Supercontraction

The direct and indirect assessment of the aneuploidy-inducing potency of a number of organotin compounds was reported by Jensen et al. (1991a). The effects of dimethyltin dichloride, diphenyltin dichloride, trimethyltin chloride, tributyltin chloride, and triphenyl-tin chloride at 10 -10 mol/1 on chromosomal contractions in cultures of human peripheral lymphocytes were investigated. Diphenyltin dichloride, trimethyltin chloride, tributyltin chloride, and triphenyl-tin chloride appeared to be very strong inducers of chromosomal supercontraction, indicating that these compounds induce aneuploidy, probably by affecting... 

Beek, J. D.v., Kummerlen, J., Vollrath, F., and Meier, B. H. (1999). Supercontracted spider dragline silk A solid-state NMR study of the local structure. Ini. J. Biol. Macromol. 24, 173-178. 

Work, R. W. (1981). A comparative study of the supercontraction of major ampullate silk fibres of orb web building spiders (Araneae)./. Arachnol. 9, 299-308. 

Eles, P.T., and Michal, C.A. "Strain dependent local phase transitions observed during controlled supercontraction reveal mechanisms in spider silk". Macromolecules 37(4), 1342-1345 (2004). 

Liu, Y., Shao, Z.Z., and Vollrath, F. "Relationships between supercontraction and mechanical properties of spider silk". Nat. Mater. 4(12), 901-905 (2005b). 

Shao, Z., Vollrath, F., Sirichaisit, J., and Young, R.J. "Analysis of spider silk in native and supercontracted states using Raman spectroscopy. Polymer 40(10), 2493-2500 (1999b). 

Specific Heat. The specific heat of textiles, particularly wool, has been the subject of recent investigations. For moisture contents above the fiber saturation point of wool, reduced, supercontracted, and chemically modified wool fabrics exhibited endothermic peaks at -30 to 0°C that resulted from the heat of fusion of absorbed water. In that temperature range, a significant increase in the specific heat of the wool fabrics was also... 

The uptake of ions may be complicated by changes in the conformation of the protein such as may occur during swelling or supercontraction. For example, Hojo and Sugawara (1958) report a 60 % increase in uptake of Cu++ from CUSO4 solution when wool fibers are stretched by 50 %. The uptake of metal ions is accompanied by the release of hydrogen ions (Hojo and Hojo, 1958) from the fiber. The presence of natural pigment in animal... 

This section is concerned primarily with the effects of chemical modifications of keratins on their physical properties—supercontraction, setting, swelling, load-extension characteristics, and other mechanical properties. Much of this work could be described by the term mechanochemical coined by Speakman (1947). The complexity of the cellular and sub-cellular structure of keratins necessitates the use of simplifying assumptions in the interpretation of mechanochemical experiments. 

The extensive investigations by Astbury and Woods (1933) of the X-ray diffraction patterns of animal fibers before and after stretcihing, setting, or supercontraction (Section VI,5,2) have had a major influence on the models proposed to account for the load-extension properties. Astbury and Woods showed that when animal fibers are stretched, the characteristic a-pattern decreases in intensity with the simultaneous appearance of a d-pattern similar to that obtained from silk. The sharpness and intensity of the /3-pattern increases with sti ain, with temperature, and with time under strain. In the Hookean region the 5.1 A meridional spacing increases by up to 2 % (Astbury and Haggith, 1953). Astbury and Woods (1933) stated that virtually no /3-pattern appears until the fiber has been stret( hed by at least 20 %, and for 25 years this observation dominated the models proposed to explain the elastic properties of wool (Alexander and Hudson, 1954). 

Chemical treatments also may cause supercontraction. Thus Speakman... 

On the other hand there is clear evidence that the forces acting in wool fibers which have been supercontracted and then stretched to a limited... 

Hence the changes which take place during supercontraction of keratin fibers are similar to those occurring when collagen or aligned crystalline polymers are converted to their elastomeric form (Mandelkern, 1959). 

Solutions of salts such as LiBr or Nal containing 1 N HCl, however, give contractions at 100°C of about 75 % (Crewther and Dowling, 1959). It was concluded that acid-labile bonds or ionic interactions are responsible for limiting the extent of supercontraction in neutral solutions of LiBr. Crewther and Dowling (1960a) showed that conversion of 94 % of the disulfide bonds of wool to methyl groups does not affect the total supercontraction of Lincoln fibers. Hence disulfide bonds place little if any restriction on the extent of total supercontraction of these fibers. 

Fig. 21. Relationships between (X) extent of first stage of supercontraction and residual disulfide content of reduced and methylated wool fibers and ( ) between total supercontraction and content of (—S—CHa—CHa—S—) cross-linkages. The theoretical relationship is shown by the unbroken line (Crewther, 1964b).

A similar relationship holds between lanthionine content of alkali-treated or cyanide-treated fibers and the extent of total supercontraction (Crewther et al, 1964a). 

No explanation has been provided for the failure of alkali treatments producing lanthionine in the fibers to depress the level of total supercontraction in 4 Af LiBr/1 N HCl at 98.5°C (Crewther et al., 1964a). 

Sikorski (1960) and Woods (1960) have criticized the concept of a non-contractile matrix on the basis of the studies of Jeffrey ei al. (1955). Electron micrographs of preparations from the interiors of cortical cells derived from supercontracted fibers showed no apparent twisting of the fibrillar material, yet X-ray diffraction patterns showed marked disorientation of the a- or j3-structures in the fibers. Jeffrey el al. (1955) attributed this result to contraction of the matrix. 

Calculations of cross-link density from stress-strain and volume-swelling measurements on supercontracted wool fibers immersed in solutions of LiBr (Haly, 1963a) gave values differing by factors of 3 to 4 from those calculated from the supercontraction data of Crewther (1964b). When extrapolated to zero disulfide content, the stress-strain data for wool fibers (Haly, 1963a) suggested that the cross-link density of the... 

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