Spatially encoded pure-shift diffusion-ordered NMR spectroscopy yielded by chirp excitation.

Spatially-encoded diffusion-ordered NMR spectroscopy (SPEN-DOSY) has emerged as a new time-efficient tool for the analysis of mixtures of small molecules in solution. Time efficiency is achieved using the concept of spatial parallelization of the effective gradient area, instead of the sequential incrementation used in conventional diffusion experiments. The data acquired with such sequences are then usually processed to extract diffusion coefficients, but cases when peak overlap in the H spectrum are difficult to address.

Ultrafast 2D H-H NMR spectroscopy of DNP-hyperpolarised substrates for the analysis of mixtures.

We show that TOCSY and multiple-quantum (MQ) 2D NMR spectra can be obtained for mixtures of substrates hyperpolarised by dissolution dynamic nuclear polarisation (D-DNP). This is achieved by combining optimised transfer settings for D-DNP, with ultrafast 2D NMR experiments based on spatiotemporal encoding. TOCSY and MQ experiments are particularly well suited for mixture analysis, and this approach opens the way to significant sensitivity gains for analytical applications of NMR, such as authentication and metabolomics.

Optimisation of spatially-encoded diffusion-ordered NMR spectroscopy for the analysis of mixtures.

Diffusion-ordered NMR spectroscopy (DOSY NMR) is a widely used method for the analysis of mixtures. It can be used to separate the spectra of a mixture's components and to analyse interactions. The classic implementation of DOSY experiments, based on an incrementation of the diffusion-encoding gradient area, requires several minutes or more to collect a 2D data set.

δ-Valerolactamic Quaternary Amino Acid Derivatives: Enantiodivergent Synthesis and Evidence for Stereodifferentiated β-Turn-Inducing Properties.

Enantiopure () and () cyclic α,α-disubstituted amino acid derivatives displaying a δ-valerolactam side chain were prepared from a common isoxazolidine precursor. The ()-configured δ-valerolactam was converted into diastereoisomeric pseudopeptides to investigate its ability to induce secondary structures in peptidomimetics. Conformational studies of these pseudopeptides were carried out in the solid state (X-ray diffraction), in solution (NMR analyses), and (computer-aided conformational analysis), which demonstrated that such quaternary amino acids induce β-turn conformations stable enough to be retained in polar media (DMSO).

Ultrafast diffusion-based unmixing of H NMR spectra.

We show that the NMR spectra of components in a mixture can be separated using 2D data acquired in less than one second, and an algorithm that is executed in just a few seconds. This NMR unmixing method is based on spatial encoding of the translational diffusion coefficients of the mixture's components, with multivariate processing of the data. This requires a new frequency swept pulse, which is designed and implemented to obtain quadratic spacing of the spatially parallelised gradient dimension.

Online reaction monitoring by single-scan 2D NMR under flow conditions.

Nuclear magnetic resonance (NMR) spectroscopy is a powerful tool for reaction monitoring. Several devices have been recently developed for online monitoring, using flow NMR, of batch reactions carried out under realistic experimental conditions in terms of, e.g.

Acceleration of 3D DOSY NMR by Spatial Encoding of the Chemical Shift.

Diffusion-ordered NMR spectroscopy (DOSY) is a powerful method for the analysis of solution mixtures. With 3D DOSY, the 2D NMR spectra of a mixture's components can be separated according to the translational diffusion coefficient of each component. The acquisition of 3D DOSY data is, however, very time-consuming because of the need to consecutively acquire scans for both the diffusion and the indirect spectral dimensions.

Ultrafast Maximum-Quantum NMR Spectroscopy for the Analysis of Aromatic Mixtures.

Maximum-quantum (MaxQ) NMR experiments have been introduced to overcome issues related to peak overlap and high spectral density in the NMR spectra of aromatic mixtures. In MaxQ NMR, spin systems are separated on the basis of the highest-quantum coherence that they can form. MaxQ experiments are however time consuming and methods have been introduced to accelerate them.