The interpretation of small molecule diffusion coefficients: Quantitative use of diffusion-ordered NMR spectroscopy

Molecular localization and exchange kinetics in pharmaceutical liposome and mRNA lipoplex nanoparticle products determined by small angle X-ray scattering and pulsed field gradient NMR diffusion measurements

We have used pulsed field gradient (PFG)-NMR diffusion experiments, also known as DOSY, in combination with small angle X-ray scattering measurements to investigate structure and molecular exchange dynamics between pharmaceutical lipid nanoparticles and the bulk phase. Using liposomes and lipoplexes formed after complexation of the liposomes with messenger mRNA as test systems, information on dynamics of encapsulated water molecules, lipids and excipients was obtained. The encapsulated fraction, having a diffusivity similar to that of the liposomes, could be clearly identified and quantified by the NMR diffusion measurements. The unilamellar liposome membranes allowed a fast exchange of water molecules, while sucrose, used as an osmolyte and model solute, showed very slow exchange. Upon interactions with mRNA a topological transition from a vesicular to a lamellar organization took place, where the mRNA was inserted in repeating lipid bilayer stacks. In the lipoplexes, a small fraction of tightly bound water molecules was present, with a diffusivity that was influenced by the additional presence of sucrose. This extended information on dynamic coherencies inside pharmaceutical nanoparticle products, provided by the combined application of SAXS and PFG-NMR diffusion measurements, can be valuable for evaluation of quality and comparability of nanoscaled pharmaceuticals.

Possibilities and limitations of solution-state NMR spectroscopy to analyze the ligand shell of ultrasmall metal nanoparticles

Ultrasmall nanoparticles have a diameter between 1 and 3 nm at the border between nanoparticles and large molecules. Usually, their core consists of a metal, and the shell of a capping ligand with sulfur or phosphorus as binding atoms. While the core structure can be probed by electron microscopy, electron and powder diffraction, and single-crystal structure analysis for atom-sharp clusters, it is more difficult to analyze the ligand shell. In contrast to larger nanoparticles, ultrasmall nanoparticles cause only a moderate distortion of the NMR signal, making NMR spectroscopy a qualitative as well as a quantitative probe to assess the nature of the ligand shell. The application of isotope-labelled ligands and of two-dimensional NMR techniques can give deeper insight into ligand-nanoparticle interactions. Applications of one- and two-dimensional NMR spectroscopy to analyze ultrasmall nanoparticles are presented with suitable examples, including a critical discussion of the limitations of NMR spectroscopy on nanoparticles.

A Squaramide-Based Organocatalyst as a Novel Versatile Chiral Solvating Agent for Carboxylic Acids

A squaramide-based organocatalyst for asymmetric Michael reactions has been tested as a chiral solvating agent (CSA) for 26 carboxylic acids and camphorsulfonic acid, encompassing amino acid derivatives, mandelic acid, as well as some of its analogs, propionic acids like profens (ketoprofen and ibuprofen), butanoic acids and others. In many cases remarkably high enantiodifferentiations at 1H, 13C and 19F nuclei were observed. The interaction likely involves a proton transfer from the acidic substrates to the tertiary amine sites of the organocatalyst, thus allowing for pre-solubilization of the organocatalyst (when a chloroform solution of the substrate is employed) or the simultaneous solubilization of both the catalyst and the substrate. DOSY experiments were employed to evaluate whether the catalyst-substrate ionic adduct was a tight one or not. ROESY experiments were employed to investigate the role of the squaramide unit in the adduct formation. A mechanism of interaction was proposed in accordance with the literature data.

