Deuterium Nuclear Magnetic Resonance Research Articles

Pluronic 123 Liquid Lyotropic Crystals for Transdermal Delivery of Caffeic Acid-Insights from Structural Studies and Drug Release.

This study aims to evaluate the percutaneous permeation profiles of caffeic acid (CA) from the cubic and hexagonal liquid crystalline phases of Pluronic P123/water mixtures. The resulting drug-loaded mesophases were subjected to characterisation through deuterium nuclear magnetic resonance spectroscopy and polarised optical microscopy observations. These analyses aimed to evaluate the structural changes that occurred in the mesophases loading with CA. Additionally, steady and dynamic rheology studies were conducted to further explore their mechanical properties and correlate them to the supramolecular structure. Finally, CA release experiments were carried out at two different temperatures to examine the behaviour of the structured systems in a physiological or hyperthermic state. As the concentration of the polymer increases, an increase in the viscosity of the gel is noted; however, the addition of caffeic acid increases microstructure fluidity. It is observed that the temperature effect conforms to expectations. The increase in temperature causes a decrease in viscosity and, consequently, an increase in the rate of permeation of caffeic acid. The CA permeation profile from the prepared formulations is mostly dependent on the structural organisation and temperature. Cubic mesophase LLC 30/CA showed greater skin permeation with good accumulation in the skin at both tested temperatures.

Aggregation behaviors of alkyl α-keto acids in water

Single-tailed α-keto acids are a kind of fatty acid derivatives and weakly acidic amphiphiles. Only the aggregation behavior of α-ketooctanoic acid (KC8) in water was investigated so far, and thus the current understanding of their aggregation behavior, such as the effect of alkyl chain length, is still limited. It is essential to investigate the aggregation behavior of alkyl α-keto acids such as α-ketodecanoic acid (KC10) and α-ketododecanoic acid (KC12), to fully understand the features of α-keto acids. The aggregation behavior of KC10 and KC12 in water was investigated by changing their concentrations (C), using equilibrium surface tension, cryogenic transmission electron microscopy, dynamic light scattering, small-angle X-ray scattering, and deuterium nuclear magnetic resonance, and compared with that of KC8. A C-dependent stepwise aggregation was observed for the KC10 and KC12 systems. With increasing C, vesicles, precipitates, micelles, and lamellar phase (or α-gel phase) form successively in the systems, where precipitates and micelles both coexist with vesicles, similar to the case of KC8. With an increase in chain length, the pKa of α-keto acids increases while their critical concentrations of stepwise aggregations decrease, arising from the enhancement of the interactions between alkyl chains. The aggregation behavior observed can be explained by the existence of multispecies (including the “acid-soap” dimers) and the interaction between alkyl chains.

Structural applications of the isotropic liquid-phase deuterium nuclear magnetic resonance.

Present review is focused on recent experimental and computational advances of the liquid-phase deuterium nuclear magnetic resonance (NMR). Nowadays, isotropic liquid-phase 2 H NMR became one of the most important instruments for the identification and certification of organic compounds of biological interest together with natural products and biosynthetic molecules. Of special interest are the 2 H NMR biochemical and microbiological applications. This review consists of three main parts. The first part deals with the practical applications of 2 H NMR to organic compounds of biological interest. The second part is connected with natural products and biosynthetic molecules, while the third part exemplifies and outlines 2 H NMR advances in biochemistry and microbiology.

In Search of Wasserman's Catenane.

We repeat the earliest claimed [2]catenane synthesis, reported by Wasserman over 60 years ago, in order to ascertain whether or not a nontemplate, statistical synthesis by acyloin macrocyclization does indeed form mechanically interlocked rings. The lack of direct experimental evidence for Wasserman's catenane has led to it being described as a "prophetic compound", a technical term used in patents for claimed molecules that have not yet been synthesized. Contemporary synthetic methods were used to reconstruct Wasserman's deuterium-labeled macrocycle and other building blocks on the 10-100 g reaction scale necessary to generate, in principle, ∼1 mg of catenane. Modern spectrometric and spectroscopic tools and chemical techniques (including tandem mass spectrometry, deuterium nuclear magnetic resonance (NMR) spectroscopy, and fluorescent tag labeling) were brought to bear in an effort to detect, isolate, and prove the structure of a putative [2]catenane consisting of a 34-membered cyclic hydrocarbon mechanically linked with a 34-membered cyclic α-hydroxyketone.

