TY - JOUR
T1 - Influence of Conformation on the EPR Spectrum of 5,5-Dimethyl-1-hydroperoxy-1-pyrrolidinyloxyl
T2 - A Spin Trapped Adduct of Superoxide
AU - Rosen, Gerald M.
AU - Beselman, Aleksandra
AU - Tsai, Pei
AU - Pou, Sovitj
AU - Mailer, Colin
AU - Ichikawa, Kazuhiro
AU - Robinson, Bruce H.
AU - Nielsen, Robert
AU - Halpern, Howard J.
AU - MacKerell, Alexander D.
PY - 2004/2/20
Y1 - 2004/2/20
N2 - Spin trapping, a technique used to characterize short-lived free radicals, consists of using a nitrone or nitroso compound to "trap" an unstable free radical as a long-lived aminoxyl that can be characterized by EPR spectroscopy. The resultant aminoxyl exhibits hyperfine splitting constants that are dependent on the spin trap and the free radical. Such is the case with 2,2-dimethyl-5-hydroxy-1-pyrrolidinyloxyl (DMPO-OH) and 2,2-dimethyl-5-hydroperoxy-1-pyrrodinyloxyl (DMPO-OOH) whose hyperfine splitting constants, AN = AH = 14.9 G and AN = 14.3 G, AHβ = 11.7 G, and AHγ = 1. 25 G, respectively, have been used to demonstrate the generation of HO . and O2.-. However, to date, the source of the apparent AHγ hyperfine splitting in DMPO-OOH is not known. We consider three possible explanations to account for the unique EPR spectrum of DMPO-OOH. The first is that the γ-splitting arises from one of the hydrogen atoms at either carbon 3 or carbon 4 of DMPO-OOH. The second is that the γ-splitting originates from the hydrogen atom of DMPO-OOH. The third is that the conformational properties of DMPO-R change upon going from DMPO-OH to DMPO-OOH. Experimental and theoretical chemical approaches as well as EPR spectral modeling were used to investigate which of these hypotheses may explain the asymmetric EPR spectrum of DMPO-OOH. From these studies it is shown that the 12-line EPR spectrum of DMPO-OOH results not from any proximal hydrogen, but from additional conformers of DMPO-OOH. Thus, the 1.25 G hyperfine splitting, which has been assigned as a γ-splitting, is actually from two individual EPR spectra associated with different conformers of DMPO-OOH.
AB - Spin trapping, a technique used to characterize short-lived free radicals, consists of using a nitrone or nitroso compound to "trap" an unstable free radical as a long-lived aminoxyl that can be characterized by EPR spectroscopy. The resultant aminoxyl exhibits hyperfine splitting constants that are dependent on the spin trap and the free radical. Such is the case with 2,2-dimethyl-5-hydroxy-1-pyrrolidinyloxyl (DMPO-OH) and 2,2-dimethyl-5-hydroperoxy-1-pyrrodinyloxyl (DMPO-OOH) whose hyperfine splitting constants, AN = AH = 14.9 G and AN = 14.3 G, AHβ = 11.7 G, and AHγ = 1. 25 G, respectively, have been used to demonstrate the generation of HO . and O2.-. However, to date, the source of the apparent AHγ hyperfine splitting in DMPO-OOH is not known. We consider three possible explanations to account for the unique EPR spectrum of DMPO-OOH. The first is that the γ-splitting arises from one of the hydrogen atoms at either carbon 3 or carbon 4 of DMPO-OOH. The second is that the γ-splitting originates from the hydrogen atom of DMPO-OOH. The third is that the conformational properties of DMPO-R change upon going from DMPO-OH to DMPO-OOH. Experimental and theoretical chemical approaches as well as EPR spectral modeling were used to investigate which of these hypotheses may explain the asymmetric EPR spectrum of DMPO-OOH. From these studies it is shown that the 12-line EPR spectrum of DMPO-OOH results not from any proximal hydrogen, but from additional conformers of DMPO-OOH. Thus, the 1.25 G hyperfine splitting, which has been assigned as a γ-splitting, is actually from two individual EPR spectra associated with different conformers of DMPO-OOH.
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U2 - 10.1021/jo0354894
DO - 10.1021/jo0354894
M3 - Article
C2 - 14961686
AN - SCOPUS:10744229627
VL - 69
SP - 1321
EP - 1330
JO - Journal of Organic Chemistry
JF - Journal of Organic Chemistry
SN - 0022-3263
IS - 4
ER -