Wide-line 1H Research Articles

Tensile yield behavior of isotactic polybutene-1

Relative to polyethylene or polypropylene, isotactic polybutene-1 (iPB-1) in form I is of high value for commercial applications due to its excellent mechanical properties; whereas, it tends to exhibit inconspicuous yield behavior closely related to poor energy consumption and thus weak toughness when subjected to uniaxial stretching. Regret, few studies had addressed how to control iPB-1 tensile yield behavior. As the tensile yield behavior of form I iPB-1 depended on the applied annealing temperature Ta and time ta as well as cyclic loading-unloading conditions, iPB-1 three-phase structure evolution was carefully characterized by wide-line solid-state 1H NMR. With Ta or ta increasing, the weakening tensile yield behavior of iPB-1 was accompanied by a decreasing rigid phase content which can be recognized by 1H NMR rather than DSC, revealing that a higher rigid phase content in iPB-1 favors a more significant typical tensile yield behavior. Furthermore, the weakening tensile yield behavior of iPB-1 due to annealing at a higher temperature can slowly recover back while further annealing at a lower temperature, implying the reversibility of destroyed rigid phase. Cyclic loading-unloading under a suitable fixed strain can promote formation of rigid phase in iPB-1, favoring appearance of the typical yield behavior. Therefore, the mutual contact possibility, dislocation and slip of iPB-1 rigid phase were proposed to be responsible for the tensile yield behavior. The results are of significance for understanding the structural origin of tensile yield behavior of iPB-1 and further tuning toughness of iPB-1 for its industrial applications.

Dynamic Sorting of Mobile and Rigid Molecules in Biomembranes by Magic-Angle Spinning 13C NMR

Understanding the membrane dynamics of complex systems is essential to follow their function. As molecules in membranes can be in a rigid or mobile state depending on external (temperature, pressure) or internal (pH, domains, etc.) conditions, we propose an in-depth examination of NMR methods to filter highly mobile molecular parts from others that are in more restricted environments. We have thus developed a quantitative magic-angle spinning (MAS) 13C NMR approach coupled with cross-polarization (CP) and/or Insensitive Nuclei Enhanced by Polarization Transfer (INEPT) on rigid and fluid unlabeled model membranes. We demonstrate that INEPT can detect only very mobile lipid headgroups in gel (solid-ordered) phases; the remaining rigid parts are only detected with CP. A direct correlation is established between the normalized line intensity as obtained by CP and the C-H (C-D) order parameters measured by wide-line 2H NMR or extracted from molecular dynamics: ICP/IDPeq ≈ 5|SCH|, indicating that when the order is greater than 0.2-0.3 (maximum value of 0.5 for chain CH2), only rigid parts can be filtered and detected using CP techniques. In very fluid (liquid-disordered) membranes, where there are many more active motions, both INEPT and CP detect resonances, with, however, a clear propensity of each technique to detect mobile and restricted molecular parts, respectively. Interestingly, the 13C NMR chemical shift of lipid hydrocarbon chains can be used to monitor order-disorder phase transitions and calculate the fraction of chain defects (rotamers) and the part of the transition enthalpy due to bond rotations (6-7 kJ·mol-1 for dimyristolphosphatidylcholine, DMPC). Cholesterol-containing membranes (liquid-ordered phases) can be dynamically contrasted as the rigid-body sterol is mainly detected by the CP technique, with a contact time of 1 ms, and the phospholipid by INEPT. Our work opens up a straightforward, robust, and cost-effective route for the determination of membrane dynamics by taking advantage of well-resolved conventional 13C NMR experiments without the need of isotopic labeling.

Wide-Line NMR Melting Diagrams, Their Thermodynamic Interpretation, and Secondary Structure Predictions for A30P and E46K α-Synuclein.

Parkinson’s disease is thought to be caused by aggregation of the intrinsically disordered protein, α-synuclein. Two amyloidogenic variants, A30P, and E46K familial mutants were investigated by wide-line 1H NMR spectrometry as a completion of our earlier work on wild-type and A53T α-synuclein (BokorM. et al. WT and A53T α-synuclein systems: melting diagram and its new interpretation. Int. J. Mol. Sci.2020, 21, 3997.). A monolayer of mobile water molecules hydrates A30P α-synuclein at the lowest potential barriers (temperatures), while E46K α-synuclein has here third as much mobile hydration, insufficient for functionality. According to wide-line 1H NMR results and secondary structure predictions, E46K α-synuclein is more compact than the A30P variant and they are more compact than the wild type (WT) and A53T variants. Linear hydration vs potential barrier sections of A30P α-synuclein shows one and E46K shows two slopes. The different slopes of the latter between potential barriers Ea,1 and Ea,2 reflect a change in water–protein interactions. The 31–32% homogeneous potential barrier distribution of the protein–water bonds refers to a non-negligible amount of secondary structures in all four α-synuclein variants. The secondary structures detected by wide-line 1H NMR are solvent-exposed α-helices, which are predicted by secondary structure models. β-sheets are only minor components of the protein structures as three- and eight-state predicted secondary structures are dominated by α-helices and coils.

