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12 pages, 2065 KiB

Open AccessArticle

Spin-Space-Encoding Magnetic Resonance Imaging: A New Application for Rapid and Sensitive Monitoring of Dynamic Swelling of Confined Hydrogels

by Rui Wang, Jiaxiang Xin, Zhengxiao Ji, Mengni Zhu, Yihua Yu and Min Xu

Molecules 2023, 28(7), 3116; https://doi.org/10.3390/molecules28073116 - 30 Mar 2023

Cited by 2 | Viewed by 1578

Abstract

An NMR method based on the gradient-based broadening fingerprint using line shape enhancement (PROFILE) is put forward to precisely and sensitively study hydrogel swelling under restricted conditions. This approach achieves a match between the resonance frequency and spatial position of the sample. A [...] Read more.

An NMR method based on the gradient-based broadening fingerprint using line shape enhancement (PROFILE) is put forward to precisely and sensitively study hydrogel swelling under restricted conditions. This approach achieves a match between the resonance frequency and spatial position of the sample. A three-component hydrogel with salt ions was designed and synthesized to show the monitoring more clearly. The relationship between the hydrogel swelling and the frequency signal is revealed through the one-dimensional imaging. This method enables real-time monitoring and avoids changing the swelling environment of the hydrogel during contact. The accuracy of this method may reach the micron order. This finding provides an approach to the rapid and non-destructive detection of swelling, especially one-dimensional swelling, and may show the material exchange between the hydrogel and swelling medium. Full article

(This article belongs to the Special Issue Advances in NMR and MRI of Materials)

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12 pages, 2914 KiB

Open AccessArticle

Monitoring the Effect of Calcium Nitrate on the Induction Period of Cement Hydration via Low-Field NMR Relaxometry

by Mihai M. Rusu, David Faux and Ioan Ardelean

Molecules 2023, 28(2), 476; https://doi.org/10.3390/molecules28020476 - 4 Jan 2023

Cited by 2 | Viewed by 1589

Abstract

The hydration process of Portland cement is still not completely understood. For instance, it is not clear what produces the induction period, which follows the initial period of fast reaction, and is characterized by a reduced reactivity. To contribute to such understanding, we [...] Read more.

The hydration process of Portland cement is still not completely understood. For instance, it is not clear what produces the induction period, which follows the initial period of fast reaction, and is characterized by a reduced reactivity. To contribute to such understanding, we compare here the hydration process of two cement samples, the simple cement paste and the cement paste containing calcium nitrate as an accelerator. The hydration of these samples is monitored during the induction period using two different low-field nuclear magnetic resonance (NMR) relaxometry techniques. The transverse relaxation measurements of the ¹H nuclei at 20 MHz resonance frequency show that the capillary pore water is not consumed during the induction period and that this stage is shortened in the presence of calcium nitrate. The longitudinal relaxation measurements, performed at variable Larmor frequency of the ¹H nuclei, reveal a continuous increase in the surface-to-volume ratio of the capillary pores, even during the induction period, and this increase is faster in the presence of calcium nitrate. The desorption time of water molecules from the surface was also evaluated, and it increases in the presence of calcium nitrate. Full article

(This article belongs to the Special Issue Advances in NMR and MRI of Materials)

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18 pages, 2316 KiB

Open AccessArticle

Reactivity of Waterlogged Archeological Elm Wood with Organosilicon Compounds Applied as Wood Consolidants: 2D ¹H–¹³C Solution-State NMR Studies

by Magdalena Broda and Daniel J. Yelle

Molecules 2022, 27(11), 3407; https://doi.org/10.3390/molecules27113407 - 25 May 2022

Cited by 10 | Viewed by 2379

Abstract

Some organosilicon compounds, including alkoxysilanes and siloxanes, proved effective in stabilizing the dimensions of waterlogged archaeological wood during drying, which is essential in the conservation process of ancient artifacts. However, it was difficult to determine a strong correlation between the wood stabilizing effect [...] Read more.

Some organosilicon compounds, including alkoxysilanes and siloxanes, proved effective in stabilizing the dimensions of waterlogged archaeological wood during drying, which is essential in the conservation process of ancient artifacts. However, it was difficult to determine a strong correlation between the wood stabilizing effect and the properties of organosilicon compounds, such as molecular weight and size, weight percent gain, and the presence of other potentially reactive groups. Therefore, to better understand the mechanism behind the stabilization effectiveness, the reactivity of organosilicons with wood polymers was studied using a 2D ¹H–¹³C solution-state NMR technique. The results showed an extensive modification of lignin through its demethoxylation and decarbonylation and also the absence of the native cellulose anomeric peak in siloxane-treated wood. The most substantial reactivity between wood polymers and organosilicon was observed with the (3-mercaptopropyl)trimethoxysilane treatment, showing complete removal of lignin side chains, the lowest syringyl/guaiacyl ratio, depolymerization of cellulose and xylan, and reactivity with the C6 primary hydroxyls in cellulose. This may explain the outstanding stabilizing effectiveness of this silane and supports the conclusion that extensive chemical interactions are essential in this process. It also indicates the vital role of a mercapto group in wood stabilization by organosilicons. This 2D NMR technique sheds new light on the chemical mechanisms involved in organosilicon consolidation of wood and reveals what chemical characteristics are essential in developing future conservation treatments. Full article

(This article belongs to the Special Issue Advances in NMR and MRI of Materials)

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12 pages, 4188 KiB

Open AccessArticle

Identification and Quantification by NMR Spectroscopy of the 22R and 22S Epimers in Budesonide Pharmaceutical Forms

by Natalia E. Kuz’mina, Sergey V. Moiseev, Elena Y. Severinova, Evgenii A. Stepanov and Natalia D. Bunyatyan

Molecules 2022, 27(7), 2262; https://doi.org/10.3390/molecules27072262 - 31 Mar 2022

Cited by 4 | Viewed by 2328

Abstract

The authors developed four variants of the qNMR technique (¹H or ¹³C nucleus, DMSO-d6 or CDCl₃ solvent) for identification and quantification by NMR of 22R and 22S epimers in budesonide active pharmaceutical ingredient and budesonide drugs (sprays, [...] Read more.

