Sample Spinning Nuclear Magnetic Resonance Research Articles

Insight into Crystalline Structure and Physicochemical Properties of Quartz-Carbon Ore

Composites made from carbon and nanominerals show great potential for thermal phase change materials, environmental water treatment, and biomass conversion. In 2019, a micro and nano-quartz-carbon ore was discovered in Feng-cheng City, Jiangxi Province. The study of the structural and physicochemical changes of quartz-carbon ore (QZC) during calcination is essential for the preparation of QZC-based composites and to broaden their application areas. Firstly, the SiO2 crystal structure evolution of QZC during calcination was investigated using in-situ X-ray diffraction (XRD), 29Si magic-angle sample spinning nuclear magnetic resonance (MAS NMR), and Fourier transform infrared FTIR spectroscopy. Then, the changes in carbon during calcination were investigated using Raman spectroscopy, 13C MAS NMR, and X-ray photoelectron spectroscopy (XPS). In addition, changes in the QZC morphology were observed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. Finally, the evolution of the physicochemical properties of QZC during calcination was revealed using thermogravimetric (TG), Brunauer–Emmet–Teller (BET), resistivity, thermal conductivity, and zeta potential techniques.

Evolution of the crystallographic structure and physicochemical aspects of rectorite upon calcination

Rectorite (Rec) with exchangeable cations has a wide range of potential applications, including adsorbents, catalyst supports, high-temperature binders, and flame retardant additives. The understanding of the variation of rectorite upon thermal treatment is vital for exploiting its application potential. This paper reports on the thermal decomposition and structural evolution of Rec in the temperature range of 25–1200 °C. Thermogravimetric (TG) analysis, in-situ X-ray diffraction (XRD), and in-situ Fourier transform infrared (FTIR) spectroscopy were used to trace real-time variations in rectorite upon calcination. Then, pristine rectorite and its calcined samples were systematically characterized by 29Si and 27Al magic-angle sample spinning nuclear magnetic resonance (MAS NMR), Brunauer-Emmet-Teller (BET), Zeta potential, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques. The results showed that Rec went through the following four stages after thermal treatment: dehydration at room temperature (RT) to 300 °C, dehydroxylation at 500–700 °C, structural collapse at 1000 °C, and formation of a new phase above 1100 °C. Furthermore, SiO4 tetrahedral units and AlO6 octahedral units in Rec were distorted around 1000 °C, so that the maximum contents of active SiO2 and Al2O3 could be simultaneously obtained. The atomic-level structural evolution mechanism of Rec upon calcination is proposed.

MAS-NMR support for Hench model in the case of bioactive glass microspheres

The structural changes occurred in bioactive glass microspheres belonging to the system SiO2–Na2O–P2O5–CaO–K2O–MgO incorporating yttrium were investigated before and after soaking in simulated body fluid (SBF) by X-ray diffraction (XRD) and 31P and 29Si magic angle sample spinning nuclear magnetic resonance (MAS-NMR). The addition of yttrium to the bioactive glass composition induces changes in the behavior of the glass microspheres in SBF. The XRD analysis proves that after the immersion in SBF a crystalline hydroxyapatite-like phase is developed on the microspheres surface. The 29Si and 31P MAS-NMR results show that silicate species with two and three bridging oxygens per SiO4 tetrahedra and PO4 monomeric units are present in the glass structure. After immersion in SBF, new silicate species with four bridging oxygens appear as result of silica-gel layer formed on microspheres surface. The formation of crystalline hydroxyapatite-type layer is reflected by the occurrence of narrow components in 31P MAS-NMR spectra. The NMR results support the Hench model for bioactive glasses behavior in biological environments.

Preparation and Biocompatible Surface Modification of Redox Altered Cerium Oxide Nanoparticle Promising for Nanobiology and Medicine.

