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PubMed1996

High resolution 1H spectra of powdered solids observed by Hahn echo pulse sequence with magic-angle spinning.

The 1H magic-angle spinning (MAS) spectrum for a typical powdered solid is composed of a high resolution component and a broadline component. The high resolution component can be well isolated from the broadline component by the Hahn echo sequence with a long echo time. Compared with CRAMPS experiment, which measures the proton system as a whole, the high resolution echo-MAS method measures only a fraction of the solid, which is usually small at room temperature and quite different from the majority of the solid in both molecular motion and chemical environment. It is shown that for a sample of fumaric acid monoethyl ester, the chemical shifts of the high resolution component are apparently distinguishable from the isotropic chemical shifts of the broadline component in the CRAMPS spectrum as the temperature approaches the melting point. In addition, for a sample of malonic acid, the echo-MAS spectrum is sensitive to moisture and temperature, while its corresponding CRAMPS spectrum is not. It is suggested that the molecules which produce the high resolution component are related to the lattice defects in a solid, including the surface disorder of the polycrystallites, while the molecules that generate the broadline component are located on the rigid lattice of the solid.

Chemical Phenomena↗
PubMed1994

Methods and reagents. On the magic of mini-preps....

Methods and reagents is a unique monthly column that highlights current discussions in the newsgroup bionet.molbio.methds-reagnts, available on the Internet. This month's column discusses the problems encountered by some people when switching from Promega's Magic mini-prep plasmid DNA isolation columns to their new Wizard mini-prep kits. For details on how to partake in the newsgroup, see the accompanying box.

Biotechnology↗
PubMed2003

Spectral editing and pattern recognition methods applied to high-resolution magic-angle spinning 1H nuclear magnetic resonance spectroscopy of liver tissues.

Principal component analysis (PCA) has been applied to three nuclear magnetic resonance (NMR) spectral editing methods, namely, the Carr-Purcell-Meiboom-Gill spin-echo, diffusion editing, and skyline projection of a two-dimensional J-resolved spectrum, obtained from high-resolution magic-angle spinning NMR spectroscopy of liver tissues, to distinguish between control and hydrazine-treated rats. The effects of the toxin on rat liver biochemistry were directly observed and characterized by depleted levels of liver glycogen, choline, taurine, trimethylamine N-oxide, and glucose and by elevated levels of lipids and alanine. The highly unsaturated omega-3-type fatty acid was observed for the first time in hydrazine-treated rat liver. The contributions of the metabolites to the separation of control from dosed liver tissues varied depending on the type of spectral editing method used. We have shown that subtle changes in the metabolic profiles can be selectively amplified using a metabonomics approach based on the different NMR spectral editing techniques in conjunction with PCA.

Alanine↗
PubMed2005

Development of a high-resolution magic-angle spinning nuclear magnetic resonance identity assay of the capsular polysaccharide from Haemophilus influenzae type b present in cetavlon precipitate.

We describe the use of high-resolution magic-angle spinning nuclear magnetic resonance to control the identity of the capsular polysaccharide from Haemophilus influenzae type b (Hib) present in the cetavlon precipitate. This step is one of the earliest in the purification of this polysaccharide, which is further used in the production of Hib polysaccharide-protein conjugate vaccine. The effects of sample procedure and magnetic field strength have been investigated. Since this assay is rapid and simple, it may represent a useful technique for characterization of polysaccharides present in complex and insoluble matrices. Moreover, it allows a rapid evaluation of the structure of the produced polysaccharides very early on during the production process and is as such an essential analytical tool before starting the purification process.

Bacterial Capsules↗
PubMed2005

Acute biochemical effects of La(NO3)3 on liver and kidney tissues by magic-angle spinning 1H nuclear magnetic resonance spectroscopy and pattern recognition.