The authors developed four variants of the qNMR technique (¹H or ¹³C nucleus, DMSO-d6 or CDCl₃ solvent) for identification and quantification by NMR of 22R and 22S epimers in budesonide active pharmaceutical ingredient and budesonide drugs (sprays, capsules, tablets). The choice of the qNMR technique version depends on the drug excipients. The correlation of ¹H and ¹³C spectra signals to molecules of different budesonide epimers was carried out on the basis of a comprehensive analysis of experimental spectral NMR data (¹H-¹H gCOSY, ¹H-¹³C gHSQC, ¹H-¹³C gHMBC, ¹H-¹H ROESY). This technique makes it possible to identify budesonide epimers and determine their weight ratio directly, without constructing a calibration curve and using any standards. The results of measuring the 22S epimer content by qNMR are comparable with the results of measurements using the reference HPLC method. Full article

(This article belongs to the Special Issue Advances in NMR and MRI of Materials)

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14 pages, 2546 KiB

Open AccessArticle

Real-Time Monitoring Polymerization Reactions Using Dipolar Echoes in ¹H Time Domain NMR at a Low Magnetic Field

by Rodrigo Henrique dos Santos Garcia, Jefferson Gonçalves Filgueiras, Luiz Alberto Colnago and Eduardo Ribeiro de Azevedo

Molecules 2022, 27(2), 566; https://doi.org/10.3390/molecules27020566 - 17 Jan 2022

Cited by 3 | Viewed by 2468

Abstract

¹H time domain nuclear magnetic resonance (¹H TD-NMR) at a low magnetic field becomes a powerful technique for the structure and dynamics characterization of soft organic materials. This relies mostly on the method sensitivity to the ¹H-¹H [...] Read more.

¹H time domain nuclear magnetic resonance (¹H TD-NMR) at a low magnetic field becomes a powerful technique for the structure and dynamics characterization of soft organic materials. This relies mostly on the method sensitivity to the ¹H-¹H magnetic dipolar couplings, which depend on the molecular orientation with respect to the applied magnetic field. On the other hand, the good sensitivity of the ¹H detection makes it possible to monitor real time processes that modify the dipolar coupling as a result of changes in the molecular mobility. In this regard, the so-called dipolar echoes technique can increase the sensitivity and accuracy of the real-time monitoring. In this article we evaluate the performance of commonly used ¹H TD-NMR dipolar echo methods for probing polymerization reactions. As a proof of principle, we monitor the cure of a commercial epoxy resin, using techniques such as mixed-Magic Sandwich Echo (MSE), Rhim Kessemeier—Radiofrequency Optimized Solid Echo (RK-ROSE) and Dipolar Filtered Magic Sandwich Echo (DF-MSE). Applying a reaction kinetic model that supposes simultaneous autocatalytic and noncatalytic reaction pathways, we show the analysis to obtain the rate and activation energy for the epoxy curing reaction using the NMR data. The results obtained using the different NMR methods are in good agreement among them and also results reported in the literature for similar samples. This demonstrates that any of these dipolar echo pulse sequences can be efficiently used for monitoring and characterizing this type of reaction. Nonetheless, the DF-MSE method showed intrinsic advantages, such as easier data handling and processing, and seems to be the method of choice for monitoring this type of reaction. In general, the procedure is suitable for characterizing reactions involving the formation of solid products from liquid reagents, with some adaptations concerning the reaction model. Full article

(This article belongs to the Special Issue Advances in NMR and MRI of Materials)

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14 pages, 2427 KiB

Open AccessArticle

NMR Relaxivities of Paramagnetic Lanthanide-Containing Polyoxometalates

by Aiswarya Chalikunnath Venu, Rami Nasser Din, Thomas Rudszuck, Pierre Picchetti, Papri Chakraborty, Annie K. Powell, Steffen Krämer, Gisela Guthausen and Masooma Ibrahim

Molecules 2021, 26(24), 7481; https://doi.org/10.3390/molecules26247481 - 10 Dec 2021

Cited by 9 | Viewed by 3083

Abstract

The current trend for ultra-high-field magnetic resonance imaging (MRI) technologies opens up new routes in clinical diagnostic imaging as well as in material imaging applications. MRI selectivity is further improved by using contrast agents (CAs), which enhance the image contrast and improve specificity [...] Read more.

The current trend for ultra-high-field magnetic resonance imaging (MRI) technologies opens up new routes in clinical diagnostic imaging as well as in material imaging applications. MRI selectivity is further improved by using contrast agents (CAs), which enhance the image contrast and improve specificity by the paramagnetic relaxation enhancement (PRE) mechanism. Generally, the efficacy of a CA at a given magnetic field is measured by its longitudinal and transverse relaxivities r₁ and r₂, i.e., the longitudinal and transverse relaxation rates T₁⁻¹ and T₂⁻¹ normalized to CA concentration. However, even though basic NMR sensitivity and resolution become better in stronger fields, r₁ of classic CA generally decreases, which often causes a reduction of the image contrast. In this regard, there is a growing interest in the development of new contrast agents that would be suitable to work at higher magnetic fields. One of the strategies to increase imaging contrast at high magnetic field is to inspect other paramagnetic ions than the commonly used Gd(III)-based CAs. For lanthanides, the magnetic moment can be higher than that of the isotropic Gd(III) ion. In addition, the symmetry of electronic ground state influences the PRE properties of a compound apart from diverse correlation times. In this work, PRE of water ¹H has been investigated over a wide range of magnetic fields for aqueous solutions of the lanthanide containing polyoxometalates [Dy^III(H₂O)₄GeW₁₁O₃₉]^5– (Dy-W₁₁), [Er^III(H₂O)₃GeW₁₁O₃₉]^5– (Er-W₁₁) and [{Er^III(H₂O)(CH₃COO)(P₂W₁₇O₆₁)}₂]¹⁶⁻ (Er₂-W₃₄) over a wide range of frequencies from 20 MHz to 1.4 GHz. Their relaxivities r₁ and r₂ increase with increasing applied fields. These results indicate that the three chosen POM systems are potential candidates for contrast agents, especially at high magnetic fields. Full article

