The Relationship of Properties of Synthetic Poly(Isoprene) and Natural Rubber in The Factory. The Effect of Non-Rubber Constituents of Natural Rubber

1973 ◽  
Vol 46 (1) ◽  
pp. 47-66 ◽  
Author(s):  
E. C. Gregg ◽  
J. H. Macey
Keyword(s):  
Natural Rubber ◽  
Protein Molecule ◽  
Insoluble Fraction ◽  
Prosthetic Group ◽  
Rubber Material ◽  
Green Strength ◽  
Denatured Protein ◽  
Low Concentrations ◽  
Relationship Of ◽  
The Relationship

Abstract The causes of some of the differences in properties between compounded natural rubber and compounded synthetic poly (isoprene) have been traced to the insoluble non-rubber material in natural rubber. This material is mostly denatured proteins and is responsible for the higher modulus, faster scorch time, higher heat buildup, and higher hot tear strength of natural rubber. These properties may be related to the pigment effect of the denatured protein to act as a reinforcing filler at low concentrations (3–4 per cent by wt) as well as a curing activator. The greater green strength of compounded natural rubber has been related to its more perfect configurational regularity which contributes to faster crystallization. The crystallite concentration increases with increasing stress and the crystallites act like a reversible reinforcing pigment which disappears when the stress is released. The faster plastication rate has been related to the synthetic stabilizers used. Natural rubber hydrocarbon has been shown to be a high molecular lactone arranged in a six membered ring. We speculate natural rubber forms as a prosthetic group connected through a lactone linkage (or the δ-hydroxy acid precursor to the lactone) to a protein molecule in the cell of hevea brasiliensis. It is this structure of a high molecular weight hydrocarbon (natural rubber) attached to a (denatured) protein molecule that accounts for the remarkable dispersability of the insoluble fraction of natural rubber in rubber solvents : the rubber end of the structure tends to dissolve in the rubber solvent while the highly polar, insoluble protein end prevents solution. This structure is the reverse of a micelle in water in principle.

VITAMIN B12 AND FOLIC ACID VALUES IN PREMATURE INFANTS

PEDIATRICS ◽  
1972 ◽  
Vol 50 (4) ◽  
pp. 584-589
Author(s):  
Ambadas Pathak ◽  
Herman A. Godwin ◽  
Luis M. Prudent
Keyword(s):  
Folic Acid ◽  
Vitamin B12 ◽  
Premature Infants ◽  
Serum Vitamin ◽  
Serum Folate ◽  
Born Infant ◽  
Low Concentrations ◽  
Folate And Vitamin B12 ◽  
Relationship Of ◽  
The Relationship

The relationship of serum vitamin B12 and folic acid was studied in 24 premature infants. In 14 of the 24, low serum vitamin B12 values were found around 40 days of age. Serum folic acid concentrations were less frequently depressed and were usually associated with normal red cell folate values. No correlation between hematocrits and vitamin B12 or folate levels was found. It is suggested that low concentrations of serum folate and vitamin B12 result from low dietary intake coupled with increased demand by the prematurely born infant.

scholarly journals Commitment to expression of the metalloendopeptidases, collagenase and stromelysin: relationship of inducing events to changes in cytoskeletal architecture.

1986 ◽  
Vol 102 (3) ◽  
pp. 697-702 ◽  
Author(s):  
Z Werb ◽  
R M Hembry ◽  
G Murphy ◽  
J Aggeler
Keyword(s):  
Cytochalasin B ◽  
Synovial Fibroblasts ◽  
Heterogeneous Population ◽  
Minimum Period ◽  
Low Concentrations ◽  
Relationship Of ◽  
The Relationship ◽  
Rate Limiting ◽  
Dose Dependent Increase ◽  
Dose Dependent

