Air-saturated Aqueous Solutions Research Articles

Synthesis and Spectroscopic Properties of 4a,14a-Diazoniaanthra[1,2-a]anthracene and 13a,16a-Diazoniahexaphene Derived from 1,7-Dimethylnaphthalene

An improved preparation of 1,7-dimethylnaphthalene is presented, which is used as a precursor for the synthesis of diazonia­hexacyclic salts, namely, 4a,14a-diazoniaanthra[1,2-a]anthracene (3) and 13a,16a-diazoniahexaphene (7). The influence of the reaction conditions on the formation of these isomers was investigated. Notably, the selectivity of the reactions depends significantly on the acid employed in the cyclization step. Both compounds exhibit similar absorption and fluorescence emission properties. Compound 3 exhibits a remarkable photopersistence in the solid state and in air-saturated aqueous solutions. However, diazoniahexaphene 7 undergoes rapid photodegradation in solution. X-ray diffraction analysis reveals that compound 3 adopts a helicene structure in the crystalline state.

Oxygen Uptake and Involvement of Superoxide Radicals upon Photolysis of Ketones in Air‐saturated Aqueous Alcohol, Formate, Amine or Ascorbic Acid Solutions

The photolysis of acetophenone, benzophenone, 4-carboxybenzophenone and benzil was studied in air-saturated aqueous solution in the presence of alcohols. The overall reaction is an oxidation of 2-propanol to acetone. The quantum yield of oxygen uptake (Phi(-O(2))) increases with increasing 2-propanol concentration up to 0.9. The photoreaction can also be initiated by quenching of the ketone triplet state by ascorbic acid, formate or an amine e.g. triethylamine. Subsequent reactions of the involved radicals with oxygen yield the superoxide radical and eventually hydrogen peroxide. For the ketones in the presence of 3-30 mM ascorbic acid or triethylamine Phi(-O(2)) = 0.3-0.9. The specific properties of ketones, including 4-methoxyacetophenone and 2-acetonaphthone, the radicals involved and the pH and concentration dependences of Phi(-O(2)) are discussed.

Cobalt(IV) corroles as catalysts for the electroreduction of O 2: Reactions of heterobimetallic dyads containing a face-to-face linked Fe(III) or Mn(III) porphyrin

A series of heterobinuclear cofacial porphyrin–corrole dyads containing a Co(IV) corrole linked by one of four different spacers in a face-to-face arrangement with an Fe(III) or Mn(III) porphyrin have been examined as catalysts for the electroreduction of O 2 to H 2O and/or H 2O 2 when adsorbed on the surface of a graphite electrode in air-saturated aqueous solutions containing 1 M HClO 4. The examined compounds are represented as (PCY)M IIIClCo IVCl where P is a porphyrin dianion, C is a corrole trianion and Y is a biphenylene (B), 9,9-dimethylxanthene (X), dibenzofuran (O) or anthracene (A) spacer. The catalytic behavior of the seven investigated dyads in the two heterobimetallic (PCY)MClCoCl series of catalysts is compared on one hand to what was previously reported for related dyads with a single Co(III) corrole macrocycle linked to a free-base porphyrin with the same set of linking bridges, (PCY)H 2Co, and on the other hand to dicobalt porphyrin–corrole dyads of the form (PCY)Co 2 which were shown to efficiently electrocatalyze the four electron reduction of O 2 at a graphite electrode in acid media. Comparisons between the four series of porphyrin–corrole dyads, (PCY)Co 2, (PCY)H 2Co, (PCY)FeClCoCl and (PCY)MnClCoCl, show that in all cases the biscobalt dyads catalyze O 2 electroreduction at potentials more positive by an average 110 mV as compared to the related series of compounds containing a Co(III) or Co(IV) corrole macrocycle linked to a free-base metalloporphyrin or a metalloporphyrin with an Fe(III) or Mn(III) central metal ion. The data indicates that the E 1/2 values where electrocatalysis is initiated is related to the initial site of electron transfer, which is the Co(III)/Co(II) porphyrin reduction process in the case of (PCY)Co 2 and the Co(IV)/Co(III) corrole reduction in the case of (PCY)MnClCoCl, (PCY)FeClCoCl and (PCY)H 2Co. The overall data also suggests that the catalytically active form of the biscobalt dyad in (PCY)Co 2 contains a Co(II) porphyrin and a Co(IV) corrole.