A Broadened Class of Donor-Acceptor Stacked Macrometallacyclic Adducts of Different Coinage Metals

A yet-outstanding supramolecular chemistry challenge is isolation of novel varieties of stacked complexes with finely-tuned donor-acceptor bonding and optoelectronic properties, as herein reported for binary adducts comprising two different cyclic trinuclear complexes (CTC@CTC'). Most previous attempts focused only on 1-2 factors among metal/ligand/substituent combinations, resulting in heterobimetallic complexes. Instead, here we show that, when all 3 factors are carefully considered, a broadened variety of CTC@CTC' stacked pairs with intuitively-enhanced intertrimer coordinate-covalent bonding strength and ligand-ligand/metal-ligand dispersion are attained (dM-M' 2.868(2) Å; ΔE>50 kcal/mol, an order of magnitude higher than aurophilic/metallophilic interactions). Significantly, CTC@CTC' pairs remain intact/strongly-bound even in solution (Keq 4.67×105 L/mol via NMR/UV-vis titrations), and the gas phase (mass spectrometry revealing molecular peaks for the entire CTC@CTC' units in sublimed samples), rather than simple co-crystal formation. Photo-/electro-luminescence studies unravel metal-centered phosphorescence useful for novel all metal-organic light-emitting diodes (MOLEDs) optoelectronic device concepts. This work manifests systematic design of supramolecular bonding and multi-faceted spectral properties of pure metal-organic macrometallacyclic donor/acceptor (inorganic/inorganic) stacks with remarkably-rich optoelectronic properties akin to well-established organic/organic and organic/inorganic analogues.

Affinity of Telluronium Chalcogen Bond Donors for Lewis Bases in Solution: A Critical Experimental-Theoretical Joint Study

Telluronium salts [Ar2 MeTe]X were synthesized, and their Lewis acidic properties towards a number of Lewis bases were addressed in solution by physical and theoretical means. Structural X-ray diffraction analysis of 21 different salts revealed the electrophilicity of the Te centers in their interactions with anions. Telluroniums' propensity to form Lewis pairs was investigated with OPPh3 . Diffusion-ordered NMR spectroscopy suggested that telluroniums can bind up to three OPPh3 molecules. Isotherm titration calorimetry showed that the related heats of association in 1,2-dichloroethane depend on the electronic properties of the substituents of the aryl moiety and on the nature of the counterion. The enthalpies of first association of OPPh3 span -0.5 to -5 kcal mol-1 . Study of the affinity of telluroniums for OPPh3 by state-of-the-art DFT and ab-initio methods revealed the dominant Coulombic and dispersion interactions as well as an entropic effect favoring association in solution. Intermolecular orbital interactions between [Ar2 MeTe]+ cations and OPPh3 are deemed insufficient on their own to ensure the cohesion of [Ar2 MeTe ⋅ Bn ]+ complexes in solution (B=Lewis base). Comparison of Grimme's and Tkatchenko's DFT-D4/MBD-vdW thermodynamics of formation of higher [Ar2 MeTe ⋅ Bn ]+ complexes revealed significant molecular size-dependent divergence of the two methodologies, with MBD yielding better agreement with experiment.

Are "Carbon Dots" Always Carbon Dots? Evidence for their Supramolecular Nature from Structural and Dynamic Studies in Solution and in the Pure Solid

A model for the morphology (size, shape, and crystallinity) of carbon dots (CDs) in the solid state consistent with the observed photoluminescence in solution is proposed herein. Overwhelming evidence has been collected that links the data coming from solid-state analysis (high-resolution transmission electron microscopy (HRTEM), atomic force microscopy (AFM), and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS)) to that of solution (pulsed-field gradient (PFG)-NMR spectroscopy, time-resolved fluorescence anisotropy (TRFA), and steady-state/time-resolved fluorescence), allowing the establishment of an overall structural model for CDs. According to this model, the so-called carbon dots, observed under HRTEM imaging, are in fact supramolecular organized structures dynamically assembled from small to medium-sized molecular species when the solvent is removed to give the solid form. In this way, the imaged nanoparticles (TEM/AFM) are not covalently bound entities formed during the synthetic process, but instead supramolecular entities formed by noncovalent interactions. These particles, if at all present in solution, have the form of loose associations of relatively small molecules. This study was conducted on CDs obtained from the hydrothermal carbonization (HTC) of a biomass waste (olive wet pomace).