(This article belongs to the Special Issue Advances in NMR and MRI of Materials)

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18 pages, 1940 KiB

Open AccessArticle

MAS-NMR of [Pyr₁₃][Tf₂N] and [Pyr₁₆][Tf₂N] Ionic Liquids Confined to Carbon Black: Insights and Pitfalls

by Steffen Merz, Jie Wang, Petrik Galvosas and Josef Granwehr

Molecules 2021, 26(21), 6690; https://doi.org/10.3390/molecules26216690 - 5 Nov 2021

Cited by 2 | Viewed by 2286

Abstract

Electrolytes based on ionic liquids (IL) are promising candidates to replace traditional liquid electrolytes in electrochemical systems, particularly in combination with carbon-based porous electrodes. Insight into the dynamics of such systems is imperative for tailoring electrochemical performance. In this work, 1-Methyl-1-propylpyrrolidinium bis(trifluoromethylsulfonyl)imide and [...] Read more.

Electrolytes based on ionic liquids (IL) are promising candidates to replace traditional liquid electrolytes in electrochemical systems, particularly in combination with carbon-based porous electrodes. Insight into the dynamics of such systems is imperative for tailoring electrochemical performance. In this work, 1-Methyl-1-propylpyrrolidinium bis(trifluoromethylsulfonyl)imide and 1-Hexyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide were studied in a carbon black (CB) host using spectrally resolved Carr-Purcell-Meiboom-Gill (CPMG) and 13-interval Pulsed Field Gradient Stimulated Echo (PFGSTE) Magic Angle Spinning Nuclear Magnetic Resonance (MAS-NMR). Data were processed using a sensitivity weighted Laplace inversion algorithm without non-negativity constraint. Previously found relations between the alkyl length and the aggregation behavior of pyrrolidinium-based cations were confirmed and characterized in more detail. For the IL in CB, a different aggregation behavior was found compared to the neat IL, adding the surface of a porous electrode as an additional parameter for the optimization of IL-based electrolytes. Finally, the suitability of MAS was assessed and critically discussed for investigations of this class of samples. Full article

(This article belongs to the Special Issue Advances in NMR and MRI of Materials)

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8 pages, 1434 KiB

Open AccessArticle

Impact of Xylose on Dynamics of Water Diffusion in Mesoporous Zeolites Measured by NMR

by Madison L. Nelson, Joelle E. Romo, Stephanie G. Wettstein and Joseph D. Seymour

Molecules 2021, 26(18), 5518; https://doi.org/10.3390/molecules26185518 - 11 Sep 2021

Cited by 2 | Viewed by 1860

Abstract

Zeolites are known to be effective catalysts in biomass converting processes. Understanding the mesoporous structure and dynamics within it during such reactions is important in effectively utilizing them. Nuclear magnetic resonance (NMR) T₂ relaxation and diffusion measurements, using a high-power radio frequency [...] Read more.

Zeolites are known to be effective catalysts in biomass converting processes. Understanding the mesoporous structure and dynamics within it during such reactions is important in effectively utilizing them. Nuclear magnetic resonance (NMR) T₂ relaxation and diffusion measurements, using a high-power radio frequency probe, are shown to characterize the dynamics of water in mesoporous commercially made 5A zeolite beads before and after the introduction of xylose. Xylose is the starting point in the dehydration into furfural. The results indicate xylose slightly enhances rotational mobility while it decreases translational motion through altering the permeability, K, throughout the porous structure. The measurements show xylose inhibits pure water from relocating into larger pores within the zeolite beads where it eventually is expelled from the bead itself. Full article

(This article belongs to the Special Issue Advances in NMR and MRI of Materials)

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19 pages, 8721 KiB

Open AccessArticle

Comparison of Five Conductivity Tensor Models and Image Reconstruction Methods Using MRI

by Nitish Katoch, Bup-Kyung Choi, Ji-Ae Park, In-Ok Ko and Hyung-Joong Kim

Molecules 2021, 26(18), 5499; https://doi.org/10.3390/molecules26185499 - 10 Sep 2021

Cited by 4 | Viewed by 2134

Abstract

Imaging of the electrical conductivity distribution inside the human body has been investigated for numerous clinical applications. The conductivity tensors of biological tissue have been obtained from water diffusion tensors by applying several models, which may not cover the entire phenomenon. Recently, a [...] Read more.

