Solid Nuclear Magnetic Resonance Research Articles

An Organic Low-k Film Deposited by Plasma-Enhanced Copolymerization

A plasma-enhanced copolymerization technology has been developed in which organic precursors are designed and synthesized to form polymerized films with low dielectric constants. In order to lower the dielectric constant, a tricyclodecane (TCD) group is introduced as an organic precursor molecule because TCD is a large aliphatic hydrocarbon group, which contributes to lowering the film density. The TCD precursors are liquid at room temperature and they have a sufficient saturated vapor pressure to be applicable to the vapor phase deposition. The optimized dielectric constant of the TCD polymer was less than 2.5. A solid nuclear magnetic resonance spectrum showed that the TCD moiety in the precursor was included in the polymer without changing the structure. The effect of the substrate temperature on the film structure was studied by analyzing Raman spectra. It was revealed that the dielectric constant was associated with carbon content in the TCD-based polymer films.

Sequestration of a fluorinated analog of 2,4-dichlorophenol and metabolic products by L. minor as evidenced by 19F NMR

Fate of halogenated phenols in plants was investigated using nuclear magnetic resonance (NMR) to identify and quantify contaminants and their metabolites. Metabolites of 4-chloro-2-fluorophenol (4-Cl-2-FP), as well as the parent compound, were detected in acetonitrile extracts using 19F NMR after various exposure periods. Several fluorinated metabolites with chemical shifts ∼3.5 ppm from the parent compound were present in plant extracts. Metabolites isolated in extracts were tentatively identified as fluorinated-chlorophenol conjugates through examination of signal-splitting patterns and relative chemical shifts. Signal intensity was used to quantify contaminant and metabolite accumulation within plant tissues. The quantity of 4-Cl-2-F metabolites increased with time and mass balance closures of 90–110% were achieved. In addition, solid phase 19F NMR was used to identify 4-Cl-2-FP which was chemically bound to plant material. This work used 19F NMR for developing a time series description of contaminant accumulation and transformation in aquatic plant systems.

Hardware modification of a 7 mm MAS NMR probe to a single-crystal goniometer

Tensorial terms of the Hamiltonian can be measured by solid-state single-crystal nuclear magnetic resonance (NMR) spectroscopy which requires a goniometer NMR probehead. Goniometer probes; however, are not standard parts of solid NMR spectrometers and are available only at a much higher price than magic-angle spinning (MAS) probeheads widely used in research. Due to requirements of MAS experiments, modern probeheads are designed for small ceramic rotors, which are 1–4 mm in diameter, to reach very high angular frequencies, so there are several older 7 mm MAS probeheads used rarely todays in NMR laboratories. In this paper, a simple method is presented how to rebuild step-by-step a 7 mm Bruker MAS probehead to be suitable for single-crystal spectroscopy. In the second part 31P chemical shift tensors of Na 4 P 2 O 7 · 10 H 2 O are determined to demonstrate the functionality of the rebuilt probehead.

Structural Studies of OH in Nominally Anhydrous Minerals Using NMR

Nuclear magnetic resonance (NMR) is a technique that is used very widely throughout science and medicine. There are approaching 20 journals devoted exclusively to NMR and magnetic resonance imaging, and well in excess of 10,000 papers published annually which involve this family of techniques. It has found extraordinarily diverse applications, and its applications to inorganic solids such as minerals represent a very small part of NMR as a whole. There had been occasional NMR studies of minerals since the discovery of the NMR effect in 1946, but until the early 1980s, the large width of NMR resonances in the solid state precluded widespread application of the technique. The most important factor in the application of NMR to minerals was the development of magic angle spinning (MAS), a technique for narrowing lines in solid state NMR. More recently the development of more complex sample spinning arrangements and multiple pulse methods together with the availability of ever higher magnetic fields opens up more and more possibilities for NMR in mineralogy and geochemistry. NMR is far too diverse and complex for the whole subject to be covered here, so this review will be tightly focused on aspects which relate to understanding the structural role of water in nominally anhydrous minerals. Two review papers (Kirkpatrick 1988; Stebbins 1988) in the “Reviews in Mineralogy” volume on Spectroscopic Methods in Mineralogy and Geology provide an excellent starting point for Earth scientists wishing to learn more about NMR in general. More recent reviews aimed at Earth scientists include those by Fechtelkord (2004) and Kohn (2004), more general reviews of NMR of inorganic solids include Engelhardt and Michel (1987) and MacKenzie and Smith (2002). The web page maintained by J.P. Hornak ( http://www.cis.rit.edu/htbooks/nmr/ ) is also an extremely good resource. NMR is a multinuclear technique, which means …

