Solid-State NMR Line Narrowing Methods for Quadrupolar Nuclei: Double Rotation and Dynamic-Angle Spinning. In: Blümich B, editor. Solid-State NMR IV Methods and Applications of Solid-State NMR. Berlin: Springer Berlin Heidelberg; 1994. pp. 79-124. [DOI: 10.1007/978-3-642-79127-7_2]

Reactions and surface interactions of saccharides in cement slurries

Glucose, maltodextrin, and sucrose exhibit significant differences in their alkaline reaction properties and interactions in aluminate/silicate cement slurries that result in diverse hydration behaviors of cements. Using 1D solution- and solid-state (13)C nuclear magnetic resonance (NMR), the structures of these closely related saccharides are identified in aqueous cement slurry solutions and as adsorbed on inorganic oxide cement surfaces during the early stages of hydration. Solid-state 1D (29)Si and 2D (27)Al{(1)H} and (13)C{(1)H} NMR techniques, including the use of very high magnetic fields (18.8 T), allow the characterization of the hydrating silicate and aluminate surfaces, where interactions with adsorbed organic species influence hydration. These measurements establish the molecular features of the different saccharides that account for their different adsorption behaviors in hydrating cements. Specifically, sucrose is stable in alkaline cement slurries and exhibits selective adsorption at hydrating silicate surfaces but not at aluminate surfaces in cements. In contrast, glucose degrades into linear saccharinic or other carboxylic acids that adsorb relatively weakly and nonselectively on nonhydrated and hydrated cement particle surfaces. Maltodextrin exhibits intermediate reaction and sorption properties because of its oligomeric glucosidic structure that yields linear carboxylic acids and stable ring-containing degradation products that are similar to those of the glucose degradation products and sucrose, respectively. Such different reaction and adsorption behaviors provide insight into the factors responsible for the large differences in the rates at which aluminate and silicate cement species hydrate in the presence of otherwise closely related saccharides.

Solid state separated-local-field NMR spectroscopy on half-integer quadrupolar nuclei: principles and applications to borane analysis

New multidimensional NMR methods correlating the quadrupolar and heteronuclear dipolar interactions affecting a half-integer quadrupolar spin in the solid state are introduced and exemplified. The methods extend separated-local-field magic-angle spinning (SLF MAS) NMR techniques that have been used successfully in spin-(1)/(2) spectroscopy to the study of S >/= (3)/(2) nuclei. In our implementation, these techniques avoid homonuclear proton decoupling requirements by relying on moderately fast MAS rates (6-15 kHz) and use rotor-synchronized constant-time pulse sequences to achieve nearly arbitrary amplifications of the apparent dipolar coupling strengths. The result is a suite of simple 2D NMR experiments, whose line shapes carry valuable information about the structure and dynamics of solids containing quadrupolar and proton nuclei. The potential of these sequences was exploited to gather new insight into the structure and dynamics of a variety of boron-containing samples. These experimental SLF schemes were also extended to 3D NMR experiments that incorporate multiple-quantum MAS, thus enabling the resolution needed to study multiple chemical sites in a solid and providing a useful tool for the assignment of inequivalent sites.

35Cl quadrupolar constants obtained by solid-state NMR: study of chlorinated Al-O-P clusters, involving OH...Cl hydrogen bonds

Simulation of static and MAS NMR spectra obtained at high field (B(0) = 14.08 T) and high spinning frequency (up to nu(rot) = 22 kHz) allows the determination of 35Cl quadrupolar parameters for various cubane-shaped, cage-like and cyclic Al-O-P clusters; the role of OH...Cl contacts is emphasized.

High resolution 3D exchange NMR spectroscopy and the mapping of connectivities between half-integer quadrupolar nuclei

A novel approach to the determination of structure and potential dynamics in the solid-state NMR spectroscopy of half-integer quadrupolar nuclei is proposed and demonstrated. The new experiment combines into a single three-dimensional sequence, 2D multiple-quantum magic-angle-spinning NMR and 2D exchange NMR protocols. The result separates for each inequivalent chemical site its spin-diffusion powder line shape to proximate homonuclei. A peculiar feature of the experiment is the asymmetry it displays in the individual 2D powder patterns, resulting from its encoding of isotropic shifts before the mixing period. The resulting spectra facilitate the interpretation of the structural and dynamic features for the individual sites; experimental applications of this new method to relative geometry determinations in 23Na-23Na spin pairs are presented, and the quantitative evaluation of the resulting data is briefly discussed.

