Nuclear Magnetic Resonance Diffusion Research Articles

Lanthanide Identity Governs Guest-Induced Dimerization in LnIII [15-MC N(L-pheHA) -5])3+ Metallacrowns.

Series of lanthanide-containing metallic coordination complexes are frequently presented as structurally analogous, due to the similar chemical and coordinative properties of the lanthanides. In the case of chiral (LnIII [15-MC N(L-pheHA) -5])3+ metallacrowns (MCs), which are well established supramolecular hosts, the formation of dimers templated by a dicarboxylate guest (muconate) in solution of neutral pH is herein shown to have a unique dependence on the identity of the MC's central lanthanide. Calorimetric data and nuclear magnetic resonance diffusion studies demonstrate that MCs containing larger or smaller lanthanides as the central metal only form monomeric host-guest complexes whereas analogues with intermediate lanthanides (for example, Eu, Gd, Dy) participate in formation of dimeric host-guest-host compartments. The driving force for the dimerization event across the series is thought to be a competition between formation of highly stable MCs (larger lanthanides) and optimally linked bridging guests (smaller lanthanides).

Explicit phenomenological solutions for magnetization exposed to an arbitrary NMR diffusion steady state pulse sequence.

Explicit phenomenological solutions to recurrence relations for the bulk transverse and longitudinal magnetization found using the Torrey-Bloch equations with relaxation effects are used to investigate nuclear magnetic resonance (NMR) diffusion measurements. Of particular interest are steady state NMR (self-)diffusion measurements that reduce experimental time that can extend the techniques to quickly reacting systems. The solutions for bulk transverse and longitudinal magnetization presented here are used to investigate the average behavior of the transverse and longitudinal magnetization in forming a steady state and are used to derive new expressions for the steady state longitudinal magnetization. These solutions can be applied to a noninteracting spin 1/2 ensemble undergoing free diffusion exposed to an arbitrary NMR pulse sequence containing arbitrary magnetic field gradient waveforms. The closed algebraic form method presented here has an advantage over iterative procedures for calculating transverse and longitudinal magnetization for the analysis and development of steady state pulse sequences. Previous theoretical results for steady state diffusion measurements are also reproduced. The Mathematica code for these solutions is provided in the supplementary material.

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

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.

Microstructural features assessment of different waterlogged wood species by NMR diffusion validated with complementary techniques

Wood is a hygroscopic, multi-scale and anisotropic natural material composed of pores with different size and differently oriented. In particular, archaeologically excavated wood generally is waterlogged wood with very high moisture content (400%–800%) that need to have a rapid investigation at the microstructural level to obtain the best treatment with preservative agents. Time-dependent diffusion coefficient D(t) quantified by Pulse Field Gradient (PFG) Nuclear Magnetic Resonance (NMR) techniques provides useful information about complex porous media, such as the tortuosity (τ) describing pore connectivity and fluid transport through media, the average-pore size, the anisotropic degree (an). However, diffusion NMR is intrinsically limited since it is an indirect measure of medium microstructure and relies on inferences from models and estimation of relevant diffusion parameters. Therefore, it is necessary to validate the information obtained from NMR diffusion parameters through complementary investigations. In this work, the structures of five waterlogged wood species were studied by PFG of absorbed water. D(t) and τ of water diffusing along and perpendicular to vessels/tracheids main axes together with relaxation times and an were quantified. From these parameters, the pore sizes distribution and the wood microstructure characterization were obtained. Results among wood species were compared, validated and integrated by micro-imaging NMR (μ-MRI), environmental-scanning electron-microscope (ESEM) images, wood dry density and imbibition times measurement of all woods. The work suggests that an vs τ rather than the estimated pore size diversifies and characterize the different wood species. As a consequence diffusion-anisotropy vs tortuosity could be an alternative method to characterize and differentiate wood species of waterlogged wood when high resolution images (μ-MRI and ESEM) are not available. Moreover, the combined use of D(t) and micro-MRI expands the scale of dimensions observable by NMR covering all the interesting length scales of wood.

