AQ Production Research Articles

Insights into plasma-catalytic nitrogen fixation from catalyst microanalysis and chemical kinetics modelling

Current industrial nitrogen fixation technology is unsustainable and has adverse environmental effects due to its reliance on fossil fuels. Using electricity-driven non-thermal plasma catalysis to fix nitrogen into NO3− is a promising solution, but the underlying mechanisms remain largely unknown. This study integrates a structured catalyst into a plasma column with a water-electrode bubble reactor that can fix nitrogen at ambient pressure and temperature with a 93% selectivity to NO3− with excellent catalytic stability. Characterizations of the catalyst and in situ plasma diagnostics indicate that the enhanced production of nitrate ions is due to abundant chemisorbed oxidized nitrogens species originating from NO and NO2 produced by the air plasma. The plasma chemistry model combined with DFT simulations demonstrates the role of structured TiO2 supported by 5% graphene oxide (GO) to improve NOx surface association while minimizing NOx backwards dissociation. The modelling results suggest the critical role of NO3(ad) in enhancing NOx production predominantly in the form of N2O5 molecule in the gas phase, resulting in efficient NO3−(aq) production as a final product in water. The study offers novel findings on plasma-catalyzed nitrogen fixation, advancing its potential for clean energy and eco-friendly chemical production through plasma-based power-to-chemical processes.

Gas absorption in a hydraulic air compressor. Part II: Experimental verification

Experimental verification of a one-dimensional steady-state bubbly flow model is presented. For initialisation of the liquid-phase concentrations of gas species, a formulation for modelling the time-evolution of the concentration of dissolved gas species in the circulating liquid of a hydraulic air compressor (HAC) was developed and integrated with the steady-state bubbly flow model. Observations from experiments conducted on a pilot scale HAC are presented employing CO2 as a tracer gas. The composition of the input gas inducted by the pilot HAC was deliberately varied by mixing different controlled amounts of CO2 gas while continuously monitoring the gas and liquid phase concentrations of CO2 at key points in the HAC process. Predictions of the concentration of CO2 in the compressed gas produced by the pilot HAC and the circulating liquid at system equilibrium were in good agreement with measured values. Concentrations of CO2 measured in the gas above the tailrace water level were elevated above background levels and responded in accordance with the input CO2 gas mass flow and liquid CO2 concentrations indicating exsolution of gas from the liquid as predicted. Observations of the pH of the circulating liquid identified the bicarbonate equilibrium as the likely mechanism for CO2(aq) production not captured by the model which caused the model to under predict CO2(aq) concentrations for experiment set points with CO2(aq) concentrations above 140 ppm.

9,10-Anthraquinone contamination in tea processing using coal as heat source

9,10-Anthraquinone (AQ) is a contaminant with a potential carcinogenic risk and occurs in tea worldwide. The maximum residue limit (MRL) of AQ in tea set by the European Union (EU) is 0.02 mg/kg. The possible sources of AQ in tea processing and the main stages of its occurrence were investigated based on a modified AQ analytical method and gas chromatography-tandem mass spectrometry (GC-MS/MS) analysis. Compared with electricity as the heat source in green tea processing, AQ increased by 4.3 to 23.9 times in tea processing with coal as the heat source, far exceeding 0.02 mg/kg, while the AQ level in the environment tripled. The same trend was observed in oolong tea processing under coal heat. The steps with direct contact between tea leaves and fumes, such as fixation and drying, are considered as the main steps of AQ production in tea processing. The levels of AQ increased with the rising contact time, suggesting that high levels of AQ pollutant in tea may be derived from the fumes caused by coal and combustion. Fourty samples from different workshops with electricity or coal as heat sources were analyzed, ranged from 50.0%−85.0% and 5.0%−35.0% for detection and exceed rates of AQ. In addition, the maximum AQ content of 0.064 mg/kg was observed in the tea product with coal as the heat source, indicating that the high levels of AQ contamination in tea products are likely to be contributed by coal.

