Click catalysis and DNA conjugation using a nanoscale DNA/silver cluster pair

Abstract

DNA-bound silver clusters are most readily recognized by their strong fluorescence that spans the visible and near-infrared regions. From this suite of chromophores, we chose a green-emitting Ag₁₀⁶⁺ bound to C₄AC₄TC₃GT₄ and describe how this DNA/cluster pair is also a catalyst. A DNA-tethered alkyne conjugates with an azide via cycloaddition, an inherently slow reaction that is facilitated through the joint efforts of the cluster and DNA. The Ag₁₀⁶⁺ structure is the catalytic core in this complex, and it has three distinguishing characteristics. It facilitates cycloaddition while preserving its stoichiometry, charge, and spectra. It also acidifies its nearby alkyne to promote H/D exchange, suggesting a silver–alkyne complex. Finally, it is markedly more efficient when compared with related multinuclear DNA–silver complexes. The Ag₁₀⁶⁺ is trapped within its C₄AC₄TC₃GT₄ host, which governs the catalytic activity in two ways. The DNA has orthogonal functional groups for both the alkyne and cluster, and these can be systematically separated to quench the click reaction. It is also a polydentate ligand that imprints an elongated shape on its cluster adduct. This extended structure suggests that DNA may pry apart the cluster to open coordination sites for the alkyne and azide reactants. These studies indicate that this DNA/silver cluster pair work together with catalysis directly driven by the silver cluster and indirectly guided by the DNA host.