Role of H202 in the radiolysis of B-group vitamins in neutral aqueous solutions. part I. reactions with vitamin radicals produced by oh radical reaction

The radiolytic decomposition of the B-group vitamins in 0.1 mM neutral aqueous solutions has been studied in oxygenated as well as N₂O saturated solutions. In the former G(-Vit) and G(H₂O₂) values suggested the occurrence of reaction between the vitamin radioals and the H₂O₂ formed during radiolysis in the oase of pyridoxin, folic acid and cyanocobalamin. The occurrence of this reaction was directly confirmed in N₂O saturated solutions initially containing hydrogen peroxide. In this case an increased vitamin decomposition and a parallel consumption of the H₂O₂ were observed. Reactivities of different types of radicals with H₂0₂ are discussed.     

Gas-phase photoreactions of anthracene, 2-aminoanthracene,and pyrene with oxygen and water vapors

Excited singlet (S ₁) and triplet (T ₁) state quenching by O₂ and by (O₂ + H₂O) gas-vapor mixtures was studied in the gas phase for polycyclic aromatic hydrocarbons (PAHs, anthracene, 2-aminoanthracene, pyrene). Addition of water vapor is shown not to influence quenching of both fluorescence and delayed fluorescence of PAHs by oxygen. The role of complexes stabilized by charge transfer and hydrogen bonds in quenching the excited states of PAHs by atmospheric gases was analyzed. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 3, pp. 342–348, May–June, 2009.     

Quenching of Long Lifetime Emitting Fluorophores with Paramagnetic Molecules

In this work, we have studied quenching of the fluorescence of two well-known oxygen probes, 1-pyrene butyric acid (PBA) and tris(2,2’-bipyridine)ruthenium ([Ru(bpy)₃]²⁺) by reactive oxygen species (superoxide anion, nitric oxide derivative, hydrogen peroxide) and by the O₂ molecule. Both, time-resolved and steady state fluorescence measurements were performed in solution (ethanol, dimethyl sufoxide, water) and in micelles of Sodium Dodecyl Sulfate that serve as a model for membrane-containing biological structures. We have found that only the free radicals and O₂ can actively quench for the two probes, but not the diamagnetic H₂O₂. Our data correspond to the classical Stern–Volmer equation. H₂O₂ has an effect only at high molar concentrations (>0.1 M). In contrast, effective concentrations of free radicals and O₂ that lead to quenching are in millimolar range. In conclusion, our methods allows for detecting global ROS that are small free radicals without interference from the reactive hydroxyl radical. Our data suggest that the method can be used for the quantification of ROS in individual living cells based on the measurement of fluorescence lifetime of those probes.     

A simple and sensitive fluorescence quenching method for the determination of H(2)O(2) using Rhodamine B and FE(3)O(4) nanocatalyst

In pH 1.99 sodium acetate-HCl buffer solutions at 60 °C, Rhodamine B exhibited a strong fluorescence peak at 584 nm using an excitation wavelength of 548 nm. The fluorescence quenching occurred when Fe₃O₄ nanoparticles catalyzed H₂O₂ oxidation of Rhodamine B. Under the chosen conditions, the fluorescence intensity at 584 nm decreased when the concentration of H₂O₂ increased. The fluorescence quenching intensity is linear with the concentration of H₂O₂ in the range of 10–200 nmol/L. Thus, a new and simple and sensitive nanocatalytic fluorescence method was proposed for the determination of H₂O₂ in synthetic sample, with satisfactory results.     

H2O2–Ng dynamics predictions using an accurate potential energy surface

ABSTRACT

Based on ab initio calculations, our research group has built an analytical ground-state potential energy surface (PES) for hydrogen peroxide– noble gas (Ng) interactions, such as H₂O₂–He, H₂O₂–Ne, H₂O₂–Ar, H₂O₂–Kr, and H₂O₂–Xe complexes. From this PES, it was verified that the Ng presence does not affect the equilibrium values of the H₂O₂ dihedral angles. This happens because the H₂O₂ intramolecular barriers have much higher energies than the atom–bond interaction within these complexes. From this point of view, it is indeed reasonable to consider the H₂O₂ system as a rigid rotor, frozen at its equilibrium configuration. We present in this work the torsional motion for the H₂O₂ isolated system, the vibration–rotation energy levels and spectroscopic constants for hydrogen peroxide–noble gas by using the aforementioned PES. The predicted H₂O₂ torsional motions are in good agreement with both theoretical and experimental results available in the literature. Regarding H₂O₂–Ng ro-vibrational energies and spectroscopic constants, it is the first time that these calculations are presented in the literature. The current theoretical predictions are expected to be useful in the future experimental investigations.     

