H NMR Cryoporometry Study of the Melting Behavior of Water in White Cement

The pore size of white cement samples is studied by the melting behaviour of water confined in it, using 1 H NMR cryopormetry. The influence of the preparing method and antifreeze admixture on the pore size and distribution in cement samples is investigated at 283 K. The addition of an antifreeze admixture [containing 1% Sika Rapid 2 by weight of the dry cement] influences the porosity. In wet prepared samples we observed a significant increase in the quantity of mesopores between 0.8 and 5 nm and a smaller increase of mesopores between 5 and 10 nm, when compared to cement without admixture. The compressive strength is related to the porosity of the cement. Therefore the cement with Sika Rapid 2, wet prepared at 278 K shows a higher strength than all other measured samples

NMR relaxometry study of gelatin based low-calorie soft candies

Soft candies are popular confectionery products. The most significant concern on the consumption of these products is the high amount of sugar and thus the high calories. The use of low-calorie sweeteners is a desirable trend in confectionery research. In this study, gelatin-based soft candies were formulated by using different sweeteners and their characterisation was performed using high and low field nuclear magnetic resonance (NMR) relaxation experiments. To complement the information obtained by NMR experiments, moisture content, water activity, texture analysis and differential scanning calorimeter experiments were also conducted. T-1 and T-2 relaxation times were measured at both low and high fields and also temperature-dependent measurements were conducted at the high field system. Candies were formulated by substitution of sucrose with maltitol, isomalt and stevia at 30%, 50% and 70% ratios. Significant difference was observed on relaxation times. T-1 values were best described by a mono-exponential model, whereas for T-2 relaxation times a bi-exponential model gave better results at both fields

Dynamics and Proton Transport in Imidazole-Doped Nanocrystalline Cellulose Revealed by High-Resolution Solid-State Nuclear Magnetic Resonance Spectroscopy

Imidazole-doped nanocrystalline cellulose (CNC-Im) is a new proton conductor based on imidazole-functionalized nanocrystalline cellulose with a conductivity of approximately 10⁻¹ S/m at 160 °C. Its conductivity is possible due to the transport of protons from imidazoles. The dynamics of local processes were studied by ¹⁵N and ¹³C nuclear magnetic resonance (NMR) spectroscopy under the conditions of ¹H⁻¹⁵N and ¹H⁻¹³C cross-polarization (CP) and magic angle spinning (MAS) and by heteronuclear correlation (HETCOR) spectroscopy. The ¹⁵N and ¹³C NMR spectra showed the coexistence of two fractions of imidazole molecules: slowly reorienting and exchanging protons and fast reorienting and fast exchanging protons. Analysis based on the two-phase model enabled the determination of the energy distribution of imidazole tautomerization, whose maximum value is 38 kJ/mol. The HETCOR experiment allowed determination of the binding of nitrogen protons from imidazoles to cellulose hydroxyl groups and possibly residual water. NMR studies conducted on the ¹³C isotope confirmed the reorientation of imidazoles. The proton transport in CNC-Im was shown to consist in the exchange of protons between imidazoles via the OH groups of cellulose and residual water conditioned by the reorientation of imidazole rings. The described proton transport leads to the observed conductivity in CNC-Im, assuming the dissociation of imidazole into anion and cation additionally

Quantification of manganous ions in wine by NMR relaxometry

International audienceProton 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 mu g/L) is proposed

The Solvent–Gelator Interaction as the Origin of Different Diffusivity Behavior of Diols in Gels Formed with Sugar-Based Low-Molecular-Mass Gelator

Organogels are soft materials consisting of low-molecular-mass gelators (LMOGs) self-assembled through noncovalent interactions into 3D structures, in which free spaces are filled by organic solvents. 4,6,4′,6′-<i>O</i>-terephthylidene-bis­(methyl-α-d-glucopyranoside) (<b>1</b>) is found to be a new LMOG. It gelatinizes only a limited number of solvents. Here, the gels of <b>1</b> with ethylene glycol (EG) and 1,3-propanediol (PG) are investigated with FT-IR, Raman, and UV–vis spectroscopies, the NMR relaxometry and diffusometry methods, and microscopic observation. The chemical structures of both solvents are closely related, but the variety of physical characteristics of the gels is large. The <b>1</b>/PG gels are thermally more stable compared to <b>1</b>/EG gels. The types of aggregates are most likely the H- and J-type in <b>1</b>/EG gels and the J-type in <b>1</b>/PG gels. Different microstructures are observed: bundles of crossing fibers for <b>1</b>/EG and a honeycomb-like matrix for <b>1</b>/PG gels. The diffusivity of the EG solvent in gels with <b>1</b> behaves as expected, decreasing with increasing gelator concentration, whereas the opposite behavior is observed for the PG solvent. This is a most fascinating result. To explain the diffusion enhancement, we suggest that a dynamic hydrogen bonding network of PG solvent in gel matrixes is disrupted due to solvent–gelator interaction. The direct proof of this interaction is given by the observed low frequency dispersion of the spin–lattice relaxation time of solvents in the gel matrixes