SCoT: Swept Coherence Transfer for quantitative heteronuclear 2D NMR

Dariusz Gołowicz, Mateusz Urbańczyk, Alexandra Shchukina, Krzysztof Kazimierczuk

Nuclear magnetic resonance (NMR) spectroscopy is frequently applied in quantitative chemical analysis (qNMR). It is easy to measure one-dimensional (1D) NMR spectra in a quantitative regime (with appropriately long relaxation delays and acquisition times); however, their applicability is limited in the case of complex samples with severe peak overlap. Two-dimensional (2D) NMR solves the overlap problem, but at the cost of biasing peak intensities and hence quantitativeness. This is partly due to the uneven coherence transfer between excited/detected ¹H nuclei and the heteronuclei coupled to them (typically ¹³C). In the traditional approach, the transfer occurs via the evolution of a spin system state under the J-coupling Hamiltonian during a delay of a fixed length. The delay length is set on the basis of the predicted average coupling constant in the sample. This leads to disturbances for pairs of nuclei with coupling constants deviating from this average. Here, we present a novel approach based on non-standard processing of the data acquired in experiments, where the coherence transfer delay is co-incremented with non-uniformly sampled evolution time. This method allows us to obtain the optimal transfer for all resonances, which improves quantitativeness. We demonstrate the concept for the coherence transfer and multiplicity-edit delays in a heteronuclear single-quantum correlation experiment (HSQC).

New Software

We are happy to introduce our new software:

TReNDS

TReNDS stands for Time Resolved N–Dimensional Spectroscopy.

The technique of time-resolved non-uniform sampling (TR-NUS) makes it possible to use standard multidimensional pulse sequences for process and reaction monitoring. It preserves the temporal resolution close to that achievable in 1D experiments.
TReNDS (Time-Resolved N-Dimensional Spectroscopy) is a free, user-friendly software kit for acquisition and processing of TR-NUS data. The program works on Bruker, Agilent and Magritek spectrometers, making it possible to carry out up to four experiments with an interleaved TR-NUS. It can be also used on data stations for spectral processing and data visualization.

New Article in Concepts Magn Reson Part A.

Alternative data processing techniques for serial NMR experiments

Alexandra Shchukina, Mateusz Urbańczyk, Paweł Kasprzak, Krzysztof Kazimierczuk

NMR measurements are often performed in a serial manner, that is, the acquisition of an FID signal is repeated under various conditions, either controlled (as temperature or pH changes) or uncontrolled (as reaction progress). The traditional approach to process “serial” data is to perform the Fourier transform of each FID in a series. However, it suffers from several problems, in particular, from the need to sample full Nyquist grid and reach a sufficient signal‐to‐noise ratio in each separate spectrum. The problems become particularly cumbersome in the case of multidimensional signals, where sampling is costly and sensitivity is an issue. Over the years, several methods of alternative, “joint” processing of FID series have been proposed. In this paper, we discuss the principles of some of them: Accordion Spectroscopy, Multidimensional Decomposition, Radon transform, a combination of Compressed Sensing and the Laplace transform. According to our knowledge, this is the first review on serial NMR data processing approaches. The reader is provided with MATLAB scripts allowing to perform simulations and processing using these algorithms.