Host-guest interactions at self-assembled monolayers of cyclodextrins on gold


Beulen, Marcel W.J. and Bugler, Jürgen and Jong, Menno R. de and Lammerink, Ben and Huskens, Jurriaan and Schönherr, Holger and Vancso, G. Julius and Boukamp, Bernard A. and Wieder, Herbert and Offenhauser, Andreas and Knoll, Wolfgang and Veggel, Frank C.J.M. van and Reinhoudt, David N. (2000) Host-guest interactions at self-assembled monolayers of cyclodextrins on gold. Chemistry: a European Journal, 6 (7). pp. 1176-1183. ISSN 0947-6539

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Abstract:We have developed synthesis routes for the introduction of short and long dialkylsulfides onto the primary side of α-, β-, and γ-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 β-cyclodextrin monolayers a quasihexagonal lattice with a lattice constant of 20.6 Å, which matches the geometrical size of the adsorbate. The α-cyclodextrin and γ-cyclodextrin monolayers are less ordered. Interactions of the anionic guests 1-anilinonaphthalene-8-sulfonic acid (1, 8-ANS) and 2-(p-toluidinyl)naphthalene-6-sulfonic acid (2, 6-TNS) and the highly ordered monolayers of heptapodant β-cyclodextrin adsorbates were studied by surface plasmon resonance (SPR) and electrochemical impedance spectroscopy. The SPR measurements clearly showed interactions between a -cyclodextrin monolayer and 1, 8-ANS. Electrochemical impedance spectroscopy measurements gave high responses even at low guest concentrations (≤5 µM). The association constant for the binding of 1, 8-ANS (K=289 000±13 000 M-1) is considerably higher than the corresponding value in solution. (Partial) methylation of the secondary side of the β-cyclodextrin strongly decreases the binding.
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Copyright:© 2000 WILEY-VCH
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