Diffusion-ordered NMR Spectroscopy Research Articles

Accounting for gradient non-uniformity in spatially-encoded diffusion-ordered NMR spectroscopy

Diffusion-ordered NMR spectroscopy (DOSY) is a powerful tool for the analysis of mixtures. Spatially-encoded (SPEN) DOSY makes it possible to collect a complete DOSY data set in a single scan, through spatial parallelisation of the gradient dimension. One limitation of current SPEN DOSY experiments is that the data is analysed assuming that the field gradient is uniform over the sample. This is usually not the case for high resolution NMR probes, and even less for triple-axis gradient probes. In this work, we have developed methods to account for gradient non-uniformity in the processing of SPEN DOSY experiment. We have first mapped the field gradient, using a stimulated echo (STE) NMR sequence with a weak readout gradient. We have then modified the calculation of the position-dependent effective gradient pulse area that is used in the analysis of SPEN DOSY data. The resulting model was validated through numerical simulations. A comparison of results obtained with and without inclusion of the effect of non-uniform gradients shows that the proposed approach increases the accuracy of SPEN DOSY experiments.

Visible-Light-Induced Control over Reversible Single-Chain Nanoparticle Folding.

We introduce a class of single-chain nanoparticles (SCNPs) that respond to visible light (λmax =415 nm) with complete unfolding from their compact structure into linear chain analogues. The initial folding is achieved by a simple esterification reaction of the polymer backbone constituted of acrylic acid and polyethylene glycol carrying monomer units, introducing bimane moieties, which allow for the photochemical unfolding, reversing the ester-bond formation. The compaction and the light driven unfolding proceed cleanly and are readily followed by size exclusion chromatography (SEC) and diffusion ordered NMR spectroscopy (DOSY), monitoring the change in the hydrodynamic radius (RH ). Importantly, the folding reaction and the light-induced unfolding are reversible, supported by the high conversion of the photo cleavage. As the unfolding reaction occurs in aqueous systems, the system holds promise for controlling the unfolding of SCNPs in biological environments.

Mechanistic Investigations of Phenoxyimine-Cobalt(II)-Catalyzed C(sp2)-C(sp3) Suzuki-Miyaura Cross-Coupling.

The mechanism of phenoxyimine (FI)-cobalt-catalyzed C(sp2)-C(sp3) Suzuki-Miyaura cross-coupling was studied using a combination of kinetic measurements and catalytic and stoichiometric experiments. A series of dimeric (FI)cobalt(II) bromide complexes, [(4-CF3PhFI)CoBr]2, [(4-OMePhFI)CoBr]2, and [(2,6-diiPrPhFI)CoBr]2, were isolated and characterized by 1H and 19F NMR spectroscopies, solution and solid-state magnetic susceptibility, electron paramagnetic resonance (EPR) spectroscopy, X-ray crystallography, and diffusion-ordered NMR spectroscopy (DOSY). One complex, [(4-CF3PhFI)CoBr]2, was explored as a single-component precatalyst for C(sp2)-C(sp3) Suzuki-Miyaura cross-coupling. Addition of potassium methoxide to [(4-CF3PhFI)CoBr]2 generated the corresponding (FI)cobalt(II) methoxide complex as determined by 1H and 19F NMR and EPR spectroscopies. These spectroscopic signatures were used to identify this compound as the resting state during catalytic C(sp2)-C(sp3) coupling. Variable time normalization analysis (VTNA) of in situ catalytic 19F NMR spectroscopic data was used to establish an experimental rate law that was first-order in a (FI)cobalt(II) precatalyst, zeroth-order in the alkyl halide, and first-order in an activated potassium methoxide-aryl boronate complex. These findings are consistent with turnover-limiting transmetalation that occurs prior to activation of the alkyl bromide electrophile. The involvement of boronate intermediates in transmetalation was corroborated by Hammett studies of electronically differentiated aryl boronic esters. Together, a cobalt(II)/cobalt(III) catalytic cycle was proposed that proceeds through a "boronate"-type mechanism.

