Abstract
Sodium calix[6]arenehexasulfonic acid (SCX~6~) was introduced into polymer molecules by the cross‐linking of SCX~6~ with epichlorohydrin (PolySCX~6~) or by the covalent binding of carboxymethylated SCX~6~ to an amino group‐carrying vinyl polymer (Poly(SCX~6~HMA‐co‐AAm)). The complexation of bisphenol A (BPA) with the SCX~6~ 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 SCX~6~ group in the polymers, the association constant (K~assoc~) of BPA with the SCX~6~ group was evaluated and the value for BPA with the SCX~6~ group in Poly(SCX~6~HMA‐co‐AAm) was much larger than that with the non‐conjugated SCX~6~, 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 SCX~6~). The K~assoc~ value for bisphenol B (BPB) with a non‐conjugated SCX~6~ 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 (SPCX~6~) 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 SPCX~6~ cavity, resulting in the loss of freedom of both the SPCX~6~ and the guest molecules. The entropy change for the complexation of BPA with the SCX~6~ group in the polymer was less negative, probably because of a partial release of water molecules around the SCX~6~ 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 = C~3~H~7~, sodium propyloxycalix[6]arenehexasulfonic acid; R = C~4~H~9~, sodium butyloxycalix[6]arenehexasulfonic acid; R = C~6~H~13~, sodium hexyloxycalix[6]arenehexasulfonic acid.
magnified imageChemical structure of various calix[6]arenes: R = H, sodium calix[6]arenehexasulfonic acid; R = C~3~H~7~, sodium propyloxycalix[6]arenehexasulfonic acid; R = C~4~H~9~, sodium butyloxycalix[6]arenehexasulfonic acid; R = C~6~H~13~, sodium hexyloxycalix[6]arenehexasulfonic acid.