Pure Shift ~1HNMR: A Resolution of the Resolution Problem?

摘要

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 homo-nuclear 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, 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.