Metabolic engineering of Escherichia coli for efficient production of l-alanyl-l-glutamine

Backgroundl-Alanyl-l-glutamine (AQ) is a functional dipeptide with high water solubility, good thermal stability and high bioavailability. It is widely used in clinical treatment, post-operative rehabilitation, sports health care and other fields. AQ is mainly produced via chemical synthesis which is complicated, time-consuming, labor-intensive, and have a low yield accompanied with the generation of by-products. It is therefore highly desirable to develop an efficient biotechnological process for the industrial production of AQ.ResultsA metabolically engineered E. coli strain for AQ production was developed by over-expressing l-amino acid α-ligase (BacD) from Bacillus subtilis, and inactivating the peptidases PepA, PepB, PepD, and PepN, as well as the dipeptide transport system Dpp. In order to use the more readily available substrate glutamic acid, a module for glutamine synthesis from glutamic acid was constructed by introducing glutamine synthetase (GlnA). Additionally, we knocked out glsA–glsB to block the first step in glutamine metabolism, and glnE–glnB involved in the ATP-dependent addition of AMP/UMP to a subunit of glutamine synthetase, which resulted in increased glutamine supply. Then the glutamine synthesis module was combined with the AQ synthesis module to develop the engineered strain that uses glutamic acid and alanine for AQ production. The expression of BacD and GlnA was further balanced to improve AQ production. Using the final engineered strain p15/AQ10 as a whole-cell biocatalyst, 71.7 mM AQ was produced with a productivity of 3.98 mM/h and conversion rate of 71.7%.ConclusionA metabolically engineered strain for AQ production was successfully developed via inactivation of peptidases, screening of BacD, introduction of glutamine synthesis module, and balancing the glutamine and AQ synthesis modules to improve the yield of AQ. This work provides a microbial cell factory for efficient production of AQ with industrial potential.

Titanium reactors for redox-sensitive hydrothermal experiments: An assessment of dissolved salt on H2 activity-concentration relations

Fixed-volume titanium alloy hydrothermal reactors permit research into fundamental aspects of mineralogy and aqueous geochemistry at the T-P conditions encountered on the frontiers of submarine and terrestrial geothermal system exploration. The impressive mechanical strength of new titanium alloys facilitate studies involving fluids and minerals at conditions up to 500 °C and 50 MPa. The corrosion resistance of titanium is a well-known attribute that also allows experiments to be performed in acidic, NaCl-bearing aqueous fluids. Titanium, however, can suffer irreversible surface reactions in aqueous fluids at high temperatures that may produce or consume appreciable concentrations of dissolved hydrogen (H2(aq)), complicating the interpretation of redox processes in homogenous and heterogeneous chemical systems. Here we report results of hydrothermal experiments designed to examine the direction and magnitude of changes in dissolved H2(aq) in deionized water and NaCl bearing aqueous fluid contained within a newly constructed Ti alloy (Ti-6242) reactor. The redox sensitivity of these and related experiments, however, required testing and assessing surface passivation involving pre-treatment with nitric acid at moderately high temperature. Results indicate that passivation procedures were required to render the Ti surface of the reactor unreactive in both low and high hydrogen-bearing fluid (H2O and NaCl-H2O systems). Once passivated, experiments were then conducted at 400 °C to assess the effect of dissolved NaCl on dissolved H2(aq) concentrations coexisting with the well-known HM (hematite-magnetite) redox buffer. These data indicate highly non-ideal activity-concentration relations for H2(aq) in the NaCl bearing fluids. Accordingly, the common assumption of unity for the activity coefficient of dissolved H2(aq) in hydrothermal fluids is not supported. The implications of this are important for accurate redox reconstruction for compositionally variable natural and experimental hydrothermal systems at elevated temperatures and pressures. The experimental strategy of monitoring the rate and magnitude of H2(aq) production and consumption in situ, during on-going experiments, provides quantitative insight on the effectiveness of the passivation process and the usefulness of redox buffers in hydrothermal geochemical applications.

