Time-domain Nuclear Magnetic Resonance Research Articles

Characterizing the structure of aerobic granular sludge using ultra-high field magnetic resonance

Despite aerobic granular sludge wastewater treatment plants operating around the world, our understanding of internal granule structure and its relation to treatment efficiency remains limited. This can be attributed in part to the drawbacks of time-consuming, labor-intensive, and invasive microscopy protocols which effectively restrict samples sizes and may introduce artefacts. Time-domain nuclear magnetic resonance (NMR) allows non-invasive measurements which describe internal structural features of opaque, complex materials like biofilms. NMR was used to image aerobic granules collected from five full-scale wastewater treatment plants in the Netherlands and United States, as well as laboratory granules and control beads. T1 and T2 relaxation-weighted images reveal heterogeneous structures that include high- and low-density biofilm regions, water-like voids, and solid-like inclusions. Channels larger than approximately 50 μm and connected to the bulk fluid were not visible. Both cluster and ring-like structures were observed with each granule source having a characteristic structural type. These structures, and their NMR relaxation behavior, were stable over several months of storage. These observations reveal the complex structures within aerobic granules from a range of sources and highlight the need for non-invasive characterization methods like NMR to be applied in the ongoing effort to correlate structure and function.

The states of water in tryptophan grafted hydroxypropyl methylcellulose hydrogels and their effect on the adsorption of methylene blue and rhodamine B

Tryptophan (Trp) decorated hydroxypropyl methylcellulose (HPMC) cryogels were prepared by a one-step reaction with citric acid. The increase of Trp content in the 3D network from 0 to 2.18 wt% increased the apparent density from 0.0267 g.cm−3 to 0.0381 g.cm−3 and the compression modulus from 94 kPa to 201 kPa, due to hydrophobic interactions between Trp molecules. The increase of Trp content in HPMC-Trp hydrogels increased the amount of non-freezing water, estimated from differential scanning calorimetry, and the amount of freezing water, which was determined by time-domain nuclear magnetic resonance. The adsorption capacity of methylene blue (MB) and rhodamine B (RB) on HPMC-Trp hydrogels increased with Trp content and the amount of freezing water. HPMC-Trp hydrogels could be recycled 6 times keeping the original adsorptive capacity. The diffusional constants of MB and RB tended to increase with Trp content. RB adsorbed on HPMC-Trp hydrogels presented a bathochromic shift of fluorescence.

High CO tolerance of Pt nanoparticles synthesized by sodium borohydride in a time-domain NMR spectrometer

The CO poisoning effect was overcome using a novel synthesis method. This method consists of using sodium borohydride reducing agent assisted by magnetic field and radiofrequency pulses in the time-domain NMR spectrometer. This synthesis was useful to disperse the Pt nanoparticles over the carbon support and to compress the lattice strain of the Pt crystalline structure. Besides that, Pt/C MFP90° showed a multi-CO oxidation component in cyclic voltammetry, and this can avoid the poisoning effect by creating a large availability of CO species to be adsorbed, desorbed, and re-adsorbed. Pt/C MFP90° has also shown the best performance in the PEMFC regarding H2 and CO + H2 experiments.

Time Domain Nuclear Magnetic Resonance (TD-NMR) to evaluate the effect of potato cell membrane electroporation

Time Domain-Nuclear Magnetic Resonance (TD-NMR) was used here for the first time to analyze potato specimens cut from tubers before and after electroporation. The proton transverse relaxation time, T2, was used to identify the modifications that occur at the cell level involving water molecules mobility in potato tubers after the electroporation treatment. Since electroporation modifies the tissue conductivity, the samples were also analyzed in terms of conductivity, water content, and microscopic morphology of the tissue. Comparison analyses were performed on dried potato (zero water content) and water-potato starch mixtures with different water contents. All the data confirm that the effect of the electroporation process can be identified with a variation of the position of the peaks in T2 distribution, associated to sub-cellular modifications.

Spectroscopic evidence of successful in situ insertion of sol–gel silica in a poly(3-hydroxybutyrate) matrix

Silica-based (SiO2) poly(3-hydroxybutyrate) (PHB) nanocomposites were obtained via an in situ sol–gel route in three distinct particle concentrations (1, 5, and 7.5% by weight of PHB). The polymer hybrids formed were analyzed via wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), Fourier transform infrared (FTIR) spectroscopy, and time-domain nuclear magnetic resonance relaxometry (TD-NMR). The SiO2 inorganic structure displayed surface fractal features at low concentration (1 wt%) and denser agglomerates at higher concentrations (5 and 7.5 wt%). FTIR and SAXS results confirmed the formation of the inorganic matrix amid the polymer chains with different levels of distribution and organization. WAXD and TD-NMR results suggested the SiO2 influence on the PHB crystallinity degree, which was reflected on the polymer’s molecular dynamics with a nonlinear dependence of particles concentration in the PHB matrix.

