Influencing the binding selectivity of self-assembled cyclodextrin monolayers on gold through their architecture

Cyclodextrin derivatives modified with seven thioether moieties (1) or with one thiol moiety (2) bind to gold. Monolayers on gold of 1 or mixed monola yers of 2 and mercaptoundecanol were characterized by electrochemistry, wet tability, and atomic force microscopy (AFM). Monolayers of 1 are well-order ed, but the order in the mixed monolayers depends on the ratio of 2 to merc aptoundecanol. With sufficient alkyl chains to fill the space under the cyc lodextrin moiety of 2, the monolayers are densely packed. Guest recognition at these monolayers in water was studied by surface plasmon resonance (SPR ) spectroscopy. For simple organic guests, monolayers, of 1 showed the same selectivity and binding strength as beta -cyclodextrin in solution; howeve r, the selectivity towards steroidal bile salts differs from solution. The mixed monolayers of 2, in which the cyclodextrin is less substituted and ha s more flexibility, bind steroidal guests (6a-6e) with the same selectivity as beta -cyclodextrin in solution.