Watanabe Eiji, Boutis Gregory S, Sato Hiroko, Sekine Sokei, Asakura Tetsuo
Department of Biotechnology, Tokyo University of Agriculture and Technology, Koganei 184-8588, Japan.
Department of Physics, Brooklyn College of The City University of New York, Brooklyn, New York 11210, United States.
Polymer (Guildf). 2014 Jan 14;55(1):278-286. doi: 10.1016/j.polymer.2013.11.015.
The thermo-responsive behavior of a unique biocompatible polymer, poly(-substituted α/β-asparagine) derivative (PAD), has been studied with several NMR methods. The H and C solution NMR measurements of the PAD in DMSO- were used to investigate the isolated polymer and perform spectral assignments. By systematic addition of DO we have tracked structural changes due to aggregation and observed contraction of hydrophilic side chains. Solution and cross polarization / magic angle spinning (CP/MAS) C NMR approaches were implemented to investigate the aggregates of the PAD aqueous solution during the liquid to gel transition as the temperature was increased. At temperatures near 20 °C, all of the peaks from the PAD were observed in the C CP/MAS and C solution NMR spectra, indicating the presence of polymer chain nodes. Increasing the temperature to 40 °C resulted in a partial disentanglement of the nodes due to thermal agitation and further heating resulted in little to no additional structural changes. Deuterium and two-dimensional relaxation spectroscopies using an inverse Laplace transform, were also implemented to monitor the water-PAD interaction during the phase transition. At temperatures near 20 °C the dynamical characteristics of water were manifested into one peak in the deuterium map. Increasing the temperature to 40 °C resulted in several distinguishable reservoirs of water with different dynamical characteristics. The observation of several reservoirs of water at the temperature of gel formation at 40 °C is consistent with a physical picture of a gel involving a network of interconnected polymer chains trapping a fluid. Further increase in temperature to 70 °C resulted in two non-exchanging water reservoirs probed by deuterium measurements.
一种独特的生物相容性聚合物聚（-取代α/β-天冬酰胺）衍生物（PAD）的热响应行为已通过多种核磁共振方法进行了研究。在二甲基亚砜-d6中对PAD进行的氢和碳溶液核磁共振测量用于研究分离的聚合物并进行光谱归属。通过系统地添加重水，我们追踪了由于聚集导致的结构变化，并观察到亲水性侧链的收缩。采用溶液和交叉极化/魔角旋转（CP/MAS）碳核磁共振方法，研究了随着温度升高，PAD水溶液在从液体到凝胶转变过程中的聚集体。在接近20℃的温度下，在碳CP/MAS和碳溶液核磁共振谱中观察到了来自PAD的所有峰，表明存在聚合物链节点。将温度升高到40℃会由于热搅动导致节点部分解缠结，进一步加热则几乎不会导致额外的结构变化。还采用了氘和二维弛豫光谱结合反拉普拉斯变换来监测相变过程中水与PAD的相互作用。在接近20℃的温度下，水的动力学特征在氘图谱中表现为一个峰。将温度升高到40℃会导致出现几个具有不同动力学特征的可区分的水储库。在40℃凝胶形成温度下观察到几个水储库，这与凝胶的物理图像一致，即凝胶涉及相互连接的聚合物链网络捕获流体。将温度进一步升高到70℃会导致通过氘测量探测到两个不交换的水储库。