Imaging of the electrical conductivity distribution inside the human body has been investigated for numerous clinical applications. The conductivity tensors of biological tissue have been obtained from water diffusion tensors by applying several models, which may not cover the entire phenomenon. Recently, a new conductivity tensor imaging (CTI) method was developed through a combination of B1 mapping, and multi-b diffusion weighted imaging. In this study, we compared the most recent CTI method with the four existing models of conductivity tensors reconstruction. Two conductivity phantoms were designed to evaluate the accuracy of the models. Applied to five human brains, the conductivity tensors using the four existing models and CTI were imaged and compared with the values from the literature. The conductivity image of the phantoms by the CTI method showed relative errors between 1.10% and 5.26%. The images by the four models using DTI could not measure the effects of different ion concentrations subsequently due to prior information of the mean conductivity values. The conductivity tensor images obtained from five human brains through the CTI method were comparable to previously reported literature values. The images by the four methods using DTI were highly correlated with the diffusion tensor images, showing a coefficient of determination (R

^{2}

) value of 0.65 to 1.00. However, the images by the CTI method were less correlated with the diffusion tensor images and exhibited an averaged R

^{2}

value of 0.51. The CTI method could handle the effects of different ion concentrations as well as mobilities and extracellular volume fractions by collecting and processing additional B1 map data. It is necessary to select an application-specific model taking into account the pros and cons of each model. Future studies are essential to confirm the usefulness of these conductivity tensor imaging methods in clinical applications, such as tumor characterization, EEG source imaging, and treatment planning for electrical stimulation. Full article

(This article belongs to the Special Issue Advances in NMR and MRI of Materials)

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10 pages, 2792 KiB

Open AccessArticle

The Effect of an Accelerator on Cement Paste Capillary Pores: NMR Relaxometry Investigations

by Ioan Ardelean

Molecules 2021, 26(17), 5328; https://doi.org/10.3390/molecules26175328 - 2 Sep 2021

Cited by 9 | Viewed by 2182

Abstract

Nuclear Magnetic Resonance (NMR) relaxometry is a valuable tool for investigating cement-based materials. It allows monitoring of pore evolution and water consumption even during the hydration process. The approach relies on the proportionality between the relaxation time and the pore size. Note, however, [...] Read more.

Nuclear Magnetic Resonance (NMR) relaxometry is a valuable tool for investigating cement-based materials. It allows monitoring of pore evolution and water consumption even during the hydration process. The approach relies on the proportionality between the relaxation time and the pore size. Note, however, that this approach inherently assumes that the pores are saturated with water during the hydration process. In the present work, this assumption is eliminated, and the pore evolution is discussed on a more general basis. The new approach is implemented here to extract information on surface evolution of capillary pores in a simple cement paste and a cement paste containing calcium nitrate as accelerator. The experiments revealed an increase of the pore surface even during the dormant stage for both samples with a faster evolution in the presence of the accelerator. Moreover, water consumption arises from the beginning of the hydration process for the sample containing the accelerator while no water is consumed during dormant stage in the case of simple cement paste. It was also observed that the pore volume fractal dimension is higher in the case of cement paste containing the accelerator. Full article

(This article belongs to the Special Issue Advances in NMR and MRI of Materials)

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35 pages, 1992 KiB

Open AccessArticle

Non-Exponential ¹H and ²H NMR Relaxation and Self-Diffusion in Asphaltene-Maltene Solutions

by Kevin Lindt, Bulat Gizatullin, Carlos Mattea and Siegfried Stapf

Molecules 2021, 26(17), 5218; https://doi.org/10.3390/molecules26175218 - 28 Aug 2021

Cited by 2 | Viewed by 2290

Abstract

The distribution of NMR relaxation times and diffusion coefficients in crude oils results from the vast number of different chemical species. In addition, the presence of asphaltenes provides different relaxation environments for the maltenes, generated by steric hindrance in the asphaltene aggregates and [...] Read more.

The distribution of NMR relaxation times and diffusion coefficients in crude oils results from the vast number of different chemical species. In addition, the presence of asphaltenes provides different relaxation environments for the maltenes, generated by steric hindrance in the asphaltene aggregates and possibly by the spatial distribution of radicals. Since the dynamics of the maltenes is further modified by the interactions between maltenes and asphaltenes, these interactions—either through steric hindrances or promoted by aromatic-aromatic interactions—are of particular interest. Here, we aim at investigating the interaction between individual protonic and deuterated maltene species of different molecular size and aromaticity and the asphaltene macroaggregates by comparing the maltenes’ NMR relaxation (

T_{1}

and

T_{2}

) and translational diffusion (D) properties in the absence and presence of the asphaltene in model solutions. The ratio of the average transverse and longitudinal relaxation rates, describing the non-exponential relaxation of the maltenes in the presence of the asphaltene, and its variation with respect to the asphaltene-free solutions are discussed. The relaxation experiments reveal an apparent slowing down of the maltenes’ dynamics in the presence of asphaltenes, which differs between the individual maltenes. While for single-chained alkylbenzenes, a plateau of the relaxation rate ratio was found for long aliphatic chains, no impact of the maltenes’ aromaticity on the maltene–asphaltene interaction was unambiguously found. In contrast, the reduced diffusion coefficients of the maltenes in presence of the asphaltenes differ little and are attributed to the overall increased viscosity. Full article

(This article belongs to the Special Issue Advances in NMR and MRI of Materials)

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14 pages, 2376 KiB

Open AccessArticle

Magnetic Resonance Imaging of Water Content and Flow Processes in Natural Soils by Pulse Sequences with Ultrashort Detection

by Sabina Haber-Pohlmeier, David Caterina, Bernhard Blümich and Andreas Pohlmeier

Molecules 2021, 26(17), 5130; https://doi.org/10.3390/molecules26175130 - 24 Aug 2021

Cited by 4 | Viewed by 2628

Abstract

Magnetic resonance imaging is a valuable tool for three-dimensional mapping of soil water processes due to its sensitivity to the substance of interest: water. Since conventional gradient- or spin-echo based pulse sequences do not detect rapidly relaxing fractions of water in natural porous [...] Read more.

