Enhanced generation of hydroxyl radical and sulfur trioxide anion radical from oxidation of sodium sulfite, nickel(II) sulfite, and nickel subsulfide in the presence of nickel(II) complexes.

Abstract

Electron spin resonance (ESR) spin trapping was utilized to investigate the generation of free radicals from oxidation of sodium sulfite, nickel(II) sulfite, and nickel subsulfide (Ni3S2) by ambient oxygen or H2O2 at pH 7.4. The spin trap used was 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). Under ambient oxygen, a solution of sodium sulfite alone generated predominantly sulfur trioxide anion radical (.SO3-) due to the autoxidation of sulfite. Addition of nickel(II) chloride [Ni(II)] enhanced the .SO3- yield about 4-fold. Incubation of sulfite with Ni(II) in the presence of chelators such as tetraglycine, histidine, beta-alanyl-3-methyl-L-histidine (anserine), beta--L-histidine (carnosine), gamma-aminobutyryl-L-histidine (homocarnosine), glutathione, and penicillamine did not have any significant effect on that enhancement. In contrast, albumin, and especially glycylglycylhistidine (GlyGlyHis), augmented the enhancing effect of Ni(II) by factors of 1.4 and 4, respectively. Computer simulation analysis of the spin-adduct spectrum and formate scavenging experiment showed that the mixture of sodium sulfite, Ni(II), and GlyGlyHis generated both hydroxyl (.OH) radical and .SO3- radical, in the ratio of approximately 1:2. The free-radical spin adduct intensity reached its saturation level in about 5 min. The yield of the radical adducts could be slightly reduced by deferoxamine and very strongly reduced by diethylenetriaminepentaacetic acid (DTPA). Aqueous suspensions of sparingly soluble nickel(II) sulfite in the presence of air and GlyGlyHis generated surface-located .SO3- and .OH radicals. The same radicals were generated in Ni3S2 suspension in the presence of GlyGlyHis and H2O2, indicating sulfite production by oxidation of the sulfide moiety of this compound.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of Reduced Sulfur Compounds on Pd-Catalytic Hydrodechlorination of Trichloroethylene in Groundwater by Cathodic H2under Electrochemically Induced Oxidizing Conditions

“…It was reported that DMPO/SO 3 •− adduct is unstable and transforms to DMPO/•OH within minutes. 45,46 The time profile of the ESR signals for the sample taken from the system with 1 mM sulfite and Pd (Figure 4b) clearly revealed the existence of DMPO/SO 3 •− which has the featured hyperfine coupling constants of a N = 14.7 G and a H = 16.0 G. 46,47 It was also observed that the signals of DMPO/SO 3 •− decreased quickly within 4 min accompanied with the increase of the signals of DMPO/•OH, proving the transformation of DMPO/SO 3 •− to DMPO/•OH. Therefore, DMPO/•OH observed with Pd and 1 mM sulfite in Figure 4a can be assumed to result from DMPO/SO 3 •− .…”

A three-electrode column for Pd-catalytic oxidation of TCE in groundwater with automatic pH-regulation and resistance to reduced sulfur compound foiling

“…Characteristic spectrum of •OH with hyperfine coupling constants of a N = 14.9 G and a H = 14.9 G was evident by the addition of Fe(II) (Yuan et al, 2011). When 1 mM sulfite was introduced at the beginning of the experiment, several new signals appeared, which can be presumably attributed to the generation of SO 4 •− and unknown S-centered radicals (Guan et al, 2011; Shi et al, 1994). When sulfite concentration was increased to 3 mM, the characteristic signals for SO 3 •− with hyperfine coupling constants of a N = 14.7 G and a H = 16.0 G were measured along with •OH (Ranguelova et al, 2012; Shi et al, 1994).…”

Degradation pathways of 4-methylmethcathinone in alkaline solution and stability of methcathinone analogs in various pH solutions

“…L-Ascorbic acid acts as a scavenger of the superoxide anion radical [19], which generates the more powerful hydroxyl radical. In contrast, sodium sulfite forms the sulfur trioxide radical ion, and at the same time generates hydroxyl radicals [20].…”