SELF-ASSEMBLED MONOLAYERS OF HEPTAPODANT BETA-CYCLODEXTRINS ON GOLD

A route was developed for the synthesis of three different cyclodextri n adsorbates: yl)propionyl)]-2,3-di-O-methyl}-beta-cyclodextrin, yl)do decanoyl)]-2,3-di-O-methyl}-beta-cyclodextrin (a short and long alkyl chain sulfide cyclodextrin adsorbate, respectively), and opropionamidy l)-2,3-di-O-methyl]-beta-cyclodextrin (a short alkyl chain thiol adsor bate). Self-assembled monolayers on gold of these three cyclodextrin a dsorbates with seven sulfur moieties were fully characterized by elect rochemistry, wettability studies, X-ray photoelectron spectroscopy (XP S), and time-of-flight secondary ion mass spectrometry (TOF-SIMS). The electrochemical capacitance measurements show the differences between the thicknesses of the P-cyclodextrin monolayers, and the XPS-(S-2p) measurements show the different effectivenesses of the sulfur moieties of the three monolayers in their binding to the gold surface. Sulfide -based beta-cyclodextrin monolayers use on average 4.5 of the 7 attach ment 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 adsorba tes on gold obtained by XPS.