Results Of Solid-state NMR Research Articles

Study on the anti-retrogradation of wheat amylopectin by addition of alkali-soluble glutenin

The retrogradation of wheat amylopectin during cold storage is the main reason for the increasing hardness of flour products such as steamed bread, bread and pastries, etc. Addition of gluten protein components is a green, safe, cheap and efficient method to inhibit the retrogradation of wheat amylopectin. In this paper, as being stored at 4 °C for 7 d, retrogradation rate of wheat amylopectin decreased from 55.02 % to 14.37 % after it was mixed with 20 % alkali-soluble glutenin (ASG) at 30 °C for 90 min, a 73.8 % reduction. The infrared results showed that the intensity of bending vibration of water molecules and intra-molecular β-sheet content of ASG decreased during the interaction between amylopectin and ASG. Meanwhile, intermolecular β-sheet and random coil contents of ASG increased. The results of 13C Solid-state NMR indicated that Qβ, Pγ and Lγ of ASG involved in interaction of wheat amylopectin, ASG and molecule of water. Under the optimal conditions, the interaction of wheat amylopectin and ASG began to form spheres containing disulfide bonds, resulting in the attenuation or disappearance of the diffraction peak at 2θ 19.7°, which may be marked as the criterion for the best mixing time of wheat amylopectin and ASG. The retrogradation kinetic index (n) of wheat amylopectin decreased significantly with the addition of ASG and formation of disulfide bond was the key factor. ASG could be potentially used as an anti-retrogradation agent for amylopectin.

Determining Local Magnetic Susceptibility Tensors in Paramagnetic Lanthanide Crystalline Powders from Solid-State NMR Chemical Shift Anisotropies

Exploring magnetic properties at the molecular level is a challenge that has been met by developing many experimental and theoretical solutions, such as polarized neutron diffraction (PND), muon-spin rotation (μ-SR), electron paramagnetic resonance (EPR), SQUID-based magnetometry measurements, and advanced modeling on open-shell systems and relativistic calculations. These methods are powerful tools that shed light on the local magnetic response in specifically designed magnetic materials such as contrast agents, for MRI, molecular magnets, magnetic tags for biological NMR, etc. All of these methods have their advantages and disadvantages. In order to complement the possibilities offered by these methods, we propose a new tool that implements a new approach combining simulation and fitting for high-resolution solid-state NMR spectra of lanthanide-based paramagnetic species. This method relies on a rigorous acquisition thanks to short high-power adiabatic pulses (SHAP) of high-resolution solid-state NMR isotropic and anisotropic data on a powdered magnetic material. It is also based on an efficient modeling of this data thanks to a semiempirical model based on a parametrization of the local magnetism and the crystal structure provided by diffraction methods. The efficiency of the calculation relies on a thorough simplification of the electron-nucleus interactions (point-dipole interaction, no Fermi contact) which is validated by experimental analysis. By taking advantage of the efficient calculation possibilities offered by our method, we can compare a great number of simulated spectra to experimental data and find the best-matching local magnetic susceptibility tensor. This method was applied to a series of isostructural lanthanide oxalates which are used as a benchmark system for many analytical methods. We present the results of thorough solid-state NMR and extensive modeling of the hyperfine interaction (including up to 400 paramagnetic centers) that yield local magnetic susceptibility tensor measurements that are self-consistent as well as consistent with bulk susceptibility measurements.

Improving resolution of solid state NMR in dense molecular hydrogen

Recent advancements in radio frequency resonator designs have led to the implementation of nuclear magnetic resonance in diamond anvil cells (DACs) at pressures well above 100 GPa. However, a relatively low resolution and the absence of decoupling sequences complicate the analysis of the results of solid state NMR in DACs. Here, we present the first application of homonuclear Lee-Goldburg (LG) decoupling on high density molecular hydrogen up to 64 GPa. Lenz lens based two-dimensional resonator structures were found to generate a homogeneous B1 field across sample cavities as small as 12 pl, a prerequisite for optimal decoupling. At ideal LG conditions, the broad 1H resonance of molecular ortho-hydrogen was narrowed 1600-fold, resulting in linewidths of 3.1 ppm.

