Chemorheology of Polysulfide Rubbers

1949 ◽  
Vol 22 (3) ◽  
pp. 712-730
Author(s):  
Marcos Mochulsky ◽  
Arthur V. Tobolsky
Keyword(s):  
Molecular Structure ◽  
Exchange Reaction ◽  
Thiol Group ◽  
Cross Linking ◽  
Thiol Groups ◽  
Disulfide Linkage ◽  
Cold Flow ◽  
Adjacent Chain ◽  
Chemical Type ◽  
Chemical Agents

Abstract Experimental results indicate that the socalled “cold flow” of polysulfide rubbers is almost certainly chemical rather than physical in nature. The term chemorheology has been adopted to describe this chemical type of plasticity. The experimental method employed in this investigation was the measurement of relaxation of stress in stretched rubber samples held at a constant elongation. The changes in relaxation rate produced by changing the molecular structure of the rubber (by cross-linking), by incorporating carbon black, by illuminating with ultraviolet light, and by treating the rubber with various chemical agents, such as sulfur, a thiol, and agents that destroy thiol groups, were studied by this method. From the results of the above experiments and from additional considerations, it is concluded that the chemical reaction responsible for cold flow is an intermolecular exchange reaction, and that this exchange reaction is probably an exchange between a terminal thiol group of one chain and a disulfide linkage of an adjacent chain.

scholarly journals Organization of thiol groups of electric-eel electric-organ sodium-plus-potassium ion-stimulated adenosine triphosphatase studied with bifunctional reagents

1980 ◽  
Vol 185 (3) ◽  
pp. 787-790 ◽  
Author(s):  
W E Harris ◽  
W L Stahl
Keyword(s):  
Adenosine Triphosphatase ◽  
Polar Solvent ◽  
Electric Organ ◽  
Thiol Group ◽  
Cross Linking ◽  
Thiol Groups ◽  
High Solubility ◽  
Efficient Inhibitor ◽  
Polar Environment ◽  
Electric Eel

The reactions of three bifunctional thiol-blocking reagents of differing cross-linking spans and two monofunctional thiol-blocking reagents with the Na+ + K+-stimulated ATPase of the electric-eel electric organ were examined. 1,5-Difluoro-2,4-dinitrobenzene with a cross-linking span of 0.3-0.5 nm (3-5 A) and high solubility in non-polar solvent was the most efficient inhibitor of enzyme activity; thus essential thiol groups exist in a non-polar environment and are approx. 0.3-0.5 nm (3-5 A) from their nearest thiol-group neighbours. Ligands promoting phosphorylation of the Na+ + K+-stimulated ATPase decreased the number of thiol groups bridged by 1,5-difluoro-2,4-dinitrobenzene and by 4,4'-difluoro-3,3'-dinitrodiphenyl sulphone [0.7-1.0 nm (7-10 A) span]. Phosphorylation is associated with a conformational change in the enzyme.

scholarly journals The role of the thiol group in protein modification with methylglyoxal

2009 ◽  
Vol 74 (8-9) ◽  
pp. 867-883 ◽  
Author(s):  
Jelena Acimovic ◽  
Bojana Stanimirovic ◽  
Ljuba Mandic
Keyword(s):  
Protein Modification ◽  
Time Course ◽  
Thiol Group ◽  
Model Systems ◽  
Cross Linking ◽  
Thiol Groups ◽  
Serum Albumins ◽  
Stable Product ◽  
Protein Cross Linking

Methylglyoxal is a highly reactive ?-oxoaldehyde with elevated production in hyperglycemia. It reacts with nucleophilic Lys and Arg side-chains and N-terminal amino groups causing protein modification. In the present study, the importance of the reaction of the Cys thiol group with methylglyoxal in protein modification, the competitiveness of this reaction with those of amino and guanidine groups, the time course of these reactions and their role and contribution to protein cross-linking were investigated. Human and bovine serum albumins were used as model systems. It was found that despite the very low levels of thiol groups on the surface of the examined protein molecules (approx. 80 times lower than those of amino and guanidino groups), a very high percentage of it reacts (25-85 %). The amount of reacted thiol groups and the rate of the reaction, the time for the reaction to reach equilibrium, the formation of a stable product and the contribution of thiol groups to protein cross-linking depend on the methylglyoxal concentration. The product formed in the reaction of thiol and an insufficient quantity of methylglyoxal (compared to the concentrations of the groups accessible for modification) participates to a significant extent (4 %) to protein cross-linking. Metformin applied in equimolar concentration with methylglyoxal prevents its reaction with amino and guanidino groups but, however, not with thiol groups.

