NMR Property Research Articles

Mechanism study on rheological response of thermally pretreated waxy crude oil

Pre-heating treatment significantly influences the low-temperature flow characteristics of waxy crude oil, yet its underlying mechanism warrants further investigation. This study explores the effects of pre-heating temperatures (60–110 °C) on the rheological characteristics of waxy crude oil from Nanyang using 1H NMR, DSC, Microscopic Observation, and Rheological Property Test. Findings reveal that asphaltenes increasingly dissolve at the pre-heating temperature of 70 °C, improving their capacity to act as nucleation sites for wax crystals. Consequently, the wax appearance temperature (WAT) increases. Meanwhile, the rheological parameters of the crude oil decrease and wax crystals exhibit smaller and tighter rod-like structures. Further growing the pre-heating temperature to 80 °C induces a comprehensive effect: alterations in asphaltene polarity, hindrance of asphaltene aggregation by alkyl side chains, and self-aggregation of alkyl side chains. This results in decreased WAT, along with the lowest rheological parameter values, with wax crystals appearing as the smallest and tightest dot-like shapes. At 80 °C, the optimal ratio between asphaltene polarity and alkyl side chain characteristics promotes strong nucleation and co-crystallization between asphaltene and wax crystals, maximizing asphaltene's ability to enhance the crude oil's low-temperature flowability. However, as the pre-heating temperature continues to rise, WAT decreases slightly and the rheological response starts to deteriorate.

Rationally designed fluorinated aromatic polyamide membrane for stable air dehumidification

Membrane based dehumidification technology has attracted wide attention. The anti-hydrolytic property of the membrane holds a significant role in its long-term operation in a wet environment. Herein, a series of fluorinated aromatic polyamides (FPA) are first proposed for stable air-dehumidification. Amide bond offers superior hydrolytic stability over chemical bond in the present dehumidification membrane. The deliberately introduced bulky fluorinated group (-CF3) increases the water permeability and enhances the anti-hydrolytic property of the FPA membranes. The membrane separation performance and membrane stability are further tuned by adjusting the molar ratio of para- and meta-amide groups to optimize the intermolecular forces and polymer chain arrangement, which is verified by the refractive index data and wide-angle X-ray diffraction results. The obtained co-FPA membranes exhibit tunable gas and water vapor permeation properties. With increasing para-amide group content, the gas and water vapor permeability of copolyamides gradually decreases and the selectivity of H2O/N2 increases. Meanwhile, the hydrolytic stability of the co-FPA membranes increases with the increase of TPC content as verified by 1H NMR, GPC, and mechanical property tests. Among these co-FPA membranes, the co-FPA-70 membrane exhibits the most excellent hydrolytic stability. The membrane shows almost no change in 1H NMR spectra and 97% retention of tensile strength after 5000 h of hydrolysis reaction. In the meanwhile, it shows excellent separation stability with a water vapor permeability retention of 74% during long-term hydrolysis aging operation. This study demonstrates the great potential of polyamide for the fabrication of dehumidification membranes with high hydrolysis resistance.

Pulse sequence induced variability combined with multivariate analysis as a potential tool for 13C solid-state NMR signals separation, quantification, and classification

