Solid Nuclear Magnetic Resonance Research Articles

Risedronate Effects on the In Vivo Bioactive Glass Behavior: Nuclear Magnetic Resonance and Histopathological Studies.

The present study aimed to enhance the anti-osteoporotic performance of bioactive glass (46S6) through its association with bisphosphonate such as risedronate with amounts of 8, 12, and 20%. Obtained composites have been called 46S6-8RIS, 46S6-12RIS, and 46S6-20RIS, respectively. In vitro and in vivo explorations have been carried out. Bioactive glass and risedronate association has been performed by adsorption process. Structure analyses have been carried out to evaluate and to understand their chemical interactions. Solid Nuclear Magnetic Resonance (NMR) has been employed to study the structural properties of obtained biocomposite. The spectra deconvolution showed the appearance of a species (Q4) in the biocomposites 46S6-8RIS, 46S6-12RIS, and 46S6-20RIS indicating their successful chemical association. In vitro experiments showed the enhancement of the chemical reactivity of the composites 46S6-xRIS compared to the pure bioactive glass. In fact, the silicon liberation after 30 days of immersion was 50 ppm for pure bioactive glass 46S6, and 41, 64, and 62 from 46S6-8RIS, 46S6-12RIS, and 46S6-20RIS, respectively. Based on the in vitro results, 46S6-8RIS was implanted in the femoral condyle of an ovariectomized rat and compared with implanted pure glass in the goal to highlight its anti-osteoporotic performance. After 60 days, implanted group with 46S6-8RIS showed the increase in bone mineral density (BMD with 10%) and bone volume fraction (BV/TV with 80%) and the decrease in trabecular separation (Tb/Sp with 74%) when compared to that of 46S6 group. These results are confirmed by the histopathological analyses, which showed the bone trabeculae reconnection after the 46S6-8RIS implantation. Chemical analyses showed the reduction in silicon (Si) and sodium (Na) ion concentrations, and the rise in calcium (Ca) and phosphorus (P) ion levels, which was explained by the dissolution of biocomposite matrix and the deposition of hydroxyapatite layer. Histomorphometric results highlighted the risedronate effect on the antiosteoporotic phenomenon. Obtained results showed good behavior with only 8% of introduced risedronate in the glass matrix.

Synthesis and Characterization of Aluminum 2-Carboxyethyl-Phenyl-Phosphinate and Its Flame-Retardant Application in Polyester.

A flame retardant aluminum 2-carboxyethyl-phenyl-phosphinate (CPA-Al) was synthesized through the salification reaction. The molecular structure of CPA-Al and thermal stability were characterized by solid nuclear magnetic resonance, Fourier transform infrared spectroscopy, and thermogravimetric analysis. Subsequently, CPA-Al mixed in polyurethane was coated on polyester textile to obtain flame-retardant samples. The addition of 14.7 wt.% CPA-Al in textile sample can bring a limited oxygen index (LOI) value of 24.5%, 0 s after flame time, and the vertical burning B1 rating. Meanwhile, the incorporated CPA-Al reduced the peak heat release rate, total heat release, average effective heat of combustion, and increased the charring capacity of polyester textiles in contrast to the samples without CPA-Al. CPA-Al exerted not only its flame inhibition effect in gas phase, but also the charring and barrier effect in the condensed phase. Besides, with an increasing CPA-Al ratio in polyester textile, the contact angle gradually decreased from 123.6° to 75.6°, indicating that the surficial property of coating from hydrophobic to hydrophilic, thereby increasing the moisture permeability of polyester textile.

Utility of newly modified chitosan in the removal of heavy metal ions from aqueous medium: ion selectivity, XPS and TGA

The purpose of this study is to evaluate the newly prepared modified chitosan, a new environmentally friendly adsorbent, in the field of wastewater treatment. Chitosan (CS) reacted with 3-chloro-2,4-pentanedione to give CS derivatives, CS-CPD. Modified CS with O–O and N–O chelating centres was treated with aqueous solution containing different metal ions to investigate its metal uptake and selectivity. The concentration of metal ions in aqueous solution was measured by inductively coupled plasma-optical emission spectrometry. The structure of the complex was identified by elemental analysis, infrared and solid-nuclear magnetic resonance. In addition, the chelating centres were determined by X-ray photoelectron spectroscopy. The morphology of the modified polymer and its metal complexes was studied to show a dramatic change in cases of the CS-CPD–Pb, CS-CPD–Hg, CS-CPD–Cr and CS-CPD–Co complexes.