The biocompatible surface modification of metal oxide nanoparticles via surface functionalization technique has been used as an important tool in nanotechnology and medicine. In this report, we have prepared aqueous dispersible, trivalent metal ion (samarium)-doped cerium oxide nanoparticles (SmCNPs) as model redox altered CNPs of biological relevance. SmCNP surface modified with hydrophilic biocompatible (6-{2-[2-(2-methoxy-ethoxy)-ethoxy]-ethoxy}-hexyl) triethoxysilane (MEEETES) were prepared using ammonia-induced ethylene glycol-assisted precipitation method and were characterized using a variety of complementary characterization techniques. The chemical interaction of functional moieties with the surface of doped nanoparticle was studied using powerful 13C cross polarization magic angle sample spinning nuclear magnetic resonance spectroscopy. The results demonstrated the production of the extremely small size MEEETES surface modified doped nanoparticles with significant reduction in aggregation compared to their unmodified state. Moreover, the functional moieties had strong chemical interaction with the surface of the doped nanoparticles. The biocompatible surface modification using MEEETES should also be extended to several other transition metal ion doped and co-doped CNPs for the production of aqueous dispersible redox altered CNPs that are promising for nanobiology and medicine.

Assessment of historic Tilia codrata wood by solid-state 13C CPMAS NMR spectroscopy

Abstract Historic lime ( Tilia cordata Mill.) wood samples, differing by their provenance, conservation status and period have been investigated by solid-state carbon-13 cross polarization magic angle sample spinning nuclear magnetic resonance ( 13 C CPMAS NMR) spectroscopy. Structural and chemical modifications were assessed by comparing the historic samples with a reference wood sample. The conventional NMR measurements followed by the 13 C resonance integral intensities of the wood samples have been carried out in order to acquire information of the chemical changes due to the natural ageing process taking place over the years. The main results concern the decrease of the carbohydrates moiety, especially the decrease of the hemicelluloses and amorphous cellulose signals, while the signals for aliphatic and methoxyl carbons from lignin present and increase of the intensity up to 120 years then start to decrease. At the same time a slight widening of the amorphous carbohydrate signals was observed, which may evidence the occurring of some chemical rearrangements, with the formation of new chemical species. These lead in the 13 C NMR spectra to the line broadening of the signals induced by their chemical shifts dispersion.

Synthesis and characterization of montmorillonite inorgano-intercalation compound assisted by microwave irradiation

A montmorillonite inorgano-intercalation compound(MIIC) was synthesized by using a purified Na-exchanged bentonite (PNaB) as a matrix and Al-pillaring ion as an intercalating reagent under microwave irradiation. The synthesized products were characterized by X-ray diffraction (XRD), 27Al magic angle sample-spinning nuclear magnetic resonance (27Al MAS NMR), specific surface area (BET) measurement, and adsorption density determination. The results show that, at 5% solid (PNaB) concentration and 7 minutes irradiation in a 130 W microwave oven, the basal spacing d(001) of the synthesized MIIC increases to 1.740 nm from the original 1.218 nm of PNaB. The MIIC has much higher adsorptive densities to F− and Cr6+ from aqueous solution than the PNaB. The adsorption isotherm of F− on the MIIC follows the Freundlich equation, and the increased adsorption is mainly due to the porous structure of the MIIC which created larger adsorption surfaces. The adsorption isotherm of Cr6+ on MIIC follows the Langmuir equation and the adsorption is mainly monolayer as a result of chemisorptions.

Investigation of the Structure of MCM‐41 Samples with a High Copper Content

AbstractA series of MCM‐41s with a high copper content were synthesized at room temperature from sodium metasilicate (Na2SiO3) as the silicon source, tetraamminecopper(II) nitrate [Cu(NH3)4(NO3)2] as the copper source and cetyltrimethylammonium bromide (CTABr) as the template. The resulting material was characterized by using the following characterization techniques: X‐ray diffraction (XRD), N2‐adsorption isotherms, high‐resolution transmission electron microscopy (HRTEM), inductively coupled plasma (ICP), temperature‐programmed reduction (H2‐TPR), X‐ray photoelectron spectroscopy (XPS), Fourier‐transform infrared spectroscopy (FTIR), UV‐vis spectroscopy, electron‐spin resonance (ESR) and 29Si magic‐angle sample spinning nuclear magnetic resonance (MAS NMR) spectroscopy. The characterization techniques demonstrated the following: i) the copper atoms are incorporated into the framework of MCM‐41 and ii) the copper species in the samples are in a distorted octahedral coordination environment, with between four and six oxygen atoms in the first coordination sphere. The maximum copper content determined by ICP was 26 wt.‐% in the ordered mesoporous sample with a surface area of 525 m2 g–1 and an average pore diameter of 3.1 nm. The synthesized materials exhibited a high activity for nitrogen monoxide (NO) reduction by carbon monoxide (CO).

