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

Abstract

Cyclodextrin derivatives modified with seven thioether moieties (1) or with one thiol moiety (2) bind to gold. Monolayers on gold of 1 or mixed monolayers of 2 and mercaptoundecanol were characterized by electrochemistry, wettability, and atomic force microscopy (AFM). Monolayers of 1 are well-ordered, but the order in the mixed monolayers depends on the ratio of 2 to mercaptoundecanol. With sufficient alkyl chains to fill the space under the cyclodextrin 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: however, the selectivity towards steroidal bile salts differs from solution. The mixed monolayers of 2, in which the cyclodextrin is less substituted and has more flexibility, bind steroidal guests (6a-6e) with the same selectivity as beta-cyclodextrin in solution.

Redox‐Controlled Interaction of Biferrocenyl‐Terminated Dendrimers with β‐Cyclodextrin Molecular Printboards

“…Figure 1 [32] Ferrocenemethanol gave a comparable binding constant of 9.9 10 3 m À1 , but with a less favorable DHA value of À6.1 kcal mol À1 and a more favorable TDSA value of À0.7 kcal mol À1 . [33] The large difference in DHA for BFc relative to Fc can be explained by the so-called "expanded hydrophobic surface", which has been proposed to explain trends observed for the inclusion of guests with an increasing number of aliphatic carbon atoms (N c ). [32] Dendrimer-b-CD assemblies: The apolar BFc dendrimers are virtually insoluble in water, but at pH 2 the addition of b-CD (b-CD/BFc = 10) resulted in soluble dendrimer-b-CD assemblies.…”

“…Previously, we showed that for small, monovalent guests the intrinsic binding constant at the surface K i,s is close to the intrinsic binding constant in solution K i,l . [39,40] To investigate if this also holds for BFc, titrations of 5 (aqueous solution at pH 12) against the b-CD SAM were performed and monitored by using SPR spectroscopy. Figure 4 shows the binding data and the fit to the Langmuir isotherm.…”

Electrochemical study of β-Cyclodextrin binding with ferrocene tethered onto a gold surface via PAMAM dendrimers

“…14 A possible explanation for our observations considers that the inclusion of ferrocene units inside the cyclodextrin cavity is mainly controlled by a positive entropic change ( Sº) for the water molecules which, 1,35 upon inclusion, are transferred from the hydrophobic basket-like cavity (S (12) Comparison of equations 11 and 12 allows to predict that the stability constants K for the interfacial Fc CD complexes (see Table 2) must be lower 36 than those observed in solution, 14 . This condition holds when we note that the dielectric constants, H2O , for interfacial and bulk water regions (related to water structure rigidity or entropy), are 6 and 80 respectively.…”

A Cyclodextrin Self-Assembled Monolayer (SAM) Based Surface Plasmon Resonance (SPR) Sensor for Enantioselective Analysis of Thyroxine

“…They have also been extensively used as chiral selectors in separation technology [18] and it has been shown that cyclodextrin based polymers could be used as sensitive layers in chiral sensing by SPR [16]. Reinhoudt has extensively studied the ability of these macrocycle to form well packed SAMs on gold surfaces [19][20][21][22][23][24].…”