Effects of Changes in Biopolymer Composition on Moisture in Acetylated Wood

To investigate the effects of changes in biopolymer composition on moisture in acetylated poplar wood (Populus euramericana Cv.), the acetylation of control wood was compared to the acetylation of wood with reduced hemicellulose or lignin content (about 9% reduction of total specimen dry weight in both cases). Time-domain nuclear magnetic resonance relaxometry of water-saturated wood gave spin–spin relaxation times (T2) of water populations, while deuteration in a sorption balance was used to characterize the hydroxyl accessibility of the wood cell walls. As expected, the acetylation of pyridine-swelled wood reduced hydroxyl accessibility and made the cell wall less accessible to water, resulting in a reduction of cell wall moisture content by about 24% compared with control wood. Hemicellulose loss per se increased the spin–spin relaxation time of cell wall water, while delignification had the opposite effect. The combined effect of hemicellulose removal and acetylation caused more than a 30% decrease of cell wall moisture content when compared with control wood. The acetylated and partially delignified wood cell walls contained higher cell wall moisture content than acetylated wood. An approximate theoretical calculation of hydroxyl accessibility for acetylated wood was in the low range, but it agreed rather well with the measured accessibility, while acetylated and partially hemicellulose-depleted and partially delignified wood for unknown reasons resulted in substantially lower hydroxyl accessibilities than the theoretical estimate.

Real-time measurement system for determining metal concentrations in water-intensive processes

Abstract The main purpose of this paper is to demonstrate the potential of time-domain nuclear magnetic resonance (TD-NMR) technology for monitoring the concentrations of metal ions in water-based solutions. The main focus of this work was paramagnetic ions, such as Mn2+, Cu2+, Fe3+, Fe2+, Zn2+ and Ni2+, which are often the principal metal components in mining waters. Laboratory samples of different concentrations of single metals and mixtures of them and samples of real mining water were used in the relaxation rate (R 2) measurements. The measurements of single metal ions were used for the determination of the relaxivities of those ions. The concentrations of the ions in the mining water as a function of pH were also estimated by means of the X-ray fluorescence (XRF) method and ChemEQL software for calculating chemical speciation equilibria. Using these concentration values and the relaxivities of the metal ions, the total relaxation rate (R 2) results were then calculated. Principally, the results of these three different determinations are in relatively good agreement. It can be concluded that TD-NMR has great potential for monitoring metal ion concentrations during water treatment.

Muscle water properties in raw intact broiler breast fillets with the woody breast condition

The purpose of this study was to investigate the relationships between muscle water properties, water-holding capacity (WHC), and woody breast (WB) severity in intact raw broiler breast fillets. Broiler pectoralis major deboned at 3 h postmortem was collected from a commercial plant and categorized as normal (NORM), moderate WB, or severe WB (SEV). Meat drip loss was calculated based on weight loss during overnight storage at 4°C. Water properties of the intact fillets were determined with time domain nuclear magnetic resonance and the T2 relaxation times were determined using an inverse Laplace algorithm (CONTIN). Three T2 water components, hydration water (T2b), intra-myofibrillar water (T21), and extra-myofibrillar water (T22), were identified. With increasing WB severity, the time constant of each water component and the relative content of T22 (P22) increased while the relative areas of T2b and T21 (P2b and P21, respectively) decreased. Spearman correlation analysis showed that there were significant correlations between the WB condition score and either the time constant or normalized area for each T2 component. T22 normalized areas (A22) were most strongly correlated with the WB score (r = 0.75); however, the weakest correlation was found between the WB score and T21 areas (A21). Pearson correlation analysis revealed that the strongest correlation (r = 0.64) was found between A22 and drip loss; however, there was no correlation between A21 and drip loss. Within the NORM group, drip loss was significantly correlated to the time constants for both T2b and T21. Within the SEV group, only A22 was significantly correlated to drip loss. These data indicate that the WB condition has a significant impact on the distribution of water within the intact muscle tissue. The content of extra-myofibrillar water in broiler breast fillets may be a key factor responsible for the poor WHC measurements in WB meat.