The Pseudomonas aeruginosa PrrF1 and PrrF2 Small Regulatory RNAs Promote 2-Alkyl-4-Quinolone Production through Redundant Regulation of the antR mRNA.

Pseudomonas aeruginosa is an opportunistic Gram-negative pathogen that requires iron for growth and virulence. Under low-iron conditions, P. aeruginosa transcribes two highly identical (95%) small regulatory RNAs (sRNAs), PrrF1 and PrrF2, which are required for virulence in acute murine lung infection models. The PrrF sRNAs promote the production of 2-akyl-4(1H)-quinolone metabolites (AQs) that mediate a range of biological activities, including quorum sensing and polymicrobial interactions. Here, we show that the PrrF1 and PrrF2 sRNAs promote AQ production by redundantly inhibiting translation of antR, which encodes a transcriptional activator of the anthranilate degradation genes. A combination of genetic and biophysical analyses was used to define the sequence requirements for PrrF regulation of antR, demonstrating that the PrrF sRNAs interact with the antR 5' untranslated region (UTR) at sequences overlapping the translational start site of this mRNA. The P. aeruginosa Hfq protein interacted with UA-rich sequences in both PrrF sRNAs (Kd [dissociation constant] = 50 nM and 70 nM). Hfq bound with lower affinity to the antR mRNA (0.3 μM), and PrrF was able to bind to antR mRNA in the absence of Hfq. Nevertheless, Hfq increased the rate of PrrF annealing to the antR UTR by 10-fold. These studies provide a mechanistic description of how the PrrF1 and PrrF2 sRNAs mediate virulence traits, such as AQ production, in P. aeruginosaIMPORTANCE The iron-responsive PrrF sRNAs play a central role in regulating P. aeruginosa iron homeostasis and pathogenesis, yet the molecular mechanisms by which PrrF regulates gene expression are largely unknown. In this study, we used genetic and biophysical analyses to define the interactions of the PrrF sRNAs with Hfq, an RNA annealer, and the antR mRNA, which has downstream effects on quorum sensing and virulence factor production. These studies provide a comprehensive mechanistic analysis of how the PrrF sRNAs regulate virulence trait production through a key mRNA target in P. aeruginosa.

Serpentinization of olivine at 300 °C and 500 bars: An experimental study examining the role of silica on the reaction path and oxidation state of iron

The generation of H2 during serpentinization of ultramafic oceanic crust along Earth's mid-ocean ridges provides a key energy source for the deep biosphere and has important implications for metal transport and mineral stability in the subseafloor hydrothermal system. Nonetheless, the driving forces and rates of the coupled processes of Fe partitioning and H2 generation during serpentinization are complicated by many factors, but especially, the activity of SiO2(aq) in the serpentinizing fluid. To examine the role of this key variable in H2 generation and Fe partitioning between magnetite and Fe-serpentine during serpentinization, San Carlos olivine was reacted with a NaCl-SiO2(aq)-bearing fluid at 300°C and 500bars for approximately 90days using flexible gold cell hydrothermal equipment. Time-series changes in solution chemistry and dissolved H2 are coupled with magnetic susceptibility, Mössbauer spectroscopy, and Fe isotope measurements of reactant olivine and coexisting alteration products to provide a complete description of Fe mass transfer and oxidation as a function of reaction progress. Utilization of talc as reactant not only provided a source of SiO2(aq) for serpentinization, but effectively prevented brucite formation, in keeping with constraints imposed by many natural hydrothermal systems, which are inherently open systems. Moreover, this experimental strategy allowed Fe derived from olivine dissolution to transfer completely to serpentine and magnetite, facilitating reaction path modeling. Initial changes in solution chemistry indicate “buffering” of dissolved SiO2(aq), owing to the apparently balanced rates of olivine dissolution and serpentine precipitation. During this stage of reaction, a negligible amount of H2 is generated, suggesting that Fe2+-serpentine is stable and the dominant Fe-bearing product. With continued reaction, the rate of SiO2(aq) production lessens likely due to reduction in surface area of talc, such that the continued hydration and hydrolysis of olivine titrates the previously buffered activity of SiO2(aq), eventually approaching serpentine-brucite coexistence. During this secondary stage of reaction, the rate of H2 generation abruptly increases, which reflects the formation of magnetite and Fe3+-serpentine. Temporal changes in the isotope composition of dissolved Fe, throughout these stages, likely reflect different mineral alteration and formation processes, where initially, 1) preferential mass transfer of isotopically light Fe into solution occurred during olivine alteration, without considerable oxidation, as demonstrated by the low H2 production rate, and, 2) the preferential removal of isotopically light Fe from solution in connection with enhanced magnetite and H2 formation during the later stages of reaction. Post experimental analysis of the Fe isotopic composition of Fe-bearing minerals demonstrates statistically negligible enrichment of δ56Fe of magnetite relative to olivine and serpentine, consistent with observations from natural altered oceanic crust. Observations from this study demonstrate the utility of using coupled chemical, isotopic, and analytical approaches to ascertain time series changes in rates of mass transfer and mechanisms of oxidation of Fe during serpentinization of olivine. Ultimately, these insights provide important constraints for the chemical and Fe isotopic evolution of fluids and minerals in ultramafic hosted hydrothermal systems at mid-ocean ridges.

