Cross-Linking in Natural-Rubber Vulcanizates

1953 ◽  
Vol 26 (4) ◽  
pp. 741-758 ◽  
Author(s):  
H. E. Adams ◽  
B. L. Johnson
Keyword(s):  
Molecular Weight ◽  
Natural Rubber ◽  
Cross Linking ◽  
Cross Link ◽  
General Validity ◽  
Tetramethylthiuram Disulfide ◽  
Cross Links ◽  
The Cross ◽  
Natural Rubber Vulcanizates ◽  
The Relationship

Abstract Recently, a method for measuring the average number of cross-links per chain of vulcanized polymer has been developed. It is possible to calculate the degree of cross-linking of the vulcanizate from its amount of swelling in a solvent such as benzene. This method was used by Flory to study the effect of primary molecular weight on the cross-linking of Butyl vulcanizates. An evaluation of the general validity of the method was ascertained by using quantitative cross-linking agents (diazodicarboxylates) to prepare vulcanizates of natural rubber and GR-S. Bardwell and Winkler have also used this technique to study the relationship between the degree of cross-linking and the force of retraction at 300 per cent elongation of GR-S latex vulcanized with potassium persulfate. The formation of cross-linking during the vulcanization by sulfur of several polymers has also been investigated. Gee has compared the formation of cross-linking in natural rubber vulcanizates with the amount of combined sulfur. Carbon-to-carbon cross-links were believed to be formed in a nonsulfur tetramethylthiuram disulfide (TMTD) cure. A similar study of Butyl rubber vulcanizates, cured with sulfur-TMTD, indicates that disulfide cross-links are formed. Scott and Magat have estimated that eight sulfur atoms are associated with each cross-link in Russian SK (sodium polybutadiene). This investigation was undertaken to extend Gee's study on the correlation of the cross-linking of natural-rubber vulcanizates with the amount of combined sulfur.

The Crystallization of Vulcanized Natural Rubber at Low Temperatures

1952 ◽  
Vol 25 (3) ◽  
pp. 397-411 ◽  
Author(s):  
E. W. Russell
Keyword(s):  
Molecular Weight ◽  
Natural Rubber ◽  
Low Temperatures ◽  
Maximum Rate ◽  
Cross Linking ◽  
Low Molecular Weight ◽  
Cross Links ◽  
Temperature Rate ◽  
Two Stages ◽  
Natural Rubber Vulcanizates

Abstract A series of natural rubber vulcanizates have been crystallized at −36° − 26° −17.5° and −2° C and the changes followed dilatometrically. As for raw rubber there is a maximum rate of crystallization at about −26° C; vulcanization decreases the rate and alters the shape of the temperature-rate curve. The amount of combined sulfur is the chief factor in determining the rate and extent of crystallization of pure-gum vulcanizates. Cross-linking, where it is efficient so that the chains between the cross-links are chemically unaffected, also depresses the rate and extent of crystallization. The use of vulcanizates which crystallize slowly permits melting to be accomplished at much lower rates of heating than was previously possible with raw rubber. Two stages of melting are distinguished the first occurring under the influence of forces between the crystalline and amorphous regions and the second analogous to the melting of low molecular weight crystalline substances.

The Cross-Linking of Rubber by Pile Radiation

1955 ◽  
Vol 28 (1) ◽  
pp. 1-11
Author(s):  
Arthur Charlesby
Keyword(s):  
Molecular Weight ◽  
Radiation Dose ◽  
Average Molecular Weight ◽  
High Energy ◽  
Cross Linking ◽  
Gel Formation ◽  
Gel Fraction ◽  
Cross Links ◽  
The Cross ◽  
The Relationship

Abstract The degree of cross-linking produced in a rubber by high-energy radiation is proportional to the radiation dose. Unit radiation, as defined in the text, links 1.1 per cent of the isoprene units. The distribution of molecular weight prior to cross-linking agrees with a Poisson distribution. Gel formation begins for γ=0.5. From the radiation dose required to initiate gel formation, the initial average molecular weight can be deduced. The increase of gel fraction with radiation dose follows the relationship deduced theoretically in the first part of the article. Measurement of gel fraction gives an alternative method of calculating the initial average molecular weight. Where some cross-linking is present in the rubber prior to cross-linking, this may be evaluated. In accordance with the theory presented in the article, the viscosity of the sol fraction rises initially, then decreases as the radiation dose increases. This provides a third method of measuring molecular weight, or of relating viscosity to molecular weight, which can be deduced from measurement of gel fraction. The swelling of very lightly cross-linked gel has been compared with the Flory-Huggins relationship, which is found to hold down to very lightly cross-linked gels for which the cross-linking index is only 0.2. To obtain this agreement, it is necessary to consider the swelling of the dry gel, rather than the whole specimen, and to ignore the cross-links required to form the gel itself.

