The response of lambda-phage DNA molecules to a well-defined elongational flow field generated by a Taylor four-roller mill was investigated by observing the flow birefringence, Delta n. Delta n in the center of the four rollers, near the stagnation point, was localized at the mill exit symmetry plane. The intensity gradually increased from the off-symmetrical plane to the center of the mill, and at the exit symmetrical plane, the intensity was maximum. Delta n also gradually increases with the strain rate, epsilon. These observations indicate that DNA molecules in the solution would be free draining in nature. From the decay of Delta n at each point in the mill after a sudden stop of the mill operation at 24 s(-1), the rotational diffusion coefficient of molecules, D-r, at each point in the mill space was estimated, where the relaxation time of the decay of Delta n was considered to be related to the molecular disorienting process. It is concluded that at 24 s(-1) lambda-phage DNA molecular coils near the stagnation point, which was assumed to be a prolate spheroid as a whole, was so deformed that the aspect ratio p (=b/a less than or equal to 1, where a and b are, respectively, the longer and shorter axes) would be 1/12 of that of the DNA molecule which has just entered the mill space. This result suggests that there is a possibility for the DNA molecule to be in a stretched conformation at a higher strain rate. (C) 1996 John Wiley & Sons, Inc. [References: 14]
展开▼
机译：通过观察流动双折射Δn，研究了λ噬菌体DNA分子对由泰勒四辊轧机产生的明确延伸流场的响应。四个辊中心的Δn位于停滞点附近，位于轧机出口对称平面上。强度从非对称平面到磨机中心逐渐增大，并且在出口对称平面处强度最大。 Δn也随着应变率ε逐渐增加。这些观察结果表明溶液中的DNA分子自然会自由排放。从在24 s（-1）突然停止研磨操作后研磨机中每个点的Delta n衰减，可以估算出研磨机空间中每个点的分子旋转扩散系数Dr，其中弛豫δn的衰变时间被认为与分子的定向过程有关。结论是，在停滞点附近被认为是整体长椭球形的24 s（-1）λ噬菌体DNA分子线圈变形，以至于长宽比p（= b / a小于或等于等于1，其中a和b分别是长轴和短轴）将是刚进入研磨空间的DNA分子的1/12。该结果表明，DNA分子有可能以较高的应变速率处于拉伸构象。 （C）1996 John Wiley＆Sons，Inc. [参考：14]
展开▼