Determination of the charge of Al13 Keggin oligocations intercalated into synthetic hectorite

Abstract Applying a nematic liquid crystalline phase of a synthetic Na-hectorite with layer separations >100 nm, the reaction time for pillaring with Al13 Keggin oligocation could be reduced to seconds ensuring that cation exchange is controlled by thermodynamics. With this material at hand we are able to resolve the long-standing dispute regarding the charge of intercalated Keggin oligocations. Micropore sizes as determined by physisorption isotherms, adsorption isotherms obtained via elemental analysis, and results of 27Al solid-state NMR and pyridine probe IR spectroscopy favor a charge of +7 for the Al13 pillars intercalated into hectorite unaltered.

Fluoroalkylated nanoporous carbons: Testing as a supercapacitor electrode

The surface of microporous Norit® GAC 830 W carbon was fluoroalkylated by heating in 1,1,1,2-tetrafluoroethane and 1,1,1,2,2-pentafluoroethane at 400 and 500 °C. Elemental analysis, FTIR ATR spectroscopy, and TG studies showed the presence of ∼0.1–0.7 mmol g−1 of the fluorine-containing groups. Nitrogen adsorption measurements and quenched solid density functional theory simulations proved an increase in the mesoporosity. By combining the results of solid-state 19F NMR and XPS analyses, we determined the functionalization of the carbon surface with CF, CF3, and CF2 fluorine-containing groups. Supercapacitor electrodes prepared from these materials were subjected to the charge-discharge tests and electrical impedance measurements. During galvanostatic cycling in the aqueous 30% KOH, they showed an enhanced charge capacitance compared to the parent (830 W) and the reference (Supra 30) carbons. These observations suggest that the fluoroalkylated surface and the modified microporous structure have an additive effect on capacitance parameters of carbon electrodes studied in symmetric, negative and positive modes. The fluoroalkylation caused an increase in the surface capacitance up to 38%. Herein, we demonstrate the fluoroalkylation is a simple way to increase a capacitance of carbon electrodes.

Synthesis and characterization of a highly conductive organic–inorganic hybrid polymer electrolyte based on amine terminated triblock polyethers and its application in electrochromic devices

A new highly ion conductive organic–inorganic hybrid electrolyte based on the reaction of triblock co-polymer poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) bis(2-aminopropyl ether) (ED2003) with 3-(glycidyloxypropyl)trimethoxysilane (GLYMO) and followed by co-condensation with 2-methoxy(polyethyleneoxy)propyl trimethoxysilane (MPEOPS) in the presence of LiClO4 was synthesized by a sol–gel process and characterized by a variety of experimental techniques. The maximum ionic conductivities of 1.1 × 10−4 S cm−1 at 30 °C and 6.0 × 10−4 S cm−1 at 80 °C were obtained for the hybrid electrolyte with a [O]/[Li] ratio of 24. The conductivity mechanism changed from Arrhenius at lower temperatures to Vogel–Tamman–Fulcher (VTF) behavior at higher temperatures. The results of solid-state NMR confirmed the structural framework of the hybrids, and provided a microscopic view of the effects of salt concentrations on the dynamic behavior of the polymer chains. The electrochemical stability window was found to be around 3.7–4.5 V, which is sufficient for electrochemical device applications. Preliminary tests performed with prototype electrochromic devices (ECDs) comprising the hybrid electrolyte with various [O]/[Li] ratios and mesoporous WO3 as the cathode layer are extremely encouraging. The best performance device exhibits an optical density change of 0.58, coloration efficiency of 375 cm2 C−1 and a good cycle life with the hybrid electrolyte with a [O]/[Li] ratio of 24. The present hybrid electrolyte offers a remarkable ionic conductivity and coloration efficiency in the solid state than previously reported organic–inorganic hybrid electrolytes.

The effect of charring and burial on the biochemical composition of cereal grains: investigating the integrity of archaeological plant material

