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Self-assembled monolayers (SAMs) of crown ether adsorbates on gold reversibly bind metal ions from aqueous solutions. The resulting changes of the electrochemical properties of the monolayers were monitored by impedance spectroscopy. The increased dielectric constant of the layer due to the complexation of ions results in an increase of the monolayer capacitance (C ML). Analysis of the response curves with a Langmuir isotherm enables the determination of association constants of the SAMs with various metal ions. The cation binding also influences the charge-transfer resistance (R CT) of a redox couple Ru(NH3)6 2+/3+ in the electrolyte. Comparison of both responses allows an accurate interpretation of the origin of the resistive response. Furthermore, the association constants enable the quantitative determination of interactions between SAMs and metal ions, using either capacitive or resistive responses.

Resorcin[4]arene cavitands 2−4 were synthesized starting from tetrol 5. With these cavitand tetrasulfides, self-assembled monolayers (SAMs) on gold were prepared and characterized by electrochemical capacitance and resistance measurements, contact angle (CA) measurements, grazing angle FT-IR spectroscopy, and X-ray photoelectron spectroscopy (XPS). In situ surface plasmon resonance (SPR) spectroscopy was employed to study the host−guest interactions at the monolayer−water interface, between receptor adsorbates 1−4 and p-toluic acid, benzoic acid, p-nitrobenzoic acid, p-hydroxybenzoic acid, p-cresol, p-nitrophenol, and p-methoxyphenol. SPR results show that the presence of functional groups on the upper rim of the adsorbate molecules induces selectivity in the guest recognition process. Furthermore, it is interesting to note that such interactions are not directly related to the degree of hydrophobicity of the receptor adsorbate or of the guest. Concentration-dependent experiments were performed with p-nitrophenol as guest for a monolayer of adsorbate 1. At a 3 mM concentration of p-nitrophenol, approximately five to eight guest molecules associate with each adsorbate molecule, implying the formation of 1−4 layers of guests on the receptor surface.

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Abstract.C15H11NO4S2, Mr = 333.39, triclinic, P1, a =20.611(7), b=9.452(5), c=7.856(4) A, a---98.52 (3), /3 = 96.05 (2), 9' = 93.0 (3) °, V = 1502 (2) ]k 3, Z = 4, Dx = 1.475 g cm-3, a(Mo Ka) = 0.7107 A, /z = 3.55 cm-1, F(000) = 688, T = 293 K, R=0.051 (wR=0.059) for 3388 reflections. The asymmetric unit contains two independent molecules which have a similar conformation. The dithiole ring is planar in both molecules and makes an angle with the phenyl ring of 2. I and 0.6 °, respectively. Thus the methylene-l,3-dithiole unit (electron donor) has a maximum zr overlap with the phenyl ring, that bears a p-cyano group (electron acceptor). In both molecules the methyl esters are planar: one is almost parallel to the dithiole ring (angles of 9.8 and 8.5 °, respectively) and the other makes angles of 54.2 and 63.8 ° , respectively.Experimental.