Constitutionally Selective Dynamic Covalent Nanoparticle Assembly

Abstract

The future of materials chemistry will be defined by our ability to precisely arrange components that have considerably larger dimensions and more complex compositions than conventional molecular or macromolecular building blocks. However, exerting structural and constitutional control in the assembly of nanoscale entities presents a considerable challenge. Dynamic covalent nanoparticles are emerging as an attractive category of reaction-enabled solution-processable nanosized building block through which the rational principles of molecular synthetic chemistry can be extended into the nanoscale. From a mixture of two hydrazone-based dynamic covalent nanoparticles with complementary reactivity, specific molecular instructions trigger selective assembly of intimately mixed heteromaterial (Au–Pd) aggregates or materials highly enriched in either one of the two core materials. In much the same way as complementary reactivity is exploited in synthetic molecular chemistry, chemospecific nanoparticle-bound reactions dictate building block connectivity; meanwhile, kinetic regioselectivity on the nanoscale regulates the detailed composition of the materials produced. Selectivity, and hence aggregate composition, is sensitive to several system parameters. By characterizing the nanoparticle-bound reactions in isolation, kinetic models of the multiscale assembly network can be constructed. Despite ignoring heterogeneous physical processes such as aggregation and precipitation, these simple kinetic models successfully link the underlying molecular events with the nanoscale assembly outcome, guiding rational optimization to maximize selectivity for each of the three assembly pathways. With such predictive construction strategies, we can anticipate that reaction-enabled nanoparticles can become fully incorporated in the lexicon of synthetic chemistry, ultimately establishing a synthetic science that manipulates molecular and nanoscale components with equal proficiency.

A General One-Step Synthesis of Alkanethiyl-Stabilized Gold Nanoparticles with Control over Core Size and Monolayer Functionality

“…The ubiquity of amine and carboxylic acid functional groups across multiple compound categories, together with their numerous facile coupling protocols, has made amides one of the most common linkages for constructing α,ω-functionalized alkanethiol or disulfide monolayer precursors . Meanwhile, 19 F NMR spectroscopy has played a critical role in our efforts to achieve nondestructive in situ characterization of nanoparticle-bound molecular structures and real-time reaction tracking. − Pleasingly, the protocol could be adapted to produce AuNP- 4 stabilized by a monolayer of fluorine-substituted amide (⟨ d ⟩ = 3.86 ± 0.39 nm, 10%; Figure S14), in this case by using THF/MeOH (10:1 v / v ) as the reaction solvent.…”

“…Furthermore, the necessity to prepare a new alkanethiol or disulfide for each desired monolayer structural change is synthetically tedious. Nanoparticle “building-block” strategies are far more versatile, wherein carefully chosen reactive groups are incorporated during nanoparticle synthesis, thereby allowing for divergent postsynthesis modification to produce any number of monolayer structural variations starting from a single nanoparticle starting point. , For example, we have developed on-nanoparticle dynamic covalent reactions for nanoparticles stabilized by ligands terminated with hydrazones, ,,, boronic acids, and acetals . The optimized AuNP synthesis protocol outlined above was applied to ligands bearing dynamic covalent reactive groups at their periphery to produce AuNP- 5 (solvent: THF/MeOH, 10:1 v / v ; ⟨ d ⟩ = 3.10 ± 0.42 nm, 14%; Figure S19), AuNP- 6 (solvent: MeOH/DMF, 1:10 v / v ; ⟨ d ⟩ = 4.87 ± 0.74 nm, 15%; Figure S22), and AuNP- 7 (solvent: THF/DMF, 9:1 v / v ; ⟨ d ⟩ = 5.0 ± 0.5 nm, 10%; Figure S26).…”

“…Consequently, the only species present that can bind strongly to the gold surface are the chosen sulfur-based ligand(s), predictably generating single-component self-assembled monolayers. This has several attractive implications for maximizing the influence of a given ligand design on nanoparticle physicochemical properties, ,, enabling in situ molecular-level characterization of surface-bound functionalities, ,, and minimizing batch-to-batch variability that may result from monolayer impurities. In contrast to many ligand-exchange protocols, the synthetically costly functional ligand is used in relatively modest excess, and the number of manipulations is minimized, making for more efficient and convenient procedures.…”

“…As well as allowing for the efficient construction of functionally sophisticated nanoparticles, this protocol meets several of the critical requirements for producing chemically reactive colloidal nanoparticle “building blocks” ,,, while still achieving systematic control over core size. Independent control over structural features of the core and the surface-stabilizing monolayer is necessary in order to access the full range of nanoparticle properties, while the ability to include reactive molecular functionality in the surface-bound ligands is essential for enabling divergent routes to a variety of functional nanoparticle-based devices and materials.…”

A Dissipative Reaction Network Drives Transient Solid–Liquid and Liquid–Liquid Phase Cycling of Nanoparticles

“…Dynamic covalent reactions can be used to reversibly modify the molecular structure of nanoparticle‐bound ligands in situ under mild, equilibrium conditions [23] . This strategy has been harnessed to construct adaptive covalently linked nanoparticle assemblies [19c, 22a, 24] or to reversibly adjust nanoparticle solvent compatibility [23b, 25] . We recently developed a rapidly adaptive dynamic covalent nanoparticle that can be transferred between organic and aqueous solvents driven only by adding simple inorganic salts [26] .…”