Chemiluminescence decrease of singlet oxygen in NaClO+H2O2 reaction in the presence of different anti-cataract drugs]

Singlet oxygen was produced in chemical reaction NaClO+ H2O2. Action of different well-known anti-cataract drugs on this reaction was studied. There is no doubt that the singlet oxygen chemiluminescence decreases in the presence of Catalin and Baineiting. Finnish Catachrom Ophthan, Vita iodurol (France) and Quinax (USA) have no such effect at all which may be a result of the interaction of these remedies with H2O2 and/or with NaClO.     

ESR spin-trapping studies on the formation of thiosulfate and sulfide radical anions in aqueous solutions

The first spin-trapping evidence for the formation of thiosulfate (S2O3-.) and sulfide (S-.) radical anions from the reactions of hydrogen peroxide with thiosulphate and sulphide ions, respectively, was presented by electron spin resonance (ESR) spectroscopy using 3,5-dibromo-4-nitrosobenzenesulfonate (DBNBS, 1a) as a spin-trap in aqueous solutions. From the facts that the short-lived radical anions, S2O3-. and S-., could be detected during the oxidation with H2O2, it is suggested that these radical anions may become one of the candidates for the toxicity of sulfide ion in the living body.     

Detection of radical species in mixtures of some retinoids with hematin by using the ESR spin-trapping technique

Radical species were detected in mixtures of some retinoids with hematin by using the ESR spin-trapping technique. The rates of radical formation were approximately proportional to the oxygen consumption during the incubation of the retinoids with hematin. HPLC analyses of the incubation mixtures of the retinoids with hematin showed that 5,6-epoxides of the retinoids were formed. The amounts of the epoxides formed were proportional to both oxygen consumption and the amounts of radicals formed. These results suggest that the 5,6-epoxidations proceed via radical intermediates.     

The role of hydroxyl radicals in irreversible inactivation of lactoperoxidase by excess H2O2. A spin-trapping/ESR and absorption spectroscopy study

H2O2 is catalytically metabolized by ferric lactoperoxidase (LPO)----compound (cpd) I----cpd II----ferric LPO cycles. An excess of the substrate, however, is degraded by a ferric LPO----cpd I----cpd II----cpd III----ferrous LPO----ferric LPO cycle. This latter pathway leads to the partial or total irreversible inactivation of the enzyme depending on the excess of H2O2 (H. Jenzer, W. Jones, and H. Kohler (1986) J. Biol. Chem. 261, 15550-15556). Spin-trapping/ESR data indicate that in the course of the reaction superoxide (HO2./O2-) and hydroxyl radicals (OH.) are formed. Since many substances known to scavenge radicals, such as a spin trap (e.g., 5,5-dimethyl-1-pyrroline-N-oxide) desferrioxamine, albumin, or mannitol, do not prevent enzyme inactivation, we conclude that OH. generation is a site-specific reaction at or near the active center of LPO where bulky scavenger molecules may not be able to penetrate. We suggest the formation of OH. by a Fenton-like reaction between H2O2 and the intermediate ferrous state of the enzyme, which substitutes for Fe2+ in the Fenton reaction. OH. is a powerful oxidant which in turn may attack rapidly the nearest partner available, either H2O2 to produce HO2. and H2O, or the prosthetic group to give rise to oxidative cleavage of the porphyrin ring structure of the heme moiety of LPO and thus to the liberation of iron.     

The reaction of hemin with H2O2

The kinetics of formation of the dominant intermediate (CII) formed between hemin and H2O2 has been studied by the stopped-flow method. CII is preceded by a precursor (CI) for which a steady state is established at an early stage of the reaction. The formation of CI from hemin and H2O2 causes only a marginal change in the optical absorbance (A). The transition CI----CII is accompanied by a substantial decrease of A in the Soret region. Relevant rate constants (or combinations of them) and the molar absorption coefficients of the intermediates at 400 nm have been determined. The absorption spectrum of CII in the Soret region has been evaluated. Aspects of the catalysis of decomposition of H2O2 by hemin in relation to the Fe3+ ion and catalase are discussed.     

