Limits...
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

The pulse sequence of a diagonal suppressed TOCSY experiment is shown in (a). The slice-selective excitation is achieved by a 40 ms EBURP-2 pulse, applied during a weak magnetic field gradient (∼1 G/cm). After the evolution and TOCSY mixing, for which we used a 12.5 kHz DIPSI-2 sequence at 500 MHz, the originally excited magnetization, which would produce the diagonal peaks is suppressed by two consecutive excitation sculpting blocks. The latter contain 4 ms rectangular shaped selective 180° pulses during a field gradient which has the same strength of the one used during initial excitation. The following phase cycling was used for (a): φ1 = x, −x; φ2 = x, x, y, y; φ3 = −x, −x, −y, −y; φ4 = x, x, x, x, y, y, y, y; φ5 = −x, −x, −x, −x, −y, −y, −y, −y; φr = x, −x, −x, x, −x, x, x, −x. The pulse sequence of a diagonal suppressed NOESY experiment is shown in (b). The selective 90° and 180° pulses are the same as in a. The phase cycle for (b) is: φ1 = x, x, −x, −x; φ2 = x; φ3 = x, x, x, x, −x, −x, −x, −x, y, y, y, y, −y, −y, −y, −y; φ4 = φ6 = x, x, x, x, y, y, y, y; φ5 = −x, −x, −x, −x, −y, −y, −y, −y; φ7 = x, y; φr = x, −x, −x, x, x, −x,−x, x, y, −y, −y, y, y, −y, −y, y. 90° and 180° pulses are indicated by white and black bars, respectively.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4020460&req=5

f0005: The pulse sequence of a diagonal suppressed TOCSY experiment is shown in (a). The slice-selective excitation is achieved by a 40 ms EBURP-2 pulse, applied during a weak magnetic field gradient (∼1 G/cm). After the evolution and TOCSY mixing, for which we used a 12.5 kHz DIPSI-2 sequence at 500 MHz, the originally excited magnetization, which would produce the diagonal peaks is suppressed by two consecutive excitation sculpting blocks. The latter contain 4 ms rectangular shaped selective 180° pulses during a field gradient which has the same strength of the one used during initial excitation. The following phase cycling was used for (a): φ1 = x, −x; φ2 = x, x, y, y; φ3 = −x, −x, −y, −y; φ4 = x, x, x, x, y, y, y, y; φ5 = −x, −x, −x, −x, −y, −y, −y, −y; φr = x, −x, −x, x, −x, x, x, −x. The pulse sequence of a diagonal suppressed NOESY experiment is shown in (b). The selective 90° and 180° pulses are the same as in a. The phase cycle for (b) is: φ1 = x, x, −x, −x; φ2 = x; φ3 = x, x, x, x, −x, −x, −x, −x, y, y, y, y, −y, −y, −y, −y; φ4 = φ6 = x, x, x, x, y, y, y, y; φ5 = −x, −x, −x, −x, −y, −y, −y, −y; φ7 = x, y; φr = x, −x, −x, x, x, −x,−x, x, y, −y, −y, y, y, −y, −y, y. 90° and 180° pulses are indicated by white and black bars, respectively.

Mentions: Here we present a completely different, generally applicable, approach for diagonal peak suppression in homonuclear two- and multidimensional spectra, which is based on transforming a homonuclear system into a spatially-separated heteronuclear system by using frequency-selective pulses during a weak field gradient [14–20]. To obtain a diagonal peak suppressed homonuclear 2D spectrum we use the pulse sequences shown in Fig. 1. A selective 90° pulse during a weak gradient excites different signals in different slices of the NMR sample tube. After the mixing period (shown for TOCSY and NOESY type spectra) the excited signals that did not change their frequency significantly during mixing (i.e. the diagonal peak signals but also any underlying or very close-by cross peaks) can be suppressed by using any signal/solvent suppression scheme, when applied during the same weak gradient field. For this purpose we used an excitation sculpting scheme (a combination of a hard and a selective 180° pulse sandwiched by two strong gradients) [21]. To increase the efficiency of the diagonal suppression this element was repeated with different purging gradient strength.


