In-situ speciation and estimation of iron(II) and iron(III) contents in anisotropic polysaccharide-based hydrogel by 1H low-field nuclear magnetic resonance.

This article aims to quantify and differentiate in-situ iron(II) and/or iron(III) in heterogeneous polygalacturonate hydrogels using the 1H-NMR relaxometry technique. This holds significant importance, for example, in addressing iron-deficiency anemia through the oral administration of iron(II) supplements. The NMR dispersion profiles of the gels exhibited markedly distinct relaxation behaviors corresponding to the different iron oxidation states. At 20 MHz, two primary relaxation mechanisms must be considered: relaxation arising from water molecules confined within the polygalacturonate fiber mesh and paramagnetic relaxation due to iron cations. When iron(III) serves as the cross-linking agent, paramagnetic interaction dominates the relaxation, while with iron(II) as the cross-linker, both mechanisms have to be considered. To distinguish labile from structuring iron, we monitored the evolution of iron concentrations within the gels during successive washes using NMR and atomic absorption spectroscopy. Eventually, a gel containing both iron(II) and iron(III) was analyzed, and successful differentiation between the two cations was achieved. NMR relaxometry demonstrates powerful capabilities in terms of in-situ experiments, rapid results, speciation (iron(II)/iron(III)), and quantification (labile/ bridging iron).

Advanced insight on the water dynamics of anisotropic hydrogels by field-cycling nuclear magnetic resonance: Application of 3-Tau model.

Fast field cycling (FFC) nuclear magnetic resonance (NMR) relaxometry is used to investigate an anisotropic polygalacturonate hydrogel formed by the diffusion of calcium ions from an external reservoir (external gelation). Such a hydrogel has a gradient of polymer density accompanied by a gradient of the mesh size of its 3D network. The NMR relaxation process is dominated by the interaction of proton spins between water molecules located at polymer interfaces and in nanoporous spaces. The FFC NMR experiment provides the spin-lattice relaxation rate R1ω as a function of Larmor frequency ω producing dispersion (NMRD) curves that are highly sensitive to the dynamics of the protons at the surfaces. The hydrogel is sliced into three parts and the NMR profile for each hydrogel slice is measured. The NMRD data for each slice is interpreted using the 3-Tau Model with the aid of user-friendly fitting software called 3TM. The key fit parameters include three nano-dynamical time constants and the average "mesh size" which collectively determine the bulk water and water surface layer contribution to the total relaxation rate. The results are consistent with independent studies where comparison is possible.

Slow water dynamics in polygalacturonate hydrogels revealed by NMR relaxometry and molecular dynamics simulation.

Diffusions in gels are of prime importance, but their measurements are mainly focused on the diffusion in the pores or through the mesh of the gels. In this study, we performed a deeper dynamic analysis of the water in close interaction with the fibers structuring two heterogeneous polygalacturonate (polyGalA) hydrogels formed by Ca and Zn ions (crosslinking agents). Nuclear magnetic resonance dispersion (NMRD) profiles recorded in-situ by fast-field cycling relaxometry allow to observe the very slow dynamics of water within the gels. Two distinct interpretations of the NMRD profiles are discussed, the first in regard of rotational and translational dynamics in the fibers and the second with respect to a Levy-walk on the fibers' surface. These discussions are confronted with molecular dynamics simulations on a model Ca-polyGalA fiber.

Quantification of manganous ions in wine by NMR relaxometry.

Proton relaxation in model and real wines is investigated for the first time by fast field cycling NMR relaxometry. The relaxation mechanism unambiguously originates form proton interaction with paramagnetic ions naturally present in wines. Profiles of a white Chardonnay wine from Burgundy, a red Medoc, and model wines are well reproduced by Solomon-Bloembergen-Morgan equations. Relaxation is primarily governed by interactions with Mn2+. A straightforward model-independent quantification of the manganese ion concentration (down to few tens of µg/L) is proposed.

Water-induced local ordering of chitosan polymer chains in thin layer films.

Carbon-13 NMR (CP-MAS and FSLG (1)H-(13)C HETCOR) have been applied to chitosan salt films synthesized in acetic acid and exposed to different relative humidity environments (32% or 75%) at 20°C for 1 month. It gives insight in the relationship between structure and functional properties according to the hydration level of this biomaterial as a film. The acetate ions trapped in the chitosan act as structuring agents between chitosan chains for the low hydration state. But, increasing the moisture content induces spontaneous removal of acetic acid and a subsequent modification in the film structure, with an increase in local ordering. HETCOR experiments also showed a multiplicity of signals for most of the observed carbon atoms and in particular those implied in the glycosidic linkage, which reveals different water-induced conformational states. Changing the water content allows to modify the polymer structure and therefore to modulate the properties such as controlled release of active compounds trapped in chitosan-based coatings, e.g., for medicated dressing or active packaging.

Restricted linear least square treatment processing of heteronuclear spectra of biomolecules using the ANAFOR strategy.

We explore the use of a processing procedure based on restricted least square minimization as a tool for reducing the time versus resolution dilemma often encountered for biomolecular multidimensional spectra. Using a 2D spectrum as a reference, we obtain the necessary input of frequency components and linewidths. Combined even with a limited time evolution in the indirect dimension, the amplitudes of the correlation peaks in all planes of the 3D spectra can be extracted, and can be used to reconstruct the interferograms in the third dimension. Parameters such as number of lines, threshold choice, resolution, lineshape, number of experimental data points and finally signal to noise ratio of the spectrum are examined starting from a triple-resonance HNCA spectrum of ubiquitin.

ANAFOR: application of a restricted linear least squares procedure to NMR data processing.

Experimental data collection time in multidimensional nuclear magnetic resonance experiments can be significantly decreased if the lineshapes of all the components of one of the ID summations of the spectrum are known. When this condition is fulfilled, a simple linear least squares fit of the time-domain signal taking the lineshapes into account not only allows saving time in data collection, but also improves sensitivity and resolution. The reliability of the proposed procedure is carefully addressed in the particular case of Lorentzian lines. This strategy applied to a 3Q-REDOR experiment reduced experimental time by a factor of 6.