The complexation of estrogens and tetralins in the cavities of azoniacyclophanes. A 1H and 13C nuclear magnetic resonance spectroscopic study

Abstract

¹ H N.m.r. shift titrations of e.g. estradiol (2), 2-tetralol (6), and the corresponding phenoxides (3) and (4) with an azoniacyclophane (CP6), containing diphenylmethane and n-hexane chains, in aqueous methanol shows association constants K between 20 and 250 l mol^–1, corresponding to 10²–10⁵ l mol^–1 in neat water (by extrapolation). The binding constants are approximately double for the steroid compared with the tetralin derivatives, although the cavity can encompass only the A and B rings of the estrogen. The enlarged cavity in a cyclophane containing n-octane chains (CP8) does not lead to increased binding of the steroid, but to a decrease by a factor of 2.5. ¹H N.m.r. complexation-induced shifts (c.i.s.) indicate the insertion of tetralin derivatives and of the corresponding A and B steroid rings inside the cyclophanes. The corresponding ¹³C c.i.s. values, although relatively large, are shown to give no reliable information about the geometries of the inclusion complexes in solution.