New pyrolytic and spectroscopic data on Orgueil and Murchison insoluble organic matter: A different origin than soluble?

Pyrolysis with and without tetramethylammonium hydroxide (TMAH), vacuum pyrolysis, and solid state 15N nuclear magnetic resonance (NMR) were used to examine the macromolecular insoluble organic matter (IOM) from the Orgueil and Murchison meteorites. Conventional pyrolysis reveals a set of poorly functionalized aromatic compounds, ranging from one to four rings and with random methyl substitutions. These compounds are in agreement with spectroscopic and pyrolytic results previously reported. For the first time, TMAH thermochemolysis was used to study extraterrestrial material. The detection of aromatics bearing methyl esters and methoxy groups reveals the occurrence of ester and ether bridges between aromatic units in the macromolecular network. No nitrogen-containing compounds were detected with TMAH thermochemolysis, although they are a common feature in terrestrial samples. Along with vacuum pyrolysis results, thermochemolysis shows that nitrogen is probably sequestered in condensed structures like heterocyclic aromatic rings, unlike oxygen, which is mainly located within linkages between aromatic units. This is confirmed by solid state 15N NMR performed on IOM from Orgueil, showing that nitrogen is present in pyrrole, indole, and carbazole moieties. These data show that amino acids are neither derived from the hydrolysis of IOM nor from a common precursor. In order to reconcile the literature isotopic data and the present molecular results, it is proposed that aldehydes and ketones (1) originated during irradiation of ice in space and (2) were then mobilized during the planetesimal hydrothermalism, yielding the formation of amino acids. If correct, prebiotic molecules are the products of the subsurface chemistry of planetesimals and are thus undetectable through astronomical probes.

Spherical tensor analysis of nuclear magnetic resonance signals

In a nuclear magnetic-resonance (NMR) experiment, the spin density operator may be regarded as a superposition of irreducible spherical tensor operators. Each of these spin operators evolves during the NMR experiment and may give rise to an NMR signal at a later time. The NMR signal at the end of a pulse sequence may, therefore, be regarded as a superposition of spherical components, each derived from a different spherical tensor operator. We describe an experimental method, called spherical tensor analysis (STA), which allows the complete resolution of the NMR signal into its individual spherical components. The method is demonstrated on a powder of a (13)C-labeled amino acid, exposed to a pulse sequence generating a double-quantum effective Hamiltonian. The propagation of spin order through the space of spherical tensor operators is revealed by the STA procedure, both in static and rotating solids. Possible applications of STA to the NMR of liquids, liquid crystals, and solids are discussed.

Isotropic proton-detected local-field nuclear magnetic resonance in solids

A nuclear magnetic resonance method is presented which produces linear, isotropic proton-detected local-field spectra for INS spin systems in powdered samples. The method, heteronuclear isotropic evolution (HETIE), refocuses the anisotropic portion of the heteronuclear dipolar coupling frequencies by evolving the system under a series of specially designed Hamiltonians and evolution pathways. The theory behind HETIE is presented along with experimental studies conducted on a powdered sample of ferrocene, demonstrating the methodology outlined in this paper. Applications of HETIE for use in structure determination in the solid state are discussed.

