Cyclodextrin Dimers as Receptor Molecules for Steroid Sensors

Abstract

The dansyl-modified dimer 9 complexes strongly with the steroidal bile salts. Relative to native beta-cyclodextrin, the binding of cholate (1a) and deoxycholate (1b) salts is especially enhanced. These steroids bind exclusively in a 1:1 fashion. For other bile salts (1c-1e) both 1:1 and 1:2 complexes were observed with stabilities similar to those of native beta-cyclodextrin. This indicates that only one cavity is used, with a small contribution from the second. The difference is attributed to the absence of a 12-hydroxy group in the second group of steroids. Comparison with a dimer that lacks the dansyl moiety (6) shows that this group especially hinders the cooperative binding of la and 1b. The smaller interference in the binding of the other 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 dansyl-appended cyclodextrin derivatives; this is indicative of a more polar micro-environment. Addition of guests causes a change in fluorescence intensity.

Influencing the Binding Selectivity of Self-Assembled Cyclodextrin Monolayers on Gold through Their Architecture

“…Comparison with the previously reported solution data [19] for the complexation of these steroids by b-cyclodextrin reveals that the association constants in solution are higher than those at the surface. More interestingly, there is a difference in selectivity.…”

“…[18] A class of steroids 6 a ± 6 e whose interaction with cyclodextrins has been well studied is that of the bile salts. Their recognition by cyclodextrin derivatives has been studied both by our group [19] and by others. [20] NMR experiments have shown that these steroids are complexed through the cavity, with the aliphatic side chain of the steroid entering the cyclodextrin from the secondary Table 2.…”

“…This difference may be explained by looking at the binding behavior in solution. In solution, steroids 1 a and 1 b are known to require a b-cyclodextrin dimer for strong complexation, [19] whereas the other steroids are already strongly complexed by native b-cyclodextrin. At the 9 % cyclodextrin surface, the cavities are fairly close to each other.…”

Complexation and (Templated) Synthesis of Rhenium Complexes with Cyclodextrins and Cyclodextrin Dimers in Water

“…The synthesis of compounds 13 (b 2 dpa) and 14 (b 2 dans) was published elsewhere. [16] 4,4'-Bis(bromomethyl)benzophenone [55] and TBDMS-protected b-cyclodextrin [56] were prepared by literature procedures.…”

Thermodynamics of Resulting Complexes Between Cyclodextrins and Bile Salts

“…Among the numerous guests researched, bile salts attracted much more attention because they are one kind of important surfactant-like biological amphipathic compounds possessing a steroid skeleton, which have distinctive detergent properties and play an important role in the metabolism and excretion of cholesterol in mammals [6]. For example: the thermodynamics and structure of inclusion compounds of glyco-and tauro-conjugated bile salts with CDs and their derivatives have been studied by Holm et al during the last years [7][8][9][10][11]; the interactions of different kinds of bile salts with -CD dimers linked through their secondary faces have been investigated by Reinhoudt and Vargas-Berenguel et al [12][13][14]. It has been demonstrated that the formation of inclusion complexes between CDs and guest molecules is cooperatively governed by several weak forces, such as van der Waals interactions, hydrophobic interactions, hydrogen bonding, electrostatic interactions, and every weak force does its contribution to the complexation.…”