Pure Shift 1H NMR: A Resolution of the Resolution Problem?
Pure Shift 1H NMR: A Resolution of the Resolution Problem?
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DOI：
10.1002/anie.201001107
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发表时间：
2010-01-01
影响因子：
16.6
通讯作者：
Morris, Gareth A.
中科院分区：
文献类型：
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作者：
Aguilar, Juan A.;Faulkner, Stephen;Morris, Gareth A.
近年来，核磁共振仪器在灵敏度方面取得了巨大的进步，特别是通过冷探针技术的发展，但分辨率仍然与磁场强度紧密相关：将现有的最高场强从500 MHz提高到1000 MHz需要28年。方法的发展，特别是多维NMR，有帮助，但即使在最高的领域1H光谱往往是广泛重叠。核心问题是由同素标量耦合引起的多重态结构;如果可以抑制这种结构，光谱中信号的密度通常会降低近一个数量级。没有多重峰的“纯位移”光谱将带来分辨率的改善，以匹配信噪比（SNR）。这样的光谱可以获得，[1-13]但直到最近很少使用，原因包括缺乏通用性，不敏感性，非线性和复杂性。在这里，我们表明第二代纯位移方法对于复杂的化学系统非常实用，其分辨率相当于灵敏度为毫米的几GHz光谱仪。图1比较了方案1的两种四烯丙基杯[4]芳烃的混合物（总浓度9mM）的常规和纯位移光谱，后者在2.8分钟内获得。
NMR instrumentation has made enormous strides in sensitivity in recent years, notably through the development of cold-probe technology, but resolution has remained stubbornly tied to magnetic field strength: it has taken 28 years to double the highest field strength available, from 500 to 1000 MHz for 1H. Methodological developments, especially multidimensional NMR, have helped, but even at the highest fields 1H spectra are often extensively overlapped. The central problem is the multiplet structure caused by homonuclear scalar coupling; if this could be suppressed, the density of signals in a spectrum would typically decrease by almost an order of magnitude. A “pure shift” spectrum, without multiplets, would bring a resolution improvement to match that achieved in signal-to-noise ratio (SNR). Such spectra can be obtained,[1–13] but until recently have been very little used, for a variety of reasons including lack of generality, insensitivity, nonlinearity, and complexity. Here we show that second-generation pure shift methods are eminently practical for complex chemical systems, giving resolution equivalent to spectrometers of several GHz with mm sensitivity. Figure 1 compares conventional and pure shift spectra, the latter acquired in 2.8 min, for a mixture (total concentration 9 mm) of the two tetraallyl calix [4] arenes of Scheme 1.