Degradation of Acid Blue 25 in aqueous media using 1700 kHz ultrasonic irradiation: ultrasound/Fe(II) and ultrasound/H2O2 combinations

In this work, the sonolytic degradation of an anthraquinonic dye, C.I. Acid Blue 25 (AB25), in aqueous phase using high frequency ultrasound waves (1700 kHz) for an acoustic power of 14 W was investigated. The sonochemical efficiency of the reactor was evaluated by potassium iodide dosimeter, Fricke reaction and hydrogen peroxide production yield. The three investigated methods clearly show the production of oxidizing species during sonication and well reflect the sonochemical effects of high frequency ultrasonic irradiation. The effect of operational conditions such as the initial AB25 concentration, solution temperature and pH on the degradation of AB25 was studied. Additionally, the influence of addition of salts on the degradation of dye was examined. The rate of AB25 degradation was dependent on initial dye concentration, pH and temperature. Addition of salts increased the degradation of dye. Experiments conducted using distilled and natural waters demonstrated that the degradation was more efficient in the natural water compared to distilled water. To increase the efficiency of AB25 degradation, experiments combining ultrasound with Fe(II) or H₂O₂ were conducted. Fe(II) induced the dissociation of ultrasonically produced hydrogen peroxide, leading to additional OH radicals which enhance the degradation of dye. The combination of ultrasound with hydrogen peroxide looks to be a promising option to increase the generation of free radicals. The concentration of hydrogen peroxide plays a crucial role in deciding the extent of enhancement obtained for the combined process. The results of the present work indicate that ultrasound/H₂O₂ and ultrasound/Fe(II) processes are efficient for the degradation of AB25 in aqueous solutions by high frequency ultrasonic irradiation.     

NO Fluorescence Sensing by Europium Tetracyclines Complexes in the Presence of H2O2

The effect on the fluorescence of the europium:tetracycline (Eu:Tc), europium:oxytetracycline (Eu:OxyTc) and europium:chlortetracycline (Eu:ClTc) complexes in approximately 2:1 ratio of nitric oxide (NO), peroxynitrite (ONOO^?), hydrogen peroxide (H₂O₂) and superoxide (O₂ ^·?) was assessed at three ROS/RNS concentrations levels, 30 °C and pH 6.00, 7.00 and 8.00. Except for the NO, an enhancement of fluorescence intensity was observed at pH 7.00 for all the europium tetracyclines complexes—the high enhancement was observed for H₂O₂. The quenching of the fluorescence of the Tc complexes, without and with the presence of other ROS/RNS species, provoked by NO constituted the bases for an analytical strategy for NO detection. The quantification capability was evaluated in a NO donor and in a standard solution. Good quantification results were obtained with the Eu:Tc (3:1) and Eu:OxyTc (4:1) complexes in the presence of H₂O₂ 200 μM with a detection limit of about 3 μM (Eu:OxyTc).     

Water enrichment by hydroxyl and hydrogen peroxide due to cavitation treatment: GHz four-wave mixing spectroscopy

Four-waves mixing spectroscopy has been applied to detection of H₂O₂ and OH molecules in water after different treatments in a cavitation jet. The considerable growth of the ortho-H₂O, OH, and H₂O₂ rotational lines amplitude in cavitation water relatively to distilled water and 1% hydrogen peroxide aqueous solution have been found. This fact was interpreted as the exhibition of H₂O molecules dissociation onto atoms and recombination into OH and H₂O₂. Four-waves mixing spectra fitting gives the evaluation of H₂O₂ rotational line’s amplitude increasing in cavitation water by factor of ～3 in comparison to 1% H₂O₂ aqueous solution.     

Spectrofluorometric Determination of Hydrogen Peroxide

A Spectrofluorometric method for microdetermination of H₂O₂ has been developed. The method is based on the oxidation of hydrogen peroxide with ceric ion in acid solution and measurement of the fluorescence during titration of the Ce(III) ions produced. The fluorescent species have excitation and emission maxima at 260 and 360 nm, respectively. The detection limit of measurement by this method was 0.1 ppm hydrogen peroxide.     

