Atomic Structure of a Fluorescent Ag8 Cluster Templated by a Multistranded DNA Scaffold.

Multinuclear silver clusters encapsulated by DNA exhibit size-tunable emission spectra and rich photophysics, but their atomic organization is poorly understood. Herein, we describe the structure of one such hybrid chromophore, a green-emitting Ag8 cluster arranged in a Big Dipper-shape bound to the oligonucleotide A2C4. Three 3' cytosine metallo-base pairs stabilize a parallel A-form-like duplex with a 5' adenine-rich pocket, which binds a metallic, trapezoidal-shaped Ag5 moiety via Ag-N bonds to endo- and exocyclic nitrogens of cytosine and adenine. The unique DNA configuration, constrained coordination environment, and templated Ag8 cluster arrangement highlight the reciprocity between the silvers and DNA in adopting this structure. These first atomic details of a DNA-encapsulated Ag cluster fluorophore illuminate many aspects of biological assembly, nanoscience, and metal cluster photophysics.