Magic-angle Sample-spinning Nuclear Magnetic Resonance Research Articles

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.

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.

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.

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.

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)

The Floquet theory of nuclear magnetic resonance spectroscopy of single spins and dipolar coupled spin pairs in rotating solids

The Floquet theory for the description of magic angle sample spinning (MASS) nuclear magnetic resonance (NMR) experiments is introduced. MASS NMR signals of single spin systems and homonuclear two-spin system in the presence of direct and indirect dipolar couplings are evaluated. The single spin system is utilized to develop our Floquet formalism for the MASS NMR experiments and the coupled spin system is discussed to demonstrate its methodology and its applicability. This theoretical approach enables the calculation of the positions, the amplitudes, and line shapes of MASS center and sideband. The diagonalization of the MASS Floquet matrices of the different spin systems provides eigenvalues and eigenvectors which in turn determine the frequencies and intensities of the various bands in the MASS spectra. Their frequency shifts can be explained in terms of anticrossing of Floquet states and their amplitudes can be calculated via the matrix elements of transition–amplitude Floquet operator. New Floquet operators are introduced and the commutation relations between them utilized to enable the evaluation of diagonalization matrices. The Floquet theory is applied to determine the rotational resonance conditions for homonuclear dipolar-coupled spin pairs. It is shown that significant band shifts are expected when degeneracies between Floquet states occur. These shifts endow the centerband and sidebands with powder line shapes from polycrystalline samples. Simulations of experimental line shapes can provide direct and indirect dipolar coupling constants, including their relative signs. This approach is valid for all possible dipolar coupling strengths as well as for all sample spinning speeds and isotropic and anisotropic chemical shift parameters. The decay of zero-quantum coherences in the coupled spin-systems is also considered in terms of the Floquet approach. The sensitivity of the MASS line shapes close to the rotational resonance conditions with respect to the relative magnitudes of the chemical shift anisotropies of the spins and their direct and indirect coupling constants is examined by the calculation of various MASS spectra. To do so the interaction parameters of the different 13C nuclei in glycine and alanine are used. Experimental results of the weakly dipolar coupled spin pairs in uniformly 13C labeled alanine are also presented and compared with theoretical results.

High-resolution aluminum-27 solid-state magic-angle sample-spinning nuclear magnetic resonance spectroscopic study of aluminum trichloride-tetrahydrofuran complexes

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTHigh-resolution aluminum-27 solid-state magic-angle sample-spinning nuclear magnetic resonance spectroscopic study of aluminum trichloride-tetrahydrofuran complexesOc Hee Han and Eric OldfieldCite this: Inorg. Chem. 1990, 29, 19, 3666–3669Publication Date (Print):September 1, 1990Publication History Published online1 May 2002Published inissue 1 September 1990https://doi.org/10.1021/ic00344a009RIGHTS & PERMISSIONSArticle Views151Altmetric-Citations20LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (431 KB) Get e-Alerts Get e-Alerts

MASS-NMR structural analysis of barium aluminofluorophosphate glasses with and without nitridation

The local structure of barium-aluminofluorophosphate (Ba–Al–P–O–F) glasses was investigated using high resolution magic-angle sample spinning nuclear magnetic resonance (MASS-NMR) spectroscopy. The 27Al spectra show three different aluminum environments [Al(4), Al(5), and Al(6)] in these glasses. Changes were observed due to the addition of fluorine and nitrogen. 31P results indicate only one type of phosphorus environment which shifts with fluorine additions. The 19F spectra suggest that fluorine has both Ba and Al as nearest neighbors.

Solid-state ‘‘magic-angle’’ sample-spinning nuclear magnetic resonance spectroscopic study of group III–V (13–15) semiconductors

We have obtained 27 Al, 69 Ga, 71 Ga, 113 In, and 115 In static and ‘‘magic-angle’’ sample-spinning (MASS) solid-state nuclear magnetic resonance (NMR) spectra of a series of polycrystalline III–V semiconductors (AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, InP, InAs, and InSb) at magnetic field strengths of 8.45 and 11.7 T. Line-broadening mechanisms have been identified by comparing static and MASS NMR results. By applying the MASS technique, dipolar, first-order quadrupolar, and pseudodipolar interactions are removed. Thus, the MASS spectral linewidth (of the central, 1/2↔−1/2, transition) is dominated by exchange and/or second-order quadrupolar interactions. For compounds having the cubic zinc blende structure, the exchange interaction dominates, and exchange interaction constants can be determined. For AlP, AlAs, AlSb, GaP, GaAs, InP, and InAs, first-order quadrupole effects are evident as spinning sidebands (SSBs), due to the satellite transitions. These effects are due to a small distribution of electric field gradients caused by lattice defects, and result in an overall Lorentzian profile for the SSB envelope. For compounds having the hexagonal wurtzite structure (GaN and AlN), the second-order quadrupolar interaction is the main line-broadening mechanism, and we find isotropic chemical shifts δi of 333 ppm [from 1 M Ga(NO3 )3 ] for GaN, and of 115 ppm [from 1M Al(H2 O)6 Cl3 ] for AlN, and nuclear quadrupole coupling constant e2 qQ/h of 2.8 MHz for 69 GaN, 1.7 MHz for 71 GaN, and of 2.2 MHz for AlN.