Multivariate Curve Resolution (MCR) is a multivariate analysis procedure commonly used to analyze spectroscopic data providing the number of components coexisting in a chemical system, the pure spectra of the components as well as their concentration profiles. Usually, this procedure relies on the existence of distinct systematic variability among spectra of the different samples, which is provided by different sources of variation associated to differences in samples origin, composition, physical chemical treatment, etc. In solid-state NMR, MCR has been also used as a post-processing method for spectral denoising or editing based on a given NMR property. In this type of use, the variability is induced by the incrementation of a given parameter in the pulse-sequence, which encodes the separation property in the acquired spectra. In this article we further explore the idea of using a specific pulse sequence to induce a controlled variability in the 13C solid-state NMR spectra and then apply MCR to separate the pure spectra of the components according to the properties associated to the induced variability. We build upon a previous study of sugarcane bagasse where a series of 13C solid-state NMR spectra acquired with the Torchia-T1 CPMAS pulse sequence, with varying relaxation periods, was combined with different sample treatments, to estimate individual 13C solid-state NMR spectra of different molecular components (cellulose, xylan and lignin). Using the same pulse sequence, we show other application examples to demonstrate the potentiality, parameter optimization and/or establish the limitations of the procedure. As a first proof of principle, we apply the approach to commercial semicrystalline medium density polyethylene (MDPE) and polyether ether ketone (PEEK) providing the estimation of the individual 13C ssNMR spectra of the polymer chains in the amorphous (short T1) and crystalline (long T1) domains. The analysis also provided the relative intensities of each estimated pure spectra, which are related to the characteristic T1 decays of the amorphous and crystalline domain fractions. We also apply the analysis to isotactic poly (1-butene) (iPB-I) as an example in which the induced T1 variability occurs due to the mobility difference between the polymer backbone and side-chains. A jack-knifing procedure and a student t text allow us to stablish the minimum number of spectra and the range of relaxation periods that need to be used to achieve a precise estimation of the individual pure spectra and their relative intensities. A detail discussion about possible drawbacks, applications to more complex systems, and potential extensions to other type of induced variability are also presented.

Hydrophilic and Hydrophobic Effects on the Structure and Themodynamic Properties of Confined Water: Water in Solutions

NMR spectroscopy is used in the temperature range 180–350 K to study the local order and transport properties of pure liquid water (bulk and confined) and its solutions with glycerol and methanol at different molar fractions. We focused our interest on the hydrophobic effects (HE), i.e., the competition between hydrophilic and hydrophobic interactions. Nowadays, compared to hydrophilicity, little is known about hydrophobicity. Therefore, the main purpose of this study is to gain new information about hydrophobicity. As the liquid water properties are dominated by polymorphism (two coexisting liquid phases of high and low density) due to hydrogen bond interactions (HB), creating (especially in the supercooled regime) the tetrahedral networking, we focused our interest to the HE of these structures. We measured the relaxation times ( and ) and the self-diffusion (D). From these times, we took advantage of the NMR property to follow the behaviors of each molecular component (the hydrophilic and hydrophobic groups) separately. In contrast, D is studied in terms of the Adam–Gibbs model by obtaining the configurational entropy (S) and the specific heat contributions (C). We find that, for the HE, all of the studied quantities behave differently. For water–glycerol, the HB interaction is dominant for all conditions; water–methanol, two different T-regions above and below 265 K are observable, dominated by hydrophobicity and hydrophilicity, respectively. Below this temperature, where the LDL phase and the HB network develops and grows, with the times and C change behaviors leading to maxima and minima. Above it, the HB becomes weak and less stable, the HDL dominates, and hydrophobicity determines the solution.

Transformation of the molecular structure of butyl methacrylate/acrylamide/acrylic acid copolymers during heat treatment

High-performance butyl methacrylate/acrylamide/acrylic acid (BMA/AM/AA) copolymers, being the precursor of PMI foam, were synthesized by free radical bulk copolymerization. Transformation of the molecular structures of AM/AA copolymers, BMA/AM copolymers and BMA/AM/AA copolymers was deeply investigated by use of 13C and 1H NMR, FTIR, DSC, TGA, DMA and mechanical property test. Results confirmed the occurrence of BMA/AM/AA copolymers. It tends to indicate the cyclization and cross-linking reactions during heat treatment, which would further induce the cyclic structures and cross-linking structures. A higher treatment temperature would result in a higher degree of cyclization and cross-linking. These findings confirmed the transformation of the molecular structures during heat treatment, which may be the key to improving the properties of BMA/AM/AA copolymers.

Toward Relatively General and Accurate Quantum Chemical Predictions of Solid-State (17)O NMR Chemical Shifts in Various Biologically Relevant Oxygen-Containing Compounds.