Stable isotope analysis of charred archaeobotanical cereal grains has the potential to provide direct evidence of crop growing conditions in the past and to refine palaeodietary predictions. If isotope values of archaeobotanical material are to be considered robust, it is necessary to characterise the compositional changes associated with their charring and burial. This study used a suite of analytical techniques, including FT-IR and solid state 13C NMR, to characterise changes in the biochemical composition of modern einkorn grains with heating at 230 °C for 2 h, 4 h, 8 h and 24 h, encompassing conditions that replicate their undistorted ancient counterparts. The biochemical composition of archaeobotanical charred einkorn grains was also investigated by FT-IR and solid state 13C NMR in order to assess the changes in composition which occur during burial. Results of FT-IR and solid-state 13C NMR show that heating of modern einkorn grains resulted in Maillard reactions between cereal proteins and starch, forming high molecular weight melanoidins, which contain both alkyl and aromatic carbon. Loss of low molecular weight carbon and nitrogen-containing volatiles resulted in a slight but non-systematic increase in the δ13C values and a systematic increase of 0.8‰ in the δ15N values of the charred einkorn grains. Solid-state 13C NMR shows that the ancient charred einkorn grains consisted entirely of aromatic carbon and retained a similar proportion of nitrogen to their modern 24 h charred counterparts, despite a significantly lower concentration of amino acids. This indicates that the amino acid nitrogen in the ancient charred grains was retained in the stable melanoidins whose polymeric structure makes them resistant to subsequent degradation.

A new, robust method for measuring average fibre wall pore sizes in cellulose I rich plant fibre walls

A new, robust method for measuring the average pore size of water-swollen, cellulose I rich fibres is presented. This method is based on the results of solid-state NMR, which measures the specific surface area (area/solids mass) of water-swollen samples, and of the fibre saturation point (FSP) method, which measures the pore volume (water mass/solids mass) of water-swollen samples. These results are suitable to combine since they are both recorded on water-swollen fibres in excess water, and neither requires the assumption of any particular pore geometry. The new method was used for three model samples and reasonable average pore size measurements were obtained for all of them. The structural characterization of water-swollen samples was compared with the dry structure of fibres as revealed using BET nitrogen gas adsorption after a liquid exchange procedure and careful drying. It was concluded that the structure of the water-swollen fibres sets an upper limit on what is obtainable in the dry state.

Structure and dynamics of guest molecules confined in a mesoporous silica matrix: Complementary NMR and PDF characterisation

We present an experimental approach to study the structure and dynamics of molecular functional complexes in porous host matrices. Combining the results of Solid-State NMR and pair distribution function analysis based on total X-ray scattering data the structural arrangement and dynamical behaviour of Na2[Fe(CN)5NO]·2H2O (SNP) embedded in amorphous SiO2 matrix is investigated. We show that the SNP complexes are embedded as isolated complexes within the SiO2 pores and propose a structural model for the cation and anion arrangement. Additionally the NMR results demonstrate the rotational dynamics of the SNP complexes.

New highly conductive organic–inorganic hybrid electrolytes based on star-branched silica based architectures

A new type of organic–inorganic hybrid electrolyte has been developed by a sol–gel process through the reaction of cyanuric chloride with poly(oxyalkylene) diamine and 3-isocyanatepropyltriethoxysilane, followed by co-condensation of 2-[methoxy(polyethyleneoxy)propyl]trimethoxysilane. A maximum ionic conductivity of 1.0 × 10−4 Scm−1 at 30 °C has been achieved with the solid hybrid electrolyte. The results of solid-state NMR not only confirm the structural framework of the hybrids, but also provide a microscopic view of the effects of salt concentrations on the dynamic behavior of the polymer chains. The hybrid materials are blended with PVdF-HFP to form the blend hybrid membrane, followed by plasticization with various electrolyte solvents, with the purpose of increasing ionic conductivity. The plasticized blend hybrid electrolyte exhibits a maximum room temperature ionic conductivity of 8.8 × 10−3 Scm−1. Such a high ionic conductivity allows it as a potential candidate for applications in lithium ion batteries.

Efficient electron injection layer based on thermo-cleavable materials for inverted bottom-emission polymer light emitting diodes

The electron injection material PF-EP was found to be thermo-cleavable. Its solubility in chlorobenzene can be adjusted by thermal treatment at different temperatures. By analyzing the results of TGA, FT-IR, and 13C solid-state NMR, we interpret that the solubility transition is caused by partial acidification, crosslinking through a hydrogen-bonded network and coordination of O, P and Li. Based on this thermo-cleavable approach, efficient fully solution-processed IBPLEDs were successfully fabricated. The maximum current efficiency of the device with 2.5% Li2CO3 doped PF-EP as the EIL reaches nearly 1.7 times of that of a conventional device. We attribute the high performance to the good electron injection and hole blocking abilities of PF-EP and Li2CO3.

