Structure and magnetic properties of (Fe2O3)n clusters (n = 1–5)

Global minimum structures of (Fe₂O₃)_n clusters (n = 1–5) determined for the first time in this size range show weak dependence of the structure and relative stabilities of different isomers on their magnetic states.

Water-medium organic synthesis over active and reusable organometal catalysts with tunable nanostructures

Robust and reusable heterogeneous organometal catalysts open a new avenue to green chemical synthesis in water.

A highly efficient and recyclable Fe3O4 magnetic nanoparticle immobilized palladium catalyst for the direct C-2 arylation of indoles with arylboronic acids

An efficient and reusable Fe₃O₄-nanoparticle-immobilized-palladium catalyst was prepared and applied to the direct C-2 arylation of indoles with arylboronic acids.

Synthesis of trisubstituted ureas by a multistep sequence utilizing recyclable magnetic reagents and scavengers

Unprecedented magnetic borohydride exchange (mBER), magnetic Wang aldehyde (mWang) and magnetic amine resins were prepared from highly magnetic polymer-coated cobalt or iron nanoparticles. Microwave irradiation was used to obtain excellent degrees of functionalization (>95 %) and loadings (up to 3.0 mmol  g(-1)) in short reaction times of 15 min or less. A small library of ureas and thioureas was synthesized by the exclusive application of these magnetic resins. As a first step, a reductive amination of aromatic and aliphatic aldehydes was carried out with mBER. The excess of primary amine needed to complete the reaction was subsequently scavenged selectively by mWang. Simple magnetic decantation from the resins resulted in secondary amines in good to excellent yields and purities. The used magnetic resins were efficiently regenerated and reused for the next run. In a second step, the secondary amines were converted to trisubstituted (thio)ureas in excellent yields and purities by stirring with an excess of iso(thio)cyanate, which was scavenged by addition of the magnetic amine resin after completion of the reaction. The whole reaction sequence is carried out without any purification apart from magnetic decantation; moreover, conventional magnetic stirring can be used as opposed to the vortexing required for polystyrene resins.

Directed self-assembly of nanoparticles for nanomotors

We report, for the first time, the design and fabrication of a nanoparticle-based nanomotor system by directly self-assembling nanoparticles onto functional, nanometer-thin lamellae, such as polymer single crystals. Tens of thousands of judiciously selected nanoparticles (gold, iron oxide, and platinum nanoparticles) with sizes ranging from <5 to a few tens of nanometers have been introduced into a single nanomotor via directed self-assembly. The resulting nanomotor realizes functions such as autonomous movement, remote control, and cargo transportation by utilizing the advantages offered by nanoparticles, such as the small size, surface plasmon resonance, catalytic and magnetic properties. Because of the structural and functional versatility of nanoparticles, the facile fabricating procedure, and the potential for mass production, our strategy shows a key step toward the development of next generation multifunctional nanomotors.

Completely regioselective direct C-H functionalization of benzo[b]thiophenes using a simple heterogeneous catalyst

The first completely selective C3 C-H arylation of benzo[b]thiophenes is reported, demonstrating previously unexploited reactivity of palladium. Benzo[b]thiophenes are coupled with readily available aryl chlorides using a ligand-free, dual catalytic system of heterogeneous Pd/C and CuCl. The reaction is operationally simple and insensitive to air and moisture, and it provides valuable products with complete selectivity. Significant investigations into the nature of the active catalytic species and mechanistic considerations are discussed.

Ring-opening metathesis polymerization-based recyclable magnetic acylation reagents

An operationally simple method for the acylation of amines utilizing carbon-coated metal nanoparticles as recyclable supports is reported. Highly magnetic carbon-coated cobalt (Co/C) and iron (Fe/C) nanobeads were functionalized with a norbornene tag (Nb-tag) through a "click" reaction followed by surface activation employing Grubbs-II catalyst and subsequent grafting of acylated N-hydroxysuccinimide ROMPgels (ROMP=ring-opening metathesis polymerization). The high loading (up to 2.6 mmolg(-1) ) hybrid material was applied in the acylation of various primary and secondary amines. The products were isolated in high yields (86-99%) and excellent purities (all >95 % by NMR spectroscopy) after rapid magnetic decantation and simple evaporation of the solvents. The spent resins were successfully re-acylated by acid chlorides, anhydrides, and carboxylic acids and reused for up to five consecutive cycles without considerable loss of activity.

Catalysis of transesterification reactions by a self-assembled nanosystem

Histidine-containing peptides self-assemble on the surface of monolayer protected gold nanoparticles to form a catalytic system for transesterification reactions. Self-assembly is a prerequisite for catalysis, since the isolated peptides do not display catalytic activity by themselves. A series of catalytic peptides and substrates are studied in order to understand the structural parameters that are of relevance to the catalytic efficiency of the system. It is shown that the distance between the His-residue and the anionic tail does not affect the catalytic activity. On the other hand, the catalytic His-residue is sensitive to the chemical nature of the flanking amino acid residues. In particular, the presence of polar Ser-residues causes a significant increase in activity. Finally, kinetic studies of a series of substrates reveal that substrates with a hydrophobic component are very suitable for this catalytic system.

Enhanced catalytic activity of self-assembled-monolayer-capped gold nanoparticles

An unprecedented substrate-selective catalytic enhancement effect of an alkanethiol-self-assembled monolayer (SAM) on Au nanoparticles (AuNPs) is reported. In the supported 2D-array of AuNPs, the alkanethiol-SAM acts as a protein-like soft reaction space in which the substrate molecules are encapsulated through non-covalent intermolecular hydrophobic interactions, and thus catalytic reactions are accelerated at AuNP surfaces.