17O nuclear magnetic resonance study of Na 2O–P 2O 5 glasses

The preparation and structural investigation of 17O-enriched xNa 2O–(100− x)P 2O 5 glasses (46.5⩽ x⩽62.8) by nuclear magnetic resonance (NMR) is described. Enriched phosphoric acid was prepared by hydrolysis of PCl 5 with 17O-enriched water and neutralized with sodium carbonate. The sodium metaphosphate was then melted at 800 °C for 15 h and quenched. Polyphosphate and ultraphosphate glass compositions were prepared by remelting the metaphosphate with sodium carbonate and phosphorus pentoxide, respectively. 31P magic angle sample spinning (MAS) NMR was used to determine the Na 2O/P 2O 5 content in the glasses. 17O NMR spectra (quadrupole echo for non-rotating samples and multiple-quantum excitation for rotating samples (MQMAS)) show two oxygen sites in the samples with large quadrupolar coupling constants (4.7 and 7.7 MHz), in accordance with the high phosphorus electronegativity. According to the correlation of 17O quadrupolar constants with bond ionicity, these two components are attributed to bridging P–O–P and non-bridging P–O⋯Na oxygens. The average P–O–P bond angle is estimated with the quadrupolar asymmetry derived from the fit of the static echo spectra. The MQMAS spectrum shows a distribution of non-bridging oxygen chemical shifts, attributed to a variation of bond length and angle.

Annealing characteristics of Si doped amorphous silica films by rf sputtering

Si doped amorphous silica films were prepared by rf magnetron sputtering technique. As-deposited films which had relatively low Si dopant were annealed in inert atmosphere, and spectroscopic analyses were performed for as-deposited and all the annealed samples by infrared (IR) absorption, X-ray fluorescence analysis, X-ray photoelectron spectroscopy (XPS) and 29Si magic angle sample spinning nuclear magnetic resonance spectroscopy (29Si MAS-NMR). When the sample was annealed at 800°C, the IR absorption peak located at 1080 cm−1 shifted to slightly higher wave number. On the other hand, the decrease of Si clusters or Si–Si bonds in as-deposited film was deduced from X-ray fluorescence and XPS spectra for the sample annealed at 800°C. These annealing characteristics of the films prepared in this study were discussed based on the random bonding model of SiOx film, and the spectral variations with thermal annealing were interpreted by the rearrangement of Si and O atoms in as-deposited films, rather than the simple clustering of excess Si atoms.

Analytical treatment of the variable-angle sample spinning nuclear magnetic resonance spectra in the presence of the second-order quadrupole interaction determination of the quadrupole parameters and the chemical shift tensor

The analytical expressions for the transition probability of the central transition of the variable-angle sample spinning nuclear magnetic resonance (VAS NMR) spectrum for non-integral spins in the presence of second-order quadrupole interactions are derived on the basis of the stationary perturbation theory. The modulating parameters of the VAS NMR spectrum due to the time-dependent part of the quadrupole energy are found to be different (asymmetry parameter η > 0.1) from those obtained from the average Hamiltonian theory. Using the conditions for saddle points and local maxima, it has been observed that there is a range of values for sample spinning angle β around 32, 44 and 72 ° to obtain the single peak; the range width can indicate the value of η. Analytical expressions for the single-peak positions corresponding to β around 32, 44 and 72 ° are derived in terms of quadrupole parameters and chemical shift tensor. Further, we have described an analytical method to find the principal values of the chemical shift tensor in addition to the quadrupole parameters, using VAS NMR. As an illustration, the quadrupole parameters are computed for Na 2MoO 4 and Na 2SO 4 and compared with the values available in the literature (computed from wide-line NMR and magic-angle sample spinning (MAS) NMR data using the position of peaks and shoulders). For Na 2MoO 4 the principal values of the chemical shift tensor are found to be + 17.5, − 12 and − 6.5 ppm. The present method is accurate and easy to apply as it involves only the positions of peaks and not of shoulders. Moreover, it is suitable for all values of the chemical shift tensor.

