A route was developed for the synthesis of three different cyclodextrin adsorbates:  heptakis{6-O-[3-(thiomethyl)propionyl)]-2,3-di-O-methyl}-β-cyclodextrin, heptakis{6-O-[12-(thiododecyl)dodecanoyl)]-2,3-di-O-methyl}-β-cyclodextrin (a short and long alkyl chain sulfide cyclodextrin adsorbate, respectively), and heptakis[6-deoxy-6-(3-mercaptopropionamidyl)-2,3-di-O-methyl]-β-cyclodextrin (a short alkyl chain thiol adsorbate). Self-assembled monolayers on gold of these three cyclodextrin adsorbates with seven sulfur moieties were fully characterized by electrochemistry, wettability studies, X-ray photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectrometry (TOF-SIMS). The electrochemical capacitance measurements show the differences between the thicknesses of the β-cyclodextrin monolayers, and the XPS-(S2p) measurements show the different effectivenesses of the sulfur moieties of the three monolayers in their binding to the gold surface. Sulfide-based β-cyclodextrin monolayers use on average 4.5 of the 7 attachment points whereas the thiol-based cyclodextrin monolayer only uses 3.2 of the 7 sulfurs. These experiments show that, for adsorbates with multiple attachment points, sulfides may be more effective than thiols. TOF-SIMS measurements confirm the robust attachment of these adsorbates on gold obtained by XPS.

Supramolecular host-guest interactions in aqueous environment were studied by dynamic single molecule force spectroscopy. The unbinding between ferrocene moieties immobilized on atomic force microscopy tips and -cyclodextrin receptors in highly ordered self-assembled monolayers on Au(111) was studied. The rupture force of individual ferrocene--cyclodextrin complexes was found to be 56 ( 10 pN. The value of this unbinding force was independent of the unloading rate. This was attributed to the fast (de)complexation kinetics of the host-guest complex.

We have developed synthesis routes for the introduction of short and long dialkylsulfides onto the primary side of a-, b-, and g-cyclodextrins. Monolayers of these cyclodextrin adsorbates were characterized by electrochemistry, wettability studies, X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), and atomic force microscopy (AFM). The differences in thickness and polarity of the outerface of the monolayers were measured by electrochemistry and wettability studies. On average about 70 % of the sulfide moieties were used for binding to the gold, as measured by XPS. Tof-SIMS measurements showed that the cyclodextrin adsorbates adsorb without any bond breakage. AFM measurements revealed for b-cyclodextrin monolayers a quasihexagonal lattice with a lattice constant of 20.6 , which matches the geometrical size of the adsorbate. The a-cyclodextrin and g-cyclodextrin monolayers are less ordered. Interactions of the anionic guests 1-anilinonaphthalene-8sulfonic acid (1,8-ANS) and 2-(p-toluidinyl)naphthalene-6-sulfonic acid (2,6-TNS) and the highly ordered monolay-ers of heptapodant b-cyclodextrin adsorbates were studied by surface plasmon resonance (SPR) and electrochemical impedance spectroscopy. The SPR measurements clearly showed interactions between a b-cyclodextrin monolayer and 1,8-ANS. Electrochemical impedance spectroscopy measurements gave high responses even at low guest concentrations ( 5 mm). The association constant for the binding of 1,8-ANS (K 289 000 AE 13 000 m À1 ) is considerably higher than the corresponding value in solution. (Partial) methylation of the secondary side of the b-cyclodextrin strongly decreases the binding.

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