Solid state multinuclear NMR: a versatile tool for studying the reactivity of solid systems

Traditionally, X-ray powder diffraction has been a favoured method for studying chemical reactions in the solid state, but the increasing importance of energy-efficient synthesis methods for solids (e.g. sol–gel synthesis, mechanochemical synthesis) has led to the need for an analytical method not dependent on long-range structural periodicity. Multinuclear solid state nuclear magnetic resonance (NMR) represents a technique which is equally applicable to amorphous or crystalline solids, and is now used in increasing numbers of solid state studies. This paper briefly outlines the principles and practical details of this powerful technique and gives examples of its use in solid-state chemistry, particularly in very recent studies of mechanochemical synthesis of advanced sialon ceramics. The temperature at which these technically important silicon aluminium oxynitride compounds are formed can be significantly lowered by high-energy grinding of their components to produce X-ray amorphous precursors. Solid-state NMR has been used to provide detailed information which could not have been obtained by any other means about the chemical environment of the Si and Al atoms in these amorphous precursors, and the various atomic movements undergone as they crystallise to the final product.

Spin-locking of half-integer quadrupolar nuclei in nuclear magnetic resonance of solids: creation and evolution of coherences.

Spin-locking of half-integer quadrupolar nuclei, such as 23Na (I=3/2) and 27Al (I=5/2), is of renewed interest owing to the development of variants of the multiple-quantum and satellite-transition magic angle spinning (MAS) nuclear magnetic resonance experiments that either utilize spin-locking directly or offer the possibility that spin-locked states may arise. However, the large magnitude and, under MAS, the time dependence of the quadrupolar interaction often result in complex spin-locking phenomena that are not widely understood. Here we show that, following the application of a spin-locking pulse, a variety of coherence transfer processes occur on a time scale of approximately 1/omegaQ before the spin system settles down into a spin-locked state which may itself be time dependent if MAS is performed. We show theoretically for both spin I=3/2 and 5/2 nuclei that the spin-locked state created by this initial rapid dephasing typically consists of a variety of single- and multiple-quantum coherences and nonequilibrium population states and we discuss the subsequent evolution of these under MAS. In contrast to previous work, we consider spin-locking using a wide range of radio frequency field strengths, i.e., a range that covers both the "strong-field" (omega1 >> omegaQPAS and "weak-field" (omega1 << omegaQPAS limits. Single- and multiple-quantum filtered spin-locking experiments on NaNO2, NaNO3, and Al(acac)3, under both static and MAS conditions, are used to illustrate and confirm the results of the theoretical discussion.

Investigation of the Chemical Differences between Native and Bypass Coronary Artery Plaques from the Same Heart Using Cross Polarization Magic Angle Spinning Nuclear Magnetic Resonance (CP/MAS-NMR)

The plaque deposits in bypass arteries and native arteries from the same heart have been studied using solid state cross polarization nuclear magnetic resonance (CP/MAS NMR). Both 13C and 31P signals were observed. The samples are of interest because plaque in native arteries may have deposited during the lifetime of the patient. However, plaque in the bypass occurred since bypass surgery. It has been observed that the mature plaque in native arteries was more calcified than that in bypass arteries, especially if the latter had not matured to become significant in size. Results showed that the concentrations of carboxylate carbons present in cholesterol esters were similar in native and bypass arteries. However, the areas of the 13C peaks of the carboxylate compared to the sum of areas of all other 13C arteries indicated that the carboxylate was attached to five or six other carbons. From this we can calculate that the carboxylate to other carbon ratio in the remainder must be 1:4 or 1:3. This indicates large quantities of other organic compounds in the deposits. Studies of 31P showed that phosphorus existed primarily as hydroxyapatite in the crystalline native plaque. However, a large proportion existed as organic phosphorus in the bypass plaque. In addition, we studied the interactions of calcium with homocysteine and cholesterol. Calcium-homocysteine and cholesterol-homocysteine precipitates were characterized using 13C solid state NMR. Results showed that calcium appeared to interact with sulphur in the homocysteine which seemed to form dimers and polymers.

