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Zhao L.,Xian Jiaotong University | Lu W.,Xian University of Science and Technology
Current opinion in chemical biology | Year: 2014

Proteins composed entirely of unnatural d-amino acids and the achiral amino acid glycine are mirror image forms of their native l-protein counterparts. Recent advances in chemical protein synthesis afford unique and facile synthetic access to domain-sized mirror image d-proteins, enabling protein research to be conducted through 'the looking glass' and in a way previously unattainable. d-Proteins can facilitate structure determination of their native l-forms that are difficult to crystallize (racemic X-ray crystallography); d-proteins can serve as the bait for library screening to ultimately yield pharmacologically superior d-peptide/d-protein therapeutics (mirror-image phage display); d-proteins can also be used as a powerful mechanistic tool for probing molecular events in biology. This review examines recent progress in the application of mirror image proteins to structural biology, drug discovery, and immunology. Copyright © 2014 Elsevier Ltd. All rights reserved. Source

Zhang S.,Xian University of Science and Technology
The Journal of the Acoustical Society of America | Year: 2012

The acoustic posterior shadowing effects of bubbles influence the accuracy for defining the location and range of ablated thermal lesions during focused ultrasound surgery when using ultrasonic monitoring imaging. This paper explored the feasibility of using Nakagami distribution to evaluate the ablated region induced by focused ultrasound exposures at different acoustic power levels in transparent tissue-mimicking phantoms. The mean value of the Nakagami parameter m was about 0.5 in the cavitation region and increased to around 1 in the ablated region. Nakagami images were not subject to significant shadowing effects of bubbles. Ultrasound-induced thermal lesions observed in the photos and Nakagami images were overshadowed by bubbles in the B-mode images. The lesion size predicted in the Nakagami images was smaller than that predicted in the photos due to the sub resolvable effect of Nakagami imaging at the interface. This preliminary study on tissue-mimicking phantom suggested that the Nakagami parameter m may have the potential use in evaluating the formation of ultrasound-induced thermal lesion when the shadowing effect of bubbles is strong while the thermal lesion was small. Further studies in vivo and in vitro will be needed to evaluate the potential application. Source

Zhang H.,Zhejiang University | Jin M.,Xian University of Science and Technology | Xiong Y.,Anhui University of Science and Technology | Lim B.,Sungkyunkwan University | Xia Y.,Georgia Institute of Technology
Accounts of Chemical Research | Year: 2013

Palladium is a marvelous catalyst for a rich variety of reactions in industrial processes and commercial devices. Most Pd-catalyzed reactions exhibit structure sensitivity, meaning that the activity or selectivity depends on the arrangement of atoms on the surface. Previously, such reactions could only be studied in ultrahigh vacuum using Pd single crystals cut with a specific crystallographic plane. However, these model catalysts are far different from real catalytic systems owing to the absence of atoms at corners and edges and the extremely small specific surface areas for the model systems. Indeed, enhancing the performance of a Pd-based catalyst, in part to reduce the amount needed of this precious and rare metal for a given reaction, requires the use of Pd with the highest possible specific surface area. Recent advances in nanocrystal synthesis are offering a great opportunity to investigate and quantify the structural sensitivity of catalysts based on Pd and other metals. For a structure-sensitive reaction, the catalytic properties of Pd nanocrystals are strongly dependent on both the size and shape. The shape plays a more significant role in controlling activity and selectivity, because the shape controls not only the facets but also the proportions of surface atoms at corners, edges, and planes, which affect the outcomes of possible reactions. We expect catalysts based on Pd nanocrystals with optimized shapes to meet the increasing demands of industrial applications at reduced loadings and costs.In this Account, we discuss recent advances in the synthesis of Pd nanocrystals with controlled shapes and their resulting performance as catalysts for a large number of reactions. First, we review various synthetic strategies based on oxidative etching, surface capping, and kinetic control that have been used to direct the shapes of nanocrystals. When crystal growth is under thermodynamic control, the capping agent plays a pivotal role in determining the shape of a product by altering the order of surface energies for different facets through selective adsorption; the resulting product has the lowest possible total surface energy. In contrast, the product of a kinetically controlled synthesis often deviates from the thermodynamically favored structure, with notable examples including nanocrystals enclosed by high-index facets or concave surfaces.We then discuss the key parameters that control the nucleation and growth of Pd nanocrystals to decipher potential growth mechanisms and build a connection between the experimental conditions and the pathways to different shapes. Finally, we present a number of examples to highlight the use of these Pd nanocrystals as catalysts or electrocatalysts for various applications with structure-sensitive properties. We believe that a deep understanding of the shape-dependent catalytic properties, together with an ability to experimentally maneuver the shape of metal nanocrystals, will eventually lead to rational design of advanced catalysts with substantially enhanced performance. © 2012 American Chemical Society. Source

Zeng X.,Xian University of Science and Technology
Chemical Reviews | Year: 2013

The article focuses on the recent advances in catalytic sequential reactions involving hydroelement addition to carbon-carbon multiple bonds. Sequential reactions, through the incorporation of several distinct transformations into one single sequence, are one of the most powerful synthetic tools in modern organic chemistry. In general, inexpensive, relatively simple and readily available starting materials can be employed to construct more sophisticated targeted molecules. Meanwhile, combining several distinct transformations into one single sequence greatly increases the complexity of the resulting compounds. Most important of all, such a practically useful 'one-pot' operation simplifies purification of the products, as well as decreasing the cost and effort of synthesis. Sonogashira cross-coupling reactions are important and ubiquitous synthetic tools in the construction of functionalized internal alkynes. Source

Qu Y.,University of California at Los Angeles | Qu Y.,Xian University of Science and Technology | Duan X.,University of California at Los Angeles
Chemical Society Reviews | Year: 2013

There is increasing interest in developing artificial systems that can mimic natural photosynthesis to directly harvest and convert solar energy into usable or storable energy resources. Photocatalysis, in which solar photons are used to drive redox reactions to produce chemical fuel, is the central process to achieve this goal. Despite significant efforts to date, a practically viable photocatalyst with sufficient efficiency, stability and low cost is yet to be demonstrated. It is often difficult to simultaneously achieve these different performance metrics with a single material component. The heterogeneous photocatalysts with multiple integrated functional components could combine the advantages of different components to overcome the drawbacks of single component photocatalysts. A wide range of heterostructures, including metal/semiconductor, semiconductor/semiconductor, molecule/semiconductor and multi-heteronanostructures, have been explored for improved photocatalysts by increasing the light absorption, promoting the charge separation and transportation, enhancing the redox catalytic activity and prolonging the functional life-time. The present review gives a concise overview of heterogeneous photocatalysts with a focus on the relationship between the structural architecture and the photocatalytic activity and stability. © 2013 The Royal Society of Chemistry. Source

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