Cationic porphyrins bearing diazolium rings: synthesis and their interaction with calf thymus DNA

Two novel cationic porphyrins bearing five-membered rings at the meso-posit ions, meso-tetrakis(1,3-dimethylimidazolium-2-yl)porphyrin (H(2)TDMImP) and meso-tetrakis(1,2-dimethylpyrazolium-4-yl)porphyin (H(2)TDMPzP), have been synthesized. These two compounds interact with calf thymus DNA (CTDNA) in different binding modes from that of meso-tetrakis(N-methylpyridinium-4-yl) porphyrin (H2TMPyP). H(2)TDMImP outside binds to the minor groove of CTDNA while H(2)TDMPzP intercalates into CTDNA. These two novel cationic porphyri ns strongly bind to CTDNA even at high ionic strength and the binding const ant of H(2)TDMPzP to CTDNA is comparable to that of H2TMPyP. The binding of H(2)TDMImP to CTDNA is enthalpically driven. The favorable free energy cha nges in binding of H(2)TDMPzP to CTDNA come from the large negative enthalp y changes accompanied by small positive entropy changes. (C) 1999 Elsevier Science B.V. All rights reserved.