Pulse dipolar spectroscopy (PDS) in Electron Paramagnetic Resonance (EPR) is the method of choice for determining the distance distribution function for mono-, bi- or multi- spin-labeled macromolecules and nanostructures. PDS acquisition schemes conventionally use uniform sampling of the dipolar trace, but non-uniform sampling (NUS) schemes can decrease the total measurement time or increase the accuracy of the resulting distance distributions. NUS requires optimization of the data acquisition scheme, as well as changes in data processing algorithms to accommodate the non-uniformly sampled data. We investigate in silico the applicability of the NUS approach in PDS, considering its effect on random, truncation and sampling noise in the experimental data. Each type of noise in the time-domain data propagates differently and non-uniformly into the distance spectrum as errors in the distance distribution. NUS schemes seem to be a valid approach for increasing sensitivity and/or throughput in PDS by decreasing and redistributing noise in the distance spectrum so that it has less impact on the distance spectrum.

While dietary fibres have a reputation of a healthy food component, the interaction between nutrients and neutral fibers is non-covalent, and its characterization is challenging for most analytical techniques. Here, on the example of barley β-glucan (BBG) and paramagnetic Cu(II) ions we demonstrate the performance of different Electron Paramagnetic Resonance (EPR) methods in the fibre studies. EPR techniques were tested on two spin probe systems with different affinity in the interaction with dietary fibres – Cu(OAc)₂ salt, which weakly dissociates under physiological conditions and CuSO₄ salt, which easily dissociates, so that in the latter case Cu(II) can be considered as a ‘free’ ion, only chelated by water molecules. The Cu(II)-BBG interaction was determined by pulse EPR relaxation measurements, but this interaction appears not strong enough for continuous wave EPR detection. The capability of the fibres for Cu(II) absorption was successfully analyzed by comparison of the results from the pulse dipolar spectroscopy with numerical simulations. The local distribution of sugar hydrogen atoms around the Cu(II) ion has been determined by electron spin echo envelope modulation (ESEEM) and electron-nuclei double resonance (ENDOR) techniques.

The interactions between dietary fibers (DFs) and small molecules are of great interest to food chemistry and nutrition science. However, the corresponding interaction mechanisms and structural rearrangements of DFs at the molecular level are still opaque due to the usually weak binding and the lack of appropriate techniques to determine details of conformational distributions in such weakly organized systems. By combining our previ-ously established methodology on stochastic spin-labelling of DFs with the appropriately revised set of pulse electron paramagnetic resonance techniques, we present here a toolkit to determine the interactions between DFs and small molecules, using barley beta-glucan as an example for neutral DF and a selection of food dye molecules as examples for small molecules. The proposed here methodology allowed us to observe subtle conformational changes of beta-glucan by detecting multiple details of the local environment of the spin labels. Substantial vari-ations of binding propensities were detected for different food dyes.