High-resolution magic-angle spinning (MAS) 1H nuclear magnetic resonance (NMR) spectroscopic and pattern recognition (PR) based methods have been applied to studies on the acute biochemical effects of La(NO3)3 on rats. Male Wistar rats were treated with various doses of La(NO3)3 (2, 10, and 50 mg/kg body weight), and MAS 1H NMR spectra of their intact liver and kidney tissues were analyzed using principal components analysis to extract metabolic information. The biochemical effects of La(NO3)3 were characterized by the increase of triglyceride and bile acid and the decrease of glycogen in liver tissue, together with a slight elevation of triglyceride level in kidney tissue. The target lesion of La(NO3)3 to liver was found by MAS NMR-PR methods. This study illustrated the power of the combination of MAS 1H NMR and pattern recognition for the analysis of biochemical effects of rare earths.

Animals↗
PubMed2004

Investigation of the membrane localization and distribution of flavonoids by high-resolution magic angle spinning NMR spectroscopy.

To investigate the structural basis for the antioxidative effects of plant flavonoids on the lipid molecules of cellular membranes, we have studied the location and distribution of five different flavonoid molecules (flavone, chrysin, luteolin, myricetin, and luteolin-7-glucoside) with varying polarity in monounsaturated model membranes. The investigated molecules differed in the number of hydroxyl groups attached to the polyphenolic benzo-gamma-pyrone compounds. To investigate the relation between hydrophobicity and membrane localization/orientation, we have applied (1)H magic angle spinning NMR techniques measuring ring current induced chemical shift changes, nuclear Overhauser enhancement cross-relaxation rates, and lateral diffusion coefficients. All investigated flavonoids show a broad distribution along the membrane normal with a maximum in the lipid/water interface. With increasing number of hydroxyl groups, the maximum of this distribution is biased towards the lipid headgroups. These results are confirmed by pulsed field gradient NMR measurements of the lateral diffusion coefficients of phospholipids and flavonoids, respectively. From the localization of different flavonoid protons in the membrane, a model for the orientation of the molecules in a lipid bilayer can be deduced. This orientation depends on the position of the polar center of the flavonoid molecule.

Antioxidants↗
PubMed2005

Magic roundabout, a tumor endothelial marker: expression and signaling.

Molecular signals that guide blood vessels to specific paths are not fully deciphered, but are thought to be similar to signals that mediate neuronal guidance. These cues are not only critical for normal blood vessel development, but may also play a major role in tumor angiogenesis. In this study, we have demonstrated the tumor endothelial specific expression of a Robo family member, magic roundabout (MRB), functionally characterized its role in endothelial cell migration and defined a signaling pathway that might mediate this function. We show that MRB is differentially over-expressed in tumor endothelial cells versus normal adult endothelial cells in numerous solid tumors. Moreover, over-expression of MRB in endothelial cells activates MRB in a ligand-independent fashion, and activation of MRB via Slit2, a putative ligand, results in inhibition of VEGF and FGF induced migration. We also demonstrate that MRB induced inhibition of endothelial migration is partially mediated by the Ras-Raf-Mek-Erk signaling pathway. We therefore hypothesize that expression of MRB is involved in regulating the migration of endothelial cells during tumor angiogenesis.

Biomarkers, Tumor↗
PubMed2004

Characterisation of commercial ionomer glasses using magic angle nuclear magnetic resonance (MAS-NMR).

Five commercial ionomer glasses (Fuji IX, Ketac Molar, G338, G2, and G2SR) used to produce glass (ionomer) polyalkenoate dental cements were studied. 29Si, 27Al, 31P and 19F magic angle spinning nuclear magnetic resonance (MAS-NMR) Spectroscopy was used to characterise the glasses and the resulting spectra compared with previous studies of model glasses. The 29Si NMR spectra were consistent with Q4(3Al) and Q4(4Al) units being present and agreed with the low non-bridging oxygen contents calculated from the elemental composition. The 27Al NMR spectra typically exhibited three distinct sites at 45-60, 20 and 0 ppm which have been attributed to Al(IV), Al(V) and Al(VI) coordinate aluminium. The presence of Al(V) and Al(VI) are consistent with previous studies of model ionomer glasses. The 31P spectra all exhibited a chemical shift between -8 and -23 ppm with the exception of the Ketac Molar glass, which exhibited a peak at 2-3 ppm consistent with orthophosphate. The chemical shift of 31P in the range -8 to -23 ppm indicates a PO(4) tetrahedra surrounded by 1-4 Al moieties. The (19)F NMR spectra indicated the presence of Al-F-Ca(n) in the G2 and G338 glasses, Al-F-Sr(n) in the G2SR and Fuji IX glasses and crystalline CaF2, LaF3, Al-F-Ca(n) in the Ketac Molar glass. The G338 glass with a high non-bridging oxygen content showed the presence of a F-Ca(n) species. There was also present in all the glasses a peak corresponding to Al-F-Na(n). The intensity of this peak was approximately proportional to the sodium content.