Preparation of superparamagnetic Fe3O4@alginate/chitosan nanospheres for Candida rugosa lipase immobilization and utilization of layer-by-layer assembly to enhance the stability of immobilized lipase

Superparamagnetic alginate nanospheres with diameter of 50 nm were prepared by self-assembly of alginate in the Ca(2+) solution; and then superparamagnetic alginate/chitosan nanospheres, which have positive charge and could adsorb lipase directly, were obtained with a following assembly of chitosan based on the electrostatic interaction between alginate and chitosan. Subsequently, oxidic poly (ethylene glycol) was used to functionalize the magnetic alginate/chitosan nanospheres. Thus, the magnetic nanospheres with aldehyde groups and a brushlike structure were formed. With various characterizations, it was verified that the magnetic alginate/chitosan nanospheres held small diameters (around 60 nm) and displayed superparamagnetism with high saturation magnetization. The Candida rugosa lipase (CRL), meanwhile, was immobilized onto the magnetic alginate/chitosan nanospheres by electrostatic adsorption and covalent bonding, respectively. Afterward, a layer-by-layer (LBL) assembly process was utilized to coat the immobilized CRL (ICRL) with covering layers made up of alginate and chitosan. After studying the properties of ICRL such as activity, kinetic behaviors, stability and reusability, it was proved that the ICRL prepared with two methods displayed more excellent properties than that prepared with electrostatic adsorption only. Additionally, coating ICRL with covering layers showed good effect on improving the stability of ICRL.

Magnetically recyclable nanocatalysts (MRNCs): a versatile integration of high catalytic activity and facile recovery

Recent advances in wet chemical synthesis of magnetically recyclable nanocatalysts (MRNCs), a versatile integration of high catalytic activity and facile recovery, have led to a dramatic expansion of their potential applications. This review focuses on the recent work in the development of metal and metal oxide based MRNCs for catalytic conversion of organic compounds in solution phase. This will be discussed in detail, according to the two main synthesis methods of MRNCs as classified by us. The two methods are: template-assisted synthetic strategy and direct synthetic strategy. And the template-assisted synthesis is further divided into three subcategories, synthetic strategies assisted by hard-, soft-, and mixed hard-soft coupling layers. At the end, we outline future trends and perspectives in these research areas.

Synthesis of Fe3O4@silica/poly(N-isopropylacrylamide) as a novel thermo-responsive system for controlled release of H3PMo12O40 nano drug in AC magnetic field

In this work, a new method is introduced for synthesis of nano drug for the first time. H₃PMo₁₂O₄₀ and Fe₃O₄@SiO₂/poly(N-isopropylacrylamide), were prepared as nano drug and magneto thermally responsive nano-carrier respectively. Then the released behavior of H₃PMo₁₂O₄₀ nano-drug from this thermo-responsive carrier was investigated in an AC magnetic field. When a drug particle is broken up to nanometer range, the total surface area is increased; therefore the rate of dissolution and the rate of release are increased. The as-synthesized nanostructures were characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), and Fourier transform infrared spectroscopy (FT-IR). Furthermore, experimental condition which lead to the released profile of H₃PMo₁₂O₄₀ nano-drug from Fe₃O₄@SiO₂/poly(N-isopropylacrylamide), such as strength of magnetic field (H), temperature (T), particle size of drug and content of loaded drug were tested. Increasing the strength of magnetic field, temperature and content of loaded drug, the rate of drug release was also increased.

Syntheses of water-soluble octahedral, truncated octahedral, and cubic Pt-Ni nanocrystals and their structure-activity study in model hydrogenation reactions

We developed a facile strategy to synthesize a series of water-soluble Pt, Pt(x)Ni(1-x) (0 < x < 1), and Ni nanocrystals. The octahedral, truncated octahedral, and cubic shapes were uniformly controlled by varying crystal growth inhibition agents such as benzoic acid, aniline, and carbon monoxide. The compositions of the Pt(x)Ni(1-x) nanocrystals were effectively controlled by choice of ratios between the Pt and Ni precursors. In a preliminary study to probe their structure-activity dependence, we found that the shapes, compositions, and capping agents strongly influence the catalyst performances in three model heterogeneous hydrogenation reactions.

Self-assembly of a catalytic multivalent peptide-nanoparticle complex

Catalytically active peptide-nanoparticle complexes were obtained by assembling small peptide sequences on the surface of cationic self-assembled monolayers on gold nanoparticles. When bound to the surface, the peptides accelerate the transesterification of the p-nitrophenyl ester of N-carboxybenzylphenylalanine by more than 2 orders of magnitude. The gold nanoparticle serves as a multivalent scaffold for bringing the catalyst and substrate into close proximity but also creates a local microenvironment that further enhances the catalysis. The supramolecular nature of the ensemble permits the catalytic activity of the system to be modulated in situ.

Lanthanide-based NMR: a tool to investigate component distribution in mixed-monolayer-protected nanoparticles

Gd(3+) ions, once bound to the monolayer of organic molecules coating the surface of gold nanoparticles, produce a paramagnetic relaxation enhancement (PRE) that broadens and eventually cancels the signals of the nuclear spins located nearby (within 1.6 nm distance). In the case of nanoparticles coated with mixed monolayers, the signals arising from the different coating molecules experience different PRE, depending on their distance from the binding site. As a consequence, observation of the signal broadening patterns provides direct information on the monolayer organization.