EXPERIMENTAL VALIDATION OF THE CHARLESBY AND HORIKX MODELS APPLIED TO DE-VULCANIZATION OF SULFUR AND PEROXIDE VULCANIZATES OF NR AND EPDM

2016 ◽  
Vol 89 (4) ◽  
pp. 671-688 ◽  
Author(s):  
M. A. L. Verbruggen ◽  
L. van der Does ◽  
W. K. Dierkes ◽  
J. W. M. Noordermeer
Keyword(s):  
Experimental Validation ◽  
Main Chain ◽  
Sol Gel ◽  
Chain Scission ◽  
Cross Linking ◽  
Cross Link ◽  
Practical Reality ◽  
Cross Links ◽  
The Cross ◽  
Theoretical Considerations

ABSTRACT The theoretical model developed by Charlesby to quantify the balance between cross-links creation of polymers and chain scission during radiation cross-linking and further modifications by Horikx to describe network breakdown from aging were merged to characterize the balance of both types of scission on the development of the sol content during de-vulcanization of rubber networks. There are, however, disturbing factors in these theoretical considerations vis-à-vis practical reality. Sulfur- and peroxide-cured NR and EPDM vulcanizates were de-vulcanized under conditions of selective cross-link and random main-chain scissions. Cross-link scission was obtained using thiol-amine reagents for selective cleavage of sulfur cross-links. Random main-chain scission was achieved by heating peroxide vulcanizates of NR with diphenyldisulfide, a method commonly employed for NR reclaiming. An important factor in the analyses of these experiments is the cross-linking index. Its value must be calculated using the sol fraction of the cross-linked network before de-vulcanization to obtain reliable results. The values for the cross-linking index calculated with sol-gel data before de-vulcanization appear to fit the experimentally determined modes of network scission during de-vulcanization very well. This study confirms that the treatment of de-vulcanization data with the merged Charlesby and Horikx models can be used satisfactorily to characterize the de-vulcanization of NR and EPDM vulcanizates.

scholarly journals Chemistry of collagen cross-linking: biochemical changes in collagen during the partial mineralization of turkey leg tendon

1997 ◽  
Vol 322 (2) ◽  
pp. 535-542 ◽  
Author(s):  
Lynda KNOTT ◽  
John F. TARLTON ◽  
Allen J. BAILEY
Keyword(s):  
Collagen Matrix ◽  
Cross Linking ◽  
Cross Link ◽  
Lysine Residues ◽  
Collagen Mineralization ◽  
Cross Links ◽  
The Cross ◽  
Calcified Tissues ◽  
Turkey Leg Tendon ◽  
Collagen Cross Linking

With age, the proximal sections of turkey leg tendons become calcified, and this phenomenon has led to their use as a model for collagen mineralization. Mineralizing turkey leg tendon was used in this study to characterize further the composition and cross-linking of collagen in calcified tissues. The cross-link profiles of mineralizing collagen are significantly different from those of other collagenous matrices with characteristically low amounts of hydroxylysyl-pyridinoline and the presence of lysyl-pyridinoline and pyrrolic cross-links. However, the presence of the immature cross-link precursors previously reported in calcifying tissues was not supported in the present study, and was found to be due to the decalcification procedure using EDTA. Analysis of tendons from young birds demonstrated differences in the cross-link profile which indicated a higher level of hydroxylation of specific triple-helical lysines involved in cross-linking of the proximal tendon. This may be related to later calcification, suggesting that this part of the tendon is predestined to be calcified. The minimal changes in lysyl hydroxylation in both regions of the tendon with age were in contrast with the large changes in the cross-link profile, indicating differential hydroxylation of the helical and telopeptide lysine residues. Changes with age in the collagen matrix, its turnover and thermal properties in both the proximal and distal sections of the tendon clearly demonstrate that a new and modified matrix is formed throughout the tendon, and that a different type of matrix is formed at each site.