Oxygen is an important element in most biologically significant molecules, and experimental solid-state (17)O NMR studies have provided numerous useful structural probes to study these systems. However, computational predictions of solid-state (17)O NMR chemical shift tensor properties are still challenging in many cases, and in particular, each of the prior computational works is basically limited to one type of oxygen-containing system. This work provides the first systematic study of the effects of geometry refinement, method, and basis sets for metal and nonmetal elements in both geometry optimization and NMR property calculations of some biologically relevant oxygen-containing compounds with a good variety of XO bonding groups (X = H, C, N, P, and metal). The experimental range studied is of 1455 ppm, a major part of the reported (17)O NMR chemical shifts in organic and organometallic compounds. A number of computational factors toward relatively general and accurate predictions of (17)O NMR chemical shifts were studied to provide helpful and detailed suggestions for future work. For the studied kinds of oxygen-containing compounds, the best computational approach results in a theory-versus-experiment correlation coefficient (R(2)) value of 0.9880 and a mean absolute deviation of 13 ppm (1.9% of the experimental range) for isotropic NMR shifts and an R(2) value of 0.9926 for all shift-tensor properties. These results shall facilitate future computational studies of (17)O NMR chemical shifts in many biologically relevant systems, and the high accuracy may also help the refinement and determination of active-site structures of some oxygen-containing substrate-bound proteins.

Self-assembled betulinic acid protects doxorubicin induced apoptosis followed by reduction of ROS–TNF-α–caspase-3 activity

Doxorubicin (DOX) is a well-known drug used to treat a wide range of solid tumor and hematological malignancies, but the use of this drug is now restricted owing to its severe side effects, including normal cellular toxicity. This study was conducted to evaluate the potency of self-assembled betulinic acid (SA-BA) against DOX induced chemotherapeutic toxicity in human peripheral blood lymphocytes (PBLs). The isolated betulinic acid from the bark of Ziziphus jujuba tree was purified by column chromatography and characterized by FT–IR, XRD, 1H NMR and self-assembly property was investigated by SEM imaging. DOX treatment produced significant reduction of viability of PBLs mainly by lowering cellular anti-oxidant pool and elevating the reactive oxygen species level. Pre-treatment with SA-BA followed by DOX exposure for 24h protected the PBLs from DOX induced oxidative stress. Potent anti-apoptotic role of SA-BA was also confirmed by FACS analysis and western blot assay. Severe inflammation is one of the major concerns in DOX treatment. We found that pre-treatment with SA-BA on PBLs significantly protected the PBLs from DOX induced inflammation. Thus, our finding confirms that SA-BA can be used to ameliorate the cytotoxic effects of DOX, which can be a helpful strategy during DOX mediated chemotherapy in cancer patients.

Purification and antioxidant effect of novel fungal polysaccharides from the stroma of Cordyceps kyushuensis

Two polysaccharides were isolated from the stroma of cultured Cordyceps kyushuensis by hot water extraction as well as ion-exchange and gel-permeation chromatography. The fourier transform infrared (FTIR) spectra revealed the general characteristic absorption peaks of polysaccharides. Preliminary structural characterizations were conducted by NMR and physicochemical property, whereas their total sugar, sulfate acid and uronic acid contents, molecular weights and monosaccharide compositions were significantly different. Antioxidant properties were evaluated by assays of various antioxidant in vitro systems. The results showed that the two polysaccharides possessed good antioxidant properties in a concentration-dependent manner, especially scavenging abilities on hydroxyl radicals. Both samples showed clearly and strong capacity on protective effect of DNA damage. With current findings, the polysaccharides from C. kyushuensis may have potential applications in health functional food.