Magnetic resonance imaging is a valuable tool for three-dimensional mapping of soil water processes due to its sensitivity to the substance of interest: water. Since conventional gradient- or spin-echo based pulse sequences do not detect rapidly relaxing fractions of water in natural porous media with transverse relaxation times in the millisecond range, pulse sequences with ultrafast detection open a way out. In this work, we compare a spin-echo multislice pulse sequence with ultrashort (UTE) and zero-TE (ZTE) sequences for their suitability to map water content and its changes in 3D in natural soil materials. Longitudinal and transverse relaxation times were found in the ranges around 80 ms and 1 to 50 ms, respectively, so that the spin echo sequence misses larger fractions of water. In contrast, ZTE and UTE could detect all water, if the excitation and detection bandwidths were set sufficiently broad. More precisely, with ZTE we could map water contents down to 0.1 cm³/cm³. Finally, we employed ZTE to monitor the development of film flow in a natural soil core with high temporal resolution. This opens the route for further quantitative imaging of soil water processes. Full article

(This article belongs to the Special Issue Advances in NMR and MRI of Materials)

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9 pages, 3292 KiB

Open AccessCommunication

Complete Assignment of the ¹H and ¹³C NMR Spectra of Carthamin Potassium Salt Isolated from Carthamus tinctorius L.

by Maiko Sasaki and Keiko Takahashi

Molecules 2021, 26(16), 4953; https://doi.org/10.3390/molecules26164953 - 16 Aug 2021

Cited by 3 | Viewed by 2124

Abstract

Carthamin potassium salt isolated from Carthamus tinctorius L. was purified by an improved traditional Japanese method, without using column chromatography. The ¹H and ¹³C nuclear magnetic resonance (NMR) signals of the pure product were fully assigned using one- and two-dimensional NMR [...] Read more.

Carthamin potassium salt isolated from Carthamus tinctorius L. was purified by an improved traditional Japanese method, without using column chromatography. The ¹H and ¹³C nuclear magnetic resonance (NMR) signals of the pure product were fully assigned using one- and two-dimensional NMR spectroscopy, while the high purity of the potassium salt and deprotonation at the 3′ position of carthamin were confirmed by atomic adsorption spectroscopy and nano-electrospray ionization mass spectrometry. Full article

(This article belongs to the Special Issue Advances in NMR and MRI of Materials)

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10 pages, 906 KiB

Open AccessArticle

MR Study of Water Distribution in a Beech (Fagus sylvatica) Branch Using Relaxometry Methods

by Urša Mikac, Maks Merela, Primož Oven, Ana Sepe and Igor Serša

Molecules 2021, 26(14), 4305; https://doi.org/10.3390/molecules26144305 - 16 Jul 2021

Cited by 6 | Viewed by 2155

Abstract

Wood is a widely used material because it is environmentally sustainable, renewable and relatively inexpensive. Due to the hygroscopic nature of wood, its physical and mechanical properties as well as the susceptibility to fungal decay are strongly influenced by its moisture content, constantly [...] Read more.

Wood is a widely used material because it is environmentally sustainable, renewable and relatively inexpensive. Due to the hygroscopic nature of wood, its physical and mechanical properties as well as the susceptibility to fungal decay are strongly influenced by its moisture content, constantly changing in the course of everyday use. Therefore, the understanding of the water state (free or bound) and its distribution at different moisture contents is of great importance. In this study, changes of the water state and its distribution in a beech sample while drying from the green (fresh cut) to the absolutely dry state were monitored by 1D and 2D ¹H NMR relaxometry as well as by spatial mapping of the relaxation times T₁ and T₂. The relaxometry results are consistent with the model of homogeneously emptying pores in the bioporous system with connected pores. This was also confirmed by the relaxation time mapping results which revealed the moisture transport in the course of drying from an axially oriented early- and latewood system to radial rays through which it evaporates from the branch. The results of this study confirmed that MRI is an efficient tool to study the pathways of water transport in wood in the course of drying and is capable of determining the state of water and its distribution in wood. Full article

(This article belongs to the Special Issue Advances in NMR and MRI of Materials)

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15 pages, 3281 KiB

Open AccessArticle

Enhanced Resolution Analysis for Water Molecules in MCM-41 and SBA-15 in Low-Field T₂ Relaxometric Spectra

by Grzegorz Stoch and Artur T. Krzyżak

Molecules 2021, 26(8), 2133; https://doi.org/10.3390/molecules26082133 - 8 Apr 2021

Cited by 1 | Viewed by 2035

Abstract

Mesoporous silica materials are the subjects for relaxometric NMR studies in which we obtain information on the properties of molecules in confined geometries. The signal analysis in such investigations is generally carried out with the help of the Inverse Laplace Transform (ILT), which [...] Read more.

Mesoporous silica materials are the subjects for relaxometric NMR studies in which we obtain information on the properties of molecules in confined geometries. The signal analysis in such investigations is generally carried out with the help of the Inverse Laplace Transform (ILT), which is accompanied by a regularization procedure. The appropriate selection of the regularization method may positively affect the resolution of the spectrum and the essence of the final conclusions. In this work, we examined the MCM-41 and SBA-15 model systems in various saturation states, using L-Curve regularization for relaxation spectra based on our own version of the fast fast ILT implementation. In a single relaxometric spectrum, the water contributions from the internal volume in the pores and between the silica particles were identified, which allowed us to trace the dynamics of the corresponding drying trends during the removal of water from the sample as a function of total water saturation. Full article

(This article belongs to the Special Issue Advances in NMR and MRI of Materials)

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10 pages, 1399 KiB

Open AccessArticle

Development and Validation of 2-Azaspiro [4,5] Decan-3-One (Impurity A) in Gabapentin Determination Method Using qNMR Spectroscopy

by Nataliya E. Kuz’mina, Sergey V. Moiseev, Mikhail D. Khorolskiy and Anna I. Lutceva

Molecules 2021, 26(6), 1656; https://doi.org/10.3390/molecules26061656 - 16 Mar 2021

Cited by 2 | Viewed by 2473

Abstract

The authors developed a ¹H qNMR test procedure for identification and quantification of impurity A present in gabapentin active pharmaceutical ingredient (API) and gabapentin products. The validation studies helped to determine the limit of quantitation and assess linearity, accuracy, repeatability, intermediate precision, [...] Read more.