Review on NMR as a tool to analyse natural products extract directly: Molecular structure elucidation and biological activity analysis

INTRODUCTION

Natural products, the small organic molecules produced by plants, microbes and invertebrates, often present in the form of a mixture, this leads to the structural characterisation of natural extracts often requiring time-consuming multistep purification procedures. Nuclear magnetic resonance (NMR) technology is traditionally utilised as a tool for the structural elucidation of pure compounds. Contemporarily, an up-to-date trend in the application of NMR in natural product research is shifting to the direct NMR analysis of crude mixtures, to obtain molecular structure and biological activity information without performing cumbersome separation.

OBJECTIVE

To review works of literature on the evolution, principle and progress of NMR technologies for analysing mixtures, we focus on the successful application of NMR technologies in direct analysis of natural product extracts.

METHODOLOGY

Based on our research experience, academic tracking and extensive literature search, which involved, but not limited to, the use of various databases, like Web of Knowledge and PubMed. The keywords used, in various combinations, to retrieve recent literature on the successful application of NMR technologies to sheer natural product extracts, and excluded artificially natural product mixture and biofluid.

RESULTS

NMR technologies for direct natural extracts analysis, including two-dimensional J-resolved spectroscopy (2D-JRES), pure shift NMR, diffusion-ordered NMR spectroscopy (DOSY), statistical correlation spectroscopy (STOCSY), concentration-ordered NMR spectroscopy (CORDY), saturation transfer difference (STD) and water-ligand observed via gradient spectroscopy (WaterLOGSY) were illustrated.

CONCLUSIONS

By these methods, molecular structure and biological activity information will be directly obtained from NMR analysis of natural products extract, aiming to save experimental time and expenses.

Tracking nitrite's deviation from Stokes-Einstein predictions with pulsed field gradient 15N NMR spectroscopy

Predicting the behavior of oxyanions in radioactive waste stored at the Department of Energy legacy nuclear sites requires the development of novel analytical methods. This work demonstrates 15N pulsed field gradient nuclear magnetic resonance spectroscopy to quantify the diffusivity of nitrite. Experimental results, supported by molecular dynamics simulations, indicate that the diffusivity of free hydrated nitrite exceeds that of free hydrated sodium despite the greater hydrodynamic radius of nitrite. Investigations are underway to understand how the compositional and dynamical heterogeneities of the ion networks at high concentrations affect rheological and transport properties.

Predicting Gaseous Solute Diffusion in Viscous Multivalent Ionic Liquid Solvents

Calculating solute diffusion in dense, viscous solvents can be particularly challenging in molecular dynamics simulations due to the long time scales involved. Here, a new scaling approach is developed for predicting solute diffusion based on analyses of CO2 and SO2 diffusion in two different multivalent ionic liquid solvents. Various scaling approaches are initially evaluated, including single and separate thermostats for the solute and solvent, as well as the application of the Arrhenius relationship and the Speedy-Angell power law. A very strong logarithmic correlation is established between the solvent-accessible surface area and solute diffusion. This relationship, reflecting Danckwerts' surface renewal theory and the Vrentas-Duda free volume model, presents a valuable method for estimating diffusion behavior from short simulation trajectories at elevated temperatures. The approach may be beneficial for enhancing predictive modeling in similar challenging systems and should be more broadly evaluated.

