Bis-porphyrin tetragonal prisms assembled through Watson-Crick hydrogen bonding between complementary nucleobases

Abstract

We report here on the self-assembly of two components, a Zn(II) porphyrin substituted with four lipophilic cytidines and a linear linker substituted with two guanosines, into a Watson-Crick hydrogen-bonded tetragonal prism. The corresponding ensemble, comprising two cofacial porphyrin macrocycles, exhibited similar supramolecular behavior as a reference cyclic tetramer previously studied by us. The establishment of strong G:C interactions in apolar chlorinated solvents was demonstrated by the chemical shift recorded for the relevant H-bonded protons. Most importantly, the hexacomponent prism assembly, when partially dissociated by the addition of the competing DMSO solvent, exhibited a slow exchange on the NMR timescale with the individual constituents, which is characteristic of kinetically stabilized discrete assemblies. Absorption, emission, and CD spectroscopy experiments revealed that the spectral features of the tetragonal prism were totally different from the ones recorded for the porphyrin and linker components, which also showed strong self-aggregation in apolar solvents. Temperature-dependent experiments, monitored by NMR and optical spectroscopy techniques, revealed remarkable thermodynamic stability for the prism assembly.