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PubMed1999

Fluorine-19 solid-state NMR magic-angle-turning experiments using multiple-pulse homonuclear decoupling

For compounds giving "crowded" 1-dimensional magic-angle-spinning spectra, information about the local atomic environment in the form of the chemical shift anisotropy (CSA) is sacrificed for high resolution of the less informative isotropic chemical shift. Magic-angle-turning (MAT) NMR pulse sequences preserve the CSA information by correlating it to the isotropic chemical shift in a 2-dimensional experiment. For low natural abundance nuclei such as 13C and 15N and under 1H heteronuclear dipolar decoupling conditions, the dominant NMR interaction is the chemical shift. For abundant nuclei such as 1H, 19F, and 31P, the homonuclear dipolar interaction becomes a significant contribution to the observed linewidth in both F1 and F2 dimensions. We incorporate MREV8 homonuclear multiple-pulse decoupling sequences into the MAT experiment to give a multiple-pulse MAT (MP-MAT) experiment in which the homonuclear dipolar interaction is suppressed while maintaining the chemical shift information. Extensive use of computer simulation using GAMMA has guided the pulse sequence development. In particular, we show how the MREV8 pulses can be incorporated into a quadrature-detected sequence such as MAT. The MP-MAT technique is demonstrated for a model two-site system containing a mixture of silver trifluoroacetate and calcium difluoride. The resolution in the isotropic evolution dimension is improved by faster sample spinning, shorter MREV8 cycle times in the evolution dimension, and modifications of the MAT component of the pulse sequence. Copyright 1999 Academic Press.

Journal Article↗

PubMed1999

Target field design for magic angle gradient coils.

The target field method of designing gradient coils is extended to the case where the gradient producing currents lie on cylinders of a general orientation with respect to the polarizing magnetic field. This provides a general approach for designing coils that require unusual sample geometries such as those required for magic angle spinning (MAS) applications. A detailed example of a magic angle gradient coil set for MAS is given.

Equipment Design↗

PubMed1999

Magnetic field gradients in solid state magic angle spinning NMR.

Magnetic field gradients have proven useful in NMR for coherence pathway selection, diffusion studies, and imaging. Recently they have been combined with magic angle spinning to permit high-resolution measurements of semi-solids, where magic angle spinning averages any residual dipolar couplings and local variations in the bulk magnetic susceptibility. Here we show the first examples of coherence pathway selection by gradients in dipolar coupled solids. When the gradient evolution competes with dipolar evolution the experiment design must take into account both the strength of the dipolar couplings and the means to refocus it. Examples of both homonuclear and heteronuclear experiments are shown in which gradients have been used to eliminate the need for phase cycling.

Glycine↗

PubMed2000

A high-resolution (13)C 3D CSA-CSA-CSA correlation experiment by means of magic angle turning.

It is shown in this paper that a previously reported 90 degrees sample flipping (13)C 2D CSA-CSA correlation experiment may be carried out alternatively by employing constant slow sample rotation about the magic angle axis and by synchronizing the read pulse to 13 of the rotor cycle. A high-resolution 3D CSA-CSA-CSA correlation experiment based on the magic angle turning technique is reported in which the conventional 90 degrees 2D CSA-CSA powder pattern for each carbon in a system containing a number of inequivalent carbons may be separated according to the isotropic chemical shift value. The technique is demonstrated on 1,2,3-trimethoxybenzene in which all of the overlapping powder patterns that cannot be segregated by the 2D CSA-CSA experiment are resolved successfully by the 3D CSA-CSA-CSA experiment, including even the two methoxy groups (M(1) and M(3)) whose isotropic shifts, confirmed by high-speed MAS, are separated by only 1 ppm. A difference of 4 ppm in the principal value component (delta(33)) between M(1) and M(3) is readily obtained.

Algorithms↗

PubMed2025

Multicolor Cell Lineage Tracing Using MAGIC Markers Strategies.

Multicolor MAGIC Markers strategies are useful lineage tracing tools to study brain development at a multicellular scale. In this chapter, we describe an in utero electroporation method to simultaneously label multiple neighboring progenitors and their respective progeny using these multicolor reporters. In utero electroporation enables the introduction of any gene of interest into embryonic neural progenitors lining the brain ventricles through a simple pipeline consisting of a micro-injection followed by the application of electrical pulses. Successful in utero electroporation requires a concise yet complete understanding of each step of the surgical protocol, spanning from the preoperative preparation to the postoperative care, as well as the MAGIC Markers tool outlined in this study. Besides a detailed protocol, we present non-integrative and integrative approaches to demonstrate the range of cell and lineage tracking possibilities of multicolored progenitors and their descent over time.

