Spin trapping of nitric oxide by aci anions of nitroalkanes.
In alkaline solutions, nitroalkanes (RCH2NO2) undergo deprotonation and rearrange to an aci anion (RHC=NO2-), which may function as a spin trap. Using electron paramagnetic resonance (EPR) spectroscopy, we have investigated suitability of aci anions of a series of nitroalkanes (CH3NO2, CH3CH2NO2, CH3(CH2)2NO2, and CH3(CH2)3NO2) to spin trap nitric oxide (*NO). Based on the observed EPR spectra, the general structure of the adducts, formed by addition of *NO to RHC=NO2-, was identified as nitronitroso dianion radicals of general formula [RC(NO)NO2]*2- in strong base (0.5 M NaOH), and as a mono-anion radical [RCH(NO)NO2]*- in alkaline buffers, pH 10-13. The hyperfine splitting on 14N in the -NO2 moiety (11.2-12.48 G) is distinctly different from the splitting on 14N in the -NO moiety of the adducts (5.23-6.5 G). The structure of the adducts was verified using 15N-labeled *NO, which produced radicals, in which triplet due to splitting on 14N (I = 1) in 14NO/aci nitro adducts was replaced by a doublet due to 15N (I = 1/2) in 15NO/aci nitro adducts. EPR spectra of aci nitromethane/NO adduct recorded in NaOH and NaOD (0.5 M) showed that the hydrogen at alpha-carbon can be exchanged for deuterium, consistent with structures of the adducts being [CH(NO)NO2]*2- and [CD(NO)NO2]*2-, respectively. These results indicate that nitroalkanes could potentially be used as prototypes for development of *NO-specific spin traps suitable for EPR analysis.
Reszka
Krzysztof J
KJ
Laboratory of Molecular Biophysics, National Institute of Environmental Health Sciences, National Institute of Health, Research Triangle Park, NC 27709, USA. reszka@icva.gov
Bilski
Piotr
P
Chignell
Colin F
CF
D000838:Anions / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy; D004980:Ethane / Q000031:analogs & derivatives* / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D008697:Methane / Q000031:analogs & derivatives* / Q000737:chemistry; D009569:Nitric Oxide / Q000737:chemistry*; D009595:Nitroparaffins / Q000737:chemistry*; D011407:Propane / Q000031:analogs & derivatives* / Q000737:chemistry; D019097:Spin Trapping / Q000379:methods*
D000838:Anions; D009595:Nitroparaffins; D009569:Nitric Oxide; C035314:1-nitropropane; C014705:nitroethane; D004980:Ethane; D008697:Methane; C008640:nitromethane; D011407:Propane