Burkholderia pseudomallei kynB plays a role in AQ production, biofilm formation, bacterial swarming and persistence

Kynurenine formamidase (KynB) forms part of the kynurenine pathway which metabolises tryptophan to anthranilate. This metabolite can be used for downstream production of 2-alkyl-4-quinolone (AQ) signalling molecules that control virulence in Pseudomonas aeruginosa. Here we investigate the role of kynB in the production of AQs and virulence-associated phenotypes of Burkholderia pseudomallei K96243, the causative agent of melioidosis. Deletion of kynB resulted in reduced AQ production, increased biofilm formation, decreased swarming and increased tolerance to ciprofloxacin. Addition of exogenous anthranilic acid restored the biofilm phenotype, but not the persister phenotype. This study suggests the kynurenine pathway is a critical source of anthranilate and signalling molecules that may regulate B. pseudomallei virulence.

Iron Depletion Enhances Production of Antimicrobials by Pseudomonas aeruginosa.

Cystic fibrosis (CF) is a heritable disease characterized by chronic, polymicrobial lung infections. While Staphylococcus aureus is the dominant lung pathogen in young CF patients, Pseudomonas aeruginosa becomes predominant by adulthood. P. aeruginosa produces a variety of antimicrobials that likely contribute to this shift in microbial populations. In particular, secretion of 2-alkyl-4(1H)-quinolones (AQs) contributes to lysis of S. aureus in coculture, providing an iron source to P. aeruginosa both in vitro and in vivo. We previously showed that production of one such AQ, the Pseudomonas quinolone signal (PQS), is enhanced by iron depletion and that this induction is dependent upon the iron-responsive PrrF small RNAs (sRNAs). Here, we demonstrate that antimicrobial activity against S. aureus during coculture is also enhanced by iron depletion, and we provide evidence that multiple AQs contribute to this activity. Strikingly, a P. aeruginosa ΔprrF mutant, which produces very little PQS in monoculture, was capable of mediating iron-regulated growth suppression of S. aureus. We show that the presence of S. aureus suppresses the ΔprrF1,2 mutant's defect in iron-regulated PQS production, indicating that a PrrF-independent iron regulatory pathway mediates AQ production in coculture. We further demonstrate that iron-regulated antimicrobial production is conserved in multiple P. aeruginosa strains, including clinical isolates from CF patients. These results demonstrate that iron plays a central role in modulating interactions of P. aeruginosa with S. aureus. Moreover, our studies suggest that established iron regulatory pathways of these pathogens are significantly altered during polymicrobial infections. Chronic polymicrobial infections involving Pseudomonas aeruginosa and Staphylococcus aureus are a significant cause of morbidity and mortality, as the interplay between these two organisms exacerbates infection. This is in part due to enhanced production of antimicrobial metabolites by P. aeruginosa when these two species are cocultured. Using both established and newly developed coculture techniques, this report demonstrates that iron depletion increases P. aeruginosa's ability to suppress growth of S. aureus. These findings present a novel role for iron in modulating microbial interaction and provide the basis for understanding how essential nutrients drive polymicrobial infections.

