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Experimental strategies for 13C–15N dipolar NMR spectroscopy in liquid crystals at the natural isotopic abundance

机译:在自然同位素丰度下液晶13C-15N双极NMR光谱的实验策略

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Direct dipolar spin couplings are informative and sensitive probes for a wide range of dynamic processes and structural properties at atomic, molecular and supramolecular levels in liquid crystals and other anisotropic materials. Usually, heteronuclear ~(13) C– ~(1) H dipolar couplings in liquid crystals with natural ~(13) C abundance are measured. Recording ~(13) C– ~(15) N NMR dipolar spectra in unlabeled materials is challenging because of the unfavorable combination of two rare isotopes. Here we design and compare various experimental strategies to measure short- and long-range heteronuclear ~(13) C– ~(15) N dipolar couplings in liquid crystalline samples with high molecular orientational order. New techniques were developed to record ~(13) C and ~(15) N spectra of naturally occurring ~(13) C– ~(15) N spin pairs with increased signal intensity and spectral resolution while suppressing the signals of the uncoupled isotopes. Highly resolved ~(13) C– ~(15) N dipolar spectra were recorded within an experimental time of a few hours. Coupling constants in a broad range of 10–1000 Hz between spins separated by up to five chemical bonds and distances of up to 5 ? were measured. Because of their relatively low demands on radio-frequency power levels, the experiments were easy to implement using conventional high-resolution solution-state NMR hardware. Experimental data were compared to the results of density functional theory and molecular dynamics computational analyses. The presented experimental methods to characterize the dipolar couplings in unlabeled materials provide novel routes to investigate molecular structure and dynamics in mesophases.
机译:直接偶极旋转偶联对液晶和其他各向异性材料中的原子,分子和超分子水平的各种动态工艺和结构性能的信息和敏感探针。通常,测量具有天然〜(13)C丰度的液晶中的异核〜(1)C-〜(1)H偶极偶联。记录〜(13)C-〜(15)未标记材料中的NMR偶极光谱是挑战,因为两种罕见同位素的不利组合。在这里,我们设计和比较各种实验策略来测量液晶样品中的短和远程异核〜(13)C-〜(15)N偶极偶联,具有高分子界定序列。开发了新技术,以记录〜(13)C和〜(15)n光谱,其天然存在的〜(13)C-(15)n旋转对,其具有增加的信号强度和光谱分辨率,同时抑制未耦合同位素的信号。高度分辨的〜(13)C-〜(15)n偶极光谱在几个小时的实验时间内记录。旋转常数在10-1000赫兹之间的旋转之间多达五个化学键和最多5的距离之间?测量了。由于它们对射频功率水平的需求相对较低,因此使用传统的高分辨率解决方案状态NMR硬件易于实现实验。将实验数据与密度函数理论和分子动力学计算分析的结果进行比较。所提出的实验方法,以表征未标记材料中的双极联轴器提供了一种研究中间蛋白酶中的分子结构和动力学的新途径。

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