Non-invasive detection of internal flesh breakdown in intact Palmer mangoes using time-domain nuclear magnetic resonance relaxometry

The advent of new compact, bench-top, inexpensive and more user-friendly low-field nuclear magnetic resonance spectrometers in the last decade opens new opportunities for new non-destructive and non-invasive analytical methods to study physical-chemical properties of the internal parts of fruits. Correlations of the internal chemical environment with NMR relaxometry signals is an important parameter for food quality control, however, differently from controlled processed food, internal fruits environment has not always a straight correlation with relaxometry signals. In this paper we demonstrate that Time Domain-NMR signals combined with chemometrics analysis are a powerful tool for studies and industrial control of the internal quality of Palmer mangoes, providing tools to evaluate the fruit ripeness and internal flesh breakdown, which are highly difficult to be detected in intact fruits by other analytical methods. Results shows that combining transverse relaxation time distribution with Principal Component Analysis it is possible to classify three groups: unripe mangoes, ripe mangoes, and ripe mangoes with physiological defects.

Monitoring of soluble pectin content in orange juice by means of MIR and TD-NMR spectroscopy combined with machine learning.

This study represents a rapid and non-destructive approach based on mid-infrared (MIR) spectroscopy, time domain nuclear magnetic resonance (TD-NMR), and machine learning classification models (ML) for monitoring soluble pectin content (SPC) changes in orange juice. Current reference methods of SPC in orange juice are laborious, requiring several extractions with successive adjustments hindering rapid process intervention. 109 fresh orange juices samples, representing different harvests, were analysed using MIR, TD-NMR and reference method. Unsupervised algorithms were applied for natural clustering of MIR and TD-NMR data in two groups. Analyses of variance of the two MIR and TD-NMR datasets show that only the MIR groups were different at 95% confidence for SPC average values. This approach allows build classification models based on MIR data achieving 85% and 89% of accuracy. Results demonstrate that MIR/ML can be a suitable strategy for the quick assessment of SPC trends in orange juices.

Time-Domain NMR in Characterization of Liquid Fuels: A Mini-Review

Low-field nuclear magnetic resonance (LF-NMR) is a highly promising method for characterizing the different physical parameters and chemical structures of liquid fuels. In particular, there have be...

Prediction of water holding capacity in intact broiler breast fillets affected by the woody breast condition using time-domain NMR

The potential of time-domain NMR (TD-NMR) was evaluated as a non-destructive method for predicting water holding capacity (WHC) in intact broiler breast fillets with the woody breast (WB) condition. Raw fillet samples were collected from a commercial plant and classified into normal, moderate WB, and severe WB groups. WHC was measured with drip loss and cook loss. Water properties were determined with TD-NMR. Pearson correlation and multiple linear regression (MLR) analysis were used to estimate relationships between WHC and muscle water properties. Principal component analysis (PCA) was performed on muscle water properties to identify similarities and differences of the WB condition. Increasing severity of the WB condition resulted in increased drip loss and cook loss. Significant Pearson correlations were found between WHC and muscle water properties, with the greatest correlation found between cook loss and the T21 time constant (r = 0.86, P < 0.001). MLR models indicate that the WHC was mainly attributed to P22 relative area and/or T21 time constant. PCA results showed a good feasibility to distinguish severe WB fillets from normal ones. This study demonstrates that TD-NMR could be applied as an alternative method for predicting the meat WHC and the severity of the WB condition.

A noninvasive method to study the evolution of extracellular fluid volume in mice using time-domain nuclear magnetic resonance.

Maintaining water homeostasis is fundamental for cellular function. Many diseases and drugs affect water balance and plasma osmolality. Water homeostasis studies in small animals require the use of invasive or terminal methods that make intracellular fluid volume and extracellular fluid volume (ECF) monitoring over time stressful and time consuming. We examined the feasibility of monitoring mouse ECF by a noninvasive method using time-domain nuclear magnetic resonance (TD-NMR). This technique allows differentiation of protons in a liquid environment (free fluid) from protons in soft tissues containing a majority of either small molecules (lean) or large molecules (fat). Moreover, this apparatus enables rapid, noninvasive, and repeated measurements on the same animal. We assessed the feasibility of coupling TD-NMR analysis to a longitudinal metabolic cage study by monitoring mice daily. We determined the effect of 24-h water deprivation on mouse body parameters and detected a sequential and overlapping decrease in free fluid and lean mass during water deprivation. Finally, we studied the effect of mineralocorticoids that are known to induce a transient increase in ECF but for which no direct measurements have been performed in mice. We showed, for the first time, that mineralocorticoids induced a transient ~15% increase in free fluid in conscious mice. TD-NMR is, therefore, the first method to allow direct measurement of discrete changes in ECF in conscious small animals. This method allows analysis of kinetic changes to stimuli before investigating with terminal methods and will allow further understanding of fluid disorders.

