SIDECHAIN ORDER PARAMETERS VIA 2H NMR IN POLYPEPTIDE LIQUID CRYSTALS
SIDECHAIN ORDER PARAMETERS VIA 2H NMR IN POLYPEPTIDE LIQUID CRYSTALS
复制标题
通过 2H NMR 测定多肽液晶中的侧链有序参数
DOI：
10.1051/jphyscol:1979393
复制
发表时间：
1979
期刊：
影响因子：
--
通讯作者：
E. Samulski
中科院分区：
文献类型：
--
作者：
E. Samulski
我们选择性地对合成多肽聚（γ-苄基-L-谷氨酸酯）PBLG的侧链进行了氘代。在PBLG的磁取向的双折射溶液中，螺旋聚合物棒平行于磁场排列。柔性PBLG侧链的布朗运动是各向异性的，导致2 H NMR共振的四极分裂。可以确定侧链中C-D键方向的序参数。这些研究使我们能够对a-螺旋外围侧链的组织性质有新的见解。本文综述了溶致多肽液晶的一般性质[1]。α-螺旋聚合物的手性在中间相中施加了螺旋织构。然而，螺旋的抗磁各向异性是积极的，并在足够强的磁场（H，2 - 5 kOe）的取向的α相持续存在。溶剂分子和客体分子添加到这个中间相行使各向异性的旋转和扩散运动在这个定向阵列的六方堆积的螺旋。虽然各向异性运动的细节是复杂的[单轴分散力场叠加在化学交换过程上，该化学交换过程涉及接近螺旋的结合客体（溶剂）与从螺旋溶剂化壳层移除的几乎各向同性的分子交换]，它允许在液晶中进行NMR光谱实验，其中观察到的物质的特征在于非常低的取向有序参数（通常比热致中间相小两到三个数量级）。低有序度有利于在氘代客体（溶剂）分子的1H NMR谱中观察到四极分裂（AV 1）[2]。在此，我们描述了液晶的多肽组分的特异性2 H标记的侧链的四极分裂。Avi的大小和它们对液晶中聚合物浓度变化的响应提供了对多肽螺旋外周上侧链的结构-动力学组织的一些一般性见解。研究了合成多肽聚（γ-苄基-L-谷氨酸酯）（PBLG）的两种1H标记的衍生物：PBLG-d，在苄基酯的苯环上的帕拉具有氘，PBLG-d，苄基酯完全氘代。在取向的π相位中，指向矢平行于光谱仪磁场（z轴）;四极分裂由下式给出：其中Qi是四极矩，Vizz是电场梯度张量的适当分量。分子固定轴系统中的张量分量间隙（a，B，c）通过Saupe有序矩阵的元素与qzz相关：（*）该研究部分得到了来自国家关节炎、代谢和消化疾病研究所的资助。如果四极耦合常数qb已知，则Δ V。文章由EDP Sciences在线发表，可在http://dx.doi.org/10.1051/jphyscol:1979393 C3-472 E上查阅。T. SAMULSKI（假设不对称参数q =（g1，qc，）/gbb可忽略不计。）小分子类似物甲苯-d提供了一组g，，。g1衍生自在PBLG液晶中取向的甲苯-d1的1H NMR谱（图1）。甲苯的取向可以如图1所示。溶解在取向的PBLG-CH，Cl溶液（30重量%）中的甲苯-d的1H NMR谱。聚合物）。可以用两阶矩阵元素S1和（S2-S1，，）来指定。前者由甲苯甲基的~ 1H NMR谱中的偶极分裂得到。结果基于甲苯和甲苯-d在液晶中的相同排序和几何形状的假设（表I）。与9 bb PINext的早期测定有很好的一致性，我们对比了溶解在多肽液晶中的游离探针分子苄醇-d与结合探针PBLG-d中的苄酯的排序。从Avi的大小差异（图2）中很容易看出，共价连接到侧链的氘代探针比游离探针受到更多的限制。前者展示跨越近25 kHz的频谱宽度的AV，而后者的频谱限于5 kHz。此外，标记侧链本身不会明显影响取向; PBLG-d和PBLG-d的光谱重叠（图3）。
We have selectively deuterated the sidechain of the synthetic polypeptide poly (-y-benzyl-L-glutamate), PBLG. In magnetically oriented nematic solutions of PBLG, the helical polymer rods are aligned parallel to the field. The Brownian motion of the flexible PBLG sidechain is anisotropic, resulting in quadrupole splittings of the 2H NMR resonances. The order parameters of C-D bond directions in the sidechain can be determined. These studies permit new insights into the nature of organization of sidechains on the periphery of the a-helix. The general features of lyotropic polypeptide liquid crystals have been reviewed recently [l]. The chirality of the cc-helical polymer imposes a cholesteric texture in the mesophase. However, the diamagnetic anisotropy of the helix is positive and an oriented nematic phase persists in sufficiently strong magnetic fields (H, 2 5 kOe). Solvent molecules and guest molecules added to this mesophase exercise anisotropic rotational and diffusional motion within this oriented array of hexagonally packed helices. While the details of the anisotropic motion are complex [a uniaxial dispersion force field superposed on a chemical exchange process involving a bound guest (solvent) proximate to the helix exchanging with nearly isotropic molecules removed from the helix solvation shell], it permits NMR spectroscopy experiments in liquid crystals wherein the species observed is characterized by very low