Chiral-at-Metal Silver-Mediated Base Pairs: Metal-Centred Chirality versus DNA Helical Chirality

When covalently incorporating ligands capable of forming chiral metal complexes into a DNA oligonucleotide duplex, an enantiospecific formation of metal-mediated base pairs is possible. We have been investigating the chirality of the silver-mediated base pair P-Ag-I-P (P, 1H-imidazo[4,5-f][1,10]phenanthroline) depending on the number of consecutive P : P pairs within a series of duplexes. Towards this end, both enantiomers of the nucleoside analogue 3-(1H-imidazo[4,5-f][1,10]phenanthrolin-1-yl)propane-1,2-diol comprising an acyclic backbone were introduced into DNA duplexes, resulting in diastereomeric metal-mediated base pairs. The same chiral-at-metal complex is formed inside the duplex for up to five neighbouring P-Ag-I-P pairs, irrespective of whether (S)-P or (R)-P is used. With six silver-mediated base pairs, the chirality of the metal complex is inverted for (S)-P but not for (R)-P. This indicates an intricate balance of what determines the configuration of the metal complex, the intrinsically preferred metal-centred chirality or the DNA helical chirality.

Automated summary

It has been discovered that by incorporating ligands capable of forming chiral metal complexes into a DNA double helix, it is possible to selectively form enantiomers of metal-mediated base pairs depending on the number of consecutive pairs. The chirality of the metal complex formed inside the DNA duplex remains the same for up to five neighboring pairs, regardless of the enantiomer used. However, with six pairs, the chirality of the metal complex is inverted for one enantiomer but not the other, suggesting a delicate balance between the metal-centered chirality and the DNA helical chirality in determining the configuration of the metal complex.