SELF-ASSEMBLED MONOLAYERS OF CAVITAND RECEPTORS FOR THE BINDING OF NEUTRAL MOLECULES IN WATER

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). Insitu surface plasmon resonance (SPR) spectroscopy was employed to s tudy the host-guest interactions at the monolayer-water interface, bet ween receptor adsorbates 1-4 and p-toluic acid, benzoic acid, p-nitrob enzoic acid, p-hydroxybenzoic acid, p-cresol, p-nitrophenol, and p-met hoxyphenol, SPR results show that the presence of functional groups on the upper rim of the adsorbate molecules induces selectivity in the g uest recognition process. Furthermore, it is interesting to note that such interactions are not directly related to the degree of hydrophobi city of the receptor adsorbate or of the guest. Concentration-dependen t experiments were performed with p-nitrophenol as guest for a monolay er of adsorbate 1. At a 3 mM concentration of p-nitrophenol, approxima tely five to eight guest molecules associate with each adsorbate molec ule, implying the formation of 1-4 layers of guests on the receptor su rface.