kilomentor | 01 December, 2010 11:45
I had occasion to read a review, Past, Present and Future of Cyclodextrin Research, Jozsef Szejtii, Pure Appl. Chem. 76(10) 1825-1845 (2004).
I did not realize how practical use of cyclodextrins for separation might be. Beta cyclodextrin only costs $2-5 dollars per kilogram. Beta cyclodextrin has a molecular weight of 1,134 and if it forms a 1:1 complex with a drug substance mw. about 500, a kilogram would complex about 500 gm of API. That is the cyclodextrin to complex a kilogram of such API would be between 4 and 10 dollars. Nor did I realize that cyclodextrin can form very strong complexes which will take an insoluble drug into aqueous solution. Beta cyclodextrin forms a strong complex with cholesterol which then crystallizes.
A cyclodextrin complex may be quite stable while in water solution but when it is dried completely the stability of the complex can completely disappear because it is the removal of the hydrophobic interactions in bulk water that accounts for the stability of the complex. When the water is removed the basis for the stabilization is removed and one gets just an intimate powder mixture.
One would anticipate therefore that slurrying a mixture of two essentially water insoluble compounds, one of which forms a stabilized inclusion complex and another that does not, would partition the former into aqueous solution and leave the latter undissolved.
Solvent switching to an organic solvent should cause the organict hat had been complexed to move into the organic layer and a complex of the new organic solvent (if that solvent forms a complex) and cyclodextrin to precipitate.