Molecular engineering 6. The enhancement of binding ability and selectivity of a cavitand by solubilizing in basic water

Molecular recognition in aqueous media is particularly interesting due to i ts similarity to a variety of biological phenomena. Designed aqueous host-g uest complexation is stabilized by various noncovalent interactions, especi ally by hydrophobic interaction. It is difficult to design a host having hi ghly organized hydrogen bonding interactions for guest, which is the most f requent in nature, due to the difficulty to compete with the strong water i nteraction to guests. If a container host(2) is to be a candidate for biological application, it should not only bind a wide variety of biologically active molecules with a high controllable selectivity and stability but it should be soluble in wa ter not far from physiological pH values.(3) CPK molecular model study shows that cavitand 4 has a well-shaped cavity co mplementary to EtOH, THF, toluene, xylene, and DMA etc., but it was only a weak THF binder at low temperature (K-a = 14 M-1 at -40 degrees C in (CDCl2 )(2)).(4) To increase its binding ability by enforcing hydrophobic interact ion, the basic-water soluble cavitand 6 was obtained and characterized.