MOLECULAR RECOGNITION IN MICELLES - THE ROLES OF HYDROGEN-BONDING ANDHYDROPHOBICITY IN ADENINE THYMINE BASE-PAIRING IN SDS MICELLES

This paper describes a new class of molecular receptors 2 that bind ad enine derivatives 3 in aqueous solution by means of hydrogen bonding ( base-pairing). The receptors are supramolecular assemblies of thymine groups embedded in micelles, which self-assemble when (thyminylalkyl)a mmonium salts 1 [Thy-(CH2)n-N+Me3] are mixed with aqueous sodium dodec yl sulfate (SDS) solutions. NMR titration studies and Job's method ind icate that binding occurs with 1:1 adenine-thymine stoichiometry in a fashion consistent with base-pairing within the micelles. In the absen ce of SDS, base-stacking occurs in preference to base-pairing. Three f actors that were anticipated to be most significant in binding were ex amined: the lipophilicity of the adenine substrate, the position of th e thymine group within the micelles, and the role of SDS in binding. T o study these factors, the length of the alkyl group on adenine 3 (m = 1, 2, 3, and 4), the length of the alkylammonium chain of thymine 1 ( n = 4, 6, 8, and 10), and the concentration of SDS (0-40 mM) were vari ed. The lipophilicity of the adenines was found to have the greatest e ffect upon the measured association constant K(obs). A binding model i s proposed in which adenine 3 first partitions between the bulk aqueou s solution and the interior of the micelle and then base-pairs to the thymine group within the micelle. In accordance with this model, a lin ear relationship is observed between log K(obs) and log K(ow) (where K (ow) is the octanol-water partition coefficient of adenine 3).