Studies On Solubility Enhancement Of Fumaric Acid By Inclusion Complexes With Cyclodextrin And Its Derivatives

Cyclodextrins (CDs) are a kind of larger-ring compounds shaped like truncated cone. Their unique structure of interior hydrophobic cavity can include guestes that local in its special cavity or between its self—aggregation. They have exterior hydrophilic surface and thus water solubility of the poorly soluble guests by inclused can be promoted.α-cyclodextrin (α-CD) andβ-cyclodextrin (β-CD) are wide used for enhancing the solubility. Because of low solubility,β-CD is often improved by introducing modified groups into edges to extend its application. One of its derivatives often used as solubility increaser is hydroxypropyl-β-cyclodextrin (HP-β-CD), which has features of low toxicity and good water solubility.Fumaric acid commonly is a sort of food and forage additive. It is used as sourness regulator in food industry for its pure sour odour. It can accelerate intestine to assimilate the protein. Fumaric acid poor aqueous solubility confines its application in food and forage industry, so it is important to enhance its solubility in water to widen its applitication. In this paper, the complexation of poorly water-soluble fumaric acid withα-CD,β-CD and HP-β-CD were investigated respectively.(1) The intermolecular reaction between the host and guest agents, the effects of 3CDs on solubility of fumaric acid and thermodynamic parameters in the complexation were determined by the phase solubility. It was found that the inclusion type of fumaric acid withβ-CD was A_L and that with HP-β-CD andα-CD were A_N. The 1:1 molar ratio of inclusion complex of fumaric acid with each CD is spontaneously formed under the experimental temperatures. Fumaric acid formed more stable complexes withα-CD than with HP-β-CD andβ-CD, which might be due to a steric hindrance of substitutive group that prevented the guest molecule from entering the CD cavity and a relatively larger cavity that could not strongly hold the guest molecue. All thermodynamic parameters of△G,△H and△S in the complexations gave negative values. Furthermore, the complex process is enthalpically driven and exothermic.(2) Various methods such as co-grounding, ultrasonic method and co-precipitation were employed to prepare the inclusion complexes of fumaric acid withα-CD,β-CD or HP-β-CD. The dissolution profiles of the inclusion complexes were determined and compared with those of fumaric acid alone. Both the preparation technique and nature of the carriers played important roles in the dissolution performance of the systems. The dissolution profiles of the inclusion complexes ofα-CD orβ-CD by ultrasonic method and co-precipitation showed better performance than co-grounding, those of inclusion complex of HP-β-CD were not detected for the little yield of the product.(3) Binary systems of fumaric acid withα-CD,β-CD or HP-β-CD prepared by various methods were characterized by Infrared Absorption Spectroscopy. It was confirmed that the inclusion complexes of fumaric acid withα-CD,β-CD or HP-β-CD prepared by ultrasonic method and co-precipitation were formed, and the inclusion complexes of fumaric acid withα-CD,β-CD or HP-β-CD prepared by co-grounding methods were not formed.