Chemical Effects at the Reaction Front in Corroding Spent Nuclear Fuel

AbstractPerformance assessment models of the U. S. repository at Yucca Mountain, Nevada suggest that neptunium from spent nuclear fuel is a potentially important dose contributor. A scientific understanding of how the UO2 matrix of spent nuclear fuel impacts the oxidative dissolution and reductive precipitation of Np is needed to predict the behavior of Np at the fuel surface during aqueous corrosion. Neptunium would most likely be transported as aqueous Np(V) species, but for this to occur it must first be oxidized from the Np(IV) state found within the parent spent nuclear fuel. In this paper we present synchrotron x-ray absorption spectroscopy and microscopy findings that illuminate the resultant local chemistry of neptunium and plutonium within uranium oxide spent nuclear fuel before and after corrosive alteration in an air-saturated aqueous environment. We find the Pu and Np in unaltered spent fuel to have a +4 oxidation state and an environment consistent with solid-solution in the UO2 matrix. During corrosion in an air-saturated aqueous environment, the uranium matrix is converted to uranyl (UO22+) mineral assemblage that is depleted in Np and Pu relative to the parent fuel. The transition from U(IV) in the fuel to a fully U(VI) character across the corrosion front is not sharp, but occurs over a transition zone of ∼ 50 micrometers. We find evidence of a thin (∼ 20 micrometer) layer that is enriched in Pu and Np within a predominantly U(IV) environment on the fuel side of the transition zone. These experimental observations are consistent with available data for the standard reduction potentials for NpO2+/Np4+ and UO22+/U4+ couples, which indicate that Np(IV) may not be effectively oxidized to Np(V) at the corrosion potential of uranium dioxide spent nuclear fuel in air-saturated aqueous solutions.

Self-assembly of 6-thioguanine and 6-thioguanosine monolayers on the mercury electrode: effects of oxygen and applied potential

The formation of self-assembled monolayers (SAMs) of 6-thioguanine and 6-thioguanosine on mercury from deaerated and air-saturated aqueous solutions has been studied. The self-assembly process was investigated using chronoamperometry, cyclic voltammetry and open circuit potential (ocp) measurements. The presence of dissolved oxygen is a necessary condition for the formation of full SAMs on a hanging mercury drop electrode (HMDE) at ocp. In the absence of oxygen, the formation of such SAMs requires application of an appropriate potential to the HMDE during a certain period of time. The effects of oxygen and applied potential are explained on the basis of the charge-transfer reaction involved in the self-assembly process.

Surface oxidation of chalcocite (Cu2S) under aqueous (pH = 2–11) and ambient atmospheric conditions: Mineralogy from CuL- and OK-edge X-ray absorption spectroscopy

We characterized the surface oxidation layer (~50 A) of chalcocite reacted with air-saturated aqueous solutions at pH = 2–11 and with the ambient atmosphere. Copper L -edge and O K -edge X-ray absorption spectroscopy probes the unoccupied electronic states in the conduction band of the surface alteration phase that, in turn, enables us to identify the mineralogy of the surface layer. At low pH, the surface alteration phase is primarily cuprite (Cu2O). At higher pH, tenorite (CuO) is the dominant phase. No evidence for sulfate or carbonate phases are present; however, chalcocite reacted only in air does develop a CuSO4 surface phase in addition to cuprite and minor tenorite.

Temperature and pH effects on the kinetics of 2-aminophenol auto-oxidation in aqueous solution

AbstractThe kinetics of the auto-oxidation of 2-aminophenol (OAP) to 2-amino-phenoxazin-3-one (APX) was followed in air-saturated aqueous solutions and the influence of temperature and pH on the auto-oxidation rate was studied. The kinetic analysis was based on a spectrophotometric method following the increase of the absorbance of APX. The process follows first order kinetics according to the rate law—d[OAP]/dt=k′[OAP]. The experimental data, within the pH range 4–9.85, were analyzed using both differential and incremental methods. The temperature variation of the overall rate constant was studied at pH=9.85 within the range 25–50°C and the corresponding activation energy was evaluated.

