Three-Dimensional TEM Study of Dendrimer-Encapsulated Pt Nanoparticles for Visualizing Structural Characteristics of the Whole Organic-Inorganic Hybrid Nanostructure

Here, we report three-dimensional (3-D) visualization of dendrimer-encapsulated Pt nanoparticles (Pt DENs) by using 3-D electron tomography to reveal intricate structural characteristics of their whole organic-inorganic hybrid nanostructure. We reconstructed the 3-D spatial volume of Pt DENs by back-projecting a tilt series of two-dimensional (2-D) projections of Pt nanoparticles encapsulated inside dendrimers negatively stained with uranyl acetate. The direct 3-D visualization of Pt DENs elucidated their encapsulation characteristics with the spatial imaging of Pt nanoparticles embraced inside dendrimers in three dimensions. The encapsulation characteristics of Pt DENs were further verified with selective electrochemical poisoning experiments. In addition, quantitative 3-D structural characterization of Pt DENs provided more accurate and precise size distributions of nanoparticles than those obtained from conventional 2-D transmission electron microscopy analysis relying only on a 3-D structure projected on a 2-D plane.

Biomolecule conjugated metal nanoclusters: bio-inspiration strategies, targeted therapeutics, and diagnostics

To help those suffering from viral infections and cancers, scientists are exploring enhanced therapeutic methods via metal nanoclusters (MNCs).

Repetitively Coupled Chemical Reduction and Galvanic Exchange as a Synthesis Strategy for Expanding Applicable Number of Pt Atoms in Dendrimer-Encapsulated Pt Nanoparticles

In this study, we report the controllable synthesis of dendrimer-encapsulated Pt nanoparticles (Pt DENs) utilizing repetitively coupled chemical reduction and galvanic exchange reactions. The synthesis strategy allows the expansion of the applicable number of Pt atoms encapsulated inside dendrimers to more than 1000 without being limited by the fixed number of complexation sites for Pt²⁺ precursor ions in the dendrimers. The synthesis of Pt DENs is achieved in a short period of time (i.e., ∼10 min) simply by the coaddition of appropriate amounts of Cu²⁺ and Pt²⁺ precursors into aqueous dendrimer solution and subsequent addition of reducing agents such as BH₄^-, resulting in fast and selective complexation of Cu²⁺ with the dendrimers and subsequent chemical reduction of the complexed Cu²⁺ while uncomplexed Pt²⁺ precursors remain oxidized. Interestingly, the chemical reduction of Cu²⁺, leading to the formation of Cu nanoparticles encapsulated inside the dendrimers, is coupled with the galvanic exchange of the Cu nanoparticles with the nearby Pt²⁺. This coupling repetitively proceeds until all of the added Pt²⁺ ions form into Pt nanoparticles encapsulated inside the dendrimers. In contrast to the conventional method utilizing direct chemical reduction, this repetitively coupled chemical reduction and galvanic exchange enables a substantial increase in the applicable number of Pt atoms up to 1320 in Pt DENs while maintaining the unique features of DENs.

Construction and application of a pH-sensitive nanoreactor via a double-hydrophilic multiarm hyperbranched polymer

A double-hydrophilic multiarm hyperbranched polymer with a hyperbranched poly(amidoamine) (HPAMAM) core and many poly(ethylene glycol) monomethyl ether (MPEG) arms connected by pH-sensitive acylhydrazone bonds (HPAMAM-g-MPEG) was successfully prepared. Benefiting from the cationic dendritic core and PEGylation shell, the double-hydrophilic multiarm hyperbranched polymer was used as a nanoreactor for CdS quantum dots (CdS QDs) synthesis in aqueous solution. The obtained HPAMAM-g-MPEG and CdS/HPAMAM-g-MPEG nanocomposites were carefully characterized by (1)H NMR, (13)C NMR, Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible absorption spectroscopy (UV-vis), fluorescence spectroscopy (FL), dynamic light scattering (DLS), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and electronic dispersive X-ray spectroscopy (EDS) analysis. Both (1)H NMR and fluorescence spectroscopy investigations confirmed that the acylhydrazone linkage between the dendritic core and linear arms was readily broken under acidic condition (pH <5.5). When MPEG arms departed from the HPAMAM core, the fluorescence intensity of CdS/HPAMAM-g-MPEG nanocomposites greatly increased. Such pH-responsive behavior of CdS/HPAMAM-g-MPEG nanocomposites was utilized as an exploration of a novel fluorescence probe in an acidic lysosome exemplified by COS-7 cells.

Electron capture dissociation and collision-induced dissociation of metal ion (Ag(+), Cu(2+), Zn(2+), Fe(2+), and Fe(3+)) complexes of polyamidoamine (PAMAM) dendrimers

The electron capture dissociation (ECD) and collision-induced dissociation (CID) of complexes of polyamidoamine (PAMAM) dendrimers with metal ions Ag(+), Cu(2+), Zn(2+), Fe(2+), and Fe(3+) were determined by Fourier transform ion cyclotron resonance mass spectrometry. Complexes were of the form [PD + M + mH](5+) where PD = generation two PAMAM dendrimer with amidoethanol surface groups, M = metal ion, m = 2-4. Complementary information regarding the site and coordination chemistry of the metal ions can be obtained from the two techniques. The results suggest that complexes of Fe(3+) and Cu(2+) are coordinated via both core tertiary amines, whereas coordination of Ag(+) involves a single core tertiary amine. The Zn(2+) and Fe(2+) complexes do not appear to involve coordination by the dendrimer core.

Bimetallic dendrimer-encapsulated nanoparticles as catalysts: a review of the research advances

Bimetallic dendrimer-encapsulated nanoparticles (DENs) are important materials, because they have demonstrated improvement in performance compared to the monometallic DENs in many systems when they are used as catalysts. This tutorial review focuses on the recent research advances in bimetallic DENs with respect to their synthesis, characterization, and applications as catalysts. Bimetallic DENs can be made mainly via three routes: co-complexation, sequential loading, and partial displacement. The research in bimetallic DENs has been significantly promoted by the advancement of characterization instruments. The performances of bimetallic DENs as homogeneous and heterogeneous catalysts in organic synthesis have been compared with both monometallic DENs and their physical mixtures. It is concluded that the synergistic electronic effect in bimetallic nanoparticles enhances their catalytic activities.