The Reaction of Ozone with SBR Rubbers

1959 ◽  
Vol 32 (4) ◽  
pp. 1062-1079 ◽  
Author(s):  
E. R. Erickson ◽  
R. A. Berntsen ◽  
E. L. Hill ◽  
Paul Kusy
Keyword(s):  
Initial Rate ◽  
Protective Action ◽  
Rate Data ◽  
High Solubility ◽  
Initial Concentration ◽  
Degree Of Protection ◽  
Effective Barrier ◽  
Gaseous Ozone ◽  
Low Concentrations ◽  
Oxidized Products

Abstract All SBR vulcanizates, when tested in a relaxed state, reacted with ozone of low concentrations to form a film of oxidized products which provided an effective barrier against further attack by gaseous ozone. SBR vulcanizates that were under stress, but which contained no effective antiozonant in their formulation, were readily attacked by ozone. The absorption of ozone appeared to begin with an initial rate of zero which was followed by rapidly increasing rates until a maximum had been reached, when ozone cracks were visible on the surface of the rubber. SBR vulcanizates that were under stress, but which contained an antiozonant, were protected from an attack by ozone to a degree that ranged from poor to excellent. The degree of protection depended (a) on the differential in the rates of reaction of the antiozonant and the rubber hydrocarbon with ozone, (b) on the initial concentration of the antiozonant on the surface of the vulcanizate which reacted with ozone to form a barrier of oxidized residues, and (c) on the rate of effusion of fresh antiozonant from within the rubber to the outer surface of the barrier. SBR vulcanizates containing a naphthenic processing oil as an extender were not so resistant to ozone as standard SBR vulcanizates. It is probable that the effectiveness of the antiozonants tested in these vulcanizates was reduced by their high solubility in the oil phase. SBR vulcanizates containing trioctyl phosphate as a plasticizer were vigorously attacked by ozone. It is possible that the gaseous ozone dissolved to some extent into the plasticizer phase, increasing the concentration of ozone in the area causing a more severe oxidation of the rubber. SBR vulcanizates that had been coated with an antiozonant by dipping the specimen several times into a solution of the antiozonant in a solvent were found to contain a higher concentration of the antioxonant directly on the surface of the vulcanizate than in the case where three parts of the antiozonant were added during vulcanization. A mechanism for the ozonization of SBR vulcanizates has been proposed which includes a possible mechanism for the protective action of antiozonants. A rate equation has been derived from this mechanism which was consistent with the experimental rate data.

scholarly journals The mechanism of in vitro clot lysis induced by vascular plasminogen activator

Blood ◽  
1984 ◽  
Vol 63 (6) ◽  
pp. 1331-1337 ◽  
Author(s):  
C Tran-Thang ◽  
EK Kruithof ◽  
F Bachmann
Keyword(s):  
Plasminogen Activator ◽  
Whole Blood ◽  
Apparent Molecular Weight ◽  
Clot Lysis ◽  
Initial Concentration ◽  
Low Concentrations ◽  
Sds Page ◽  
Tissue Plasminogen ◽  
Low Rate

Abstract The contribution of vascular plasminogen activator (v-PA) to the lysis of whole blood and plasma clots was investigated. v-PA released into the circulation after infusion of deamino-D-arginine vasopressin (DDAVP) was shown to bind quantitatively to plasma clots. Its apparent molecular weight, determined by the SDS-PAGE fibrin-agarose underlay method, was approximately 68,000 daltons, and its activity was quenched by antibodies against human tissue plasminogen activator (t-PA). Clots prepared from post-DDAVP plasma or post-DDAVP whole blood, rich in v- PA, did not lyse when incubated in imidazole buffer or normal plasma, as determined by the release of 125I from radiolabeled clots. However, clots made of v-PA-poor plasma or whole blood, incubated in v-PA-rich plasma, underwent substantial lysis. The concentration of PA in clots incubated in v-PA-rich plasma progressively increased in relation to the initial concentration of v-PA in the surrounding plasma. The results suggest that, at low concentrations of circulating v-PA, a hemostatic plug will lyse at a very low rate. However, when the v-PA concentration in the clot environment is increased, v-PA will accumulate progressively onto fibrin and induce thrombolysis.

scholarly journals Effects of the Translocation Status of Human Immunodeficiency Virus Type 1 Reverse Transcriptase on the Efficiency of Excision of Tenofovir

