Addressing the properties of "Metallo-DNA" with a Ag(i)-mediated supramolecular duplex.

Liam Mistry,Osama El-Zubir,Gema Dura,Nick G Wright,Thomas Pope,Paul G Waddell,Benjamin R Horrocks,Andrew Houlton,Werner A Hofer,William Clegg

doi:10.1039/c8sc05103h

Abstract

The silver-nucleoside complex [Ag(i)-(N3-cytidine)2], 1, self-assembles to form a supramolecular metal-mediated base-pair array highly analogous to those seen in metallo-DNA. A combination of complementary hydrogen-bonding, hydrophobic and argentophilic interactions drive the formation of a double-helix with a continuous silver core. Electrical measurements on 1 show that despite having Ag···Ag distances within <5% of the metallic radii, the material is electrically insulating. This is due to the electronic structure which features a filled valence band, an empty conduction band dominated by the ligand, and a band gap of 2.5 eV. Hence, as-prepared, such Ag(i)-DNA systems should not be considered molecular nanowires but, at best, proto-wires. The structural features seen in 1 are essentially retained in the corresponding organogel which exhibits thixotropic self-healing that can be attributed to the reversible nature of the intermolecular interactions. Photo-reduced samples of the gel exhibit luminescence confirming that these poly-cytidine sequences appropriately pre-configure silver ions for the formation of quantum-confined metal clusters in line with contemporary views on DNA-templated clusters. Microscopy data reveals the resulting metal cluster/particles are approximately spherical and crystalline with lattice spacing (111) similar to bulk Ag.

Highlights

The hydrogen bonds between base pairs of natural DNA are replaced by coordinate bonds resulting in a metallic core running through the double helix (Scheme 1)
This has proven to be a powerful method for controlling the assembly of metal ions into linear arrays and both homo- and heterometallic systems have been demonstrated
For most metal ions arti cial nucleosides are required to accommodate the various demands of metal ion coordination.[5,6,8,9]

Summary

Introduction

Metallo-DNA, that is double-stranded DNA containing metalmediated base pairs, is an important class of nano-materials that seeks to combine the programmability of DNA with the unique properties of metals.[1,2,3,4,5,6,7] Essentially, the hydrogen bonds between base pairs of natural DNA are replaced by coordinate bonds resulting in a metallic core running through the double helix (Scheme 1). We show for the rst time that this type of self-assembled metallo-array exhibits self-healing properties when in the gel form, a feature which can be rationalised from the reversibility of the inter-complex hydrogen- and argentophilic-bonding in the supramolecular structure.

Results

Conclusion