EPR spectroscopy reveals nanoinhomogeneities in the structure and reactivity of thermoresponsive hydrogels
EPR spectroscopy reveals nanoinhomogeneities in the structure and reactivity of thermoresponsive hydrogels
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DOI：
10.1002/smll.200800127
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发表时间：
2008-09-01
期刊：
影响因子：
13.3
通讯作者：
Hinderberger, Dariush
中科院分区：
文献类型：
--
作者：
Junk, Matthias J. N.;Jonas, Ulrich;Hinderberger, Dariush
通过连续波电子顺磁共振波谱研究了新型热响应水凝胶（光交联聚（N-异丙基丙烯酰胺）（pNiPAAm）共聚物）内溶质分子的动态和化学行为。通过添加顺磁性示踪分子（所谓的自旋探针），可以获得分子尺度上热致塌缩的图像，该塌缩在比急剧的宏观体积转变所指示的温度范围要宽得多的温度范围内进行。亲水和疏水环境的采样表明了一种不连续的塌陷机制，塌陷和扩张的网络区域并存。这些纳米尺度上的结构不均匀性也导致化学反应性的不均匀性。亲水区域形成纳米反应器，极大地加速反应，而疏水区域充当纳米庇护所，其中封闭的自旋探针受到保护免遭衰变。结果表明，由统计二元或三元共聚物组成的系统表现出非常复杂的行为，模拟了在功能性生物聚合物（例如酶）中观察到的空间和化学不均匀性。
The dynamic and chemical behavior of solute molecules inside new thermoresponsive hydrogels (photocrosslinked poly(N-isopropylacryla-mide) (pNiPAAm) copolymers) is studied by continous-wave electron paramagnetic resonance spectroscopy. Via addition of paramagnetic tracer molecules (so-called spin probes) a picture is obtained of the thermally induced collapse on the molecular scale, which proceeds over a substantially broader temperature range than indicated by the sharp macroscopic volume transition. The sampling of hydrophilic and hydrophobic environments suggests a discontinous collapse mechanism with a coexistence of collapsed and expanded network regions. These structural inhomogeneities on the nanoscale also lead to an inhomogeneity in chemical reactivity. The hydrophilic regions form nanoreactors, which strongly accelerate the reaction while the hydrophobic regions act as nanoshelters, in which enclosed spin probes are protected from the decay. The results show that the system consisting of a statistical binary or tertiary copolymers displays remarkably complex behavior that mimics spatial and chemical inhomogeneities observed in functional biopolymers such as enzymes.