MOLECULAR RECOGNITION BETWEEN UNCHARGED MOLECULES IN AQUEOUS MICELLES

Micelles provide microenvironments that permit hydrogen bonding to occur between small molecules in aqueous solution. 1-Alkylthymine derivatives 2 hydrogen-bond (base-pair) with N-6-acetyl-9-alkyladenine derivatives 3 in the presence of sodium dodecyl sulfate (SDS) micelles but base-stack with the adenine derivatives in the absence of SDS. When the adenine-thymine interactions are analyzed by H-1 NMR titration, the adenine and thymine groups play different roles in the binding process; the thymine derivative acts as a receptor, whereas the adenine derivative acts as a ligand. For base pairing to be observed, the alkylthymine derivative must be sufficiently hydrophobic to be largely incorporated within the micelles. This requirement reflects the thymine group's role as the spectroscopic probe in the H-1 NMR titration studies. In contrast, the adenine derivative may be considerably less hydrophobic and need not be largely incorporated within the micelles. More lipophilic adenine derivatives are bound with greater observed binding constants (K-obs), and a linear relationship is observed between log K-obs and log K-ow (where K-ow is the octanol-water partition coefficient of adenine 3). These observations are consistent with a model in which the adenine derivative partitions between the exterior and interior of the micelles and the thymine binds the intramicellar adenine. These studies establish that uncharged hydrogen-bonding receptor molecules can incorporate into micelles to form supramolecular receptors that bind hydrogen-bonding ligands in aqueous solution.