Transient electric birefringence of agarose gels. II. Reversing electric fields and comparison with other polymer gels.
Transient electric birefringence of agarose gels. II. Reversing electric fields and comparison with other polymer gels.
复制标题
琼脂糖凝胶的瞬态电双折射。
DOI：
10.1002/bip.360340914
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发表时间：
1994
期刊：
影响因子：
2.9
通讯作者：
Stellwagen,NC
中科院分区：
文献类型：
--
作者：
Stellwagen,J;Stellwagen,NC
由脉冲单向电场定向的低电内渗（LE）琼脂糖凝胶的瞬时电双折射在第I部分[J. Stellwagen和N. C. Stellwagen（1994），Biopolymers，第34卷，第187页]。本文报道了LE琼脂糖凝胶在快速反向电场中的双折射现象，这种电场的振幅和持续时间与场反转凝胶电泳的电场相似，对称的反向电场使LE琼脂糖凝胶双折射的符号和琼脂糖纤维的取向方向随外加电场同相振荡。由于持久的记忆效应，双折射的交替符号似乎是由于电场诱导的凝胶结构的亚稳态变化。如果反向场脉冲的幅度相等但持续时间不同，则取向行为关键取决于所施加的电压。如果E < 7 V/cm，则双折射的幅度随着脉冲数的增加而逐渐减小，并且变得不可测量地小。然而，如果E> 7 V/cm，则在对凝胶施加1020个脉冲后，双折射的幅度增加超过10倍，这表明凝胶结构发生了协同变化。因为没有伴随的变化，双折射一定是由于电场中定向的琼脂糖纤维和/或纤维束数量的增加，这反过来表明将纤维交联到fgel基质中的非共价“连接区”的协同破坏。LE琼脂糖凝胶的双折射的符号在广泛的接合区击穿后总是正的，表明琼脂糖纤维和纤维束在它们从凝胶基质的约束中释放时优先平行于电场取向。在单向和快速反向电场中研究了β-卡拉胶（一种变化更大的琼脂糖）、β-卡拉胶（琼脂糖的立体异构体）和聚丙烯酰胺（一种化学交联聚合物）。HEEO琼脂糖主链的双折射。β-卡拉胶凝胶在反向电场中表现出可变的取向行为，表明其内部凝胶结构不像琼脂糖凝胶那样紧密互连。当向凝胶施加> 7 V/cm的非对称反向脉冲时，HEEO琼脂糖和β-卡拉胶凝胶的双折射幅度都随着脉冲数的增加而大幅增加，这表明多糖凝胶的共同特征是连接区破裂。化学交联聚丙烯酰胺凝胶的双折射信号非常小，这表明在脉冲电场中很少发生取向。双折射的符号与电场的极性无关，正如克尔定律所预期的那样，并且在反向电场中观察到正常取向行为。因此，在反向电场中观察到的琼脂糖凝胶的双折射的符号的异常变化必须是由于在琼脂糖凝胶基质中的亚稳结区，这使得凝胶纤维重排发生。John Wiley & Sons，Inc.
The transient electric birefringence of low electroendosmosis (LE) agarose gels oriented by pulsed unidirectional electric fields was described in detail in Part I [J. Stellwagen and N. C. Stellwagen (1994),Biopolymers, Vol. 34, p. 187]. Here, the birefringence of LE agarose gels in rapidly reversing electric fields, similar in amplitude and duration to those used for field inversion gel electrophoresis, is reported.Symmetric reversing electric fields cause the sign of the birefringence of LE agarose gels, and hence the direction of orientation of the agarose fibers, to Oscillate in phase with the applied electric field. Because of long‐lasting memory effects, the alternating sign of the birefringence appears to be due to metastable changes in gel structure induced by the electric field. If the reversing field pulses are equal in amplitude but different in duration, the orientation behavior depends critically on the applied voltage. IfE< 7 V/cm, the amplitude of the birefringence gradually decreases with increasing pulse number and becomes unmeasurably small. However, ifE> 7 V/cm, the amplitude of the birefringence increase more than 10‐fold after ∼ 20 pulses have been applied to the gel, suggesting that a cooperative change in gel structure has occurred. Because there is no concomitant change birefringence must be due to an increase in the number of agarose fibers and /or fiber bundles orienting in the lectric field, which in turn indicates a cooperatice breakdown of the noncovalent “junction zones” that corss‐link the fibers in to the fgel matrix. The sign of the birefringence of LE agarose gels is always positive after extensive junction zone breakdown, indicating that the agarose fibers and fiber bundles preferentially orient parallel to the lectric field when they are freed from the constraints of the gel matrix.Three other gel‐forming polymers, high electroendosmosis (HEEO) agarose (a more highly changed agarose), β‐carrageenan (a stereoisomer of agarose), and polyacrylamide (a chemically corss‐linked polymer) were alos studied in unidirectional and rapidly reversing electric fields. The birefringence of HEEO agarose backbone chain. The β‐carrageenan gels exhibit variable orientation behavior in reversing electric fields, suggesting that its internal gel structure is not as tightly interconnected as that of agaroise gels. Both HEEO agarose and β‐carrageenan gels exhibit a large increase in the amplitude of the birefringence with increasing pulse number when asymmetric reversing pulses > 7 V/cm are applied to the gels, suggesting that junction zone breakdown in a common feature of polysaccharide gels.Chemically cross‐linked polyacrylamide gels exhibit very small birefringence signals, indicating that very little orientation occurs in pulsed lectric fields. The sign of the birefringence is independent of the polarity of the lectric field, as expected from the Kerr law, and normal orientation behavior is observed in reversing electric fields. Hence, the anomalous change in sign of the birefringence observed for agarose gels in reversing electric fields must be due to the metastable junction zones in the agarose gel matrix, which allow gel fiber rearrangements to occur. © 1994 John Wiley & Sons, Inc.