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At least 433 records · Page 24Linked to original sources
PubMed2000

The biochemical profile of rat testicular tissue as measured by magic angle spinning 1H NMR spectroscopy.

The testis is the principal organ of male fertility, responsible for the production of spermatozoa and their maturation into sperm. However, the underlying biochemistry of the testis is relatively understudied. The fluidic and homogeneous nature of the testis makes it an ideal organ for high resolution magic angle spinning (MAS) 1H NMR spectroscopy. In this study we have catalogued the low molecular weight metabolites. The testis contains large amounts of creatine, of which a substantial proportion was shown to be extracellular using bipolar gradients to measure apparent diffusion coefficients. The tissue also contained relatively high amounts of uridine.

Alanine↗
PubMed2002

Magic-angle spinning (31)P NMR spectroscopy of condensed phosphates in parasitic protozoa: visualizing the invisible.

We report the results of a solid-state (31)P nuclear magnetic resonance (NMR) spectroscopic investigation of the acidocalcisome organelles from Trypanosoma brucei (bloodstream form), Trypanosoma cruzi and Leishmania major (insect forms). The spectra are characterized by a broad envelope of spinning sidebands having isotropic chemical shifts at approximately 0, -7 and -21 ppm. These resonances are assigned to orthophosphate, terminal (alpha) phosphates of polyphosphates and bridging (beta) phosphates of polyphosphates, respectively. The average polyphosphate chain length is approximately 3.3 phosphates. Similar results were obtained with whole L. major promastigotes. (31)P NMR spectra of living L. major promastigotes recorded under conventional solution NMR conditions had spectral intensities reduced with respect to solution-state NMR spectra of acid extracts, consistent with the invisibility of the solid-state phosphates. These results show that all three parasites contain large stores of condensed phosphates which can be visualized by using magic-angle spinning NMR techniques.

Animals↗
PubMed2003

A study of metabolic compartmentation in the rat heart and cardiac mitochondria using high-resolution magic angle spinning 1H NMR spectroscopy.

High-resolution magic angle spinning (MAS) (1)H nuclear magnetic resonance (NMR) spectroscopy is increasingly being used to monitor metabolic abnormalities within cells and intact tissues. Many toxicological insults and metabolic diseases affect subcellular organelles, particularly mitochondria. In this study high-resolution (1)H NMR spectroscopy was used to examine metabolic compartmentation between the cytosol and mitochondria in the rat heart to investigate whether biomarkers of mitochondrial dysfunction could be identified and further define the mitochondrial environment. High-resolution MAS spectra of mitochondria revealed NMR signals from lactate, alanine, taurine, choline, phosphocholine, creatine, glycine and lipids. However, spectra from mitochondrial extracts contained additional well-resolved resonances from valine, methionine, glutamine, acetoacetate, succinate, and aspartate, suggesting that a number of metabolites bound within the mitochondrial membranes occur in 'NMR invisible' environments. This effect was further investigated using diffusion-weighted measurements of water and NMR spectroscopy during state 2 and state 3 respiration. State 3 respiration caused a decrease in the resonance intensity of endogenous succinate compared with state 2 respiration, suggesting that coupled respiration may also modulate the NMR detection of metabolites within mitochondria.

Amino Acids↗
PubMed2001

Magnetic resonance: magic angle imaging of the Achilles tendon.

Tendons do not normally produce detectable signals with conventional magnetic-resonance techniques and are recognised as dark signal voids. However, if tendons are examined at 55 degrees to the static magnetic field (the "magic angle"), signals become detectable and the tendons can become the brightest structure on the image. We have used this approach to establish tendon relaxation times and magnetisation transfer ratios and to show contrast enhancement. We have also shown more detail of acute and chronic tendon rupture by this method compared with images made with the tendon parallel to the static magnetic field.

Achilles Tendon↗
PubMed2003

Experimental and theoretical evidence for the magic angle in transmission electron energy loss spectroscopy.

We present experimental measurements of the C K-ELNES of high temperature pyrolysed graphite and related crystalline materials as a function of collection angle and sample tilt. These results together with a corresponding theoretical analysis indicate that the so-called "magic angle" for EELS measurements of an anisotropic crystal such as graphite, where spectra are independent of sample orientation, is approximately two times the characteristic scattering angle. We briefly discuss the implications of this result for the experimental measurement of anisotropic structures, including interfaces, as well as for the detailed modelling of ELNES structures using advanced electronic structure calculations.