Chemical and photochemical reactivity of 6‐hydroxymethyl‐7,8‐dihydropterin in aqueous solutions

6‐Hydroxymethyl‐7,8‐dihydropterin (H₂Hmp) is an intermediate in the biosynthesis of folate, a precursor of coenzymes involved in the metabolism of nucleotides and amino acids. In this work, we have investigated the reactions undergone by H₂Hmp in aqueous solutions at physiological pH, in the absence and in the presence of UV‐A radiation (320–400 nm). In air‐equilibrated solutions, H₂Hmp undergoes slow thermal oxidation (half‐life 37 h) to yield 7,8‐dihydroxanthopterin (H₂Xap) as the main product. The reaction of H₂Hmp with hydrogen peroxide also yields H₂Xap as a main product. In contrast, UV‐A excitation of H₂Hmp leads to the formation of a dimer identified by electrospray ionization mass spectrometry. The corresponding quantum yield of H₂Hmp consumption (Φ_?R) was independent of O₂ and reactant concentration and has a value of 0.10 (±0.02), more than twice higher than that measured for other 6‐subtituted 7,8‐dihydropterins. Copyright © 2012 John Wiley & Sons, Ltd.     

Reactivity of hydrogen peroxide with respect to ozone

Ozone decomposition in pure water, H₂O₂ aqueous solution, and water with ethanol admixture is investigated. It is found that, in the presence of H₂O₂, ozone decomposes significantly faster than in pure water owing to its interaction with H₂O₂. The effective rate constant (k = (0.023 ± 0.002) l/(mol s)) is determined, which is much higher than the overall rate constant of ozone decomposition in water, but much lower than the specific rate of ozone decomposition in water in the presence of common organic admixtures (fulvic acids, ethanol). It is concluded that at the combined use of O₃ and H₂O₂ for the decomposition of organic admixtures in water, the contribution of their interaction with each other is little.     

A quenching fluoroimmunoassay for analysis of the pesticide propazine in an apolar organic solvent, reverse micelles of AOT inn-octane: Effect of the micellar matrix and labeled antigen structure

A simple way of directly observing antigen-antibody binding in a reverse micellar system,n-octane containing reverse micelles of aerosol OT (AOT), using the hydrophobic pesticide propazine as antigen, is described. We observed two processes during fluorescein-labeled propazine (FP)-antibody (Ab) interaction in reverse micelles: (1) quenching of the fluorescence of FP after mixing of Ab and FP (due immune complex formation) and (2) restoration of FP fluorescence after addition of excess propazine to the immune complex formed. We found that the quenching efficiency depends on both the properties of the reverse micellar system (surfactant concentration, hydration degreeW ₀ = [water]/[surfactant]) and the structure of the labeled antigen. A quenching fluoroimmunoassay of propazine both in apolar organic solvents and in water is developed. The method is homogeneous. The quenching time is 10–30 min, and the detection limit of propazine is 100 nM (20 Μg/L) in organic solvent and 10nM (2 Μg/L) in water. Propazine can be added to the reverse micellar system when dissolved in AOT/octane, or in an octane/chloroform mixture, or in chloroform. This makes possible the use of the analysis directly for pesticide extracts in nonpolar organic solvents.     

Investigations into the spectral and luminescent properties of methylphenols in neutral and ionic forms in aqueous micelle solutions

The special features of the absorption and fluorescence spectra of some substituted phenols (2-, 4-methylphenol and 2-amino-4-methylphenol) in aqueous micelle solutions are investigated on addition of an alkali and acid. A fluorescence band of 4-methylphenol in the anion form is detected in the presence of a cation surfactant. The fluorescence efficiency of 4-methylphenol in the presence of the triton X100 micelle decreases in comparison with aqueous solutions. It is established that the quantum yield of fluorescence of 2-methylphenol in the presence of N-cetyltrimethyl ammonium bromide (CTAB) increases in comparison with the aqueous solution (ϕ_fl = 0.25 and 0.17, respectively). The constant of fluorescence quenching for methylphenol in aqueous micelle solutions by the alkali is two orders of magnitude higher than by the acid. The proton-acceptor properties of 2-amino-4-methylphenol are higher than of 4-methylphenol. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 54–61, November, 2005.     