NMR Spectroscopy Study of the Effect of the Molecular Mass of Hypromellose Phthalate on Its Solubility

Scientific relevance. Hypromellose phthalate is used in enteric coatings for oral medicinal products. The proportion of phthalate groups in the polymer is standardised because it has a significant effect on solubility. Whereas, the molecular mass of hypromellose phthalate is not controlled, and its impact on solubility in media with different pH values is understudied.Aim. The study aimed to employ NMR spectroscopy to investigate the effect the molecular mass of hypromellose phthalate may have on the dissolution kinetics at the pH value declared by the polymer manufacturer.Materials and methods. The study analysed hypromellose phthalate isolated from proton-pump inhibitor enteric coatings and the hypromellose phthalate reference standard. The molecular mass of the polymer was estimated by diffusion-ordered NMR spectroscopy (DOSY) with polyethylene glycols of known molecular masses for calibration. The authors studied the dissolution profiles of hypromellose phthalates of different molecular masses using 1H NMR spectra.Results. The authors developed a procedure for estimating the average molecular mass of hypromellose phthalate by DOSY. The procedure showed variations in the molecular mass of the polymer in the test samples; the molecular mass scatter amounted to 10 kDa. The dissolution profile of the test samples in an aqueous buffer solution (pH 5.59) was described by a linear function during the first hour. The slope characterising the dissolution rate varied from 10° to 36°.Conclusions. The variation in the molecular mass of hypromellose phthalate significantly affects the dissolution rate of the test samples. The function of the dissolution rate against the molecular mass of hypromellose phthalate is non-linear. The article provides a compelling reason for further research to derive a correlation equation for the dissolution rate of hypromellose phthalate as a function of two variables (molecular mass and proportion of phthalate groups in the polymer).

Short-chain polyphosphates: Extraction effects on migration and size estimation of Saccharomyces cerevisiae extracts with polyacrylamide gel electrophoresis.

Polyacrylamide gel electrophoresis is commonly used to characterize the chain length of polyphosphates (polyP), more generally called condensed phosphates. After separation, nonradioactive, optical polyP staining is limited to chain lengths greater than 15 monomers with toluidine blue or 4',6-diamidino-2-phenylindole. PolyP chain lengths longer than 62 monomers were correlated to the shortest DNA ladders. In this study, synthetic linear polyPs (Sigma-Aldrich "Type 45", estimated mean length of 45 monomers), trimetaphosphate (trimetaP: 3 ring), tripolyphosphate (tripolyP), pyrophosphate (PPi ), and inorganic orthophosphate (o-Pi ) were visualized after separation by an in situ hydrolytic degradation process to o-Pi that was subsequently stained with methyl green. Statistically insignificant migration reduction of synthetic short-chain polyP after perchloric acid or phenol-chloroform extraction was confirmed with the Friedman test. 31 P diffusion-ordered NMR spectroscopy confirmed that extraction also reduced PPi diffusivity by <10%. Linear regression between the Rf peak migration value and the logarithm of synthetic polyP molecular weights enabled estimation of extracted polyP chain lengths from 2 to 45 monomers. Linear polyP extracts from Saccharomyces cerevisiae grown in aerobic conditions were generally shorter than extracts cultured in anaerobic conditions. Extractions from both aerobic and anaerobic S. cerevisiae included tripolyP and o-Pi , but no PPi .

Combination of Drug Delivery Properties of PAMAM Dendrimers and Cytotoxicity of Platinum(IV) Complexes-A More Selective Anticancer Treatment?

Based on their drug delivery properties and activity against tumors, we combined PAMAM dendrimers with various platinum(IV) complexes in order to provide an improved approach of anticancer treatment. Platinum(IV) complexes were linked to terminal NH2 moieties of PAMAM dendrimers of generation 2 (G2) and 4 (G4) via amide bonds. Conjugates were characterized by 1H and 195Pt NMR spectroscopy, ICP-MS and in representative cases by pseudo-2D diffusion-ordered NMR spectroscopy. Additionally, the reduction behavior of conjugates in comparison to corresponding platinum(IV) complexes was investigated, showing a faster reduction of conjugates. Cytotoxicity was evaluated via the MTT assay in human cell lines (A549, CH1/PA-1, SW480), revealing IC50 values in the low micromolar to high picomolar range. The synergistic combination of PAMAM dendrimers and platinum(IV) complexes resulted in up to 200 times increased cytotoxic activity of conjugates in consideration of the loaded platinum(IV) units compared to their platinum(IV) counterparts. The lowest IC50 value of 780 ± 260 pM in the CH1/PA-1 cancer cell line was detected for an oxaliplatin-based G4 PAMAM dendrimer conjugate. Finally, in vivo experiments of a cisplatin-based G4 PAMAM dendrimer conjugate were performed based on the best toxicological profile. A maximum tumor growth inhibition effect of 65.6% compared to 47.6% for cisplatin was observed as well as a trend of prolonged animal survival.