Cell Lineage↗

PubMed1991

Magic-angle 13C NMR analysis of hard wheat flour and dough.

Samples of hard wheat flour and dough are analyzed by magic-angle spinning 13C NMR spectroscopy. Cross-polarization magic-angle spinning (CPMAS) 13C NMR spectra of the dry flour allow its starch and protein content to be accurately measured. These two components are phase-separated. Spectra of hydrated hard wheat doughs are collected under both CPMAS and single-pulse carbon with low-power 1H decoupling conditions. The former report on the macromolecular components of the dough, while the latter reveal small molecules which are solubilized by the water. Results of the present study are interpreted as indicating that the protein is largely unaffected by the added water and remains phased-separated from the starch, while water causes significant changes in polymer dynamics of the starch component.

Flour↗

PubMed1983

Magical thinking by inpatient staff members.

Magical thinking is a primitive form of mental activity which, nevertheless, the author contends, is common among mental health professionals. Four examples of magical thinking by inpatient staff members are presented and briefly explored, in order to shed light on our work and ourselves.

Health Occupations↗

PubMed2003

Analysis of histamine and modeling of ligand-receptor interactions in the histamine H(1) receptor for Magic Angle Spinning NMR studies.

OBJECTIVE AND DESIGN: Investigation of the principles of ligand-receptor interaction in histamine receptors can help to provide a solid foundation for structure-based drug design. Stable isotope labelling of the ligand 'Histamine' has been performed and 1D (13)C CP MAS and 2D Radio Frequency Dipolar Recoupling (RFDR) spectra for the ligand are presented. Hyperfine signals were well spread and did not suffer from any sizable line broadening. The production of H(1) receptor for Magic Angle Spinning NMR studies is currently in progress. TREATMENT: An agonist binding domain is proposed using homology modeling, database searches and mutagenesis data for the H(1) receptor. METHODS: Homology modeling, Database searches for Expressed sequence Tag (ESTs), Magic Angle Spinning Nuclear Magnetic Resonance analysis of the ligand histamine. RESULTS: The three-dimensional receptor model and mutagenesis studies suggest that the amine of the agonist histamine may form an ion pair with the TM III Asp, whereas the imidazole ring of histamine may associate with TM V Asp and Thr. CONCLUSIONS: Homology modeling studies confirms the absence of TM VIII in the H(1) receptor. According to the model the histamine in particular interacts with the transmembrane (TM) regions of the H(1) receptor structure, in particular TM helix III and V. This is in line with recent mutagenesis studies. Database search methods for ESTs have been used for electronic prediction of tissue distribution of H(1) receptor expression. The results indicate that the H(1) expression is highest in heart and skeletal muscle, which may be of importance for drug targeting.

Biophysical Phenomena↗

PubMed1998

Orientation-dependent changes in MR signal intensity of articular cartilage: a manifestation of the "magic angle" effect.

OBJECTIVE: To study magnetic resonance (MR) imaging pattern of normal hyaline articular cartilage in the knee joint with regard to the contribution of the "magic angle" effect to the MR signal. DESIGN: Thirty-two healthy volunteers were imaged in a standard supine position in a 1.5-T unit using spin echo and gradient echo sequences. Nine volunteers were reimaged with the knee flexed. The signal behavior of the hyaline cartilage of the femoral condyles was evaluated qualitatively and quantitatively. The extended and flexed positions of the nine volunteers were compared. RESULTS: A superficial and a deep hyperintense layer and a hypointense middle cartilage layer were observed. Segments of increased signal intensity were visible along the condyles; a magic angle effect on signal intensity was evident in the hypointense middle layer with both gradient echo and spin echo images. CONCLUSION: The MR signal behavior of hyaline cartilage is influenced by the alignment of the collagen fibers within the cartilage in relation to the magnetic field. Failure to recognize this effect may lead to inaccurate diagnosis.

Cartilage, Articular↗

PubMed2006

Separated local field NMR experiments on oriented samples rotating at the magic angle.

