Orientational effect of surface-confined cyclodextrin on the inclusion of bisphenols

The molecular recognition of various kinds of bisphenols (BPs) and a bisphenol A - polymer conjugate (BPA - polymer) by a self-assembled monolayer (SAM) of thiolated β-cyclodextrin (CD) on a gold electrode was examined using cyclic voltammetry (CV). Based on the inhibitory effect of BPs on the inclusion of hydroquinone (HQ) as a probe by the surface-confined CD, the association constants (K_assoc) of BPs with the immobilized β-CD were estimated. The K_assoc values for BPs with the SAM of 3-dithiobis-(undecanoylamido)-3-deoxy-β-cyclodextrin (DTUA-β-CD) were smaller than those in the free β-CD system reported previously. A similar tendency was obtained when 6-(lipoylamido)-6-deoxy-β-cyclodextrin (LPβ-CD) was used in place of DTUA-β-CD. The K_assoc values for all the BPs except for bisphenol B with the SAM of LP-β-CD were always larger than those with the SAM of DTUA-β-CD, due to a difference in the orientation of the β-CD moiety in the SAMs. Furthermore, adsorption and desorption processes of the BPA-polymer from the surface-confined β-CD was followed using local surface plasmon resonance spectroscopy.