The authors developed a ¹H qNMR test procedure for identification and quantification of impurity A present in gabapentin active pharmaceutical ingredient (API) and gabapentin products. The validation studies helped to determine the limit of quantitation and assess linearity, accuracy, repeatability, intermediate precision, specificity, and robustness of the procedure. Spike-and-recovery assays were used to calculate standard deviations, coefficients of variation, confidence intervals, bias, Fisher’s F test, and Student’s t-test for assay results. The obtained statistical values satisfy the acceptance criteria for the validation parameters. The authors compared the results of impurity A quantification in gabapentin APIs and capsules by using the ¹H qNMR and HPLC test methods. Full article

(This article belongs to the Special Issue Advances in NMR and MRI of Materials)

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16 pages, 2518 KiB

Open AccessArticle

Compact NMR Spectroscopy for Low-Cost Identification and Quantification of PVC Plasticizers

by Anton Duchowny and Alina Adams

Molecules 2021, 26(5), 1221; https://doi.org/10.3390/molecules26051221 - 25 Feb 2021

Cited by 14 | Viewed by 3842

Abstract

Polyvinyl chloride (PVC), one of the most important polymer materials nowadays, has a large variety of formulations through the addition of various plasticizers to meet the property requirements of the different fields of applications. Routine analytical methods able to identify plasticizers and quantify [...] Read more.

Polyvinyl chloride (PVC), one of the most important polymer materials nowadays, has a large variety of formulations through the addition of various plasticizers to meet the property requirements of the different fields of applications. Routine analytical methods able to identify plasticizers and quantify their amount inside a PVC product with a high analysis throughput would promote an improved understanding of their impact on the macroscopic properties and the possible health and environmental risks associated with plasticizer leaching. In this context, a new approach to identify and quantify plasticizers employed in PVC commodities using low-field NMR spectroscopy and an appropriate non-deuterated solvent is introduced. The proposed method allows a low-cost, fast, and simple identification of the different plasticizers, even in the presence of a strong solvent signal. Plasticizer concentrations below 2 mg mL⁻¹ in solution corresponding to 3 wt% in a PVC product can be quantified in just 1 min. The reliability of the proposed method is tested by comparison with results obtained under the same experimental conditions but using deuterated solvents. Additionally, the type and content of plasticizer in plasticized PVC samples were determined following an extraction procedure. Furthermore, possible ways to further decrease the quantification limit are discussed. Full article

(This article belongs to the Special Issue Advances in NMR and MRI of Materials)

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13 pages, 33025 KiB

Open AccessArticle

Imaging Sequences for Hyperpolarized Solids

by Xudong Lv, Jeffrey Walton, Emanuel Druga, Raffi Nazaryan, Haiyan Mao, Alexander Pines, Ashok Ajoy and Jeffrey Reimer

Molecules 2021, 26(1), 133; https://doi.org/10.3390/molecules26010133 - 30 Dec 2020

Cited by 1 | Viewed by 2398

Abstract

Hyperpolarization is one of the approaches to enhance Nuclear Magnetic Resonance (NMR) and Magnetic Resonance Imaging (MRI) signal by increasing the population difference between the nuclear spin states. Imaging hyperpolarized solids opens up extensive possibilities, yet is challenging to perform. The highly populated [...] Read more.

Hyperpolarization is one of the approaches to enhance Nuclear Magnetic Resonance (NMR) and Magnetic Resonance Imaging (MRI) signal by increasing the population difference between the nuclear spin states. Imaging hyperpolarized solids opens up extensive possibilities, yet is challenging to perform. The highly populated state is normally not replenishable to the initial polarization level by spin-lattice relaxation, which regular MRI sequences rely on. This makes it necessary to carefully “budget” the polarization to optimize the image quality. In this paper, we present a theoretical framework to address such challenge under the assumption of either variable flip angles or a constant flip angle. In addition, we analyze the gradient arrangement to perform fast imaging to overcome intrinsic short decoherence in solids. Hyperpolarized diamonds imaging is demonstrated as a prototypical platform to test the theory. Full article

(This article belongs to the Special Issue Advances in NMR and MRI of Materials)

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9 pages, 1623 KiB

Open AccessArticle

Gas and Liquid Phase Imaging of Foam Flow Using Pure Phase Encode Magnetic Resonance Imaging

by Alexander Adair, Sebastian Richard and Benedict Newling

Molecules 2021, 26(1), 28; https://doi.org/10.3390/molecules26010028 - 23 Dec 2020

Cited by 3 | Viewed by 2302

Abstract

Magnetic resonance imaging (MRI) is a non-invasive and non-optical measurement technique, which makes it a promising method for studying delicate and opaque samples, such as foam. Another key benefit of MRI is its sensitivity to different nuclei in a sample. The research presented [...] Read more.

