Zinc ferrite nanoparticles as MRI contrast agents.

Mixed spinel hydrophobic ZnxFe1-xO x Fe2O3 (up to x = 0.34) nanoparticles encapsulated in polymeric micelles exhibited increased T2 relaxivity and sensitivity of detection over clinically used Feridex.

One-pot synthesis of bi-disperse FePt nanoparticles and size-selective self-assembly into AB2, AB5, and AB13 superlattices.

By chemically modifying the nucleation burst that generates monodisperse FePt nanocrystals, a mixture of Pt and Fe(x)Pt(1-x) nanoparticles forms during a one-pot reaction that includes a small amount of Cu as a catalyst; size-selective precipitation yields a bi-disperse population of Fe(x)Pt(1-x) nanoparticles, which can assemble into high-quality AB2, AB5, and AB13 superlattice structures.

One-pot synthesis of hollow superparamagnetic CoPt nanospheres.

Hollow metal nanospheres are of interest for a variety of academic and technological applications, including drug delivery, catalysis, plasmonics, and lightweight structural composites. Despite recent advances in synthesizing metal nanostructures with controlled morphologies, there are very few reports of hollow bimetallic nanospheres, although such systems promise to offer advantages over single-metal systems. Here, were report a one-pot synthetic strategy for accessing hollow CoPt nanospheres with a Co-Pt alloy structure. The approach utilizes an in situ Co template and exploits galvanic displacement reactions to selectively dissolve the Co core while depositing a Pt shell. The combination of reducing conditions and a polymer stabilizer appears to allow the Co and Pt to co-reduce and form a Co-Pt fcc alloy phase with a morphology that is templated by the sacrificial Co core. The hollow CoPt nanospheres, which show magnetic hysteresis at low temperatures, are thermally stable up to 300 degrees C. The approach, which adds to a growing toolbox of reactions that yield morphologically controlled magnetic CoPt and FePt nanomaterials, is likely to be general for a variety of alloy systems.

Metallurgy in a beaker: nanoparticle toolkit for the rapid low-temperature solution synthesis of functional multimetallic solid-state materials.

Intermetallic compounds and alloys are traditionally synthesized by heating mixtures of metal powders to high temperatures for long periods of time. A low-temperature solution-based alternative has been developed, and this strategy exploits the enhanced reactivity of nanoparticles and the nanometer diffusion distances afforded by binary nanocomposite precursors. Prereduced metal nanoparticles are combined in known ratios, and they form nanomodulated composites that rapidly transform into intermetallics and alloys upon heating at low temperatures. The approach is general in terms of accessible compositions, structures, and morphologies. Multiple compounds in the same binary system can be readily accessed; e.g., AuCu, AuCu3, Au3Cu, and the AuCu-II superlattice are all accessible in the Au-Cu system. This concept can be extended to other binary systems, including the intermetallics FePt3, CoPt, CuPt, and Cu3Pt and the alloys Ag-Pt, Au-Pd, and Ni-Pt. The ternary intermetallic Ag2Pd3S can also be rapidly synthesized at low temperatures from a nanocomposite precursor comprised of Ag2S and Pd nanoparticles. Using this low-temperature solution-based approach, a variety of morphologically diverse nanomaterials are accessible: surface-confined thin films (planar and nonplanar supports), free-standing monoliths, nanomesh materials, inverse opals, and dense gram-scale nanocrystalline powders of intermetallic AuCu. Importantly, the multimetallic materials synthesized using this approach are functional, yielding a room-temperature Fe-Pt ferromagnet, a superconducting sample of Ag2Pd3S (Tc = 1.10 K), and a AuPd4 alloy that selectively catalyzes the formation of H2O2 from H2 and O2. Such flexibility in the synthesis and processing of functional intermetallic and alloy materials is unprecedented.

Competitive 15N kinetic isotope effects of nitrogenase-catalyzed dinitrogen reduction.

Biological N2 fixation is achieved under ambient conditions by enzymatic catalysis. The enzyme nitrogenase has been studied extensively, but the N2 chemical reduction step is, by far, not rate limiting and hard to examine. A new method was developed that allows studying the reduction transition state within the enzyme's complex kinetic cascade by means of the 15N kinetic isotope effect on the reaction's second-order rate constant, V/K. A value of 1.7% +/- 0.2% was measured.

Synthesis of atomically ordered AuCu and AuCu(3) nanocrystals from bimetallic nanoparticle precursors.

A new multistep approach was developed to synthesize atomically ordered intermetallic nanocrystals, using AuCu and AuCu(3) as model systems. Bimetallic nanoparticle aggregates are used as precursors to atomically ordered nanocrystals, both to precisely define the stoichiometry of the final product and to ensure that atomic-scale diffusion distances lower the reaction temperatures to prevent sintering. In a typical synthesis, PVP-stabilized Au-Cu nanoparticle aggregates synthesized by borohydride reduction are collected by centrifugation and annealed in powder form. At temperatures below 175 degrees C, diffusion of Cu into Au occurs, and the atomically disordered solid solution Cu(x)Au(1)(-)(x) exists. For AuCu, nucleation occurs by 200 degrees C, and atomically ordered AuCu exists between 200 and 400 degrees C. For AuCu(3), an AuCu intermediate nucleates at 200 degrees C, and further diffusion of Cu into the AuCu intermediate at 300 degrees C nucleates AuCu(3). Atomically ordered AuCu and AuCu(3) nanocrystals can be redispersed as discrete colloids in solution after annealing between 200 and 300 degrees C.