Secondary Structures of Proteins: A Comparison of Models and Experimental Results

Secondary structure predictions of proteins were compared to experimental results by wide-line 1H NMR. IUPred2A was used to generate predictions of disordered protein or binding regions. Thymosin-β4 and the stabilin-2 cytoplasmic domain were found to be mainly disordered, in agreement with the experimental results. α-Synuclein variants were predicted to be disordered, as in the experiments, but the A53T mutant showed less predicted disorder, in contrast with the wide-line 1H NMR result. A disordered binding site was found for thymosin-β4, whereas the stabilin-2 cytoplasmic domain was indicated as such in its entire length. The last third of the α-synuclein variant’s sequence was a disordered binding site. Thymosin-β4 and the stabilin-2 cytoplasmic domain contained only coils and helices according to five secondary structure prediction methods (SPIDER3-SPOT-1D, PSRSM, MUFold-SSW, Porter 5, and RaptorX). β-Sheets are present in α-synucleins, and they extend to more amino acid residues in the A53T mutant according to the predictions. The latter is verified by experiments. The comparison of the predictions with the experiments suggests that helical parts are buried.

Residual Solvent in Highly Oriented Ultrahigh Molecular Weight Polyethylene Fibers

The use of a solvent, Vaseline oil, for the orientational drawing of high-strength and high-modulus UHMWPE fibers is considered. Since the side effect of the residual solvent during orientational drawing of UHMWPE fibers is the formation of pores that reduce the packing density of macromolecules, then at a certain stage of drawing the fiber, the solvent is removed from it by washing in n-heptane. The task of monitoring the residual solvent is studied by wide-line 1H NMR and ATR IR spectroscopy. In terms of methodology, the task is complicated by the accumulation of low molecular weight fragments of broken UHMWPE macromolecules, which are difficult to distinguish from short solvent molecules, in highly oriented fibers.

The Melting Diagram of Protein Solutions and Its Thermodynamic Interpretation.

Here we present a novel method for the characterization of the hydration of protein solutions based on measuring and evaluating two-component wide-line 1H NMR signals. We also provide a description of key elements of the procedure conceived for the thermodynamic interpretation of such results. These interdependent experimental and theoretical treatments provide direct experimental insight into the potential energy surface of proteins. The utility of our approach is demonstrated through the examples of two proteins of distinct structural classes: the globular, structured ubiquitin; and the intrinsically disordered ERD10 (early response to dehydration 10). We provide a detailed analysis and interpretation of data recorded earlier by cooling and slowly warming the protein solutions through thermal equilibrium states. We introduce and use order parameters that can be thus derived to characterize the distribution of potential energy barriers inhibiting the movement of water molecules bound to the surface of the protein. Our results enable a quantitative description of the ratio of ordered and disordered parts of proteins, and of the energy relations of protein–water bonds in aqueous solutions of the proteins.

Comparing the efficacy of solid and magic-echo refocusing sequences: Applications to 1H NMR echo spectroscopy of shale rock

Quantitative evaluation of the solid and viscous components of unconventional shale rock, namely kerogen and bitumen, is important for understanding reservoir quality. Short transverse coherence times, due to strong 1H-1H dipolar interactions, motivates the application of solid state refocusing pulse sequences that allow for investigating components of the free-induction decay that are otherwise obscured by instrumental effects such as probe ringdown. This work reports on static, wide-line 1H spectroscopy of shale rock and their extracted components, which include kerogen and bitumen, by the application of solid echo and magic echo pulse sequences. We characterize the efficiency of these cycles as a function of the radio frequency power and inter-pulse spacing. Magic echos are shown to provide superior refocusing in comparison to solid echo based experiments, as can be understood from the truncation of the Magnus expansion and ability to also refocus any Iz Hamiltonians (e.g. static field inhomogeneity). We characterize the optimal echo spacing and RF power for two shale samples of different maturity, motivating routine core and cuttings analysis and applications.