Soft Side of Aliphatic Polycarbonates: with PCHC-b-PDMS Copolymers toward Ductile Materials

Aliphatic polycarbonates based on CO2 and epoxides are a promising group of polymers due to the utilization of CO2 as a monomer combined with a versatile epoxide feedstock. To increase the attractiveness of these polymers as a material, the poor mechanical properties have to be improved. Herein, we present the synthesis of block copolymers from poly(cyclohexene carbonate) and poly(dimethyl siloxane) (PDMS), where diffusion-ordered NMR spectroscopy measurements indicate a successful synthesis of block structures. The resulting material shows an elongation at break of up to 24% in tensile testing with an incorporation ratio of only 27% PDMS in the copolymer. At the same time, a high tensile strength (27.9 MPa) and modulus of elasticity (1726 MPa) are observed.

Polymer Molecular Weights via DOSY NMR

Diffusion-ordered spectroscopy (DOSY) 1H nuclear magnetic resonance (1H NMR) has become a powerful tool to characterize the molecular weights of polymers. Compared to common characterization techniques, such as size exclusion chromatography (SEC), DOSY is faster, uses less solvent, and does not require a purified polymer sample. Poly(methyl methacrylate) (PMMA), polystyrene (PS), and polybutadiene (PB) molecular weights were determined by the linear correlation between the logarithm of their diffusion coefficients (D) and the logarithm of their molecular weights based on SEC molecular weights. Here, we emphasize the importance of the preparation needed to generate the calibration curves, which includes choosing the correct pulse sequence, optimizing parameters, and sample preparation. The limitation of the PMMA calibration curve was investigated by increasing the dispersity of PMMA. Additionally, by accounting for viscosity in the Stokes-Einstein equation, a variety of solvents were used to produce a "universal" calibration curve for PMMA to determine molecular weight. Furthermore, we place a spotlight on the increasing importance of DOSY NMR being incorporated into the polymer chemist's toolbox.

Exceptionally Stable Dimers and Trimers of Au25 Clusters Linked with a Bidentate Dithiol: Synthesis, Structure and Chirality Study.

A bidentate chiral dithiol (diBINAS) is utilised to bridge Au25 nanoclusters to form oligomers. Separation by size allows the isolation of fractions that are stable thanks to the bidentate nature of the linker. The structure of the products is elucidated by small-angle X-ray scattering and calculated using density functional theory. Additional structural details are studied by diffusion-ordered nuclear magnetic resonance spectroscopy, transmission electron microscopy and matrix-assisted laser desorption/ionization time of flight mass spectrometry. Significant changes in the optical properties are analysed by UV/Vis and fluorescence spectroscopies, with the latter demonstrating a strong emission enhancement. Furthermore, the emergent chiral characteristics are studied by circular dichroism. Due to the geometry constraints of the nanocluster assemblies, diBINAS can be regarded as a templating molecule, taking a step towards the directed self-assembly of metal clusters.

Poly(ε-caprolactone)-poly(ethylene glycol) Tri-Block Copolymer as Quercetin Delivery System for Human Colorectal Carcinoma Cells: Synthesis, Characterization and In Vitro Study.

