Host-Guest Interactions at Self-Assembled Monolayers of Cyclodextrins on Gold

Abstract

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.

Molecular printboards: versatile platforms for the creation and positioning of supramolecular assemblies and materials

“…Several years ago, we reported self-assembled monolayers of a b-cyclodextrin (CD) heptathioether derivative on gold (Fig. 6), 19 at that stage a logical extension of the ongoing efforts to immobilize various receptors on surfaces, e.g. for sensor development.…”

Anchoring and packing of self-assembled monolayers of semithio-bambusurils on Au(111)

“…Hence, with bound sulfur 2p 3/2 to the gold surface the XPS signal is observed at 161.9 eV compared to unbound sulfur 2p 3/2 observed at 163.4 eV. 10,12 Both XPS spectra of SAMs of 1 and 2 in the S 2p region showed broad peaks with a binding energy (BE) of sulfur (S2p 3/2 ) located around ∼162 eV (Fig. 2e and f).…”

“…The electrode adsorbs ions, resulting in an electrochemical double layer, which provides a capacitance to the surface. The capacitance of the monolayer electrical double layer (C dl ) is related to the effective thickness and order of the SAM on the gold substrate 10 and can be calculated from the measured current density.…”

“…[1][2][3][4][5][6][7][8] A high degree of order and dense packing of molecules in the film is a prerequisite for the use of SAMbased sensor devices. [9][10][11] Furthermore, the complexation sites must show high binding affinity and specificity to maximize the electrical response and minimize fouling. 12 One of the most useful SAM-based sensing devices involves immobilization of highly selective receptors to bind charged molecules and ions in electrochemical sensors and biosensing applications.…”

Individually addressable recessed gold microelectrode arrays with monolayers of thio-cyclodextrin nanocavities

“…Reinhoudt et al attached short and long chain dialkyl sulfides onto the primary side of a-, b-and c-CDs, assembled and characterised monolayers of these adsorbates on crystalline gold using a range of techniques, including electrochemistry and AFM. 12 They observed that b-CD monolayers formed well-ordered hexagonal structures whereas a-and c-CDs were less ordered. Other work on sulfur-modified CD derivatives for the preparation of monolayers on gold has been reported.…”