Diffusion-Ordered Spectroscopy (DOSY) as a Powerful NMR Method to Investigate Molecular Mobilities and Intermolecular Interactions in Complex Oil Mixtures

Studying the characteristics and molecular mechanisms of liquid self-diffusion coefficient and viscosity changes is of great significance for, e. g., chemical and petroleum processing. As examples of highly complex liquid,an asphaltene-free high-acid and high-viscosity crude oil and its extracted fractions were studied by comparing their 1 H DOSY diffusion maps. The crude oil exhibited a polydisperse diffusion distribution, including multiple diffusion portions with diffusion coefficients much smaller than that of any single fraction in independent diffusion. The main mechanism that leads to the decreases in the diffusion coefficients of crude oil is attributed to diffusion resistance enhanced by Dynamical Molecular-Interaction Networks (DMINs), rather than by enlargement of the diffusion species caused by molecular aggregation. Constructed through the synergistic interactions of various polar molecules in crude oil, DMINs dynamically bind polar molecules, trap polarizable molecules, and spatially hinder the free motion of non-polar molecules. Overall, this reduces the mobility of all molecular species, as illustrated by the decreased diffusion coefficients. This study demonstrates that DOSY is a powerful NMR method to investigate molecular motion abilities also in complex mixtures. In addition, the insights in the influence of the interaction matrix on the molecular mobility also help to understand the contribution of "structural viscosity" to the viscosity of heavy oil.

Hypersensitive MR angiography based on interlocking stratagem for diagnosis of cardiac-cerebral vascular diseases

Magnetic resonance (MR) angiography is one of the main diagnostic approaches for cardiac-cerebral vascular diseases. Nevertheless, the non-contrast-enhanced MR angiography suffers from its intrinsic problems derived from the blood flow-dependency, while the clinical Gd-chelating contrast agents are limited by their rapid vascular extravasation. Herein, we report a hypersensitive MR angiography strategy based on interlocking stratagem of zwitterionic Gd-chelate contrast agents (PAA-Gd). The longitudinal molar relaxivity of PAA-Gd was 4.6-times higher than that of individual Gd-chelates as well as appropriate blood half-life (73.8 min) and low immunogenicity, enabling sophisticated micro-vessels angiography with a resolution at the order of hundred micrometers. A series of animal models of cardiac-cerebrovascular diseases have been built for imaging studies on a 7.0 T MRI scanner, while the clinical translation potential of PAA-Gd has been evaluated on swine on a 3.0 T clinical MRI scanner. The current studies offer a promising strategy for precise diagnosis of vascular diseases.

Raman Diffusion-Ordered Spectroscopy

The Stokes-Einstein relation, which relates the diffusion coefficient of a molecule to its hydrodynamic radius, is commonly used to determine molecular sizes in chemical analysis methods. Here, we combine the size sensitivity of such diffusion-based methods with the structure sensitivity of Raman spectroscopy by performing Raman diffusion-ordered spectroscopy (Raman-DOSY). The core of the Raman-DOSY setup is a flow cell with a Y-shaped channel containing two inlets: one for the sample solution and one for the pure solvent. The two liquids are injected at the same flow rate, giving rise to two parallel laminar flows in the channel. After the flow stops, the solute molecules diffuse from the solution-filled half of the channel into the solvent-filled half at a rate determined by their hydrodynamic radius. The arrival of the solute molecules in the solvent-filled half of the channel is recorded in a spectrally resolved manner by Raman microspectroscopy. From the time series of Raman spectra, a two-dimensional Raman-DOSY spectrum is obtained, which has the Raman frequency on one axis and the diffusion coefficient (or equivalently, hydrodynamic radius) on the other. In this way, Raman-DOSY spectrally resolves overlapping Raman peaks arising from molecules of different sizes. We demonstrate Raman-DOSY on samples containing up to three compounds and derive the diffusion coefficients of small molecules, proteins, and supramolecules (micelles), illustrating the versatility of Raman-DOSY. Raman-DOSY is label-free and does not require deuterated solvents and can thus be applied to samples and matrices that might be difficult to investigate with other diffusion-based spectroscopy methods.