Investigation of crosslinking in the thermooxidative aging of nitrile–butadiene rubber

ABSTRACTChemical crosslinking is possibly the most significant factor affecting the mechanical behavior of rubbers. In this study, we investigated the evolution of network structures (the crosslinking degree and crosslinking density) during the thermooxidative aging of a nitrile–butadiene rubber (NBR) using characterization methods such as low‐dimensional NMR, solvent extraction, solvent swelling, IR spectroscopy, and mechanical property measurements. The NMR and solvent extraction results show the change of the crosslinking degree. The solvent swelling results show the change of the crosslinking density. The IR results show the chemical changes relating to crosslinking and chain scissions. Therefore, a comprehensive picture of the thermal oxidative aging of the NBR compound was drawn by the integration of various results from these methods. Crosslinking occurred throughout the aging process, whereas chain scissions took place and competed with crosslinking in the later stage. The crosslinking density increased at a nearly constant rate, whereas the increase in the crosslinking degree slowed down in the later stage. The crosslinking density was closely correlated with the hardness and Young's modulus. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41319.

Structure Lattice-Dimensionality and Spectroscopic Property Correlations in Novel Binary and Ternary Materials of Group 13 Elements with α-Hydroxycarboxylic Benzilic Acid and Phenanthroline

To probe and understand the structural and coordinative flexibility of Group 13 ions with α-hydroxycarboxylic acids, leading to crystalline inorganic–organic hybrid materials with distinct lattice architecture, dimensionality, and spectroscopic properties, the systematic synthesis and physicochemical properties of binary and ternary B(III), Al(III), Ga(III), In(III), and Tl(I)-benzilic acid-(phenanthroline) systems were investigated in water–alcohol mixtures. Stoichiometric reactions of Group 13 ions with benzilic acid and phenanthroline (phen) afforded the new materials [B(C14H10O3)2](C3H5N2)·H2O (1), [Al(C14H11O3)3]·0.5C2H5OH·4.5H2O (2), [Ga(C14H11O3)3]·CH3OH·3H2O (3), [In(C14H11O3)4]·C3H5N2·C2H5OH·H2O (4), [Tl(C14H11O3)]n (5), [Tl2(C14H11O3)2(phen)2] (6), and [Tl(C14H11O3)(phen)(H2O)](C14H12O3)(phen) (7). All materials were characterized by elemental analysis, Fourier transform infrared spectroscopy, 13C, 11B, 27Al, 71Ga, and 205Tl cross-polarization/magic-angle spinning NMR, thermogravimetric analysis, luminescence, and single crystal X-ray diffraction. The nature of the benzilate ligand and phenanthroline in the chemical reaction mixtures with Group 13 ions led to the emergence of distinct lattice composition-dimensionality (1D-2D) correlations at the binary-ternary level, providing spectroscopic fingerprint identity to M(I,III)-coordination and luminescence activity. The interplay between the benzilate ligand, phenanthroline, and Group 13 ions, (a) reveals well-defined contributions of the chemical and structural factors influencing the arising binary and ternary interactions at the M(I) and M(III) oxidation levels, and (b) clarifies correlations between crystal-lattice architecture and dimensionality with unique heteronuclear solid-state NMR and optical property signatures in inorganic–organic hybrid materials.

Synthesis and Characterization of Well-Controlled Isotactic Polypropylene Ionomers Containing Ammonium Ion Groups

This paper discusses the synthesis of a new family of well-controlled isotactic polypropylene ionomers (iPP-NH3+Cl–) containing up to 5 mol % of NH3+Cl– ionic groups, with high molecular weight and narrow molecular weight and composition distributions, as well as good processability in melt and solution. A systematic study was conducted using various isospecific Ziegler–Natta and metallocene catalysts in the copolymerization of propylene and a high α-olefin comonomer containing a silane-protected amino group and the subsequent work-up procedures that can prevent undesirable side reactions in forming iPP-NH3+Cl– ionomers in a one-pot process. The resulting copolymers were carefully monitored by polymer solubility and a combination of NMR, GPC-triple detectors, DSC, and mechanical property measurements. Evidently, the most suitable reaction process requires a combination of the rac-Me2Si[2-Me-4-Ph(Ind)]2ZrCl2 metallocene catalyst system with a purified d-MAO (TMA-free), 6-bis(trimethylsilyl)amino-1-hexene comonomer during the copolymerization reaction and a work-up procedure to directly interconvert the silane-protected amino groups (−N(SiMe3)2) into −NH3+Cl– ionic groups before exposing to air. The attempt of isolating both iPP-N(SiMe3)2 and iPP-NH2 intermediates resulted in the insoluble (cross-linked) products. On the other hand, the resulting iPP-NH3+Cl– ionomers were melt processed in air and showed a systematic increase of mechanical properties and high-temperature stability with the increase of NH3+Cl– content.

