Complexation of Bisphenol A with Calix[6]arene‐Polymer Conjugates

Abstract

AbstractSodium calix[6]arenehexasulfonic acid (SCX6) was introduced into polymer molecules by the cross‐linking of SCX6 with epichlorohydrin (PolySCX6) or by the covalent binding of carboxymethylated SCX6 to an amino group‐carrying vinyl polymer (Poly(SCX6HMA‐co‐AAm)). The complexation of bisphenol A (BPA) with the SCX6 group in the polymers was examined fluorimetrically using acridine red (AR) as a probe. From the inhibitory effect of BPA on the complexation of AR with the SCX6 group in the polymers, the association constant (Kassoc) of BPA with the SCX6 group was evaluated and the value for BPA with the SCX6 group in Poly(SCX6HMA‐co‐AAm) was much larger than that with the non‐conjugated SCX6, probably because of the support of hydrophobic interactions between the guest and the hydrocarbon moieties in the polymer (polymer main chain and hexamethylene groups introduced for the conjugation of SCX6). The Kassoc value for bisphenol B (BPB) with a non‐conjugated SCX6 was larger than those for bisphenol A and bisphenol F, because of the higher hydrophobicity of BPB among the bisphenols examined. Thermodynamic parameters indicated that the inclusion of BPA into the cavity of sodium propyloxycalix[6]arenehexasulfonic acid (SPCX6) was enthalpy driven, and the entropy change was largely negative (−92 J · mol−1 · K−1). This is probably because of a tight fit of guest molecules in the SPCX6 cavity, resulting in the loss of freedom of both the SPCX6 and the guest molecules. The entropy change for the complexation of BPA with the SCX6 group in the polymer was less negative, probably because of a partial release of water molecules around the SCX6 group upon the complexation. The effect of the structure of guest and host molecules on the complexation was also examined.Chemical structure of various calix[6]arenes: R = H, sodium calix[6]arenehexasulfonic acid; R = C3H7, sodium propyloxycalix[6]arenehexasulfonic acid; R = C4H9, sodium butyloxycalix[6]arenehexasulfonic acid; R = C6H13, sodium hexyloxycalix[6]arenehexasulfonic acid.magnified imageChemical structure of various calix[6]arenes: R = H, sodium calix[6]arenehexasulfonic acid; R = C3H7, sodium propyloxycalix[6]arenehexasulfonic acid; R = C4H9, sodium butyloxycalix[6]arenehexasulfonic acid; R = C6H13, sodium hexyloxycalix[6]arenehexasulfonic acid.