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)

The pulse sequence of a diagonal suppressed TOCSY experiment is shown in (a). The slice-selective excitation is achieved by a 40 ms EBURP-2 pulse, applied during a weak magnetic field gradient (∼1 G/cm). After the evolution and TOCSY mixing, for which we used a 12.5 kHz DIPSI-2 sequence at 500 MHz, the originally excited magnetization, which would produce the diagonal peaks is suppressed by two consecutive excitation sculpting blocks. The latter contain 4 ms rectangular shaped selective 180° pulses during a field gradient which has the same strength of the one used during initial excitation. The following phase cycling was used for (a): φ1 = x, −x; φ2 = x, x, y, y; φ3 = −x, −x, −y, −y; φ4 = x, x, x, x, y, y, y, y; φ5 = −x, −x, −x, −x, −y, −y, −y, −y; φr = x, −x, −x, x, −x, x, x, −x. The pulse sequence of a diagonal suppressed NOESY experiment is shown in (b). The selective 90° and 180° pulses are the same as in a. The phase cycle for (b) is: φ1 = x, x, −x, −x; φ2 = x; φ3 = x, x, x, x, −x, −x, −x, −x, y, y, y, y, −y, −y, −y, −y; φ4 = φ6 = x, x, x, x, y, y, y, y; φ5 = −x, −x, −x, −x, −y, −y, −y, −y; φ7 = x, y; φr = x, −x, −x, x, x, −x,−x, x, y, −y, −y, y, y, −y, −y, y. 90° and 180° pulses are indicated by white and black bars, respectively.
© Copyright Policy
Related In: Results  -  Collection

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

f0005: The pulse sequence of a diagonal suppressed TOCSY experiment is shown in (a). The slice-selective excitation is achieved by a 40 ms EBURP-2 pulse, applied during a weak magnetic field gradient (∼1 G/cm). After the evolution and TOCSY mixing, for which we used a 12.5 kHz DIPSI-2 sequence at 500 MHz, the originally excited magnetization, which would produce the diagonal peaks is suppressed by two consecutive excitation sculpting blocks. The latter contain 4 ms rectangular shaped selective 180° pulses during a field gradient which has the same strength of the one used during initial excitation. The following phase cycling was used for (a): φ1 = x, −x; φ2 = x, x, y, y; φ3 = −x, −x, −y, −y; φ4 = x, x, x, x, y, y, y, y; φ5 = −x, −x, −x, −x, −y, −y, −y, −y; φr = x, −x, −x, x, −x, x, x, −x. The pulse sequence of a diagonal suppressed NOESY experiment is shown in (b). The selective 90° and 180° pulses are the same as in a. The phase cycle for (b) is: φ1 = x, x, −x, −x; φ2 = x; φ3 = x, x, x, x, −x, −x, −x, −x, y, y, y, y, −y, −y, −y, −y; φ4 = φ6 = x, x, x, x, y, y, y, y; φ5 = −x, −x, −x, −x, −y, −y, −y, −y; φ7 = x, y; φr = x, −x, −x, x, x, −x,−x, x, y, −y, −y, y, y, −y, −y, y. 90° and 180° pulses are indicated by white and black bars, respectively.
Mentions: Here we present a completely different, generally applicable, approach for diagonal peak suppression in homonuclear two- and multidimensional spectra, which is based on transforming a homonuclear system into a spatially-separated heteronuclear system by using frequency-selective pulses during a weak field gradient [14–20]. To obtain a diagonal peak suppressed homonuclear 2D spectrum we use the pulse sequences shown in Fig. 1. A selective 90° pulse during a weak gradient excites different signals in different slices of the NMR sample tube. After the mixing period (shown for TOCSY and NOESY type spectra) the excited signals that did not change their frequency significantly during mixing (i.e. the diagonal peak signals but also any underlying or very close-by cross peaks) can be suppressed by using any signal/solvent suppression scheme, when applied during the same weak gradient field. For this purpose we used an excitation sculpting scheme (a combination of a hard and a selective 180° pulse sandwiched by two strong gradients) [21]. To increase the efficiency of the diagonal suppression this element was repeated with different purging gradient strength.

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