Ultrasmall atomically precise monolayerprotected gold thiolate nanoclusters are an intensely researched nanomaterial framework, but there is a lack of a system that can be directly synthesized and undergo interfacial surface chemistry. We report an [Au 25 (SCH 2 CH 2 -p-C 6 H 4 -N 3 ) 18 ] − nanocluster platform with azide moieties appended onto each surface ligand. The structure of this surface reactive cluster has been confirmed by single-crystal X-ray crystallography, mass spectrometry and ultraviolet visible, infrared and nuclear magnetic resonance spectroscopies. We show that all surface azide moieties are amenable to cluster-surface strain-promoted alkyne−azide cycloaddition chemistry with a strained cyclooctyne, opening this as a new platform to allow functional, postassembly surface modifications to this very prominent nanocluster.

The ability to regulate small-molecule release from metallic nanoparticle substrates offers unprecedented opportunities for nanocarrier-based imaging, sensing, and drug-delivery applications. Herein we report a novel and highly specific release methodology off gold nanoparticle (AuNP) surfaces based on the bioorthogonal Staudinger-Bertozzi ligation. A thiol ligand bearing the molecular cargo, a Rhodamine B dye derivative, was synthesized and used to modify small water-soluble 5 nm AuNPs. Upon incorporation into the AuNP monolayer, we observed efficient quenching of the dye emission, resulting in a very low level of fluorescence emission that provided the baseline from which cargo release was monitored. We examined the ability of these AuNPs to react with azide molecules via Staudinger-Bertozzi ligation on the nanoparticle surface by monitoring the fluorescence emission after the introduction of an organic azide. We observed an immediate increase in emission intensity upon azide addition, which corresponded to the release of the dye into the bulk solution. The P NMR spectrum of the AuNP product also agrees with the formation of the ligation product. Thus this system represents a novel and highly specific release methodology off AuNP surfaces that can have potential applications in drug delivery, sensing, and materials science.

Highly accelerated inverse-electron-demand strain-promoted alkyne-nitrone cycloaddition (IED SPANC) between a stable cyclooctyne (bicyclo[6.1.0]nonyne (BCN)) and nitrones delocalized into a C α -pyridinium functionality is reported, with the most electron-deficient "pyridiniumnitrone" displaying among the most rapid cycloadditions to BCN that is currently reported. Density functional theory (DFT) and X-ray crystallography are explored to rationalize the effects of N-and C α -substituent modifications at the nitrone on IED SPANC reaction kinetics and the overall rapid reactivity of pyridinium-delocalized nitrones.

Ultrasmall atomically precise monolayer-protected gold thiolate nanoclusters are an intensely researched nanomaterial framework, but there is a lack of a system that can be directly synthesized and undergo interfacial surface chemistry. We report an [Au₂₅(SCH₂CH₂-<i>p</i>-C₆H₄-N₃)₁₈]^- nanocluster platform with azide moieties appended onto <i>each </i>surface ligand. The structure of this surface reactive cluster has been confirmed by single-crystal X-ray crystallography, mass spectrometry and UV-Vis, IR and NMR spectroscopies. We show that <i>all</i> surface azide moieties are amenable to cluster-surface strain-promoted alkyne-azide cycloaddition (CS-SPAAC) chemistry with a strained cyclooctyne, opening this as a new <i>platform </i>to allow functional, post-assembly surface modifications to this very prominent nanocluster.

An efficient method for the large-scale preparation of rhodamine B clickable derivatives has been developed. Starting from inexpensive rhodamine B as the starting material it was possible to functionalize the carboxylic functionality of rhodamine B with an azide, a strained-alkyne, a substituted triphenylphosphine, a thiol, and a maleimide. Through the synthetic strategy it was possible to obtain stable and pure clickable rhodamine compounds that can be readily used not only for chemoselectively probing biomolecules, but also for materials science.