High-field, high-resolution proton "magic-angle" sample-spinning nuclear magnetic resonance spectroscopic studies of gel and liquid crystalline lipid bilayers and the effects of cholesterol

We have obtained proton ('H) magic-angle sample-spinning (MASS) nuclear magnetic resonance (NMR) spectra of a variety of smectic liquid crystalline phases, including sodium decanoate (30.1 wt %)-decanol(38.9 wt %)-water, potassium oleate (72 wt %)-water, and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (lecithin)(50 wt %)-water, in addition to investigating the effects of temperature and cholesterol (CHOL) addition on the lecithin spectrum. Our results indicate that even relatively slow (-3 kHz) MASS causes averaging of the dipolar interactions causing line broadening in the static NMR spectra, at least for the non-CHOL species. All of the major proton-containing groups are well resolved, the resolution being at least as good as obtained in previous studies of oriented samples or sonicated systems. The methylene chain protons in each liquid crystalline lipid bilayer system give rise to intense, sharp, spinning sidebands (SSBs) due to the special form of the dipolar Hamiltonian. The methyl groups of the lipids, and the trimethylammonium group in lecithin, do not yield intense SSB patterns. Addition of CHOL causes attenuation of the center-band methylene peak of the lecithin, and a corresponding increase in SSB intensity. All or nearly all of the non-CHOL protons present in the samples appear to contribute to the high-resolution spectra, within our experimental error of - 10-20%. Use of a chain-deuterated lecithin allows peaks arising from the side chain of CHOL to be observed. In the gel phase of lecithin, only the trimethylammonium peak is apparent. The high-resolution afforded by MASS of the liquid crystalline phases permits rapid determination of the spin-lattice relaxation times (TI) of all resolved resonances. In addition, the observation of numerous chemically shifted peaks permits the use of two-dimensional (2-D) NMR techniques, which can give information on the spatial proximity of the various groups in the bilayer. Taken together, our results indicate a very promising future for high-field 'H MASS NMR studies of other lipid and membrane systems because of the extremely high sensitivity of the IH nucleus and the unique ability to obtain chemical shift, TI, and 2-D information from a single sample, without recourse to isotopic labeling, macroscopic sample orientation, or ultrasonic irradiation. Nuclear magnetic resonance (NMR) spectroscopy has been used to investigate the structure of model and biological mem- branes for over 20 years, and studies of molecular motion in simple lipids and hydrocarbons can be traced back even further.'S2 The earliest studies concentrated on the 'H nucleus, which because of its high sensitivity and abundance was expected to be a useful probe of membrane structure. Early studies by Cerb~jn~,~ identified mobile lipid components in Nocardia asteroides; then Chapman et al. began an extensive series of studies of model- and biological membrane systems.+l2 The early 'H NMR experiments utilized wide-line methods, and assumed that 'H-IH dipolar interactions dominated the observed line widths, since very broad lines were, in general, obtained. These line widths could be reduced by sonicating the (liquid crystalline) lipid bilayers, or membranes, reducing their particle size and permitting faster vesicle tumbling. Shortly after the first papers by Chapman et al., numerous other groups published similar studies on related sy~tems.l~-*~ Three main questions arose from the early studies. These centered around the nature of the line-broadening mechanisms in the liquid crystalline phases, the effects of sonication (does it cause line narrowing due to a change in lipid bilayer structure, or because of increased rates of particle rotation?), and whether spin diffusion occurs in the liquid crystalline phases. These questions have (at least in part) been answered over the past 15 years. Thus, Chan et a1.,26 Tidd~,~' and Oldfield et aLZ8 showed that line broadening in various liquid crystalline phases (at least up to -90 MHz) was purely dipolar in origin, since the line widths (or effective T2 values, T2*) were field independent. This view was supported by the results of 'H 'magic-angle sample-spinning (MASS) NMR,29 by multiple-pulse line narrowing,30 and by magic-angle alignment of oriented sample^.^'-^^ The effects of sonication have been widely studied, and the early view, that sonication causes line narrowing only due to increased particle tumbling, has received considerable s~pport,~~-~~ although it is

High-resolution proton and carbon-13 NMR of membranes: why sonicate?