Borehole measurements of adsorbed gas content in coals using stimulated diffusion nuclear magnetic resonance

We present an NMR measurement technique which has the unique ability to determine the in-situ adsorbed gas concentration within coal seams. The measurement of adsorbed gas content is of critical importance for operational safety and commercial resource evaluation in the development of coal mining operations and coal seam gas (CSG) resources. The current measurement technique involves laboratory core analysis, using a canister desorption measurement which is subject to significant measurement uncertainty due to the gas lost between coring and analysis. The NMR measurement technique enables in-situ measurement of fluid content within the coal seams without disturbing the coal seams. The technique utilises the stimulated echo diffusion editing (SEDE) pulse sequence which simultaneously captures relaxation and diffusion behaviour of fluids contained within coal seams. In this work, we have optimised the SEDE pulse sequence by using two diffusion times which are appropriate for capturing the diffusive behaviour of water and adsorbed gas. The measured signal captured by the SEDE sequence is inverted to provide a T2-StimD distribution. The appropriate interpretation of the T2-StimD distribution enables the determination of the free and adsorbed gas concentrations. The adsorbed gas concentration measured using the optimised SEDE sequence shows very good agreement with core canister desorption measurements. The sequence also enables the detection of free gas which is important for understanding the depressurisation of the coal seams and the impact on development strategies.

Interrogating the relationship between the microstructure of amphiphilic poly(ethylene glycol-b-caprolactone) copolymers and their colloidal assemblies using non-interfering techniques

Understanding the microstructural parameters of amphiphilic copolymers that control the formation and structure of aggregated colloids (e.g., micelles) is essential for the rational design of hierarchically structured systems for applications in nanomedicine, personal care and food formulations. Although many analytical techniques have been employed to study such systems, in this investigation we adopted an integrated approach using non-interfering techniques – diffusion nuclear magnetic resonance (NMR) spectroscopy, dynamic light scattering (DLS) and synchrotron small-angle X-ray scattering (SAXS) – to probe the relationship between the microstructure of poly(ethylene glycol-b-caprolactone) (PEG-b-PCL) copolymers [e.g., block molecular weight (MW) and the mass fraction of PCL (fPCL)] and the structure of their aggregates. Systematic trends in the self-assembly behaviour were determined using a large family of well-defined block copolymers with variable PEG and PCL block lengths (number-average molecular weights (Mn) between 2 and 10 and 0.5–15 kDa, respectively) and narrow dispersity (Ð < 1.12). For all of the copolymers, a clear transition in the aggregate structure was observed when the hydrophobic fPCL was increased at a constant PEG block Mn, although the nature of this transition is also dependent on the PEG block Mn. Copolymers with low Mn PEG blocks (2 kDa) were observed to transition from unimers and loosely associated unimers to metastable aggregates and finally, to cylindrical micelles as the fPCL was increased. In comparison, copolymers with PEG block Mn of between 5 and 10 kDa transitioned from heterogenous metastable aggregates to cylindrical micelles and finally, well-defined ellipsoidal micelles (of decreasing aspect ratios) as the fPCL was increased. In all cases, the diffusion NMR spectroscopy, DLS and synchrotron SAXS results provided complementary information and the grounds for a phase diagram relating copolymer microstructure to aggregation behaviour and structure. Importantly, the absence of commonly depicted spherical micelles has implications for applications where properties may be governed by shape, such as, cellular uptake of nanomedicine formulations.

Nuclear Magnetic Resonance Spectroscopy: A Multifaceted Toolbox to Probe Structure, Dynamics, Interactions, and Real-Time In Situ Release Kinetics in Peptide-Liposome Formulations.

