Cyclodextrin dimers as receptor molecules for steroid sensors

The dansyl-modified dimer 9 complexes strongly with the steroidal bile salt s Relative to native beta -cyclodextrin, the binding of cholate (la) and de oxycholate (1b) salts is especially enhanced. These steroids bind exclusive ly in a 1:1 fashion. For other bile salts (le-le) both 1:I and 1:2 complexe s were observed with stabilities similar to those of native B-cyclodextrin. This indicates that only one cavity is used. with a small contribution fro m the second. The difference is attributed to the absence of a 12-hydroxy g roup in the second group of steroids. Comparison with a dimer that lacks th e dansyl moiety (6) shows that this group especially hinders the cooperativ e binding of la and 1b. The smaller interference in the binding of the othe r steroids indicates that self-inclusion of the dansyl moiety hardly occurs . This weak self-inclusion is supported by fluorescence studies. The dansyl fluorescence of dimer 9 is less blue-shifted than that of other known dans yl-appended cyclodextrin derivatives; this is indicative of a more polar mi cro-environment. Addition of guests causes a change in fluorescence intensi ty.