Youngjin Jang

Simple and Generalized Synthesis of Oxide−Metal Heterostructured Nanoparticles and their Applications in Multimodal Biomedical Probes

Heterostructured nanoparticles composed of metals and Fe3O4 or MnO were synthesized by thermal decomposition of mixtures of metal-oleate complexes (for the oxide component) and metal-oleylamine complexes (for the metal component). The products included flowerlike-shaped nanoparticles of Pt-Fe3O4 and Ni-Fe3O4 and snowmanlike-shaped nanoparticles of Ag-MnO and Au-MnO. Powder X-ray diffraction patterns showed that these nanoparticles were composed of face-centered cubic (fcc)-structured Fe3O4 or MnO and fcc-structured metals. The relaxivity values of the Au-MnO and Au-Fe3O4 nanoparticles were similar to those of the MnO and Fe3O4 nanoparticles, respectively. Au-Fe3O4 heterostructured nanoparticles conjugated with two kinds of 12-base oligonucleotide sequences were able to sense a complementary 24-mer sequence, causing nanoparticle aggregation. This hybridization-mediated aggregation was detected by the overall size increase indicated by dynamic light scattering data, the red shift of the surface plasmon band of the Au component, and the enhancement of the signal intensity of the Fe3O4 component in T2-weighted magnetic resonance imaging.

Sizing by Weighing: Characterizing Sizes of Ultrasmall-Sized Iron Oxide Nanocrystals Using MALDI-TOF Mass Spectrometry

We present a rapid and reliable method for determining the sizes and size distributions of <5 nm-sized iron oxide nanocrystals (NCs) using matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) mass spectrometry (MS). MS data were readily converted to size information using a simple equation. The size distribution obtained from the mass spectrum is well-matched with the data from transmission electron microscopy, which requires long and tedious analysis work. The size distribution obtained from the mass spectrum is highly resolved and can detect size differences of only a few angstroms. We used this MS-based technique to investigate the formation of iron oxide NCs, which is not easy to monitor with other methods. From ex situ measurements, we observed the transition from molecular precursors to clusters and then finally to NCs.

One-pot synthesis of magnetically recyclable mesoporous silica supported acid–base catalysts for tandem reactions

We report one-pot synthesis of magnetically recyclable mesoporous silica catalysts for tandem acid-base reactions. The catalysts could be easily recovered from the reaction mixture using a magnet, and the pore size of the catalysts could be controlled by introducing a swelling agent, resulting in the significant enhancement of the reaction rate.

Magnetically Recoverable Nanoflake-Shaped Iron Oxide/Pt Heterogeneous Catalysts and Their Excellent Catalytic Performance in the Hydrogenation Reaction

In this study, a kind of unique Fe2O3/Pt hybrid consisting of uniform platinum nanoparticles deposited on a nanoflake-shaped Fe2O3 support was prepared by using a solvothermal reaction followed by a heat-induced reduction process. The prepared Fe2O3 sample displays well-defined nanoflake-like morphology; remarkably, there are many specific cavities on its surface. In addition, uniform Pt nanoparticles with narrow size distribution were deposited onto the surface of the preformed flake-like Fe2O3 support to form the Fe2O3/Pt hybrid via a facile heat-induced reduction reaction. Thus, the prepared Fe2O3/Pt hybrid can serve as heterogeneous catalyst over the hydrogenation reaction. Results demonstrated that the specific Fe2O3/Pt heterogeneous catalyst exhibits good catalytic performances, including high conversion, specific selectivity, and excellent recycling durability, over hydrogenation reactions for different substrates. Furthermore, the prepared Fe2O3/Pt heterogeneous catalyst could be easily separated from the product mixture by using a magnet and could be recycled for 10 cycles without catalytic activity loss. In a word, the present synthetic approach is facile, scalable, and reproducible, which can be easily facilitated to prepare other types of noble metals/metal oxide composite systems.

Highly selective Wacker oxidation of terminal olefins using magnetically recyclable Pd–Fe3O4 heterodimer nanocrystals

A new highly selective and environment-friendly Wacker oxidation process employing superparamagnetic Pd–Fe3O4 heterodimer nanocrystals in EtOH–H2O under 1 atm O2 has been developed. Consistently high yields of the desired Wacker product and excellent reaction selectivity were observed in almost all of the reactions examined. This operationally simple oxidation protocol allows recycling of the Pd–Fe3O4 catalyst after the reaction through the use of an external magnet.

pH-Sensitive Pt Nanocluster Assembly Overcomes Cisplatin Resistance and Heterogeneous Stemness of Hepatocellular Carcinoma

Response rates to conventional chemotherapeutics remain unsatisfactory for hepatocellular carcinoma (HCC) due to the high rates of chemoresistance and recurrence. Tumor-initiating cancer stem-like cells (CSLCs) are refractory to chemotherapy, and their enrichment leads to subsequent development of chemoresistance and recurrence. To overcome the chemoresistance and stemness in HCC, we synthesized a Pt nanocluster assembly (Pt-NA) composed of assembled Pt nanoclusters incorporating a pH-sensitive polymer and HCC-targeting peptide. Pt-NA is latent in peripheral blood, readily targets disseminated HCC CSLCs, and disassembles into small Pt nanoclusters in acidic subcellular compartments, eventually inducing damage to DNA. Furthermore, treatment with Pt-NA downregulates a multitude of genes that are vital for the proliferation of HCC. Importantly, CD24+ side population (SP) CSLCs that are resistant to cisplatin are sensitive to Pt-NA, demonstrating the immense potential of Pt-NA for treating chemoresistant HCC.

