1H NMR Diffusometry Research Articles

Dynamics and Structure of a Bitumen Emulsion as Studied by 1H NMR Diffusometry.

Self-diffusion in a bitumen emulsion was studied by 1H NMR. The emulsion forms two phases: continuous and dispersed. The continuous aqueous phase contains mainly water, with the energy of activation of the diffusion process equal to that of bulk water, while its diffusivity is smaller than that of bulk water by a factor of 2. The dispersed phase consists of bitumen droplets containing confined water, whose dynamics is characterized by a fully restricted diffusion regime in cavities with sizes of ∼0.11 μm. Therefore, the studied bitumen emulsion can be described by a model of a complex multiple emulsion of the water/oil/water (WOW) type. The suggested model does agree well with data from 1H NMR spectroscopy and diffusometry of the bitumen emulsion doped with paramagnetic MnSO4(aq) as well as with an additional 1H NMR study of the emulsion structure, in which emulsion stability was compromised by freezing at 253 K.

Humidity effect on temperature behavior of proton diffusion coefficient in sulfonated co-polynaphthoyleneimide membranes measured by 1H NMR diffusometry

Proton diffusion in the co-PNIS85/15 membrane was investigated in the temperature range from 200 to 363 K at different water contents (4 ≤ λ ≤ 21) using 1H SFG NMR diffusometry. At high hydration values, above the threshold value λ0 = 10.5, the ln(DNMR(1/T)) dependences show two different activation modes, separated by a crossover point Tcr ≈ 250–260 K. At temperatures above Tcr, the activation energy is Ea ~ 0.20 eV, which is close to the value for bulk water (Ea ~ 0.17 eV). At temperatures below the crossover point, the ln(DNMR(1/T)) dependences for different water contents merge together into one straight line characterized by a much higher Ea = 0.46 eV. At low hydration values λ < λ0, the activation energies for the high-temperature and low-temperature modes converge, so that at λ = 4, the dependence ln(DNMR(1/T)) is described by one straight line throughout the studied temperature range with Ea = 0.38 eV. A model is proposed that phenomenologically describes the diffusion in the co-PNIS membrane at different moisture contents λ.

Probing self-assembled micellar topologies via micro-scale diffusive dynamics of surfactants

HypothesisSurfactants spontaneously self-assemble in aqueous solutions and are critical in energy, biotechnology, and the environment. The self-assembled micelles may experience distinct topological transitions beyond a critical counter-ion concentration, yet the associated mechanical signatures are identical. By monitoring self-diffusion dynamics of individual surfactants in micelles via a non-invasive 1H NMR diffusometry, we may distinguish various topological transitions overcoming challenges associated with traditional microstructural probing techniques. ExperimentsThree micellar systems based on CTAB/5mS, OTAB/NaOA and CPCl/NaClO3 are considered at various counter-ion concentrations, and their rheological properties are assessed. A systematic 1H NMR diffusometry is conducted and the resulting signal attenuation is measured. FindingsWith no counter-ion, surfactants self-diffuse freely with a mean squared displacement Z2∼Tdiff in the micelles. As counter-ion concentration increases, self-diffusion becomes restricted with Z2∼Tdiffα, and α→0.5. Beyond the viscosity peak, for the OTAB/NaOA system that shows a linear-shorter linear micelle transition, Z2∼Tdiff0.5. Conversely, for the CTAB/5mS system that experiences a linear wormlike-vesicle transition above the viscosity peak, a free self-diffusion is recovered. The diffusion dynamics in CPCl/NaClO3 are similar to those of OTAB/NaOA. Hence, a similar topological transition is surmised. These results highlight the unique sensitivity of the 1H NMR diffusometry to micelles topological transitions.

