Tunable Alignment for All Polymer Gel/Solvent Combinations for the Measurement of Anisotropic NMR Parameters
Tunable Alignment for All Polymer Gel/Solvent Combinations for the Measurement of Anisotropic NMR Parameters
复制标题
DOI：
10.1002/chem.201000108
复制
发表时间：
2010-01-01
影响因子：
4.3
通讯作者：
Luy, Burkhard
中科院分区：
文献类型：
--
作者：
Kummerloewe, Grit;McCord, Elizabeth F.;Luy, Burkhard
残余偶极耦合（RDC）和其他各向异性NMR参数提供了有关生物分子[1]以及小有机分子（如糖、肽和天然或合成产物）构象和构型的有价值的结构信息。[2]其准确测量的基本要求是调节溶质分子的适当程度的部分排列。机械拉伸的聚合物凝胶允许在几乎所有NMR溶剂中无下限地缩放配向，[3]但是直接在NMR管中拉伸凝胶的经典方式[2]需要每个配向强度的新样品。由于小的有机分子的取向顺序的预测仍然不容易实现，这经常导致不必要的和耗时的样品制备，并最终导致相应的有价值的材料的损失。只有随着Kuchel组[4，5]引入拉伸装置，情况才发生了变化，现在可以使用标准的液态NMR设备快速可逆地调节单个样品中的取向度。虽然原始的拉伸装置可以用于明胶[4，6]和其他含有极性溶剂如D2 O和DMSO的凝胶，[5]它与更非极性的有机溶剂如氯仿、二氯甲烷或四氢呋喃不相容。作为设备主要部分的硅胶管还允许水和湿气渗透到凝胶样品中[5]，并在相应的1H NMR光谱中产生约0.1 ppm的强烈、宽信号。因此，它对大多数有机化合物的分析用途非常有限。在这里，我们提出了一种新的拉伸装置的基础上定制的全氟弹性体管，克服了现有的主要限制的原始设备，并提供了所需的拉伸能力，几乎所有的聚合物/溶剂的组合。根据我们设计的配有硅胶管的拉伸装置[5]，将柔性全氟弹性体管放置在切开的5 mm NMR管内，并使用由PCTFE制成的特殊设计的螺旋夹固定在底部（图1）。弹性体管作为一个可膨胀的容器，用于容纳内部含有溶质分子的溶胀凝胶。在拉伸柔性管时，聚合物凝胶也被拉伸，这又导致溶质和可测量的各向异性NMR参数的部分对准。
Residual dipolar couplings (RDCs) and other anisotropic NMR parameters provide valuable structural information on the conformation and configuration of biomolecules [1] as well as small organic molecules such as sugars, peptides, and natural or synthetic products.[2] A fundamental requirement for their accurate measurement is the adjustment of a proper degree of partial alignment of the solute molecule. Mechanically stretched polymer gels allow the scaling of alignment without lower limit in practically all NMR solvents,[3] but the classical way of stretching the gel directly in an NMR tube [2] demands a new sample for each alignment strength. Since the prediction of the orientational order for small organic molecules is still not easily achieved, this frequently leads to unnecessary and time-consuming sample preparations and eventually to a corresponding loss of valuable material. Only with the introduction of a stretching apparatus by the Kuchel group [4, 5] the situation changed and it is now possible to rapidly and reversibly adjust the degree of orientation within a single sample using standard liquid state NMR equipment.While the original stretching apparatus can be used with gelatin [4, 6] and other gels containing polar solvents such as D2O and DMSO,[5] it is incompatible with more apolar organic solvents such as chloroform, dichloromethane, or tetrahydrofuran. The silicone tube as the main part of the device also allows water and humidity to penetrate into the gel sample [5] and leads to an intense, broad signal around 0.1 ppm in corresponding 1H NMR spectra. It is therefore of very limited use for the analysis of most organic compounds. Here we present a novel stretching device based on a tailormade perfluorinated elastomer tube which overcomes the main existing limitations of the original apparatus and provides the desired stretching capabilities for practically all polymer/solvent combinations. Following our design of the stretching device equipped with a silicone tube,[5] the flexible perfluorinated elastomer tube is placed inside a cut-open 5 mm NMR tube and fixed at the bottom with a specially designed screw clamp made out of PCTFE (Figure 1). The elastomer tube works as an expandable container for the swollen gel with the solute molecule inside. Upon stretching of the flexible tube the polymer gel is stretched as well, which in turn leads to partial alignment of the solute and measurable anisotropic NMR parameters.