FANCD2 Localizes to Cross-Linked Induced Nuclear Foci That Are Distinct From Those to Which αaII Spectrin and the Cross-Link Repair Protein, XPF, Co-Localize, Indicating An Involvement of These Proteins in Different Steps of the DNA Interstrand Cross-Link Repair Process.

Blood ◽  
2009 ◽  
Vol 114 (22) ◽  
pp. 3196-3196
Author(s):  
Pan Zhang ◽  
Deepa Sridharan ◽  
Michael Acosta ◽  
Muriel Lambert
Keyword(s):  
Time Course ◽  
Repair Process ◽  
Myelogenous Leukemia ◽  
Cross Linking ◽  
Cross Link ◽  
Repair Protein ◽  
Interstrand Cross Links ◽  
Cross Links ◽  
Nuclear Foci ◽  
The Cross

Abstract Abstract 3196 Poster Board III-133 The hereditary bone marrow failure disorder, Fanconi anemia (FA), is characterized by a markedly increased incidence of acute myelogenous leukemia, diverse congenital abnormalities and a defect in ability to repair DNA interstrand cross-links. We have previously shown that in FA cells there is a deficiency in the structural protein nonerythroid a spectrin (aSpII), which is involved in repair of DNA interstrand cross-links and binds to cross-linked DNA. aSpII co-localizes in nuclear foci with FANCA and the cross-link repair protein, XPF, after normal human cells are damaged with a DNA interstrand cross-linking agent. One of the FA proteins which is thought to play an important role in the repair of DNA interstrand cross-links is FANCD2, which is known to form nuclear foci after cross-link damage. The present study was undertaken in order to get a better understanding of the relationship between aSpII and FANCD2, whether they interact with each other during the DNA repair process and co-localize in damage-induced nuclear foci. Immunofluorescence microscopy was carried out to determine whether these proteins co-localized in nuclear foci after cells were damaged with a DNA interstrand cross-linking agent, 8-methylpsoralen plus UVA light (8-MOP) or mitomycin C (MMC). Time course measurements showed that FANCD2 foci were first visible at 2 hours after damage and increased up to 16 hours and were still present at 72 hours after damage. This time course of foci formation correlated with levels of monoubiquitination of FANCD2. Measurement of gH2AX foci formation showed that the time course of foci formation was similar to that of FANCD2 measured up to 72 hours post damage. In contrast, aSpII foci were first visible between 8-10 hours after damage. The number of these foci peaked at 16 hours and by 24 hours foci were no longer observed. Co-localization studies showed that there was little co-localization of the FANCD2 and aSpII foci over this time course. This indicates that these two proteins may be involved in different steps in the DNA interstrand cross-link repair process. Based on models that have been proposed for the role of FANCD2 in the repair of DNA interstrand cross-links, we propose that, after DNA damage, FANCD2 localizes at DNA replication forks stalled at sites of interstrand cross-links and aids in the assembly of proteins at this site. This is followed by localization of aSpII and XPF and other proteins involved in the initial incision steps in DNA interstrand cross-link repair where they play a role in the unhooking of the cross-link. FANCD2 is then involved in subsequent steps in the repair process, which involve homologous recombination. Thus two proteins, FANCD2 and aSpII, both of which have been shown to be critical for the DNA interstrand cross-link repair process may be involved in different or distinct steps in this repair process. Deficiencies in these proteins would impact on DNA interstrand cross-link repair and, as we have shown for aIISp, would have an adverse effect on the genomic stability of FA cells. . Disclosures No relevant conflicts of interest to declare.

scholarly journals Investigation of the organization of rhodopsin in the sheep photoreceptor membrane by using cross-linking reagents

1979 ◽  
Vol 177 (1) ◽  
pp. 215-223 ◽  
Author(s):  
M Brett ◽  
J B C Findlay
Keyword(s):  
Molecular Weight ◽  
Mechanism Of Action ◽  
Cross Linking ◽  
Rod Outer Segments ◽  
Cross Link ◽  
Photoreceptor Membrane ◽  
Outer Segments ◽  
The Cross ◽  
Collision Complexes