Encapsulation and delivery of protein from within poly(sulfobetaine) hydrogel beads

AbstractAdvancement of therapeutic protein therapies can be hindered by their poor stability and short in vivo half‐life. There is emerging evidence that biocompatible zwitterionic materials can prevent nonspecific interactions within proteins systems that contribute to protein instability. Here, zwitterionic hydrogel beads are synthesized from poly(sulfobetaine methyl methacrylate), pSB, using an inverse emulsion, free radical polymerization reaction technique. The transport properties within the zwitterionic hydrogels were characterized using 1H NMR diffusometry. Equilibrium water content as high as 0.90 was measured for the synthesized hydrogels. Our study revealed that the pSB hydrogels are nontoxic, ion responsive, and their swelling is temperature dependent. The zwitterionic hydrogel beads were capable of undergoing lyophilization without aggregation. Hydrogel beads were loaded with a model protein, bovine serum albumin (BSA), using a postfabrication loading technique. The protein loading was studied using confocal laser microscopy, indicating homogenous protein dispersion of up to 40 μg BSA/mg hydrogel within the beads. Furthermore, the release rate of the protein from the synthesized hydrogel was studied at different crosslinker to monomer ratios. The protein encapsulated within the zwitterionic hydrogel had slower rates of thermal aggregation compared to nonencapsulated protein in solution. Furthermore, the protein‐loaded inside the zwitterionic hydrogel better maintained its bioactivity.

Study of Liquid Crystals Showing Two Isotropic Phases by 1H NMR Diffusometry and 1H NMR Relaxometry

In this work, we report a study of two thermotropic liquid crystalline samples showing a not common mesophase behavior. The samples, namely a di-benzyloxy biphenyl derivative labelled 9/2 RS/RS, and a bimesogenic liquid crystal labelled L1, show a direct transition between two isotropic phases followed, at lower temperatures, by the optically isotropic, 3D structured, cubic phase. These systems have been investigated by means of 1H NMR diffusometry and 1H NMR relaxometry in order to characterize their isotropic–isotropic’–cubic mesophase behavior, mainly on the dynamic point of view. In particular, the temperature trend of the self-diffusion coefficients measured for both samples allowed us to significantly distinguish between the two isotropic phases, while the temperature dependence of the 1H spin-lattice relaxation time (T1) did not show significant discontinuities at the isotropic–isotropic’ phase transition. A preliminary analysis of the frequency-dependence of 1H T1 at different temperatures gives information about the main motional processes active in the isotropic mesophases.

Morphology of Human Cystatin C Oligomers - Towards the Construction of Hcc Nanodetector

Human cystatin C (HCC) is a commonly known inhibitor of cysteine proteases and also macromolecule used as a marker in the clinical diagnosis of the kidney function. This protein exhibits a strong tendency to misfolding via the domain swapping mechanism and then it is able to form oligomers, fibrils and amyloid deposits that can be built in brain blood vessels. The aim of our study was precise characterisation of morphology of these oligomers obtained in various conditions. Different types of HCC oligomers and aggregates were generated using native cystatin C and its covalently stabilised variant. These HCC oligomer species were generated in different compositions of solution, pH values, ionic strength, and also using various temperature and agitation conditions. The micromorphology of obtained HCC aggregates and oligomers was described on the basis of electron microscopy images and topographic data from the atomic force microscopy. In parallel the process of oligomer formation was characterised using 1H NMR diffusometry. In the next step, these HCC oligomers were selected as targets for nanosensing studies. At this stage, preliminary construction studies of a nanosensor selective for detection of HCC variants were initiated. For this research stage the initial immobilisation protocol of antibodies, selective to HCC oligomers, on the gold nanoparticles was tested. The work was supported by the grant POLTUR2/3/2017 from National Centre for Research and Development (Poland) and grant 117Z009 from TÜBİTAK (Turkey).