Cannabidiol and cannabinol have distinct effects on membrane structure.

Despite widespread public use, relatively little is known about the compounds cannabidiol (CBD) and cannabinol (CBN), or their interactions with cellular targets. Produced by Cannabis sativa, CBD and CBN have similar chemical structures and are used both pharmaceutically and commercially/recreationally; the former is not psychoactive while the latter is mildly so. Previously CBD was shown to affect the organization of membrane lipids, which indirectly alters sodium channel function (Ghovanloo et al (2021) Cannabidiol inhibits the skeletal muscle Nav1.4 by blocking its pore and by altering membrane elasticity J Gen Physiol; 153 (5): e202012701). Here we use deuterium nuclear magnetic resonance (2H NMR) spectroscopy to investigate the effects of CBD and CBN on 1-palmitoyl-d31-2-oleoyl-sn-glycero-3-phosphocholine (POPC-d31) and POPC-d31/cholesterol multilamellar dispersions as a function of temperature. CBD and CBN affect POPC-d31 membrane organization in a similar way, with increased order in the region of the bilayer near the lipid-water interface and decreased order in the middle of the bilayer. However, CBD and CBN have markedly different effects when added to POPC-d31/cholesterol membranes. Both cannabinoids disorder POPC-d31 in the presence of cholesterol, but CBN's impact on lipid chain organization is significantly greater than that of CBD. These results add support to the theory that CBD and CBN can exert effects on membrane proteins indirectly by altering cell membrane physical properties.

Electronic modulation of metal-support interactions improves polypropylene hydrogenolysis over ruthenium catalysts

Ruthenium (Ru) is the one of the most promising catalysts for polyolefin hydrogenolysis. Its performance varies widely with the support, but the reasons remain unknown. Here, we introduce a simple synthetic strategy (using ammonia as a modulator) to tune metal-support interactions and apply it to Ru deposited on titania (TiO2). We demonstrate that combining deuterium nuclear magnetic resonance spectroscopy with temperature variation and density functional theory can reveal the complex nature, binding strength, and H amount. H2 activation occurs heterolytically, leading to a hydride on Ru, an H+ on the nearest oxygen, and a partially positively charged Ru. This leads to partial reduction of TiO2 and high coverages of H for spillover, showcasing a threefold increase in hydrogenolysis rates. This result points to the key role of the surface hydrogen coverage in improving hydrogenolysis catalyst performance.

Tailoring the Selective Permeation Properties of Asymmetric Cellulose Acetate/Silica Hybrid Membranes and Characterisation of Water Dynamics in Hydrated Membranes by Deuterium Nuclear Magnetic Resonance.

In this work, the water order and dynamics in hydrated films of flat asymmetric cellulose acetate (CA)/silica, CA/SiO2, and hybrid membranes, covering a wide range of nanofiltration (NF) and ultrafiltration (UF) permeation properties, were characterised by deuterium nuclear magnetic resonance (DNMR) relaxation. The range of NF/UF characteristics was attained by subjecting three CA/SiO2 membranes, prepared from casting solutions with different acetone/formamide ratios to drying post-treatments of solvent exchange and conditioning with surfactant mixtures. Post-treated and pristine CA/SiO2 membranes were characterised in terms of hydraulic permeability, selective permeation properties and molecular weight cut-off. These results were correlated with the DNMR relaxation findings. It was found that the post-treatment by solvent exchange caused membrane shrinkage that led to very different permeation characteristics and a significant enhancement of the DNMR relaxation observables. In contrast, conditioning with surfactant solutions exhibited a weaker effect over those properties. Scanning electron microscopy (SEM) images were obtained for the membranes post-treated with solvent exchange to confirm their asymmetric nature. This work provides an essential indication that DNMR relaxometry is a reliable tool to characterise the asymmetric porous structures of the NF/UF CA/SiO2 hybrid membranes.