Quantitative Evaluation of the Crystallinity of Indomethacin Using 1H T2 Relaxation Behaviors Measured by Time Domain NMR

We sought to demonstrate the usefulness of the T2 relaxation behaviors measured by time domain NMR (TD-NMR) for the quantitative evaluation of the crystallinity of an active pharmaceutical ingredient (API). This study used indomethacin as a model API. After blending amorphous and crystalline indomethacin powders at a designated ratio, T2 relaxation curves were measured by TD-NMR. Subsequently, we acquired a calibration curve to quantify crystallinity by curve fitting analysis. Validation demonstrated a good correlation between the theoretical and experimental percentage of crystallinity. Thus, this study succeeded in a precise estimation of crystallinity of indomethacin using TD-NMR. We also investigated whether the technique is practical by testing indomethacin powders with unknown proportion of crystallinity, and then compared their estimated crystallinity with that found using conventional evaluation techniques. The quantitative performance of the TD-NMR technique was comparable to that of Raman spectroscopy. Furthermore, indomethacin powder blended with excipients, which can be used to produce tablets, was tested. The TD-NMR technique was still able to quantify the crystallinity of indomethacin, even when excipients were incorporated into the sample. Therefore, the present study expands the horizon for evaluating the crystallinity of APIs in pharmaceutical sciences.

Effect of modified microcrystalline cellulose on poly(3-hydroxybutyrate) molecular dynamics by proton relaxometry

Hybrid films of poly(3-hydroxybutyrate) (PHB) and modified cellulose by solution casting method were prepared, aiming to study the influence of modified cellulose (0.25%, 0.5% and 0.75% w/w) on the structural organization and thermal properties of PHB matrix. The modified cellulose showed good dispersion in polymer matrix, due to the high compatibility between phases explained by similarity of polymer and filler structures. The composites were studied by wide-angle X-ray diffractometry, differential scanning calorimetry, thermogravimetric analysis, and time-domain nuclear magnetic resonance (NMR) spectroscopy. The conjugation of results coming from those techniques allowed to determine the cellulose concentration that had the highest influence on crystalline planes and degree of crystallinity of PHB, that is, the influence in the composite structure. The molecular dynamics obtained by NMR showed a reciprocal influence between polymer matrix and cellulose particles, enhancing the interactions present in the agglomerated particles.

New and rapid pulse sequences for two-dimensional D-T1 correlation measurements

Longitudinal relaxation time (T1), transverse relaxation time (T2) and diffusion coefficient (D) values have been widely used for the characterizations of materials using low field Time Domain Nuclear Magnetic Resonance (TD-NMR). Each parameter can be determined using one-dimensional techniques or their values and correlations by multi-dimensional experiments such as T1-T2, D-T2, and T1-D-T2. In this work, we studied four D-T1 sequences for TD-NMR combining Stejskal-Tanner Pulse Gradient Spin Echo (PGSE) diffusion measurement with Inversion-Recovery (IR), Saturation-Recovery (SR), Small-Angle Continuous Wave Free Precession (CWFP-T1) and Small-Angle Flip-Flop (SAFF) for T1 measurement. The results show that rapid D-T1 measurements can be obtained with single shot CWFP-T1 and SAFF sequences. The two sequences were two and eight time fast than sequences based on SR and IR, respectively. Although the two fast sequences yield low signal-to-noise ratio signal, they can be as fast as the traditional D-T2 experiment, or even faster, because it is not necessary to wait a recycle delay of 5 T1. Another advantage of the CWFP-T1 and SAFF methods, when compared to the one based on SR or CPMG (for D-T2) are the low specific absorption rate (SAR) of these sequences due the low flip angles in the sequences, that reduces the sample heating problem. These sequences were initially studied using phantom samples. They also were used to study plant tissues to observe the anisotropic diffusion in asparagus. Therefore, they can be useful methods for practical application in TD-NMR.