2007 ◽  
Vol 51 (8) ◽  
pp. 2911-2919 ◽  
Author(s):  
Bruno Marchand ◽  
Kirsten L. White ◽  
John K. Ly ◽  
Nicolas A. Margot ◽  
Ruth Wang ◽  
...  
Keyword(s):  
Human Immunodeficiency Virus ◽  
Complex Formation ◽  
Reverse Transcriptase ◽  
High Rate ◽  
Human Immunodeficiency Virus Replication ◽  
Degree Of Protection ◽  
Cellular Environment ◽  
Dead End ◽  
Low Concentrations ◽  
Immunodeficiency Virus

ABSTRACT The ATP-dependent phosphorolytic excision of nucleoside analogue reverse transcriptase inhibitors can diminish their inhibitory effects on human immunodeficiency virus replication. Previous studies have shown that excision can occur only when the reverse transcriptase complex exists in its pretranslocational state. Binding of the next complementary nucleotide causes the formation of a stable dead-end complex in the posttranslocational state, which blocks the excision reaction. To provide mechanistic insight into the excision of the acyclic phosphonate nucleotide analog tenofovir, we compared the efficiencies of the reaction in response to changes in the translocation status of the enzyme. We found that rates of excision of tenofovir with wild-type reverse transcriptase can be as high as those seen with 3′-azido-3′-deoxythymidine monophosphate (AZT-MP). Thymidine-associated mutations, which confer >100-fold and 3-fold decreased susceptibility to AZT and tenofovir, respectively, caused substantial increases in the efficiency of excision of both inhibitors. However, in contrast to the case for AZT-MP, the removal of tenofovir was highly sensitive to dead-end complex formation. Site-specific footprinting experiments revealed that complexes with AZT-terminated primers exist predominantly pretranslocation. In contrast, complexes with tenofovir-terminated primers are seen in both configurations. Low concentrations of the next nucleotide are sufficient to trap the complex posttranslocation despite the flexible, acyclic character of the compound. Thus, the relatively high rate of excision of tenofovir is partially neutralized by the facile switch to the posttranslocational state and by dead-end complex formation, which provides a degree of protection from excision in the cellular environment.

scholarly journals The quantitative analysis of ligand binding and initial-rate data for allosteric and other complex enzyme mechanisms

1976 ◽  
Vol 153 (1) ◽  
pp. 101-117 ◽  
Author(s):  
W G Bardsley
Keyword(s):  
Kinetic Data ◽  
Quantitative Data ◽  
Initial Rate ◽  
Graphical Methods ◽  
Enzyme Kinetic ◽  
Rate Data ◽  
Curve Shape ◽  
High Substrate Concentration ◽  
Complex Curve ◽  
Complex Curves

1. The eight methods for plotting enzyme kinetic data are classified and analysed, and it is shown how, in each case, it is only possible to obtain quantitative data on the coefficients of the lowest- and highest-degree terms in the rate equation. 2. The combinations of coefficients that are accessible experimentally from limiting slopes and intercepts at both low and high substrate concentration are stated for all the graphical methods and the precise effects of these on curve shape in different spaces is discussed. 3. Ambiguities arising in the analysis of complex curves and certain special features are also investigated. 4. Four special ordering functions are defined and investigated and it is shown how knowledge of these allows a complete description of all possible complex curve shapes.

STUDIES ON THE FORMATION OF HEXAMINE

1952 ◽  
Vol 30 (9) ◽  
pp. 687-693 ◽  
Author(s):  
T. R. Ingraham ◽  
C. A. Winkler
Keyword(s):  
Activation Energy ◽  
Acetic Acid ◽  
Acid Solution ◽  
Induction Period ◽  
Ammonium Nitrate ◽  
Sodium Acetate ◽  
Glacial Acetic Acid ◽  
Initial Rate ◽  
Acetic Acid Solution ◽  
Rate Data

Rate curves have been determined for the reaction of ammonium nitrate with formaldehyde in glacial acetic acid solution at 25 °C., 35 °C., 45 °C., and 55 °C. over a range of Initial mole ratios (formaldehyde: ammonia) of 0.75:1 to 9.0:1. Data obtained at 25 °C. show a definite induction period in the formation of hexamine. The length of the induction period is not changed by increasing ammonium nitrate concentrations above the theoretical (1.5:1), but may be appreciably shortened by initial additions of excess formaldehyde or of sodium acetate. From 35 °C. upward, the induction period is not apparent. The order of the reaction with respect to formaldehyde has been determined from initial rate data, and an activation energy calculated. The reactions in general appear analogous to those found in slightly acid aqueous systems.

