Magnetic Resonance in Chemistry最新文献

Understanding how soil formation processes influence the microstructure and the dynamic behavior of clay-rich materials is essential for both pedological interpretation and technological assessment. In this study, we applied fast field cycling nuclear magnetic resonance (FFC NMR) relaxometry to investigate the microstructural heterogeneity of Moroccan clays developed under diverse pedogenetic conditions. Nuclear magnetic relaxation dispersion (NMRD) profiles were processed using a model-free inversion algorithm to retrieve the distribution of correlation times. The latter provides a phenomenological mapping of proton–surface interactions across distinct dynamic domains. Complementary indicators of micro-scale hydrological connectivity were, then, computed from the T₁ distributions, integrating both structural (SCI) and functional (FCI) heterogeneity. While the former indicates the breadth of molecular environments experienced by water across the system, the latter captures the dynamic contrast between fast- and slow-relaxing populations associated with variations in surface accessibility and magnetic heterogeneity. The results showed that the clay sample from Khemisset exhibited the greatest relaxation heterogeneity, consistent with advanced pedogenetic reorganization related to redox-driven redistribution of paramagnetic metals. In contrast, the clay samples from Berrechid and Tiflet displayed a more ordered architecture and lower magnetic heterogeneity, reflecting earlier-stage pedogenetic development. This study demonstrated that FFC NMR relaxometry reveals the microstructural memory encoded into water dynamics, offering a powerful tool to infer the pedogenetic pathways leading to soil formation. Beyond its relevance for pedological studies, the method also offers valuable insights into the technological behavior of clays, supporting the selection of raw materials for industrial purposes based on their microstructural properties.

Humic acids (HAs), key components of soil organic matter, undergo significant conformational rearrangements upon complexation with metal ions, yet the molecular-scale dynamics of these interactions remain poorly understood. In this study, solid-state 13C CPMAS NMR spectroscopy was employed to probe Fe (III)–induced structural changes in a soil-derived HA, focusing on cross-polarization time constants (T_CH) and proton rotating-frame relaxation times (T_₁ρ[H]) as indicators of spatial and dynamic reorganization. Exponential decay analysis of T_CH versus Fe/C ratios revealed distinct binding hierarchies: carboxyl groups (187–163 ppm) exhibited the strongest response (decay constant k_TCH = 3.5), reflecting Fe (III)–driven local compaction and rigidification, whereas aromatic (163–92 ppm; k_TCH = 2.5) and oxygenated aliphatic (92–46 ppm; k_TCH = 1.5) domains showed intermediate sensitivity. Aliphatic carbons (46–0 ppm; k_TCH ≈ 0.05) remained inert, confirming their exclusion from metal coordination. Complementary T_1ρ(H) data highlighted the role of Fe (III) in restricting molecular mobility, particularly in carboxyl and aromatic regions.

These findings support a model in which Fe (III) acts as a supramolecular cross-linker, selectively rigidifying HA domains through primary carboxylate binding and secondary aromatic interactions, whereas aliphatic regions retain dynamic freedom. The study demonstrates that paramagnetic Fe (III) not only perturbs NMR detectability but also serves as a structural probe, with T_CH and T_1ρ(H) providing quantitative metrics for metal-induced reorganization. This work advances the mechanistic understanding of organo–mineral interactions in soils and highlights NMR relaxation parameters as powerful tools for characterizing environmental organic matter.

We present a compact, 3D-printed device designed to facilitate the efficient packing of semisolid or highly viscous samples into 3.2-mm rotors compatible with cryogenic solid-state NMR probes. The tool enables sample loading by centrifugation under standard laboratory conditions, significantly improving packing reproducibility and minimizing sample loss. In contrast to previously reported designs for conventional rotors, this device is optimized for the expanded volume and geometrical constraints of 90-μL rotors used in the Bruker CPMAS cryoprobe. A complementary unloading tool is also described to recover samples or enable rotor reuse. Both tools are compatible with standard benchtop centrifuges and are fully customizable. Their implementation improves sample handling for biological or material samples with limited availability or challenging rheological properties. Open-access 3D design files are provided to support broad adoption and future adaptation to other rotor sizes or sample formats. These devices represent a scalable solution for routine use and may inspire further development of customized tools for challenging sample types.

Fast iterative filtering (FIF) is a recently introduced signal decomposition technique related to empirical mode decomposition (EMD), which has been developed for the analysis of non-stationary signals. When applied to the analysis of NMR data, FIF effectively partitions broad and narrow features by decomposing signals into intrinsic mode functions. In this work, we prove that FIF excels at separating baseline components from peaks, even in heavily distorted spectra. This capability is precious for processing spectra of paramagnetic compounds.

The use of lyotropic, chiral bimesophasic systems and spatially resolved ²H nD NMR spectroscopy has recently been pioneered (J. Phys. Chem. Lett. 2024) as an original tool capable of providing two independent sets of anisotropic spectral data with a single NMR sample. In this work, we explore the analytical potential of spatially localized ¹³C and ¹³C-{¹H} 1D and 2D NMR experiments (CLIP-HSQC, T_CH-resolved) combined with bimesophasic samples composed of polypeptide and polyacetylene chiral polymers (PBLG and L-MSP). The effectiveness of this original anisotropic approach is being explored in the context of the enantiomeric analysis of chiral molecules such as ibuprofen, as well as the configurational and 3D structural analysis of multi-stereocenter chiral compounds (case of (+)-IPC).