High resolution in heteronuclear ¹H–¹³C NMR experiments by optimizing spectral aliasing with one‐dimensional carbon data

Abstract

In the chemistry literature it is common to provide NMR data on both proton and carbon spectra based on one-dimensional experiments, but often only proton spectra are assigned. The absence of a complete attribution of the carbons is in good part due to the difficulty in reaching the necessary resolution in the carbon dimension of two-dimensional experiments. It has already been shown that high-resolution heteronuclear spectra can be acquired within nearly the same acquisition time using a violation of the Nyquist condition. For a spectral width reduction by a given factor k, the resolution increases by the same factor as long as it is not limited by relaxation. The price to pay for such an improvement is a k-fold ambiguity in the chemical shift of the signal along the folded or aliased dimension. The computer algorithm presented in this paper takes advantage of the peak list stemming from one-dimensional spectra in order to calculate spectral widths for which the ambiguities in the aliased dimension of heteronuclear experiments are eliminated or at least minimized. The resolution improvement factor is only limited by the natural lineshape and reaches a typical value higher than 100. The program may be set to run automatically on spectrometers equipped with automatic sample changers. Applications to short-range HSQC experiments and long-range HMBC spectra of steroids, carbohydrates, a peptide and a mixture of isomers are shown as examples.

Improving resolution in single-scan 2D spectroscopy

“…Powerful methods exist to choose a spectral width that is as small as possible without generating any ambiguities due to folding [25][26][27]. If the proton spectrum is unknown, one should repeat the experiment with a slightly different spectral width in the direct x 2 dimension.…”

Speeding up nuclear magnetic resonance spectroscopy by the use of SMAll Recovery Times – SMART NMR

“…This technique does not require any special processing and is fully compatible with other time-saving methods such as filter diagonalization [9], covariance spectroscopy [10], linear prediction [11], nonCartesian sampling [12][13][14], spectral aliasing [15,16], and maximum entropy reconstruction [17]. The experiments require pulsed field gradients along three orthogonal axes.…”

Computer optimized spectral aliasing in the indirect dimension of 1H–13C heteronuclear 2D NMR experiments. A new algorithm and examples of applications to small molecules

“…In earlier developments, the approach for determining the optimal spectral width consisted of simulating aliased spectra [11] or setting spectral widths arbitrarily [12]. One inconvenience of simulations was that they could miss solutions when the calculated set of tentative spectral widths was not large enough.…”

“…Other considerations about the interdependence between spectral width, number of time increments and maximal t 1 evolution time can be found elsewhere [11].…”