Recognition of steroids by self-assembled monolayers of calix[4]arene - Resorcin[4]arene receptors

Calix[4]arene-resorcin[4]arene (2:1) receptor adsorbate 2 equipped with fou r didecyl, sulfide groups self-assembles in monolayers (SAMs) on gold. Thes e monolayers were characterized by contact angle measurements, polarized in frared external reflectance spectroscopy (PIERS), electrochemical capacitan ce and resistance measurements, and X-ray photoelectron spectroscopy (XPS). Interactions of a monolayer of 2 with steroid guests were investigated by surface plasmon resonance (SPR) spectroscopy. The results show that steroid s interact more strongly with a monolayer of 2 than with a hydrophobic refe rence monolayer of octadecanethiol. There is virtually no detectable intera ction with a hydrophilic reference monolayer of 11-mercaptoundecan-1-ol. Mi xed monolayers of 2/11-mercaptoundecan-1-ol and of 2/decanethiol showed low er SPR responses with the steroids than the pure monolayer of 2. Concentrat ion-dependent experiments with prednisolone-21-acetate, corticosterone-21-a cetate, and cortisone-21-acetate on the mixed monolayer showed Langmuir-typ e adsorption with affinity constants between 2.0 x 10(5) and 3.5 x 10(5)M(- 1).