Liposomal formulations represent attractive biocompatible and tunable drug delivery systems for peptide drugs. Among the tools to analyze their physicochemical properties, nuclear magnetic resonance (NMR) spectroscopy, despite being an obligatory technique to characterize molecular structure and dynamics in chemistry as well as in structural biology, yet appears to be rather sparsely used to study drug-liposome formulations. In this work, we exploited several facets of liquid-state NMR spectroscopy to characterize liposomal delivery systems for the apelin-derived K14P peptide and K14P modified by Nα-fatty acylation. Various liposome compositions and preparation modes were analyzed. Using NMR, in combination with cryo-electron microscopy and dynamic light scattering, we determined structural, dynamic, and self-association properties of these peptides in solution and probed their interactions with liposomes. Using 31P and 1H NMR, we characterized membrane fluidity and thermotropic phase transitions in empty and loaded liposomes. Based on diffusion and 1H NMR experiments, we localized and quantified peptides with respect to the interior/exterior of liposomes and changes over time and upon thermal treatments. Finally, we assessed the release kinetics of several solutes and compared various formulations. Taken together, this work shows that NMR has the potential to assist the design of peptide/liposome systems and more generally drug delivery systems.

Rechargeable Thin‐Film Lithium Microbattery Using a Quasi‐Solid‐State Polymer Electrolyte

AbstractA thin‐film microbattery was designed after synthesizing a unique gel polymer electrolyte (GPE), using polyvinylidene fluoride‐co‐hexafluoropropylene (PVdF‐HFP) and cross‐linked poly(ethylene oxide) (PEO), with an ionic liquid and salt (LiTFSI) mixture. The polymers resulted in a semi‐interpenetrated polymer network (semi‐IPN), hosting an ionic liquid (IL)/salt mixture, and thus exhibited high ionic conductivity and excellent mechanical properties. Nuclear magnetic resonance (NMR) diffusion measurements and relaxation rates analysis highlighted the existence of interactions between Li+ ions and oxygen within the polymers, preventing electrolyte leakage and ensuring excellent mechanical strength which enabled a unique quasi‐solid electrolyte. Such mechanical strength and chemical stability made this electrolyte to be first ever reported GPE to withstand thermal evaporation deposition and hence direct deposition of lithium metal. The electrolyte could be shaped as self‐standing thin films, and thus worked as both separator and electrolyte in a thin‐film lithium microbattery. The thin‐film microbattery exhibited excellent performances showing no short‐circuit current, an open circuit voltage of ∼3.0 V, higher nominal voltage plateau, lower equivalent series resistance by comparison to a thin‐film microbattery designed in conventional way with a popular ceramic electrolyte LiPON.

Direct observation of the active sites in methane dehydroaromatization by NMR

Direct observation of the active sites in methane dehydroaromatization by NMR

Study of the premicellar state in aqueous solutions of sodium dodecyl sulfate by nuclear magnetic resonance diffusion.

Self-diffusion coefficients of sodium dodecyl sulfate (SDS) were measured in aqueous solutions in the premicellar range of the SDS concentrations 7-34.7 mM and temperatures 30-90°C. Average effective hydrodynamic radii and aggregation numbers of SDS in the premicellar region were determined. At C < CMC at all temperatures, the SDS solution is the solution of monomers. At C > CMC, the increase of temperature leads to decrease in the effective hydrodynamic radii and the average aggregation numbers. At C > > CMC, it is impossible to reach the monomeric state by increasing the temperature.

Physicochemical aspects of zwitterionic core-shell tecto dendrimers characterized by a thorough NMR investigation