Surface oxidation of chalcopyrite (CuFeS 2) under ambient atmospheric and aqueous (pH 2-10) conditions: Cu, Fe L- and O K-edge X-ray spectroscopy

X-ray absorption and emission spectra were used to characterize the surface of chalcopyrite after oxidation both in air and in air-saturated aqueous solution (pH = 2–10). For chalcopyrite oxidized in aqueous solution, the Cu and Fe L-edge spectra show that the surface oxidation layer is copper deficient. As the pH increases, O K-edge spectra reveal a change in the nature of the oxidation layer. An iron (hydroxy)sulfate is dominant at low pH, whereas FeOOH is the major surface phase under alkaline conditions. Fe 2O 3 may be present at intermediate pH. The surfaces of chalcopyrite samples oxidized in air consist of a mixture of copper oxides, FeOOH, and sulfate phases. Sulfate is much more abundant on the surface of air-oxidized chalcopyrite because of its high solubility in aqueous solution. Likewise, copper oxidation products can be observed in the O K-edge spectra of air-oxidized chalcopyrite in contrast to the aqueous samples.

Multibubble Sonoluminescence from Aqueous Solutions Containing Mixtures of Surface Active Solutes

The effect of mixing surfactants (anionic, zwitterionic, and nonionic) and alcohols on the sonoluminescence (SL) generated by 3.5 ms pulses of 515 kHz ultrasound in air-saturated aqueous solutions has been examined. Each surfactant/alcohol system influenced the SL in significantly different ways. It was concluded that the surface active solutes competitively adsorbed to the cavitation bubble/solution interface and affected the sonoluminescence through both inter- and intrabubble processes. Modeling of the competitive adsorption of the solutes based on Langmuir type adsorption isotherms, however, could not completely account for the trends observed in the SL data. The poor quantitative correlation between the experimental results and model calculations was attributed to the cavitation bubbles not being sufficiently long-lived to allow the solution species to equilibrate with the surface of the cavitation bubbles. It was estimated that the persistence time of the sonoluminescing bubbles in the sound field, under the experimental conditions used, was less than 10 ms.

Ultrasonically induced cell damage and active oxygen generation by 4-formyloximeetylidene-3-hydroxyl-2-vinyl-deuterio-porphynyl(IX)-6-7-diaspartic acid: on the mechanism of sonodynamic activation

Ultrasonically induced cell damage and active oxygen generation with 4-formyloximeetylidene-3-hydroxyl-2-vinyl-deuterio-porphynyl(IX)-6-7-diaspartic acid (ATX-S10) were compared in the same in vitro insonation setup. Sarcoma 180 cells suspended in air-saturated PBS were exposed to ultrasound at 2 MHz for up to 60 s in the presence and absence of ATX-S10. The viability was determined by Trypan blue exclusion test. Ultrasonically induced active oxygen generation in the presence and absence of ATX-S10 in air-saturated aqueous solutions of 50 mM 2,2,6,6-tetramethyl-4-piperidone was detected by electron spin resonance (ESR). Significant enhancement of the rates of both ultrasonically induced cell damage and nitroxide generation was demonstrated with 40–160 μM ATX-S10. Both rates correlated very well. The enhancement of both rates with ATX-S10 was suppressed by 10 mM histidine. These results suggest that ultrasonically generated active oxygen plays a primary role in the ultrasonically induced cell damage in the presence of ATX-S10.

Comparison of the Effects of Water-Soluble Solutes on Multibubble Sonoluminescence Generated in Aqueous Solutions by 20- and 515-kHz Pulsed Ultrasound

The influence of aliphatic alcohols, sodium dodecyl sulfate and sodium chloride on the intensity of sonoluminescence (SL) generated by 3.5-ms pulses of 20-kHz and 515-kHz ultrasound in air-saturated aqueous solutions has been examined. The water-soluble solutes were found to affect the SL quite differently at the two frequencies when applied at approximately the same range of power. At 20 kHz, the solutes had only a small effect on the SL signal generated, whereas at 515 kHz, the effect observed depended strongly on the specific solute present in solution. The contrasting results obtained at the two ultrasound frequencies have been interpreted in terms of transient bubbles giving rise to the SL at 20 kHz and repetitive transient bubbles producing the SL at 515 kHz.

Quantum yields of hydroxyl radicals in illuminated TiO 2 nanocrystallite layers

The yield of hydroxyl radicals has been determined by illumination of TiO 2 layers immersed in air saturated aqueous methanol solutions. This yield is equal to half the measured formaldehyde yield in the pH range 7–13. A detailed mechanism is proposed, accounting for the lack of accumulation of hydrogen peroxide. The effect of changing methanol concentration, pH and light intensity (the latter by three orders of magnitude) is in agreement with a very simple mechanism. In contrast to hydroxyl radicals, which react via hydrogen abstraction, leading to formation of HCHO, there is no sign for reaction of methanol with mobile holes. Thus, the limiting quantum yield observed at high methanol concentration is related to the maximum yield of OH ads under air saturated conditions at the given pH and light intensity. The effect of light intensity shows the expected inverted square root dependency. The yield of OH ads is nearly constant in the range 7<pH<12. This system may be useful for comparative tests of different TiO 2 preparations.