Analysis by nuclear magnetic resonance and raman spectroscopies of the structure of bioactive alkaline-earth silicophosphate glasses

Structural knowledge of bioactive glass systems is necessary to understand their biological properties and improve their mechanical and clinical performance. In this work, the local structure of P and Si in bioactive glasses of the system CaO-SiO 2-P 2O 5-CaF 2 with different Mg or Sr contents was determined, by means of 31P and 29Si magic-angle sample-spinning nuclear magnetic resonance (MASS NMR) and Raman spectroscopies. The results show that phosphorus is located in calcium-orthophosphate domains, surrounded by silicate species containing 1, 2 and 3 bridging-oxygens per SiO 4 tetrahedra. The type and relative distribution of the silicate units do not depend on the nature of the alkaline earth cations present in the system. However, the increase of RO content decreases the degree of polymerization of silicon tetrahedra, while PO 4 monomeric units remain unchanged. An interpretation of the medium-range structure of the glass is suggested.

Editing 13C-NMR spectra of membranes

We report the carbon-13 ‘magic-angle’ sample-spinning nuclear magnetic resonance (NMR) spectra of several lipid-water systems, under a variety of radiofrequency excitation conditions. Our results show that complex lipid or membrane spectra can be greatly simplified by using ‘spectral editing’ techniques. For example, in a 1,2-dimyristoyl- sn-glycero-3-phosphocholine (DMPC)-water mesophase, the glycerol (C-1, C-2 and C-3) carbons are readily distinguished from the headgroup C α, C β and C γ carbons, on the basis of their mix-time behavior in a cross-polarization (CP) experiment, while in the more complex DMPC/cholesterol-water system, many of the more rigid cholesterol carbon resonances can be edited from the phospholipid peaks. In very complex systems, such as human myelin membranes, editing permits the unambiguous observation of the mobile lipid headgroup carbon resonances, as well as the much more rigid sterol ring carbons. We also report the observation of a large differential CP due to C-H vector ‘magic-angle’ orientational effects in the DMPC/desipramine system. Thus, both motional or orientational reduction of the C-H dipolar interaction can lead to considerable simplifications of complex membrane spectra, and are of interest from both spectral assignment and membrane dynamics aspects.

Carbon‐13 “magic‐angle” sample‐spinning nuclear magnetic resonance studies of human myelin, and model membrane systems

We have obtained high-field (11.7 Tesla), high-resolution carbon-13 solid-state "magic-angle" sample-spinning nuclear magnetic resonance (NMR) spectra of a variety of phospholipids, sphingolipids, myelin and white matter samples, resolving and assigning over 40 resonances in the spectra of human and bovine myelin. The NMR results indicated no large spectral changes due to sample preparation, sample freezing, or brain location, and also no changes in myelin structure detectable via light microscopy, electron microscopy, thin layer chromatography, or sodium dodecyl sulfate-polyacrylamide gel electrophoresis, attributable to the sometimes lengthy NMR data acquisition process. Human myelin and white matter chemical shift assignments were made based on 13C "magic angle" sample spinning (MAS) NMR spectra of individual model lipids, as well as on spectra of lipid mixtures. In all myelin samples there were essentially no features attributable to membrane proteins, with the exception of one small feature due to C zeta of Arg residues, primarily in the myelin basic proteins. The general similarity between the model lipid and intact myelin spectra suggested no major effects of protein on lipid mobility. We have also investigated human myelin samples as a function of developmental age (4, 15, 48 months and adult), and our results showed only small changes in overall lipid composition, although there were significant decreases in lipid hydrocarbon chain unsaturation with age, as determined by computer line-shape simulations of myelin and model compounds. The spectrum of an infant leukoencephalopathy myelin showed marked decreases in galactocerebrosides. Overall, the ability to resolve and assign over 40 resonances in the 13C MAS NMR spectra of myelin, and to detect changes as a function of development and disease, should provide a useful starting point for further more detailed studies of myelin membrane molecular motions, and function.