Core-shell tecto dendrimers (CSTDs) are a class of superstructured dendrimeric nanoconstructs with similar structural characteristics and biomedical performances to the high-generation dendrimers that can be decorated with zwitterions to be availed of good antifouling properties for different biomedical applications. Characterization of the CSTD-based dendrimeric derivatives remains to be a great challenge. Here, we attempted to utilize nuclear magnetic resonance (NMR) technologies to investigate the structure and hydrodynamic size of CSTDs functionalized with zwitterionic carboxybetaine acrylamide (CBAA) and confirmed their antifouling property through protein resistance assay. In this study, we initially prepared CSTDs by supramolecular assembly of beta-cyclodextrin (β-CD)-modified generation 5 (G5) poly(amidoamine) (PAMAM) dendrimers as cores and adamantane (Ad)-decorated G3 PAMAM dendrimers as shells, and then partially modified the CSTD terminal amines with CBAA. The dendrimeric products were thoroughly characterized. Our results show that the obtained CSTDs display strong correlation signals between the Ad and β-CD protons in the two-dimensional NMR spectrum, indicating the strong host-guest interaction existing between G3-Ad and G5-CD in the structure of CSTDs. Diffusion NMR measurements reveal that the hydrodynamic diameter of CSTDs is smaller after partial CBAA surface modification, possibly due to the tightened molecular volume after zwitterionic modification. Lastly, the CBAA-modified CSTDs were demonstrated to have good antifouling property through protein resistance assay. Our findings provide a new strategy to study the framework of the developed CSTDs and CBAA-modified CSTDs, facilitating their further design and surface modification for various biomedical applications.

Effect of CO2-brine-rock reactions on pore architecture and permeability in dolostone: Implications for CO2 storage and EOR

Geologic carbon sequestration (GCS) is considered a feasible technology for storing substantive volumes of greenhouse gases in subsurface geological formations. In the reservoir, far from carbon dioxide (CO2) injection wells or in post-injection scenarios, diffusion dominates over advection. This condition conjoins with spatially distributed geochemical reactions to induce heterogeneous changes in pore architecture, i.e. pore body and throat sizes or surface roughness. These changes can affect CO2 transport properties and storage capacity. In this work, we investigated mineral dissolution and precipitation in dolomite samples saturated with a CO2-saturated brine at 93 °C and 34.5 MPa, aged without flow. Two rock types samples, i.e. intergranular- and vuggy-dominant, were selected to investigate changes in pore size, porosity and permeability under reactive conditions. Mineral dissolution and precipitation were characterized using scanning electron microscopy. Changes in pore size were quantified via time-domain nuclear magnetic resonance (TD-NMR) transverse relaxation time (T2) and diffusion coefficient (D) distributions. We show that mineral dissolution likely occurs in highly permeable pathways. These observations are confirmed through analysis of (T2) and diffusion coefficient (D) distributions. In contrast to results during CO2-enriched brine continuous injection, mineral precipitation was observed in micropores. The leftward shift of the T2 peaks, corresponding to micropores, also evidenced mineral precipitation in low-permeability zones. However, microscale alterations resulted only in a subtle increase in porosity and permeability. Results in this study shed light on effects of geochemical reactions on alteration of rock properties in diffusion-dominated regions during CO2 storage.

Determining the effect of dissolved CO2 on solution phase Li+ diffusion in common Li-ion battery electrolytes

Electrolyte decomposition in Li-ion batteries (LIB) and its entailing gas evolution significantly impacts cell performance. CO2 is one of the most abundantly evolved gases from common LIB electrolytes and could potentially affect Li+ solution transport during LIB operation. To this end, a comparative analysis of the Li+ diffusion coefficient (DLi+) which governs mass transport is required. Herein a methodology is established to saturate common battery electrolytes with a soluble gas without introducing other contaminants, so as to determine DLi+ in saturated and unsaturated samples. As a proof of concept, the values of DLi+ are determined in 1 M LiPF6 and 1 M LiClO4 in ethylene carbonate (EC):dimethyl carbonate (DMC) with and without dissolved CO2, confirmed by gas chromatography–mass spectrometry (GC–MS). The results obtained by pulse field gradient nuclear magnetic resonance (PFG-NMR) diffusion measurements agree for both electrolytes; saturating the electrolyte with CO2 has no measurable effect on DLi+ and therefore does not hinder Li+ mass transport.