Key parameters controlling OH‐initiated formation of secondary organic aerosol in the aqueous phase (aqSOA)

AbstractSecondary organic aerosol formation in the aqueous phase of cloud droplets and aerosol particles (aqSOA) might contribute substantially to the total SOA burden and help to explain discrepancies between observed and predicted SOA properties. In order to implement aqSOA formation in models, key processes controlling formation within the multiphase system have to be identified. We explore parameters affecting phase transfer and OH(aq)‐initiated aqSOA formation as a function of OH(aq) availability. Box model results suggest OH(aq)‐limited photochemical aqSOA formation in cloud water even if aqueous OH(aq) sources are present. This limitation manifests itself as an apparent surface dependence of aqSOA formation. We estimate chemical OH(aq) production fluxes, necessary to establish thermodynamic equilibrium between the phases (based on Henry's law constants) for both cloud and aqueous particles. Estimates show that no (currently known) OH(aq) source in cloud water can remove this limitation, whereas in aerosol water, it might be feasible. Ambient organic mass (oxalate) measurements in stratocumulus clouds as a function of cloud drop surface area and liquid water content exhibit trends similar to model results. These findings support the use of parameterizations of cloud‐aqSOA using effective droplet radius rather than liquid water volume or drop surface area. Sensitivity studies suggest that future laboratory studies should explore aqSOA yields in multiphase systems as a function of these parameters and at atmospherically relevant OH(aq) levels. Since aerosol‐aqSOA formation significantly depends on OH(aq) availability, parameterizations might be less straightforward, and oxidant (OH) sources within aerosol water emerge as one of the major uncertainties in aerosol‐aqSOA formation.

Stabilization or Oxidation of Nanoscale Zerovalent Iron at Environmentally Relevant Exposure Changes Bioavailability and Toxicity in Medaka Fish

Nanoscale zerovalent iron (nZVI)-based nanotechnologies are increasingly being used for environmental remediation; however, the fate and ecotoxicologic effects of nZVI remain unclear. Larvae of medaka fish (Oryzias latipes) underwent 3-14 days' aqueous exposure to thoroughly characterized solutions containing carboxymethyl cellulose (CMC)-stabilized nZVI, bare nZVI, nanoscale iron oxide (nFe(3)O(4)) or ferrous ion [Fe(II)(aq)] at μg/L-mg/L levels to assess the causal toxic effect(s) of iron nanoparticles (NPs). Acute larval mortality was decreased in the order of Fe(II)(aq) > CMC-nZVI > nZVI > nFe(3)O(4). CMC-nZVI (100 mg/L) increased hypoxia and reactive oxygen species (ROS) and Fe(II)(aq) production, thus increasing mortality and oxidative stress response as compared with unstabilized nZVI. Additionally, nFe(3)O(4) and nZVI were more bioavailable than suspended CMC-nZVI or Fe(II)(aq). Antioxidant activities were significantly altered by induced intracellular ROS levels in larvae with subchronic exposure to nFe(3)O(4) or Fe(II)(aq) at environmentally relevant concentrations (0.5-5 mg/L). We report on different organizational biomarkers used for rapidly assessing the lethal and sublethal toxicity of nZVI and its stabilized or oxidized products. The toxicity results implicate a potential ecotoxicological fate and impact of nZVI on the aquatic environment.