Acrylic Resins↗
PubMed2004

Adaptive chronic infection, structured stress, and medical magic bullets: do reductionist cures select for holistic diseases?

With a generalized language-of-thought argument for immune cognition, we model how population-directed, structured, psychosocial stress can impose an image of itself on the coevolutionary conflict between a highly adaptive chronic infection and the immune response. As population-level structured stress appears a fundamental part of the biology of disease, we raise the possibility that simplistic individual-oriented magic-bullet drug treatments, vaccines, and risk-reduction programs that do not address the fundamental living and working conditions which underlie disease ecology will fail to control many current epidemics. In addition, such reductionist interventions may go so far as to select for more holistic pathogens characterized by processes operating at multiple levels of biocultural organization. The complications are representative of the concerns of cultural immunology, a new field of study.

Adaptation, Physiological↗
PubMed2004

Characterization of a beta-D-(1-->3)-glucan from the marine diatom Chaetoceros mülleri by high-resolution magic-angle spinning NMR spectroscopy on whole algal cells.

High-resolution magic-angle spinning (hr-MAS) NMR spectroscopy was used to record NMR spectra of a cell paste from the marine diatom Chaetoceros mülleri. This gave information on a cellular storage polysaccharide identified as a beta-D-(1-->3)-linked glucan, using hr-MAS one-dimensional 1H and 13C, two-dimensional 1H,1H-COSY and 13C,1H-correlation spectroscopy. The same structural information was deduced from the liquid state NMR data on the glucan extracted from C. mülleri. The extracted glucan proved to be a beta-D-(1-->3)-linked glucan with a degree of polymerization of 19 and a degree of beta-D-(1-->6) branching of 0.005. The hr-MAS spectrum of the diatom showed several nonglucan resonances in the carbohydrate region of the NMR spectrum (60-103 ppm) that were shown to be noncarbohydrate resonances by means of two-dimensional 13C,1H- and 1H,1H-correlated NMR data.

Carbohydrate Conformation↗
PubMed2006

In vivo determination of Neisseria meningitidis serogroup A capsular polysaccharide by whole cell high-resolution magic angle spinning NMR spectroscopy.

High resolution-magic angle spinning (HRMAS) NMR spectroscopy was applied to serogroup A Neisseria meningitidis (NMA) to determine precise structures of capsular polysaccharide (CPS) expressed on the meningococcal surface. Both the O-acetylated (OAc) NMA parent and a mynC::aphA3 OAc- mutant demonstrated characteristic CPS-derived NMR signals indicating cell-surface expression of CPS, but only the parent expressed O-3 and O-4 acetylation signals. A capsule-defective strain showed no NMR signals for CPS. The (1)H NMR HRMAS spectral patterns correlated with the purified CPS (1)H NMR profiles. HRMAS NMR can distinguish detailed complex carbohydrate structures expressed on bacteria. NMA express both O-3 and O-4 acetylated polymers but not in equimolar ratio amounts in vivo.

Bacterial Capsules↗
PubMed2006

Clinical trials update from the American Heart Association 2006: OAT, SALT 1 and 2, MAGIC, ABCD, PABA-CHF, IMPROVE-CHF, and percutaneous mitral annuloplasty.

