Self-assembly of azaphthalocyanine–oligodeoxynucleotide conjugates into J-dimers: towards biomolecular logic gates

Abstract

The formation of J-dimers is rarely reported in the scientific literature, even though these architectures often have important consequences for various applications. Octasubstituted azaphthalocyanines (AzaPcs) bearing dialkylamino substituents form very stable (K_D > 10¹⁰ M⁻¹ in toluene) J-dimers by the coordination of the peripheral amino nitrogens to the central zinc(II) cation of the second molecule. For AzaPc 1, bearing N,N-diethylamino substituents, this self-assembly occurs even after the attachment of the AzaPcs to oligodeoxynucleotide (ODN) chains in buffers. The J-dimers of ODNs are stable even after hybridization with complementary antisense ODNs and can be dissociated only by exposure to coordinating molecules (e.g., pyridine). An ODN probe labeled with both fluorescein and AzaPc 1 formed a unique supramolecular assembly (F-ODN-1)₂ resembling the figure “8” in which the two end-labeled ODN chains are joined together at a central connection point. The connection is formed by a heterotetramer composed of the J-dimer of AzaPc 1 and two molecules of fluorescein where the fluorescence is highly quenched. The AzaPc J-dimer in this probe can be utilized as a dark quencher in real-time PCR assays and has quenching properties superior to those of AzaPcs that formed only the monomer. Additionally, the selective dissociation of the molecules in the heterotetramer by hybridization with an antisense strand or by the introduction of a coordinating molecule (pyridine) leads to changes in the absorption spectra and fluorescence intensities that were utilized in designing OR, AND, and NOT Boolean operators for biomolecular logic gates based on the combination of these two distinct switching mechanisms.