a pronounced enhancement of aqueous stability with the TEA association complex, while this effect was lower with the HP-beta-CD inclusion complex. NMR experiments showed evidence of the formation of aggregates. (c) 2007 Elsevier B.V. All rights reserved.