Journal Article↗
PubMed2003

Cellular environment of metabolites and a metabonomic study of tamoxifen in endometrial cells using gradient high resolution magic angle spinning 1H NMR spectroscopy.

High resolution magic angle spinning (HRMAS) 1H NMR spectroscopy was used to metabolically characterise Ishikawa cells, a human cell line derived from endometrial adenocarcinoma. The spectra obtained had well-resolved resonances from the nucleotide derivatives of uridine and adenosine. Using a combination of diffusion- and relaxation-weighted spectroscopy, the cellular environment of key metabolites previously identified as related to cell growth was also investigated. As Ishikawa cells are hormone-responsive, the metabolic action of tamoxifen, a selective estrogen receptor modulator (SERM), was also investigated. Cells were exposed to 5, 1 and 0.1 microM tamoxifen. Using the statistical regression technique of prediction to latent structures by partial least squares, a predictive model was built modelling the metabolic profile of the cells against exposure to tamoxifen. These spectral changes were characterised by increased resonance intensities from ethanolamine (3.26 ppm), glucose (3.34-3.94 ppm), glutamate (2.14, 2.32 ppm), tyrosine (7.24 ppm), uridine (7.85 ppm) and adenosine (8.20 ppm), and a relative decrease in contributions from myo-inositol resonances (3.30, 3.62, 3.55 ppm). The nucleotide changes suggest that tamoxifen affects RNA transcription, while the changes in ethanolamine and myo-inositol concentrations are indicative of cell membrane turnover.

Adenocarcinoma↗
PubMed2002

Quantification of neurons in Alzheimer and control brains with ex vivo high resolution magic angle spinning proton magnetic resonance spectroscopy and stereology.

Samples from human brains were examined with both stereologic methods for neuronal counting and high resolution magic angle spinning (HRMAS) proton magnetic resonance spectroscopy (1HMRS) for quantification of cellular metabolites. A statistically significant linear correlation between neuronal density and the concentration of N-acetylaspartate (NAA) in the superior temporal sulcus (STS) area was observed. Although NAA has been widely utilized as a neuronal marker in in vivo MRS, an emerging sub-discipline of diagnostic neuroradiology, the experimental proof of the unilateral relationship between NAA and neurons has yet to be confirmed. The observed correlation provides experimental evidence that NAA concentration is proportional to the neuronal density. Metabolite ratios measured from the STS area were compared to those from frontal association cortex for their sensitivities in differentiating Alzheimer disease brains from control brains.

Aged↗
PubMed1998

Biochemical classification of kidney carcinoma biopsy samples using magic-angle-spinning 1H nuclear magnetic resonance spectroscopy.

High resolution 1H nuclear magnetic resonance (NMR) spectra using spinning at the magic angle (1H MAS NMR) have been obtained on intact normal and pathological kidney tissue samples from patients undergoing surgery for renal cell carcinoma (RCC). The spectra were measured on ca. 80 mg samples and provided high resolution 1H NMR spectra in which effects of dipolar couplings, chemical shift anisotropy and magnetic susceptibility differences are minimised thus yielding high spectral resolution. Conventional one-dimensional and spin-echo spectra and two-dimensional J-resolved, TOCSY and 1H-13C HMQC spectra were also measured on selected samples and these allowed the assignment of resonances of endogenous substances comprising both cytosolic and membrane components. The tumour tissues were characterised principally by an increased lipid content. These are the first reported results on human tumour tissues using this technique and the approach offers potential for the rapid classification of different types of tumour tissue.

Biopsy↗
PubMed2001

Unilateral olfactory perception and magical ideation.