Laser induced singlet-oxygen-sensitised delayed fluorescence of dyes in aqueous solutions

It is shown that water-soluble derivatives of phthalocyanines — poly(diethoxyphosphinylmethyl)substituted aluminium phthalocyanines — emit intense singlet-oxygen-sensitised delayed fluorescence upon laser-induced formation of singlet oxygen in air-saturated aqueous (D2O) solutions. The delayed fluorescence is emitted by the dye molecules which accepted energy from two molecules of singlet oxygen. The quantum efficiency of delayed fluorescence in aerated D2O of the chloroaluminium complex of octa(diethoxyphosphinylmethyl) phthalocyanine corresponds to the rate constant of population of excited dye molecules which is equal to (5.5 ± 3) × 1012 mole-2 L2 s-1. This value is only an order of magnitude smaller than that for tetra(4-tert.-butyl)phthalocyanine earlier studied in aerated organic solvents. It is shown that these phthalocyanine derivatives can be used as highly sensitive luminescence indicators of singlet oxygen produced in aqueous solutions of different compounds upon laser excitation.

Role of membrane charge and semiquinone structure on oxygen consumption rates

Rates of oxygen consumption of air-saturated aqueous solutions containing either 2,3-dimethoxy-5-methylbenzoquinone (UQ-0), 1,4-naphthoquinone (NQ) or phenanthroquinone (PHQ) and ascorbate were measured in the presence or absence of large unilamellar vesicles (LUVs) composed of either dimyristoylphosphatidylcholine (DMPC) or equimolar mixtures of DMPC with dimyristoylphospahtidic acid (DMPA) or hexadecyltrimethylammonium bromide (CTAB), at physiological pH. Semiquinone hydrophobicities follow the same order as that of the corresponding quinones. Rates increase with positively charged LUV concentration and decrease with either neutral or negatively charged LUV concentration in samples containing the hydrophobic quinones NQ and PHQ. Rates remain essentially unchanged in the presence of the most hydrophilic quinone, UQ-0. An increase in the ionic strength of the solution partially inhibits the observed changes in the rate of oxygen consumption, Rox, caused by the presence of positively charged membranes, thus implying that such changes are of electrostatic nature. Similar trends with membrane charge are observed for the rates of oxygen consumption in the presence of PHQ and dithiothreitol. The observed increase in the ascorbate oxidation rate in the presence of positively charged lipids occurs in systems where a decrease in semiquinone disproportionation is also detected, thus, implying that an increase in the quinone one-electron redox potential, caused by semiquinone–positively-charged-membrane interaction, could contribute to the observed effects.

Photochemical behaviour of 1,4-dichlorobenzene in aqueous solution

Several photoproducts were identified in the direct photolysis of 1,4-dichlorobenzene (1,4-DCB) in air-saturated aqueous solution, namely 4-chlorophenol, hydroquinone, hydroxybenzoquinone, and 2,5-dichlorophenol. In the absence of oxygen the latter is not formed and phenol was detected, but the unexpected formations of 4,4'-dichlorobiphenyl, 2,4',5-trichlorobiphenyl, and a terphenyl derivative are observed. Mechanisms are proposed to explain the formations of identified photoproducts. The phototransformation of 1,4-DCB may be photoinduced by NO–3 or FeIII salts. The main primary product is 2,5-dichlorophenol, which results from a hydroxylation without dechlorination. Some other products have been identified in particular 4-chlorophenol and 2,5-dichlorobenzoquinone in the case of FeIII salts.Key words: 1,4-dichlorobenzene, photolysis, aqueous solution, induced phototransformation.

Comparative studies of the Fe 3+/2+–UV, H 2O 2–UV, TiO 2–UV/vis systems for the decolorization of a textile dye X-3B in water

The degradation of a common textile dye, Reactive-brilliant red X-3B, by several advanced oxidation technologies was studied in an air-saturated aqueous solution. The dye was resistant to the UV illumination (wavelength λ ⩾ 320 nm), but was decolorized when one of Fe 3+, H 2O 2 and TiO 2 components was present. The decolorization rate was observed to be quite different for each system, and the relative order evaluated under comparable conditions followed the order of Fe 2+–H 2O 2–UV ⩾ Fe 2+–H 2O 2 > Fe 3+–H 2O 2–UV > Fe 3+–H 2O 2 > Fe 3+–TiO 2–UV > TiO 2–UV > Fe 3+–UV > TiO 2–visible light ( λ ⩾ 450 nm) > H 2O 2–UV > Fe 2+–UV. The mechanism for each process is discussed, and linked together for understanding the observed differences in reactivity.

