Aggregation and counter ion binding ability of sulfonatomethylcalix[4]resorcinarenes in aqueous solutions

1H NMR spectroscopy, 1H NMR spin-lattice relaxation, conductivity and pH-metric titration data have been used to study the aggregation and counter-ion binding of tetrasulfonatomethylcalix[4]resorcinarenes with methyl (H8XNa4) and amyl (H8YNa4) substituents. The data obtained reveal the self-aggregation of H8YNa4 driven by hydrophobic interactions. The NMR relaxation data indicate that Gd3+ is bound by both H8XNa4 and H8YNa4. The Gd3+ ions were found to induce the aggregation of H8YNa4 with critical association concentration (CAC) value less than in case of its self-aggregation. Using Gd3+ as a probe of counter-ion binding with the aggregate interface it was found out that binding of quaternary ammonium cations (QUATSs) with H8YNa4 aggregates and SDS aggregates is quite different, while binding of inorganic ions by both types of aggregates is similar. The most outstanding peculiarity of QUATSs binding with H8YNa4 aggregates is selective recognition of QUATSs, possessing trimethylammonium group, detected by NMR relaxation method.