PdGa intermetallic hydrogenation catalyst: an NMR and physical property study

The PdGa intermetallic compound is a highly selective and stable heterogeneous hydrogenation catalyst for the semi-hydrogenation of acetylene. We have studied single crystals of PdGa grown by the Czochralski technique. The 69Ga electric-field-gradient (EFG) tensor was determined by means of NMR spectroscopy, giving experimental confirmation of both the recently refined structural model of PdGa and the theoretically predicted Pd–Ga covalent bonding scheme. The hydrogenation experiment has detected no hydrogen uptake in the PdGa, thus preventing in situ hydride formation that leads to a reduction of the catalytic selectivity. We have also determined bulk physical properties (the magnetic susceptibility, the electrical resistivity, the thermoelectric power, the Hall coefficient, the thermal conductivity and the specific heat) of single-crystalline PdGa. The results show that PdGa is a diamagnet with metallic electrical resistivity and moderately high thermal conductivity. The thermoelectric power is negative with complicated temperature dependence, whereas the Hall coefficient is positive and temperature-dependent, indicating complexity of the Fermi surface. Partial fulfillment of the NMR Korringa relation reveals that the charge carriers are weakly correlated. Specific heat measurements show that the density of electronic states (DOS) at the Fermi energy of PdGa is reduced to 15% of the DOS of the elemental Pd metal.

NMR property of rubidium loaded sodalite

27Al NMR property of rubidium-loaded potassium-type sodalite, which has antiferromagnetic transition temperature TN of 80K, is reported. Similar to the case of potassium-loaded one, monotonous narrow spectrum is seen above TN and broadened one is observed below TN. Separately shifted component, which is seen in the case of sodium-loaded one, is not observed as the potassium-loaded one. When two Gaussian functions are used for fitting, widths of each Gaussian component fairly scale to each other. The ratio between two Gaussian widths takes close value to the case of potassium loading below 65K and shows difference above 65K. This difference comes from the raising of TN by replacement of K to Rb.

NMR property calculations and experimental study of the 1,6‐epoxycarvone and α‐epoxypinene: a comparison of models

This work aims at using theoretical calculations of shielding tensors (σ) through different methods [gauge-independent atomic orbital (GIAO), continuous set of gauge transformations (CSGT) and individual gauges for atoms in molecules (IGAIM)] and spin-spin coupling constants J using GIAO method to compare these methods and to corroborate the data obtained with the assignment of all of (1)H and (13)C NMR signals and the relative stereochemistry of the 1,6-epoxycarvone and the α-epoxypinene. All the (1)H and (13)C NMR signals were assigned unequivocally. The stereochemistry for the epoxides is trans and the B3LYP theory level with CSGT and IGAIM methods is the best choice to evaluate theoretical chemical shifts for compounds studied.

Investigation on the activation of coal gangue by a new compound method

In order to comprehensively utilize coal gangue as the main raw material in cementitious materials, improving its cementitious activity is a question of fundamental importance. In this paper, we present a new compound mechanical-hydro-thermal activation (CMHTA) technology to investigate the activation effect of coal gangue, and the traditional mechanical–thermal activation (TMTA) technology was used as reference. The purpose of this study is to give a detailed comparison between these two methods with regard to the mineral composition, crystal structure and microstructure, by XRD, IR, MAS NMR, XPS and mechanical property analysis. The prepared coal gangue based blended cement, containing 52% of activated coal gangue C (by CMHTA technology), has a better mechanical property than activated coal gangue T (by TMTA technology) and raw coal gangue. The results show that both of the TMTA and CMHTA technologies can improve the cementitious activity of raw gangue greatly. Moreover, compared with TMTA, the mineral phases such as feldspar and muscovite in raw coal gangue were partially decomposed, and the crystallinity of quartz decreased, due to the effect of adding CaO and hydro-thermal process of CMHTA technology.

