DNA as supramolecular scaffold for porphyrin arrays

Abstract

Modified nucleotides are becoming increasingly attractive, e.g. to create supramolecular assemblies by using the Watson-Crick base pairing motif, or to incorporate various functionalities such as fluorophores or amino acid side chain mimics into the DNA itself. Here, we present a general synthetic route to porphyrinyl-nucleosides 31-38, where the substitution pattern and the metallation state of the porphyrin residue can be varied to introduce diversity. Based on the synthetic route, the corresponding phosphoramidites 39-42 were synthesized. First, diphenylporphyrin dimers were synthesised both in solution (46a, 46b) and on solid support 47. The building block was then successfully incorporated into trimer 57, tetranucleotides 54-56 and 21-mer oligo-deoxynucleotides 64-70 on solid support via an automated DNA synthesiser. The 21-mer DNA contains one central modification, two porphyrins separated by one thymidine, three consecutive and five consecutive porphyrins. These strands were purified by hybridisation of the complementary strand on support solid or by fluorous affinity chromatography. First results on the interaction of the dimer, the tetramer, and the 21-mer with the complementary strands are discussed. The UV-Visible and fluorescence spectroscopy show an electronic interaction between the different porphyrins in the hetero-tetranucleotide 55. Similarly, in the 21-mer porphyrin DNA strands, an electronic coupling between the chromatophore is evident from the broadened UV-Vis absorbances (porphyrin B-band).