Controlling the Structure, Properties and Surface Reactivity of Clickable Azide-Functionalized Au25 (SR)18 Nanocluster Platforms Through Regioisomeric Ligand Modifications

Abstract

To fine-tune structure-property correlations of thiolate-protected gold nanoclusters through post-assembly surface modifications, we report the synthesis of the o, m, and p regioisomeric forms of the anionic azide-functionalized [Au₂₅ (SCH₂ CH₂ -C₆ H₄ -N₃ )₁₈ ]^1- platform. They can undergo cluster-surface strain-promoted alkyne-azide cycloaddition (CS-SPAAC) chemistry with complementary strained-alkynes. Although their optical properties are similar, the electrochemical properties appear to correlate with the position of the azido group. The ability to conduct CS-SPAAC chemistry without altering the parent nanocluster structure is different as the isomeric form of the surface ligand is changed, with the [Au₂₅ (SCH₂ CH₂ -p-C₆ H₄ -N₃ )₁₈ ]^1- isomer having the highest reaction rates, while the [Au₂₅ (SCH₂ CH₂ -o-C₆ H₄ -N₃ )₁₈ ]^1- isomer is not stable following CS-SPAAC. Single-crystal X-ray diffraction provide the molecular structure of the neutral forms of the three regioisomeric clusters, [Au₂₅ (SCH₂ CH₂ -o/m/p-C₆ H₄ -N₃ ]⁰ , which illustrates correlated structural features of the central core as the position of the azido moiety is changed.

Keywords: Azides; Bioorthogonal Chemistry; Cluster-Surface SPAAC; Gold Nanocluster; Nanostructures.