We assessed olfactory detection thresholds and discrimination abilities in 40 healthy right-handers (20 women and 20 men). All subjects were also required to complete the Magical Ideation (MI) scale, a well-validated 30-item schizotypy inventory. Over both nostrils, we found elevated thresholds for subjects with high MI scores (at or above the median score of 9.0) compared with those with low scores. In men but not women, specifically left-nostril acuity was inversely correlated to MI raw scores. MI was unrelated to olfactory discrimination performance. These results suggest an association, at least in healthy men, between even moderate signs of schizotypy and deficits in odor detection. The selective impairment of left-nostril performance adds to the growing evidence for left temporal lobe functional abnormalities in people high on MI. This laterality effect is known from previous studies in patients with schizophrenia. However, as a rule, in psychiatric patients olfactory identification rather than simple detection performance was found to be impaired, indicating that the integration of odor information is affected at different levels of processing in schizotypy compared with schizophrenia. Work with completely normal subjects may reasonably complement clinical studies of olfactory perception. Among its advantages are the good subject compliance and the absence of medication effects.

Adult↗
PubMed2000

Heating of samples induced by fast magic-angle spinning.

Intense sample heating through high-speed magic-angle spinning (MAS; up to 58 K temperature difference) is demonstrated. The role of probehead and spinner design, as well as that of the temperature of the bearing air on the heating of a rotating sample, is examined. MAS-induced heating can affect the accurate determination of the isotropic value of the chemical shift as well as the principal values, asymmetry and anisotropy parameters of the chemical shift tensor. In some cases, a very large temperature gradient (12 K) within the fast rotating sample was found, which may limit the resolution of high-speed 1H MAS nuclear magnetic resonance (NMR) spectra.

Anisotropy↗
PubMed2000

One- and two-dimensional 13C-1H/15N- 1H dipolar correlation experiments under fast magic-angle spinning for determining the peptide dihedral angle phi.

A recently proposed 13C-1H recoupling sequence operative under fast magic-angle spinning (MAS) [K. Takegoshi, T. Terao, Solid State Nucl. Magn. Reson. 13 (1999) 203-212.] is applied to observe 13C-1H and 15N-1H dipolar powder patterns in the IH-15N- 3C- H system of a peptide bond. Both patterns are correlated by 15N-to-13C cross polarization to observe one- or two-dimensional (1D or 2D) correlation spectra, which can be simulated by using a simple analytical expression to determine the H-N-C-H dihedral angle. The 1D and 2D experiments were applied to N-acetyl[1,2-13C,15N] DL-valine, and the peptide q angle was determined with high precision by the 2D experiment to be +/- 155.0 degrees +/- 1.2 degrees. The positive one is in good agreement with the X-ray value of 154 degrees +/- 5 degrees. The 1D experiment provided the value of phi = +/- 156.0 degrees +/- 0.8 degrees.

Carbon Isotopes↗
PubMed2004

Molecular dynamics as studied by static-powder and magic-angle spinning 2H NMR.

The 2H NMR magic-angle spinning (MAS) technique is compared to the static-powder quadrupole echo (QE) and Jeener-Brockaert (JB) pulse sequences for a quantitative investigation of molecular dynamics in solids. The linewidth of individual spinning sidebands of the one-dimensional MAS spectra are observed to be characteristic of the correlation time from approximately 10(-2) to approximately 10(-8) s so that the dynamic range is increased by approximately three orders of magnitude when compared to the QE experiment. As a consequence, MAS 2H NMR is found to be more sensitive to the presence of an inhomogeneous distribution of correlation times than the QE and JB experiments which rely upon lineshape distortions due to anisotropic T2 and T1Q relaxation, respectively. All these results are demonstrated experimentally and numerically using the two-site flip motion of dimethyl sulfone and of the nitrobenzene guest in the alpha-p-tert-butylcalix[4]arene-nitrobenzene inclusion compound.

Computer Simulation↗
PubMed1997

51V magic-angle-spinning NMR and electric field gradient calculations in V2O5 and gamma-LiV2O5 crystals.

51V Magic-angle-spinning (MAS) NMR has been applied to V2O5 at two different magnetic field strengths (4.7 and 7.1 T). Both the magnitude and relative orientation of the quadrupole and chemical shift (CS) tensors have been determined by iterative fitting of the 51V MAS NMR lineshapes at the two magnetic field strengths. The reliability of the results is discussed. Moreover, it is shown that previous low-field single-crystal data are fully consistent with the high-field powder-sample MAS NMR results provided that a slight noncoincidence between the CS tensor and the crystal frame axes is considered. The electric field gradient tensor at the vanadium and lithium sites is subsequently used to test several electronic structure calculation at an ab initio Hartree-Fock level in V2O5 and gamma-LiV2O5 crystals. It is shown that a wide distribution of oxygen charges must be considered to describe the particular environment of each type of oxygen atoms. Furthermore, this analysis supports the fact that the vanadyl bond is likely a short ionic bond. NMR is found to be a valuable experimental tool to get insight into the nature of chemical bonds in vanadium oxides.

