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Direct Attack (direct + attack)

Distribution by Scientific Domains

Humanities and Social Sciences	50%

Selected Abstracts

The effect of the sixth sulfur ligand in the catalytic mechanism of periplasmic nitrate reductase

JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 15 2009
N. M. F. S. A. Cerqueira
Abstract The catalytic mechanism of nitrate reduction by periplasmic nitrate reductases has been investigated using theoretical and computational means. We have found that the nitrate molecule binds to the active site with the Mo ion in the +6 oxidation state. Electron transfer to the active site occurs only in the proton-electron transfer stage, where the MoV species plays an important role in catalysis. The presence of the sulfur atom in the molybdenum coordination sphere creates a pseudo-dithiolene ligand that protects it from any direct attack from the solvent. Upon the nitrate binding there is a conformational rearrangement of this ring that allows the direct contact of the nitrate with MoVI ion. This rearrangement is stabilized by the conserved methionines Met141 and Met308. The reduction of nitrate into nitrite occurs in the second step of the mechanism where the two dimethyl-dithiolene ligands have a key role in spreading the excess of negative charge near the Mo atom to make it available for the chemical reaction. The reaction involves the oxidation of the sulfur atoms and not of the molybdenum as previously suggested. The mechanism involves a molybdenum and sulfur-based redox chemistry instead of the currently accepted redox chemistry based only on the Mo ion. The second part of the mechanism involves two protonation steps that are promoted by the presence of MoV species. MoVI intermediates might also be present in this stage depending on the availability of protons and electrons. Once the water molecule is generated only the MoVI species allow water molecule dissociation, and, the concomitant enzymatic turnover. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009 [source]

Incubation period in the 2,2,4,4-tetramethyl-1-piperidinyloxy-mediated thermal autopolymerization of styrene: Kinetics and simulations

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 24 2006
Enrique Saldívar-Guerra
Abstract Mechanisms and simulations of the induction period and the initial polymerization stages in the nitroxide-mediated autopolymerization of styrene are discussed. At 120,125 °C and moderate 2,2,4,4-tetramethyl-1-piperidinyloxy (TEMPO) concentrations (0.02,0.08 M), the main source of radicals is the hydrogen abstraction of the Mayo dimer by TEMPO [with the kinetic constant of hydrogen abstraction (kh)]. At higher TEMPO concentrations ([N,] > 0.1 M), this reaction is still dominant, but radical generation by the direct attack against styrene by TEMPO, with kinetic constant of addition kad, also becomes relevant. From previous experimental data and simulations, initial estimates of kh , 1 and kad , 6 × 10,7 L mol,1 s,1 are obtained at 125 °C. From the induction period to the polymerization regime, there is an abrupt change in the dominant mechanism generating radicals because of the sudden decrease in the nitroxide radicals. Under induction-period conditions, the simulations confirm the validity of the quasi-steady-state assumption (QSSA) for the Mayo dimer in this regime; however, after the induction period, the QSSA for the dimer is not valid, and this brings into question the scientific basis of the well-known expression kth[M]3 (where [M] is the monomer concentration and kth is the kinetic constant of autoinitiation) for the autoinitiation rate in styrene polymerization. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6962-6979, 2006 [source]

The Bishops' Ban of 1599 and the Ideology of English Satire

LITERATURE COMPASS (ELECTRONIC), Issue 5 2010
William R. Jones
On June 1, 1599, the Archbishop of Canterbury and the Bishop of London banned the further printing of satires, epigrams, and unlicensed histories and plays. Furthermore, the order demanded the immediate recall and burning of specific works, many of which were verse imitations of the Roman satirist Juvenal. Although the order itself lacks specific motivational language, current explanations tend to foreground the potentially obscene and/or libelous nature of the recalled works. Comparatively little attention has been paid, however, to the internal ideologies of the banned satires themselves and to the dialogue between the satires and the cultural and political conditions that inspired them. Instead of an ad hoc response to any one particular transgression, this essay argues for the Ban as an attempt to stem the growing cultural influence of a particularly unorthodox mode of Juvenalian imitative satire expressed most forcefully in John Marston's banned work, The Scourge of Villanie. Marston's rejection of all established belief systems, especially the conservative literary traditions of native English and Horatian imitative satire, in favor of a highly individualistic and indecorous mode of social representation, was simply too ideologically destabilizing for the bishops to tolerate. In support of this reading, two relatively underexplored pieces of evidence are examined: first, the reprieve granted to Joseph Hall's imitative satire entitled Virgidemiarum, which attempts to negotiate an ideologically safe middle-ground between the radical Juvenalian mode and the conservative Horatian tradition; and second, the contemporary reflections on the bishops' prohibition within John Weever's 1599 Epigrams, his 1600 pastoral Faunus and Melliflora, and his 1601 direct attack on Marston in The Whipping of the Satyre. Weever's support of the bishops' actions derives from his identification of the banned Juvenalian mode as not merely morally offensive or personally defamatory, but as a tangible threat to the ideological stability of the English nation. [source]

JUST WAR AND THE SUPREME EMERGENCY EXEMPTION

THE PHILOSOPHICAL QUARTERLY, Issue 221 2005
Christopher Toner
Recently a number of liberal political theorists, including Rawls and Walzer, have argued for a ,supreme emergency exemption' from the traditional just war principle of discrimination which absolutely prohibits direct attacks against innocent civilians, claiming that a political community threatened with destruction may deliberately target innocents in order to save itself. I argue that this ,supreme emergency exemption' implies that individuals too may kill innocents in supreme emergencies. This is a significant theoretical cost. While it will not constitute a decisive refutation of all arguments for a supreme emergency exemption, my hope is that many will see this cost of endorsing the exemption as unacceptable. [source]