Carbonate Radical Anion Research Articles

Nature of Scapolite Color: Ab Initio Calculations, Spectroscopy, and Structural Study

The article describes the results of a comprehensive study of the extra-framework components of scapolites using quantum–chemical calculations, electronic and vibrational spectroscopy, and single-crystal X-ray diffraction and crystal structure refinement. The ab initio calculations were performed using an embedded-cluster approach of extra-framework components in various cation surroundings. As a result, through comparing the experimental and ab initio calculation results, the energies of the electronic and vibrational transitions of various extra-framework components (CO3)2−, (CO3)·−, S3·−, S2·−—as well as the role of these components in the process of the lowering of the symmetry—were determined for scapolites belonging to the marialite–meionite solid–solution series. The nature of the various colors of the scapolites has also been established. Colors from purple to blue are a result of the presence of radiation-induced pairs of defects: carbonate radical anions (CO3)·− and F-centers. However, polysulfide S3·− radical anions are found in some violet scapolites.

CO2 protects cells from iron-Fenton oxidative DNA damage in E. coli and humans.

Whereas hydroxyl radical is commonly named as the Fenton product responsible for DNA and RNA damage in cells, here we demonstrate that the cellular reaction generates carbonate radical anion due to physiological levels of bicarbonate. Analysis of the metabolome, transcriptome and, in human cells, the nuclear genome shows a consistent buffering of H2O2-induced oxidative stress leading to one common pathway, namely guanine oxidation. Particularly revealing are nanopore-based studies of direct RNA sequencing of cytosolic and mitochondrial ribosomal RNA along with glycosylase-dependent qPCR studies of oxidative DNA damage in telomeres. The focusing of oxidative modification on one pathway is consistent with the highly evolved base excision repair suite of enzymes and their involvement in gene regulation in response to oxidative stress.

Oxidation Chemistry of Bicarbonate and Peroxybicarbonate: Implications for Carbonate Management in Energy Storage.

Carbonate formation presents a major challenge to energy storage applications based on low-temperature CO2 electrolysis and recyclable metal-air batteries. While direct electrochemical oxidation of (bi)carbonate represents a straightforward route for carbonate management, knowledge of the feasibility and mechanisms of direct oxidation is presently lacking. Herein, we report the isolation and characterization of the bis(triphenylphosphine)iminium salts of bicarbonate and peroxybicarbonate, thus enabling the examination of their oxidation chemistry. Infrared spectroelectrochemistry combined with time-resolved infrared spectroscopy reveals that the photoinduced oxidation of HCO3- by an Ir(III) photoreagent results in the generation of the short-lived bicarbonate radical in less than 50 ns. The highly acidic bicarbonate radical undergoes proton transfer with HCO3- to furnish the carbonate radical anion and H2CO3, leading to the eventual release of CO2 and H2O, thus accounting for the appearance of H2O and CO2 in both electrochemical and photochemical oxidation experiments. The back reaction of the carbonate radical subsequently oxidizes the Ir(II) photoreagent, leading to carbonate. In the absence of this back reaction, dimerization of the carbonate radical provides entry into peroxybicarbonate, which we show undergoes facile oxidation to O2 and CO2. Together, the results reported identify tangible pathways for the design of catalysts for the management of carbonate in energy storage applications.

Overlooked Formation of Carbonate Radical Anions in the Oxidation of Iron(II) by Oxygen in the Presence of Bicarbonate

AbstractIron(II), (Fe(H2O)62+, (FeII) participates in many reactions of natural and biological importance. It is critically important to understand the rates and the mechanism of FeII oxidation by dissolved molecular oxygen, O2, under environmental conditions containing bicarbonate (HCO3−), which exists up to millimolar concentrations. In the absence and presence of HCO3−, the formation of reactive oxygen species (O2⋅−, H2O2, and HO⋅) in FeII oxidation by O2 has been suggested. In contrast, our study demonstrates for the first time the rapid generation of carbonate radical anions (CO3⋅−) in the oxidation of FeII by O2 in the presence of bicarbonate, HCO3−. The rate of the formation of CO3⋅− may be expressed as d[CO3⋅−]/dt=[FeII[[O2][HCO3−]2. The formation of reactive species was investigated using 1H nuclear magnetic resonance (1H NMR) and gas chromatographic techniques. The study presented herein provides new insights into the reaction mechanism of FeII oxidation by O2 in the presence of bicarbonate and highlights the importance of considering the formation of CO3⋅− in the geochemical cycling of iron and carbon.

