Multifrequency Two-Dimensional Fourier Transform ESR: An X/Ku–Band Spectrometer

A two-dimensional Fourier Transform ESR (2D FT ESR) spectrometer operating at 9.25 and 17.35 GHz is described. The Ku-band bridge uses an efficient heterodyne technique wherein 9.25 GHz is the intermediate frequency. At Ku-band the sensitivity is increased by almost an order of magnitude. One may ro...

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Bibliographic Details
Published in:Journal of magnetic resonance (1997) 1997-08, Vol.127 (2), p.155-167
Main Authors: Borbat, Petr P., Crepeau, Richard H., Freed, Jack H.
Format: Article
Language:English
Subjects:
Animals
Egg Yolk - chemistry
Electron Spin Resonance Spectroscopy - instrumentation
Electron Spin Resonance Spectroscopy - methods
ESR
Fourier Analysis
Fourier spectroscopy
heterodyne
Ku band ESR
Lipid Bilayers - chemistry
lipids
Membrane Lipids - chemistry
multifrequency
Phosphatidylglycerols - chemistry
sensitivity
Signal Processing, Computer-Assisted
Spin Trapping
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Description
Summary:A two-dimensional Fourier Transform ESR (2D FT ESR) spectrometer operating at 9.25 and 17.35 GHz is described. The Ku-band bridge uses an efficient heterodyne technique wherein 9.25 GHz is the intermediate frequency. At Ku-band the sensitivity is increased by almost an order of magnitude. One may routinely collect a full 2D ELDOR spectrum in less than 20 min for a sample containing 0.5–5 nmol of nitroxide spin-probe in the slow-motional regime. Broad spectral coverage at Ku-band is obtained by use of a bridged loop-gap resonator (BLGR) and of a dielectric ring resonator (DR). It is shown that an even more uniform spectral excitation is obtained by using shorter microwave pulses of about 3 ns duration. The dead-time at Ku-band is just 30–40 ns, yielding an improved SNR in 2D ELDOR spectra of nitroxide spin-probes withT2as short as 20–30 ns. A comparison of 2D ELDOR spectra obtained at 9.25 and 17.35 GHz for spin-labeled phospholipid probes (16PC) in 1,2-dimyristoyl-sn-glycero-3-phosphoglycerol (DMPG) membrane vesicles showed that both spectra could be satisfactorily simulated using the same set of model parameters even though they are markedly different in appearance. The improved sensitivity and shorter dead-time at Ku-band made it possible to obtain orientation-dependent 2D ELDOR spectra of the Cholestane (CSL) spin-probe in macroscopically aligned lipid bilayers of egg yolk PC using samples containing only 1 mg of lipid and just 5 nmol of spin-probe.
ISSN:1090-7807
1096-0856
DOI:10.1006/jmre.1997.1201