蚕丝中蛋白构象含量与其力学性质间的关系

丝蛋白 (Ｆｉｂｒｏｉｎ)是一种具有优异力学性能的天然有机高分子材料 ,蚕丝是最具代表性的一种 .它既有较高的强度 ,又有较强的韧性 ,其强度甚至超过钢丝 .但蚕丝具有如此优异力学性能的机理还不很清楚1～ 3 ] .通常认为在丝蛋白中有 3种二级结构 (构象 ) ,即α 螺旋 (α ｈｅｌｉｘ) ,β 片层 ( β ｓｈｅｅｔ)和无规线团 (Ｒａｎｄｏｍｃｏｉｌ) 4,5] .α 螺旋是由链内氢键引起的蛋白结构 ,而 β 片层是由链间氢键引起的蛋白结构 .但有研究表明3 ,6] ,丝蛋白中还存在另一种由 4个氨基酸残基组成的发夹式结构 :β 转角 ( β ｔｕｒｎ)…

RELATIONS BETWEEN MECHANICAL PROPERTIES AND CONFORMATIONAL CONTENTS OF NATIVE SILKWORM SILK

Relations between mechanical properties and conformational contents of native silkworm silk are investigated.Three species of silkworm cocoons,bombyx mori,tussah and eri silkworm,are chosen and the three corresponding degummed silks are obtained by a strong alkaline solution and a relative neutral solution,respectively.For the six kinds of silk fibers,the load elongation curves and the infrared spetra of protein are measured.To transfer load into stress,the section area of silk is directly measured by SEM observation.The contents of four conformations, α \|helix, β \|sheet, β \|turn and random coil,can be calculated by the infrared spectra.Infrared analysis shows that the β \|sheet and α \|helix structures may be destroyed by the strong alkaline solution during the degumming and the destroyed molecular chains transform into random coils.So the strength and elastic modulus of bombyx mori and tussah silks are reduced drastically after degumming.In contrast,there is no significant change in the mechanical properties and the conformational content of protein for the degummed eri silkworm silk treated by relative neutral solution.The experimental results show that fractions of β sheet and α helix structures,especially β sheet,contribute to the strength and rigidity of silkworm silk.There is a good correlation between β \|sheet content and mechanical properties.But the correlation is not very significant for α \|helix because its content is very low.The infrared analysis also shows that the contents of β \|turn structures for all silks retain invariant,which indicates that β \|turn structure indeed exists in native silkworm silk and its contents seem not to be influenced by the species and the degumming.