Agents that alter the morphology of rabbit synovial fibroblasts induce synthesis of the metalloendopeptidases, collagenase and stromelysin. We studied the relationship of cytoskeletal changes to the commitment to expression of these metalloendopeptidases. Cells treated with cytochalasin B (CB) or 12-O-tetradecanoylphorbol-13-acetate rounded, and only cells that had lost their stress fibers expressed collagenase and stromelysin, as determined by immunofluorescence. We concentrated on the effects of CB because of its rapid reversibility. When CB was added for 1-24 h, then removed, the cells respread within 30-60 min. The minimum period of CB treatment that committed cells to the subsequent synthesis of collagenase and stromelysin was 3 h. After initial treatment with 2 micrograms/ml CB for 3-24 h, or with various concentrations of CB (0-2 micrograms/ml) for 24 h, both enzyme activity and biosynthesis of the proenzymes showed a graded increase when measured at 24 h. Even after treatment with 2 micrograms/ml CB for only 3 h, greater than 85% of all cells were positive for both collagenase and stromelysin when cells were monitored by immunofluorescence. In contrast, when the dependence of collagenase and stromelysin expression on the inducing concentration of CB was examined, there was a dose-dependent increase in the number of cells positive for collagenase and stromelysin, as determined by immunofluorescence. Thus, at low concentrations of CB (less than 0.5 micrograms/ml), a heterogeneous population response was observed. These results suggest that the commitment of fibroblasts to induction of the metalloproteinases is a stochastic process in which a second signal that correlates with the disruption of the actin cytoskeleton may be rate-limiting for collagenase and stromelysin gene expression.

Dependence of Tensile Strength of Vulcanized Rubber on the Degree of Cross-Linking

1950 ◽  
Vol 23 (1) ◽  
pp. 27-43
Author(s):  
Paul J. Flory ◽  
Norman Rabjohn ◽  
Marcia C. Shaffer
Keyword(s):  
Tensile Strength ◽  
Natural Rubber ◽  
Chain Scission ◽  
General Character ◽  
Cross Linking ◽  
Vulcanized Rubber ◽  
Relationship Of ◽  
The Relationship ◽  
Considerable Detail ◽  
Proportionality Relationship

Abstract The suitability of disazodicarboxylates as quantitative cross-linking agents for the preparation of rubber vulcanizates of known degrees of cross-linking has been emphasized previously. In a recent paper we have presented the results of an investigation on the dependence of the equilibrium force of retraction on the elongation and degree of cross-linking of rubber and GR-S vulcanized with these compounds. The present paper reports an extension of these investigations of the relationship of physical properties of rubberlike materials to their network structure. Specifically, the tensile strength of azo vulcanized natural rubber has been explored as a function of the degree of cross-linking and of the extent of modification of the chain units. The tensile strengths of natural rubber specimens vulcanized to various extents using sulfur alone or sulfur in conjunction with various accelerators have been investigated in considerable detail recently by Gee, who has emphasized the critical dependence of the tensile strength on the degree of cross-linking. Values for the latter quantity, however, were deduced indirectly from the equilibrium force of retraction using the simple proportionality relationship between force of retraction and degree of cross-linking afforded by the theory of rubber elasticity. This relationship is known to be only approximately valid. Furthermore, the effects on the force of retraction of chain scission, which doubtless accompanied some of the vulcanizations to a considerable degree, were disregarded. For these reasons, Gee's values for the degrees of cross-linking occurring in his vulcanizates are only approximate estimates, and in a few cases they may be seriously in error. Nevertheless, the general character of the relationship between tensile strength and degree of cross-linking which he obtained is confirmed by our results on rubber samples quantitatively cross-linked with measured proportions of decamethylene-dismethyl azodicarboxylate.

The surface activity of the phytotoxin cerato-ulmin

1982 ◽  
Vol 60 (8) ◽  
pp. 1414-1422 ◽  
Author(s):  
Paul S. Russo ◽  
Frank D. Blum ◽  
John D. Ipsen ◽  
Yusuf J. Abul-Hajj ◽  
Wilmer G. Miller
Keyword(s):  
Surface Activity ◽  
Aqueous Ethanol ◽  
Vascular System ◽  
Wilt Disease ◽  
Air Bubbles ◽  
Low Concentrations ◽  
Air Water Interface ◽  
Response To Stress ◽  
Relationship Of ◽  
The Relationship

