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51.
Courtney H. Lanier Ann N. Chiaramonti Laurence D. Marks Kenneth R. Poeppelmeier 《Surface science》2009,603(16):2574-2579
The so-called Biphase termination on α-Fe2O3 has been widely accepted to be a structure with a 40 Å unit supercell composed of coexisting islands of Fe1−xO and α-Fe2O3. Based on thermodynamic arguments and experimental evidence, including transmission electron diffraction, imaging, magnetic and spectroscopic information, it is found that the previously proposed structure model is inaccurate. The actual Biphase structure is instead a layered structure related to the reduction of α-Fe2O3 to Fe3O4. A model for the Biphase termination is proposed which does not contain islands of Fe1−xO but instead consists of bulk α-Fe2O3 and a Fe3O4-derived overlayer. The proposed model is consistent with all current and previously reported experimental findings. 相似文献
52.
Sessler JL Jayawickramarajah J Sathiosatham M Sherman CL Brodbelt JS 《Organic letters》2003,5(15):2627-2630
[reaction: see text] Synthesis and assembly studies of a guanosine-cytidine dinucleoside 1 that self-assembles into a trimeric supramolecule (I) are presented. Dinucleoside 1 was obtained by utilizing two consecutive palladium-catalyzed cross-coupling reactions. Ensemble I was analyzed by ESI-MS, NMR spectroscopies, size exclusion chromatography (SEC), and vapor pressure osmometry (VPO). 相似文献
53.
54.
Colton D. Payne Bastian Franke Mark F. Fisher Fatemeh Hajiaghaalipour Courtney E. McAleese Angela Song Carl Eliasson Jingjing Zhang Achala S. Jayasena Grishma Vadlamani Richard J. Clark Rodney F. Minchin Joshua S. Mylne K. Johan Rosengren 《Chemical science》2021,12(19):6670
Head-to-tail cyclized peptides are intriguing natural products with unusual properties. The PawS-Derived Peptides (PDPs) are ribosomally synthesized as part of precursors for seed storage albumins in species of the daisy family, and are post-translationally excised and cyclized during proteolytic processing. Here we report a PDP twice the typical size and with two disulfide bonds, identified from seeds of Zinnia elegans. In water, synthetic PDP-23 forms a unique dimeric structure in which two monomers containing two β-hairpins cross-clasp and enclose a hydrophobic core, creating a square prism. This dimer can be split by addition of micelles or organic solvent and in monomeric form PDP-23 adopts open or closed V-shapes, exposing different levels of hydrophobicity dependent on conditions. This chameleonic character is unusual for disulfide-rich peptides and engenders PDP-23 with potential for cell delivery and accessing novel targets. We demonstrate this by conjugating a rhodamine dye to PDP-23, creating a stable, cell-penetrating inhibitor of the P-glycoprotein drug efflux pump.The cyclic peptide PDP-23 adopts a different structure depending on conditions. In water it forms a dimer, but can unfold allowing its hydrophobic core to interact with membranes. PDP-23 shows promise as a cell penetrating scaffold for drug delivery. 相似文献
55.
Beck BJ Aldrich CC Fecik RA Reynolds KA Sherman DH 《Journal of the American Chemical Society》2003,125(41):12551-12557
The unique ability of the pikromycin (Pik) polyketide synthase to generate 12- and 14-membered ring macrolactones presents an opportunity to explore the fundamental processes underlying polyketide synthesis, specifically the mechanistic details of the chain extension process. We have overexpressed and purified PikAIII (module 5) and PikAIV (module 6) and assessed the ability of these proteins to generate tri- and tetraketide lactone products using N-acetylcysteamine-activated diketides and (14)C-methylmalonyl-CoA as substrates. Comparison of the stereochemical specificities for PikAIII and PikAIV and the reported values for the DEBS modules reveals significant differences between these systems. 相似文献
56.
57.