An orphan sensor kinase controls quinolone signal production via MexT in Pseudomonas aeruginosa

Pseudomonas aeruginosa employs both N-acylhomoserine lactone and 2-alkyl-4(1H)-quinolone (AQ)-mediated interbacterial signalling for the orchestration of a genome-wide gene regulatory network. Despite the many advances that have been made in understanding the target genes of quorum sensing regulation, little is known on how quorum sensing systems are influenced by environmental cues. In this study, we show that AQ production is modulated by an orphan P. aeruginosa sensor kinase. Transcriptional studies of the sensor kinase (MxtR) mutant demonstrated that an induced expression of MexT, a LysR-type transcriptional regulator, largely determined the global transcriptional profile. Thereby, overexpression of the MexT-regulated MexEF-OprN efflux pump led to a delayed expression of the AQ biosynthetic genes and of AQ-dependent virulence factors. Furthermore, we demonstrated that autophosphorylation of MxtR was inhibited by ubiquinone, the central electron carrier of respiration in in vitro experiments. Our results elucidate on a mechanism by which P. aeruginosa senses environmental conditions and adapts by controlling the production of interbacterial AQ signal molecules. A regulatory function of a sensor kinase may indicate that there is a pre-emptive role of adaptation mechanisms that are turned on under distinct environmental conditions and that are important for efficient colonization and pathogenesis.

Absence of a Signature of Aqueous I(2P1/2) after 200-nm Photodetachment of I-(aq)

Ultrafast pump-broadband probe spectroscopy was used to study the transient photoproducts following 200-nm photodetachment of I(-)(aq). Resonant detachment at 200 nm in the second charge-transfer-to-solvent (CTTS) band of I(-)(aq) is expected to produce an electron and iodine in its spin-orbit excited state, I*((2)P(1/2)). The transients in solution following photodetachment were probed from 200 to 620 nm. Along with strong absorption in the visible region due to solvated electrons and a strong bleach of the I(-)(aq) ground-state absorption, a weaker transient absorption near 260 nm was observed that is consistent with a previously assigned ground-state I((2)P(3/2)) charge-transfer band. However, no evidence was found for an equivalent I*(aq) charge-transfer absorption, and I((2)P(3/2)) was produced within the instrument response. This suggests either that I* is electronically relaxed in less than 300 fs or that excitation in the second CTTS band does not in fact lead to I*. The consequences for previous experimental work where I*(aq) production has been postulated, as well as for halogen electron ejection mechanisms, are discussed. In addition, the broad spectral coverage of this study reveals in the bleach recovery the rapid cooling of the solvent surrounding the re-formed iodide after geminate recombination of the iodine with the solvated electron.

Soda Pulping of Hardwoods Catalyzed by Anthraquinone and Methyl Substituted Anthraquinones

Black liquor gasification (BLG) as well as the recovery of lignin and other organic compounds from pulping black liquor would be aided if an efficient sulfur‐free pulping process could be developed. This has provided new impetus for research on soda pulping with redox catalysts instead of sodium sulfide that is presently used in the kraft process. Soda/anthraquinone (AQ) pulping afforded white birch (Betula papyrifera) and sugar maple (Acer saccharum) pulps with equal if not superior strength to kraft pulps. However, the delignification rate was significantly lower for soda/AQ pulping. When AQ was replaced by 2‐methylanthraquinone (2‐MAQ) a delignification rate only slightly lower than that of kraft pulping was obtained at the same effective alkali (EA). At a kappa number of ∼20, a soda/2‐MAQ pulp was produced from sugar maple at a higher yield (1.2% on chips) than for a kraft pulp. 2‐MAQ was synthesized, as a powder, at 75% yield using an AlCl3–mediated Friedel‐Crafts reaction that is one of the methods used for commercial production of AQ.

Intracellular calcium mobilization: A key step for chitosan-induced anthraquinone production in Rubia tinctorum L.