The glycoprotein cerato-ulmin, which shows surface activity at concentrations as low as 30 ng/mL, has been found to stabilize air bubbles, both spheroidal and of unusual morphology, in aqueous and aqueous ethanol solutions. In response to stress on a cerato-ulmin thin film, perhaps a monolayer, at an air–water interface, cylindrical and fibrilliform air bubbles are generated. They may be manipulated by application of tension, pressure, or temperature. The relationship of these observations to elm trees infected with the cerato-ulmin producing fungus Ceratocystis ulmi suggests a mechanism whereby exceedingly low concentrations of cerato-ulmin may be concentrated and delivered to intercellular openings, thereby blocking the vascular system of elm trees. The correctness of this mechanism as a major factor in any tree wilt disease remains to be tested.

scholarly journals Physiological genetics of melanotic tumours in Drosophila melanogaster VII. The relationship of dietary sterols to tumour penetrance

1972 ◽  
Vol 20 (3) ◽  
pp. 317-329 ◽  
Author(s):  
Jonathan Cooke ◽  
J. H. Sang
Keyword(s):  
Low Concentrations ◽  
Tumour Formation ◽  
Metabolic Products ◽  
Adult Body ◽  
Adult Body Weight ◽  
Growth Promoting ◽  
Relationship Of ◽  
Dietary Sterols ◽  
The Relationship ◽  
Molecular Nature

SUMMARYA strain of Drosophila, homozygous for the variably penetrant gene tu bw, which causes the formation of abnormal masses of melanizing haemocytes (melanotic tumours), has been reared on defined axenic diets containing various sterols, both singly and in pairs. Both optimal and deficient nutritional levels of sterol have been employed, as well as certain sterols inadequate by themselves to support development. The effect of these diets upon probability of tumour formation has been studied in relation to their nutritional adequacy, as defined by the growth-rate, survival, and in one case, adult body-weight.The results demonstrate a rather complex pattern of interaction between dietary sterols in determining the variables of the phenotype produced, under circumstances suggesting that all the sterols investigated have entered the developing larvae. There is only a partial overall correlation, and occasionally an inverse relationship, between tumour suppressant and growth-promoting properties of particular sterols. Within single molecules, structural sterol features tend to exert their characteristic effects additively upon the phenotype, except for an inadequacy in utilization of molecules containing the Δ7 double bond, which dominates at low concentrations. With pairs of dietary sterols, however, non-additive or ‘saving’ effects are sometimes seen.It is suggested that the tu bw allele allows the resolution of several discrete developmental functions for sterols and/or their immediate metabolic products in Drosophila, which cannot synthesize its own sterol. However, the molecular nature of these functions is little understood.

scholarly journals SULFHYDRYL AND DISULFIDE GROUPS OF PROTEINS

1936 ◽  
Vol 19 (3) ◽  
pp. 427-438 ◽  
Author(s):  
A. E. Mirsky ◽  
M. L. Anson
Keyword(s):  
Serum Albumin ◽  
Quantitative Methods ◽  
Protein Denaturation ◽  
Protein Molecule ◽  
Insoluble Fraction ◽  
Egg Albumin ◽  
Sh Groups ◽  
Denatured Protein ◽  
Hydrolyzed Protein ◽  
Air Water Interface

1. In native egg albumin no SH groups are detectable, whereas in completely coagulated albumin as many groups are detectable as are found in the hydrolyzed protein. In egg albumin partially coagulated by heat the soluble fraction contains no detectable groups, and the insoluble fraction contains the number found after hydrolysis. 2. In the reversal of denaturation of serum albumin, when insoluble protein regains its solubility, S-S groups which have been detectable in the denatured protein, disappear. 3. When egg albumin coagulates at an air-water interface, all the SH groups in the molecule become detectable. 4. In egg albumin coagulated by irradiation with ultraviolet light, the same number of SH groups are detectable as in albumin coagulated by a typical denaturing agent. 5. When serum albumin is denatured by urea, there is no evidence that S-S groups appear before the protein loses its solubility. 6. Protein denaturation is a definite chemical reaction: different quantitative methods agree in estimates of the extent of denaturation, and the same changes are observed in the protein when it is denatured by different agents. A protein molecule is either native or denatured. The denaturation of some proteins can be reversed.