1-D fractal model for bentonite colloid diffusion without seepage

This paper investigates the 1-D diffusion process of bentonite particle, which is affected by the friction related to the fractal structure of colloid pore. The expression of the pore tortuosity containing pore fractal dimension is deduced to determine the friction, and the evolution rule of pore fractal dimension during diffusion with bentonite volume fraction is reached. The rationality of the modified fractal model is validated via 1-D diffusion test and nuclear magnetic resonance (NMR). Then the influences of electrolyte concentration, initial volume fraction of bentonite, and surface charge density on the colloid diffusion process are analyzed. The results show that the diffusion of bentonite decreases with the increase of electrolyte concentration, and increases with the increase of initial volume fraction and surface charge density. The interfacial volume fraction is correlated with the concentration of electrolyte solution, but not with the initial volume fraction and surface charge density.

Bacterial Cell Wall Analogue Peptides Control the Oligomeric States and Activity of the Glycopeptide Antibiotic Eremomycin: Solution NMR and Antimicrobial Studies.

For some time, glycopeptide antibiotics have been considered the last line of defense against Methicillin-resistant Staphylococcus aureus (MRSA). However, vancomycin resistance of Gram-positive bacteria is an increasingly emerging worldwide health problem. The mode of action of glycopeptide antibiotics is essentially the binding of peptidoglycan cell-wall fragments terminating in the d-Ala-d-Ala sequence to the carboxylate anion binding pocket of the antibiotic. Dimerization of these antibiotics in aqueous solution was shown to persist and even to enhance the antibacterial effect in a co-operative manner. Some works based on solid state (ss) Nuclear Magnetic Resonance (NMR) studies questioned the presence of dimers under the conditions of ssNMR while in a few cases, higher-order oligomers associated with contiguous back-to-back and face-to-face dimers were observed in the crystal phase. However, it is not proved if such oligomers persist in aqueous solutions. With the aid of 15N-labelled eremomycin using 15N relaxation and diffusion NMR methods, we observed tetramers and octamers when the N-Ac-d-Ala-d-Ala dipeptide was added. To the contrary, the N-Ac-d-Ala or (N-Ac)2-l-Lys-d-Ala-d-Ala tripeptide did not induce higher-order oligomers. These observations are interesting examples of tailored supramolecular self-organization. New antimicrobial tests have also been carried out with these self-assemblies against MRSA and VRE (resistant) strains.

Comment on "Boosted molecular mobility during common chemical reactions".

The apparent "boosted mobility" observed by Wang et al (Reports, 31 July 2020, p. 537) is the result of a known artifact. When signal intensities are changing during a nuclear magnetic resonance (NMR) diffusion measurement for reasons other than diffusion, the use of monotonically increasing gradient amplitudes produces erroneous diffusion coefficients. We show that no boosted molecular mobility is observed when shuffled gradient amplitudes are applied.

Determining chemical exchange rate constants in nanoemulsions using nuclear magnetic resonance.

In this work, the second-order kinetics of molecules exchanging between chemically distinct microenvironments, such as those found in nanoemulsions, is studied using nuclear magnetic resonance (NMR). A unique aspect of NMR exchange studies in nanoemulsions is that the difference in molecular resonance frequencies between the two phases, which determines whether the exchange is fast, intermediate, or slow on the NMR timescale, can depend upon the emulsion droplet composition, which is also determined by the kinetic exchange constants themselves. Within the fast-exchange regime, changes in resonance frequencies and line widths with dilution were used to extract the exchange rate constants from the NMR spectra in a manner analogous to determining the kinetic parameters in NMR ligand binding experiments. As a demonstration, the kinetic exchange parameters of isoflurane release from an emulsification of isoflurane and perflurotributylamine (FC43) were determined using NMR dilution and diffusion studies.

On Complex Formation between 5-Fluorouracil and β-Cyclodextrin in Solution and in the Solid State: IR Markers and Detection of Short-Lived Complexes by Diffusion NMR.

