Abstracted/indexed

The cosmetic industry integrates in its products active ingredients of vegetal origin. For this purpose, plant extracts are prepared and their content must be characterized to check their conformity with safety regulations. Many plant extracts contain a high proportion of high-boiling-point solvents that may conflict with analytical protocols. Extract analysis by fractionation and subsequent ¹³C NMR analysis required a new solvent signal suppression technique to provide better analytical data.

Quantitative analysis of mixtures is a challenge in applications ranging from foods to industrial chemistry. Nuclear magnetic resonance (NMR) is increasingly used for analysis; however, overlapping peaks in the spectrum pose a major difficulty, especially for the new generation of benchtop NMR instruments. We propose a fast and simple model-based approach to enhance the accuracy of quantification. We demonstrate it on industrially relevant test samples where the accuracy is increased by 40 %.

The combination of magnetic resonance with laser spectroscopy provides some interesting options for increasing the sensitivity and information content of magnetic resonance by many orders of magnitude. This review covers the basic physics behind the relevant processes, such as angular momentum conservation during absorption and emission.

We have assembled a few off-the-shelf electronic chips and a popular Arduino Uno microcomputer board in an automatic system that performs so-called tuning and matching of an arbitrary NMR probe head at very low cost. This removes the tedium of doing the job by hand, the bane of many NMR analysts. It also brings accuracy and repeatability into the process, which is so necessary for high throughput analysis or when working with low-field permanent magnesystems with excessive magnetic field drift.

We have recently demonstrated the capability to rapidly spin spherical rotors inclined precisely at the magic angle (54.74°) with respect to the external magnetic field used for nuclear magnetic resonance (NMR) experiments. We show that it is possible to spin a spherical rotor without using turbine grooves and that these rotors are extremely stable because of the inherent spherical-ring geometry. These results portend the facile implementation of spherical rotors for solid-state NMR experiments.

A dipolar cross-polarization (dCP) sequence employing simple radiofrequency pulse shapes with reduced power requirements is demonstrated to transfer proton polarization to insensitive heteronuclei.

Measuring distances between unpaired electron spins is an important application of electron paramagnetic resonance. The longest distance that is accessible is limited by the phase memory time of the electron spins. Here we show that strong continuous microwave irradiation can significantly slow down relaxation. Additionally, we introduce a phase-modulation scheme that allows measurement of the distance during the irradiation. Our approach could thus significantly extend the accessible distances.

The determination of distance distributions in the nanometre range is an important application of pulsed electron paramagnetic resonance spectroscopy. However, low sensitivity is often a major challenge. In this paper, we compare several broadband-shaped pulses and compare their performance to classical rectangular pulses in order to increase the sensitivity of double electron–electron resonance to a commercial setup. We show that improvements in sensitivity of up to 86 % are possible.

DNP is a method used to enhance NMR signals by transferring polarization from radicals to nuclear spins using microwave irradiation. The EPR spectrum of the radical during the irradiation is determined by a process called spectral diffusion and affects the DNP efficiency. This process can be measured by electron–electron double resonance. We explored experimentally and theoretically the contribution of the hyperfine coupling of the ¹⁴N nuclei in the nitroxide radical to the spectral diffusion.