Radical formation on gamma-radiolysis of poly [(methacrylic acid)-co-acrylonitri

The radicals formed on gamma-radiolysis of a series of copolymers of methacrylic acid and acrylonitrile have been investigated by ESR spectroscopy. This series of copolymers spanned the full composition range and the study was carried out at 77 K and ambient temperature. The radicals formed in the copolymers at 77 and 303 K were found to be similar to those found in the two homopolymers, but in the intermediate composition range the presence of acrylonitrile propagation radicals was also detected. These radicals were not observed to be formed in significant quantities on the radiolysis of polyacrylonitrile. They are believed to result from a scission of the main chain at methacrylic acid/acrylonitrile diad sequences following loss of the methacrylic acid carboxyl group. At 77 K, the copolymers with high methacrylic acid contents were found to be more sensitive to radical formation than the methacrylic acid homopolymer, but this enhanced sensitivity was not evident at ambient temperature, where the G-values for radical formation for the copolymers were slightly less than the values for the homopolymers. (C) 2003 Society of Chemical Industry.

A kinetic study of the thermally initiated free radical reactions of styrene with octanedithiol as a model for the reactions of multifunctional thiols with divinylbenzene

The kinetics of chain reactions of octanedithiol with styrene, thermally initiated with TX29B50 (a 50:50 wt% solution of TX29 diperoxy initiator in a phthalate plasticizer), have been studied over a range of initiator concentrations, a range of mixture formulations and a range of temperatures. This system has been investigated as a model system for the reactions of polyfunctional thiols with divinyl benzene. The reactions have been shown to follow first-order kinetics for both the thiol and the ene species and to be characterized by a dependence on the initiator concentration to the power of one half. The kinetic rate parameters have been shown to adhere to Arrhenius behaviour. A kinetic model for the chain reactions for this system has been proposed. (C) 2003 Society of Chemical Industry.

From radical to banal evil: Hannah Arendt against the justification of the unjustifiable

Two central strands in Arendt's thought are the reflection on the evil of Auschwitz and the rethinking in terms of politics of Heidegger's critique of metaphysics. Given Heidegger's taciturnity regarding Auschwitz and Arendt's own taciturnity regarding the philosophical implications of Heidegget's political engagement in 1933, to set out how these strands interrelate is to examine the coherence of Arendt's thought and its potential for a critique of Heidegger. By refusing to countenance a theological conception of the evil of Auschwitz, Arendt consolidates the break with theology that Heidegger attempts through his analysis of the essential finitude of Dasein. In the light of Arendt's account of evil, it is possible to see the theological vestiges in Heidegger's ontology. Heidegger's resumption of the question concerning the categorical interconnections of the ways of Being entails an abandonment of finitude: he accommodates and tacitly justifies that which can have no human justification.

Modeling the molecular weight distribution of block copolymer formation in a reversible addition-fragmentation chain transfer mediated living radical polymerization

Block copolymers have become an integral part of the preparation of complex architectures through self-assembly. The use of reversible addition-fragmentation chain transfer (RAFT) allows blocks ranging from functional to nonfunctional polymers to be made with predictable molecular weight distributions. This article models block formation by varying many of the kinetic parameters. The simulations provide insight into the overall polydispersities (PDIs) that will be obtained when the chain-transfer constants in the main equilibrium steps are varied from 100 to 0.5. When the first dormant block [polymer-S-C(Z)=S] has a PDI of 1 and the second propagating radical has a low reactivity to the RAFT moiety, the overall PDI will be greater than 1 and dependent on the weight fraction of each block. When the first block has a PDI of 2 and the second propagating radical has a low reactivity to the RAFT moiety, the PDI will decrease to around 1.5 because of random coupling of two broad distributions. It is also shown how we can in principle use only one RAFT agent to obtain block copolymers with any desired molecular weight distribution. We can accomplish this by maintaining the monomer concentration at a constant level in the reactor over the course of the reaction. (c) 2005 Wiley Periodicals, Inc.

