Self-assembled monolayers of metallosalophenes on gold

Salophene complexes of transition metals exhibit a reversible electro- chemistry. We have synthesized salophene complexes with sulfur-containing substituents aimed at the formation of self-assembled monolayers on a gold surface. Such monolayers have interesting cation complexating properties. The monolayers were fully characterized by wettability studies, grazing-angle Fourier transform infrared spectroscopy (FT-IRS), X-ray photoelectron spectroscopy (XPS), time-of-flight secondary-ion mass spectrometry (TOF-SIMS), and electrochemical capacitance measurements. These measurements indicate liquid-like monolayers. Cation complexation could be monitored indirectly by electrochemical impedance spectroscopy measurements, showing responses for Na+ and K+. This complexation behavior of the metallosalophene monolayers could not be studied directly by electrochemistry of the metallosalophene either due to electrochemical instability of the monolayer or a smeared redox response

Coupling of acid-base and redox functions in mixed sulfide monolayers on gold

A mixed acid-ferrocene self-assembled sulfide monolayer on gold shows a pH-dependent electrochemical response by through-space communication between the receptor and ferrocene readout unit

Electrochemical stability of self-assembled monolayers on gold

Most applications of functionalized self-assembled monolayers (SAMs) are based on changes in electrochemical properties. Such applications require electrochemical stability. This study reveals that there is only a limited potential window from -0.8 to +0.4 VMSE where self-assembled monolayers of sulfur-containing adsorbates (thiols and alkyl sulfides) on gold are electrochemically stable. A sensitive parameter describes the quality/stability of the monolayers (viz. the charge-transfer resistance). The substitution pattern of the adsorbates influences the window. Highly ordered monolayers, like that of tetrasulfide-based cavitand (10), are more resistant to extreme potentials. The stability window from -0.9 to +0.5 VMSE for this sulfide-based monolayer is comparable to that for a decanethiol monolaye

Synthesis, characterization and thin film formation of end-functionalized organometallic polymers

Poly(ferrocenyldimethylsilanes) (PFS) end-functionalized by ethylene sulfide form stable, electroactive layers on Au. \u

Self-assembled monolayers of heptapodant ß-cyclodextrins on gold

A route was developed for the synthesis of three different cyclodextrin adsorbates: heptakis{6-O-[3-(thiomethyl)propionyl)]-2,3-di-O-methyl}-ß\ud -cyclodextrin, heptakis{6-O-[12-(thiododecyl)dodecanoyl)]-2,3-di-O-methyl}-ß\ud -cyclodextrin (a short and long alkyl chain sulfide cyclodextrin adsorbate, respectively), and heptakis[6-deoxy-6-(3-mercaptopropionamidyl)-2,3-di-O-methyl]-ß-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 ß-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 -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

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

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