Quercetin is a hydrophobic molecule with short blood circulation times and instability. The development of a nano-delivery system formulation of quercetin may increase its bioavailability, resulting in greater tumor suppressing effects. Triblock ABA type polycaprolactone-polyethylenglycol- polycaprolactone (PCL-PEG-PCL) copolymers have been synthetized using ring-opening polymerization of caprolactone from PEG diol. The copolymers were characterized by nuclear magnetic resonance (NMR), diffusion-ordered NMR spectroscopy (DOSY), and gel permeation chromatography (GPC). The triblock copolymers self-assembled in water forming micelles consisting of a core of biodegradable polycaprolactone (PCL) and a corona of polyethylenglycol (PEG). The core-shell PCL-PEG-PCL nanoparticles were able to incorporate quercetin into the core. They were characterized by dynamic light scattering (DLS) and NMR. The cellular uptake efficiency of human colorectal carcinoma cells was quantitatively determined by flow cytometry using nanoparticles loaded with Nile Red as hydrophobic model drug. The cytotoxic effect of quercetin-loaded nanoparticles was evaluated on HCT 116 cells, showing promising results.

Synthesis of Supramolecular A8 Bn Miktoarm Star Copolymers by Host-Guest Complexation.

We report a new synthetic method to construct supramolecular A8 Bn (n=1, 2, 4) miktoarm star copolymers by host-guest complexation between a resorcinarene-based coordination capsule possessing eight polystyrene chains and 4,4-diacetoxybiphenyl guest molecules that retain one, two or four polymethyl acrylate chains. The formation of the supramolecular A8 Bn (n=1, 2, 4) miktoarm star copolymers was confirmed by dynamic light scattering (DLS), size-exclusion chromatography (SEC), and diffusion-ordered NMR spectroscopy (DOSY). Differential scanning calorimetry (DSC) measurements revealed that the miktoarm copolymers were phase-separated in the bulk. The micro-Brownian motion of the A8 B4 structure was markedly enhanced in the bulk due to a weak segregation interaction between the immiscible arms.

Synthesis of Supramolecular A8Bn Miktoarm Star Copolymers by Host‐Guest Complexation

AbstractWe report a new synthetic method to construct supramolecular A8Bn (n=1, 2, 4) miktoarm star copolymers by host‐guest complexation between a resorcinarene‐based coordination capsule possessing eight polystyrene chains and 4,4‐diacetoxybiphenyl guest molecules that retain one, two or four polymethyl acrylate chains. The formation of the supramolecular A8Bn (n=1, 2, 4) miktoarm star copolymers was confirmed by dynamic light scattering (DLS), size‐exclusion chromatography (SEC), and diffusion‐ordered NMR spectroscopy (DOSY). Differential scanning calorimetry (DSC) measurements revealed that the miktoarm copolymers were phase‐separated in the bulk. The micro‐Brownian motion of the A8B4 structure was markedly enhanced in the bulk due to a weak segregation interaction between the immiscible arms.

1H DOSY analysis of high molecular weight acrylamide-based copolymer electrolytes using an inverse-geometry diffusion probe

Copolymers of [2-(acryloyloxy)ethyl]trimethylammonium chloride (AETAC) and acrylamide (AAm) (AETAC-co-AAm) are polyelectrolytes used as flocculants in wastewater purification. Diffusion-ordered two-dimensional NMR spectroscopy (DOSY) experiments for AETAC-co-AAm samples with Mw ranging from 1.9 to 3.9 million and a polyacrylamide sample with Mw of 1.3 million were carried out in pure D2O and in D2O containing 0.1 or 1 M NaCl using an inverse-geometry diffusion probe system. Projections of the DOSY contour plots onto the diffusion coefficient (D) dimension gave distributions of D for the AETAC and AAm units in the samples. The D values at the maximum point of the distribution (Dp) agreed fairly well with those determined by dynamic light scattering.

Optimization of Diffusion-Ordered NMR Spectroscopy Experiments for High-Throughput Automation in Human Metabolic Phenotyping.

The diffusion-ordered nuclear magnetic resonance spectroscopy (DOSY) experiment allows the calculation of diffusion coefficient values of metabolites in complex mixtures. However, this experiment has not yet been broadly used for metabolic profiling due to lack of a standardized protocol. Here we propose a pipeline for the DOSY experimental setup and data processing in metabolic phenotyping studies. Due to the complexity of biological samples, three experiments (a standard DOSY, a relaxation-edited DOSY, and a diffusion-edited DOSY) have been optimized to provide DOSY metabolic profiles with peak-picked diffusion coefficients for over 90% of signals visible in the one-dimensional 1H general biofluid profile in as little as 3 min 36 s. The developed parameter sets and tools are straightforward to implement and can facilitate the use of DOSY for metabolic profiling of human blood plasma and urine samples.