Magnetic resonance imaging (MRI) is a non-invasive and non-optical measurement technique, which makes it a promising method for studying delicate and opaque samples, such as foam. Another key benefit of MRI is its sensitivity to different nuclei in a sample. The research presented in this article focuses on the use of MRI to measure density and velocity of foam as it passes through a pipe constriction. The foam was created by bubbling fluorinated gas through an aqueous solution. This allowed for the liquid and gas phases to be measured separately by probing the ¹H and ¹⁹F behavior of the same foam. Density images and velocity maps of the gas and liquid phases of foam flowing through a pipe constriction are presented. In addition, results of computational fluid dynamics simulations of foam flow in the pipe constriction are compared with experimental results. Full article

(This article belongs to the Special Issue Advances in NMR and MRI of Materials)

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Graphical abstract

12 pages, 12987 KiB

Open AccessArticle

Magnetic Resonance Methods as a Prognostic Tool for the Biorelevant Behavior of Xanthan Tablets

by Urša Mikac and Julijana Kristl

Molecules 2020, 25(24), 5871; https://doi.org/10.3390/molecules25245871 - 11 Dec 2020

Cited by 3 | Viewed by 2018

Abstract

Hydrophilic matrix tablets with controlled drug release have been used extensively as one of the most successful oral drug delivery systems for optimizing therapeutic efficacy. In this work, magnetic resonance imaging (MRI) is used to study the influence of various pHs and mechanical [...] Read more.

Hydrophilic matrix tablets with controlled drug release have been used extensively as one of the most successful oral drug delivery systems for optimizing therapeutic efficacy. In this work, magnetic resonance imaging (MRI) is used to study the influence of various pHs and mechanical stresses caused by medium flow (at rest, 80, or 150 mL/min) on swelling and on pentoxifylline release from xanthan (Xan) tablets. Moreover, a bimodal MRI system with simultaneous release testing enables measurements of hydrogel thickness and drug release, both under the same experimental conditions and at the same time. The results show that in water, the hydrogel structure is weaker and less resistant to erosion than the Xan structure in the acid medium. Different hydrogel structures affect drug release with erosion controlled release in water and diffusion controlled release in the acid medium. Mechanical stress simulating gastrointestinal contraction has no effect on the hard hydrogel in the acid medium where the release is independent of the tested stress, while it affects the release from the weak hydrogel in water with faster release under high stress. Our findings suggest that simultaneous MR imaging and drug release from matrix tablets together provide a valuable prognostic tool for prolonged drug delivery design. Full article

(This article belongs to the Special Issue Advances in NMR and MRI of Materials)

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10 pages, 868 KiB

Open AccessArticle

Diffusion Spectrum of Polymer Melt Measured by Varying Magnetic Field Gradient Pulse Width in PGSE NMR

by Aleš Mohorič, Gojmir Lahajnar and Janez Stepišnik

Molecules 2020, 25(24), 5813; https://doi.org/10.3390/molecules25245813 - 9 Dec 2020

Cited by 3 | Viewed by 2260

Abstract

The translational motion of polymers is a complex process and has a big impact on polymer structure and chemical reactivity. The process can be described by the segment velocity autocorrelation function or its diffusion spectrum, which exhibit several characteristic features depending on the [...] Read more.

The translational motion of polymers is a complex process and has a big impact on polymer structure and chemical reactivity. The process can be described by the segment velocity autocorrelation function or its diffusion spectrum, which exhibit several characteristic features depending on the observational time scale—from the Brownian delta function on a large time scale, to complex details in a very short range. Several stepwise, more-complex models of translational dynamics thus exist—from the Rouse regime over reptation motion to a combination of reptation and tube-Rouse motion. Accordingly, different methods of measurement are applicable, from neutron scattering for very short times to optical methods for very long times. In the intermediate regime, nuclear magnetic resonance (NMR) is applicable—for microseconds, relaxometry, and for milliseconds, diffusometry. We used a variation of the established diffusometric method of pulsed gradient spin-echo NMR to measure the diffusion spectrum of a linear polyethylene melt by varying the gradient pulse width. We were able to determine the characteristic relaxation time of the first mode of the tube-Rouse motion. This result is a deviation from a Rouse model of polymer chain displacement at the crossover from a square-root to linear time dependence, indicating a new long-term diffusion regime in which the dynamics of the tube are also described by the Rouse model. Full article

(This article belongs to the Special Issue Advances in NMR and MRI of Materials)

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19 pages, 4707 KiB

Open AccessArticle

The Role of Titanium Dioxide on the Hydration of Portland Cement: A Combined NMR and Ultrasonic Study

by George Diamantopoulos, Marios Katsiotis, Michael Fardis, Ioannis Karatasios, Saeed Alhassan, Marina Karagianni, George Papavassiliou and Jamal Hassan

Molecules 2020, 25(22), 5364; https://doi.org/10.3390/molecules25225364 - 17 Nov 2020

Cited by 21 | Viewed by 2947

Abstract

Titanium dioxide (TiO₂) is an excellent photocatalytic material that imparts biocidal, self-cleaning and smog-abating functionalities when added to cement-based materials. The presence of TiO₂ influences the hydration process of cement and the development of its internal structure. In this article, [...] Read more.

Titanium dioxide (TiO₂) is an excellent photocatalytic material that imparts biocidal, self-cleaning and smog-abating functionalities when added to cement-based materials. The presence of TiO₂ influences the hydration process of cement and the development of its internal structure. In this article, the hydration process and development of a pore network of cement pastes containing different ratios of TiO₂ were studied using two noninvasive techniques (ultrasonic and NMR). Ultrasonic results show that the addition of TiO₂ enhances the mechanical properties of cement paste during early-age hydration, while an opposite behavior is observed at later hydration stages. Calorimetry and NMR spin–lattice relaxation time T₁ results indicated an enhancement of the early hydration reaction. Two pore size distributions were identified to evolve separately from each other during hydration: small gel pores exhibiting short T₁ values and large capillary pores with long T₁ values. During early hydration times, TiO₂ is shown to accelerate the formation of cement gel and reduce capillary porosity. At late hydration times, TiO₂ appears to hamper hydration, presumably by hindering the transfer of water molecules to access unhydrated cement grains. The percolation thresholds were calculated from both NMR and ultrasonic data with a good agreement between both results. Full article