Bioinorganic study on [Fe(promethazine)2H2O Cl]2+ complex

The coordination chemistry of iron (III) is the environment of an antihistaminic drug, promethazine has been explained to include a low spin, six-coordinate complex [Fe(Prometha)2(H2O) Cl] Cl2. Metaldrug interaction in vitro in aqueous KCl phase was studied polarographically at physiological pH and temperature. On the basis of elemental, magnetic, conductometric, IR, UV-visible, NMR spectroscopic analysis it is concluded that in solid phase two promethazine molecules with their N,N donor sites encompass the metal. Mass spectral study on the complex confirms that one of the three chlorides is involved in the coordination. The respective changes in the antihistaminic activity of the drug as a result of complexation has been determined and a possible mechanism is suggested.     

Theoretical studies on reaction mechanism of H2 with COS

The reaction mechanisms of H₂ with OCS have been investigated theoretically by using density function theory method. Three possible pathways leading to major products CO and H₂S, as well as two possible pathways leading to by-product CH₄ have been proposed and discussed. For these reaction pathways, the structure parameters, vibrational frequencies and energies for each stationary point have been calculated, and the corresponding reaction mechanism has been given by the potential energy surface, which is drawn according to the relative energies. The calculated results show that the corresponding major products CO and H₂S as well as by-product CH₄ are in agreement with experimental findings, which provided a new illustration and guidance for the reaction of H₂ with OCS.     

Phospholipid polar heads affect the generation of oxygen active species by Fe2+ autoxidation.

The possibility that phospholipid polar heads may influence Fe2+ reaction with molecular oxygen and, thus, the generation of oxygen active species was investigated. Dipalmitoyl phosphatidylcholine (DPPC) and DPPC/dipalmitoyl phosphatidic acid (DPPA) were utilized as model liposomes. Fe2+ oxidation, oxygen consumption, nitro blue tetrazolium reduction and 2-deoxyribose degradation were the parameters evaluated. Comparison of the results obtained clearly shows that the two types of polar heads differently affect iron chemistry. DPPC liposomes are ineffective. By contrast, Fe2+ oxidation by oxygen occurs in the presence of DPPC/DPPA liposomes. During this reaction, species able to reduce nitro blue tetrazolium and to degrade 2-deoxyribose are generated. The results obtained indicate that the polar heads of phospholipids, by influencing Fe2+ autoxidation, generate dangerous oxygen species which may exert an active role in the oxidation of the associated hydrophobic components of the phospholipids.     

Influence of Ca2+ ions on metabolism of active oxygen species in combined cultures of wheat calluses with the fungus Tilletia caries

The effect of Ca2+ on morphophysiological parameters of calluses of wheat Triticum aestovum L., the level of active oxygen species, and the activity of oxalate oxidase, peroxidase, and catalase is investigated in the case of infestation with the fungus Triticum aestivum causing ball smut. The concentration of O2-, H2O2, and activity of oxidoreductases (oxalate oxidase, peroxidase, and catalase) depends on the content of Ca2+ ions in the culture medium of calluses. The increase in the concentration of Ca2+ ions in the culture medium led to higher structuring of calluses, induction of activity of oxalate oxidase and of some forms of peroxidase, and to accumulation of active oxygen species. These changes contributed to inhibition of development of the fungus. Discovery of such dependence agrees with the role of calcium as the intermediary in biochemical reactions related to the formation of the protective response of plant cells in case of infestation.     

Kinetics and DFT studies on the reaction of copper(II) complexes and H2O2

Copper(II) complexes supported by bulky tridentate ligands L1^H (N,N-bis(2-quinolylmethyl)-2-phenylethylamine) and L1^Ph (N,N-bis(2-quinolylmethyl)-2,2-diphenylethylamine) have been prepared and their crystal structures as well as some physicochemical properties have been explored. Each complex exhibits a square pyramidal structure containing a coordinated solvent molecule at an equatorial position and a weakly coordinated counter anion (or water) at an axial position. The copper(II) complexes reacted readily with H₂O₂ at a low temperature to give mononuclear hydroperoxo copper(II) complexes. Kinetics and DFT studies have suggested that, in the initial stage of the reaction, deprotonated hydrogen peroxide attacks the cupric ion, presumably at the axial position, to give a hydroperoxo copper(II) complex retaining the coordinated solvent molecule (H ^R ·S). H ^R ·S then loses the solvent to give a tetragonal copper(II)-hydroperoxo complex (H ^R ), in which the –OOH group may occupy an equatorial position. The copper(II)–hydroperoxo complex H ^R exhibits a relatively high O–O bond stretching vibration at 900 cm⁻¹ compared to other previously reported examples.Electronic Supplementary Material Supplementary material is available for this article at     

