X-Ray structure of a metalled double-helix generated by infinite and consecutive C*-Ag-C* (C*: N1-hexylcytosine) base pairs through argentophilic and hydrogen bond interactions

Abstract

[eng] The synthesis of a metalled double-helix containing exclusively silver-mediated C*-C* base pairs is reported herein (C* = N1hexylcytosine). Remarkably, it is the first crystal structure containing infinite and consecutive C*-AgI-C* base pairs that form a double helix. The AgI ion occupies the center between two C* residues with N(3)-Ag bond distances of 2.1 Å and short AgI-AgI distances (3.1 Å) suggesting an interesting argentophilic attraction as a stabilization source of the helical disposition. The solid state structure is further stabilized by metal-mediated base-pairs, hydrogen bonding and π-stacking interactions. Moreover, the angle N(3)-Ag-N(3) is almost linear in the [Ag(N1hexylcytosine)2]+ motif and the bases are not coplanar thus generating a double strand helical aggregate in the solid state. The noncovalent and argentophilic interactions have been rationalized by means of DFT calculations.