Diastereochemically controlled porphyrin dimer formation on a DNA duplex scaffold.

DNA-porphyrin conjugates were designed and synthesized for the preparation of the conformationally controlled porphyrin dimer structures constructed on a d(GCGTATACGC)2. Porphyrin derivatives were introduced to the central TATpA sequence where p represents the phosphoramidate for the attachment of the free-base porphyrin (FbP) and zinc-coordinated porphyrin (ZnP), which allows contact of the two porphyrins in the minor groove. The porphyrin dimers were characterized using CD, UV-vis, steady-state, and time-resolved fluorescence spectroscopies, indicating that the porphyrins form face-to-face conformations. Also the co-facial conformation was confirmed by comparison with spectra of the non-self-complementary duplex containing one porphyrin moiety. Introduction of zinc into porphyrin moiety destabilized the duplex formation. Two diastereomers showed different thermal stabilities and affected the conformations of porphyrin dimers. The temperature-dependent assembly and the conformational change of the porphyrin dimer on the duplex DNA were observed in the UV-vis spectra, indicating that the dynamic movement of the porphyrin dimer occurs on the duplex. The results indicate that the porphyrin dimers of DNA-FbP conjugates are overlapped clockwise and are located in the minor groove of the usual B-form DNA backbone. The interaction and conformation of two porphyrin moieties are controlled by the following three factors: (1) temperature change during and after formation of the duplex porphyrins at lower temperature; (2) diastereochemistry of the phosphoramidates where porphyrins are connected via a linker; and (3) zinc ion coordination that destabilizes the interaction of porphyrins as well duplex formation.