Poly(ethylene glycol)-based ammonium ionenes containing nucleobases

Adenine-functionalized ionenes (ionene-A) and thymine-functionalized ionenes (ionene-T) were synthesized from novel nucleobase-containing monomers from an efficient aza-Michael addition to an acrylate precursor. Complexes of ionenes with nucleobase-containing guest molecules (n-butyl thymine, nBT and n-butyl adenine, nBA) exhibited well-defined complementary hydrogen bonding interactions. Job's analysis revealed a 1:1 stoichiometry for the hydrogen-bonded complexes of [ionene-A]:[nBT], [ionene-T]:[nBA], and [nBA]:[nBT]. A mathematical fit of the chemical shifts to the Benesi-Hildebrand method revealed the association constants of 94 M^-1, 130 M ^-1, and 137 M^-1 for complexes of [ionene-A]:[nBT], [ionene-T]:[nBA], and [nBA]:[nBT], respectively. Furthermore, DSC thermograms of 1:1 [ionene-A/T]:[guest molecule] complexes showed the disappearance of the melting transition for the guest molecule, confirming the absence of macrophase separation of the nucleobase guest in the polymer matrix. Morphological studies including atomic force microscopy (AFM) and small-angle X-ray scattering (SAXS) revealed a microphase-separated morphology for the nucleobase-containing ionenes and less defined microphase separation for the 1:1 complexes.