Crystallization↗
PubMed1997

Multiple-pulse assisted line-narrowing by fast magic-angle spinning.

Combined rotation and multiple-pulse experiments (CRAMPS) are reported that are performed under the conditions of fast magic-angle spinning. Quasi-static conditions, as are required for CRAMPS experiments, can be fulfilled approximately also for fast sample spinning conditions when windowless or semiwindowless sequences are applied. In order to allow direct detection for these cases also, appropriately timed detection windows are introduced without loss of resolution. In contrast to conventional CRAMPS experiments, high-speed MAS was found to play an important role also in the averaging of residual dipolar contributions. The resolution achieved in these first experiments is comparable to that of conventional CRAMPS experiments and the demands with respect to spectrometer hardware and tuning are much lower.

Magnetic Resonance Spectroscopy↗
PubMed1997

Multiple-quantum magic-angle spinning and dynamic-angle spinning NMR spectroscopy of quadrupolar nuclei.

Several aspects of the Multiple-Quantum Magic-Angle Spinning (MQMAS) technique (L. Frydman and J.S. Harwood, J. Am. Chem. Soc., 117 (1995) 5367) are compared with Dynamic-Angle Spinning (DAS). Examples of MQMAS spectra are shown for I = 3/2 nuclei with CQ up to 3.6 MHz, and for 27Al (I = 5/2) with CQ up to 10 MHz. The MQMAS linewidth is largely independent of the magnitude of the homonuclear dipolar interaction, while the spinning sideband manifold is similar to that observed in DAS experiments. MQMAS is technically simple and routinely useful for studying nuclei with short spin-lattice relaxation times, but care must be taken in its use for quantitative studies as the excitation of the triple-quantum coherence is not uniform. In this regard, MQMAS is most useful for samples with small quadrupolar coupling constants. In the specific case of 17O, DAS would give spectra with excellent resolution in comparison to MQMAS. The different advantages of DAS and MQMAS make them useful complementary techniques in many cases. Two additional methods are also presented for extracting the chemical shift anisotropy (CSA) directly for quadrupolar nuclei using the multiple-quantum scheme.

Magnetic Resonance Spectroscopy↗
PubMed1997

Multiple-quantum magic-angle spinning NMR with cross-polarization: spectral editing of high-resolution spectra of quadrupolar nuclei.

An experiment is presented that combines the multiple-quantum magic-angle spinning (MQMAS) technique with cross-polarization (CP). As a preliminary test of this new method, we measured and compared the 27Al 3QMAS and 19F-->27Al CP 3QMAS spectra of a fluorinated AlPO4 aluminophosphate. Complete discrimination between the fluorinated and nonfluorinated Al sites was easily achieved, which demonstrates the usefulness of CP MQMAS for spectral editing. Future applications of this experiment will include other spin pairs and heteronuclear correlation NMR spectroscopy.

Magnetic Resonance Spectroscopy↗
PubMed1997

Correlations between 9Be magic-angle spinning nuclear magnetic resonance spectra and the geometry of beryllium containing framework structures.

A range of sodalite framework structures containing beryllium with general formula M8[BeZO4]6X2; M = Cd, Zn, Z = Si, Ge and X = S, Se or Te have been synthesised. The structures of these materials, which contain a single beryllium environment, have been refined from powder neutron diffraction or powder X-ray diffraction data and the compounds further characterised using 9Be magic-angle spinning nuclear magnetic resonance (MASNMR). Spectra show a single sharp resonance for 9Be(OSi)4 in the chemical shift range +/- 1 ppm from 0.1 M BeCl2. Correlations between the Be-O-Z bond angles and the 9Be chemical shift are reported and show upfield shifts for larger angles as seen previously in MASNMR spectra for 29Si and 27Al.

Beryllium↗