Monitoring the Solution Persistence of Porous Coordination Cages with Diffusion NMR Spectroscopy and Cryogenic Transmission Electron Microscopy

As a unique class of molecular adsorbents, porous coordination cages (PCCs) have garnered interest because of their potential solubility, which enables applications not available to activated carbons, zeolites, metal–organic frameworks (MOFs), and covalent organic frameworks (COFs), such as covalent membrane incorporation, solution-based ion binding, and facile incorporation into porous liquids. The identification of key aspects of cage behavior in solution such as the self-assembly process, structural integrity in solution, conformational changes, and cage interactions with guest molecules is necessary to broaden the utility of soluble porous cages. Many characterization strategies for permanently porous coordination cages have been limited to the solid state and have relied heavily on X-ray diffraction, electron microscopy, and infrared (IR), UV–vis, and nuclear magnetic resonance (NMR) spectroscopies. As such, definitive evidence of cage behavior while in solution has been lacking, as the often-paramagnetic nature of permanently porous coordination cages complicates one-dimensional NMR spectroscopy experiments. Here, we explore the combined use of diffusion-ordered spectroscopy NMR (DOSY NMR), transmission electron microscopy (TEM), and cryogenic transmission electron microscopy (cryo-TEM) to confirm the persistence of soluble PCCs in various solutions.

Perfluorocarbon emulsion enhances MR-ARFI displacement and temperature in vitro: Evaluating the response with MRI, NMR, and hydrophone.

Sonosensitive perfluorocarbon F8TAC18-PFOB emulsion is under development to enhance heating, increase thermal contrast, and reduce treatment times during focused ultrasound tumor ablation of highly perfused tissue. The emulsion previously showed enhanced heating during ex vivo and in vitro studies. Experiments were designed to observe the response in additional scenarios by varying focused ultrasound conditions, emulsion concentrations, and surfactants. Most notably, changes in acoustic absorption were assessed with MR-ARFI. Phantoms were developed to have thermal, elastic, and relaxometry properties similar to those of ex vivo pig tissue. The phantoms were embedded with varying amounts of F8TAC18-PFOB emulsion or lecithin-PFOB emulsion, between about 0.0-0.3% v:w, in 0.05% v:w increments. MR-ARFI measurements were performed using a FLASH-ARFI-MRT sequence to obtain simultaneous displacement and temperature measurements. A Fabry-Perot hydrophone was utilized to observe the acoustic emissions. Susceptibility-weighted imaging and relaxometry mapping were performed to observe concentration-dependent effects. 19F diffusion-ordered spectroscopy NMR was used to measure the diffusion coefficient of perfluorocarbon droplets in a water emulsion. Increased displacement and temperature were observed with higher emulsion concentration. In semi-rigid MR-ARFI phantoms, a linear response was observed with low-duty cycle MR-ARFI sonications and a mono-exponential saturating response was observed with sustained sonications. The emulsifiers did not have a significant effect on acoustic absorption in semi-rigid gels. Stable cavitation might also contribute to enhanced heating.

One-Pot Synthesis of Miktoarm Star Polymers Based on Orthogonal Metal–Ligand Interactions

Miktoarm star polymers are a particular type of branched polymers featuring a star-shaped architecture with arms based on different polymer types. Such materials exhibit unique thermal, mechanical, and self-assembly properties. Hence, this polymer class is of great interest in different research fields. So far, the synthesis of these entities can be rather challenging, particularly applying covalent strategies for linking of the different polymers. Thus, an approach for the synthesis of such polymer architectures is presented using orthogonal metal–ligand interactions to connect the different building blocks, resulting in a miktoarm topology. The obtained structures are investigated via diffusion-ordered nuclear magnetic resonance spectroscopy, by analytical ultracentrifugation and dynamic light scattering.

