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Proton Spectra (proton + spectrum)

Distribution by Scientific Domains

Medical Sciences	27%

Selected Abstracts

Impact of cerebrospinal fluid contamination on brain metabolites evaluation with 1H-MR spectroscopy: A single voxel study of the cerebellar vermis in patients with degenerative ataxias

JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 1 2009
Laura Guerrini MD PhD
Abstract Purpose To investigate the impact of cerebrospinal fluid (CSF) contamination on metabolite evaluation in the superior cerebellar vermis with single-voxel 1H-MRS in normal subjects and patients with degenerative ataxias. Materials and Methods Twenty-nine healthy volunteers and 38 patients with degenerative ataxias and cerebellar atrophy were examined on a 1.5 Tesla scanner. Proton spectra of a volume of interest placed in the superior vermis were acquired using a four TE PRESS technique. We calculated N-acetyl aspartate (NAA)/creatine (Cr), choline (Cho)/Cr, and NAA/Cho ratios, T2 relaxation times and concentrations of the same metabolites using the external phantom method. Finally, concentrations were corrected taking into account the proportion of nervous tissue and CSF, that was determined as Volume Fraction (VF). Results In healthy subjects, a significant difference was observed between metabolite concentrations with and without correction for VF. As compared to controls, patients with ataxias showed significantly reduced NAA/Cr and NAA concentrations, while only corrected Cr concentration was significantly increased. The latter showed an inverse correlation with VF. Conclusion CSF contamination has a not negligible effect on the estimation of brain metabolites. The increase of Cr concentration in patients with cerebellar atrophy presumably reflects the substitutive gliosis which takes place along with loss of neurons. J. Magn. Reson. Imaging 2009;30:11,17. © 2009 Wiley-Liss, Inc. [source]

Broadband proton-decoupled proton spectra,

MAGNETIC RESONANCE IN CHEMISTRY, Issue 4 2007
Andrew J. Pell
Abstract We present a new method for recording broadband proton-decoupled proton spectra with absorption mode lineshapes and substantially correct integrals; in both these respects, the new method has significant advantages over conventional J -spectroscopy. In our approach, the decoupled spectrum is simply obtained from the 45° projection of the diagonal-peak multiplets of an anti z -COSY spectrum. This method is straightforward to apply, and does not require any unusual data processing. However, there is a significant reduction in sensitivity when compared to a conventional proton spectrum. The method is demonstrated for typical medium-sized molecules, and it is also shown how such a decoupled spectrum can be used to advantage in measurements of diffusion constants (DOSY), the measurement of relaxation parameters, and the analysis of complex mixtures. Copyright © 2007 John Wiley & Sons, Ltd. [source]

NMR methods for studying the structure and dynamics of oncogenic and antihistaminic peptides in biomembranes

MAGNETIC RESONANCE IN CHEMISTRY, Issue 2 2004
Christina Sizun
Abstract We present several applications of both wide-line and magic angle spinning (MAS) solid-state NMR of bicelles in which are embedded fragments of a tyrosine kinase receptor or enkephalins. The magnetically orientable bicelle membranes are shown to be of particular interest for studying the functional properties of lipids and proteins in a state that is very close to their natural environment. Quadrupolar, dipolar and chemical shielding interactions can be used to determine minute alterations of internal membrane dynamics and the orientation of peptides with respect to the membrane plane. MAS of bicelles can in turn lead to high-resolution proton spectra of hydrated membranes. Using deuterium,proton contrast methods one can then obtain pseudo-high-resolution proton spectra of peptides or proteins embedded in deuterated membranes and determine their atomic 3D structure using quasi-conventional liquid-state NMR methods. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Proton high-field NMR study of tomato juice

MAGNETIC RESONANCE IN CHEMISTRY, Issue 4 2003
Anatoli P. Sobolev
Abstract A detailed analysis of the proton high-field (600 MHz) NMR spectra of tomato juice and pulp is reported for the first time. A combination of J -resolved, COSY, TOCSY, DOSY, 1H,13C HSQC and 1H,13C HMBC 2D sequences was used to assign each spin system and to separate the components of the complex patterns in the 1D overlapped proton spectra. To obtain resolved proton spectra of tomato pulps the high-resolution magic angle spinning technique was used; a comparison with the liquid-state NMR spectra of the corresponding juices was accomplished. On the basis of the assignments made, the chemical composition of tomato juices from two cultivars (Red Setter and Ciliegino) was determined. Copyright © 2003 John Wiley & Sons, Ltd. [source]

High resolution in heteronuclear 1H,13C NMR experiments by optimizing spectral aliasing with one-dimensional carbon data