In this work, the nuclear magnetic resonance (NMR) and IR spectroscopic markers of the complexation between 5-fluorouracil (5-FU) and β-cyclodextrin (β-CD) in solid state and in aqueous solution are investigated. In the attenuated total reflectance(ATR) spectra of 5-FU/β-CD products obtained by physical mixing, kneading and co-precipitation, we have identified the two most promising marker bands that could be used to detect complex formations: the C=O and C-F stretching bands of 5-FU that experience a blue shift by ca. 8 and 2 cm−1 upon complexation. The aqueous solutions were studied by NMR spectroscopy. As routine NMR spectra did not show any signs of complexation, we have analyzed the diffusion attenuation of spin–echo signals and the dependence of the population factor of slowly diffusing components on the diffusion time (diffusion NMR of pulsed-field gradient (PFG) NMR). The analysis has revealed that, at each moment, ~60% of 5-FU molecules form a complex with β-CD and its lifetime is ca. 13.5 ms. It is likely to be an inclusion complex, judging from the independence of the diffusion coefficient of β-CD on complexation. The obtained results could be important for future attempts of finding better methods of targeted anticancer drug delivery.

Revealing Molecular Mechanisms in Hierarchical Nanoporous Carbon via Nuclear Magnetic Resonance

Author(s): Mao, H; Tang, J; Xu, J; Peng, Y; Chen, J; Wu, B; Jiang, Y; Hou, K; Chen, S; Wang, J; Lee, HR; Halat, DM; Zhang, B; Chen, W; Plantz, AZ; Lu, Z; Cui, Y; Reimer, JA | Abstract: Hierarchical nanoporous carbons combining pore sizes of different length scales are highly important for separation processes. However, critical questions remain regarding the hierarchical structure regulation and the molecular mechanisms of gaseous adsorbate uptake and interactions within the hierarchical nanoporous carbons. These materials present characterization challenges in that there are no experimental techniques that can elucidate the molecular mechanisms of the organic compounds and CO within the materials. We deployed multidimensional solid-state nuclear magnetic resonance (NMR) to generate maps of guest-framework interactions as a function of adsorbate concentrations and adsorption times. The NMR spectra provide insight toward the design of effective hierarchical pore structures. Our materials show a high volatile organic compounds/CO physisorption capacity, which reveals promising application to carbon-capture strategies to mitigate global warming. 2 2

Magic-angle-spinning-induced local ordering in polymer electrolytes and its effects on solid-state diffusion and relaxation NMR measurements.

Magic-angle-spinning (MAS) enhances sensitivity and resolution in solid-state nuclear magnetic resonance (NMR) measurements. MAS is obtained by aerodynamic levitation and drive of a rotor, which results in large centrifugal forces that may affect the physical state of soft materials, such as polymers, and subsequent solid-state NMR measurements. Here, we investigate the effects of MAS on the solid-state NMR measurements of a polymer electrolyte for lithium-ion battery applications, poly(ethylene oxide) (PEO) doped with the lithium salt LiTFSI. We show that MAS induces local chain ordering, which manifests itself as characteristic lineshapes with doublet-like splittings in subsequent solid-state 1 H, 7 Li, and 19 F static NMR spectra characterizing the PEO chains and solvated ions. MAS results in distributions of stresses and hence local chain orientations within the rotor, yielding distributions in the local magnetic susceptibility tensor that give rise to the observed NMR anisotropy and lineshapes. The effects of MAS were investigated on solid-state 7 Li and 19 F pulsed-field-gradient (PFG) diffusion and 7 Li longitudinal relaxation NMR measurements. Activation energies for ion diffusion were affected modestly by MAS. 7 Li longitudinal relaxation rates, which are sensitive to lithium-ion dynamics in the nanosecond regime, were essentially unchanged by MAS. We recommend that NMR researchers studying soft polymeric materials use only the spin rates necessary to achieve the desired enhancements in sensitivity and resolution, as well as acquire static NMR spectra after MAS experiments to reveal any signs of stress-induced local ordering.