A review of the production of slow-release flavor by formation inclusion complex with cyclodextrins and their derivatives

Flavors have been widely used in many products. They are volatile compounds and do not often last long in air especially at high temperature. The techniques for slow flavor release and long-lasting scents, for the stability of sensory perception, are much desired. The inclusion complex method encompasses the idea of molecular recognition and interactions through noncovalent bonding. It can provide protection and prevent the loss of volatile aroma materials, and improve shelf-life and enhance the stability of the entrapped ingredients of flavors. In this article, the production of control-release flavor by inclusion complex method was reviewed in considerable detail. The host materials, the method of production flavor inclusion complex, and the methods of characterization of flavor inclusion complex were depicted. The complexation thermodynamics and calculations were also discussed. Cyclodextrins and their derivatives as the host materials were discussed in this paper. Methods of production flavor inclusion complex include solution method (water or water as the main component of the solution, cosolublizer), suspension method, gas/liquid interface method, and solid phase method (co-grinding method, heating in a closed container method, shaking method at room temperature). The methods of characterization of solid inclusion complex mainly include x-ray diffraction technique, Infrared and Raman spectra, solid nuclear magnetic resonance spectroscopy, thermal analysis, mass spectrometry analysis, scanning and transmission electron microscopy. Structures, energies, and some properties of molecules can be studied by computational chemistry. The application of computational chemistry to the study of flavor compound inclusion complexes were discussed. The review indicates that inclusion complex method is an efficient way for encapsulation of flavor compounds. By this method slow flavor release and long-lasting scents can be obtained.

Preparation and performance of a novel multi-mode COF-300@SiO2 chromatographic stationary phase

A novel multimode COF-300@SiO2 chromatographic stationary phase was successfully prepared via an in situ growth strategy. Powder X-ray diffraction, solid nuclear magnetic resonance and scanning electron microscope confirmed the successful preparation of COF-300@SiO2 chromatographic stationary phase. Multimode chromatographic performance and multiple retention mechanisms were investigated. Neutral and polar compounds were efficiently separated in reverse phase chromatography mode due to hydrophobic interaction, π-π interaction, electron-donor-acceptor interaction and size selectivity of porous structure, and the column exhibited comparable hydrophobic selectivity with C18 column. Especially, the size selectivity of porous structure promoted the separation of multicomponent compounds on the novel column. Only neutral compounds were completely or partly separated in normal phase chromatography mode based on π-π interaction, and the column showed better separation performance than SiO2 column. Moreover, the column also presented weaker hydrophilic interaction than NH2/SiO2 column in hydrophilic phase chromatography mode. Nucleosides, nucleobases and alkaloids were partly or completely separated on the developed column because of the presence of amino groups on the surface of COF-300. This work indicates promising application values of COFs-based chromatographic stationary phases in chromatographic separation areas.

Magic angle spinning spheres.

Magic angle spinning (MAS) is commonly used in nuclear magnetic resonance of solids to improve spectral resolution. Rather than using cylindrical rotors for MAS, we demonstrate that spherical rotors can be spun stably at the magic angle. Spherical rotors conserve valuable space in the probe head and simplify sample exchange and microwave coupling for dynamic nuclear polarization. In this current implementation of spherical rotors, a single gas stream provides bearing gas to reduce friction, drive propulsion to generate and maintain angular momentum, and variable temperature control for thermostating. Grooves are machined directly into zirconia spheres, thereby converting the rotor body into a robust turbine with high torque. We demonstrate that 9.5-mm-outside diameter spherical rotors can be spun at frequencies up to 4.6 kHz with N2(g) and 10.6 kHz with He(g). Angular stability of the spinning axis is demonstrated by observation of 79Br rotational echoes out to 10 ms from KBr packed within spherical rotors. Spinning frequency stability of ±1 Hz is achieved with resistive heating feedback control. A sample size of 36 μl can be accommodated in 9.5-mm-diameter spheres with a cylindrical hole machined along the spinning axis. We further show that spheres can be more extensively hollowed out to accommodate 161 μl of the sample, which provides superior signal-to-noise ratio compared to traditional 3.2-mm-diameter cylindrical rotors.

