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Cross-polarization schemes for peptide samples oriented in hydrated phospholipid bilayers.
Hyeongnam Kim1, Timothy A Cross, Riqiang Fu
1Center for Interdisciplinary Magnetic Resonance, National High Magnetic Field Laboratory, and Department of Chemistry and Biochemistry, Florida State University, Tallahassee, USA.
Journal of Magnetic Resonance (San Diego, Calif. : 1997)
|April 15, 2004
Summary
Frequency modulated cross-polarization (FMCP) and ramped amplitude cross-polarization (RACP) enhance polarized signal intensity by 20% compared to continuous-wave cross-polarization (CWCP) for oriented peptide samples. FMCP also offers a broader matching bandwidth and lower RF amplitude requirements.
Area of Science:
- Solid-state Nuclear Magnetic Resonance (NMR) spectroscopy.
- Biophysical chemistry and structural biology.
Background:
- Cross-polarization (CP) is a key technique in solid-state NMR for enhancing sensitivity.
- Optimizing CP pulse sequences is crucial for studying complex biological systems like oriented peptides.
Purpose of the Study:
- To evaluate and compare continuous-wave, ramped amplitude, and frequency modulated cross-polarization schemes for static samples in anisotropic phases.
- To assess the impact of different CP schemes on signal intensity, matching bandwidth, and radiofrequency (RF) amplitude requirements.
Main Methods:
- Experimental evaluation of continuous-wave cross-polarization (CWCP), ramped amplitude cross-polarization (RACP), and frequency modulated cross-polarization (FMCP).
- Utilized static samples in anisotropic phases, specifically [(15)N]Leu(4) labeled gramicidin A oriented in lipid bilayers.
- Measured polarized signal intensity, CP matching bandwidths, and RF amplitude profiles for each CP scheme.
Main Results:
- Both RACP and FMCP yielded a 20% higher polarized signal intensity compared to CWCP.
- CWCP and RACP exhibited similar CP matching bandwidths.
- FMCP demonstrated a significantly broader CP matching bandwidth due to its adiabaticity.
- FMCP required a substantially lower (15)N RF amplitude at the center of the matching profile compared to CWCP and RACP.
Conclusions:
- Frequency modulated cross-polarization (FMCP) and ramped amplitude cross-polarization (RACP) offer significant advantages over continuous-wave cross-polarization (CWCP) for oriented biological samples.
- FMCP is particularly advantageous due to its broader matching bandwidth and reduced RF power demands, making it a superior technique for solid-state NMR studies of anisotropic systems.