Is There Stereoselectivity in Spin Trapping Superoxide by 5-tert-Butoxycarbonyl-5-methyl-1-pyrroline N-Oxide?

EPR Study of KO2 as a Source of Superoxide and •BMPO-OH/OOH Radical That Cleaves Plasmid DNA and Detects Radical Interaction with H2S and Se-Derivatives

Superoxide radical anion (O₂^•−) and its derivatives regulate numerous physiological and pathological processes, which are extensively studied. The aim of our work was to utilize KO₂ as a source of O₂^•− and the electron paramagnetic resonance (EPR) spin trapping 5-tert-butoxycarbonyl-5-methyl-1-pyrroline N-oxide (BMPO) technique for the preparation of ^•BMPO-OOH and/or ^•BMPO-OH radicals in water solution without DMSO. The method distinguishes the interactions of various compounds with ^•BMPO-OOH and/or ^•BMPO-OH radicals over time. Here, we show that the addition of a buffered BMPO-HCl mixture to powdered KO₂ formed relatively stable ^•BMPO-OOH and ^•BMPO-OH radicals and H₂O₂, where the ^•BMPO-OOH/OH ratio depended on the pH. At a final pH of ~6.5–8.0, the concentration of ^•BMPO-OOH radicals was ≥20 times higher than that of ^•BMPO-OH, whereas at pH 9.0–10.0, the ^•BMPO-OH radicals prevailed. The ^•BMPO-OOH/OH radicals effectively cleaved the plasmid DNA. H₂S decreased the concentration of ^•BMPO-OOH/OH radicals, whereas the selenium derivatives 1-methyl-4-(3-(phenylselanyl) propyl) piperazine and 1-methyl-4-(4-(phenylselanyl) butyl) piperazine increased the proportion of ^•BMPO-OH over the ^•BMPO-OOH radicals. In conclusion, the presented approach of using KO₂ as a source of O₂^•−/H₂O₂ and EPR spin trap BMPO for the preparation of ^•BMPO-OOH/OH radicals in a physiological solution could be useful to study the biological effects of radicals and their interactions with compounds.

•BMPO-OOH Spin-Adduct as a Model for Study of Decomposition of Organic Hydroperoxides and the Effects of Sulfide/Selenite Derivatives. An EPR Spin-Trapping Approach

Lipid hydroperoxides play an important role in various pathophysiological processes. Therefore, a simple model for organic hydroperoxides could be helpful to monitor the biologic effects of endogenous and exogenous compounds. The electron paramagnetic resonance (EPR) spin-trapping technique is a useful method to study superoxide (O₂^•−) and hydroxyl radicals. The aim of our work was to use EPR with the spin trap 5-tert-butoxycarbonyl-5-methyl-1-pyrroline-N-oxide (BMPO), which, by trapping O₂^•− produces relatively stable ^•BMPO-OOH spin-adduct, a valuable model for organic hydroperoxides. We used this experimental setup to investigate the effects of selected sulfur/selenium compounds on ^•BMPO-OOH and to evaluate the antioxidant potential of these compounds. Second, using the simulation of time-dependent individual BMPO adducts in the experimental EPR spectra, the ratio of ^•BMPO-OH/^•BMPO-OOH—which is proportional to the transformation/decomposition of ^•BMPO-OOH—was evaluated. The order of potency of the studied compounds to alter ^•BMPO-OOH concentration estimated from the time-dependent ^•BMPO-OH/^•BMPO-OOH ratio was as follows: Na₂S₄ > Na₂S₄/SeO₃²⁻ > H₂S/SeO₃²⁻ > Na₂S₂ ~Na₂S₂/SeO₃²⁻ ~H₂S > SeO₃²⁻ ~SeO₄²⁻ ~control. In conclusion, the presented approach of the EPR measurement of the time-dependent ratio of ^•BMPO-OH/^•BMPO-OOH could be useful to study the impact of compounds to influence the transformation of ^•BMPO-OOH.

High-light induced superoxide radical formation in cytochrome b₆f complex from Bryopsis corticulans as detected by EPR spectroscopy

The generation of superoxide radical (O₂·⁻) in Cyt b₆f of Bryopsis corticulans under high light illumination was studied using electron paramagnetic resonance (EPR) spectroscopy. This could be evidenced by the addition of SOD which specifically reacted with O₂·⁻. The generation of O₂·⁻ was lost in the absence of oxygen and was found to be suppressed in the presence of NaN₃ and be scavenged by extraneous antioxidants such as ascorbate, β-carotene and glutathione which could also scavenged ¹O₂*. These results indicated that O₂·⁻ which produced under high light illumination in Cyt b₆f of B. corticulans might rise from a reaction which ¹O₂* could participated in. Also the photo-protection mechanism to Cyt b₆f complex by antioxidants which might contain in thylakoid was speculated.

Superoxide radical anion adduct of 5,5-dimethyl-1-pyrroline N-oxide. 4. Conformational effects on the EPR hyperfine splitting constants

Spin trapping has been commonly employed in the detection of superoxide radical anion in chemical and biological systems; hence, accurate interpretation of the hyperfine splitting constants (hfsc's) arising from the O(2)(*-) adducts (also referred to as hydroperoxyl (HO(2)(*)) radical adducts) of various nitrones is important. In this work, the nature of the relevant hfsc's was investigated by examining the effect of conformational changes in the hydroperoxyl moiety of the O(2)(*-) adducts of 5,5-dimethyl-1-pyrroline N-oxide (DMPO), 5-ethoxycarbonyl-5-methyl-1-pyrroline N-oxide (EMPO), 5-diethoxyphosphoryl-5-methyl-1-pyrroline N-oxide (DEPMPO), 5-carbamoyl-5-methyl-1-pyrroline N-oxide (AMPO), and 7-oxa-1-azaspiro[4.4]non-1-en-6-one N-oxide, (CPCOMPO) on the magnitude of a(N), a(beta-H), and a(gamma-H). Conformational change around the substituents and their effect on the hfsc's were also explored. Results indicate that a(beta-H) is most sensitive to conformational changes of the hydroperoxyl and substituent groups relative to hfsc's of other nuclei. The orbital overlap between the C-H sigma-orbital and the SOMO of the nitroxyl nitrogen plays a crucial factor in determining the magnitude of the a(beta-H). The hfsc values for the O(2)(*-) adducts were predicted with high accuracy by using a low-cost computational method at the PCM(water)/BHandHLYP/EPR-III//B3LYP/6-31G* level of theory without taking into account the explicit water interaction.

Free radical trapping properties of several ethyl-substituted derivatives of 5-ethoxycarbonyl-5-methyl-1-pyrroline N-oxide (EMPO)

The spin trapping behavior of several ethyl-substituted EMPO derivatives, cis- and trans-5-ethoxycarbonyl-3-ethyl-5-methyl-pyrroline N-oxide (3,5-EEMPO), 5-ethoxycarbonyl-4-ethyl-5-methyl-pyrroline N-oxide (4,5-EEMPO), cis- and trans-5-ethoxycarbonyl-5-ethyl-3-methyl-pyrroline N-oxide (5,3-EEMPO), and 5-ethoxycarbonyl-5-ethyl-4-methyl-pyrroline N-oxide (5,4-EEMPO), toward a series of different oxygen- and carbon-centered radicals, is described. Considerably different stabilities of the superoxide adducts (ranging from about 12 to 55 min) as well as the formation of other radical adducts were observed.