Spatially Resolved Production of Platinum Nanoparticles in Metallosupramolecular Polymers

Advanced mechanical properties of amphiphilic polymer conetworks through hierarchical reinforcement with peptides and cellulose nanocrystals

Amphiphilic polymer conetworks (APCNs) have been explored for various applications, including soft contact lenses, biomaterials, and membranes. They combine important properties of hydrogels and elastomers, including elasticity, transparency, and the capability to swell in water. Moreover, they also swell in organic solvents. However, their mechanical properties could be improved. We developed a two-level, bio-inspired, hierarchical reinforcement of APCNs using cellulose nanocrystals (CNCs) to reinforce peptide-reinforced APCNs formed from hydrophobic poly-β-benzyl-l-aspartate-block-polydimethylsiloxane-block-poly-β-benzyl-l-aspartate (PBLA-b-PDMS-b-PBLA) triblock copolymer crosslinkers and hydrophilic poly(2-hydroxyethyl acrylate) (PHEA) chain segments. Bio-inspired peptide-polymer hybrids combine the structural hierarchy often found in natural materials with synthetic macromolecules, such as block copolymers with soft and hard segments, to enhance their mechanical properties. On the other hand, CNCs provide an additional means to dissipate mechanical energy in polymeric materials, thereby enhancing reinforcement. The key to homogeneously incorporating CNCs into the APCNs is the combination of hydrophobic CNCs (HCNCs) with peptide-blocks in the APCNs, exploiting the hydrogen bonding capability of the peptides to disperse the HCNCs. The effect of HCNCs on the ability of APCNs to swell in water and organic solvents, as well as on their thermal and mechanical properties, was characterized. Additionally, the nanostructure of the materials was analyzed via small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS). The swellability of the HCNC-containing APCNs was independent of the HCNC concentration, and all samples were highly transparent. The ideal HCNC concentration, in terms of maximal stress, strain, toughness, and reinforcement, was found to be between 6 and 15 wt%. An increase in Young's modulus of up to 500% and toughness of up to 200% was achieved. The hierarchical reinforcement also greatly strengthened the APCNs when swollen in water or n-hexane. Thus, HCNCs and peptide segments can be used to reinforce APCNs and to tailor their properties.

Supramolecular nanocapsules as two-fold stabilizers of outer-cavity sub-nanometric Ru NPs and inner-cavity ultra-small Ru clusters

The synthesis of metallic nanoparticles (MNP) with high surface area and controlled shape is of paramount importance to increase their catalytic performance. The detailed growing process of NP is mostly unknown and understanding the specific steps would pave the way for a rational synthesis of the desired MNP. Here we take advantage of the stabilization properties exerted by the tetragonal prismatic supramolecular nanocapsule 8·(BArF)8 to develop a synthetic methodology for sub-nanometric RuNP (0.6-0.7 nm). The catalytic properties of these sub-nanometric nanoparticles were tested on the hydrogenation of styrene, obtaining excellent selectivity for the hydrogenation of the alkene moiety. In addition, the encapsulation of [Ru5] clusters inside the nanocapsule is strikingly observed in most of the experimental conditions, as ascertained by HR-MS. Moreover, a thorough DFT study enlightens the nature of the [Ru5] clusters as tb-Ru5H2(η6-PhH)2(η6-pyz)3 (2) trapped by two arene moieties of the clip, or as tb-Ru5H2(η1-pyz)6(η6-pyz)3 (3) trapped between the two Zn-porphyrin units of the nanocapsule. Both options fulfill the Wade-Mingos counting rules, i.e. 72 CVEs for the closotb. The trapped [Ru5] metallic clusters are proposed to be the first-grown seeds of subsequent formation of the subnanometric RuNP. Moreover, the double role of the nanocapsule in stabilising ∼0.7 nm NPs and also in hosting ultra-small Ru clusters, is unprecedented and may pave the way towards the synthesis of ultra-small metallic clusters for catalytic purposes.

Metallosupramolecular polymers as precursors for platinum nanocomposites

Nanocomposites comprising a polymer matrix and metallic nanoparticles (NPs) can merge the structural features of the matrix material with the functional characteristics of the NPs. While such materials are promising for a wide range of applications, their preparation typically requires multi-step processes that can be difficult to control. Alternatively, materials with NPs can be directly accessed in a controlled manner by exploiting zero-valent metallosupramolecular polymer (MSP) precursors. We here report how the nature of the polymer and its molecular weight affect the nanocomposite formation and structure. Poly(tetrahydrofuran)-based macromonomers with suitable ligands are used to prepare MSPs based on bis(η2-alkyne)platinum(0) complexes. Heating these materials causes disassembly of the complexes and, upon the release of Pt0-atoms, Pt-NPs form in the matrix polymer. The Pt content in the MSP influences the NP formation and thereby the characteristics of the nanocomposites. It is also possible to trigger the complex dissociation and NP formation by exposure to UV light. This allows photolithographic processing and thus the preparation of nanocomposites that contain Pt-NPs in a spatially controlled manner.

Regulating Heterogeneous Catalysis of Gold Nanoparticles with Polymer Mechanochemistry

Polymer mechanochemistry has emerged as a unique approach to regulate homogeneous catalysis in chemical transformations. The utilization of polymer mechanochemistry to regulate heterogeneous catalysis, however, still remains to be investigated. In this study, using polymer-grafted gold nanoparticles as the model heterogeneous catalysts, we show that polymer chains can be mechanically ruptured from the surface of gold nanoparticles, and thus, the catalytic activity of gold nanoparticles can be accelerated under sonication. The mechanical activation of polymer-grafted gold nanoparticles only occurs when the grafted polymer chains exceed a threshold molecular weight. This mechanical behavior is similar to those mechanophore-linked polymers. More importantly, further characterizations reveal that the Au-Au bonds instead of the Au-S bonds are broken at the heterointerfaces of polymer chains and gold nanoparticles. Our study unveils an unprecedented characteristic of polymer-grafted metallic nanoparticles in response to external mechanical stress.