Measurement of \u03b418O and \u03b42H of water and ethanol in wine by Off-Axis Integrated Cavity Output Spectroscopy and Isotope Ratio Mass Spectrometry

There are two officially approved methods for stable isotope analysis for wine authentication. One describes δ18O measurements of the wine water using Isotope Ratio Mass Spectrometry (IRMS), and the other one uses Deuterium-Nuclear Magnetic Resonance (2H-NMR) to measure the deuterium of the wine ethanol. Recently, off-axis integrated cavity output (laser) spectroscopy (OA-ICOS) has become an easier alternative to quantify wine water isotopes, thanks to the spectral contaminant identifier (SCI). We utilized an OA-ICOS analyser with SCI to measure the δ18O and δ2H of water in 27 wine samples without any pre-treatment. The OA-ICOS results reveal a wealth of information about the growth conditions of the wines, which shows the advantages to extend the official δ18O wine water method by δ2H that is obtained easily from OA-ICOS. We also performed high-temperature pyrolysis and chromium reduction combined with IRMS measurements to illustrate the “whole wine” isotope ratios. The δ18O results of OA-ICOS and IRMS show non-significant differences, but the δ2H results of both methods differ much more. As the δ2H difference between these two methods is mainly caused by ethanol, we investigated the possibility to deduce deuterium of wine ethanol from this difference. The results present large uncertainties and deviate from the obtained 2H-NMR results. The deviation is caused by the other constituents in the wine, and the uncertainty is due to the limited precision of the SCI-based correction, which need to improve to obtain the 2H values of ethanol as alternative for the 2H-NMR method.

Probing n-Octyl α-d-Glycosides Using Deuterated Water in the Lyotropic Phase by Deuterium NMR.

The lyotropic phase behavior of four common and easily accessible glycosides, n-octyl α-d-glycosides, namely, α-Glc-OC8, α-Man-OC8, α-Gal-OC8, and α-Xyl-OC8, was investigated. The presence of normal hexagonal (HI), bicontinuous cubic (VI), and lamellar (Lα) phases in α-Glc-OC8 and α-Man-OC8 including their phase diagrams in water reported previously was verified by deuterium nuclear magnetic resonance (2H NMR), via monitoring the D2O spectra. Additionally, the partial binary phase diagrams and the liquid crystal structures formed by α-Gal-OC8 and α-Xyl-OC8 in D2O were constructed and confirmed using small- and wide-angle X-ray scattering and 2H NMR. The average number of bound water molecules (nb) per headgroup in the Lα phase was determined by the systematic measurement of the quadrupolar splitting of D2O over a wide range of molar ratio values (glycoside/D2O), especially at high glucoside composition. The number of bound water molecules bound to the headgroup was found to be around 1.5-2.0 for glucoside, mannoside, and galactoside, all of which possesses four OH groups. In the case of xyloside, which has only three OH groups, the bound water content is ∼2.0. Our findings confirmed that the bound water content of all n-octyl α-d-glycosides studied is lower compared to the number of possible hydrogen bonding sites possibly due to the fact that most of the OH groups are involved in intralayer interaction that holds the lipid assembly together.

Defining the epitope of a blood–brain barrier crossing single domain antibody specific for the type 1 insulin-like growth factor receptor

Ligand-activated signaling through the type 1 insulin-like growth factor receptor (IGF1R) is implicated in many physiological processes ranging from normal human growth to cancer proliferation and metastasis. IGF1R has also emerged as a target for receptor-mediated transcytosis, a transport phenomenon that can be exploited to shuttle biotherapeutics across the blood–brain barrier (BBB). We employed differential hydrogen–deuterium exchange mass spectrometry (HDX-MS) and nuclear magnetic resonance (NMR) to characterize the interactions of the IGF1R ectodomain with a recently discovered BBB-crossing single-domain antibody (sdAb), VHH-IR5, in comparison with IGF-1 binding. HDX-MS confirmed that IGF-1 induced global conformational shifts in the L1/FnIII-1/-2 domains and α-CT helix of IGF1R. In contrast, the VHH-IR5 sdAb-mediated changes in conformational dynamics were limited to the α-CT helix and its immediate vicinity (L1 domain). High-resolution NMR spectroscopy titration data and linear peptide scanning demonstrated that VHH-IR5 has high-affinity binding interactions with a peptide sequence around the C-terminal region of the α-CT helix. Taken together, these results define a core linear epitope for VHH-IR5 within the α-CT helix, overlapping the IGF-1 binding site, and suggest a potential role for the α-CT helix in sdAb-mediated transcytosis.