Effect of magnetic field on diffusion of ethylammonium nitrate – water mixtures confined between polar glass plates

We used 1H NMR diffusometry to study mixtures of ethylammonium nitrate (EAN) with water (3.1–12.4 mol% of added H2O) confined between polar glass plates and exposed to a static magnetic field of 9.4 T. The presence of such restrictions reverses the concentration dependence of the diffusivities of the EA (ethylammonium) cation and water typical for the bulk system. The presence of water weakens the effects of a static magnetic field on diffusion of the EA cation as well as on proton exchange of –NH3 groups. Surprisingly, the amplitude of the echo signal of water protons decreases during exposure to the magnetic field and finally disappears, a phenomenon that depends on the concentration of water in the system. Based on experimental data, we suggest that water in the system is present in two states with different dynamic properties. One type of water formed in confinement possesses NMR relaxation time typical for liquids; its diffusivity can be measured by 1H NMR. The second type of water is formed upon exposure of the sample of the first type to the magnetic field and eventually includes all the water in the system. This type of water possesses “solid-like” NMR relaxation features that makes it “invisible” to the NMR diffusometry technique. We suggest that this second type of water is adsorbed onto the glass plates. Correspondingly, EAN exists in two liquid phases: the first one contains an EAN-water mixture, while the second one contains neat EAN, and forms on the microscopic scale range under the influence of a static magnetic field.

Conformational Flexibility and Self-Association of Fibrinogen in Concentrated Solutions.

We studied the hydrodynamic behavior of fibrinogen, a blood plasma protein involved in blood clotting, in a broad 0.3-60 mg/mL range of concentration and 5-42 °C temperature using pulsed-field gradient 1H NMR-diffusometry. Arrhenius plots revealed the activation energy for fibrinogen diffusion Ed = 21.3 kJ/mol at 1.4 mg/mL and 28.4 kJ/mol at 38 mg/mL. We found a dramatic slowdown in fibrinogen self-diffusion with concentration beginning at 1.7-3.4 mg/mL, which deviated from the standard hard-particle behavior, suggesting a remarkable intermolecular entanglement. This concentration dependence was observed regardless of the absence or presence of the GPRP peptide (inhibitor of fibrin polymerization), and also in samples free of fibrin oligomers. By contrast, diffusivity of fibrinogen variant I-9 with truncated C-terminal portions of the Aα chains was much less concentration-dependent, indicating the importance of intermolecular linkages formed by the αC regions. Theoretical models combined with all-atom molecular dynamics simulations revealed partially bent fibrinogen solution conformations that interpolate between a flexible chain and a rigid rod observed in the crystal. The results obtained illuminate the important role of the αC regions in modulating the fibrinogen molecular shape through formation of weak intermolecular linkages that control the bulk properties of fibrinogen solutions.

NMR investigation of a thermotropic liquid crystal showing isotropic-isotropic'-(columnar)-cubic phase transitions

ABSTRACTIn this work, we report a first detailed study of the mesophasic behaviour of the calamitic liquid crystal, a (4,4′-bis(4″-carboxybelzyloxy)biphenyl derivate, labelled 9/2 RS/RS, showing an isotropic-isotropic-(columnar)-cubic phase behaviour on cooling. 1H NMR diffusometry allowed to distinguish between the two isotropic phases in terms of diffusion characterized by different Arrhenius activation energy, while 13C NMR static measurements and 2H NMR investigations were of help in understanding the orientational ordering properties of the metastable columnar phase and confirmed the isotropic state of the sample in the cubic phase.

Characteristics of water and ion exchange of Elodea nuttallii cells at high concentrations of lanthanides

Changes of diffusive permeability of membranes of Elodea nuttallii cells following a short-term (60 min) treatment with high concentrations of lanthanides were recorded by the 1H NMR-diffusometry and conductometry methods. The 1-h infiltration of segments of Elodea nuttallii internodes in 10 mM solutions of nitrates of La, Nd and Lu resulted in the increased leakage of electrolytes from cells, but has no effect on a water diffusive permeability of membranes. In samples subjected to a 30 min pretreatment with a water channel inhibitor HgCl2 the water diffusive permeability of membranes (Pd) drops down under the influence of lanthanides, as well as an outcome of electrolytes. To explain the observed effects the change of spontaneous curvature of membrane lipid layer has been taken into consideration. The interaction of lanthanides with lipids of plasmalemma leads to the negative spontaneous curvature of lipid layer at which membrane channels are unclosed. Blocking of the ionic and water channels by mercury ions compensate the effect of change of spontaneous curvature of lipid layer.