The organization of rhodopsin in the photoreceptor membrane of sheep rod outer segments was investigated by using a variety of bifunctional reagents. Of the nine reagents used, seven gave oligomeric opsin species, whereas two, copper phenanthroline and dithiobisphenyl azide, failed to cross-link the protein. In general, the cross-linked species obtained showed diminishing yields from dimer to tetramer, together with some higher-molecular-weight aggregates. It is proposed that the patterns of cross-linking arise as a result of collision complexes and best describe a monomeric organization for native rhodopsin. No significant differences between the patterns obtained with dark-adapted bleached or regenerated protein states were observed. This interpretation is discussed in relation to the postulated mechanism of action of rhodopsin.

scholarly journals Targeted in situ cross-linking mass spectrometry and integrative modeling reveal the architectures of Nsp1, Nsp2, and Nucleocapsid proteins from SARS-CoV-2

2021 ◽  
Author(s):  
Moriya Slavin ◽  
Joanna Zamel ◽  
Keren Zohar ◽  
Siona Eliyahu ◽  
Merav Braitbard ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Full Length ◽  
Integrative Model ◽  
Cross Linking ◽  
Cross Link ◽  
Integrative Modeling ◽  
Cellular Context ◽  
Cross Links ◽  
The Cross

AbstractAtomic structures of several proteins from the coronavirus family are still partial or unavailable. A possible reason for this gap is the instability of these proteins outside of the cellular context, thereby prompting the use of in-cell approaches. In situ cross-linking and mass spectrometry (in situ CLMS) can provide information on the structures of such proteins as they occur in the intact cell. Here, we applied targeted in situ CLMS to structurally probe Nsp1, Nsp2, and Nucleocapsid (N) proteins from SARS-CoV-2, and obtained cross-link sets with an average density of one cross-link per twenty residues. We then employed integrative modeling that computationally combined the cross-linking data with domain structures to determine full-length atomic models. For the Nsp2, the cross-links report on a complex topology with long-range interactions. Integrative modeling with structural prediction of individual domains by the AlphaFold2 system allowed us to generate a single consistent all-atom model of the full-length Nsp2. The model reveals three putative metal binding sites, and suggests a role for Nsp2 in zinc regulation within the replication-transcription complex. For the N protein, we identified multiple intra- and inter-domain cross-links. Our integrative model of the N dimer demonstrates that it can accommodate three single RNA strands simultaneously, both stereochemically and electrostatically. For the Nsp1, cross-links with the 40S ribosome were highly consistent with recent cryo-EM structures. These results highlight the importance of cellular context for the structural probing of recalcitrant proteins and demonstrate the effectiveness of targeted in situ CLMS and integrative modeling.

Model Elastomers

1997 ◽  
Author(s):  
Burak Erman ◽  
James E. Mark
Keyword(s):  
Molecular Weight ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Polymer Networks ◽  
Length Distribution ◽  
Quantitative Information ◽  
Cross Linking ◽  
Cross Links ◽  
End Linking ◽  
The Cross

Until quite recently, there was relatively little reliable quantitative information on the relationship of stress to structure, primarily because of the uncontrolled manner in which elastomeric networks were generally prepared. Segments close together in space were linked irrespective of their locations along the chain trajectories, thus resulting in a highly random network structure in which the number and locations of the cross-links were essentially unknown. Such a structure is shown in figure 10.1. New synthetic techniques are now available, however, for the preparation of “model” polymer networks of known structure. More specifically, if networks are formed by end linking functionally terminated chains instead of haphazardly joining chain segments at random, then the nature of this very specific chemical reaction provides the desired structural information. Thus, the functionality of the cross links is the same as that of the end-linking agent, and the molecular weight Mc between cross-links and the molecular weight distribution are the same as those of the starting chains prior to their being end-linked. An example is the reaction shown in figure 10.2, in which hydroxyl-terminated chains of poly(dimethylsiloxane) (PDMS) are end-linked using tetraethyl orthosilicate. Characterizing the un-cross-linked chains with respect to molecular weight Mn and molecular weight distribution, and then carrying out the specified reaction to completion, gives elastomers in which the network chains have these characteristics; in particular, a molecular weight Mc between cross-links equal to Mn, a network chain-length distribution equal to that of the starting chains, and cross-links having the functionality of the end-linking agent. It is also possible to use chains having a known number of potential cross-linking sites placed as side chains along the polymer backbone, so long as their distribution is known as well. Because of their known structures, such model elastomers are now the preferred materials for the quantitative characterization of rubberlike elasticity. Such very specific cross-linking reactions have also been shown to be useful in the preparation of liquid-crystalline elastomers. Trifunctional and tetrafunctional PDMS networks prepared in this way have been used to test the molecular theories of rubber elasticity with regard to the increase in non-affineness of the network deformation with increasing elongation.