Haiwen Zhang Jennifer E. Enman Maren L. Conrad Marcy J. Manning Courtney S. Turner Susan L. Wheaton Christopher M. Vogels Stephen A. Westcott Andreas Decken Felix J. Baerlocher 《Transition Metal Chemistry》2006,31(1):13-18
Pyridinecarboxaldimines (N–N′) derived from pyridin-2-ylcarboxaldehydes and unsaturated amines add to [PdCl2(coe)]2 (coe = cis-cyclooctene) to give complexes of the type PdCl2(N–N′) in moderate yields. The palladium complexes have been investigated as substrates for hydroboration reactions and as
antifungal agents against Aspergillus niger, A. flavus, Candida albicans, and Saccharomyces cerevisiae. 相似文献
58.
Iris H. Hall Courtney E. Tolmie Betsy Jo Barnes Michael A. Curtis J. Monte Russell M. G. Finn Russell N. Grimes 《应用有机金属化学》2000,14(2):108-118
The metallacarboranes (Et2C2B4H4)‐TaCl2(C5H5) ( 1 ), (Et2C2B4H4)NbCl2(C5H5) ( 2 ), (Et2C2B4H4)TaCl2(C5Me5) ( 3 ), [(Me3Si)2C2B4H4]TaCl2(C5H5) ( 4 ) and (Me2C2B4H4)‐TaCl2(C5H5) ( 5 ) are potent cytotoxic agents against suspended tumors, producing cell death in several tissue culture lines; for example, all were effective against murine L1210 lymphoid leukemia, and all except 5 against murine P388 lymphocytic growth. Human leukemic growth is also retarded since 1–4 were effective against Tmolt3 cell leukemia, all except 4 against Tmolt4 leukemia, and 1, 2 , and 5 against HI‐60 leukemia. Cytotoxicity was found towards HuT‐8 lymphoma, THP‐1 acute monocytic leukemia and suspended HeLa‐S3 uterine carcinoma. Some but not all of the complexes were active against Sk‐2 melanoma and Mcf‐7 breast effusion growth. Mode‐of‐action studies in P388 lymphocytic leukemia cells showed that de novo purine synthesis was inhibited; this inhibition reduces DNA and RNA syntheses. Purine synthesis was reduced by compounds 3 and 4 at the regulatory enzymes, i.e. phosphoribosyl pyrophosphate (PRPP) amidotransferase and dihydrofolate reductase. The agents lowered d[ATP] and d[CTP] pools, further reducing DNA synthesis. The complexes afforded DNA fragmentation leading to apoptosis, but this was not by a mechanism of nucleoside alkylation, intercalation between base‐pairs or cross‐linking of the DNA strands. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
59.
Amanda C. Evans Jared Skey Megan Wright Wenjun Qu Courtney Ondeck Deborah A. Longbottom Rachel K. O'Reilly 《Journal of polymer science. Part A, Polymer chemistry》2009,47(24):6814-6826
We report the application of reversible addition‐fragmentation chain transfer polymerization using a novel chain transfer agent toward the synthesis of a variety of copolymers containing proline‐derived monomeric units. This methodology enables ready access to a number of polymeric species with narrow molecular weight distributions, reliable functional unit incorporations, and high conversions. The methodology is also a facile approach to novel copolymeric species incorporating amino acids, which possess unique material properties and the potential for further organocatalytic application. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009 相似文献
60.
Donagh O’Mahony Thomas Dumont Thomas Lippert Alexander Wokaun 《Applied Surface Science》2007,254(4):811-815
Laser ablation is widely used to assist in the fabrication of prototype lithium manganate (LiMn2O4) thin film structures for Li-ion battery electrodes via the pulsed laser deposition technique. However, films can be considerably Li and/or O deficient, depending the deposition conditions used. Here we present data on the ionic component of laser-produced plasma in laser ablation of lithium manganate with ns excimer laser. Plasma was monitored using an electrical Langmuir ion probe, in time-of-flight mode in conjunction with mass spectrometry to identify the dominant ionic species. Ablation in vacuum at ∼2.5 J cm−2 revealed the plasma's ionic component was composed primarily of singly charged Li and Mn ions. The time-of-flight data indicates significant deceleration of the plasma when ablation is carried out in an oxygen background gas pressure of the order of 10 Pa. The implications for thin film growth are considered in terms of the possible gas phase interactions and/or thin film re-sputtering yield. 相似文献