ChemInform Abstract: Advanced Solid‐State NMR Techniques for the Study of Molecular Sieves

AbstractReview: 238 refs.

Water scaffolding in collagen: Implications on protein dynamics as revealed by solid‐state NMR

Solid-state NMR studies of collagen samples of various origins confirm that the amplitude of collagen backbone and sidechain motions increases significantly on increasing the water content. This conclusion is supported by the changes observed in three different NMR observables: (i) the linewidth dependence on the 1H decoupling frequency; (ii) 13C CSA changes for the peptide carbonyl groups, and (iii) dephasing rates of 1H-13C dipolar couplings. In particular, a nearly threefold increase in motional amplitudes of the backbone librations about C-Cα or N-Cα bonds was found on increasing the added water content up to 47 wt%D2 O. On the basis of the frequencies of NMR observables involved, the timescale of the protein motions dependent on the added water content is estimated to be of the order of microseconds. This estimate agrees with that from wideline T2(1)H NMR measurements. Also, our wideline 1H NMR measurements revealed that the timescale of the microsecond motions in proteins reduces significantly on increasing the added water content, i.e., an ∼15-fold increase in protein motional frequencies is observed on increasing the added water content to 45 wt% D2 O. The observed changes in collagen dynamics is attributed to the increase in water translational diffusion on increasing the amount of added water, which leads to more frequent "bound water/free water" exchange on the protein surface, accompanied by the breakage and formation of new hydrogen bonds with polar functionalities of protein.

Melting Point Elevation of Tetramethylsilane Confined in a Zn-Based Metal–Organic Framework

Abstract The thermal anomaly and molecular motion of tetramethylsilane (TMS) confined in a metal–organic framework, [Zn4O(O2CC6H4CO2)3]n (IRMOF-1), have been examined by differential thermal analysis and solid-state wide-line 1H NMR. Endothermic peaks were observed at 198 and 227 K, which were attributed to the disordered intermediate phase and molten phase, respectively, employing the temperature dependence of 1H NMR line width. This result suggests an elevation of the melting point of TMS confined in IRMOF-1.

Covalent Grafting to μ-Hydroxy-Capped Surfaces? A Kaolinite Case Study

All μ-hydroxyl groups are frequently encountered capping groups found on the external surfaces of various minerals that are often used as fillers in composite materials. Covalent grafting to this functional group would therefore offer a versatile and attractive route to surface modification. The octahedral layer of kaolinite is composed of μ-bridged aluminol groups. In particular, intercalation compounds of kaolinite, where all basal planes are exposed and may be modified, are ideally suited to study the feasibility of such covalent graftings. The huge (internal) specific surface area greatly improves the sensitivity of the analytics and renders kaolinite an ideal model compound. Herein we analyze the mode of bonding of ethylene glycol (EG), intercalated into kaolinite (EG kaolinite), by solid-state NMR techniques. 27Al MQMAS allows for distinction between intercalated and grafted EG molecules because the chemical surroundings of octahedrally coordinated aluminum nuclei in the layer are significantly changed by the formation of a covalent bond. Moreover, the temperature-dependent dynamics of the EG molecules in the interlamellar space are examined by wide-line solid-state 1H NMR measurements. The EG molecules perform a circular motion around the covalently bonded hydroxyl group in the interlamellar space. Analysis of the 13C–27Al REAPDOR measurement in conjunction with the EG dynamics allows for determination of the 13C···27Al distance between octahedral aluminum and the bonded carbon atom of EG. This distance is 3.1 Å. A thorough description of the bonding mode of the EG molecules is provided and proves beyond any doubt the covalent grafting. This suggests that the reactivity of μ-hydroxyl groups, in general, is sufficient to realize a covalent surface modification of a wide range of minerals.

Wide-line 1H NMR and DSC study of mesomorphic transformations of p-(alkoxybenzylidene)-p′-toluidines

p-(Alkoxybenzylidene)-p′-toluidines (ABTs) with 7, 8, and 10 carbon atoms in the alkyl moiety have been studied by wide-line 1H NMR and DSC. The thermotropic properties of these compounds have been studied in the temperature range 20–80°C, including main mesomorphic transformations of ABTs. The 1H NMR line shapes, widths, and second moments, as well as specific features of their temperature-induced changes, are discussed. The DSC data are compared with the character of mesomorphic transformations and 1H NMR data. The formation limits and ranges and stabilities of liquid-crystalline states of the ABT structure emerging on heating are determined.

