JACS133 1pp 1166.docx

1、JACS133 1pp 1166Solution-Processed, High-Performance Nanoribbon Transistors Based on DithioperyleneSolution-processed, high-performance 1D single-crystalline nanoribbon transistors fabricated from dithioperylene are described. The integration of two sulfur atoms into the perylene skeleton induces a

2、compressed highly ordered packing mode directed by SS interactions. The mobilities of up to 2.13 cm2 V1 s1 for a dithioperylene individual nanoribbon make it particularly attractive for electronic applications.X-ray and NMR Crystallography in an Enzyme Active Site: The Indoline Quinonoid Intermediat

3、e in Tryptophan SynthaseChemical-level details such as protonation and hybridization state are critical for understanding enzyme mechanism and function. Even at high resolution, these details are difficult to determine by X-ray crystallography alone. The chemical shift in NMR spectroscopy, however,

4、is an extremely sensitive probe of the chemical environment, making solid-state NMR spectroscopy and X-ray crystallography a powerful combination for defining chemically detailed three-dimensional structures. Here we adopted this combined approach to determine the chemically rich crystal structure o

5、f the indoline quinonoid intermediate in the pyridoxal-5-phosphate-dependent enzyme tryptophan synthase under conditions of active catalysis. Models of the active site were developed using a synergistic approach in which the structure of this reactive substrate analogue was optimized using ab initio

6、 computational chemistry in the presence of side-chain residues fixed at their crystallographically determined coordinates. Various models of charge and protonation state for the substrate and nearby catalytic residues could be uniquely distinguished by their calculated effects on the chemical shift

7、s measured at specifically 13C- and 15N-labeled positions on the substrate. Our model suggests the importance of an equilibrium between tautomeric forms of the substrate, with the protonation state of the major isomer directing the next catalytic step.Water-Soluble Peptide-Coated Nanoparticles: Cont

8、rol of the Helix Structure and Enhanced Differential Binding to Immune CellsThe stabilizing action of C-tetrasubstituted -amino acids inserted into a sequence of short peptides allowed for the first time the preparation of water-soluble nanoparticles of different materials coated with a helix-struct

9、ured undecapeptide. This peptide coating strongly favors nanoparticle uptake by human immune system cells.A Photocleavable Rapamycin Conjugate for Spatiotemporal Control of Small GTPase ActivityWe developed a novel method to spatiotemporally control the activity of signaling molecules. A newly synth

10、esized photocaged rapamycin derivative induced rapid dimerization of FKBP (FK-506 binding protein) and FRB (FKBP-rapamycin binding protein) upon UV irradiation. With this system and the spatially confined UV irradiation, we achieved subcellularly localized activation of Rac, a member of small GTPase

11、s. Our technique offers a powerful approach to studies of dynamic intracellular signaling events.Cysteine-Activated Hydrogen Sulfide (H2S) DonorsH2S, the newly discovered gasotransmitter, plays important roles in biological systems. However, the research on H2S has been hindered by the lack of contr

12、ollable H2S donors that could mimic the slow and continuous H2S generation process in vivo. Herein we report a series of cysteine-activated H2S donors. Structural modifications of these molecules can regulate the rates of H2S generation. These compounds can be useful tools in H2S research.Enantiosel

13、ective Synthesis of Biphenols from 1,4-Diketones by Traceless Central-to-Axial Chirality ExchangeA method for the enantioselective synthesis of biphenols from readily prepared 1,4-diketones is reported. Key to the success of this method is the highly selective transfer of central to axial chirality

14、during a double aromatization event triggered by BF3OEt2. On the basis of X-ray crystallographic data, a stereochemical model for this chirality exchange process is put forth.Formation of SnO2 Hollow Nanospheres inside Mesoporous Silica NanoreactorsWe report an interesting approach for efficient syn

15、thesis of SnO2 hollow spheres inside mesoporous silica “nanoreactors”. The as-prepared products are shown to have a uniform size distribution and good structural stability. When evaluated for their lithium storage properties, these SnO2 hollow spheres manifest improved capacity retention.Bright and

16、Compact Alloyed Quantum Dots with Broadly Tunable Near-Infrared Absorption and Fluorescence Spectra through Mercury Cation ExchangeWe report a new strategy based on mercury cation exchange in nonpolar solvents to prepare bright and compact alloyed quantum dots (QDs) (HgxCd1xE, where E = Te, Se, or S

17、) with equalized particle size and broadly tunable absorption and fluorescence emission in the near-infrared. The main rationale is that cubic CdE and HgE have nearly identical lattice constants but very different band gap energies and electron/hole masses. Thus, replacement of Cd2+ by Hg2+ in CdTe

