X-Band Rapid-Scan EPR

<p>The advantages of rapid-scan EPR relative to CW and pulse techniques for samples with long longitudinal relaxation time T₁ (N_s⁰ defects in diamond, N@C₆₀, and amorphous hydrogenated silicon), heterogeneous samples (crystalline 1:1 α,γ-bisdiphenylene-β-phenylallyl (BDPA):benzene), lossy samples (aqueous nitroxyl radicals), and transient radicals (5-tert-butoxycarbonyl-5-methyl-1-pyrroline-N-oxide (BMPO)-superoxide adduct) were studied.</p> <p>For samples with long relaxation times, CW (continuous wave) EPR is challenging due to power saturation and distortions from passage effects. In rapid-scan EPR, the field is swept through resonance in a time that is short relative to T₂. In rapid-scan EPR, the magnetic field is on resonance for a short time relative to CW EPR. Because of this, the energy absorbed by the spins, for the same microwave B₁, is less than in conventional CW spectra, and the signal does not saturate as readily. For samples with long electron relaxation times, pulse techniques can also be challenging, particularly if T₂ is long and T₂* is short. Rapid-scan EPR is a powerful alternative to CW and pulse EPR because it is a straight-forward technique that does not require the high power of pulse EPR. For the samples studied, improvements in signal-to-noise ranging from factors of 10 to 250 were observed.</p> <p>Rapid-scan can also be used to extract relaxation information from a sample. The rapid-scan spectra for lithium phthalocyanine (LiPc) and ¹⁵N-PDT (4-oxo-2,2,6,6-tetra-perdeuteromethyl-piperidinyl-¹⁵N-oxyl-d₁₆) were simulated to determine T₂. The extraction of T₂ from the rapid-scan spectra of BDPA was also attempted. Through our difficulty in simulating the rapid-scan spectra of BDPA, we realized that commercial BDPA was not a homogeneous sample. The experiments studying BDPA demonstrated that rapid-scan experiments can give insight into the relaxation of a sample that might not otherwise be evident with conventional CW EPR.</p> <p>Finally, rapid-scan EPR at X-band was applied to spin trapping experiments. Superoxide was generated by the reaction of xanthine oxidase and hypoxanthine and trapped with BMPO. Spin trapping with 5-tert-butoxycarbonyl-5-methyl-1-pyrroline N-oxide (BMPO) to form BMPO-OOH adduct converts the short-lived superoxide into a more stable spin adduct. The detection limit for spin-trapped superoxide was compared between CW and rapid-scan EPR. The signal-to-noise ratio was more than 40 times greater for rapid-scan than for CW EPR. We also demonstrated detection of superoxide produced by <em>Enterococcus faecalis</em> at rates that are too low for detection by CW EPR.</p>

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Year dc:date.available

2013

Author dc:creator

• Mitchell, Deborah Gale

Contributors dc:contributor

• Gareth R. Eaton, Ph.D.
• Sandra S. Eaton, Ph.D.
• Andrei G. Kutateladze
• Michelle Knowles
• Martin Margittai
• Daniel Linseman

• Continuous wave
• Electron paramagnetic resonance
• Rapid-scan
• Spin-trapping
• X-band
• Biochemistry
• Chemistry
• Physical Chemistry

Statement dc:rights

• <p>Copyright is held by the author. User is responsible for all copyright compliance.</p>

Language dc:language

en

Repository record dc:identifier

https://digitalcommons.du.edu/etd/436

OAI identifier oai:identifier

oai:digitalcommons.du.edu:etd-1435