The effects of pre-weaning undernutrition on the expression levels of free radical deactivating enzymes in the mouse brain

A mild degree of undernutrition brought about by restricting the amount of food in the diet is known to alter the life span of an animal. It has been hypothesised that this may be related to the effects of undernutrition on an animals anti-oxidant defense system. We have therefore, used real-time PCR (rt-PCR) techniques to determine the levels of mRNA expression for manganese superoxide dismutase (MnSOD), copper/zinc superoxide dismutase (Cu/ZnSOD), glutathione peroxidase 1 (GPx 1) and catalase in the brains of Quackenbush mice undernourished from conception until 21-post-natal days of age. It was found that 21- and 61-day-old undernourished mice had a deficit in the expression of Cu/ZnSOD in both the cerebellum and forebrain regions compared to age-matched controls. The expression of MnSOD was found to be greater in the cerebellum, but not the forebrain region, of 21-day-old undernourished mice. There were no significant differences in the expression of GPx 1 and catalase between control and undernourished or previously undernourished mice. Our results confirm that undernutrition during the early life of a mouse may disrupt some of the enzymes involved in the anti-oxidant defense systems.

Controlled Radical Polymerization of Styrene and Methyl Acrylate in the Presence of Reversible Addition-Fragmentation Chain Transfer Agents, Phenylethyl Phenyl Dithioacetate and Phenyldithioacetic Acid

The use of phenyldithioacetic acid (PDA) in homopolymerizations of styrene or methyl acrylate produced only a small fraction of chains with dithioester end groups. The polymerizations using 1-phenylentyl phenyldithioacetate (PEPDTA) and PDA in the same reaction showed that PDA had little or no influence on the rate or molecular weight distribution even when a 1:1 ratio is used. The mechanistic pathway for the polymerizations in the presence of PDA seemed to be different for each monomer. Styrene favors addition of styrene to PDA via a Markovnikov type addition to form a reactive RAFT agent. The polymer was shown by double detection SEC to contain dithioester end groups over the whole distribution. This polymer was then used in a chain extension experiment and the M-n was close to theory. A unique feature of this work was that PDA could be used to form a RAFT agent in situ by heating a mixture of styrene and PDA for 24 h at 70 degrees C and then polymerizing in the presence of AIBN to give a linear increase in Mn and low values of PDI (< 1.14). In the case of the polymerization of MA with PDA, the mechanism was proposed to be via degradative chain transfer. (c) 2005 Wiley Periodicals, Inc.

Design strategies for controlling the molecular weight and rate using reversible addition-fragmentation chain transfer mediated living radical polymerization

Living radical polymerization has allowed complex polymer architectures to be synthesized in bulk, solution, and water. The most versatile of these techniques is reversible addition-fragmentation chain transfer (RAFT), which allows a wide range of functional and nonfunctional polymers to be made with predictable molecular weight distributions (MWDs), ranging from very narrow to quite broad. The great complexity of the RAFT mechanism and how the kinetic parameters affect the rate of polymerization and MWD are not obvious. Therefore, the aim of this article is to provide useful insights into the important kinetic parameters that control the rate of polymerization and the evolution of the MWD with conversion. We discuss how a change in the chain-transfer constant can affect the evolution of the MWD. It is shown how we can, in principle, use only one RAFT agent to obtain a poly-mer with any MWD. Retardation and inhibition are discussed in terms of (1) the leaving R group reactivity and (2) the intermediate radical termination model versus the slow fragmentation model. (c) 2005 Wiley Periodicals, Inc.

Macrophages overexpressing tartrate-resistant acid phosphatase show altered profile of free radical production and enhanced capacity of bacterial killing

Activated macrophages and osteoclasts express high amounts of tartrate-resistant acid phosphatase (TRACP, acp5). TRACP has a binuclear iron center with a redox-active iron that has been shown to catalyze the formation of reactive oxygen species (ROS) by Fenton's reaction. Previous Studies Suggest that ROS generated by TRACP may participate in degradation of endocytosed bone matrix products in resorbing osteoclasts and degradation of foreign Compounds during. antigen presentation in activated macrophages. Here we have compared free radical production in macrophages of TRACP overexpressing (TRACP +) and wild-type (WT) mice. TRACP overexpression increased both ROS levels and Superoxide production. Nitric oxide production was increased in activated macrophages or WT mice, but not in TRACP+ mice, Macrophages from TRACP+ mice showed increased capacity or bacterial killing. Recombinant TRACP enzyme was capable of bacterial killing in the presence of hydrogen peroxide. These results suggest that TRACP has an important biological function in immune defense systern.

Prosecution and radical discourse during the 1790s: The case of the Scottish sedition trials

This essay looks at the sedition trials in Scotland during the 1790s to examine how prosecution was exploited by radicals as a forum for political expression. As the government instituted a concerted campaign against radical activism, an increasing number of reformers faced trial on sedition and treason in this period. The courtroom emerged as an alternative venue for political discourse and this essay will explore some of the ways by which radicals challenged the dominant discursive and performative elements of trial proceedings. (c) 2005 Elsevier Ltd. All rights reserved.