18、nanocrystals does not change the particle size, but it greatly alters the band gap energy. After capping with a multilayer shell and solubilization with a multidentate ligand, this class of cation-exchanged QDs are compact (6.5 nm nanocrystal size and 10 nm hydrodynamic diameter) and very bright (60

19、80% quantum yield), with narrow and symmetric fluorescence spectra tunable across the wavelength range from 700 to 1150 nm.Low Reflectivity and High Flexibility of Tin-Doped Indium Oxide Nanofiber Transparent ElectrodesTin-doped indium oxide (ITO) has found widespread use in solar cells, displays, a

20、nd touch screens as a transparent electrode; however, two major problems with ITO remain: high reflectivity (up to 10%) and insufficient flexibility. Together, these problems severely limit the applications of ITO films for future optoelectronic devices. In this communication, we report the fabricat

21、ion of ITO nanofiber network transparent electrodes. The nanofiber networks show optical reflectivity as low as 5% and high flexibility; the nanofiber networks can be bent to a radius of 2 mm with negligible changes in the sheet resistance.A Porphyrin Fused to Four AnthracenesWe have synthesized a f

22、used tetraanthracenylporphyrin by oxidation of a meso-anthracenyl nickel(II) porphyrin with FeCl3. This compound exhibits an intense red-shifted absorption spectrum (max = 1417 nm; = 1.2 105 M1 cm1) and a small electrochemical HOMOLUMO gap (0.61 eV). The crystal structure shows that it forms -stacke

23、d dimers with a short NiNi distance (3.32 ).Rhodium-Catalyzed Anti-Markovnikov Intermolecular Hydroalkoxylation of Terminal AcetylenesWe report here the first transition-metal-catalyzed anti-Markovnikov intermolecular hydroalkoxylation of terminal acetylenes to give enol ethers in high yields withou

24、t using bases. Arylacetylenes as well as alkenyl- and alkylacetylenes were coupled with aliphatic alcohols, and the products were obtained with high Z selectivity in most cases. Effective catalysts were 8-quinolinolato rhodium complexes, which are structurally simple but have been relatively unexplo

25、red as catalysts.Surface-Mediated Production of Hydroxyl Radicals as a Mechanism of Iron Oxide Nanoparticle BiotoxicityEmerging applications of nanosized iron oxides in nanotechnology introduce vast quantities of nanomaterials into the human environment, thus raising some concerns. Here we report th

26、at the surface of -Fe2O3 nanoparticles 2040 nm in diameter mediates production of highly reactive hydroxyl radicals (OH) under conditions of the biologically relevant superoxide-driven Fenton reaction. By conducting comparative spin-trapping EPR experiments, we show that the free radical production

27、is attributed primarily to the catalytic reactions at the nanoparticles surface rather than being caused by the dissolved metal ions released by the nanoparticles as previously thought. Moreover, the catalytic centers on the nanoparticle surface were found to be at least 50-fold more effective in OH

28、 radical production than the dissolved Fe3+ ions. Conventional surface modification methods such as passivating the nanoparticles surface with up to 935 molecules of oleate or up to 18 molecules of bovine serum albumin per iron oxide core were found to be rather ineffective in suppressing production

29、 of the hydroxyl radicals. The experimental protocols developed in this study could be used as one of the approaches for developing analytical assays for assessing the free radical generating activity of a variety of nanomaterials that is potentially related to their biotoxicity.Postsynthetic Guanin

30、e Arylation of DNA by SuzukiMiyaura Cross-CouplingDirect radical addition reactions at the C8-site of 2-deoxyguanosine (dG) can afford C8-Ar-dG adducts that are produced by carcinogenic arylhydrazines, polycyclic aromatic hydrocarbons, and certain phenolic toxins. Such modified nucleobases are also

31、highly fluorescent for sensing applications and possess useful electron transfer properties. The site-specific synthesis of oligonucleotides containing the C8-Ar-G adduct can be problematic. These lesions are sensitive to acids and oxidants that are commonly used in solid-phase DNA synthesis and are

32、 too bulky to be accepted as substrates for enzymatic synthesis by DNA polymerases. Using the SuzukiMiyaura cross-coupling reaction, we have synthesized a number of C8-Ar-G-modified oligonucleotides (dimers, trimers, decamers, and a 15-mer) using a range of arylboronic acids. Good to excellent yields were obtained, and the reaction is insensitive to the nature of the bases flanking the convertible 8-Br-G nucleobase, as both pyrimidines and purines are tolerated. The impact of the C8-Ar-G lesion was also characterized by electrospray ionization tandem mass spectrometry, UV melting temp