Different Molecular Conformations in Ferroelectric and Antiferroelectric Liquid Crystals Studied by 19F-NMR Spectroscopy

In order to discuss the relationship between molecular conformation and phase sequence, static 19F-NMR measurements were performed using a high-resolution solid nuclear magnetic resonance spectrometer. In the homologous series of 10BIMFn, dipole coupling constants between fluorines of the phenyl ring and CF3 were found to be larger in the antiferroelectric compounds (n=8 and 10) than in the ferroelectric ones (n=7 and 9). This result indicates that the molecules exhibiting SmC* have a different conformation around the chiral part from those exhibiting SmCA*. Based on the MOPAC calculation in 10BIMF7, which gives two stable conformations with bent and extended chiral end chains, two different conformations obtained by NMR in 10BIMFn are suggested to correspond to the bent and extended structures in antiferroelectric and ferroelectric compounds, respectively.

Solid-state 27Al Nuclear Magnetic Resonance Investigation of Plasma-facilitated NOx Reduction Catalysts

Aluminum coordination distribution for alumina catalysts supported on mesoporous silica was examined. It was shown that aluminum coordination correlates to activity of the catalysts for plasma-enhanced, selective catalytic reduction of NOx with propene. Catalysts were prepared by incorporating aluminum onto the surface of a mesoporous silica support via three different post-synthesis routes to produce varying aluminum coordination. Aluminum trichloride, sodium aluminate, and aluminum isopropoxide precursors were examined. High-resolution, solid state 27Al nuclear magnetic resonance was used to determine aluminum coordination distributions for the resulting catalysts. Unsaturated aluminum sites (i.e., structural defects) correlated with increased activity at high temperatures while tetrahedrally-coordinated aluminum or BrØnsted acid sites correlated with activity at low temperatures.

A 13C and 15N Solid State NMR Study of the Reactions of Acetone Oxime Adsorbed on FeZSM-5

The reactions of acetone oxime, a proposed reaction intermediate for the SCR (Selective Catalytic Reduction) of NO with propane on FeZSM-5, have been studied with 13C and 15N solid state MAS NMR (magic angle spinning nuclear magnetic resonance). FeZSM-5 with three different loading levels was prepared by the sublimation method. The thermal reactions of acetone [2-13C] oxime adsorbed on FeZSM-5 samples with different iron loadings were monitored by 13C MAS NMR by heating to the desired temperature and then cooling to room temperature for data acquisition. For the sample with the lowest iron loading (Fe/Al = 0.11), acetic acid and N-methyl-2-propanamine were formed by the decomposition of acetone oxime. For the samples with the higher iron loadings (Fe/Al = 0.69 and 0.91), acetone, N,N′-methyl-2,2-propanediamine, and N-methyl-2-propanimine were formed by the decomposition of acetone oxime. 15N MAS NMR was used to investigate reactions of 15NO and acetone oxime on the FeZSM-5 samples. The formation of gas phase N2 and N2O was observed.

31P nuclear magnetic resonance studies on alkyl phosphate emulsifiers in cosmetic oil‐in‐water emulsions

AbstractCosmetic oil‐in‐water emulsions with a stearyl phosphate emulsifier are examined by means of static and dynamic 31P nuclear magnetic resonance (NMR) techniques to characterize the molecular properties of the emulsifier in situ. The interfacially bound emulsifier can be deteced by high‐resolution NMR spectroscopy, whereas the excess emulsifier exists as a solid lipid phase not detectable by this technique. The emulsions and the emulsifier raw material, consisting of monostearyl phosphate as well as distearly phosphate, are examined by solid state cross polarization magic angle spinning NMR spectroscopy to prove the existence of solid emulsifier phases in the emulsions. By applying dynamic 31P NMR methods to the interfacially bound emulsifier, information about the molecular dynamics at the interface is obtained. The results of the T1 and T2 relaxation time measurements indicate a restricted motion of the molecules that is dependent on the oil droplet size in the emulsions. This is verified by 31P NMR pulsed gradient spin echo self‐diffusion measurements on emulsions with different droplet sizes. Only about 5 wt% of the total emulsifier used is bound at the interface; the excess forms solid lipid phases. The coverage of the interface seems to be independent of the emulsifier concentration. Only the monoester of the emulsifier raw material shows interfacial activity. Its mobility indicates the two‐dimensional environment of the molecules on the surface of the oil droplets.

