16,948 research outputs found

    Copper(II)- and gold(III)-mediated cyclization of a thiourea to a substituted 2-aminobenzothiazole

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    Benzothiazole derivatives are a class of privileged molecules due to their biological activity and pharmaceutical applications. One route to these molecules is via intramolecular cyclization of thioureas to form substituted 2-aminobenzothiazoles, but this often requires harsh conditions or employs expensive metal catalysts. Herein, the copper(II)- and gold(III)-mediated cyclizations of thioureas to substituted 2-aminobenzothiazoles are reported. The single-crystal X-ray structures of the thiourea N-(3-methoxyphenyl)-N\u27- (pyridin-2-yl)thiourea, C13H13N3OS, and the intermediate metal complexes aquabis[5-methoxy-N-(pyridin-2-yl-κN)-1,3-benzothiazol-2-amine-κN3]copper(II) dinitrate, [Cu(C13H11N3OS)2(H2O)](NO3)2, and bis{2-[(5-methoxy-1,3-benzothiazol- 2-yl)amino]pyridin-1-ium} dichloridogold(I) chloride monohydrate, (C13H12N3OS)2[AuCl2]Cl⋅H2O, are reported. The copper complex exhibits a distorted trigonal–bipyramidal geometry, with direct metal-to-benzothiazoleligand coordination, while the gold complex is a salt containing the protonated uncoordinated benzothiazole, and offers evidence that metal reduction (in this case, AuIII to AuI) is required for the cyclization to proceed. As such, this study provides further mechanistic insight into the role of the metal cations in these transformations

    Energies of Quantum QED Flux Tubes

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    In this talk I present recent studies on vacuum polarization energies and energy densities induced by QED flux tubes. I focus on comparing three and four dimensional scenarios and the discussion of various approximation schemes in view of the exact treatment.Comment: 9 pages latex, Talk presented at the QFEXT 05 workshop in Barcelona, Sept. 2005. To appear in the proceeding

    THE INCIDENCE OF ROOT DENTINAL MICRO-CRACKS CAUSED BY RECIPROCATING AND CONTINUOUS ROTARY INSTRUMENTATION

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    The aim of this study was to compare the incidence of root canal dentinal micro-cracks after canal instrumentation using reciprocating files (WaveOne Gold® and Twisted Adaptive®) and continuous rotation files (Edge Evolve® and EndoSequence®) in an ex-vivo benchtop study. This project used a novel methodology of finding dentinal defects using the “K-cube”, which allows evaluators to visualize sectioned root surfaces before instrumentation and after instrumentation. Mesial roots from 40 human mandibular first molars were divided into 4 groups of 10 for each file type. Root section pictures were taken with a Zeiss Discovery V20 stereomicroscope before and after canal instrumentation. Each of the pre-instrumentation and post-instrumentation images were evaluated for dentinal defects by four calibrated endodontists utilizing REDCap survey. Using a chi-square analysis, there was no statistically significant difference between dentinal defects created by continuous and reciprocating rotation (p=0.1924) and no difference between the four file types (p=0.2317)

    Quantum stabilization of Z-strings, a status report on D=3+1 dimensions

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    We investigate an extension to the phase shift formalism for calculating one-loop determinants. This extension is motivated by requirements of the computation of Z-string quantum energies in D=3+1 dimensions. A subtlety that seems to imply that the vacuum polarization diagram in this formalism is (erroneously) finite is thoroughly investigated.Comment: Based on talk by O.S. at QFEXT07, Leipzig Sept. 2007. 8 page

    Negotiation in Multi-Agent Systems

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    In systems composed of multiple autonomous agents, negotiation is a key form of interaction that enables groups of agents to arrive at a mutual agreement regarding some belief, goal or plan, for example. Particularly because the agents are autonomous and cannot be assumed to be benevolent, agents must influence others to convince them to act in certain ways, and negotiation is thus critical for managing such inter-agent dependencies. The process of negotiation may be of many different forms, such as auctions, protocols in the style of the contract net, and argumentation, but it is unclear just how sophisticated the agents or the protocols for interaction must be for successful negotiation in different contexts. All these issues were raised in the panel session on negotiation

    Syndecan-4 knockout leads to reduced extracellular transglutaminase-2 and protects against tubulointerstitial fibrosis

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    Transglutaminase type 2 (TG2) is an extracellular matrix crosslinking enzyme with a pivotal role in kidney fibrosis. The interaction of TG2 with the heparan sulfate proteoglycan syndecan-4 (Sdc4) regulates the cell surface trafficking, localization, and activity of TG2 in vitro but remains unstudied in vivo. We tested the hypothesis that Sdc4 is required for cell surface targeting of TG2 and the development of kidney fibrosis in CKD. Wild-type and Sdc4-null mice were subjected to unilateral ureteric obstruction and aristolochic acid nephropathy (AAN) as experimental models of kidney fibrosis. Analysis of renal scarring by Masson trichrome staining, kidney hydroxyproline levels, and collagen immunofluorescence demonstrated progressive fibrosis associated with increases in extracellular TG2 and TG activity in the tubulointerstitium in both models. Knockout of Sdc-4 reduced these effects and prevented AAN-induced increases in total and active TGF-b1. In wild-type mice subjected to AAN, extracellular TG2 colocalized with Sdc4 in the tubular interstitium and basement membrane, where TG2 also colocalized with heparan sulfate chains. Heparitinase I, which selectively cleaves heparan sulfate, completely abolished extracellular TG2 in normal and diseased kidney sections. In conclusion, the lack of Sdc4 heparan sulfate chains in the kidneys of Sdc4-null mice abrogates injury-induced externalization of TG2, thereby preventing profibrotic crosslinking of extracellular matrix and recruitment of large latent TGF-b1. This finding suggests that targeting the TG2- Sdc4 interaction may provide a specific interventional strategy for the treatment of CKD

    Density-functional theory study on the arrangement of adsorbed formate molecules on Cu(110)

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    The interaction of formate molecules with the Cu(110) surface is investigated using density-functional theory calculations. We find that in the most stable structures for low and high coverage, the formate molecules are sitting perpendicular to the Cu(110) surface, and they are adsorbed in a bridge position, i.e., the O-C-O group forms a bridge between two Cu atoms. Other tested configurations are less stable by at least 0.45 eV per formate molecule. In the case of an oxygen-precovered Cu(110) surface with high formate coverage [two molecules in a (2x2) unit cell] we find a very similar adsorption geometry. We find an attractive interaction between adsorbed formate molecules on the copper surface. Our results are consistent with experimental results by scanning tunneling microscopy and photoelectron diffraction
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