Coalification and coal alteration under mild thermal conditions

Coalification temperatures are often considered to be approximately 100–170 °C for bituminous coal and 170–275 °C for anthracite. However, our micropetrographic observations, solid state 27Al magic-angle spinning nuclear magnetic resonance measurements, interpretation of δ13C values for whewellite in pelosiderite concretions from Carboniferous sediments, and assessment of whewellite thermal stability show that coalification temperatures can be significantly lower. Also the temperatures of coal alteration may be substantially lower than is stated. Ordinarily, high-temperature alteration is reported, but microthermometric measurements of fluids temperatures and micropetrographic observations show that the coal alteration can take place at low temperatures. For this reason, coals from the Kladno–Rakovník Basin, part of Late Paleozoic continental basins of the Czech Republic, were analyzed. Regarding coalification, micropetrographic characterizations of unaltered coals, the presence of thermally unstable Al complexes in the coal organic mass documented using 27Al MAS NMR method, and proven occurrence of whewellite in pelosiderite concretions suggest a lower coalification temperature, max. ~ 70 °C. Regarding coal alteration, micropetrographic observations revealed (a) the weaker intensity of fluorescence of liptinite, (b) mylonitic structures and microbreccia with carbonate fluid penetration, and (c) high oxygen content in coals (37–38 wt.%). These phenomena are typical for thermal and oxidative alteration of coal. As the temperature of carbonate fluids inferred from fluid inclusion analysis was evaluated as ~ 100–113 °C, the temperature of coal alteration was suggested as ~ 113 °C; the alteration was caused by hot hydrothermal fluids.

Highly Selective Lithium Ion Adsorbents: Polymeric Porous Microsphere with Crown Ether Groups

In this study, we prepared and applied polymeric porous microsphere adsorbents with selectivity for Li+ extraction from aqueous solution. We synthesized the adsorbents by suspension polymerization using methacryloyoxyme-12-crown-4 (M12C4) as a functional monomer, which had been synthesized from 2-hyroxymethyl-12-crown-4 and methacryloyl chloride. We verified the chemical composition by solid nuclear magnetic resonance (13C-NMR) spectroscopy and observed the porous structure by scanning electron microscopy (SEM). We conducted adsorption isothermal and kinetic tests to determine the adsorption properties. It was found that the adsorbents showed high adsorption efficiency and an adsorption equilibrium time of 200 min. In addition, since the crown ether used in this work could form a stable complex with Li+, we observed good selectivity for Li+ in the prepared solution compared with other ions such as Na+, K+, Mg2+, and Ca2+. We reused the adsorbents five times with no significant decrease in adsorptive capacity.

Cationic effect of charge compensation on the sulfide capacity of aluminosilicate slags

AbstractThe effect of CaO on the sulfide capacity of CaO‐Al2O3‐SiO2 slags was studied from the viewpoint of the ionic structure of alumina in slag. The aluminum coordination number was analyzed using 27Al 500‐MHz solid nuclear magnetic resonance spectroscopy and the results were compared with those of the sulfide capacity analysis. The sulfide capacity of slag, in the peralkaline region (), exhibited a linear relationship with respect to basicity () as excess free Ca2+ formed a 4‐coordinated aluminum unit structure ([IV]Al; ) and stabilized the sulfide ions (). However, sulfide capacity in the peraluminous region () exhibited a nonlinear relationship with respect to basicity () owing to the structure of higher‐coordinated aluminum units ([V]Al, [VI]Al; Al3+) and the relative lack of Ca2+. Therefore, the sulfide capacity of high Al2O3‐bearing slags strongly depended on the basicity () and stability of sulfide ions (), which depended on the competitive behavior of Ca2+ owing to the structural changes in Al2O3. The effect of the aluminum coordination number on the sulfide capacity was discussed in detail using an analysis of the slag structure and thermodynamics model.