Accelerated carbonatation of sewage sludge–cement–sand mortars and its environmental impact

One of the main objectives of this work is to present an effective alternative for the final destination of sludge from urban waste water treatment plants by its use as a component of mortar or concrete. Assessment of the environmental quality of the final product and the consequent guarantee of its use in the building industry demand that it meets a number of requisites, one of which is that the effluents extracted by water action should be contamination-free or at least that the concentration of contaminants should be below certain preset limits. To this end, a durability study was performed on the system. The study consisted in subjecting the mortar samples to a process of accelerated carbonation and subsequently assessing the products of the carbonation by 29Si RNM-MA nuclear magnetic resonance of solids and its environmental impact by the NEN-7345 monolithic leaching test. Carbonation at very high concentrations of CO 2 favours the polymerization of the C–S–H and the breakdown of the ettringite, which affects the leaching processes and the concentration of heavy metals and other pollutants in the leachates obtained from the NEN 7345 leaching test.

ChemInform Abstract: Recent Progress in Solid State NMR

Publisher Summary This article reviews the progress of solid-state nuclear magnetic resonance (NMR). It emphasizes on the methodological developments. The applications of the technical advances, particularly those that are significant to chemistry, biochemistry, biology, and materials science have been discussed. Higher magnetic fields, more intense decoupling power, higher spinning rates, more robust pulse sequences, and novel designs of RF coils remain the routes pursued in achieving better solid-state NMR spectra. These advances, mainly in hardware, along with developments of pulse sequences, have tremendous potential in virtually every aspect of solid-state NMR and nuclear magnetic resonance imaging. Each of these is covered in the chapter. It discusses the theoretical and computational progress in solid-state NMR, which includes calculations of the lineshapes and dynamic processes based on density matrix theory or computations of the interaction parameters based on quantum mechanics. The chapter is also devoted to progresses in the efficient decoupling of dipolar interactions in solid samples, which is another method for obtaining high-resolution NMR spectra. It summarizes recently proposed recoupling schemes and reviews various types of correlation spectroscopy. Developments in cross-polarization and spin diffusion/ exchange are reviewed and the main achievements in solid NMR imaging have also been summarized.

Effect of paramagnetic cations on solid state 13C nuclear magnetic resonance spectra of natural organic materials

The effect of cation (Zn2+, Cu2+, Pr3+) amendment on the solid state 13C nuclear magnetic resonance (NMR) spectral properties of organic materials was investigated. The organic materials were chosen to represent structures found in natural organic matter (NOM) from soils, waters, sediments, sewage sludges and plant residues, and included cellulose, pectin, chitin, collagen, a commercial humic acid, and charcoal. Cation amendment was shown to have little effect on the observability of 13C NMR signal, except for the paramagnetic amended pectin samples, for which observability was decreased from near 100% in the unamended sample to 19% for the Cu2+ amended sample and 71% for the Pr3+ amended sample. NMR relaxation parameters (T1p H, T1H) were more sensitive to cation amendment. For a number of the samples, a decrease in relaxation rate (increase in TlpH and T1H) was observed on amendment with Zn2+. This was ascribed to a decrease in molecular motion due to the chelating effects of Zn2+. An increase in relaxation rate (decrease in T1pH and T1H) was generally observed on amendment with Cu2+. The effects of amendment with Pr3+ varied. T1H was more sensitive to the presence of paramagnetic species than was T1pH. These results suggest that bound paramagnetic cations will only decrease the observability of 13C NMR signal in NOM samples (or domains within NOM samples) at high paramagnetic cation concentrations (>3%). There is great potential for the use of paramagnetic cation amendment to differentiate relaxation rates of domains within NOM samples, subspectra for which can then be generated using the proton spin relaxation editing (PSRE) technique.