scholarly journals Half-sites oxidation of bovine liver uridine diphosphate glucose dehydrogenase

1978 ◽  
Vol 173 (2) ◽  
pp. 701-704 ◽  
Author(s):  
J S Franzen ◽  
P Marchetti ◽  
R Ishman ◽  
J Ashcom
Keyword(s):  
Catalytic Activity ◽  
Glucose Dehydrogenase ◽  
Bovine Liver ◽  
Thiol Group ◽  
Catalytic Site ◽  
Uridine Diphosphate ◽  
Thiol Groups ◽  
Irreversible Denaturation ◽  
Diphosphate Glucose ◽  
Uridine Diphosphate Glucose Dehydrogenase

6,6-Dithiodinicotinate shows half-of-the-sites reactivity towards the six catalytic-site thiol groups of bovine liver UDP-glucose dehydrogenase. The reagent introduces three intrasubunit disulphide linkages between catalytic-site thiol groups and non-catalytic-site thiol groups and abrogates 60% of the catalytic activity of the hexameric enzyme; excess 2-mercaptoethanol rapidly restores full catalytic activity. These results show the half-of-the-sites behaviour of the enzyme with the reagent and the presence of a non-catalytic-site thiol group capable of forming a disulphide linkage with a catalytic-site thiol group on the same subunit without irreversible denaturation.

Thiol derivatives of cellulose as supports for the immobilization of non-thiol enzymes

1981 ◽  
Vol 46 (7) ◽  
pp. 1693-1700 ◽  
Author(s):  
Peter Gemeiner ◽  
Jiří Zemek
Keyword(s):  
Exchange Reaction ◽  
Proteolytic Activity ◽  
Acetylcholine Esterase ◽  
Mercaptoacetic Acid ◽  
Thiol Groups ◽  
Nucleophilic Reaction ◽  
Disulfide Exchange ◽  
Immobilized Trypsin ◽  
Esterolytic Activity ◽  
Derivatives Of

Thiosulfate derivatives, which can be reduced with mercaptoacetic acid, are suitable intermediates for the preparation of thiol derivatives of polymers. Thiosulfate derivatives of cellulose were prepared via chlorodeoxy- or via 3-chloro-2-hydroxy-propylcellulose, while mercaptodeoxycellulose prepared via chlorodeoxy derivative had more convenient properties for the immobilization of non-thiol enzymes (acetylcholine esterase, butyrylcholine esterase and trypsin). Before immobilization SH groups were introduced into choline esterases by i) reduction of the cystine residues, ii) reaction with methyl 4-mercaptobutyrimidate, and the isothiocyanate groups were introduced into trypsin on reaction with 3-isothiocyanatopropyl 1-isocyanate. The immobilization of the enzymes treated in this way was carried out under the conditions of the oxidation of thiol groups (i), thiol-disulfide exchange reaction (ii), or an addition nucleophilic reaction of isothiocyanates with thiols. In contrast to the proteolytic activity of the immobilized trypsin the esterolytic activity of immobilized choline esterases attained satisfactory values.

Polymer-Derived Ceramics (PDCs)

2014 ◽  
pp. 1108-1139 ◽  
Author(s):  
Emanuel Ionescu ◽  
Gabriela Mera ◽  
Ralf Riedel
Keyword(s):  
Molecular Structure ◽  
Phase Composition ◽  
Network Topology ◽  
Creep Resistance ◽  
Intimate Relationship ◽  
Harsh Environments ◽  
Cross Linking ◽  
Polymer Derived Ceramics ◽  
Ultrahigh Temperature ◽  
Corrosive Environments

Polymer-derived ceramics (PDCs) represent a rather novel class of ceramics which can be synthesized via cross-linking and pyrolysis of suitable polymeric precursors. In the last decades, PDCs have been attaining increased attention due to their outstanding ultrahigh-temperature properties, such as stability with respect to decomposition and crystallization processes as well as resistance in oxidative and corrosive environments. Moreover, their creep resistance is excellent at temperatures far beyond 1000 °C. The properties of PDCs were shown to be strongly related to their microstructure (network topology) and phase composition, which are determined by the chemistry and molecular structure of the polymeric precursor used and by the conditions of the polymer-to-ceramic transformation. Within this chapter, synthesis approaches, the nano/microstructure, as well as the behavior of PDCs at ultrahigh temperatures and in harsh environments will be presented. The emphasis of the highlighted and discussed results will focus on the intimate relationship between the precursors (molecular structure/architecture) and the resulting PDCs (phase composition, nano/microstructure, and UHT properties).