Protective effect of artificially induced ‘hibernation’ against lethal doses of whole body x-irradiation in CF1 male mice

1959 ◽  
Vol 196 (6) ◽  
pp. 1211-1213 ◽  
Author(s):  
Sondra M. Kuskin ◽  
S. C. Wang ◽  
Roberts Rugh
Keyword(s):  
Protective Action ◽  
Lethal Dose ◽  
Lethal Effect ◽  
The Body ◽  
Whole Body ◽  
Protective Mechanism ◽  
Slight Reduction ◽  
Male Mice ◽  
Degree Of Protection ◽  
X Irradiation

Hypothermia induced by the use of neuroplegic drugs such as Hydergine, chlorpromazine or promethazine, followed by refrigeration, does not significantly enhance the protective action afforded by refrigeration alone against the lethal dose of whole body x-irradiation in CF1 male mice. The neuroplegic drugs, without refrigeration, provide a slight degree of protection, probably due to the slight reduction in the body temperature. It appears that the action of hypothermia as a protective mechanism depends not on depression of metabolism alone, but on a general depression of bodily processes. Urethane, in conjunction with refrigeration, appears to augment the lethal effect of x-irradiation in the CF1 strain of male mice.

scholarly journals Specific Conditions for Resveratrol Neuroprotection against Ethanol-Induced Toxicity

2012 ◽  
Vol 2012 ◽  
pp. 1-11 ◽  
Author(s):  
Brigitte Gonthier ◽  
Nathalie Allibe ◽  
Cécile Cottet-Rousselle ◽  
Frédéric Lamarche ◽  
Laurence Nuiry ◽  
...  
Keyword(s):  
Free Radical ◽  
Cell Injury ◽  
Fluorescent Dyes ◽  
Protective Action ◽  
Primary Cultures ◽  
Radical Scavenging ◽  
Brain Cell ◽  
Ethanol Exposure ◽  
Low Concentrations ◽  
Radical Scavenging Properties

Aims. 3,5,4′-Trihydroxy-trans-stilbene, a natural polyphenolic compound present in wine and grapes and better known as resveratrol, has free radical scavenging properties and is a potent protector against oxidative stress induced by alcohol metabolism. Today, the mechanism by which ethanol exerts its toxicity is still not well understood, but it is generally considered that free radical generation plays an important role in the appearance of structural and functional alterations in cells. The aim of this study was to evaluate the protective action of resveratrol against ethanol-induced brain cell injury.Methods. Primary cultures of rat astrocytes were exposed to ethanol, with or without a pretreatment with resveratrol. We examined the dose-dependent effects of this resveratrol pretreatment on cytotoxicity and genotoxicity induced by ethanol. Cytotoxicity was assessed using the MTT reduction test. Genotoxicity was evidenced using single cell gel electrophoresis. In addition, DNA staining with fluorescent dyes allowed visualization of nuclear damage using confocal microscopy.Results. Cell pretreatment with low concentrations oftrans-resveratrol (0.1–10 μM) slowed down cell death and DNA damage induced by ethanol exposure, while higher concentrations (50–100 μM) enhanced these same effects. No protection bycis-resveratrol was observed.Conclusion. Protection offered bytrans-resveratrol against ethanol-induced neurotoxicity was only effective for low concentrations of this polyphenol.

Vulcanization of Elastomers. 26. Vulcanization of Natural and Synthetic Rubbers by Sulfur in the Presence of Organic Bases

1960 ◽  
Vol 33 (3) ◽  
pp. 834-845
Author(s):  
Walter Scheele ◽  
Wolfgang Redetzky
Keyword(s):  
Initial Rate ◽  
Reaction Order ◽  
Research Work ◽  
Intermediate Compound ◽  
Sulfur Concentration ◽  
Kcal Mole ◽  
Initial Concentration ◽  
Organic Bases ◽  
Single Power ◽  
Theory And Experiment

Abstract In connection with earlier research work, we have carefully studied the decrease of sulfur during the vulcanization of Perbunan N 2818 in the presence of DPG, at various temperatures and with varied molar concentrations of sulfur and accelerator. We found : 1. The sulfur concentration decreases at all temperatures according to a time law of order 0.8. An activation energy of about 28 kcal/mole is derived from the temperature dependence of the rate constant. 2. The reaction order is independent of the initial concentration of reactants. 3. A discrepancy is found in the order of the reaction with respect to time and with respect to concentration, and it is clearly shown that the dependence of the initial rate on the initial concentration can not be expressed by a single power law. 4. The attempt is made to explain the discrepancy by postulating catalysis by an intermediate compound. The consequences from this consideration are compared with the experimental results, and, on the whole, agreement is found between theory and experiment.

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