Self-Diffusion in Confined Water: A Comparison between the Dynamics of Supercooled Water in Hydrophobic Carbon Nanotubes and Hydrophilic Porous Silica

Confined liquids are model systems for the study of the metastable supercooled state, especially for bulk water, in which the onset of crystallization below 230 K hinders the application of experimental techniques. Nevertheless, in addition to suppressing crystallization, confinement at the nanoscale drastically alters the properties of water. Evidently, the behavior of confined water depends critically on the nature of the confining environment and the interactions of confined water molecules with the confining matrix. A comparative study of the dynamics of water under hydrophobic and hydrophilic confinement could therefore help to clarify the underlying interactions. As we demonstrate in this work using a few representative results from the relevant literature, the accurate assessment of the translational mobility of water molecules, especially in the supercooled state, can unmistakably distinguish between the hydrophilic and hydrophobic nature of the confining environments. Among the numerous experimental methods currently available, we selected nuclear magnetic resonance (NMR) in a field gradient, which directly measures the macroscopic translational self-diffusion coefficient, and quasi-elastic neutron scattering (QENS), which can determine the microscopic translational dynamics of the water molecules. Dielectric relaxation, which probes the re-orientational degrees of freedom, are also discussed.

Supramolecular interactions between ethylene-bridged oligoureas: nanorings and chains formed by cooperative positive allostery

Ethylene-bridged oligoureas are dynamic foldamers in which the polarity of a coherent chain of intramolecular hydrogen bonds may be controlled by intra- or intermolecular interactions with hydrogen-bond donors or acceptors. In this paper, we describe the way that supramolecular interactions between ethylene-bridged oligoureas bearing a 3,5-bis(trifluoromethyl)phenylurea (BTMP) terminus leads to higher-order structures both in the crystalline state and in solution. The oligoureas self-assemble by head-to-tail hydrogen bonding interactions to form either supramolecular 'nanorings' with cyclic hydrogen bond chain directionality, or supramolecular helical chains of hydrogen bonds. The self-assembly process features a cascade of cooperative positive allostery, in which each intermolecular hydrogen bond formation at the BTMP terminus switches the native hydrogen bond chain directionality of monomers, favouring further assembly. Monomers with a benzyl urea terminus self-assemble into nanorings, whereas monomers with a N-ethyl urea terminus form helical chains. In the crystal state, parallel helices have identical handedness and polarity, whereas antiparallel helices have opposite handedness. The overall dipole moment of crystals is zero due to the antiparallel arrangements of local dipoles in the crystal packing. Supramolecular interactions in solution were also examined by VT and DOSY NMR spectroscopy, up to the point of crystal formation. The size of higher aggregates in dichloromethane was estimated by their hydrodynamic radius. The relative orientation of the monomers within the aggregates, determined by 2D ROESY NMR, was the same as in the crystals, where syn-orientations lead to the formation of rings and anti-orientations result in chains. Overall, the switch of hydrogen bond polarity propagates intermolecularly in crystal and solution states, constituting an example of intermolecular communication within supramolecular polymers.

Prediction of self-diffusion coefficients of chemically diverse pure liquids by all-atom molecular dynamics simulations

Molecular self-diffusion coefficients underlie various kinetic properties of the liquids involved in chemistry, physics, and pharmaceutics. In this study, 547 self-diffusion coefficients are calculated based on all-atom molecular dynamics (MD) simulations of 152 diverse pure liquids at various temperatures employing the OPLS4 force field. The calculated coefficients are compared with experimental data (424 extracted from the literature and 123 newly measured by pulsed-field gradient nuclear magnetic resonance). The calculations well agree with the experimental values. The determination coefficient and root mean square error between the observed and calculated logarithmic self-diffusion coefficients of the 547 entries are 0.931 and 0.213, respectively, demonstrating that the MD calculation can be an excellent industrial tool for predicting, for example, molecular transportation in liquids such as the diffusion of active ingredients in biological and pharmaceutical liquids. The self-diffusion coefficients collected in this study are compiled into a database for broad researches including artificial intelligence calculations.

