Synthesis and Circular Dichroism of Tetraarylporphyrin−Oligonucleotide Conjugates

The preparation and circular dichroic (CD) studies of self-complimentary 8-mer DNA sequences with a porphyrin at the 3‘ end are presented. Electronic interaction between the two porphyrins (the interchromophoric distance is in the range of 28−40 Å), attached to both ends of the double-stranded helix, gives rise to a long-range exciton-coupled CD in the visible region (400−450 nm). The porphyrin chromophores act as sensitive probes of geometrical changes in the DNA backbone and sensitively reflect the double-strand to single-strand transition. This study demonstrates the possibility of using exciton-coupled porphyrin CDs for conformational studies of DNA.