scholarly journals Oxidation of human haemoglobin by copper. Mechanism and suggested role of the thiol group of residue β-93

1977 ◽  
Vol 165 (1) ◽  
pp. 141-148 ◽  
Author(s):  
C C Winterbourn ◽  
R W Carrell
Keyword(s):  
Electron Transfer ◽  
Binding Sites ◽  
Equilibrium Dialysis ◽  
Thiol Group ◽  
Thiol Groups ◽  
Human Haemoglobin ◽  
High Affinity ◽  
Rate Determining Step ◽  
Haemoglobin Molecule

Addition of Cu(II) ions to human oxyhaemoglobin caused the rapid oxidation of the haem groups of the beta-chain. Oxidation required binding of Cu(II) to sites involving the thiol group of beta-93 residues and was prevented when these groups were blocked with iodoacetamide or N-ethylmaleimide. Equilibrium-dialysis studies showed three pairs of binding sites, two pairs with high affinity for Cu(II) and one pair with lower affinity. It was the second pair of high-affinity sites that were blocked with iodoacetamide and were involved in haem oxidation. Cu(II) oxidized deoxyhaemoglobin at least ten times as fast as oxyhaemoglobin, and analysis of rates suggested that binding rather than electron transfer was the rate-determining step. No thiol-group oxidation to disulphides occurred during the period of haem oxidation, although it did occur subsequently in the presence of oxygen, or when Cu(II) was added to methaemoglobin. It is proposed that thiol oxidation did not occur because there exists a pathway of electron transfer between the haem group and copper bound to the beta-93 thiol groups. The route for this electron transfer is discussed, as well as the implications as to the function of the beta-93 cysteine in the haemoglobin molecule.

Effect of garlic oil extract on glutathione reductase levels in rats fed on high sucrose and alcohol diets: A possible mechanism of the activity of the oil

1986 ◽  
Vol 6 (10) ◽  
pp. 909-912 ◽  
Author(s):  
Godwin I. Adoga
Keyword(s):  
Glutathione Reductase ◽  
Exchange Reaction ◽  
Albino Rats ◽  
Active Principle ◽  
Thiol Groups ◽  
Garlic Oil ◽  
Oil Extract ◽  
High Sucrose

The effect on glutathione reductase activities of feeding garlic oil to white albino rats maintained on high sucrose and alcohol diets was studied. Whereas high sucrose and alcohol diets resulted in significant increases in the activity of glutathione reductase in liver, kidneys and serum, the presence of garlic oil restored the levels to near normal. It is proposed that the mechanism of this action of garlic oil involves the active principle, diallyl disulphide, which interacts in an exchange reaction with enzymes and substrates such as glutathione reductase and glutathione which contain thiol groups.

scholarly journals The binding and catalytic activities of forms of ligandin after modification of its thiol groups

1979 ◽  
Vol 177 (2) ◽  
pp. 433-439 ◽  
Author(s):  
T Carne ◽  
E Tipping ◽  
B Ketterer
Keyword(s):  
Thiol Group ◽  
Performic Acid ◽  
Acid Oxidation ◽  
Thiol Groups ◽  
Glutathione S Transferase ◽  
Catalytic Activities ◽  
Nitrobenzoic Acid ◽  
Number Of Binding Sites ◽  
The Common ◽  
Hydrophobic Ligand

Ligandin (glutathione S-transferase B, EC 2.5.1.18)was treated with p-mercuribenzoate, N-(4-dimethylamino-3,5-dinitrophenyl)-maleimide, 5,5,-dithiobis-(2-nitrobenzoic acid), N-ethylmaleimide, iodoacetamide or iodoacetate. Although performic acid oxidation revealed the presence of four cysteines, p-mercuribenzoate and N-(4-dimethylamino-3,5-dinitrophenyl)maleimide, the most effective of the reagents studied, reacted with only three residues. N-Ethylmaleimide and 5,5′-dithiobis-(2-nitrobenzoic acid) each reacted with two cysteines: iodoacetamide reacted with only one cysteine and iodoacetate was essentially unreactive. Modification of three thiol groups decreased both the enzymic and binding activities of ligandin although the number of binding sites was unaffected. Modification of only one or two of the thiol groups had little effect on the ligandin activities. It therefore appears that there is a thiol group in the common hydrophobic-ligand- and substrate-binding site of ligandin. Ligandin was separated into two fractions on CM-cellulose. Both fractions gave the same results with p-mercuribenzoate and iodoacetamide.

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