Supercooled nano-droplets of water confined in hydrophobic rubber.

Hydrophobic elastomers are capable of absorbing a small amount of water that forms droplets around hydrophilic sites. These systems allow the study of confinement effects by a hydrophobic environment on the dynamics and thermodynamic behaviour of water molecules. The freezing-melting properties and the dynamics of water inside nano-droplets in butyl rubber are affected, as revealed by differential scanning calorimetry (DSC) and deuterium nuclear magnetic resonance (2H-NMR). Upon cooling down, all water crystalizes with a bimodal droplet population (da = 3.4 nm and db = 4.4 nm) in a temperature range associated with the droplet size distribution. However, the melting temperature is not shifted according to the Gibbs-Thomson equation. The relative decrease of the 2H-NMR longitudinal magnetization is not a single exponential and, by inverse Laplace transformation, it was deduced to be bimodal in agreement with the DSC measurements (T1,a ∼ 10 ms and T1,b ∼ 200 ms). The deduced correlation time of molecular reorientation is longer than that of bulk water and the behaviour with temperature follows the Vogel-Fulcher-Tammann (VFT) equations with a changing fragility as the droplet size is reduced when reducing hydration.

Solid-State NMR Spectroscopy Study of Molecular Dynamics of Pyridine 1-Oxide Encapsulated in p-tert-Butylcalix[4]arene.

The mixture of guests 25% pyridine 1-oxide (PNO) and 75% nitrobenzene (NB) encapsulated in a host cavity of p-tert-butylcalix[4]arene (p-tBC) is a suitable system for the study of intermolecular weak interactions, and the preferred orientation of the guest molecules within the host was derived. Variable temperature deuterium nuclear magnetic resonance line shape and spin-lattice relaxation studies were performed on three samples of 25% PNO as a guest (selectively and entirely deuterated) with 75% NB encapsulated in p-tBC as a host system. It is found that the PNO molecular motion supports the two-site jump model and is highly mobile throughout the temperature range from -130 to 20 °C. PNO reorients about its C2 molecular symmetry axis followed by reorientation around the compound's C4 axis of symmetry of a host. Calculation showed that besides precise molecular jumping, the guest also experiences the vibrational motion with a variation angle dispute about 15°. The correlation times for the molecular guest motion and two-dimensional exchange spectroscopy confirmed a fast exchange limit inside the cavity. These molecular dynamics follow an Arrhenius behavior motion from which the small activation energy is delivered that strongly suggests a relatively weak intermolecular interaction between the host and guest species. PNO has definite dipole orientational motion in the cavity where its aromatic covalent bond structure minimizes contact with the host p-tert-butyl groups. Experimentally found, PNO-d5 deuterons in the single crystal collapse at 55 and 125° at ambient temperature. The first splitting of 124 kHz belongs to D3(D5), the second splitting of 100 kHz belongs to D2(D6), and the last splitting of 52 kHz belongs to D4 of the ring of PNO inside the p-tBC.

Revisiting water speciation in hydrous alumino-silicate glasses: A discrepancy between solid-state 1H NMR and NIR spectroscopy in the determination of X-OH and H2O

The speciation of water dissolved into and reacted with hydrous alumino-silicate glasses (of NaAlSi3O8 and “rhyolitic” compositions) quenched from high temperature is re-investigated where the predominant species are expected to be “X(Si and Al)-OH” and “H2O”. Only, two analytical methods are capable of assessing such speciation: Near InfraRed (NIR) spectroscopy and solid-state 1H Nuclear Magnetic Resonance (NMR) spectroscopy. It is observed that the apparent water speciation, as a function of total water content, as determined by NIR spectroscopy is nearly the opposite from what the 1H NMR data reveal. Deuterium (2H) NMR and silicon (29Si) NMR report consistent trends in apparent speciation (depolymerization) with those indicated by the 1H NMR data. Compared with four previous NMR studies of hydrous NaAlSi3O8 glasses it is shown that whereas NIR data always report the same apparent systematic variation in the intensity of the 4500 (“X-OH”) and 5200 (“H2O”) cm−1 bands with total water content, multiple 1H NMR studies of hydrous NaAlSi3O8 report a wide range in OH/H2O. The discrepancy between the various NMR studies likely reflects differences in how the various glasses were made. Specifically, quench rate (fast or slow) and synthesis pressure (higher or lower), might impose a strong effect on observed water speciation in glasses via 1H NMR. It is concluded that the application of NIR spectroscopy, specifically the use of the intensities of the 4500 (“X-OH”) and 5200 (“H2O”) cm−1 NIR bands, does not provide an accurate assessment of water speciation in hydrous alumino-silicate glasses. NIR spectroscopy does remain a very valuable analytical tool for determination of total water content.

