Host-guest chemistry with water-soluble gold nanoparticle supraspheres

The uptake of molecular guests, a hallmark of the supramolecular chemistry of cages and containers, has yet to be documented for soluble assemblies of metal nanoparticles. Here we demonstrate that gold nanoparticle-based supraspheres serve as a host for the hydrophobic uptake, transport and subsequent release of over two million organic guests, exceeding by five orders of magnitude the capacities of individual supramolecular cages or containers and rivalling those of zeolites and metal-organic frameworks on a mass-per-volume basis. The supraspheres are prepared in water by adding hexanethiol to polyoxometalate-protected 4 nm gold nanoparticles. Each 200 nm assembly contains hydrophobic cavities between the estimated 27,400 gold building blocks that are connected to one another by nanometre-sized pores. This gives a percolated network that effectively absorbs large numbers of molecules from water, including 600,000, 2,100,000 and 2,600,000 molecules (35, 190 and 234 g l(-1)) of para-dichorobenzene, bisphenol A and trinitrotoluene, respectively

Regioselective placement of alkanethiolate domains on tetrahedral and octahedral gold nanocrystals

Electrostatically stabilized monolayer shells of metal-oxide cluster anions (polyoxometalates, or POMs) on the surfaces of ca. 8 nm tetrahedral and octahedral gold nanocrystals regioselectively direct water-soluble alkanethiolate ligands to the corners and edges of the gold polyhedra

Role of the Alkali-Metal Cation Size in the Self-Assembly of Polyoxometalate-Monolayer Shells on Gold Nanoparticles

Polyoxometalate (POM)-monolayer stability constants, <i>K</i>, for three POM anions vary with the cation size, in the same order as that for increasing ion-pair formation with α-SiW₁₁O₃₉^8– (<b>1</b>) in the early nucleation phase of monolayer self-assembly: Li⁺ < Na⁺ < K⁺ < Cs⁺. Cryo-TEM images demonstrating the use of the cation size to rationally control monolayer formation provide definitive evidence that the POM monolayers are electrostatically stabilized (ionic) shells, analogous in that respect to the monolayer walls of “hollow” POM-macroanion vesicles

Nucleation and Island Growth of Alkanethiolate Ligand Domains on Gold Nanoparticles

The metal oxide cluster α-AlW₁₁O₃₉^9– (<b>1</b>), readily imaged by cryogenic transmission electron microscopy (cryo-TEM), is used as a diagnostic protecting anion to investigate the self-assembly of alkanethiolate monolayers on electrostatically stabilized gold nanoparticles in water. Monolayers of <b>1</b> on 13.8 ± 0.9 nm diameter gold nanoparticles are displaced from the gold surface by mercaptoundecacarboxylate, HS(CH₂)₁₀CO₂^– (<b>11-MU</b>). During this process, no aggregation is observed by UV–vis spectroscopy, and the intermediate ligand-shell organizations of <b>1</b> in cryo-TEM images indicate the presence of growing hydrophobic domains, or “islands”, of alkanethiolates. UV–vis spectroscopic “titrations”, based on changes in the surface plasmon resonance upon exchange of <b>1</b> by thiol, reveal that the 330 ± 30 molecules of <b>1</b> initially present on each gold nanoparticle are eventually replaced by 2800 ± 30 molecules of <b>11-MU</b>. UV–vis kinetic data for <b>11-MU</b>-monolayer formation reveal a slow phase, followed by rapid self-assembly. The Johnson, Mehl, Avrami, and Kolmogorov model gives an Avrami parameter of 2.9, indicating continuous nucleation and two-dimensional island growth. During nucleation, incoming <b>11-MU</b> ligands irreversibly displace <b>1</b> from the Au-NP surface <i>via</i> an associative mechanism, with <i>k</i>_nucleation = (6.1 ± 0.4) × 10² M^–1 s^–1, and 19 ± 8 nuclei, each comprised of <i>ca</i>. 8 alkanethiolates, appear on the gold-nanoparticle surface before rapid growth becomes kinetically dominant. Island growth is also first-order in [<b>11-MU</b>], and its larger rate constant, <i>k</i>_growth, (2.3 ± 0.2) × 10⁴ M^–1 s^–1, is consistent with destabilization of molecules of <b>1</b> at the boundaries between the hydrophobic (alkanethiolate) and the electrostatically stabilized (inorganic) domains

Nucleation and Island Growth of Alkanethiolate Ligand Domains on Gold Nanoparticles

The metal oxide cluster α-AlW₁₁O₃₉^9– (<b>1</b>), readily imaged by cryogenic transmission electron microscopy (cryo-TEM), is used as a diagnostic protecting anion to investigate the self-assembly of alkanethiolate monolayers on electrostatically stabilized gold nanoparticles in water. Monolayers of <b>1</b> on 13.8 ± 0.9 nm diameter gold nanoparticles are displaced from the gold surface by mercaptoundecacarboxylate, HS(CH₂)₁₀CO₂^– (<b>11-MU</b>). During this process, no aggregation is observed by UV–vis spectroscopy, and the intermediate ligand-shell organizations of <b>1</b> in cryo-TEM images indicate the presence of growing hydrophobic domains, or “islands”, of alkanethiolates. UV–vis spectroscopic “titrations”, based on changes in the surface plasmon resonance upon exchange of <b>1</b> by thiol, reveal that the 330 ± 30 molecules of <b>1</b> initially present on each gold nanoparticle are eventually replaced by 2800 ± 30 molecules of <b>11-MU</b>. UV–vis kinetic data for <b>11-MU</b>-monolayer formation reveal a slow phase, followed by rapid self-assembly. The Johnson, Mehl, Avrami, and Kolmogorov model gives an Avrami parameter of 2.9, indicating continuous nucleation and two-dimensional island growth. During nucleation, incoming <b>11-MU</b> ligands irreversibly displace <b>1</b> from the Au-NP surface <i>via</i> an associative mechanism, with <i>k</i>_nucleation = (6.1 ± 0.4) × 10² M^–1 s^–1, and 19 ± 8 nuclei, each comprised of <i>ca</i>. 8 alkanethiolates, appear on the gold-nanoparticle surface before rapid growth becomes kinetically dominant. Island growth is also first-order in [<b>11-MU</b>], and its larger rate constant, <i>k</i>_growth, (2.3 ± 0.2) × 10⁴ M^–1 s^–1, is consistent with destabilization of molecules of <b>1</b> at the boundaries between the hydrophobic (alkanethiolate) and the electrostatically stabilized (inorganic) domains