Mechanisms of Saccharomyces Cerevisiae PMA1 H+-ATPase inactivation by Fe2+, H2O2 and Fenton reagents

Although considerably more oxidation-resistant than other P-type ATPases, the yeast PMA1 H⁺-ATPase of Saccharomyces cerevisiae SY4 secretory vesicles was inactivated by H₂O₂, Fe²⁺, Fe- and Cu-Fenton reagents. Inactivation by Fe²⁺ required the presence of oxygen and hence involved auto-oxidation of Fe²⁺ to Fe³⁺. The highest Fe^2- (100 μM) and H₂O₂ (100 mM) concentrations used produced about the same effect. Inactivation by the Fenton reagent depended more on Fe²⁺ content than on H₂O₂ concentration, occurred only when Fe²⁺ was added to the vesicles first and was only slightly reduced by scavengers (mannitol, Tris, NaN₃, DMSO) and by chelators (EDTA, EGTA, DTPA, BPDs, bipyridine, 1, 10-phenanthroline). Inactivation by Fe- and Cu- Fenton reagent was the same; the identical inactivation pattern found for both reagents under anaerobic conditions showed that both reagents act via OH^·. The lipid peroxidation blocker BHT prevented Fenton-induced rise in lipid peroxidation in both whole cells and in isolated membrane lipids but did not protect the H⁺-ATPase in secretory vesicles against inactivation. ATP partially protected the enzyme against peroxide and the Fenton reagent in a way resembling the protection it afforded against SH-specific agents. The results indicate that Fe²⁺ and the Fenton reagent act via metal-catalyzed oxidation at specific metal-binding sites, very probably SH-containing amino acid residues. Deferrioxamine, which prevents the redox cycling of Fe²⁺, blocked H⁺-ATPase inactivation by Fe²⁺ and the Fenton reagent but not that caused by H₂O₂, which therefore seems to involve a direct non-radical attack. Fe-Fenton reagent caused fragmentation of the H⁺-ATPase molecule, which, in Western blots, did not give rise to defined fragments bands but merely to smears.     

Effect of Hb-encapsulation with vesicles on H2O2 reaction and lipid peroxidation

We encapsulated a purified and concentrated hemoglobin (Hb) solution with a phospholipid bilayer membrane to form Hb vesicles (particle diameter, ca. 250 nm) for the development of artificial oxygen carriers. Reaction of Hb inside the vesicle with hydrogen peroxide (H(2)O(2)) is one of the important safety issues to be clarified and compared with a free Hb solution. During the reaction of the Hb solution with H(2)O(2), metHb (Fe(III)) and ferrylHb (Fe(IV)=O) are produced, and H(2)O(2) is decomposed by the catalase-like reaction of Hb. The aggregation of discolored Hb products due to heme degradation is accompanied by the release of iron (ferric ion). On the other hand, the concentrated Hb within the Hb vesicle reacts with H(2)O(2) that permeated through the bilayer membrane, and the same products as the Hb solution are formed inside the vesicle. However, there is no turbidity change, no particle diameter change of the Hb vesicles, and no peroxidation of lipids comprising the vesicles after the reaction with H(2)O(2). Furthermore, no free iron is detected outside the vesicle, though ferric ion is released from the denatured Hb inside the vesicle, indicating the barrier effect of the bilayer membrane against the permeation of ferric ion. When vesicles composed of egg york lecithin (EYL) as unsaturated lipids are added to the mixture of Hb and H(2)O(2), the lipid peroxidation is caused by ferrylHb and hydroxyl radical generated from reaction of the ferric iron with H(2)O(2), whereas no lipid peroxidation is observed in the case of the Hb vesicle dispersion because the saturated lipid membrane of the Hb vesicle should prevent the interaction of the ferrylHb or ferric iron with the EYL.     