Magnetic Pd nanoparticles: effects of surface atoms

We have investigated the magnetic properties of trioctylphosphine (TOP)-stabilized monodisperse palladium nanoparticles of 2, 3, 5 and 10 nm in size, in order to study the possible effects of surface Pd atoms. These nanoparticles display clear signatures of ferromagnetism such as hysteresis and saturation magnetization over the entire temperature range studied here from 2 to 380 K. The magnetization of the nanoparticles increases with decreasing particle size, indicating a possibly important role played by Pd atoms on the surface of the nanoparticles. More importantly, we also found that the magnetization of our TOP-stabilized Pd nanoparticles is one order of magnitude smaller than those of other Pd nanoparticles reported so far, which is most likely to be due to the weak nature of interface interaction between TOP ligands and Pd nanoparticles compared to other ligands. This observation is consistent with the view that the magnetism of Pd nanoparticles is strongly influenced by the interaction of surface atoms with the ligands. We discuss our experimental findings in terms of a charge transfer mechanism due to a covalent bond of Pd atoms with the protective TOP ligand, which would increase the 4d density of states of Pd atoms due to localization by the bonded P atoms.

Controlling the size of hot injection made nanocrystals by manipulating the diffusion coefficient of the solute.

We investigate the relation between the chain length of ligands used and the size of the nanocrystals formed in the hot injection synthesis. With two different CdSe nanocrystal syntheses, we consistently find that longer chain carboxylic acids result in smaller nanocrystals with improved size dispersions. By combining a more in-depth experimental investigation with kinetic reaction simulations, we come to the conclusion that this size tuning is due to a change in the diffusion coefficient and the solubility of the solute. The relation between size tuning by the ligand chain length and the coordination of the solute by the ligands is further explored by expanding the study to amines and phosphine oxides. In line with the weak coordination of CdSe nanocrystals by amines, no influence of the chain length on the nanocrystals is found, whereas the size tuning brought about by phosphine oxides can be attributed to a solubility change. We conclude that the ligand chain length provides a practical handle to optimize the outcome of a hot injection synthesis in terms of size and size dispersion and can be used to probe the interaction between ligands and the actual solute.

Cation Exchange Combined with Kirkendall Effect in the Preparation of SnTe/CdTe and CdTe/SnTe Core/Shell Nanocrystals

Controlling the synthesis of narrow band gap semiconductor nanocrystals (NCs) with a high-quality surface is of prime importance for scientific and technological interests. This Letter presents facile solution-phase syntheses of SnTe NCs and their corresponding core/shell heterostructures. Here, we synthesized monodisperse and highly crystalline SnTe NCs by employing an inexpensive, nontoxic precursor, SnCl2, the reactivity of which was enhanced by adding a reducing agent, 1,2-hexadecanediol. Moreover, we developed a synthesis procedure for the formation of SnTe-based core/shell NCs by combining the cation exchange and the Kirkendall effect. The cation exchange of Sn(2+) by Cd(2+) at the surface allowed primarily the formation of SnTe/CdTe core/shell NCs. Further continuation of the reaction promoted an intensive diffusion of the Cd(2+) ions, which via the Kirkendall effect led to the formation of the inverted CdTe/SnTe core/shell NCs.

Self-assembled dendritic Pt nanostructure with high-index facets as highly active and durable electrocatalyst for oxygen reduction

The durability issues of Pt catalyst should be resolved for the commercialization of proton exchange membrane fuel cells. Nanocrystal structures with high-index facets have been recently explored to solve the critical durability problem of fuel cell catalysts as Pt catalysts with high-index facets can preserve the ordered surfaces without change of the original structures. However, it is very difficult to develop effective and practical synthetic methods for Pt-based nanostructures with high-index facets. The current study describes a simple one-pot synthesis of self-assembled dendritic Pt nanostructures with electrochemically active and stable high-index facets. Pt nanodendrites exhibited 2 times higher ORR activity and superior durability (only 3.0 % activity loss after 10 000 potential cycles) than a commercial Pt/C. The enhanced catalytic performance was elucidated by the formation of well-organized dendritic structures with plenty of reactive interfaces among 5 nm-sized Pt particles and the coexistence of low- and high-index facets on the particles.