scholarly journals Grafting of n-butyl acrylate with natural rubber latex film by gamma radiation: a reaction mechanism

1970 ◽  
Vol 5 (1) ◽  
pp. 81-88 ◽  
Author(s):  
KMZ Hossain ◽  
AM Sarwaruddin Chowdhury
Keyword(s):  
Reaction Mechanism ◽  
Natural Rubber ◽  
Butyl Acrylate ◽  
Natural Rubber Latex ◽  
Latex Film ◽  
Cross Linking ◽  
Swelling Ratio ◽  
Cross Link ◽  
Rubber Latex ◽  
The Cross

Natural rubber latex (NRL) and n-butyl acrylate (n-BA) were blended and irradiated at various absorbed doses by gamma rays from Co-60 source at room temperature. The stabilizing effect was determined by measuring the pH and viscosity of NRL with n-BA with the storage time of five weeks. The cross-link density, swelling ratio of the radiation vulcanized rubber film were measured. The cross-link density of the n-BA grafted NRL film was found increasing and the swelling ratio of that film decreasing with the increased absorbed dose. The optimum radiation dose for better cross-linking of natural rubber latex blended with five parts per hundred rubber (phr) n-BA was found 15 kGy absorbed dose. Based on the cross-linking properties a probable cross-linking reaction mechanism for the n-BA grafted natural rubber latex film was developed. Keywords: Natural rubber latex, n-butyl acrylate, Irradiation, Swelling ratio, Cross-link, Reaction mechanism. DOI: 10.3329/diujst.v5i1.4386 Daffodil International University Journal of Science and Technology Vol.5(1) 2010 pp.81-88

scholarly journals Mutational Analysis of a Conserved Glutamic Acid Required for Self-Catalyzed Cross-Linking of Bacteriophage HK97 Capsids

2008 ◽  
Vol 83 (5) ◽  
pp. 2088-2098 ◽  
Author(s):  
Lindsay E. Dierkes ◽  
Craig L. Peebles ◽  
Brian A. Firek ◽  
Roger W. Hendrix ◽  
Robert L. Duda
Keyword(s):  
Glutamic Acid ◽  
Large Scale ◽  
Mutational Analysis ◽  
Chemical Mechanism ◽  
Proton Acceptor ◽  
Cross Linking ◽  
Side Chains ◽  
Cross Link ◽  
Cross Links ◽  
The Cross

ABSTRACT The capsid of bacteriophage HK97 is stabilized by ∼400 covalent cross-links between subunits which form without any action by external enzymes or cofactors. Cross-linking only occurs in fully assembled particles after large-scale structural changes bring together side chains from three subunits at each cross-linking site. Isopeptide cross-links form between asparagine and lysine side chains on two subunits. The carboxylate of glutamic acid 363 (E363) from a third subunit is found ∼2.4 Å from the isopeptide bond in the partly hydrophobic pocket that contains the cross-link. It was previously reported without supporting data that changing E363 to alanine abolishes cross-linking, suggesting that E363 plays a role in cross-linking. This alanine mutant and six additional substitutions for E363 were fully characterized and the proheads produced by the mutants were tested for their ability to cross-link under a variety of conditions. Aspartic acid and histidine substitutions supported cross-linking to a significant extent, while alanine, asparagine, glutamine, and tyrosine did not, suggesting that residue 363 acts as a proton acceptor during cross-linking. These results support a chemical mechanism, not yet fully tested, that incorporates this suggestion, as well as features of the structure at the cross-link site. The chemically identical isopeptide bonds recently documented in bacterial pili have a strikingly similar chemical geometry at their cross-linking sites, suggesting a common chemical mechanism with the phage protein, but the completely different structures and folds of the two proteins argues that the phage capsid and bacterial pilus proteins have achieved shared cross-linking chemistry by convergent evolution.

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