A Pure Shift-Based Nuclear Magnetic Resonance Method for In-Phase Three-Dimensional Diffusion-Ordered Spectroscopy.

Diffusion-ordered nuclear magnetic resonance spectroscopy (DOSY) plays a vital role in mixture studies. However, its applications to complex mixture samples are generally limited by spectral congestion along the chemical shift domain caused by extensive J coupling networks and abundant compounds. Herein, we develop the in-phase multidimensional DOSY strategy for complex mixture analyses by simultaneously revealing molecular self-diffusion behaviors and multiplet structures with optimal spectral resolution. As a proof of concept, two pure shift-based three-dimensional (3D) DOSY protocols are proposed to record high-resolution 3D spectroscopic view with separated mixture components and their resolved multiplet coupling structures, thus suitable for analyzing complex mixtures that contain abundant compounds and complicated molecular structures, even under adverse magnetic field conditions. Therefore, this study shows a promising tool for component analyses and multiplet structure studies on practical mixture samples.

Effect of sweeteners and carbonation on aroma partitioning and release in beverage systems

The effect of monosaccharides (glucose, fructose and galactose) and disaccharides (sucrose and lactose) at 10, 20 and 30 % w/v on the in-vitro aroma partitioning of C4 – C10 aldehydes and ethyl esters, as well as limonene (concentration of aroma compounds at 1 μg mL−1), was studied using atmospheric pressure chemical ionisation–mass spectrometry. An increase in sugar concentration from 0 to 30 % w/v resulted in a significant increase in partitioning under static headspace conditions for the majority of the compounds (p < 0.05), an effect generally not observed when 10 % w/v sucrose was substituted with low-calorie sweeteners (p > 0.05). The complexity of the system was increased to model a soft drink design – comprising water, sucrose (10, 20 and 30 % w/v), acid (0.15 % w/v), carbonation (∼7.2 g/L CO2) and aroma compounds representative of an apple style flavouring, namely ethyl butanoate and hexanal (10 μg mL−1 each). Although the addition of sucrose had no significant in-vivo effect, carbonation significantly decreased breath-by-breath (in-vivo) aroma delivery (p < 0.05). To understand the physical mechanisms behind aroma release from the beverage matrix, the effect of sucrose on the kinetics of the matrix components was explored. An increase in sucrose concentration from 0 to 30 % w/v resulted in a significant decrease in water activity (p < 0.05), which accounted for the significantly slower rate of self-diffusion of aroma compounds (p < 0.05), measured using diffusion-ordered spectroscopy–nuclear magnetic resonance spectroscopy. No significant effect of sucrose on carbon dioxide volume flux was found (p > 0.05).

From Hofmeister to hydrotrope: Effect of anion hydrocarbon chain length on a polymer brush

HypothesisSpecific ion effects govern myriad biological phenomena, including protein–ligand interactions and enzyme activity. Despite recent advances, detailed understanding of the role of ion hydrophobicity in specific ion effects, and the intersection with hydrotropic effects, remains elusive. Short chain fatty acid sodium salts are simple amphiphiles which play an integral role in our gastrointestinal health. We hypothesise that increasing a fatty acid’s hydrophobicity will manifest stronger salting-out behaviour. ExperimentsHere we study the effect of these amphiphiles on an exemplar thermoresponsive polymer brush system, conserving the carboxylate anion identity while varying anion hydrophobicity via the carbon chain length. Ellipsometry and quartz crystal microbalance with dissipation monitoring were used to characterise the thermoresponse and viscoelasticity of the brush, respectively, whilst neutron reflectometry was used to reveal the internal structure of the brush. Diffusion-ordered nuclear magnetic resonance spectroscopy and computational investigations provide insight into polymer-ion interactions. FindingsSurface sensitive techniques unveiled a non-monotonic trend in salting-out ability with increasing anion hydrophobicity, revealing the bundle-like morphology of the ion-collapsed system. An intersection between ion-specific and hydrotropic effects was observed both experimentally and computationally; trending from good anti-hydrotrope towards hydrotropic behaviour with increasing anion hydrophobicity, accompanying a change in hydrophobic hydration.