Detection of molasses-spirit in rice-spirits from TK-8 and TCS-10 by SNIF-NMR method

The objective of this study was to identify the origin of edible alcohol usually added in Taiwanese rice-spirits by using deuterium nuclear magnetic resonance (SNIF-NMR method). Rice-spirits labeled TK-8, TCS-10 were made from two rice varieties, Taikeng 8 and Taichung sen 10, whereas molasses-spirit labeled MS was obtained from Taiwan Sugar Corporation. The proportion of ethanol molecules monodeuterated on the methyl site (D/H)I and methylene site (D/H)II, and the ratio R between the intensities of methyl and methylene signals in deuterium spectra were significantly different among TK-8, TCS-10, and MS. Of the three indices, only (D/H)I linearly (R2 > 0.96) increased with addition of MS in both TK-8 and TCS-10. Therefore, (D/H)I was an index for the identification of pure rice-spirits mixed with ethanol originated from molasses.

Structural Properties of Inverted Hexagonal Phase: A Hybrid Computational and Experimental Approach.

Inverted/reverse hexagonal (HII) phases are of special interest in several fields of research, including nanomedicine. We used molecular dynamics (MD) simulation to study HII systems composed of dioleoylphosphatidylethanolamine (DOPE) and palmitoyloleoylphosphatidylethanolamine (POPE) at several hydration levels and temperatures. The effect of the hydration level on several HII structural parameters, including deuterium order parameters, was investigated. We further used MD simulations to estimate the maximum hydrations of DOPE and POPE HII lattices at several given temperatures. Finally, the effect of acyl chain unsaturation degree on the HII structure was studied via comparing the DOPE with POPE HII systems. In addition to MD simulations, we used deuterium nuclear magnetic resonance (2H NMR) and small-angle X-ray scattering (SAXS) experiments to measure the DOPE acyl chain order parameters, lattice plane distances, and the water core radius in HII phase DOPE samples at several temperatures in the presence of excess water. Structural parameters calculated from MD simulations are in excellent agreement with the experimental data. Dehydration decreases the radius of the water core. An increase in hydration level slightly increased the deuterium order parameter of lipids acyl chains, whereas an increase in temperature decreased it. Lipid cylinders undulated along the cylinder axis as a function of hydration level. The maximum hydration levels of PE HII phases at different temperatures were successfully predicted by MD simulations based on a single experimental measurement for the lattice plane distance in the presence of excess water. An increase in temperature decreases the maximum hydration and consequently the radius of the water core and lattice plane distances. Finally, DOPE formed HII structures with a higher curvature compared to POPE, as expected. We propose a general protocol for constructing computational HII systems that correspond to the experimental systems. This protocol could be used to study HII systems composed of molecules other than the PE systems used here and to improve and validate force field parameters by using the target data in the HII phase.

Order Parameter Analysis of Lipids Organization in the Presence of ATP

Adenosine triphosphate (ATP) is an essential component which provides the energy needed in biological interaction in the vicinity of lipid membranes. In this regard, we investigate on the C-D bond order parameter components of phospholipid in presence of ATP for various temperatures obtained by deuterium nuclear magnetic resonance (²H NMR). In addition, simulations were done using a mean-torque potential model to determine the alignment field, which shows the orientational tendency of each carbon segment. We find that the presence of ATP changes the order parameter component as well as the alignment field. These results also indicate that ATP increases membrane order, which results in a stronger alignment field. When increasing temperature, the order parameter goes down because of increasing entropy. These results suggest that the stronger alignment field could influence ion-transport through membranes, which has applications in many biological processes. However, to determine the influence that carbon position and temperature have on this alignment field, more theoretical work is needed.