Hydration water/interfacial water in crystalline lens

Wide-line 1H NMR signal intensity, spin–lattice and spin–spin relaxation rates and differential scanning calorimetry (DSC) measurements were done on avian (chicken and turkey) crystalline lenses between −70 °C and +45 °C to provide quantitative measures of protein hydration characteristic of the protein–water interfacial region. These measures are of paramount importance in understanding both the physiology of crystalline lens and its transitions to the cataractous pathological state characterized by the formation of opaque protein aggregates. Water mobility shows a characteristic transition at about −60 °C, which is identified as the melting of the interfacial/hydrate water. The amount of water in the low-temperature mobile fraction is about h = 0.4 g water/g protein, which equals the hydration required for protein activity. The amount of mobile water is temperature-independent up to about −10 °C, with a significant increase at higher temperatures below 0 °C. Above 0 °C, the relaxation processes can be described by a single (for spin–lattice) and by a triple (for spin–spin relaxation) exponential function. The spin–spin relaxation rate component of R 2 = 10–20 s −1 and its dynamical parameters characterize the interfacial water at ambient or physiological temperatures. When considered an independent phase, the specific heat of the hydrate water obtained by a combination of DSC and NMR data in the temperature range −43 °C to −28 °C is higher than that of pure/bulk water. This discrepancy can only be resolved by assuming that the hydrate water is in strong thermodynamic coupling with the protein matrix. The specific heat for the system composed of the protein molecule and its hydration water is 4.6 ± 0.3 J g −1 K −1. Thus, in a thermodynamic sense, crystalline protein and its hydrate layer behave as a highly-interconnected single phase.

Wide-Line 1H NMR and DSC study of phase states of mesomorphic states of 4′-n-alkoxy-4-biphenylcarbonitrile mesogens (n = 3 and 7)

4′-(Propyloxy)-4-cyanobiphenyl (3OCB) and 4′-(heptyloxy)-4-cyanobiphenyl (7OCB) have been studied in the temperature range 20–80°C by wide-line 1H NMR and DSC. The 1H NMR line shapes, half-widths, and second moments, as well as the relaxation characteristics of separate lines, are discussed. The DSC data are compared with the specific features of mesogenic transformations of these homologues and 1H NMR data. At certain temperatures depending on the composition of alkyl moieties, a dynamically disordered fraction of molecules appear in solid crystals. These molecules are involved in the thermotropic transitions of 3OCB to isotropic liquid and of 7OCB to nematic liquid crystal. The temperature ranges, stabilities, and other characteristics of the transitions of 3OCB to isotropic liquid and of 7OCB to nematic liquid crystal were determined.

Wide-line 1H NMR study of mesomorphic states of 4′-(octyloxy)-4-biphenylcarbonitrile

A sample of 4′-(octyloxy)-4-cyanobiphenyl (8OCB) was studied in the temperature range −60–80°C by wide-line 1H NMR. The line shapes, half-widths, and second moments were determined. For the smectic phase of 8OCB, the relaxation times T1 and T2, the correlation time τc, and the degree of order were estimated. The 1H NMR spectral patterns and characteristics were found to be quite different for the crystalline, smectic, and nematic phases of 8OCB, which makes it possible to reliably identify the corresponding transitions and assess the molecular dynamics and molecular order of a structure. The temperature ranges, stability conditions, and other characteristics of the liquid crystalline phases that form on heating 8OCB were determined.

Morphology and side-chain dynamics in hydrated hard α-keratin fibres by 1H solid-state NMR

The effect of hydration on phase composition, aminoacids side-chain dynamics, and domain thickness of hard α-keratin was investigated by 1H solid-state NMR. Decomposition of wide-line 1H NMR spectra was used to determine the phase composition and to obtain information on molecular motion. Proton spin-diffusion NMR experiments using a double-quantum dipolar filter were used to estimate the rigid domain sizes for the hydrated Caucasian hair fibres. The relative domain sizes were obtained from the solution of spin-diffusion equation for cylindrical morphologies in the initial-rate approximation by a novel approach. A qualitative model describing the morphological and molecular dynamics changes induced by hydration was developed.

