title: [Acidity and interaction with superoxide anion radical of echinochrome and its structural analogs].
abstract: Weak acid properties, autoxidation and interaction of natural polyhydroxy1,4-naphthoquinones (PHNQ) with superoxide anion-radical (O2-.) were studied by methods of potentiometric titration, polarography, and UV- and visible spectrophotometry. Sea urchin pigments 3-acetyl-2,6,7-trihydroxynaphthazarin (spinochrome C), 2,3,6,7-trihydroxynaphthazarin (spinochrome D), 2,3,6,7-trihydroxynaphthazarin (spinochrome E), 6-ethyl-2,3,7-trihydroxynaphthazarin (echinochrome A), synthetic 2,3-dihydroxy-6,7-dimethylnaphthazarin and 6-ethyl-2,3,7-trimethoxynaphthazarin (trimethoxyechinochrome A) were tested. Determined dissociation constants (pKi) were in the range of pH 5.3-8.5 (40% ethanol solvent). PHNQ autoxidation observrd in basic pH were inhibited by superoxide dismutase. Xanthine and xanthine oxidase was applied for O2-. generation. Interaction with O2-. led to sufficient time-dependent changing in spectra of echinochrome A, spinochromes D and E. There was weak O2-. influence on spinochrome C spectrum and no changing in trimethoxyechinochrome A spectrum. The spectra, that were transforming during time of reaction, contained pronounced isobestic point. It means formation the single reaction product. We proposed formation of 1,2,3,4-tetraketones from 2,3,5,8-tetrahydroxy-1,4-naphthoquinones (echinochrome A, spinochromes D and E) due to O2-.-induced oxidation of their OH-groups in 2 and 3 positions. Reaction constants were determined by competition method using nitro blue tetrazolium (NBT). The reaction constants were about 10(4)-10(5) M-1s-1. They were decreased in the order: echinochrome A > spinochrome D > spinochrome C > NBT > trimethoxyechinochrome A. Thus, we concluded that some of the natural PGNQ, containing hydroxyl groups in 2nd and 3rd positions, could operate as powerful superoxide anion-radical scavengers.
authors.affiliation: Cardiology Research Centre, Moskow.
authors.forename: A V
authors.initials: AV
authors.lastname: Lebedev
authors.forename: M V
authors.initials: MV
authors.lastname: Ivanova
authors.forename: N I
authors.initials: NI
authors.lastname: Krasnovid
authors.forename: E A
authors.initials: EA
authors.lastname: Kol'tsova
mesh_terms: D000975:Antioxidants / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D009285:Naphthoquinones / Q000737:chemistry*; D013329:Structure-Activity Relationship; D013481:Superoxides / Q000737:chemistry*
chemical_list: D000975:Antioxidants; D009285:Naphthoquinones; D013481:Superoxides; C007573:echinochrome A
vernacular_title: Kislotnye svoĭstva i vzaimodeĭstvie s superoksid anion-radikalom ékhinokhroma i ego strukturnykh analogov.