Diffusion coefficient and power spectrum of active particles with a microscopically reversible mechanism of self-propelling

Catalytically active macromolecules are envisioned as key building blocks in development of artificial nanomotors. However, theory and experiments report conflicting findings regarding their dynamics. The lack of consensus is mostly caused by a limited understanding of specifics of self-propulsion mechanisms at the nanoscale. Here, we study a generic model of a self-propelled nanoparticle that does not rely on a particular mechanism. Instead, its main assumption is the fundamental symmetry of microscopic dynamics of chemical reactions: the principle of microscopic reversibility. Significant consequences of this assumption arise if we subject the particle to an action of an external time-periodic force. The particle diffusion coefficient is then enhanced compared to the unbiased dynamics. The enhancement can be controlled by the force amplitude and frequency. We also derive the power spectrum of particle trajectories. Among new effects stemming from the microscopic reversibility are the enhancement of the spectrum at all frequencies and sigmoid-shaped transitions and a peak at characteristic frequencies of rotational diffusion and external forcing. The microscopic reversibility is a generic property of a broad class of chemical reactions, therefore we expect that the presented results will motivate new experimental studies aimed at testing of our predictions. This could provide new insights into dynamics of catalytic macromolecules.

Ultrafast 2D NMR for the analysis of complex mixtures

2D NMR is extensively used in many different fields, and its potential for the study of complex biochemical or chemical mixtures has been widely demonstrated. 2D NMR gives the ability to resolve peaks that overlap in 1D spectra, while providing both structural and quantitative information. However, complex mixtures are often analysed in situations where the data acquisition time is a crucial limitation, due to an ongoing chemical reaction or a moving sample from a hyphenated technique, or to the high-throughput requirement associated with large sample collections. Among the great diversity of available fast 2D methods, ultrafast (or single-scan) 2D NMR is probably the most general and versatile approach for complex mixture analysis. Indeed, ultrafast NMR has undergone an impressive number of methodological developments that have helped turn it into an efficient analytical tool, and numerous applications to the analysis of mixtures have been reported. This review first summarizes the main concepts, features and practical limitations of ultrafast 2D NMR, as well as the methodological developments that improved its analytical potential. Then, a detailed description of the main applications of ultrafast 2D NMR to mixture analysis is given. The two major application fields of ultrafast 2D NMR are first covered, i.e., reaction/process monitoring and metabolomics. Then, the potential of ultrafast 2D NMR for the analysis of hyperpolarized mixtures is described, as well as recent developments in oriented media. This review focuses on high-resolution liquid-state 2D experiments (including benchtop NMR) that include at least one spectroscopic dimension (i.e., 2D spectroscopy and DOSY) but does not cover in depth applications without spectral resolution and/or in inhomogeneous fields.

Monitoring Protein Global and Local Parameters in Unfolding and Binding Studies: The Extended Applicability of the Diffusion Coefficient─Molecular Size Empirical Relations

Protein unfolding and denaturation are main issues in biochemical and pharmaceutical research. Using a global parameter, the translational diffusion coefficient D, folded, unfolded, and intrinsically disordered proteins of a given molar mass M can be distinguished based on their distinct hydrodynamic properties. For broader applications, we provide generalized, PFG-NMR-based empirical D-M relations validated at different temperatures and ready to use with the corresponding corrections in different media. We demonstrate that these relations enable a more accurate molecular mass determination and show fewer potential errors than those of the common methods based on small-molecular diffusion standards. We monitor unfolding of three model proteins using 8 M urea and dimethyl sulfoxide (DMSO)-water mixtures as denaturing agents, highlighting the effect of disulfide bonds. Denaturation in 8 M urea is pH-dependent; in addition, for proteins with highly stable disulfide bonds, a reducing agent (TCEP) is required to achieve complete unfolding. Regarding the effect of local parameters, we show that at low DMSO concentrations─common conditions in pharmaceutical binding studies─the PFG-NMR-derived global parameters are not significantly affected. Still, the atomic environments can change, and the bound solvent molecule can inhibit the binding of a partner molecule. Using proteins with natural isotopic abundance, this effect can be proven by fast ¹H-¹⁵N 2D correlation spectra. Our results enable fast and easy estimation of protein molecular mass and the degree of folding in various media; moreover, the effect of the cosolvent on the atomic-level structure can be traced without the need of isotope labeling.