New research progress of nuclear magnetic resonance quantum information processing

In the last 20 years, there have been lots of novel developments and remarkable achievements in quantum information processing theoretically and experimentally. Among them, the coherent control of nuclear spin dynamics is a powerful tool for the experimental implementation of quantum schemes in liquid and solid nuclear magnetic resonance (NMR) system, especially in liquid-state NMR. Compared with other quantum information processing systems, NMR platform has many advantages such as the long coherence time, the precise manipulation and well-developed quantum control techniques, which make it possible to accurately control a quantum system with up to 12-qubits. Extensive applications of liquid-state NMR spectroscopy in quantum information processing such as quantum communication, quantum computing and quantum simulation have been thoroughly studied over half a century. There are also many outstanding researches in the recent several years. So we focus on the recent researches in this review article. First, we introduce the basic principle of the liquid-state NMR quantum computing and two new methods reported in the pseudo-pure state preparation which has more advantages than the traditional methods. The quantum noise-injection methods and the quantum tomography technology in liquid-state NMR are also mentioned. Then we overview Horrow-Hassidim-Lioyd algorithm, quantum support vector machine algorithm, duality quantum computing and their implementations in liquid-state NMR system. Also, we report recent researches about quantum simulations, including quantum tunneling, high-energy physics and topological sequences. Then we display the quantum cloud platform of our group. In order to let more people, either amateurs or professionals, embrace and more importantly participate in the tidal wave of quantum science, we launch our NMR quantum cloud computing (NMRCloudQ) service. Through NMRCloudQ, we offer a direct access to a real, physical spectrometer in our laboratory and encourage users to explore quantum phenomena and demonstrate quantum algorithms. Finally, we discuss the development prospects and development bottlenecks of NMR, and point out the prospects for the future development direction.

Chemical Characterization of Non-Saccharidic and Saccharidic Components of Rapeseed Hulls and Sunflower Shells

The main compositional characteristics of rapeseed hulls (RH) and sunflower shells (SS) were examined in terms of non-cellulosic components. The non-sugar fractions were analyzed by solid nuclear magnetic resonance (NMR) and pyrolysis-gas-chromatography/mass spectrometry (Pyr-GC-MS). Unlike SS, RH is a non-lignified biomass. The presence of large amounts of catechol and cresol suggested the presence of phytomelanin in both materials. Sugars accounted for 60% of RH and 45% of SS. Pectic compounds were extracted from the holocellulose of RH with ammonium oxalate or with citric acid, with 17% and 31% yield, respectively. A glucuronoxylan was isolated from the holocellulose of SS in basic conditions with 16% yield.

Using solid 13C NMR coupled with solution 31P NMR spectroscopy to investigate molecular species and lability of organic carbon and phosphorus from aquatic plants in Tai Lake, China.

Forms and labilities of plant-derived organic matters (OMs) including carbon (C) and phosphorus (P) were fundamental for understanding their release, degradation and environmental behaviour in lake ecosystems. Thus, solid 13C and solution 31P nuclear magnetic resonance (NMR) spectroscopy were used to characterize biomass of six aquatic plants in Tai Lake, China. The results showed that carbohydrates (61.2% of the total C) were predominant C functional group in the solid 13C NMR spectra of plant biomass, which may indicate high lability and bioavailability of aquatic plants-derived organic matter in lakes. There was 72.6-103.7% of the total P in aquatic plant biomass extracted by NaOH-EDTA extracts. Solution 31P NMR analysis of these NaOH-EDTA extracts further identified several molecular species of P including orthophosphate (50.1%), orthophosphate monoesters (46.8%), DNA (1.6%) and pyrophosphate (1.4%). Orthophosphate monoesters included β-glycerophosphate (17.7%), hydrolysis products of RNA (11.7%), α-glycerophosphate (9.2%) and other unknown monoesters (2.1%). Additionally, phytate, the major form of organic P in many lake sediments, was detected in floating plant water poppy. These inorganic P (e.g. orthophosphate and pyrophosphate) and organic P (e.g. diester and its degradation products) identified in plant biomass were all labile and bioavailable P, which would play an important role in recycling of P in lakes. These results increased knowledge of chemical composition and bioavailability of OMs derived from aquatic plants in lakes.