Spin-1/2 and beyond: a perspective in solid state NMR spectroscopy

Novel applications of solid state nuclear magnetic resonance (NMR) to the study of small molecules, synthetic polymers, biological systems, and inorganic materials continue at an accelerated rate. Instrumental to this uninterrupted expansion has been an improved understanding of the chemical physics underlying NMR. Such deeper understanding has led to novel forms of controlling the various components that make up the spin interactions, which have in turn redefined the analytical capabilities of solid state NMR measurements. This review presents a perspective on the basic phenomena and manipulations that have made this progress possible and describes the new opportunities and challenges that are being opened in the realms of spin-1/2 and quadrupole nuclei spectroscopies.

Very fast MAS and MQMAS NMR studies of the spectroscopically challenging minerals kyanite and andalusite on 400, 500, and 800 MHz spectrometers

The well-characterized minerals kyanite and andalusite have long presented great challenges in using solid state 27Al NMR to determine the isotropic chemical shift deltaCS, quadrupole coupling constant e2qQ/h, and asymmetry parameter eta for each of the inequivalent aluminum sites in these minerals. Indeed, these minerals have frequently been used to test advances in instrumentation. Recent advances in magnet technology (up to 18.8 T = 800 MHz 1H) and in MAS probe technology (spinning up to 35 kHz and considerably stronger rf) and refinements of the two-dimensional, multiple quantum magic angle spinning (MQMAS) technique suggested that these developments could be profitably used to study kyanite and andalusite by solid state 27Al NMR. The benefit of being able to study kyanite both by MAS and MQMAS techniques on 400, 500, and 800 MHz spectrometers is demonstrated. The two octahedral aluminum sites with the largest (and nearly equal) e2qQ/h values give overlapping 1D MAS or 2D 3QMAS signals at all three field strengths. Nevertheless, quantitatively accurate 3Q signal intensities at 9.4 T for all four octahedral aluminum sites (with e2qQ/h values up to 10 MHz) allow more detailed analysis. Even if the 3Q signal intensities are not quantitative, their isotropic shifts provide an approach (if accurate e2qQ/h and eta values are available) other than deconvolution of the MAS spectrum for calculating deltaCS values. For andalusite, 34 kHz MAS on the 800 MHz spectrometer significantly narrows the extremely broad signal for the octahedral aluminum, and only slight difficulties are encountered in quantitating the relative amounts of AlO5 and AlO6 present. Even with e2qQ/h = 15.3 MHz, the octahedral aluminum in andalusite gives a signal in a MQMAS experiment, albeit of reduced intensity. As appropriate, we discuss some of the benefits and limitations of these advances in instrumentation and of different experimental approaches for studying non-integral spin quadrupolar nuclei in solids.

Quadrupolar and chemical shift tensors characterized by 2D multiple-quantum NMR spectroscopy

The present work discusses a new 2D NMR method for characterizing the principal values and relative orientations of the electric field gradient and the chemical shift tensors of half-integer quadrupolar sites. The technique exploits the different contributions that quadrupolar and shielding interactions impart on the evolution of multiple-quantum and of single-quantum coherences, in order to obtain 2D powder lineshapes that are highly sensitive to these nuclear spin coupling parameters. Different spinning variants of this experiment were assayed, but it was concluded that a static version can yield the highest sensitivity to the values of the principal components and to the relative geometries of the local coupling tensors. It was found that correlating the central transition evolution with the highest available order of the spin coherence was also helpful for maximizing this spectral information. Good agreement between data obtained on 87Rb (S = 32) and 59Co (S = 72) samples and ideal theoretical lineshape predictions of this experiment was obtained, provided that heterogeneities in the multiple-quantum excitation and conversion processes were suitably accounted by procedures similar to those described in the spin-(1/2) multiple-quantum NMR literature. Copyright 1999 Academic Press.

Off-angle correlation spectroscopy applied to spin-1/2 and quadrupolar nuclei

A two-dimensional correlation experiment is described, in which homonuclear dipolar couplings are used to realize through-space magnetization exchange on spin-1/2 (31P) and on quadrupolar nuclei (23Na and 11B). In the detection period, Magic Angle Spinning is applied to enhance resolution, and the dipole couplings are re-introduced in the mixing period by spinning off the Magic Angle. The dependency of the exchange rates on the mixing time and the spinning angle is investigated. The influence of strong spin-locking during mixing is discussed, and shown in the spin-1/2 case to remove the dependence on chemical shift offset effects. For quadrupolar spins, the experiment yields information on the relative tensor orientations of the coupled quadrupoles. Applications to crystalline sodium aluminum diphosphate, sodium sulphite, and potassium borate glasses are shown.