Multimode Diffusion of Ring Polymer Molecules Revealed by a Single-Molecule Study
Multimode Diffusion of Ring Polymer Molecules Revealed by a Single-Molecule Study
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DOI：
10.1002/anie.200904394
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发表时间：
2010-01-01
影响因子：
16.6
通讯作者：
Vacha, Martin
中科院分区：
文献类型：
--
作者：
Habuchi, Satoshi;Satoh, Norihiro;Vacha, Martin
合成聚合物分子的扩散过程对于决定其流变特性以及随后的聚合物加工和塑料、薄膜和纤维的制造至关重要。 [1]聚合物的拓扑结构，无论是线性、支化还是环状，都会极大地影响致密缠结溶液或熔体中的运动。对于线性和支化聚合物，蠕动模型 [2-5] 已被认为是有效的扩散机制，并通过光散射、核磁共振和粘弹性测量进行了实验验证。 [6-8] 在线性和支化聚合物的蠕动模型中，缠结的聚合物在由相邻聚合物链限制的动态管中扩散。对天然大分子和合成聚合物的单分子研究已经证明了管的真实性和扩散比例定律。[9-11] 端基的数量和结构是线性或支化聚合物扩散动力学的关键因素。另一方面，环状聚合物由于不存在自由链端而具有拓扑独特性。[12, 13]因此，它们的扩散机制引起了持续关注，[14-17]但仍然是一个重要的挑战。[18]除了环状 DNA 之外，[19, 20] 各种具有足够长链和保证纯度的合成环状聚合物最近已变得可行。[17, 21] 因此，通过使用具有特定链段结构和可选官能团的定制环状聚合物，现在已经揭示了明确的拓扑效应。[21–26] 在此，我们在单链水平上展示了直接、实时的扩散观察 [27-31] 单分子光谱被认为是监测聚合物动力学的有力工具，并且能够揭示其扩散过程中的拓扑效应。[20, 32] 我们合成了含有苝的线性 (1) 和环状 (2) 聚四氢呋喃 (poly (THF) s) 通过静电自组装和共价固定过程将二酰亚胺单元作为荧光团 [27, 28]（图 1；有关合成和表征的详细信息，请参阅其中的支持信息和参考文献）。对于单分子成像实验，聚合物 1 和 2 与未标记的线性聚 (THF) 在甲苯中以半稀浓度方案混合。未标记的基质聚合物的半稀释浓度比链重叠的临界浓度高约20倍。基质中 1 和 2 的最终浓度约为 10-9 m。将样品溶液夹在两个干净的显微镜盖玻片之间，导致样品厚度为10μm；使用荧光显微镜和 EM-CCD 相机测量它们的荧光图像。图2显示了1（图2a）和2（图2b）与线性聚（THF）在甲苯中混合的单分子荧光图像。使用二维高斯拟合确定分子的位置（有关粒子跟踪分析的详细信息，请参阅支持信息）。 [33]图2c、d分别显示了通过绘制测量的分子位置而获得的1和2的扩散轨迹的示例。轨迹的长度主要受到扩散的三维特征的限制。
Diffusion processes of synthetic polymer molecules are crucial in deciding their rheological properties, and subsequently in polymer processing and fabrication of plastics, films, and fibers.[1] The topology of a polymer, whether linear, branched, or cyclic, can dramatically affect the motion in a dense entangled solution or in a melt. For linear and branched polymers, the reptation model [2–5] has been accepted as a valid diffusion mechanism and verified experimentally by light scattering, NMR, and viscoelastic measurements.[6–8] In the reptation model for linear and branched polymers, an entangled polymer diffuses in a dynamic tube confined by neighboring polymer chains. Single-molecule studies on naturally occurring macromolecules and also on synthetic polymers have demonstrated the reality of the tube and the diffusion scaling laws.[9–11] The number and structure of end groups is a critical factor in the dynamics of the diffusion of linear or branched polymers. Ring polymers are, on the other hand, topologically unique by the absence of free chain ends.[12, 13] Therefore, their diffusion mechanism has attracted continuous attention,[14–17] but is still an important challenge.[18] Apart from cyclic DNA,[19, 20] a variety of synthetic ring polymers of sufficiently long chains and of guaranteed purity have recently become accessible.[17, 21] As a result, unequivocal topology effects have now been disclosed by using custom-made ring polymers with specific segment structures and optional functional groups.[21–26] Herein, we show, at the single-chain level, the direct and real-time observation of diffusion dynamics of synthetic ring and linear polymers incorporating a fluorophore.[27–31] Singlemolecule spectroscopy is recognized as a powerful tool for monitoring of polymer dynamics, and is capable of revealing topology effects in their diffusion process.[20, 32] We synthesized linear (1) and cyclic (2) poly (tetrahydrofuran) s (poly (THF) s) containing perylene diimide unit as a fluorophore by means of an electrostatic self-assembly and covalent fixation process [27, 28](Figure 1; see the SupportingInformation and references therein for details on the synthesis and characterization). For single-molecule imaging experiments, polymers 1 and 2 were mixed with unlabeled linear poly (THF) in toluene in a semi-dilute concentration regime. The semi-dilute concentration of the unlabeled matrix polymer is about 20 times more than the critical concentration for chain overlap. The final concentrations of 1 and 2 in the matrix were on the order of 10À9 m. The sample solutions were sandwiched between two clean microscope cover slips, resulting in the sample thickness of 10 μm; their fluorescence images were measured using a fluorescence microscope and an EM-CCD camera. Figure 2 shows single-molecule fluorescence images of 1 (Figure 2 a) and 2 (Figure 2 b) mixed with linear poly (THF) in toluene. The positions of the molecules were determined using a two-dimensional Gaussian fitting (see Supporting Information for details on the particle tracking analysis).[33] Figure 2c, d shows examples of diffusion trajectories of 1 and 2, respectively, obtained by plotting the measured molecular positions. The length of the trajectories was limited primarily by the three-dimensional character of the diffusion of the