NMR property of sodalite loaded with potassium

27Al NMR property of potassium-loaded sodalite, which shows antiferromagnetic transition around 70 K, is reported. Monotonic narrow spectrum above 70 K is broadened below 70 K. The broadened spectrum is analyzed with an assumption that the broadening is given by dipolar field from magnetic moment in the cage of sodalite. Two Gaussian functions are used for fitting. Widths of each component proportionally scale each other. The ratio between the Gaussian widths of each component of the narrower and the broader components is 15±3.

Prediction of the 1H and 13C NMR Spectra of α-d-Glucose in Water by DFT Methods and MD Simulations

We have applied computational protocols based on DFT and molecular dynamics simulations to the prediction of the alkyl 1H and 13C chemical shifts of alpha-d-glucose in water. Computed data have been compared with accurate experimental chemical shifts obtained in our laboratory. 13C chemical shifts do not show a marked solvent effect. In contrast, the results for 1H chemical shifts provided by structures optimized in the gas phase are only fair and point out that it is necessary to take into account both the flexibility of the glucose structure and the strong effect exerted by solvent water thereupon. Thus, molecular dynamics simulations were carried out to model both the internal geometry as well as the influence of solvent molecules on the conformational distribution of the solute. Snapshots from the simulation were used as input to DFT NMR calculations with varying degrees of sophistication. The most important factor that affects the accuracy of computed 1H chemical shifts is the solute geometry; the effect of the solvent on the shielding constants can be reasonably accounted for by self-consistent reaction field models without the need of explicitly including solvent molecules in the NMR property calculation.

Can Changes in One-bond Spin−spin Coupling Constants in Acids Be Related to Gas-Phase Proton Affinities of Bases?

Ab initio EOM-CCSD calculations have been carried out in search of acids with one-bond spin-spin coupling constants which could serve as probes of molecular basicity upon complex formation. Only 1J(F-H) and 1J(B-Li) in complexes F-H...Y and H2B-Li...Y, respectively, are able to differentiate among the protonation energies of bases containing Y. Changes in 1J(F-H) upon complex formation are related to the protonation energies of bases, but only when these energies are about 200 kcal/mol or greater. On the other hand, changes in 1J(B-Li) upon complexation are related to base protonation energies in the range between 100 and about 190 kcal/mol. Thus, these two one-bond coupling constants 1J(F-H) and 1J(B-Li) are complementary probes. For the first time, the computed NMR property of a gas-phase one-bond spin-spin coupling constant has been related to the experimental gas-phase thermodynamic property of proton affinity.

NMR property of low silica X zeolite with incorporated potassium

23 Na- and 27 Al- NMR spectra between 300 and 4 K of a potassium-loaded low silica X zeolite which shows ferrimagnetism are obtained. For 23 Na, positively shifted components are observed on the spectrum other than an unshifted one. We consider that those shifted components are given by the hyperfine interaction between the magnetic electrons in cages and 23 Na nuclei, which are located at several sites inside of the cages. On the other hand, like the case of zeolite A with Rb cluster, 27 Al shows symmetrically widened spectrum but gives no apparent shift. We consider that this feature is revealed by the coupling only through the dipolar interaction between the magnetic electrons and the 27 Al nuclei.

NMR property of arrayed K clusters in zeolite LTA with Si/Al=1.5

Abstract NMR property of 27Al in K-loaded LTA-type zeolite with Si/Al=1.5 is reported. The higher frequency side of the monotonous spectrum of not loaded sample is changed as expanded, only at the higher frequency side, to higher frequency direction by loading of external K. Some NMR parameters, T2 and T 2 * , of the expanded components are different from those of the original one. Since the potential for external atoms is shallower for the case of Si/Al=1.5 than for that of Si/Al=1.0, the origin of the shift may be attributed to Knight shift by Fermi contact interaction between nuclei and electron from adsorbed K.