The effect of benzo‐annelation on intermolecular hydrogen bond and proton transfer of 2‐methyl‐3‐hydroxy‐4(1H)‐quinolone in methanol: A TD‐DFT study

Excited‐state intermolecular or intramolecular proton transfer (ESIPT) reaction has important potential applications in biological probes. In this paper, the effect of benzo‐annelation on intermolecular hydrogen bond and proton transfer reaction of the 2‐methyl‐3‐hydroxy‐4(1H)‐quinolone (MQ) dye in methanol solvent is investigated by the density functional theory and time‐dependent density functional theory approaches. Both the primary structure parameters and infrared vibrational spectra analysis of MQ and its benzo‐analogue 2‐methyl‐3‐hydroxy‐4(1H)‐benzo‐quinolone (MBQ) show that the intermolecular hydrogen bond O₁―H₂?O₃ significantly strengthens in the excited state, whereas another intermolecular hydrogen bond O₃―H₄?O₅ weakens slightly. Simulated electron absorption and fluorescence spectra are agreement with the experimental data. The noncovalent interaction analysis displays that the intermolecular hydrogen bonds of MQ are obviously stronger than that of MBQ. Additionally, the energy profile analysis via the proton transfer reaction pathway illustrates that the ESIPT reaction of MBQ is relatively harder than that of MQ. Therefore, the effect of benzo‐annelation of the MQ dye weakens the intermolecular hydrogen bond and relatively inhibits the proton transfer reaction.     

Two Mn(II) and Zn(II) Coordination Polymers: Aqueous-Phase Detection of Nitroaromatic Explosives and Protective Effect on Atherosclerosis

Via the solvothermal reaction between Zn(II) or Mn(II) salts and 5-(3,4-dicarboxylphenoxy)nicotinic acid (H₃L) ligand, a trifunctional N,O-building block having three diverse kinds of functional groups (O-ether, N-pyridyl and COOH), two new coordination polymers (CPs) could be generated, and their chemical formulae respectively are {[Mn₃(L)₂(H₂O)₂]·4H₂O} (1) and {[Zn(HL)]·NMP} (2). The complex 2 based on Zn(II) possesses high efficiency of fluorescence quenching for the nitrophenol (2,4,6-trinitrophenol, TNP; 4-nitrophenol, 4-NP; 3-nitrophenol, 3-NP; 2-nitrophenol, 2-NP) in the aqueous solution. Furthermore, the treatment activity of compounds on the atherosclerosis was assessed, and relevant mechanism was investigated. First of all, the ELISA assay was used to measure the content of the inflammatory cytokines released into the plasma. Besides, the levels of the NF-κb signaling pathway in the vascular endothelial cells were measured with real time RT-PCR. The hemolysis test was conducted in this research to measure the biocompatibility of the new compound.

     

Fluorescence Spectrometric Studies on the Binding of an Amino-Functionalized Ionic Liquid to Cytochrome c

The interaction of an amino-functionalized ionic liquid, 1-(2-aminoethyl)-3-butylimidazolium bromide ([NH₂C₂C₄im]Br), with cytochrome c (cyt c) at pH 7.4 was investigated using fluorescence and UV-Vis absorption spectroscopic techniques. From the experimental results, it is found that cyt c has a strong ability to quench the intrinsic fluorescence of [NH₂C₂C₄im]Br and the quenching mechanism is considered as a static quenching process. The binding constants and the number of binding sites (n) were calculated at different temperatures. The thermodynamic parameters such as free energy change (ΔG), enthalpy change (ΔH), and entropy change (ΔS) were calculated by thermodynamic equations. According to the results, the values of ΔG, ΔH, and ΔS are all negative, suggesting that interaction between [NH₂C₂C₄im]Br and cyt c is spontaneous and mainly driven by hydrogen bonding and van der Waals forces.     

Understanding the mechanism of DNA deactivation in ion therapy of cancer cells: hydrogen peroxide action*

Changes in the medium of biological cells under ion beam irradiation has been considered as a possible cause of cell function disruption in the living body. The interaction of hydrogen peroxide, a long-lived molecular product of water radiolysis, with active sites of DNA macromolecule was studied, and the formation of stable DNA-peroxide complexes was considered. The phosphate groups of the macromolecule backbone were picked out among the atomic groups of DNA double helix as a probable target for interaction with hydrogen peroxide molecules. Complexes consisting of combinations including: the DNA phosphate group, H₂O₂ and H₂O molecules, and Na⁺ counterion, were considered. The counterions have been taken into consideration insofar as under the natural conditions they neutralise DNA sugar-phosphate backbone. The energy of the complexes have been determined by considering the electrostatic and the Van der Waals interactions within the framework of atom-atom potential functions. As a result, the stability of various configurations of molecular complexes was estimated. It was shown that DNA phosphate groups and counterions can form stable complexes with hydrogen peroxide molecules, which are as stable as the complexes with water molecules. It has been demonstrated that the formation of stable complexes of H₂O₂-Na⁺-PO₄ ^- may be detected experimentally by observing specific vibrations in the low-frequency Raman spectra. The interaction of H₂O₂ molecule with phosphate group of the double helix backbone can disrupt DNA biological function and induce the deactivation of the cell genetic apparatus. Thus, the production of hydrogen peroxide molecules in the nucleus of living cells can be considered as an additional mechanism by which high-energy ion beams destroy tumour cells during ion beam therapy.     