Mechanistic analysis by NMR spectroscopy: A users guide

A 'principles and practice' tutorial-style review of the application of solution-phase NMR in the analysis of the mechanisms of homogeneous organic and organometallic reactions and processes. This review of 345 references summarises why solution-phase NMR spectroscopy is uniquely effective in such studies, allowing non-destructive, quantitative analysis of a wide range of nuclei common to organic and organometallic reactions, providing exquisite structural detail, and using instrumentation that is routinely available in most chemistry research facilities. The review is in two parts. The first comprises an introduction to general techniques and equipment, and guidelines for their selection and application. Topics include practical aspects of the reaction itself, reaction monitoring techniques, NMR data acquisition and processing, analysis of temporal concentration data, NMR titrations, DOSY, and the use of isotopes. The second part comprises a series of 15 Case Studies, each selected to illustrate specific techniques and approaches discussed in the first part, including in situ NMR (^1/2H, ^10/11B, ¹³C, ¹⁵N, ¹⁹F, ²⁹Si, ³¹P), kinetic and equilibrium isotope effects, isotope entrainment, isotope shifts, isotopes at natural abundance, scalar coupling, kinetic analysis (VTNA, RPKA, simulation, steady-state), stopped-flow NMR, flow NMR, rapid injection NMR, pure shift NMR, dynamic nuclear polarisation, ¹H/¹⁹F DOSY NMR, and in situ illumination NMR.

27 Al NMR diffusometry of Al13 Keggin nanoclusters

Although nanometer-sized aluminum hydroxide clusters (i.e., ϵ-Al₁₃ , [Al₁₃ O₄ (OH)₂₄ (H₂ O)₁₂ ]⁷⁺ ) command a central role in aluminum ion speciation and transformations between minerals, measurement of their translational diffusion is often limited to indirect methods. Here, ²⁷ Al pulsed field gradient stimulated echo nuclear magnetic resonance (PFGSTE NMR) spectroscopy has been applied to the AlO₄ core of the ϵ-Al₁₃ cluster with complementary theoretical simulations of the diffusion coefficient and corresponding hydrodynamic radii from a boundary element-based calculation. The tetrahedral AlO₄ center of the ϵ-Al₁₃ cluster is symmetric and exhibits only weak quadrupolar coupling, which results in favorable T₁ and T₂ ²⁷ Al NMR relaxation coefficients for ²⁷ Al PFGSTE NMR studies. Stokes-Einstein relationship was used to relate the ²⁷ Al diffusion coefficient of the ϵ-Al₁₃ cluster to the hydrodynamic radius for comparison with theoretical simulations, dynamic light scattering from literature, and previously published ¹ H PFGSTE NMR studies of chelated Keggin clusters. This first-of-its-kind observation proves that ²⁷ Al PFGSTE NMR diffusometry can probe symmetric Al environments in polynuclear clusters of greater molecular weight than previously considered.

A Direct NMR Method To Measure Self-Diffusion Coefficients in Liquids by Monitoring Diffusing Molecules through One-Dimensional Imaging

Diffusion processes can be followed directly by recording one-dimensional images of a selected slice at variable intervals after selective inversion of the magnetization. The resulting diffusion coefficients of H₂ O and DMSO are consistent with earlier studies at different temperatures, obtained by monitoring the attenuation of NMR signals as a function of the gradient amplitude in gradient echo sequences.