New in vivo glucose test by localized dynamic deuterium nuclear magnetic resonance

New in vivo glucose test by localized dynamic deuterium nuclear magnetic resonance

Measuring molecular order for lipid membrane phase studies: Linear relationship between Laurdan generalized polarization and deuterium NMR order parameter

Two dimensional phase separation in lipid membranes and cell membranes is of interest to biology because of the idea of membrane rafts — compositionally heterogeneous liquid crystal domains with cellular functions. Few quantitative tools exist for characterizing and differentiating coexisting phases on a molecular scale. Lipid acyl chain order can be measured directly using deuterium nuclear magnetic resonance spectroscopy (2H NMR), or inferred using fluorescence microscopy along with the environment-sensitive probe Laurdan. We found a linear relationship between the 2H NMR order parameter and Laurdan generalized polarization. This observed correlation supports the idea that lipid chain order is tightly associated with the amount and dynamics of water molecules at the glycerol backbone level of the membrane.

Exploring the Dual Interaction of Natural Rhamnolipids with Plant and Fungal Biomimetic Plasma Membranes through Biophysical Studies.

Rhamnolipids (RLs) are potential biocontrol agents for crop culture protection. Their mode of action has been proposed as dual, combining plant protection activation and antifungal activities. The present work focuses on the interaction of natural RLs with plant and fungi membrane models at the molecular scale. Representative models were constructed and the interaction with RLs was studied by Fourier transform infrared (FTIR) and deuterium nuclear magnetic resonance (2H NMR) spectroscopic measurements. Molecular dynamic (MD) simulations were performed to investigate RL insertion in lipid bilayers. Our results showed that the RLs fit into the membrane models and were located near the lipid phosphate group of the phospholipid bilayers, nearby phospholipid glycerol backbones. The results obtained with plant plasma membrane models suggest that the insertion of RLs inside the lipid bilayer did not significantly affect lipid dynamics. Oppositely, a clear fluidity increase of fungi membrane models was observed. This effect was related to the presence and the specific structure of ergosterol. The nature of the phytosterols could also influence the RL effect on plant plasma membrane destabilization. Subtle changes in lipid dynamics could then be linked with plant defense induction and the more drastic effects associated with fungal membrane destabilization.

Effects of Amphipathic Polypeptides on Membrane Organization Inferred from Studies Using Bicellar Lipid Mixtures

SP-B63-78, a lung surfactant protein fragment, and magainin 2, an antimicrobial peptide, are amphipathic peptides with the same overall charge but different biological functions. Deuterium nuclear magnetic resonance has been used to compare the interactions of these peptides with dispersions of 1,2-dimyristoyl- sn-glycero-3-phophocholine (DMPC)/1,2-dihexanoyl- sn-glycero-3-phophocholine (DHPC) (4:1) and DMPC/1,2-dimyristoyl- sn-glycero-3-phopho-(1'-rac-glycerol) (DMPG)/DHPC (3:1:1), two mixtures of long-chain and short-chain lipids that display bicellar behavior. This study exploited the sensitivity of a bicellar system structural organization to factors that modify partitioning of their lipid components between different environments. In small bicelle particles formed at low temperatures, short-chain components preferentially occupy curved rim environments around bilayer disks of the long-chain components. Changes in chain order and lipid mixing, on heating, can drive transitions to more extended assemblies including a magnetically orientable phase at intermediate temperature. In this work, neither peptide had a substantial effect on the behavior of the zwitterionic DMPC/DHPC mixture. For bicellar mixtures containing the anionic lipid DMPG, the peptide SP-B63-78 lowered the temperature at which magnetically orientable particles coalesced into more extended lamellar structures. SP-B63-78 did not promote partitioning of the zwitterionic and anionic long-chain lipid components into different environments. Magainin 2, on the other hand, was found to promote separation of the anionic lipid, DMPG, and the zwitterionic lipid, DMPC, into different environments for temperatures above 34 °C. The contrast between the effects of these two peptides on the lipid mixtures studied appears to be consistent with their functional roles in biological systems.