Biophysical studies on membrane proteins by solid state NMR (SSNMR) can be carried out directly in a membrane environment. Samples are usually prepared in form of multi-lamellar dispersions for magic angle sample spinning or as aligned multi-layers for orientation dependent NMR experiments without sample rotation. A new development is the application of MAS NMR to aligned samples (MAOSS; Magic Angle Oriented Sample Spinning). In combination with separated local field (SLF) experiments, size and orientation of heteronuclear dipolar couplings may be extracted from two-dimensional experiments which correlate dipolar couplings with isotropic chemical shifts. The orientation of these (1)H-X dipolar couplings can be directly related to the orientation of molecular groups in the sample. Here, we demonstrate the feasibility of these experiments on highly ordered polyethylene fibers which serve as model compound. Based on these data, the experiment is also applied to ordered multi-layers of bacteriorhodopsin (purple membrane) which is used as a model for aligned membrane proteins. We present a detailed analysis of different experimental designs with respect to angular sensitivity and the influence of residual sample disorder ("mosaic spread"). The results of the MAOSS-SLF experiment are discussed within the context of established solid state NMR experiments which are usually performed without sample rotation and we compare the data to orientation information obtained from X-ray diffraction.

Bacteriorhodopsins↗

PubMed1992

Systematic comparison of ILWAS, MAGIC, and ETD watershed acidification models: 3. Mass balance budgets for acid neutralizing capacity.

Three watershed acidification models-ILWAS, MAGIC, and ETD-were quantitatively compared to determine model structural differences by using a combination of input mapping and ANC mass balance budgets. Input mapping is a set of rules and algorithms to ensure that consistent input values were simultaneously derived for all three models. ANC budget analysis under current SO4(2-) deposition and a 70% reduction in SO4(2-) deposition allows examination of the relative importance of biogeochemical processes in affecting predictions of ANC or predicted changes in ANC. Model inputs were based on two dissimilar watersheds having characteristics typical of watersheds in the northeastern US. After mapping inputs, the three models predicted values of outflow ANC fluxes that were similar among the models for each watershed and deposition scenario. Within each watershed, the changes in outflow ANC fluxes between the scenarios were similar for the three models. Terrestrial weathering was the major source of ANC for all three models for both watersheds and deposition scenarios. The contributions of other processes to the ANC of the two watersheds were, under certain conditions, model-specific. Cation exchange was responsible for changes in ANC when deposition decreased for the three models. Other processes responsible for changes in ANC between scenarios were SO4(2-) sorption (for MAGIC) and in-lake weathering (for ETD). The processes responsible for the change in ANC from a change in deposition (cation exchange, SO4(2-) sorption, and in-lake weathering) were different from the processes contributing to the absolute ANC for a given deposition scenario (terrestrial weathering). The budget analysis complements an earlier Monte Carlo analysis that showed that the three models are structurally different and that predictions viewed on a relative scale are more similar than absolute scale predictions.

Journal Article↗

PubMed1992

NMR imaging of solids with magic angle spinning.

Different aspects of solid state NMR imaging are reviewed, with emphasis on imaging in combination with line narrowing, especially in combination with magic angle spinning. Experimental results obtained with the latter technique are discussed, along with the implications of magic angle spinning on slice selection.

Magnetic Resonance Spectroscopy↗

PubMed1995

Magic-echo phase-encoding solid imaging with improved time resolution.

The magic-echo phase-encoding solid imaging (MEPSI) sequence is based on the magic-echo pulse sequence for the refocusing of the dipolar interaction and on pure phase-encoding for spatial resolution in all dimensions. MEPSI has many advantages; however, as a consequence of pure phase-encoding, it is very time-consuming. In the following, two strategies are proposed to decrease the time necessary for the acquisition of an image by a factor of 2 per dimension.

Magnetic Resonance Spectroscopy↗

PubMed1993

One-dimensional double-quantum magic-angle-spinning NMR of deuterated solids.

An approach to double-quantum magic-angle spinning (2Q-MAS) of spin I = 1 with a time-share irradiation, resulting in a one-dimensional (1D) MQ spectrum, is demonstrated in this paper. The experiment was carried out with perdeuterated dimethoxybenzene and showed that the 2Q transitions were insensitive to the spinning axis deviation from the magic angle. The 1D-2Q-MAS scheme may also be applied to nitrogen-containing solids.

Anisoles↗

PubMed1994

Application of nuclear magnetic resonance magic sandwich echo imaging to solid polymers.

