Superoxide radical anion adduct of 5,5-dimethyl-1-pyrroline N-oxide (DMPO). 3. Effect of mildly acidic pH on the thermodynamics and kinetics of adduct formation

作者：Burgett Randy A; Bao Xiaofeng; Villamena Frederick A^*

来源：Journal of Physical Chemistry A, 2008, 112(11): 2447-2455.

DOI：10.1021/jp7107158

The nitrone, 5,5-dimethylpyrroline N-oxide (DMPO), is a commonly used spin trap for the detection of superoxide radical anion (O(2)(center dot-)) using electron paramagnetic resonance spectroscopy. This work investigates the reactivity of DMPO to O(2)(center dot-) in mildly acidic pH (5.0-7.0). Mild acidity is characteristic of acidosis and has been observed in hypoxic systems, e.g., ischemic organs and cancer cells. Although the established pK(a) for O(2)(center dot-) is 4.8, the pK(a) for DMPO is unknown. The pK(a) of the conjugate acid of DMPO was determined to be 6.0 using potentiometric, spectrophotometric, (1)H and (13)C NMR, and computational methods. (1)H and (13)C NMR were employed to investigate the site of protonation. An alternative mechanism for the spin trapping of O(2)(center dot-) in mildly acidic pH was proposed, which involves protonation of the oxygen to form the N-hydroxy imino cation and subsequent addition of O(2)(center dot-). The exoergicity of O(2)(center dot-) addition to protonated DMPO was rationalized using density functional theory (DFT) at the PCM/B3LYP/6-31+GB3LYP/6-31G* level of theory.

• 出版日期2008-3-20