Optimized decoupling schemes in ultrafast HSQC experiments.

Ultrafast (UF) 2D NMR, which enables the acquisition of 2D spectra within a single scan, is nowadays used in a large array of applications. However, the use of UF-HSQC experiments is still limited by the need to compromise between spectral widths and resolution. Interleaved acquisitions can overcome this limitation, albeit at the cost of strong artifacts. We show that the occurrence of these artifacts is mainly related to the discontinuous decoupling scheme which is generally used in UF-HSQC. In this paper, four continuous decoupling schemes using adiabatic pulses are optimized for this kind of experiments, giving access to full-range UF-HSQC spectra.

Ultrafast acquisition of 1H-1H dipolar correlation experiments in spinning elastomers.

We show that two widely used 2D solid-state NMR (ssNMR) pulse sequences can be implemented in an ultrafast (UF) manner, and yield 2D spectra of elastomers in a single scan, under magic-angle spinning. UF 2D ssNMR provides an acceleration of one to several orders of magnitude for classic experiments.

Precise and rapid isotopomic analysis by (1)H-(13)C 2D NMR: Application to triacylglycerol matrices.

An optimized HSQC sequence was tested and applied to triacylglycerol matrices to determine their isotopic and metabolomic profiles. Spectral aliasing and non-uniform sampling approaches were used to decrease the experimental time and to improve the resolution, respectively. An excellent long-term repeatability of signal integrals was achieved enabling to perform isotopic measurements. Thirty-two commercial vegetable oils were analyzed by this methodology. The results show that this method can be used to classify oil samples according to their geographical and botanical origins.

Ultrafast double-quantum NMR spectroscopy with optimized sensitivity for the analysis of mixtures.

Ultrafast (UF) 2D NMR enables the acquisition of 2D spectra within a single-scan. This methodology has become a powerful analytical tool, used in a large array of applications. However, UF NMR spectroscopy still suffers from the need to compromise between sensitivity, spectral width and resolution. With the commonly used UF-COSY pulse sequence, resolution issues are compounded by the presence of strong auto-correlation signals, particularly in the case of samples with high dynamic ranges. The recently proposed concept of UF Double Quantum Spectroscopy (DQS) allows a better peak separation as it provides a lower spectral peak density. This paper presents the detailed investigation of this new NMR tool in an analytical chemistry context. Theoretical calculations and numerical simulations are used to characterize the modulation of peak intensities as a function of pulse-sequence parameters, and thus enable a significant enhancement of the sensitivity. The analytical comparison of UF-COSY and UF-DQS shows similar performances, however the ultrafast implementation of the DQS approach is found to have some sensitivity advantages over its conventional counterpart. The analytical performance of the pulse sequence is illustrated by the quantification of taurine in complex mixtures (homemade and commercial energy drinks). The results demonstrate the high potential of this experiment, which forms a valuable alternative to UF-COSY spectra when the latter are characterized by strong overlaps and high dynamic ranges.

Understanding J-Modulation during Spatial Encoding for Sensitivity-Optimized Ultrafast NMR Spectroscopy.

Ultrafast (UF) NMR spectroscopy is an approach that yields 2D spectra in a single scan. This methodology has become a powerful analytical tool that is used in a large array of applications. However, UF NMR spectroscopy still suffers from an intrinsic low sensitivity, and from the need to compromise between sensitivity, spectral width, and resolution. In particular, the modulation of signal intensities by the spin-spin J-coupling interaction (J-modulation) impacts significantly on the intensities of the spectral peaks. This effect can lead to large sensitivity losses and even to missing spectral peaks, depending on the nature of the spin system. Herein, a general simulation package (Spinach) is used to describe J-modulation effects in UF experiments. The results from simulations match with experimental data and the results of product operator calculations. Several methods are proposed to optimize the sensitivity in UF COSY spectra. The potential and drawbacks of the different strategies are also discussed. These approaches provide a way to adjust the sensitivity of UF experiments for a large range of applications.

Processing strategies to obtain clean interleaved ultrafast 2D NMR spectra.

Ultrafast (UF) 2D NMR enables the acquisition of 2D spectra in a single-scan. In spite of its promising potential, the accessible spectral width is highly limited by the maximum gradient amplitude, which limits the general applicability of the method. A number of solutions have been recently described to deal with this limitation, among which stands the possibility to record several interleaved scans. However, this alternative acquisition scheme leads to numerous ghost peaks characteristic of interleaved acquisitions. These artefacts highly affect the readability of 2D spectra for structural elucidation, as well as their quantitative performance. Here, we propose several pre-FT or post-FT processing corrections to clean artefacts from interleaved ultrafast NMR spectra. Their performances are compared, and their potentialities are illustrated in a small organic molecule context. Post-FT processing corrections such as ArSub (Artefact Subtraction) or symmetrisation appear to be the most efficient ones in terms of artefact removal. While not purely single-scan, these strategies open new perspectives towards the routine use of UF 2D NMR for structural or quantitative analysis.

Limitation of diffusion effects in ultrafast 2D nuclear magnetic resonance by encapsulation of analytes in phospholipidic vesicles.

Increased sensitivity: A new sample-preparation procedure is described to limit molecular diffusion effects in NMR experiments. It is based on analyte encapsulation in liposomes and is particularly useful for ultrafast multidimensional NMR experiments.