Synthesis and Characterization of Covalent Organic Polymer

Development of covalent organic polymer (COP) is a potential new class of adsorbent for gas separation due to their good hydrothermal stability, chemical tuning flexibility and low cost. COP-1 was prepared via one-step polycondensation of cyanuric chloride and piperazine under catalyst free and N2 atmosphere condition. The properties of COP-1 were characterized using several analytical methods such as Fourier Transform Infra-Red (FTIR), solid Nuclear Magnetic Resonance (s-NMR), Thermal gravimetric analysis (TGA) and N2 adsorption and desorption measurement. The C-N bond of COP-1 which has non-rigid framework was successfully linked in this study. It is found that COP-1 has low thermal degradation temperature i.e. 483 K. As compared to literature, lower surface area (75.5 m2/g) and slightly large pore size (8 nm) are noticed. The difference of physical properties of COP-1 synthesized between in this study and literature revealed the challenge of reproducibility for COP-1.

Fast Pyrolysis of Nitrogen-Rich Wood Waste Pretreated by Microwave-Assisted Glycerolysis

The high nitrogen content in wood waste containing urea formaldehyde from furniture industry hampers its utilization as a clean fuel. Herein, microwave-assisted organosolv pretreatment of wood waste using glycerol as solvent was conducted in a commercial microwave reactor with varying temperature of 120–240 °C for reducing nitrogen content. The elemental analysis shows that up to 88.1 % of nitrogen and 92.9 % of alkali and alkaline earth metals in wood waste can be removed by microwave-assisted glycerolysis. The solid nuclear magnetic resonance spectrometry analysis illustrate that the urea–formaldehyde resin, lignin and hemicellulose fractions in wood waste can also be simultaneously reduced by pretreatment. Raw and pretreated wood waste was subsequently fast pyrolyzed in a semi-batch pyroprobe reactor. The experimental results demonstrate that the relative content of levoglucosan in pyrolysis vapors was significantly enhanced by pretreatment, whereas the relative content of nitrogen-containing compounds was reduced obviously. These findings provide a simple and efficient pretreatment method for reducing the formation of nitrogenous compounds during fast pyrolysis of nitrogen-rich wood waste.

Structural biology applications of solid state MAS DNP NMR

Dynamic Nuclear Polarization (DNP) has long been an aim for increasing sensitivity of nuclear magnetic resonance (NMR) spectroscopy, delivering spectra in shorter experiment times or of smaller sample amounts. In recent years, it has been applied in magic angle spinning (MAS) solid-state NMR to a large range of samples, including biological macromolecules and functional materials. New research directions in structural biology can be envisaged by DNP, facilitating investigations on very large complexes or very heterogeneous samples. Here we present a summary of state of the art DNP MAS NMR spectroscopy and its applications to structural biology, discussing the technical challenges and factors affecting DNP performance.

Room-temperature in situ nuclear spin hyperpolarization from optically pumped nitrogen vacancy centres in diamond.

Low detection sensitivity stemming from the weak polarization of nuclear spins is a primary limitation of magnetic resonance spectroscopy and imaging. Methods have been developed to enhance nuclear spin polarization but they typically require high magnetic fields, cryogenic temperatures or sample transfer between magnets. Here we report bulk, room-temperature hyperpolarization of 13C nuclear spins observed via high-field magnetic resonance. The technique harnesses the high optically induced spin polarization of diamond nitrogen vacancy centres at room temperature in combination with dynamic nuclear polarization. We observe bulk nuclear spin polarization of 6%, an enhancement of ∼170,000 over thermal equilibrium. The signal of the hyperpolarized spins was detected in situ with a standard nuclear magnetic resonance probe without the need for sample shuttling or precise crystal orientation. Hyperpolarization via optical pumping/dynamic nuclear polarization should function at arbitrary magnetic fields enabling orders of magnitude sensitivity enhancement for nuclear magnetic resonance of solids and liquids under ambient conditions.

Probing the Carbonyl Functionality of a Petroleum Resin and Asphaltene through Oximation and Schiff Base Formation in Conjunction with N-15 NMR.