Interaction of K7Fe3+P2W17O62H2 with supported bilayer lipid membranes on platinum electrode

The influence of K(7)Fe(3+)P(2)W(17)O(62)H(2) on l-alpha-phosphatidylcholine/cholesterol bilayer lipid membrane on Pt electrode was studied by voltammetry and AC impedance spectroscopy. The interaction of the polyoxometalates with the BLM can promote the access of Ru(NH(3))(6)(3+) and [Fe(CN)(6)](3-/4-) to the electrode surface. It was found that some kind of pores had been formed on the BLM by AFM. The phenomenon is attributed to the interaction of K(7)Fe(3+)P(2)W(17)O(62)H(2) with phosphatidylcholine phosphate groups located in its outer leaflet. Experimental results are helpful to understand the biological activity of the polyoxometalates in vivo.     

Differential contractile actions of reactive oxygen species on rat aorta: selective activation of ATP receptor by H2O2

This study aims to examine the effects of different reactive oxygen species (ROS) on the resting tension of endothelium-denuded rat aortic rings. In these preparations, H2O2 (30 microM) induced a fast and transient contraction, which could be abolished by pretreatment of catalase (800 U/ml), but not affected by superoxide anion scavenger, superoxide dismutase (SOD; 150 U/ml) or the hydroxyl free radical scavenger, DMSO/mannitol (each 3 mM). In contrast, pyrogallol, a putative superoxide anion donor, induced a biphasic contraction, which could be abolished by SOD, but not by catalase or DMSO/mannitol. Unlike H2O2 and pyrogallol, Vitamin C(VitC)/Fe2+ (each 100 microM), a commonly used hydroxyl radical-generating system, triggered a tonic contraction which could be prevented by DMSO/mannitol, but not by SOD or catalase. Interestingly, H2O2-induced contraction could be concentration-dependently (10-100 microM) inhibited by suramin and reactive blue-2 (RB-2), two widely used ATP receptor antagonists. On the other hand, suramin or RB-2, at concentration up to 100 microM, affected neither pyrogallol nor VitC/Fe2+-induced contraction. In conclusion, we showed for the first time that different ROS could contract rat aorta with different mechanisms of action, and H2O2 elicits a transient contraction probably as a result of the ATP receptor activation.     

Direct detection of Fe(IV)[double bond]O intermediates in the cytochrome aa3 oxidase from Paracoccus denitrificans/H2O2 reaction

We report the first evidence for the formation of the "607- and 580-nm forms" in the cytochrome oxidase aa3/H2O2 reaction without the involvement of tyrosine 280. The pKa of the 607-580-nm transition is 7.5. The 607-nm form is also formed in the mixed valence cytochrome oxidase/O2 reaction in the absence of tyrosine 280. Steady-state resonance Raman characterization of the reaction products of both the wild-type and Y280H cytochrome aa3 from Paracoccus denitrificans indicate the formation of six-coordinate low spin species, and do not support, in contrast to previous reports, the formation of a porphyrin pi-cation radical. We observe three oxygen isotope-sensitive Raman bands in the oxidized wild-type aa3/H2O2 reaction at 804, 790, and 358 cm-1. The former two are assigned to the Fe(IV)[double bond]O stretching mode of the 607- and 580-nm forms, respectively. The 14 cm-1 frequency difference between the oxoferryl species is attributed to variations in the basicity of the proximal to heme a3 His-411, induced by the oxoferryl conformations of the heme a3-CuB pocket during the 607-580-nm transition. We suggest that the 804-790 cm-1 oxoferryl transition triggers distal conformational changes that are subsequently communicated to the proximal His-411 heme a3 site. The 358 cm-1 mode has been found for the first time to accumulate with the 804 cm-1 mode in the peroxide reaction. These results indicate that the mechanism of oxygen reduction must be reexamined.