Effect of Metal Ion Incorporation on the Properties of Peptide Nucleic Acid Duplexes

Peptide nucleic acid (PNA), a DNA synthetic analog, assembles into helical duplexes as a consequence of Watson-Crick hydrogen bonds formed between nucleobases but has an achiral pseudo-peptide backbone, in contrast to DNA which has a phosphodiester backbone. Placing ligandmodified monomers in complementary positions in PNA oligomers makes possible metal ion incorporation within the PNA duplex (Figure 1). We have synthesized an 8-hydroxyquinolinemodified PNA monomer (Q, Figure 2) and have included it in PNA oligomers with different degrees of complementarity. Thermal denaturation experiments demonstrated high-affinity binding of Cu 2+ to Q-modified PNA duplexes. UV spectrophotometric titrations and EPR spectroscopy indicated the formation within the PNA duplex of a CuQ2 complex with square-planar geometry (Figure 3). The high changes in absorbance at 260 nm observed in the melting curves of