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Efficient amplitude-modulated pulses for triple- to single-quantum coherence conversion in MQMAS NMR.

Colaux H, Dawson DM, Ashbrook SE - J Phys Chem A (2014)

Bottom Line: This conversion is relatively inefficient when effected by a single pulse, and many composite pulse schemes have been developed to improve this efficiency.The optimization is performed using the SIMPSON and MATLAB packages and results in efficient pulses that can be used without experimental reoptimisation.Most significant signal enhancements are obtained when good estimates of the inherent radio-frequency nutation rate and the magnitude of the quadrupolar coupling are used as input to the optimization, but the pulses appear robust to reasonable variations in either parameter, producing significant enhancements compared to a single-pulse conversion, and also comparable or improved efficiency over other commonly used approaches.

View Article: PubMed Central - PubMed

Affiliation: School of Chemistry, EaStCHEM and Centre for Magnetic Resonance, University of St. Andrews , North Haugh, St. Andrews KY16 9ST, U.K.

ABSTRACT
The conversion between multiple- and single-quantum coherences is integral to many nuclear magnetic resonance (NMR) experiments of quadrupolar nuclei. This conversion is relatively inefficient when effected by a single pulse, and many composite pulse schemes have been developed to improve this efficiency. To provide the maximum improvement, such schemes typically require time-consuming experimental optimization. Here, we demonstrate an approach for generating amplitude-modulated pulses to enhance the efficiency of the triple- to single-quantum conversion. The optimization is performed using the SIMPSON and MATLAB packages and results in efficient pulses that can be used without experimental reoptimisation. Most significant signal enhancements are obtained when good estimates of the inherent radio-frequency nutation rate and the magnitude of the quadrupolar coupling are used as input to the optimization, but the pulses appear robust to reasonable variations in either parameter, producing significant enhancements compared to a single-pulse conversion, and also comparable or improved efficiency over other commonly used approaches. In all cases, the ease of implementation of our method is advantageous, particularly for cases with low sensitivity, where the improvement is most needed (e.g., low gyromagnetic ratio or high quadrupolar coupling). Our approach offers the potential to routinely improve the sensitivity of high-resolution NMR spectra of nuclei and systems that would, perhaps, otherwise be deemed "too challenging".

No MeSH data available.


Schematic description of the computationaloptimization processfor the generation of FAM-N pulses. Simulations have been performedfor 87Rb (I = 3/2) at B0 = 14.1 T with ω1/2π = 150 kHz,ωR/2π = 12.5 kHz, CQ = 1.2 MHz, and ηQ = 0. The plot shows the amountof central-transition single-quantum coherence generated from a unitamount of triple-quantum coherence as a function of the duration ofthe pulse(s). Highlighted are the duration (and maximum efficiency)of a single pulse (blue dotted line), FAM-II (green dotted line),and FAM-N (red dotted line). For the case shown, the optimum FAM-Npulse has six consecutive pulses of opposite phase.
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fig2: Schematic description of the computationaloptimization processfor the generation of FAM-N pulses. Simulations have been performedfor 87Rb (I = 3/2) at B0 = 14.1 T with ω1/2π = 150 kHz,ωR/2π = 12.5 kHz, CQ = 1.2 MHz, and ηQ = 0. The plot shows the amountof central-transition single-quantum coherence generated from a unitamount of triple-quantum coherence as a function of the duration ofthe pulse(s). Highlighted are the duration (and maximum efficiency)of a single pulse (blue dotted line), FAM-II (green dotted line),and FAM-N (red dotted line). For the case shown, the optimum FAM-Npulse has six consecutive pulses of opposite phase.

Mentions: Thecomputer-based optimization procedure used is shown schematicallyin Figure 2. This can be broken down into anumber of key steps. See Supporting Information for a more detailed description.


Efficient amplitude-modulated pulses for triple- to single-quantum coherence conversion in MQMAS NMR.

Colaux H, Dawson DM, Ashbrook SE - J Phys Chem A (2014)

Schematic description of the computationaloptimization processfor the generation of FAM-N pulses. Simulations have been performedfor 87Rb (I = 3/2) at B0 = 14.1 T with ω1/2π = 150 kHz,ωR/2π = 12.5 kHz, CQ = 1.2 MHz, and ηQ = 0. The plot shows the amountof central-transition single-quantum coherence generated from a unitamount of triple-quantum coherence as a function of the duration ofthe pulse(s). Highlighted are the duration (and maximum efficiency)of a single pulse (blue dotted line), FAM-II (green dotted line),and FAM-N (red dotted line). For the case shown, the optimum FAM-Npulse has six consecutive pulses of opposite phase.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4126738&req=5

fig2: Schematic description of the computationaloptimization processfor the generation of FAM-N pulses. Simulations have been performedfor 87Rb (I = 3/2) at B0 = 14.1 T with ω1/2π = 150 kHz,ωR/2π = 12.5 kHz, CQ = 1.2 MHz, and ηQ = 0. The plot shows the amountof central-transition single-quantum coherence generated from a unitamount of triple-quantum coherence as a function of the duration ofthe pulse(s). Highlighted are the duration (and maximum efficiency)of a single pulse (blue dotted line), FAM-II (green dotted line),and FAM-N (red dotted line). For the case shown, the optimum FAM-Npulse has six consecutive pulses of opposite phase.
Mentions: Thecomputer-based optimization procedure used is shown schematicallyin Figure 2. This can be broken down into anumber of key steps. See Supporting Information for a more detailed description.

Bottom Line: This conversion is relatively inefficient when effected by a single pulse, and many composite pulse schemes have been developed to improve this efficiency.The optimization is performed using the SIMPSON and MATLAB packages and results in efficient pulses that can be used without experimental reoptimisation.Most significant signal enhancements are obtained when good estimates of the inherent radio-frequency nutation rate and the magnitude of the quadrupolar coupling are used as input to the optimization, but the pulses appear robust to reasonable variations in either parameter, producing significant enhancements compared to a single-pulse conversion, and also comparable or improved efficiency over other commonly used approaches.

View Article: PubMed Central - PubMed

Affiliation: School of Chemistry, EaStCHEM and Centre for Magnetic Resonance, University of St. Andrews , North Haugh, St. Andrews KY16 9ST, U.K.

ABSTRACT
The conversion between multiple- and single-quantum coherences is integral to many nuclear magnetic resonance (NMR) experiments of quadrupolar nuclei. This conversion is relatively inefficient when effected by a single pulse, and many composite pulse schemes have been developed to improve this efficiency. To provide the maximum improvement, such schemes typically require time-consuming experimental optimization. Here, we demonstrate an approach for generating amplitude-modulated pulses to enhance the efficiency of the triple- to single-quantum conversion. The optimization is performed using the SIMPSON and MATLAB packages and results in efficient pulses that can be used without experimental reoptimisation. Most significant signal enhancements are obtained when good estimates of the inherent radio-frequency nutation rate and the magnitude of the quadrupolar coupling are used as input to the optimization, but the pulses appear robust to reasonable variations in either parameter, producing significant enhancements compared to a single-pulse conversion, and also comparable or improved efficiency over other commonly used approaches. In all cases, the ease of implementation of our method is advantageous, particularly for cases with low sensitivity, where the improvement is most needed (e.g., low gyromagnetic ratio or high quadrupolar coupling). Our approach offers the potential to routinely improve the sensitivity of high-resolution NMR spectra of nuclei and systems that would, perhaps, otherwise be deemed "too challenging".

No MeSH data available.