Elicitation with chitosan (200 mg/l) significantly stimulates (∼100%) anthraquinone (Aq) synthesis in Rubia tinctorum L. cultures, but the mechanism of elicitation is largely unknown. We recently showed that the effects of the elicitor involve phospholipase C (PLC), protein kinase C (PKC), phosphoinositide 3-kinase (PI3K) and mitogen activated protein kinase (MAPK) cascades. Here, we show that the elicitor action on Aq production can be blocked with the intracellular Ca 2+ chelator BAPTA-AM but not in a Ca 2+-free medium (+EGTA) or in the presence of the voltage-dependent Ca 2+ channel antagonists verapamil and nifedipine. In agreement with these observations, spectrofluorimetric measurements in Fura 2-loaded R. tinctorum cells show that chitosan increases intracellular Ca 2+ concentration in a medium devoid of calcium. Short treatment intervals (1–5 min) of cells with the elicitor significantly increased DAG and IP 3 formation. Moreover, the PI-PLC inhibitors neomycin and U73122 diminished to a great extent chitosan-induced Aq synthesis. Blockers of Ca 2+ release from inner stores such as 2-APB, TMB-8, caffeine, ruthenium red and dantrolene inhibited elicitation. Chitosan rapidly stimulated (phosphorylated) MAPK. This effect was significantly decreased by the calcium modulators used above. However, EGTA did not prevent activation of MAPK. Compound LY24009, a blocker of PI3K, inhibited MAPK phosphorylation by chitosan. Accordingly, an increase in PI3K activity was observed in parallel. The results of this study show that chitosan induction of anthraquinone synthesis in R. tinctorum involves the stimulation of PLC, intracellular Ca 2+ mobilization and PI3K, which mediate MAPK activation.

Photoproduction of hydrated electron from constituents of natural waters.

The wavelength dependence for the photoproduction of the hydrated electron (e-(aq)) from various humic and fulvic acids and from natural waters was determined, employing a method that converts e-(aq) to a methyl radical that is detected fluorimetrically as the O-methylhydroxylamine of a stable nitroxide. Quantum yields for e-(aq) production from potassium ferrocyanide and N,N-dimethylaniline are in agreement with previously reported values. The quantum yields for production of e-(aq) from colored dissolved organic matter (CDOM) decrease precipitously with increasing wavelength with the rate of decline increasing in the order: humic acid < fulvic acid < natural water in the UV-B region. For Suwannee River fulvic acid, quantum yields ranged from 7.9 x 10(-6) at 366 nm to 1.9 x 10(-4) at 296 nm indicating that previously reported values for e-(aq) production from CDOM involving laser sources of irradiation are high due to experimental artifact. Apparent natural water quantum yields at 296 nm are higher than those for humic substances, ranging from 9.4 x 10(-5) to 3.7 x 10(-3) depending on location. The highly absorbing waters of the Delaware and Chesapeake Bays show insignificant production of e-(aq). These results indicate that the hydrated electron, through its reaction with dioxygen, is not a significant source of hydrogen peroxide in many natural waters and that humic substances may not be the principal source of e-(aq) production.

Photoinduced reductive dissolution of .alpha.-iron oxide (.alpha.-Fe2O3) by bisulfite

The kinetics of the photoinduced reductive dissolution of ɑ-Fe_2O_3 by bisulfite in anoxic colloidal suspensions have been investigated. Quantum yields, Φ_(Fe(II)), as a function of wavelength for Fe(II)_(aq) production were obtained. Photochemical reactivity has been discussed in terms of the excitation of the O^(2-) to Fe^(3+) charge-transfer band of α-Fe_2O_3 and in terms of photoassisted charge-transfer reactions of Fe(III)-S(IV) surficial complexes.

The problem of radial excitations of light mesons

Strong decays of the ground and radial-excited (L=0) states of light mesons are calculated within a relativistic (Lorentz-contraction-modified) version of the model of spontaneous production of aq\(\bar q\)-pair from vacuum.