Synthesis and characterization of a metal-salen base pair for the assembly of programmed metal arrays inside the DNA double helix
Base pairing in natural oligonucleotides relies on hydrogen bonding and pi-stacking. Applying coordinative interactions between ligand-like nucleobases and metal cations is a new way of assembling artificial oligonucleotide duplexes. The incorporation of numerous metal-base pairs into oligonucleotides may lead to interesting compounds for nano-technological applications. In this thesis, the synthesis of the salen-metal base pair is described, which comprises preparation of a suitable protected salicylic aldehyde precursor and an organo-cuprate mediated C-glycosidation as the key step. An x-ray structure of the monomeric copper-salen base pair shows a very good geometrical match with natural Watson-Crick base pairs. Up to 10 consecutive salicylic aldehyde-nucleobases could be incorporated into DNA oligonucleotides by means of phosphoramidite chemistry. The synthesized double strands with one ligand show typical B-DNA CD-spectra and distinct melting characteristics. Addition of excess ethylenediamine and 1 eq of Mn2+ or Cu2+ increase the melting temp. by 28 °C and 42 °C, respectively. The complexation of these and other metals was examined by UV-, CD- and EPR-spectroscopy and high res. ESI mass spectrometry. It was possible to stack 10 manganese atoms inside the double helix and to prepare sequence specifically arrays of up to 5 copper ions plus 5 mercury ions inside one duplex.