Some Applications of a Field Programmable Gate Array Based Time-Domain Spectrometer for NMR Relaxation and NMR Cryoporometry

NMR Relaxation (NMRR) is an extremely useful quantitative technique for material science, particularly for studying polymers and porous materials. NMR Cryoporometry (NMRC) is a powerful technique for the measurement of pore-size distributions and total porosities. This paper discusses the use, capabilities and application of a newly available compact NMR time-domain relaxation spectrometer, the Lab-Tools Mk3 NMR Relaxometer &amp; Cryoporometer [Lab-Tools (nano-science), Ramsgate, Kent, UK (2019)]. Being Field Programmable Gate Array based means that it is unusually compact, which makes it particularly suitable for the lab bench-top, in the field and also mobile use. Its use with a variable-temperature NMR probe such as the Lab-Tools Peltier thermo-electrically cooled variable-temperature (V-T) probe is also discussed. This enables the NMRC measurement of pore-size distributions in porous materials, from sub-nano- to over 1 micron sized pores. These techniques are suitable for a wide range of porous materials and also polymers. This instrument comes with a Graphical User Interface (GUI) for control, which also enables both online and offline analysis of the measured data. This makes it is easy to use for material science studies both in the field and in university, research institute, company and even school laboratories. The Peltier cooling gives the precision temperature control and smoothness needed by NMR Cryoporometry, particularly near the probe liquid bulk melting point. Results from example NMR Relaxation and NMR Cryoporometric measurements are given.

Stability of the Meat Protein Type I Collagen: Influence of pH, Ionic Strength, and Phenolic Antioxidant.

The water-holding capacity (WHC) is among the key factors in determining the quality of meat and its value, which is strongly influenced by the content and quality of the connective tissue proteins like collagen. Therefore, the factors that influence the proteins’ stability, e.g., pH, ionic strength, and the antioxidants which are used to increase the meat shelf-life, also affect the WHC. The interaction of collagen, whose structure is strongly influenced by the interaction with water molecules, can be studied following the behavior of water diffusion by low-resolution 1H NMR experiments. The present study is addressed to study the collagen stability as a function of pH, ionic strength, and phenolic antioxidants like catechin. The experimental study demonstrated how the 1H NMR time domain (TD) experiments are able to evaluate the hydration properties of collagen, not only as a function of ionic strength and pH, but also in determining the ability of catechin to interact both on the surface of the collagen fibrils and inside the fibrillar domain.

Role of aleurone cell walls in water diffusion and distribution within cereal grains

Wheat (Triticum aestivum L) and barley (Hordeum vulgare L) are two important cereals cultivated worldwide. The effect of aleurone cell wall structure on water diffusion and distribution within wheat and barley grains was evaluated at different relative humidity levels. Time domain nuclear magnetic resonance was used to measure the transverse relaxation time T2 of grains. Two water states were distinguished within grains, namely W1 (lower mobility) and W2 (higher mobility). Grains with thicker aleurone layer cell walls had a higher W2. The water-absorption and desorption rates were mainly determined by the thickness of the aleurone cell walls and decreased with increasing cell wall thickness. The higher W2 values observed in grains with thicker aleurone cell walls with the a water content of 2.0% (w/w) and 12.1% (w/w) were probably related to a higher water motion within the grains, in response to higher porosity. Arabinoxylan and (1,3)(1,4)-β-glucan alternating multilayer films were prepared, each film had 20 layers, one layer was approximately 1 μm thick. The film was used as a model to simulate the aleurone layers. These results show that cell walls of the aleurone layer regulate the diffusion and distribution of water within grains.

The role of graphene on thermally induced shape memory properties of poly(lactic acid) extruded composites

In this work, the effect of reduced graphene oxide (rGO) on the thermally induced shape memory properties of poly(lactic acid) (PLA) was studied. rGO was incorporated within PLA at various contents (0.1–1.0 mass%) by melt-extrusion. X-ray diffraction showed that PLA/rGO nanocomposites presented decreased crystallinity compared to PLA alone. Differential scanning calorimetry revealed that rGO particles favored the formation of more imperfect PLA crystals. Results from thermogravimetric analyses showed that the PLA/rGO composites presented slightly improved thermal stability. Time-domain nuclear magnetic resonance indicated increased molecular mobility for PLA/rGO nanocomposites in relation to PLA. Dynamic mechanical analysis results showed that Tg = 62.9 °C for PLA and that this value was reduced for the composites, reaching 54.2 °C when the rGO content was 1.0 mass%. The storage moduli (E′) were reduced with the increase in rGO content, with a 44% decrease for the composition with 1.0 mass% of rGO. However, above 65 °C the E′ values increased substantially, which suggested the role of graphene to fix the heat-relaxed molecules of PLA. For the composites, the thermally induced shape memory data revealed an increase in the maximum strain ( $$\varepsilon_{\text{m}}$$ ), reaching 39% and 51% for the composites with the incorporation of rGO at 0.5 and 1.0 mass% content, respectively. The effect of rGO particles on enhancing the shape memory properties of PLA was confirmed by the increases in the recovery rates (Rr) observed for the composites.