A solid-state 1H nuclear magnetic resonance (NMR) imaging technique based on magic sandwich echoes (MSE) is described for obtaining spatial projections of solid polymer samples. The modification of MSE multiple echo detection is combined with short gradient pulses applied during the sandwich windows. This allows proton homonuclear decoupling in solids with dipolar couplings up to 50 kHz. For a rapid gating of the gradients a fast gradient pulse driver was constructed with switching times between 550 and 910 ns giving a maximum gradient strength of 330 mT/m. With our detection technique the spectral width can be doubled. One-dimensional projections and spatially resolved spectra of rigid polymer phantoms are presented. For contrast enhancement the use of the T1 relaxation time and the number of the magic sandwiches functioning as an adjustable magnetization filter discriminating between different strengths of the dipolar coupling is demonstrated.

Echo-Planar Imaging↗

PubMed1996

Two-dimensional magic-angle spinning isotropic reconstruction sequences for quadrupolar nuclei.

Two-dimensional magic-angle spinning (triple quantum, single quantum) correlation pulse sequences and phase cycles based on the technique of Frydman and Harwood for the reconstruction of the isotropic spectrum of half-integer spin quadrupolar nuclei broadened to second-order are described. These sequences provide pure absorption mode two-dimensional lineshapes and increased sensitivity. Experimental examples on spin I = 3/2 (87Rb in RbNO3) and I = 5/2 (27Al in NaSi3AlO8) are presented. The isotropic chemical shift and quadrupolar coupling parameters could be obtained from a simple analysis of the triple quantum filtered single quantum magic-angle spinning cross-sections.

Absorption↗

PubMed2004

Acute ST-segment elevation myocardial infarction and prior stroke: an analysis from the Magnesium in Coronaries (MAGIC) trial.

BACKGROUND: Patients with prior stroke represent a substantial proportion of patients presenting with acute ST-segment elevation myocardial infarction (STEMI). However, the impact of prior stroke on prognosis has not been rigorously examined in the reperfusion era. METHODS: The baseline characteristics, treatments, and clinical outcomes of patients with prior stroke enrolled in the Magnesium in Coronaries (MAGIC) trial were evaluated and compared to those of patients without prior stroke. RESULTS: MAGIC enrolled 6213 patients with STEMI, of whom 558 (9.0%) had prior stroke. Patients with prior stroke were more likely to have a history of hypertension (88.0% vs 70.3%), diabetes (19.9% vs 14.5%), myocardial infarction (38.2% vs 25.1%), and congestive heart failure (15.6% vs 9.7%). The mean Thrombolysis in Myocardial Infarction Risk Score was higher in patients with prior stroke compared to those without prior stroke (4.37 vs 3.93, P < .0001). Patients with prior stroke were less likely to receive reperfusion therapy, even among those considered eligible at presentation (66.3% vs 80.6%, P < .0001). Compared to patients without prior stroke, inhospital stroke (3.0% vs 1.0%, P < .0001), severe congestive heart failure (23.3% vs 18.2%, P = .003), and 30-day mortality (21.0% vs 14.7%, P < .0001) were higher among patients with prior stroke. On multivariable analysis, prior stroke was independently associated with a significantly higher risk of death at 30 days (odds ratio 1.44, P = .0023). CONCLUSIONS: Patients with prior stroke who present with STEMI are at very high risk for short-term morbidity and mortality. Aggressive treatment of these patients appears warranted.

Aged↗

PubMed2004

Proton magic-angle spinning-NMR investigation of surfactant aqueous suspensions.

In this Note we present the advantages of 1H magic-angle spinning nuclear magnetic resonance (MAS-NMR) for the investigation of surfactant suspensions via transverse relaxation rate (R2) measurements. 1H-relaxation rates can be determined by the classical CPMG method from high-resolution spectra obtained either under conditions of liquid-state NMR for monomers and small spherical micelles or by using MAS-NMR for larger aggregates. For a mixture of alkyl dioxyethylene sulfate and alkylbetaine (80:20, w/w), up to a percentage of surfactant in water of 20%, we found that R2 increased, in accordance with an increased micellar size and very likely the formation of an HI phase. However, above 25%, R2 decreased. This result suggests a change from a hexagonal to a lamellar phase that would be difficult to observe by proton NMR without magic-angle spinning because the lines would be very broad, or by light scattering because of sample opacity. This NMR approach seems to have been overlooked by the community of surfactant physical chemists. It can be complementary to other analytical techniques and presents the advantage of not requiring isotopic labeling.

Journal Article↗