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Shen Y.,CAS Beijing National Laboratory for Molecular | Shen Y.,University of Chinese Academy of Sciences | Chen C.-F.,CAS Beijing National Laboratory for Molecular
Chemical Reviews | Year: 2012

Work done in the field of helicenes from 1900s to the early 2011 is reviewed. In 1967, Martin and co-workers reported the first photoinduced synthesis of heptahelicene. Katz et al. developed another impressive strategy using excess propylene oxide plus a stoichiometric amount of iodine in an inert atmosphere, which not only enhances the yields greatly compared with the traditional conditions for the photocyclization of stilbenes but also prevents photoreduction or photooxidative side reactions of the double bonds. A Ru-catalyzed double cyclization through a naphthoannulation procedure based on 1,1-diaryl-2,2-diethynylethylenes, was disclosed by Scott and Donovan in 2004. Hassine and coworkers utilized β-styrylpyridine as one aryl moiety to give two helicene isomers after Mizoroki-Heck coupling and a photocyclization. Staab and co-workers reported the use of Stille-Kelly coupling to synthesize 1,16-diaza[6]helicene in 52% yield in the presence of hexamethyldistannane. Source

Zhou X.,University of Chinese Academy of Sciences
Nature Genetics | Year: 2014

Colobines are a unique group of Old World monkeys that principally eat leaves and seeds rather than fruits and insects. We report the sequencing at 146× coverage, de novo assembly and analyses of the genome of a male golden snub-nosed monkey (Rhinopithecus roxellana) and resequencing at 30× coverage of three related species (Rhinopithecus bieti, Rhinopithecus brelichi and Rhinopithecus strykeri). Comparative analyses showed that Asian colobines have an enhanced ability to derive energy from fatty acids and to degrade xenobiotics. We found evidence for functional evolution in the colobine RNASE1 gene, encoding a key secretory RNase that digests the high concentrations of bacterial RNA derived from symbiotic microflora. Demographic reconstructions indicated that the profile of ancient effective population sizes for R. roxellana more closely resembles that of giant panda rather than its congeners. These findings offer new insights into the dietary adaptations and evolutionary history of colobine primates. © 2014 Nature Publishing Group, a division of Macmillan Publishers Limited. All Rights Reserved. Source

Tian Z.,University of Chinese Academy of Sciences | Li A.D.Q.,Washington State University
Accounts of Chemical Research | Year: 2013

Because of its ultrasensitivity, fluorescence offers a noninvasive means to investigate biomolecular mechanisms, pathways, and regulations in living cells, tissues, and animals. However, real-world applications of fluorescence technologies encounter many practical challenges. For example, the intrinsic heterogeneity of biological samples always generates optical interferences. High background such as autofluorescence can often obscure the desired signals. Finally, the wave properties of light limit the spatial resolution of optical microscopy.The key to solving these problems involves using chemical structures that can modulate the fluorescence output. Photoswitchable fluorescent molecules that alternate their emissions between two colors or between bright-and-dark states in response to external light stimulation form the core of these technologies. For example, molecular fluorescence modulation can switch fluorophores on and off. This feature supports super-resolution, which enhances resolution by an order of magnitude greater than the longstanding diffraction-limit barrier. The reversible modulation of such probes at a particular frequency significantly amplifies the frequency-bearing target signal while suppressing interferences and autofluorescence.In this Account, we outline the fundamental connection between constant excitation and oscillating fluorescence. To create molecules that will convert a constant excitation into oscillating emission, we have synthesized photoswitchable probes and demonstrated them as proofs of concept in super-resolution imaging and frequency-domain imaging. First, we introduce the design of molecules that can convert constant excitation into oscillating emission, the key step in fluorescence modulation. Then we discuss various technologies that use fluorescence modulation: super-resolution imaging, dual-color imaging, phase-sensitive lock-in detection, and frequency-domain imaging. Finally, we present two biological applications to demonstrate the power of photoswitching-enabled fluorescence imaging. Because synthetic photoswitchable probes can be much smaller, more versatile, and more efficient at high-performance modulation experiments, they provide a complement to photoswitchable fluorescent proteins. Although new challenges remain, we foresee a bright future for photoswitching-enabled imaging and detection. © 2012 American Chemical Society. Source

Lu Y.,CAS Changchun Institute of Applied Chemistry | Lu Y.,University of Chinese Academy of Sciences | Chen W.,CAS Changchun Institute of Applied Chemistry
Chemical Society Reviews | Year: 2012

Sub-nanometre sized metal clusters, with dimensions between metal atoms and nanoparticles, have attracted more and more attention due to their unique electronic structures and the subsequent unusual physical and chemical properties. However, the tiny size of the metal clusters brings the difficulty of their synthesis compared to the easier preparation of large nanoparticles. Up to now various synthetic techniques and routes have been successfully applied to the preparation of sub-nanometre clusters. Among the metals, gold clusters, especially the alkanethiolate monolayer protected clusters (MPCs), have been extensively investigated during the past decades. In recent years, silver and copper nanoclusters have also attracted enormous interest mainly due to their excellent photoluminescent properties. Meanwhile, more structural characteristics, particular optical, catalytic, electronic and magnetic properties and the related technical applications of the metal nanoclusters have been discovered in recent years. In this critical review, recent advances in sub-nanometre sized metal clusters (Au, Ag, Cu, etc.) including the synthetic techniques, structural characterizations, novel physical, chemical and optical properties and their potential applications are discussed in detail. We finally give a brief outlook on the future development of metal nanoclusters from the viewpoint of controlled synthesis and their potential applications. © The Royal Society of Chemistry 2012. Source

Zhou K.,University of Chinese Academy of Sciences | Li Y.,Tsinghua University
Angewandte Chemie - International Edition | Year: 2012

Using bottom-up chemistry techniques, the composition, size, and shape in particular can now be controlled uniformly for each and every nanocrystal (NC). Research into shape-controlled NCs have shown that the catalytic properties of a material are sensitive not only to the size but also to the shape of the NCs as a consequence of well-defined facets. These findings are of great importance for modern heterogeneous catalysis research. First, a rational synthesis of catalysts might be achieved, since desired activity and selectivity would be acquired by simply tuning the shape, that is, the exposed crystal facets, of a NC catalyst. Second, shape-controlled NCs are relatively simple systems, in contrast to traditional complex solids, suggesting that they may serve as novel model catalysts to bridge the gap between model surfaces and real catalysts. Shape-controlled nanocrystals (NCs) are a new frontier in heterogeneous catalysis. Research into these NCs has shown that the catalytic properties of a material are sensitive not only to the size but also to the shape of the NCs owing to well-defined facets. Shape-controlled NCs may serve to bridge the gap between model surfaces and real catalysts. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

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