The relationship of the scleractinian corals to the rugose corals

Paleobiology ◽  
1980 ◽  
Vol 6 (02) ◽  
pp. 146-160 ◽  
Author(s):  
William A. Oliver
Keyword(s):  
Critical Points ◽  
Scleractinian Corals ◽  
Convincing Evidence ◽  
Early Triassic ◽  
Rugose Corals ◽  
History Of ◽  
The Subject ◽  
Relationship Of ◽  
The Relationship ◽  
Biologic Factors

The Mesozoic-Cenozoic coral Order Scleractinia has been suggested to have originated or evolved (1) by direct descent from the Paleozoic Order Rugosa or (2) by the development of a skeleton in members of one of the anemone groups that probably have existed throughout Phanerozoic time. In spite of much work on the subject, advocates of the direct descent hypothesis have failed to find convincing evidence of this relationship. Critical points are:(1) Rugosan septal insertion is serial; Scleractinian insertion is cyclic; no intermediate stages have been demonstrated. Apparent intermediates are Scleractinia having bilateral cyclic insertion or teratological Rugosa.(2) There is convincing evidence that the skeletons of many Rugosa were calcitic and none are known to be or to have been aragonitic. In contrast, the skeletons of all living Scleractinia are aragonitic and there is evidence that fossil Scleractinia were aragonitic also. The mineralogic difference is almost certainly due to intrinsic biologic factors.(3) No early Triassic corals of either group are known. This fact is not compelling (by itself) but is important in connection with points 1 and 2, because, given direct descent, both changes took place during this only stage in the history of the two groups in which there are no known corals.

Skeletal elements of crinoid echinoderms: High-resolution structural and microanalytical results

1983 ◽  
Vol 41 ◽  
pp. 194-195
Author(s):  
D. F. Blake ◽  
L. F. Allard ◽  
D. R. Peacor
Keyword(s):  
High Resolution ◽  
Marine Invertebrates ◽  
Sea Urchins ◽  
Structural Features ◽  
Sea Stars ◽  
High Resolution Tem ◽  
Relationship Of ◽  
The Relationship ◽  
Insight Into

Echinodermata is a phylum of marine invertebrates which has been extant since Cambrian time (c.a. 500 m.y. before the present). Modern examples of echinoderms include sea urchins, sea stars, and sea lilies (crinoids). The endoskeletons of echinoderms are composed of plates or ossicles (Fig. 1) which are with few exceptions, porous, single crystals of high-magnesian calcite. Despite their single crystal nature, fracture surfaces do not exhibit the near-perfect {10.4} cleavage characteristic of inorganic calcite. This paradoxical mix of biogenic and inorganic features has prompted much recent work on echinoderm skeletal crystallography. Furthermore, fossil echinoderm hard parts comprise a volumetrically significant portion of some marine limestones sequences. The ultrastructural and microchemical characterization of modern skeletal material should lend insight into: 1). The nature of the biogenic processes involved, for example, the relationship of Mg heterogeneity to morphological and structural features in modern echinoderm material, and 2). The nature of the diagenetic changes undergone by their ancient, fossilized counterparts. In this study, high resolution TEM (HRTEM), high voltage TEM (HVTEM), and STEM microanalysis are used to characterize tha ultrastructural and microchemical composition of skeletal elements of the modern crinoid Neocrinus blakei.

Studies on Leukemogenic and Sarcomagenic Viruses

1970 ◽  
Vol 28 ◽  
pp. 156-157
Author(s):  
Leon Dmochowski
Keyword(s):  
Electron Microscopy ◽  
Electron Microscope ◽  
Morphological Properties ◽  
Mode Of Development ◽  
Relationship Of ◽  
The Relationship

Electron microscopy has proved to be an invaluable discipline in studies on the relationship of viruses to the origin of leukemia, sarcoma, and other types of tumors in animals and man. The successful cell-free transmission of leukemia and sarcoma in mice, rats, hamsters, and cats, interpreted as due to a virus or viruses, was proved to be due to a virus on the basis of electron microscope studies. These studies demonstrated that all the types of neoplasia in animals of the species examined are produced by a virus of certain characteristic morphological properties similar, if not identical, in the mode of development in all types of neoplasia in animals, as shown in Fig. 1.

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