Localisation of hydrogen peroxide accumulation during Solanum tuberosum cv. Rywal hypersensitive response to Potato virus Y

The reactive oxygen species hydrogen peroxide (H₂O₂) was detected cytochemically in Solanum tuberosum cv. Rywal tissues as a hypersensitive response (HR) 24 and 48 h after a Potato virus Y (PVY) infection.Hydrogen peroxide was detected in vivo by its reaction with 3.3-diaminobenzidine, producing a reddish-brown staining in contact with H₂O₂. Hydrogen peroxide was detected in the necrotic area of the epidermal and mesophyll cells 24 and 48 h after the PVY infection. Highly localised accumulations of H₂O₂ were found within xylem tracheary elements, and this was much more intensive than in non-infected leaves. Hydrogen peroxide was detected cytochemically in HR also by its reaction with cerium chloride, producing electron-dense deposits of cerium perhydroxides.Inoculation with PVY^NTN and also PVY^N Wi induced a rapid hypersensitive response during which highly localised accumulations of H₂O₂ was detected in plant cell walls. The most intensive accumulation was present in the bordering cell walls of necrotic mesophyll cells and the adjacent non-necrotic mesophyll cells. Intensive electron-dense deposits of cerium perhydroxide were found along ER cistrenae and chloroplast envelopes connected with PVY particles. The precipitates of hydrogen peroxide were detected in the nuclear envelope and along tracheary elements, especially when virus particles were present inside. The intensive accumulation of H₂O₂ at the early stages of potato–PVY interaction is consistent with its role as an antimicrobial agent and for this reason it has been regarded as a signalling molecule.     

The effects of hydrogen peroxide on the sonochemical degradation of phenol and bisphenol A

This report describes the effects of H₂O₂ concentration (0.01, 0.1, 1, and 10 mM) on the sonochemical degradation of phenol and bisphenol A (BPA) using an ultrasonic source of 35 kHz and 0.08 W/mL. The concentration of the target pollutants (phenol or BPA), total organic carbon (TOC), and H₂O₂ were monitored for each input concentration of H₂O₂. The effects of H₂O₂ on the sonochemical degradation of phenol was more significant than that of BPA because phenol has a high solubility and low octanol–water partition coefficient (K_ow) value and is subsequently very likely to remain in the aqueous phase, giving it a greater probability of reacting with H₂O₂. The removal of TOC was also enhanced by the addition of H₂O₂. Some intermediates of BPA have a high K_ow value and subsequently have a greater probability of pyrolyzing by the high temperatures and pressures inside of cavitation bubbles. Thus the removal efficiency of TOC in BPA was higher than that of phenol. The removal efficiencies of TOC were lower than the degradation efficiencies of phenol and BPA. This result is due to the fact that some intermediates cannot readily degrade during the sonochemical reaction. The H₂O₂ concentration decreased but was not completely consumed during the sonochemical degradation of pollutants. The initial H₂O₂ concentration and the physical/chemical characteristics of pollutants were considered to be important factors in determining the formation rate of the H₂O₂. When high concentration of H₂O₂ was added to the solution, the formation rates were relatively low compared to when low concentrations of H₂O₂ were used.     

The molecular basis for the behaviour of niobia species in oxidation reaction probed by theoretical calculations and experimental techniques

This paper describes the preparation and use of a new class of materials based on synthetic niobia as catalysts in the oxidation of organic compounds in aqueous medium. The chemical reactions were carried out in the presence of hydrogen peroxide (H₂O₂). The material was characterized with X-ray diffraction, XPS and H₂-TPR (temperature-programmed reduction) measurements. The organic molecule methylene-blue was used in the decomposition study as a probe contaminant. The analysis using the ESI-MS technique showed complete oxidation observed through different intermediates. This suggests the use of niobia species as an efficient Fenton-like catalyst in degradation reactions. Theoretical quantum DFT calculations were carried out in order to understand the degradation mechanism.