orientational order parameters (usually two to three orders of magnitude smaller than thermotropic mesophases). The low degree of order facilitates the observation of quadrupolar splittings (AV,) in the 'H NMR spectra of deuterated guest (solvent) molecules [2]. Herein we describe quadrupolar splittings for specifically 2H labeled sidechains of the polypeptide component of the liquid crystal. The magnitude of the Avi and their response to changes in the polymer concentration in the liquid crystal provide some general insights into the structural-dynamical organization of the sidechains on the periphery of the polypeptide helix. Two 'H labeled derivatives of the synthetic polypeptide polyf-y-benzyl-L-glutamate) (PBLG), were studied : PBLG-d, with deuterium at the para position on the phenyl ring of the benzyl ester and, PBLG-d, with the benzyl ester fully deuterated. In the oriented nematic phase, the director is parallel to the spectrometer magnetic field (z-axis) ; the quadrupolar splitting is given by where Qi is the quadrupole moment and Vizz is the appropriate component of the electric field gradient tensor. The tensor components gap in a molecule-fixed axis system (a, b, c) are related to qzz via the elements of the Saupe order matrix : (*) This research was supported in part by a grant from the In practice the average orientation or order parameter National Institute of Arthritis, Metabolism and Digestive Diseases of the C-D bond @-direction) can be extracted from (AM 19 497). AV if the quadmpole coupling constant qb, is known. Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979393 C3-472 E. T. SAMULSKI (The asymmetry parameter q = (g,, qc,)/gbb is assumed to be negligible.) The small-molecule analogue toluene-d, provides a set of g,,. The g,, are derived from the 'H NMR spectrum of toluene-d, oriented in the PBLG liquid crystal (Fig. 1). The orientation of the toluene can FIG. 1. The 'H NMR spectrum of toluene-d, dissolved in an oriented PBLG-CH,CI, solution (30 % by wt. polymer). be specified with two order matrix elements, S,, and (Sz2-S,,). The former is obtained from the dipolar splittings in the 'H NMR spectrum of toluene methyl group. The results are based on the assumption of identical ordering and geometries for toluene and toluene-d, in the liquid crystal (Table I). There is good agreement with earlier determinations of the 9bb PINext we contrast the ordering of the free probe molecule benzyl alcohol-d, dissolved in the polypeptide liquid crystal with the bound probe, the benzyl ester in PBLG-d,. It is readily apparent from the difference in the magnitude of the Avi's (Fig. 2), that the deuterated probe covalently attached to sidechain is considerably more constrained than the free probe. The former exhibits AV's spanning a spectral width of nearly 25 kHz whereas the spectrum of the latter is limited to 5 kHz. Also, labeling the sidechain in itself does not appreciably influence the orientation ; spectra of PBLG-d, and PBLG-d, superpose (Fig. 3).