MAGNETIC RESONANCE IN CHEMISTRY, Issue 1 2003
Damien Jeannerat
Abstract In the chemistry literature it is common to provide NMR data on both proton and carbon spectra based on one-dimensional experiments, but often only proton spectra are assigned. The absence of a complete attribution of the carbons is in good part due to the difficulty in reaching the necessary resolution in the carbon dimension of two-dimensional experiments. It has already been shown that high-resolution heteronuclear spectra can be acquired within nearly the same acquisition time using a violation of the Nyquist condition. For a spectral width reduction by a given factor k, the resolution increases by the same factor as long as it is not limited by relaxation. The price to pay for such an improvement is a k -fold ambiguity in the chemical shift of the signal along the folded or aliased dimension. The computer algorithm presented in this paper takes advantage of the peak list stemming from one-dimensional spectra in order to calculate spectral widths for which the ambiguities in the aliased dimension of heteronuclear experiments are eliminated or at least minimized. The resolution improvement factor is only limited by the natural lineshape and reaches a typical value higher than 100. The program may be set to run automatically on spectrometers equipped with automatic sample changers. Applications to short-range HSQC experiments and long-range HMBC spectra of steroids, carbohydrates, a peptide and a mixture of isomers are shown as examples. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Human rectal adenocarcinoma: Demonstration of 1H-MR spectra in vivo at 1.5 T

MAGNETIC RESONANCE IN MEDICINE, Issue 4 2002
A.S.K. Dzik-Jurasz
This study was designed to determine whether 1H-MR spectra of locally advanced human rectal adenocarcinoma could be acquired in vivo at 1.5 T. Despite the relatively large size of these neoplasms, only six out of 21 tumors accommodated a voxel size of 8 cm3. This was due to air pockets within the tumor mass, which limited voxel positioning. Localized proton spectra were acquired at short (20 ms) and long (135 ms) echo times (TEs) using a single-voxel technique. The most commonly detected metabolites were choline and lipid. Magn Reson Med 47:809,811, 2002. © 2002 Wiley-Liss, Inc. [source]

Maximum likelihood constrained deconvolution.

CONCEPTS IN MAGNETIC RESONANCE, Issue 2 2003
II: Application to experimental two-, three-dimensional NMR spectra
Abstract The maximum likelihood method (MLM) and related protocols were applied to the experimental 2-D nuclear Overhauser effect (NOE) spectrum of a 24-nucleotide RNA hairpin loop molecule. The output becomes more valuable when diagonal symmeterization is followed by MLM. This symmeterized maximum likelihood (SML) protocol restores the original spectral information with high fidelity by accurately partitioning components from overlapped peaks and provides substantial improvements in line shape and spectral resolution, in particular in the F1 dimension. These advantages lead to a simpler interpretation of the resonance frequencies, intensities, multiplet fine structure, and J -coupling values from a heavily overlapped peak region. This promises a more effective tool for peak picking, assignment, and integration. Also, application of MLM and related protocols to the 2-D NOE proton spectrum of a 24-mer RNA dramatically increases the number of NOE-based distance constraints that can be used for determination of its 3-D molecular structure. By application of 3-D MLM to a simple 3-D spectrum, the spectral resolution and signal-to-noise (S/N) ratio was greatly improved by effective line sharpening and reduction of cross-talk between planes. © 2003 Wiley Periodicals, Inc. Concepts Magn Reson 18A: 146,156, 2003 [source]

Broadband proton-decoupled proton spectra,

Correlation between the reactivity and spectroscopic properties of N -substituted secondary thioamides.

MAGNETIC RESONANCE IN CHEMISTRY, Issue 3 2003
New intramolecular N···H+···N binding approach, proton complexes based on thioamide ligation
Abstract On the basis of a comparison of chemical shifts and wavenumbers of several secondary thioamides and amides having monocationic substituents attached to thiocarbamoyl or carbamoyl groups by a polymethylene chain, new intramolecular unconventional N···H+···N hydrogen bonding effects were discovered. It is argued that the CH2,N rotation is hindered and two +H···NHCH3 non-equivalent protons occur in a proton spectrum of hydrochloride 1a (at 10.68 and 2.77 ppm, respectively) instead of two +NH2CH3 protons. Presumably, the above steric factors inhibit the acidic hydrolysis of 1a (stabilized by strong intramolecular N···H+···N hydrogen bonds) to an amide and prevent intramolecular cyclization of 2a (stabilized by strong intramolecular neutral,neutral N···HN hydrogen bonds) to a cyclic amidine. Postulation of additional dihydrogen bond formation is helpful in understanding the spectroscopic differences of 4 and 5. The above new bonding is also compared with intramolecular N···H,N+ hydrogen bonds in primary amine salts 7 and 8. In contrast to 3, a cooperative hydrogen bonded system is observed in 9 and 10. The weak hydrogen bonds in 7,10 facilitate the hydrolysis and cyclization reactions of secondary thioamides. The spectroscopic data for secondary (thio)amides are especially useful for characterizing the electronic situation at the (thio)carbamoyl nitrogen atoms and they are perfectly correlated with the reactivity. Examples of chelation of protons by thioamides (11 and 12), which contain strongly electron-donating pyrimidine groups, are presented to show the contribution of dihydrogen bonding in the protonation reaction similar to 1 and 4. Copyright © 2003 John Wiley & Sons, Ltd. [source]