Jian Gao, Steven Warner
Department of Textile Sciences
College of Engineering, University of Massachusetts, Dartmouth



Introduction

Spider silk fibers are of much interest in recent years because of their extraordinary mechanical properties, including high strain-to-fail and moderately high tenacity ^[1].

Spider Web.

Spider silk shown as normal size, stretched 5 times and 20 times its original length.

Spider silk’s mechanical properties are largely dependent on a high degree of molecular orientation, which has previously been demonstrated in both the crystalline and the amorphous domains of dragline silk. Spider’s internal liquid crystalline spinning induces the high orientation of protein molecules. In the spider changes in physiological conditions such as pH and salt concentrations in the gland accompany the silk processing. Potassium phosphate (KH₂PO₄) is suggested to help generate hydrogen ions during the spider’s spinning process, which is possible to assist the protein’s phase separation ^[2].

It is assumed that the hydrogen bonds in the spider silk molecular chains play a crucial role in the structure. When these bonds are gradually destroyed, the molecular chains disorient and coil-uncoil step by step. Some salts, such as KNO₃ and KH₂PO₄, can in principle influence the silk protein’s intermolecular hydrogen bonding by cation interactions with the protein’s carbonyl groups, and effect the protein’s conformational changes ^[3,4].

Raman spectroscopy will be utilized to investigate whether intermolecular hydrogen bonding and crystallinity in the spider silk change with the different salt treatments. This may help ascertain the effects of salts in the spider’s gland on the spider silk’s secondary structures. Such changes may affect the spider silk’s mechanical properties.

1. F. Vollrath, Strength and structure of spider's silks, Review in Molecular Biotechnology. 2000, Vol. 74, 67-83
   
   
2. D. Kaplan, W. W. Adams, B. Farmer and C. Viney, Raman spectroscopic analysis of the secondary structure of spider silk fiber, Silk polymers: Materials Science and Biotechnology. American Chemical Society, Washington, DC 1994
   
   
3. R. F. Foelix, Spider web, Biology of spiders. New York: Oxford University Press: Georg Thieme Verlag, 1996.
   
   
4. P. Rath, O. Bousche, A. R. Merrill, Biophysics Journal. 1991, Vol. 59, 516-522