(This article belongs to the Special Issue Advances in NMR and MRI of Materials)

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16 pages, 6009 KiB

Open AccessArticle

Local Structures of Two-Dimensional Zeolites—Mordenite and ZSM-5—Probed by Multinuclear NMR

by Marina G. Shelyapina, Rosario I. Yocupicio-Gaxiola, Iuliia V. Zhelezniak, Mikhail V. Chislov, Joel Antúnez-García, Fabian N. Murrieta-Rico, Donald Homero Galván, Vitalii Petranovskii and Sergio Fuentes-Moyado

Molecules 2020, 25(20), 4678; https://doi.org/10.3390/molecules25204678 - 14 Oct 2020

Cited by 13 | Viewed by 2855

Abstract

Mesostructured pillared zeolite materials in the form of lamellar phases with a crystal structure of mordenite (MOR) and ZSM-5 (MFI) were grown using CTAB as an agent that creates mesopores, in a one-pot synthesis; then into the CTAB layers separating the 2D zeolite [...] Read more.

Mesostructured pillared zeolite materials in the form of lamellar phases with a crystal structure of mordenite (MOR) and ZSM-5 (MFI) were grown using CTAB as an agent that creates mesopores, in a one-pot synthesis; then into the CTAB layers separating the 2D zeolite plates were introduced by diffusion the TEOS molecules which were further hydrolyzed, and finally the material was annealed to remove the organic phase, leaving the 2D zeolite plates separated by pillars of silicon dioxide. To monitor the successive structural changes and the state of the atoms of the zeolite framework and organic compounds at all the steps of the synthesis of pillared MOR and MFI zeolites, the nuclear magnetic resonance method (NMR) with magic angle spinning (MAS) was applied. The ²⁷Al and ²⁹Si MAS NMR spectra confirm the regularity of the zeolite frameworks of the as synthetized materials. Analysis of the ¹H and ¹³C MAS NMR spectra and an experiment with variable contact time evidence a strong interaction between the charged “heads” –[N(CH₃)₃]⁺ of CTAB and the zeolite framework at the place of [AlO₄]⁻ location. According to ²⁷Al and ²⁹Si MAS NMR the evacuation of organic cations leads to a partial but not critical collapse of the local zeolite structure. Full article

(This article belongs to the Special Issue Advances in NMR and MRI of Materials)

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18 pages, 57396 KiB

Open AccessReview

Solid-State NMR Spectroscopy: A Key Tool to Unravel the Supramolecular Structure of Drug Delivery Systems

by Marianna Porcino, Xue Li, Ruxandra Gref and Charlotte Martineau-Corcos

Molecules 2021, 26(14), 4142; https://doi.org/10.3390/molecules26144142 - 7 Jul 2021

Cited by 6 | Viewed by 3391

Abstract

In the past decades, nanosized drug delivery systems (DDS) have been extensively developed and studied as a promising way to improve the performance of a drug and reduce its undesirable side effects. DDSs are usually very complex supramolecular assemblies made of a core [...] Read more.

In the past decades, nanosized drug delivery systems (DDS) have been extensively developed and studied as a promising way to improve the performance of a drug and reduce its undesirable side effects. DDSs are usually very complex supramolecular assemblies made of a core that contains the active substance(s) and ensures a controlled release, which is surrounded by a corona that stabilizes the particles and ensures the delivery to the targeted cells. To optimize the design of engineered DDSs, it is essential to gain a comprehensive understanding of these core–shell assemblies at the atomic level. In this review, we illustrate how solid-state nuclear magnetic resonance (ssNMR) spectroscopy has become an essential tool in DDS design. Full article

(This article belongs to the Special Issue Advances in NMR and MRI of Materials)

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26 pages, 5463 KiB

Open AccessReview

The Renal Clearable Magnetic Resonance Imaging Contrast Agents: State of the Art and Recent Advances

by Xiaodong Li, Yanhong Sun, Lina Ma, Guifeng Liu and Zhenxin Wang

Molecules 2020, 25(21), 5072; https://doi.org/10.3390/molecules25215072 - 1 Nov 2020

Cited by 15 | Viewed by 3502

Abstract

The advancements of magnetic resonance imaging contrast agents (MRCAs) are continuously driven by the critical needs for early detection and diagnosis of diseases, especially for cancer, because MRCAs improve diagnostic accuracy significantly. Although hydrophilic gadolinium (III) (Gd³⁺) complex-based MRCAs have achieved [...] Read more.

The advancements of magnetic resonance imaging contrast agents (MRCAs) are continuously driven by the critical needs for early detection and diagnosis of diseases, especially for cancer, because MRCAs improve diagnostic accuracy significantly. Although hydrophilic gadolinium (III) (Gd³⁺) complex-based MRCAs have achieved great success in clinical practice, the Gd³⁺-complexes have several inherent drawbacks including Gd³⁺ leakage and short blood circulation time, resulting in the potential long-term toxicity and narrow imaging time window, respectively. Nanotechnology offers the possibility for the development of nontoxic MRCAs with an enhanced sensitivity and advanced functionalities, such as magnetic resonance imaging (MRI)-guided synergistic therapy. Herein, we provide an overview of recent successes in the development of renal clearable MRCAs, especially nanodots (NDs, also known as ultrasmall nanoparticles (NPs)) by unique advantages such as high relaxivity, long blood circulation time, good biosafety, and multiple functionalities. It is hoped that this review can provide relatively comprehensive information on the construction of novel MRCAs with promising clinical translation. Full article

(This article belongs to the Special Issue Advances in NMR and MRI of Materials)

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