We have obtained high-field (11.7-T) proton and carbon-13 Fourier transform (FT) nuclear magnetic resonance (NMR) spectra of egg lecithin and egg lecithin-cholesterol (1:1) multibilayers, using "magic-angle" sample spinning (MASS) techniques, and sonicated egg lecithin and egg lecithin-cholesterol (1:1) vesicles, using conventional FT NMR methods. Resolution of the proton and carbon-13 MASS NMR spectra of the pure egg lecithin samples is essentially identical with that of sonicated samples, but spectra of the unsonicated lipid, using MASS, can be obtained very much faster than with the more dilute, sonicated systems. With the 1:1 lecithin-cholesterol systems, proton MASS NMR spectra are virtually identical with conventional FT spectra of sonicated samples, while with 13C NMR, we demonstrate that most 13C nuclei in the cholesterol moiety can be monitored, even though these same nuclei are essentially invisible, i.e., are severely broadened, in the corresponding sonicated systems. In addition, 13C MASS NMR, spectra can again be recorded much faster than with sonicated samples, due to concentration effects. Taken together, these results strongly suggest there will seldom be need in the future to resort to ultrasonic disruption of lipid bilayer membranes in order to obtain high-resolution proton or carbon-13 NMR spectra.

Solid‐state NMR Evidence of 4‐, 5, and 6‐Fold Aluminum Sites in Roller‐Quenched SiO2‐A12O3 Glasses

The structures of roller‐quenched SiO2‐Al2O3 glasses containing 10 to 50 wt% Al2O3 were investigated by TEM and high‐resolution 27Al and 29Si magic angle sample spinning nuclear magnetic resonance (MASS‐NMR) spectroscopy. The chemical shifts observed in the NMR spectra of these phase‐separated (on the TEM scale) glasses provide evidence, for the existence of all three (4‐, 5‐, and 6‐jold) Al‐coordination units in these glasses and for the presence of A1 in both the Si‐rich and Si‐poor phases.

ChemInform Abstract: SOLID‐STATE NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY OF MINERALS

Nuclear magnetic resonance (NMR) spectroscopy has been a useful tool for examining the structure of molecules in solution since the 1950s. It has only been since the late 1970s and early 1980s, though, that developments in very high field superconducting magnets and magic-angle sample-spinning (MASS) have made NMR routinely useful for examining the structure of solids. In this paper, we briefly review the theory of MASS NMR spectroscopy and some of the recent experimental results for minerals. N MR spectroscopy examines the local structural environment of atoms, to at most the third and fourth nearest neighbors. For crystalline silicates, silicon-29 and aluminum-27 MASS NMR have already proven useful in examining the validity of the aluminum avoidance principle and the extent of Al(4)/Si order/disorder, in determining the extent of polymerization, in determining the number of crystallographically distinct silicon sites present, in estimating bond strength sums and Si-O-(Si, AI) bond angles, and in detecting the presence of Al(4) and Al(6) and estimating Al(4)/Si and Al(6)/Al(4) ratios. As the NMR behavior of more nuclides (certainly including boron-H, nitrogen-IS, oxygen-17, fluorine-19, sodium-23, magnesium-25, and phosphorus-31) becomes better understood, we feel that this method will become a powerful tool for examining the local structural environment of a wide variety of species in a broad range of

SOLID-STATE NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY OF MINERALS

Nuclear magnetic resonance (NMR) spectroscopy has been a useful tool for examining the structure of molecules in solution since the 1950s. It has only been since the late 1970s and early 1980s, though, that developments in very high field superconducting magnets and magic-angle sample-spinning (MASS) have made NMR routinely useful for examining the structure of solids. In this paper, we briefly review the theory of MASS NMR spectroscopy and some of the recent experimental results for minerals. N MR spectroscopy examines the local structural environment of atoms, to at most the third and fourth nearest neighbors. For crystalline silicates, silicon-29 and aluminum-27 MASS NMR have already proven useful in examining the validity of the aluminum avoidance principle and the extent of Al(4)/Si order/disorder, in determining the extent of polymerization, in determining the number of crystallographically distinct silicon sites present, in estimating bond strength sums and Si-O-(Si, AI) bond angles, and in detecting the presence of Al(4) and Al(6) and estimating Al(4)/Si and Al(6)/Al(4) ratios. As the NMR behavior of more nuclides (certainly including boron-H, nitrogen-IS, oxygen-17, fluorine-19, sodium-23, magnesium-25, and phosphorus-31) becomes better understood, we feel that this method will become a powerful tool for examining the local structural environment of a wide variety of species in a broad range of