Degradation of 13C–U–Glucose in Sphagnum majus Litter Responses to Redox, pH, and Temperature

We studied the utilization of 13C–U–glucose by the microbial community in shallow Sphagnum majus (Russ.) C. Jens. ssp. norvegicum Flatb. litter and its regulation by pH, temperature, and redox conditions. The transformation of 13C–glucose was monitored by solution‐ and solid‐state 13C–nuclear magnetic resonance (NMR) spectroscopy. The aerobic microbial community used the glucose C for respiration and, to a lesser degree, for storage as mannitol, triglycerides, and polysaccharides. Under both aerobic and anaerobic conditions, the allocation of glucose C for storage was greater at pH 6.8 than at 4.3; however, the amount of C used for building new biomass was the same at both pH settings. At 15°C, 15 to 18% of the utilized C under aerobic conditions was found in new microbial biomass: less than the previously reported values of 40 to 72%. This indicates that peat soils may promote significantly different microbial growth patterns from other minerogenic and moor humus soils. The production of mannitol and triglycerides suggests that fungi dominated the microbial community and utilized the glucose under aerobic conditions. Using a combination of solid and liquid NMR techniques we were able, for the first time, to follow the anaerobic pathways of glucose degradation in a natural soil sample. The anaerobic microbial community produced mainly volatile fatty acids (VFA), ethanol, and CO2 from the added glucose, and only minor amounts were converted to methane, storage C, and new microbial biomass. Nuclear magnetic resonance spectroscopy allows nondestructive assays of metabolic events and, therefore, was shown to be an excellent tool for studying the microbial utilization of 13C–glucose in peat.

Influence of the CaO/MgO ratio on the structure of phase-separated glasses: a solid state 29Si and 31P MAS NMR study

29Si and 31P magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy was used to investigate structural aspects of glasses of the series (mol%) 31SiO 2–11P 2O 5–(58− x)CaO– xMgO, with x ranging from 0 to 32, in which precipitation of amorphous silica occurs. As expected for alkaline-earth silicates, a strong 29Si MAS NMR peak was recorded, shifting to higher frequencies with decreasing CaO/MgO molar ratios. Q 2 species predominate in the alkaline-earth rich phase and the observed shift in the 29Si spectra is attributed to a decrease in the average degree of Si polymerization in the matrix. The experimental evidence suggests that Mg 2+ replaces Ca 2+ and also promotes the disruption of Si–O–Si bonds. Substitution of CaO by MgO increases the amount of dispersed phase. 29Si MAS NMR showed the presence of Q 4 species in the dispersed phase and also suggested the presence of Q 0 species. A disproportionation reaction 2Q 2⇌Q 0+Q 4 is proposed to balance the silicate charges. 31P MAS NMR showed that phosphorus is present in an orthophosphate environment. The shift of the 31P MAS NMR peak was attributed to the replacement of Ca by Mg.

Biodegradable blends of high molecular weight poly(ethylene oxide) with poly(3-hydroxypropionic acid) and poly(3-hydroxybutyric acid): a miscibility study by DSC, DMTA and NMR spectroscopy

The miscibility of high molecular weight poly(ethylene oxide) blends with poly(3-hydroxypropionic acid) and poly(3-hydroxybutyric acid) (P(3HB)) has been investigated by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA) and high-resolution solid state 13C nuclear magnetic resonance (NMR). The DSC thermal behaviour of the blends revealed that the binary blends of poly(ethylene oxide)/poly(3-hydroxypropionic acid) (OP blends) were miscible over the whole composition range while the miscibility of poly(ethylene oxide)/poly(3-hydroxybutyric acid) blends (OB blends) was dependent on the blend composition. OB blends were found to be partly miscible at the middle P(3HB) contents (25 %, 50 %) and miscible at other P(3HB) contents (10 %, 75 % and 90 %). Single-phase behaviour for OP blends and phase separation behaviour for OB blends were observed from DMTA. The results from NMR spectroscopy revealed that the two components in the OP50 blend were intimately mixed on a scale of about 35 nm, while the domain sizes in the OB blend with a P(3HB) content of 50 % were larger than about 32 nm. © 2000 Society of Chemical Industry