Lateral Diffusion of Dispersing Molecules on Nanotubes As Probed by NMR

Noncovalent dispersion of carbon nanotubes is essential to most applications but still poorly understood at the molecular level. The interaction of the dispersing molecule with the nanotube, wrapping or nonwrapping, still awaits consensus. Herein, we have studied by 1H NMR diffusometry some features of molecular dynamics in the system of carbon nanotubes dispersed by triblock copolymer Pluronics F127 in water. The diffusional decays obtained at different diffusion times, Δ, are not single-exponential and have a complex Δ-dependent profile, ultimately implying that the polymer is observed in two states: free (in unimeric form) and nanotube-bound. Fitting a two-site exchange model to the data indicates that at any instant, only a small fraction of polymers are adsorbed on the nanotubes, with polydisperse residence times in the range of 100–400 ms. Most significantly, we further provide an estimate of D = (3–8) × 10–12 m2 s–1 for the coefficient of lateral diffusion of the polymer along the nanotube surface, which is an order of magnitude slower than the corresponding self-diffusion coefficient in water. The emerging picture is that of a nonwrapping mode for the polymer–nanotube interaction.

Translational self-diffusion in the smectic phases of ferroelectric liquid crystals: an overview

In this work, we present our recent results obtained in the field of translational self-diffusion studies by means of 1H NMR diffusometry in smectic phases formed by calamitic chiral liquid crystals. In particular, the diffusional behavior of chiral smectic phases with different clinicity, such as the ferroelectric and antiferroelectric phases, will be discussed on the basis of the results obtained on three different chiral smectogens. This research demonstrates that, despite previous assertions, out-of-plane translational diffusion in smectic phases is poorly affected by the clinicity of the phases, showing no discontinuity at the transition from synclinic to anticlinic structures, typical of the smectic C* phases. We can conclude that diffusion basically reflects the layered smectic structure where in-plane diffusion is much faster and less hindered than the out-of-plane one.

Translational self diffusion anisotropy in the smectic A phase measured by a static fringe field gradient 1H NMR diffusometry approach

Self diffusion along the phase director in the nematic phase and parallel to and across the layer in the smectic A phase of the OAB smectogen has been measured exploiting a static fringe field gradient 1H NMR diffusometry approach.

NMR Experiments on Molecular Dynamics in Nanoporous Media: Evidence for Lévy Walk Statistics

ABSTRACTField-cycling 1H and 2H NMR relaxometry and field-gradient 1H NMR diffusometry were applied to polar and nonpolar liquids filled into porous glasses and fineparticle agglomerates (SiO2, ZnO, TiO2, globular proteins). The orders of magnitude of the length scales of the pore spaces ranged from 100 to several 102 nm. Pronounced differences of the spin-lattice relaxation dispersion for “weak” (nonpolar) and “strong” (polar) adsorption were found. In the latter case, the correlation times of the adsorbate orientation are up to eight orders of magnitude longer than in bulk. Trans-lational diffusion in liquid surface layers was directly studied with the aid of field-gradient NMR diffusometry in systems where the free liquid was frozen. The spin-lattice relaxation dispersion can be explained on the basis of reorientations mediated by translational displacements (RMTD) of adsorbate molecules on the surfaces. Thisprocess appears to be enhanced by a Levy walk mechanism so that the propagator adopts the form of a Cauchy distribution. The evaluated surface correlation functions are characterized by surface correlation lengths in the same order as the pore diameters, that is, up to three orders ofmagnitude larger than the length scale of dipolar interaction.