The use of lysine to enhance the supercritical complexation of ketoprofen andcyclodextrins

The inclusion complexation of ketoprofen and b-cyclodextrin, a natural cyclodextrin, is compared with that of ketoprofen and 2-hydroxypropyl-b-cyclodextrin, a chemically modified one. The experiments were performed through supercritical CO2impregnation varying temperature and pressure, and investigating the addition of small amounts of water and l-lysine to the samples before the supercritical treatment. The use of auxiliary agents, such as lysine, in supercritical complexation processes has been scarcely investigated until now. The best results were obtained at 70°C and 30 MPa for both systems and showed that complexation increased when water was added. Further addition of lysine resulted in considerable enhancement of the complexation yield: from 28 to 92% for the ketoprofen/-cyclodextrin system and from 55 to 83% for the ketoprofen/2-hydroxypropyl-b-cyclodextrin one. The comparison between the two systems highlight that, at the same water content, complexation is promoted when 2-hydroxypropyl-b-cyclodextrin is employed. Samples with higher amounts of water, instead, can be more conveniently prepared with b-cyclodextrin.