This article provides information and a commentary on trials presented at the American Heart Association meeting held in November 2006, relevant to the pathophysiology, prevention and treatment of heart failure. All reports should be considered as preliminary data, as analyses may change in the final publication. The OAT study failed to show a benefit of PCI over optimal medical therapy in patients with persistent total occlusion of the infarct related artery following a myocardial infarction. In SALT 1 and 2, tolvaptan was found to correct hyponatraemia of various aetiologies; however, whether this has an impact on heart failure prognosis requires further evaluation. A placebo controlled study of myocardial implantation of skeletal myoblasts in patients with moderate to severe LVSD (MAGIC) showed equivocal/uncertain effects, long term follow-up data are awaited. The ABCD study which compared the ability of an invasive and a non-invasive test to identify patients at risk of arrhythmic events prior to ICD implantation, suggested that the two strategies were comparable, although the practical value of either test remains uncertain and the study had many major flaws. The PABA-CHF study hinted that pulmonary vein antrum isolation might be more effective than AV node ablation with bi-ventricular pacing for the treatment of patients with heart failure in atrial fibrillation. In IMPROVE-CHF, an NT-pro BNP guided treatment strategy was found to reduce the cost of managing patients with acute breathlessness.

American Hospital Association↗
PubMed2006

Detection of nucleotide binding to Na,K-ATPase in an aqueous membrane suspension by 13C cross-polarization magic-angle spinning NMR spectroscopy.

Binding of uniformly (13)C labelled ATP to Na,K-ATPase was studied by (13)C cross-polarization magic-angle spinning (CP-MAS) NMR. In the presence of 30 mM Na(+) , and with sample- and time-averaging, NMR spectra obtained at 4 degrees C exhibited several resonances for the bound nucleotide. Chemical shifts suggested that site-specific changes in the micro-environment or conformation of the nucleotide occurred in the high affinity binding site. These experiments permit further studies of nucleotide dynamics, structure and binding under physiologically relevant conditions.

Animals↗
PubMed2004

Background gradient suppression in stimulated echo NMR diffusion studies using magic pulsed field gradient ratios.

By evaluating the spin echo attenuation for a generalized 13-interval PFG NMR sequence consisting of pulsed field gradients with four different effective intensities (F(p/r) and G(p/r)), magic pulsed field gradient (MPFG) ratios for the prepare (G(p)/F(p)) and the read (G(r)/F(r)) interval are derived, which suppress the cross term between background field gradients and the pulsed field gradients even in the cases where the background field gradients may change during the z-store interval of the pulse sequence. These MPFG ratios depend only on the timing of the pulsed gradients in the pulse sequence and allow a convenient experimental approach to background gradient suppression in NMR diffusion studies with heterogeneous systems, where the local properties of the (internal) background gradients are often unknown. If the pulsed field gradients are centered in the tau-intervals between the pi and pi/2 rf pulses, these two MPFG ratios coincide to eta=G(p/r)/F(p/r)=1-8/[1+(1/3)(delta/tau)(2)]. Since the width of the pulsed field gradients (delta) is bounded by 0< or =delta< or =tau, eta can only be in the range of 5< or =-eta< or =7. The predicted suppression of the unwanted cross terms is demonstrated experimentally using time-dependent external gradients which are controlled in the NMR experiment as well as spatially dependent internal background gradients generated by the magnetic properties of the sample itself. The theoretical and experimental results confirm and extend the approach of Sun et al. (J. Magn. Reson. 161 (2003) 168), who recently introduced a 13-interval type PFG NMR sequence with two asymmetric pulsed magnetic field gradients suitable to suppress unwanted cross terms with spatially dependent background field gradients.

Diffusion↗
PubMed2004

A solid-state 14N magic-angle spinning NMR study of some amino acids.

Experimental strategies for the acquisition of high-quality 14N magic-angle spinning (MAS) NMR spectra of the simple amino acids, which exhibit 14N quadrupole coupling constants (C(Q)) on the order of 1.2 MHz, are devised. These are the first useful 14N MAS spectra reported for nitrogen compounds having a C(Q)(14N) value in excess of 1 MHz. The complete manifolds of spinning sidebands (ssbs), i.e., about 300 ssbs for a spinning frequency of 6.0 kHz, have been observed in the 14N MAS NMR spectra of a series of amino acids. In their crystal structure these amino acids all exhibit the zwitterionic form and thus the 14N MAS NMR spectra represent those of a rotating -NH(3)(+) group and not of an amino (-NH(2)) group. Computer simulations combined with fitting of simulated to the experimental ssb intensities result in the determination of precise values for the 14N quadrupole coupling (C(Q)) and its associated asymmetry parameter (eta(Q)) for the nitrogen sites in these molecules. For some of the amino acids the 14N MAS NMR spectra exhibit overlap between the manifolds of ssbs from two different nitrogen sites in accordance with their crystal structures. Computer analysis of these spectra results in two different sets of (C(Q), eta(Q)) values which mainly differ in the magnitudes for eta(Q).