Chiral mesoporous organosilicas with R-(+)-Binol integrated in the framework

Bifunctionalized chiral mesoporous organosilicas with both R-(+)-Binol and ethylene moieties integrated in the framework was synthesized by co-condensation of 1,2-bis(trimethoxysilyl)ethane (BTME) and ( R)-2,2′-dimethoxy-6,6′-di-[(2-trimethoxysilyl)-ethenyl]-1,1′-binaphthyl ( R-MMB) in acidic medium using P123 as template for the first time. With the molar fraction of R-MMB increasing from10 to 20% in the initial mixture, the mesostructure of the material changes from a well-ordered 2D hexagonal mesostructure to a worm-like structure. The materials have a pore diameter in the range of 4.8–5.2 nm with BET surface areas varying from 356 to 894 m 2 g −1. The results of FT-IR, 13C and 29Si solid-state NMR shows the integration of the organic groups in the material though some Si–C bond cleavage was observed during the synthesis. The circular dichroism spectrum of the material dissolved in NaOH confirms that the chirality of R-(+)-Binol in the material remains unchanged compared with the molecular precursor. The hydroxyl groups of the R-(+)-Binol units were liberated by treatment of the material with BBr 3. The resultant materials were used in Ti-promoted asymmetric addition of diethylzinc to benzaldehyde. High catalytic activity (99%) with moderate enantioselectivity (39.7%) was achieved, which also confirms that R-Binol was incorporated in the PMOs successfully.

The study on the conductivity of styrene–maleic anhydride copolymer electrolytes based on poly(ethylene glycol)400 and LiClO4

Polyelectrolytes, in this study were synthesized from styrene–maleic anhydride (SMA) copolymer, poly(ethylene glycol)400 (PEG400), and lithium perchlorate (LiClO4). Fourier transform infrared spectroscopy (FTIR), and 7Li magic angle spinning (MAS) solid-state NMR were used to monitor the interaction between Li+ ions and polymer. The results of FTIR and 7Li MAS solid-state NMR indicate the Li+ ions are preferentially coordinated to the ether oxygen of PEG. The Tg of the PEG segments in polyelectrolyte increases with LiClO4 concentration, as determined by differential scanning calorimetry (DSC), indicating that solubility of the Li+ ions in the host polymer increases with the PEG content. Impedance spectroscopy (IS) shows that the bulk conductivity of polyelectrolytes and the conductivity behavior obeys the Vogel–Tamman–Fulcher (VTF) equation.

Nanocomposites from in-Situ Polymerization of Substituted Polyacetylene within Lamellar Surface of the Montmorillonite: A Solid-State NMR Study

Nanocomposites prepared by in-situ polymerization of 2-ethynylpyridine (2EPy) in the presence of a layered aluminosilicate such as Ca2+−montmorillonite (MMT) were characterized by solid-state 13C cross-polarization/magic angle spinning (CP/MAS) NMR spectroscopy. The structure and dynamics of the polymer layer inserted between the montmorillonite lamellae were investigated. The 13C NMR chemical shifts of the polymer component of the nanocomposite that was prepared by in-situ polymerization were assigned by analyzing the difference between the chemical shift values of the bulk and bulk-intercalated poly(2-ethynylpyridine) (P2EPy) nanocomposite material. The results of solid-state NMR and X-ray diffraction studies clearly demonstrate a spontaneous polymerization of 2EPy within the galleries of MMT. The polymer thus formed is mostly bound to the surface of MMT at either the Bronsted or Lewis acid sites. Infrared analysis suggests the existence of positive charge on the nitrogen atom of the polymer inside the ...

ORF2 gene involves in the construction of high-order structure of bacterial cellulose

An ORF2 gene located upstream of the cellulose synthase ( bcs) operon of Acetobacter xylinum BPR2001 was disrupted and a mutant (M2-2) was constructed. In static cultivation, the parent strain produced a tough, colorless, and insoluble cellulose pellicle, whereas M2-2 culture produced a thin, yellow, and fragile pellicle. The results of X-ray diffraction and 13C solid-state NMR indicated that the product of M2-2 is a mixture of cellulose I, cellulose II, and amorphous cellulose. The cellulose I to cellulose II ratio of the mixture was evaluated from the signal areas of C6 to be about 1:2. Electron microscopy revealed that the product of M2-2 included ribbon-like cellulose and irregularly shaped particles attached to the ribbons. On the other hand, the mutant complemented with plasmid pSA-ORF2/k containing the ORF2 gene and BPR2001 produced only cellulose I. These results indicate that the ORF2 gene is involved in the production and crystallization of cellulose I microfibrils by this microorganism.