ThIV-Desferrioxamine: characterization of a fluorescent bacterial probe

Diversifying our ability to guard against emerging pathogenic threats is essential for keeping pace with global health challenges, including those presented by drug-resistant bacteria. Some modern diagnostic and therapeutic innovations to address this challenge focus on targeting methods that exploit bacterial nutrient sequestration pathways, such as the desferrioxamine (DFO) siderophore used by Staphylococcus aureus (S. aureus) to sequester FeIII. Building on recent studies that have shown DFO to be a versatile vehicle for chemical delivery, we show proof-of-principle that the FeIII sequestration pathway can be used to deliver a potential radiotherapeutic. Our approach replaces the FeIII nutrient sequestered by H4DFO+ with ThIV and made use of a common fluorophore, FITC, which we covalently bonded to DFO to provide a combinatorial probe for simultaneous chelation paired with imaging and spectroscopy, H3DFO_FITC. Combining insight provided from FITC-based imaging with characterization by NMR spectroscopy, we demonstrated that the fluorescent DFO_FITC conjugate retained the ThIV chelation properties of native H4DFO+. Fluorescence microscopy with both [Th(DFO_FITC)] and [Fe(DFO_FITC)] complexes showed similar uptake by S. aureus and increased intercellular accumulation as compared to the FITC and unchelated H3DFO_FITC controls. Collectively, these results demonstrate the potential for the newly developed H3DFO_FITC conjugate to be used as a targeting vector and bacterial imaging probe for S. aureus. The results presented within provide a framework to expand H4DFO+ and H3DFO_FITC to relevant radiotherapeutics (like 227Th).

1H Diffusion-Ordered Nuclear Magnetic Resonance Spectroscopic Analysis of Water-Extractable Arabinoxylan in Wheat (Triticum aestivum L.) Flour

The structural heterogeneity of water-extractable arabinoxylan (WE-AX) impacts wheat flour functionality. ¹H diffusion-ordered (DOSY) nuclear magnetic resonance (NMR) spectroscopy revealed structural heterogeneity within WE-AX fractions obtained via graded ethanol precipitation. Combination with high-resolution ¹H-¹H correlation NMR spectroscopy (COSY) allowed identifying the relationship between the xylose substitution patterns and diffusion properties of the subpopulations. WE-AX fractions contained distinct subpopulations with different diffusion rates. WE-AX subpopulations with a high self-diffusivity contained high levels of monosubstituted xylose. In contrast, those with a low self-diffusivity were rich in disubstituted xylose, suggesting that disubstitution mainly occurs in WE-AX molecules with large hydrodynamic volumes. In general, WE-AX fractions precipitating at higher and lower ethanol concentrations had higher and lower self-diffusivity and more and less complex substitution patterns. Although ¹H DOSY NMR, as performed in this study, was valuable for elucidating WE-AX structural heterogeneity, physical limitations arose when studying WE-AX populations with high molecular weight dispersions.

Molar mass effect in food and health

It is demanded to supply foods with good quality for all the humans. With the advent of aging society, palatable and healthy foods are required to improve the quality of life and reduce the burden of finance for medical expenditure. Food hydrocolloids can contribute to this demand by versatile functions such as thickening, gelling, stabilising, and emulsifying, controlling texture and flavour release in food processing. Molar mass effects on viscosity and diffusion in liquid foods, and on mechanical and other physical properties of solid and semi-solid foods and films are overviewed. In these functions, the molar mass is one of the key factors, and therefore, the effects of molar mass on various health problems related to noncommunicable diseases or symptoms such as cancer, hyperlipidemia, hyperglycemia, constipation, high blood pressure, knee pain, osteoporosis, cystic fibrosis and dysphagia are described. Understanding these problems only from the viewpoint of molar mass is limited since other structural characteristics, conformation, branching, blockiness in copolymers such as pectin and alginate, degree of substitution as well as the position of the substituents are sometimes the determining factor rather than the molar mass. Nevertheless, comparison of different behaviours and functions in different polymers from the viewpoint of molar mass is expected to be useful to find a common characteristics, which may be helpful to understand the mechanism in other problems.

Exchange-modified DOSY experiments. the use of chiral solvating agents and lanthanide shift reagents as matrices

(S)-BINOL and Eu(fod)₃ were tried as matrices to improve DOSY performance and D^t and MW prediction power on small organic molecules.