Amino Acids↗
PubMed2004

Rotational resonance in uniformly 13C-labeled solids: effects on high-resolution magic-angle spinning NMR spectra and applications in structural studies of biomolecular systems.

We describe investigations of the effects of rotational resonance (R(2)) on solid state (13)C NMR spectra of uniformly (13)C-labeled samples obtained under magic-angle spinning (MAS), and of the utility of R(2) measurements as structural probes of peptides and proteins with multiple uniformly labeled residues. We report results for uniformly (13)C-labeled L-alanine and L-valine in polycrystalline form, and for amyloid fibrils formed by the 15-residue peptide A beta(11-25) with uniform labeling of a four-residue segment. The MAS NMR spectra reveal a novel J-decoupling effect at R(2) conditions that may be useful in spectral assignments for systems with sharp (13)C MAS NMR lines. Pronounced dependences of the apparent isotropic (13)C NMR chemical shifts on MAS frequency near R(2) conditions are also observed. We demonstrate the feasibility of quantitative (13)C-(13)C distance determinations in L-valine, and qualitative determinations of inter-residue (13)C-(13)C contacts in A beta(11-25) fibrils. Finally, we demonstrate a "relayed" R(2) technique that may be useful in structural measurements on systems with poorly resolved (13)C MAS NMR lines.

Alanine↗
PubMed2004

Variable temperature system using vortex tube cooling and fiber optic temperature measurement for low temperature magic angle spinning NMR.

We describe the construction and operation of a variable temperature (VT) system for a high field fast magic angle spinning (MAS) probe. The probe is used in NMR investigations of biological macromolecules, where stable setting and continuous measurement of the temperature over periods of several days are required in order to prevent sample overheating and degradation. The VT system described is used at and below room temperature. A vortex tube is used to provide cooling in the temperature range of -20 to 20 degrees C, while a liquid nitrogen-cooled heat exchanger is used below -20 degrees C. Using this arrangement, the lowest temperature that is practically achievable is -140 degrees C. Measurement of the air temperature near the spinning rotor is accomplished using a fiber optic thermometer that utilizes the temperature dependence of the absorption edge of GaAs. The absorption edge of GaAs also has a magnetic field dependence that we have measured and corrected for. This dependence was calibrated at several field strengths using the well-known temperature dependence of the (1)H chemical shift difference of the protons in methanol.

Biopolymers↗
PubMed2005

Triple-quantum dynamics in multiple-spin systems undergoing magic-angle spinning: application to 13C homonuclear correlation spectroscopy.

We analyze the multiple-quantum dynamics governed by a new homonuclear recoupling strategy effecting an average dipolar Hamiltonian comprising three-spin triple-quantum operators (e.g., S(p)+S(q)+S(r)+) under magic-angle spinning conditions. Analytical expressions are presented for polarization transfer processes in systems of three and four coupled spins-1/2 subject to triple-quantum filtration (3QF), and high-order multiple-quantum excitation is investigated numerically in moderately large clusters, comprising up to seven spins. This recoupling approach gives highly efficient excitation of triple-quantum coherences: ideally, up to 67% of the initial polarization may be recovered by 3QF in three-spin systems in polycrystalline powders. Two homonuclear 2D correlation strategies are demonstrated experimentally on powders of uniformly 13C-labeled alanine and tyrosine: the first correlates the single-quantum spectrum in the first dimension with the corresponding 3QF spectrum along the other. The second protocol correlates triple-quantum coherences with their corresponding single-quantum coherences within triplets of coupled spins.

Alanine↗