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A general method for diagonal peak suppression in homonuclear correlated NMR spectra by spatially and frequency selective pulses.

Glanzer S, Schrank E, Zangger K - J. Magn. Reson. (2013)

Bottom Line: In the large majority of homonuclear correlated spectra the diagonal contains the most intense peaks.Cross-peaks near the diagonal could overlap with huge tails of diagonal peaks and can therefore be easily overlooked.In addition to the auto correlation removal, these experiments are also less affected by magnetic field inhomogeneities due to the slice selective excitation, which on the other side leads to a reduced intensity compared to regular homonuclear correlated spectra.

View Article: PubMed Central - PubMed

Affiliation: Institute of Chemistry/Organic and Bioorganic Chemistry, University of Graz, Heinrichstrasse 28, A-8010 Graz, Austria.

No MeSH data available.


Related in: MedlinePlus

Traces taken along the signals at ∼4.3 ppm in the indirect dimension of a short regular NOESY (red) and a diagonal suppressed version (blue) of the glucopyranosides with absolutely equal acquisition and processing parameters. The trace from the diagonal suppressed NOESY is multiplied by 64, showing the expected lower sensitivity of the slice-selective pulse sequence. For these comparative NOESY spectra 64 scans and 64 complex data points in the indirect dimension were recorded.
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f0030: Traces taken along the signals at ∼4.3 ppm in the indirect dimension of a short regular NOESY (red) and a diagonal suppressed version (blue) of the glucopyranosides with absolutely equal acquisition and processing parameters. The trace from the diagonal suppressed NOESY is multiplied by 64, showing the expected lower sensitivity of the slice-selective pulse sequence. For these comparative NOESY spectra 64 scans and 64 complex data points in the indirect dimension were recorded.

Mentions: Positive and negative peaks are colored red and blue, respectively. Close to the diagonal it is difficult to differentiate artifacts from real peaks in the regular NOESY spectrum. This is most pronounced in the region between 3.1 and 3.8 ppm. Some peaks are visible only in the diagonal-free spectrum (indicated by arrows), while others are stronger in the regular NOESY (marked by asterisks). All peaks which are stronger in the regular NOESY correspond to signals that show strong diagonal peaks. On the other hand the peaks which are seen only in the diagonal free spectrum have relatively weak diagonal peaks in the regular NOESY spectrum. This is probably a result of the elevated baseline along the ω1-direction. Cross peaks at the same ω2-frequency of a strong diagonal peak appear stronger than they are. In the regular NOESY some of the very strong cross peaks have much weaker counterparts on their symmetrized position. In contrast, the diagonal suppressed NOESY shows cross peak intensities which are much more similar on both sides of the diagonal. To confirm that all peaks observed in the diagonal-free NOESY are actual NOE peaks and not artifacts, their assignment is indicated. They all correspond to proton pairs which are close in space, like axial protons on the same side of the glucose ring (2–4 and 3–5) or neighboring protons (1–2, 1′–2′). The regular NOESY experiment (Fig. 5a) was recorded with 32 scans per increment and the diagonal suppressed NOESY spectrum (Fig. 5b) by using 256 scans per increment and otherwise identical parameters. To experimentally determine the signal/noise changes of the regular versus the spatially-selective, diagonal-suppressed NOESY spectrum, representative traces at the frequency 4.3 ppm for two short NOESY spectra recorded with the same acquisition parameters (number of scans, increments, receiver gain, etc.) and processing scheme is shown in Fig. 6. As expected, for a selective pulse with an excitation bandwidth of ∼80 Hz and a 1.2 G/cm gradient the signal/noise ratio drops to about 2% of a regular NOESY spectrum.


A general method for diagonal peak suppression in homonuclear correlated NMR spectra by spatially and frequency selective pulses.

Glanzer S, Schrank E, Zangger K - J. Magn. Reson. (2013)

Traces taken along the signals at ∼4.3 ppm in the indirect dimension of a short regular NOESY (red) and a diagonal suppressed version (blue) of the glucopyranosides with absolutely equal acquisition and processing parameters. The trace from the diagonal suppressed NOESY is multiplied by 64, showing the expected lower sensitivity of the slice-selective pulse sequence. For these comparative NOESY spectra 64 scans and 64 complex data points in the indirect dimension were recorded.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4020460&req=5

f0030: Traces taken along the signals at ∼4.3 ppm in the indirect dimension of a short regular NOESY (red) and a diagonal suppressed version (blue) of the glucopyranosides with absolutely equal acquisition and processing parameters. The trace from the diagonal suppressed NOESY is multiplied by 64, showing the expected lower sensitivity of the slice-selective pulse sequence. For these comparative NOESY spectra 64 scans and 64 complex data points in the indirect dimension were recorded.
Mentions: Positive and negative peaks are colored red and blue, respectively. Close to the diagonal it is difficult to differentiate artifacts from real peaks in the regular NOESY spectrum. This is most pronounced in the region between 3.1 and 3.8 ppm. Some peaks are visible only in the diagonal-free spectrum (indicated by arrows), while others are stronger in the regular NOESY (marked by asterisks). All peaks which are stronger in the regular NOESY correspond to signals that show strong diagonal peaks. On the other hand the peaks which are seen only in the diagonal free spectrum have relatively weak diagonal peaks in the regular NOESY spectrum. This is probably a result of the elevated baseline along the ω1-direction. Cross peaks at the same ω2-frequency of a strong diagonal peak appear stronger than they are. In the regular NOESY some of the very strong cross peaks have much weaker counterparts on their symmetrized position. In contrast, the diagonal suppressed NOESY shows cross peak intensities which are much more similar on both sides of the diagonal. To confirm that all peaks observed in the diagonal-free NOESY are actual NOE peaks and not artifacts, their assignment is indicated. They all correspond to proton pairs which are close in space, like axial protons on the same side of the glucose ring (2–4 and 3–5) or neighboring protons (1–2, 1′–2′). The regular NOESY experiment (Fig. 5a) was recorded with 32 scans per increment and the diagonal suppressed NOESY spectrum (Fig. 5b) by using 256 scans per increment and otherwise identical parameters. To experimentally determine the signal/noise changes of the regular versus the spatially-selective, diagonal-suppressed NOESY spectrum, representative traces at the frequency 4.3 ppm for two short NOESY spectra recorded with the same acquisition parameters (number of scans, increments, receiver gain, etc.) and processing scheme is shown in Fig. 6. As expected, for a selective pulse with an excitation bandwidth of ∼80 Hz and a 1.2 G/cm gradient the signal/noise ratio drops to about 2% of a regular NOESY spectrum.

Bottom Line: In the large majority of homonuclear correlated spectra the diagonal contains the most intense peaks.Cross-peaks near the diagonal could overlap with huge tails of diagonal peaks and can therefore be easily overlooked.In addition to the auto correlation removal, these experiments are also less affected by magnetic field inhomogeneities due to the slice selective excitation, which on the other side leads to a reduced intensity compared to regular homonuclear correlated spectra.

View Article: PubMed Central - PubMed

Affiliation: Institute of Chemistry/Organic and Bioorganic Chemistry, University of Graz, Heinrichstrasse 28, A-8010 Graz, Austria.

No MeSH data available.


Related in: MedlinePlus