Despite recent advances in spectroscopic techniques, there is uncertainty regarding the nature of the carbonyl groups in the asphaltene and resin fractions of crude oil, information necessary for an understanding of the physical properties and environmental fate of these materials. Carbonyl and hydroxyl group functionalities are not observed in natural abundance 13C nuclear magnetic resonance (NMR) spectra of asphaltenes and resins and therefore require spin labeling techniques for detection. In this study, the carbonyl functionalities of the resin and asphaltene fractions from a light aliphatic crude oil that is the source of groundwater contamination at the long term USGS study site near Bemidji, Minnesota, have been examined through reaction with 15N-labeled hydroxylamine and aniline in conjunction with analysis by solid and liquid state 15N NMR. Ketone groups were revealed through 15N NMR detection of their oxime and Schiff base derivatives, and esters through their hydroxamic acid derivatives. Anilinohydroquinone adducts provided evidence for quinones. Some possible configurations of the ketone groups in the resin and asphaltene fractions can be inferred from a consideration of the likely reactions that lead to heterocyclic condensation products with aniline and to the Beckmann reaction products from the initially formed oximes. These include aromatic ketones and ketones adjacent to quaternary carbon centers, β-hydroxyketones, β-diketones, and β-ketoesters. In a solid state cross polarization/magic angle spinning (CP/MAS) 15N NMR spectrum recorded on the underivatized asphaltene as a control, carbazole and pyrrole-like nitrogens were the major naturally abundant nitrogens detected.

Synthesis and characterization of aluminum poly-hexamethylenephosphinate and its flame-retardant application in epoxy resin

A flame retardant additive, aluminum poly-hexamethylenephosphinate (APHP) with a polymeric structure was synthesized from 1,5-hexadiene, hypophosphorous acid and aluminum ions. The molecular structure of APHP and thermal stability were characterized by solid nuclear magnetic resonance, Fourier transform infrared and thermogravimetric analysis. Then, APHP was applied into diglycidyl ether of bisphenol-A cured by 4,4′-diamino-diphenylmethane. APHP showed flame-retardant effect on the epoxy thermosets in limited oxygen index (LOI), UL94 vertical test and cone calorimeter. The thermosets with only 4 wt.% APHP obtained an LOI value of 32.7% and reached the UL94 V-1 rating. The APHP/EP thermosets decreased the pk-HRR, THR and av-EHC values, decreased CO2Y and enhanced the COY ratios, and also reserved more residual char comparing with neat thermoset. The less incorporation of APHP in thermosets will impose the better flame retardancy to epoxy thermosets. The flame-retardant effect of APHP was resulted by its two main pyrolyzed contents phosphorus and alkyl-phosphinic fragments. In condensed phase, the phosphorus-containing contents facilitated to the higher char yields and the formation of intumescent char layer, which led to a reduction of the released fuel and a strong barrier effect to weaken the combustion intensity. In gas phase, the PO, PO2 and alkyl-phosphinic fragments with quenching effect were released from the phosphorus-containing contents, and can decrease the heat release and weaken the combustion intensity.