Probing the presence of hydrophobic sites in anionic polyelectrolytes with tris(polypyridine)chromium(III) complexes

The emission properties of tris(polypyridine)chromium(III) complexes, [Cr(LL) 3] 3+ (LL=2,2′-bipyridine (bpy), 1,10-phenanthroline (phen), 4,7-dimethylphenanthroline (dim), and 4,7-diphenylphenanthroline (dip)), in air-saturated aqueous solutions, are dramatically modified in the presence of anionic polyelectrolytes. Investigated polyions included poly(acrylic acid) (PAA), poly(methacrylic acid) (PMA), and sodium poly(styrenesulfonate) (PSS). All four chromium complexes displayed tunable emission properties in the polyelectrolyte microenvironment, in a degree that depended on the hydrophobic character of both the macromolecule and the polyamine. The largest effect was observed for 2.5×10 −5 M aqueous solutions of [Cr(dip) 3] 3+ in 4×10 −3 M PMA at approximately pH 5 and t=15°C, where I PMA/ I w=25.66 ( I PMA=emission intensity in aqueous solutions containing PMA; I w=emission intensity in water). Decay lifetimes revealed that [Cr(dip) 3] 3+ units are distributed in hydrophobic and hydrophilic sites of the PMA, giving rise to short and long-lived intermediates. Distribution of [Cr(dip) 3] 3+ units in PAA and PSS is homogeneous throughout the polyelectrolyte, and the excited-state intermediates decay following a first order exponential rate law. All other investigated chromium polypyridines showed a homogeneous distribution in solutions containing PMA, PAA or PSS.

Degradation of the dye X-3B by UV/Fe(III)-generated hydroxyl radicals in aqueous solution

Bleaching of the dye, Reactive Brilliant Red X-3B, by irradiation with light at λ≥320nm in an air-saturated aqueous solution of Fe(III) species was investigated under various conditions. It was observed that the dye, quite stable to the UV light, could be degraded efficiently when it was irradiated in the ferric solution. The initial rate degradation was almost independent of the initial [X-3B], but was greatly influenced by the initial [Fe(III)], pH, light intensity, and the anions of chloride or sulfate added to the solution. A further analysis showed that the degradation began with a simultaneous formation of ferrous ions. When all the ferric ions were transferred into Fe(II), the dye disappearance terminated no matter how much of the dye was left in the solution. The molar ratio of the Fe(II) formed to the X-3B disappeared was evaluated to be over 3, depending on the yield of the dye degradation. The result suggests that the process is initiated by the photolysis of Fe(III)-hydroxy species, from which the hydroxyl radicals are generated to oxidize the dye substrate subsequently.

Photoredox chemistry of mercury ions in aqueous ethanol solutions

Mercury(II) is reduced to mercury(I) upon irradiation (λir=254nm) in air-saturated aqueous solution containing ethanol. The quantum yield of this reaction linearly depends on the alcohol concentration. The product of this process is Hg22+, which is photoactive too. Photostationary state with Hg(I)/Hg(II) ratio depending on the alcohol concentration can be reached in this system. Thus, photoassisted catalytic oxidation of alcohol to aldehyde takes place in such a state. Flash photolysis experiments confirmed that the reactions of Hg+ and Hg2+ formed in the primary steps of the photoinduced process are strongly affected by mercury(II), oxygen, and alcohol.

Mechanism of the photochemical transformation of naphthalene in water

Upon irradiation in air-saturated aqueous solution, naphthalene is mainly converted into 7-hydroxy-1,4-naphthoquinone, 2-formylcinnamaldehyde and 2-carboxycinnamaldehyde. The quantum yield of photolysis is equal to 0.0025±0.0005. Naphthalene is likely to be phototransformed via monophotonic ionization that occurs with a quantum yield equal to 0.02. The radical cations formed after the electron ejection can deprotonate or react with water yielding radicals that are oxidized by molecular oxygen. Finally, 2-formylcinnamaldehyde and 2-carboxycinnamaldehyde are yielded. The production of 7-hydroxy-1,4-naphthoquinone is consistent with the intermediary formation of photolabile 1,4-naphtoquinone.