Younan Xia

Bio: Younan Xia is an academic researcher from The Wallace H. Coulter Department of Biomedical Engineering. The author has contributed to research in topics: Nanocages & Nanowire. The author has an hindex of 216, co-authored 943 publications receiving 175757 citations. Previous affiliations of Younan Xia include Washington University in St. Louis & University of Texas at Dallas.

Separating Growth from Nucleation for Facile Control over the Size and Shape of Palladium Nanocrystals.

Abstract: In order to maximize the performance of nanocrystals in a specific application, it is necessary to control both their size and shape. Here we report a one-pot protocol that allows us to separate growth from nucleation for achieving better control over the size and shape of Pd nanocrystals. The two processes are temporally separated from each other, although the synthesis is carried out in the same reaction container. Size control is achieved by simply varying the ratio between the amounts of precursor allocated to the growth and nucleation processes. With the involvement of seeds at a fixed number, increasing the amount of precursor for growth leads to increasingly larger nanocrystals. Shape control is made possible by varying the capping agent, with bromide leading to a cubic shape and citrate inducing the formation of an octahedral shape. The synthesis can also be scaled up by at least tenfold without compromising the quality.

Shape‐Controlled Metal Nanocrystals for Catalytic Applications

Abstract: The implication of shape control in nanocrystal synthesis goes far beyond aesthetic appeal. For metal nanocrystals, the shape not only determines their physicochemical properties but also their technological relevance for catalytic, plasmonic, photonic, and electronic applications. In particular, heterogeneous catalysis is a field that can benefit tremendously from the availability of metal nanocrystals with well-controlled shapes, which may serve to significantly increase reaction efficiency while decreasing material cost. This article provides a brief overview of our recent progress in generating shape-controlled nanocrystals with enhanced catalytic activity toward oxygen reduction and formic acid oxidation, two reactions that are crucial for the successful commercialization of fuel cell technology. The impact on other industrially important reactions will be discussed as well. We hope that this article provides a roadmap for further development of metal nanocrystal-based catalysts with enhanced performance through shape-controlled synthesis.

Polyhedral metal nanocages with well-defined facets and ultrathin walls and methods of making and uses thereof

Abstract: A variety of polyhedral nanocages are provided having a hollow interior, ultrathin walls, and well-defined facets of metal atoms The nanocages can include a variety of precious metals such as Pt, Au, Ru, Rh, or Ir The metal atoms can take a face-centered cubic structure with {111} facets on the surface The walls can be thin, sometimes less than 1 nm in thickness or only a few atomic layers in thickness The nanocages can provide for efficient uses of valuable precious metals, among other things, in catalysis For example, catalysts are provided exhibiting high mass activities in oxygen reduction reactions Methods of making and methods of using the nanocages and catalysts are also provided

Facile Synthesis of Ag@PdnL Icosahedral Nanocrystals as a Class of Cost-Effective Electrocatalysts toward Formic Acid Oxidation

Abstract: We report a facile synthesis of Ag@Pd core−shell icosahedral nanocrystals for the development of cost‐effective electrocatalysts toward formic acid oxidation. With 12.4 nm Ag icosahedra serving as seeds, Pd shells of controlled thicknesses in the range of 3.6–5.8 atomic layers are grown by adjusting the experimental parameters. When examined as catalysts toward formic acid oxidation, all the Ag@Pd nanocrystals exhibit enhanced mass activities relative to a commercial Pd/C catalyst, with the Ag@Pd4.2L nanocrystals showing enhanced mass activity that is almost twice that of a commercial Pd/C. The chronoamperometry measurements indicate that all the Ag@Pd/C catalysts are more robust than the Pd/C, with the catalyst based on Ag@Pd4.2L nanocrystals showing a mass activity greater than that of the pristine Pd/C after holding in a mixture of HCOOH and HClO4 at 0.75 V for 1,000 s. We believe that the strategy demonstrated here can also be extended to the development of other types of advanced electrocatalysts.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

Gold nanoparticles: assembly, supramolecular chemistry, quantum-size-related properties, and applications toward biology, catalysis, and nanotechnology.

Abstract: Although gold is the subject of one of the most ancient themes of investigation in science, its renaissance now leads to an exponentially increasing number of publications, especially in the context of emerging nanoscience and nanotechnology with nanoparticles and self-assembled monolayers (SAMs). We will limit the present review to gold nanoparticles (AuNPs), also called gold colloids. AuNPs are the most stable metal nanoparticles, and they present fascinating aspects such as their assembly of multiple types involving materials science, the behavior of the individual particles, size-related electronic, magnetic and optical properties (quantum size effect), and their applications to catalysis and biology. Their promises are in these fields as well as in the bottom-up approach of nanotechnology, and they will be key materials and building block in the 21st century. Whereas the extraction of gold started in the 5th millennium B.C. near Varna (Bulgaria) and reached 10 tons per year in Egypt around 1200-1300 B.C. when the marvelous statue of Touthankamon was constructed, it is probable that “soluble” gold appeared around the 5th or 4th century B.C. in Egypt and China. In antiquity, materials were used in an ecological sense for both aesthetic and curative purposes. Colloidal gold was used to make ruby glass 293 Chem. Rev. 2004, 104, 293−346