Solid state 31P cross-polarization/magic angle sample spinning nuclear magnetic resonance studies of crystalline glycogen phosphorylase b

(31)P cross-polarization/magic angle sample spinning nuclear magnetic resonance spectra have been obtained for pyridoxal 5'-phosphate (PLP) bound to glycogen phosphorylase b (GPb) in two different crystalline forms, monoclinic and tetragonal. Analysis of the intensities of the spinning sidebands in the nuclear magnetic resonance spectra has enabled estimates of the principal values of the (31)P chemical shift tensors to be obtained. Differences between the two sets of values suggest differences in the environment of the phosphate moiety of the pyridoxal phosphate in the two crystalline forms. The tensor for the tetragonal crystalline form, T state GPb, is fully consistent with those found for dianionic phosphate groups in model compounds. The spectrum for the monoclinic crystalline form, R state GPb, although closer to that of dianionic than monoanionic model phosphate compounds, deviates significantly from that expected for a simple dianion or monoanion. This is likely to result from specific interactions between the PLP phosphate group and residues in its binding site in the protein. A possible explanation for the spectrum of the monoclinic crystals is that the shift tensor is averaged by a proton exchange process between different ionization states of the PLP associated with the presence of a sulfate ion bound in the vicinity of the PLP.

A “magic-angle” sample-spinning nuclear magnetic resonance spectroscopic study of interference effects in the nuclear spin relaxation of polymers

The proton-coupled, carbon-13 “magic-angle” sample-spinning nuclear magnetic resonance spin-lattice relaxation behavior of poly ( cis-isoprene) and poly ( cis-butadiene) as a function of temperature is reported. Analysis of the relaxation behavior of the methine carbons reveals strong temporal correlations between the 13CH dipolar and 13C anisotropic chemical shielding interactions. Equations are presented which enable the interpretation of these interferences for non-axially symmetric shielding tensors, subject to cylindrically symmetric reorientation. In the context of these expressions, the results indicate that the methine moiety in each of the two polymers executes relatively rapid, isotropic motions, on the time scale of the carbon-13 Larmor frequency. It is also shown that in certain polymeric systems, the sign of the interference term may change with frequency. This intriguing property provides additional insight into the relative reorientational anisotropies of the low- and high-frequency motions, and the specific case of the spin-lattice relaxation and differential line broadening of the methine carbons in poly (cis-isoprene) and poly ( trans-isoprene) is considered in detail.

Differential line broadening in coupled carbon-13 magic-angle sample-spinning nuclear magnetic resonance spectra of solid polymers

Large differential line broadening (DLB) of the individual components of 13 -C 1 H coupled multiplets were observed in 13 C MAS NMR spectra of solid poly(cis-butadiene), poly(cis-isoprene), poly(cis,trans-butadiene), butadien-styrene and acrylonitrile-butadiene-styrene block polymers, and poly(trans-isoprene). DLB of olefine methine carbons is manifest as broadening of the high-field doublet component in poly(cis-butadiene) and poly(cis-isoprene), while in trans segments in poly(cis-trans-butadiene) and in poly(trans-isoprene) the low-field component broadens first, on cooling

Spectroscopic studies of lipids and biological membranes: carbon-13 and proton magic-angle sample-spinning nuclear magnetic resonance study of glycolipid-water systems.

We have obtained 1H and 13C magic-angle sample-spinning (MAS) nuclear magnetic resonance (NMR) spectra of three glycosyldiacylglycerol-water (1:1, weight ratio) mesophases, at 11.7 T, as a function of temperature, in order to probe lipid headgroup, backbone, and acyl chain dynamics by using natural-abundance NMR probes. The systems investigated were monogalactosyldiacyldiglyceride [MGDG; primarily 1,2-di[(9Z,12Z,15Z)octadec-9,12,15-trienoyl++ +]-3-beta-D-galactopyranosyl- sn-glycerol]; digalactosyldiacyldiglyceride [DGDG; primarily 1,2-di[(9Z,12Z,15Z)octadec-9,12,15-trienoyl++ +]-3- (alpha-D-galactopyranosyl-1-6-beta-D-glactopyranosyl)-sn-glycerol] ; and sulfoquinovosyldiacyldiglyceride [SQDG; primarily 1-[(9Z,12Z,15Z)octadec-9,12,15-trienoyl]-2 -hexadecanoyl-3-(6-deoxyl-6- sulfono-alpha-D-glucopyranosyl)-sn-glycerol]. At approximately 22 degrees C, all three lipid-water systems give well-resoled 13C and 1H MAS NMR spectra, characteristic of fluid, liquid-crystalline mesophases. 13C spin-lattice relaxation times of the headgroup and glycerol backbone carbons of all three materials give, within experimental error, the same NT1 values (approximately 400 ms), implying similar high-frequency motions, independent of headgroup size and charge. Upon cooling, pronounced line broadenings are observed, due to an increase in slow motional behavior. For each lipid, the onset of line broadening is seen with the glycosyl headgroup, glycerol backbone, and the first two or three carbons of the acyl chains. By approximately -20 degrees, all headgroup carbon resonances are broadened beyond detection. Both galactose moieties in DGDG "freeze out" together, implying a rigid-body motion of the disaccharide unit. Upon further cooling, the bulk polymethylene chain resonances in all three systems (in both 13C and 1H MAS) broaden greatly, followed by the olefinic and allylic carbon resonances.(ABSTRACT TRUNCATED AT 250 WORDS)