John Stewart Waugh

John Stewart Waugh, a chemical-physics authority recognized as the founder of the field of high- resolution nuclear magnetic resonance (NMR) in solids, died from complications from Alzheimer’s disease in Lincoln, Massachusetts, on 22 August 2014.John Stewart WaughPPT|High resolutionJohn was born on 25 April 1929 in Storrs, Connecticut, and was raised near the University of Connecticut, where his father, who sparked his interest in science, was a professor of economics and statistics. After high school, John attended Dartmouth College; he graduated in 1949 with highest distinction in chemistry. He then went to graduate school at Caltech, where his thesis supervisor was Donald Yost and his research focused on a topic discovered about three years earlier—NMR. As part of his thesis, “Line profiles in nuclear magnetic resonance absorption,” John assembled a continuous-wave NMR instrument.After receiving his PhD in chemistry and physics in 1953, John returned to the East Coast to be an instructor in the chemistry department at MIT. He was promoted to assistant professor in 1955 and rose through the academic ranks; in 1989 he became an institute professor, the highest honor that MIT bestows on its faculty.During his first 15 years at MIT, John focused his research on various intriguing problems in chemistry and physics that arose during the early years of NMR. For example, he explained the anomalous chemical shifts in 1H NMR spectra of aromatic molecules, coupling in strongly interacting spin systems, and relaxation in liquids and gases. In 1968 he introduced a method for using Fourier-transform spectroscopy to measure spin–lattice relaxation times T1 in complex spin systems. That “inversion recovery” technique remains the method of choice for calculating spin–lattice relaxation rates in gases, liquids, and solids.In 1966 John and engineer Edward Ostroff, who worked at spectrometer manufacturer Magnion, serendipitously discovered that applying a train of intense RF pulses to a spin system in a solid would extend the length of a free induction decay. That led in 1968 to a series of three articles by John, with various coauthors, on multiple-pulse NMR; those papers laid the foundations for high-resolution NMR in solids. One of them, now famous as the WAHUHA experiment, described the initial suppression of the homonuclear dipolar interactions in calcium fluoride and observation of the underlying chemical shifts and their spatial anisotropy, the feature of NMR spectra that renders the technique so useful to physics, chemistry, and biology.Equally important, John and Ulrich Haeberlen introduced a theoretical framework to understand the experiments: the average Hamiltonian theory (AHT), an especially powerful form of time-dependent perturbation theory. Today AHT provides the intellectual underpinnings for spin decoupling, recoupling, and many other stimulating ideas in magnetic resonance and other fields. It is considered an intellectual triumph and the most important theoretical approach in the field.In the early 1970s, John, together with graduate students Alexander Pines and Michael Gibby, published a paper demonstrating that high-resolution NMR experiments could be extended to observe carbon-13, nitrogen-15, phosphorus-31, and other nuclei with smaller dipolar couplings. The experiment’s central feature was the transfer of polarization from abundant spins, namely 1H, to the other nuclei. That circumvented the problematic long T1 of the nuclei. A second feature they incorporated was 1H decoupling, which ensures high resolution. Today that seminal approach to high-resolution NMR is routinely used in labs worldwide.Subsequently, John and his colleagues combined the experiment with multiple-pulse NMR in a manner that reintroduced high-resolution dipole couplings into NMR spectra. That approach allows measurement of internuclear distances. Integration of magic-angle spinning led to what is today known as dipole recoupling, which permits the determination of protein structures in membranes and amyloid fibrils.John is remembered fondly for his well-developed sense of humor. He called the method outlined in his seminal paper on multiple-pulse NMR the WAHUHA experiment after the three authors: Waugh, Huber, and Haeberlen. Following the abandonment of “cycles/second” for the hertz in the early 1970s, John rescued “radian/ second,” the preferred unit in all magnetic resonance calculations, by defining a new unit, the As, so that 1 Hz = 2π As. Aficionados of magnetic resonance use the As to express angular velocity in inverse seconds, or an “Avis.”An avid sailor, John owned many sailboats, including one aptly named Magic Angle and a dinghy called Spin Echo. With Susan, his wife of 31 years, he sailed the coast of Maine, traveled, and raised a succession of beloved Labrador retrievers.John Waugh was a towering figure in NMR and electron paramagnetic resonance, and his intellect, achievements, and wonderful sense of humor were an inspiration to those who knew and worked with him. He will be sorely missed by all of us in the magnetic resonance community.© 2015 American Institute of Physics.

Solid state 27Al NMR and X-ray diffraction study of alumina–carbon composites

The structural and chemical transformations occurring in alumina–carbon composites upon heat treatment were investigated by using a combination of X-ray diffraction (XRD) and solid-state 27Al nuclear magnetic resonance (NMR) spectroscopy. Two different carbon precursors were employed: a commercial activated carbon and a char obtained by carbonization of the endocarp of babassu coconut at 700°C. The alumina–carbon composites were prepared by aqueous impregnation of the carbon supports with aluminum nitrate and, after filtering and drying, the as-synthesized powders were heat-treated under argon flow at temperatures up to 1000°C. The Al compounds present in the as-synthesized samples were identified by XRD and solid-state 27Al NMR as nanocrystalline aluminum oxyhydroxides or hydroxides, depending on the synthesis conditions. All Al-containing phases were XRD-amorphous in the char-derived nanocomposites, with the presence of a distribution of AlO6 (octahedral Al site), AlO5 (pentacoordinated Al) and AlO4 (tetrahedral Al site) units revealed by solid-state 27Al NMR spectroscopy. The heat treatments caused the formation of transition aluminas dispersed over the carbon supports, with the occurrence of different amounts of AlO6, AlO5 and AlO4 units depending on the heat treatment temperature and on the type of carbon precursor used for the preparation of the composites.