Programmable dynamic covalent nanoparticle building blocks with complementary reactivity.

Nicolas Marro,Flavio Della Sala,Euan R Kay

doi:10.1039/c9sc04195h

Nicolas Marro, Flavio Della Sala + Show 1 more

Open Access

https://doi.org/10.1039/c9sc04195h

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Abstract

Nanoparticle-based devices, materials and technologies will demand a new era of synthetic chemistry where predictive principles familiar in the molecular regime are extended to nanoscale building blocks. Typical covalent strategies for modifying nanoparticle-bound species rely on kinetically controlled reactions optimised for efficiency but with limited capacity for selective and divergent access to a range of product constitutions. In this work, monolayer-stabilized nanoparticles displaying complementary dynamic covalent hydrazone exchange reactivity undergo distinct chemospecific transformations by selecting appropriate combinations of 'nucleophilic' or 'electrophilic' nanoparticle-bound monolayers with nucleophilic or electrophilic molecular modifiers. Thermodynamically governed reactions allow modulation of product compositions, spanning mixed-ligand monolayers to exhaustive exchange. High-density nanoparticle-stabilizing monolayers facilitate in situ reaction monitoring by quantitative 19F NMR spectroscopy. Kinetic analysis reveals that hydrazone exchange rates are moderately diminished by surface confinement, and that the magnitude of this effect is dependent on mechanistic details: surface-bound electrophiles react intrinsically faster, but are more significantly affected by surface immobilization than nucleophiles. Complementary nanoparticles react with each other to form robust covalently connected binary aggregates. Endowed with the adaptive characteristics of the dynamic covalent linking process, the nanoscale assemblies can be tuned from extended aggregates to colloidally stable clusters of equilibrium sizes that depend on the concentration of a monofunctional capping agent. Just two 'dynamic covalent nanoparticles' with complementary thermodynamically governed reactivities therefore institute a programmable toolkit offering flexible control over nanoparticle surface functionalization, and construction of adaptive assemblies that selectively combine several nanoscale building blocks.

Highlights

Generalizable principles of chemical reactivity are the bedrock of molecular and macromolecular synthetic chemistry methods
Nanoparticle-based devices, materials and technologies will demand a new era of synthetic chemistry where predictive principles familiar in the molecular regime are extended to nanoscale building blocks
Using the same synthetic conditions and puri cation procedure as for AuNP-2, the nanoparticles produced in this case were signi cantly larger (AuNP-3, hdcorei 1⁄4 3.4–3.8 nm for four independent batches, Fig. S14†), highlighting the unpredictable and sensitive relationship between ligand molecular structure and metal nanoparticle nucleation/ growth processes.1h,18 Analysis by 1H and 19F nuclear magnetic resonance (NMR) spectroscopy indicated an almost identical hydrazone-terminated surface-bound monolayer on AuNP-3 and AuNP-3(e) (Fig. S17†), with one exception that the material produced by direct synthesis retained some tert-butylamine impurity from the reducing agent

Summary

Introduction

Generalizable principles of chemical reactivity are the bedrock of molecular and macromolecular synthetic chemistry methods. Using the same synthetic conditions and puri cation procedure as for AuNP-2, the nanoparticles produced in this case were signi cantly larger (AuNP-3, hdcorei 1⁄4 3.4–3.8 nm for four independent batches, Fig. S14†), highlighting the unpredictable and sensitive relationship between ligand molecular structure and metal nanoparticle nucleation/ growth processes.1h,18 Analysis by 1H and 19F NMR spectroscopy indicated an almost identical hydrazone-terminated surface-bound monolayer on AuNP-3 and AuNP-3(e) (Fig. S17†), with one exception that the material produced by direct synthesis retained some tert-butylamine impurity from the reducing agent.

Results

Conclusion