2H NMR Studies of Polymer Multilayer Capsules, Films, and Complexes

The chain dynamics of aqueous suspensions of polyelectrolyte complexes, supported multilayers deposited on submicron silica colloids, and hollow capsules were characterized by wide-line 2H NMR spectroscopy (DNMR) as a function of layer number, temperature, and ionic strength. The strong polyelectrolytes, poly(diallyldimethyl ammonium chloride) (PDADMAC) and poly(styrene sulfonate) (PSS) were employed with selective deuteration of the PDADMAC methyl group. DNMR line-shape analyses showed that there is enhanced chain mobility in the systems with excess positive monomer units, that is, supported multilayers and capsules capped with PDADMAC. Selective deuteration of the first, fifth, and ninth layers confirms that the alternation in chain mobility with the capping layer is a through-film effect. Differential scanning calorimetry (DSC)-detected phase transitions were found to occur between 32 and 45 °C for the PSS/PDADMAC complexes, supported multilayers, and capsules. Whereas the glass transitions of bulk-state polymers are detected by DNMR typically 30 to 40° above the DSC-detected Tg, the onset of fast chain motion for the water-saturated polyelectrolyte complexes and supported multilayers coincides with calorimetric transitions.

Wide-line 1H NMR study of 4′-(pentyloxy)-4-biphenylcarbonitrile in different phase states

A sample of 4′-(pentyloxy)-4-biphenylcarbonitrile was studied in the temperature range 20–70°C by wide-line 1H NMR. The line shapes, half-widths, and second moments were determined. At 20°C, the spectrum is a broad structureless line, which was split into three components at temperatures above 47°C. This pattern persisted up to 65°C, with the components becoming narrower. Above 68°C, the spectrum rapidly collapses to give a structureless narrow line with a width δH < 0.01 G. Analysis of the spectra and comparison with theoretical calculations made it possible to elucidate the transition of the sample from the crystalline to the nematic and isotropic phases, as well as to determine the temperature range of the stability of the liquid-crystalline phase and the role of rotational mobility of protons of different functional groups and sometimes of these groups as a whole in the mechanisms of phase transitions.

A Solid-State NMR Spectroscopic Study of the Adsorption of Toluene in Zeolite LiK-L

The adsorption of toluene in partially Li+-exchanged zeolite K-L (LiK-L) was examined by solid-state NMR spectroscopy. The environment of the Li+ ions at different sites in the zeolite before and after adsorption was characterized by 7Li magic-angle spinning (MAS) NMR. 1H → 7Li cross polarization (CP) and 7Li{1H} rotational-echo double-resonance (REDOR) experiments were performed to probe the cation−sorbate interactions. The data were also used for spectral assignment. The 7Li NMR results indicate that most of the Li+ ions occupy the sites A (39%) and B (43%) and that there are fewer Li+ ions at sites C (17%) and D (1%). The four 7Li NMR signals corresponding to the Li+ ions at four sites are not resolved in the spectrum of the dehydrated zeolite, but are well-separated after the adsorption of toluene. The NMR results show that a toluene molecule is directly coordinated to the Li+ ion at site D near the wall of the main channel via formation of a π-complex, resulting in a significant change in 7Li chemical shift toward a more shielded direction. Although not directly accessible by the toluene molecules, the Li+ ions at sites A and C also exhibit an observable shift upon adsorption. Only the Li+ ions at site B do not experience a significant change in chemical shift. The effect of the adsorption on 7Li chemical shift is discussed. Dynamic behavior of toluene molecules inside the channels was also investigated by wide-line 2H NMR.

An investigation of the adsorption of aromatic hydrocarbons in zeolite Na–Y by solid-state NMR spectroscopy

The adsorption of toluene inside zeolite Na–Y was investigated by solid-state NMR spectroscopy. The environment of Na + ions at different sites in Na–Y before and after adsorption was characterized by 23Na magic-angle spinning (MAS) NMR. The information on the dynamic behavior of guest molecules inside the supercage of Na–Y was obtained by analyzing wideline 2H NMR spectra. The effect of loading level and temperature on molecular dynamics was also examined. The cation–sorbate interactions were directly probed by 23Na{ 1H} rotational-echo double-resonance (REDOR) experiments at different temperatures. Molecular Monte Carlo simulations were also performed to assist in the interpretation of the NMR data. 23Na MAS and 23Na{ 1H} REDOR results show that each toluene molecule is facially coordinated to a Na + ion at the SII site in the supercage, forming a π-complex. The adsorption also causes the Na + ions initially located at the SI′ site to slightly shift to a new position within the sodalite cage, but has little effect on the Na + at the SI site. The 2H NMR results indicate that the toluene molecules undergo a 2-site flip around the molecular long axis in addition to the methyl group rotation about its C 3 axis. 23Na MAS spectra suggest that the adsorptive behavior of benzene and p-xylene in Na–Y is similar to that of toluene/Na–Y. 23Na{ 1H} REDOR results further indicate that inside the supercage, the degree of molecular motion follows the order of benzene > toluene > p-xylene.