A static and “magic-angle” sample-spinning nuclear magnetic resonance spectroscopic study of 11B in Si[B]. An analysis of spin—spin and spin—lattice relaxation behavior in the metallic state

We have investigated the signal intensity, lineshape, spin—lattice and spin—spin (spin-echo decay) relaxation behavior of 11B nuclei in a Si[B] extrinsic semiconductor in the metallic state, as a function of magnetic field strength and temperature. We find that essentially all boron spins are in a highly symmetric environment, characterized by a mean nuclear quadrupole coupling constant ( e 2 qQ/ h) of ≈ 12 kHz. The spin—lattice relaxation is Korringa like, with a T 1 T ≈ 550 s K, at both 5 and 300 K, indicating a mean Knight shift of ≈ 70 ppm. The spin—spin relaxation time, T 2E, is 25 ms at 8.45 T, independent of temperature, or magnetic field strength in the range 2.35 to 11.7 T, at 300 K. The T 2E value is in good agreement with the predictions of a model of homonuclear dipolar interactions within metallic Si[B] clusters.

Characterization of very young mineral phases of bone by solid state 31Phosphorus magic angle sample spinning nuclear magnetic resonance and X-ray diffraction

The properties of bone mineral change with age and maturation. Several investigators have suggested the presence of an initial or "precursor" calcium phosphate phase to help explain these differences. We have used solid state 31P magic angle sample spinning (MASS) nuclear magnetic resonance (NMR) and X-ray radial distribution function (RDF) analyses to characterize 11- and 17-day-old embryonic chick bone and fractions obtained from them by density fractionation. Density fractionation provides samples of bone containing Ca-P solid-phase deposits even younger and more homogeneous with respect to the age of mineral than the calcium phosphate (Ca-P) deposits in the whole bone samples. The analytical techniques yield no evidence for any distinct phase other than the poorly crystalline hydroxyapatite phase characteristic of mature bone mineral. In particular, there is no detectable crystalline brushite [DCPD, CaHPO4 2H2O less than 1%] or amorphous calcium phosphate (less than 8-10%) in the most recently formed bone mineral. A sizeable portion of the phosphate groups exist as HPO4(2-) in a brushite (DCPD)-like configuration. These acid phosphate moieties are apparently incorporated into the apatitic lattice. The most likely site for the brushite-like configuration is probably on the surface of the crystals.

Quantitative triacylglycerol analysis of whole vegetable seeds by1H and13C magic angle sample spinning NMR spectroscopy

High‐resolution13C and1H magic angle sample spinning nuclear magnetic resonance (NMR) spectra have been obtained and used to define the relative unsaturated acyl distribution of triacylglycerols in whole oil seeds. Inverse gated proton decoupled13C and1H NMR spectra permit the quantitative analysis of seeds containing simple oils,e.g., sunflower seeds containing oleyl and linoleyl unsaturates only. More sensitive13C NMR techniques are necessary for the analysis of specific seed classes. One such class is the rapeseed, which is especially difficult due to its low oil content (≈ 2 mg oil/seed) and complex unsaturated acyl profile of oleyl, linoleyl, linolenyl, erucyl, and eicosenoyl. The Distortionless Enhancement by Polarization Transfer technique significantly improves sensitivity to the extent that single rapeseeds can be examined within an hour of acquisition time. Furthermore, some positional (1,3‐ or 2‐glycerol attachment) groups can be identified leading to a partial estimation of the 1,3‐, 2‐acyl distribution.