Overlooked Formation of Carbonate Radical Anions in the Oxidation of Iron(II) by Oxygen in the Presence of Bicarbonate.

Iron(II), (Fe(H2 O)6 2+ , (FeII ) participates in many reactions of natural and biological importance. It is critically important to understand the rates and the mechanism of FeII oxidation by dissolved molecular oxygen, O2 , under environmental conditions containing bicarbonate (HCO3 - ), which exists up to millimolar concentrations. In the absence and presence of HCO3 - , the formation of reactive oxygen species (O2 ⋅- , H2 O2 , and HO⋅) in FeII oxidation by O2 has been suggested. In contrast, our study demonstrates for the first time the rapid generation of carbonate radical anions (CO3 ⋅- ) in the oxidation of FeII by O2 in the presence of bicarbonate, HCO3 - . The rate of the formation of CO3 ⋅- may be expressed as d[CO3 ⋅- ]/dt=[FeII [[O2 ][HCO3 - ]2 . The formation of reactive species was investigated using 1 H nuclear magnetic resonance (1 H NMR) and gas chromatographic techniques. The study presented herein provides new insights into the reaction mechanism of FeII oxidation by O2 in the presence of bicarbonate and highlights the importance of considering the formation of CO3 ⋅- in the geochemical cycling of iron and carbon.

Photocatalytic reforming of acetic acid into methane over platinized TiO2 mediated by carbonate radical anion

In this research, Pt-loaded TiO2 was prepared by photodeposition used for acetic acid photocatalytic reforming. CO2 was injected into an acetic acid solution for removing O2 and inducing the formation of CO32–. The production rate of CH4 were higher in a CO2 atmosphere than that in an Ar atmosphere (about 69%). According to electron spin resonance (ESR) analysis, more •CH3 radical was produced in CO2 atmosphere, suggesting that CO2 introduced in acetic acid solution can better promote acetic acid reforming to CH4. On the contrary, the production rate of H2 is higher under an Ar atmosphere than that under CO2, suggesting a peroxidation of acetic acid transferred to H2.

Theoretical and experimental evidences for the formation of carbonate anion radical (CO3−•) in the atmosphere

Troposphere is the lowest layer where the oxidation reactions responsible for the atmospheric self-purification of contaminants occur, which are initiated mostly by hydroxyl radicals (HO•). In this context, the objective of the present work was to carry out theoretical and experimental studies on the formation of the carbonate anion radical (CO3−•) in the atmosphere and evaluate the spontaneity of chemical reactions that occur at molecular. Experimental tests to evaluate the formation of CO3−• in the atmosphere were conducted using rainwater samples containing 5, 10, and 15 mg L−1 of sodium carbonate, and the addition of methylene blue dye was used to indicate the formation of the CO3−• by monitoring its degradation. Exposure of the samples to solar radiation led to a greater degradation of the dye in rainwater samples with higher concentrations of bicarbonate. The determination of the alkalinity of the samples revealed that the predominant chemical species in the medium was the bicarbonate anion and that the increase in its concentration promotes the formation of CO3−•. As a result of the simulation of the reactions with the radicals •OH, •OOH, and CO3−• at the level of theory MP2/6–311++G (2df,p), it was obtained that the formation of the radical CO3−• is possible (HO• + CO32− → HO− + CO3−• and HCO3− + HO• → H2O + CO3−•). The simulations were carried out in aqueous phase with implicit solvent, in the gas and showed the same trends. Furthermore, the reactions involving CO3−• with atmospheric molecules are spontaneous (ΔrG298 < 0) for electron-rich groups as H2S compounds, indicating that the radical CO3−• can react with some atmospheric molecules, and thus contribute to the atmospheric oxidation mechanisms.

Eggshell powder as an efficient recyclable catalyst generates H2O2 prompted radicals for selective oxidative mineralization of crystal violet dye at room temperature

Eggshell powder (ESP) was explored as a selective heterogeneous catalyst for oxidative degradation of crystal violet (CV) dye in aqueous media in presence of H2O2 at room temperature. Natural but throw-away material ESP as a carbonate (CO32−) source facilitated the formation of carbonate anion radicals in presence of H2O2. Carbonate anion radicals (CO3•−), though a weaker oxidant than ∙OH radical, efficiently served as a selective oxidant. Selective degradation of CV dye in aqueous solution was confirmed from the quenching experiments. Synergistic effects of both the radicals (CO3•− and ∙OH) in the dye degradation process was experimentally verified. At a dose of 10 g/L of ESP, 91% removal of CV (initial concentration: 10 mg/L) was achieved in 60 min. The reaction kinetics followed first order rate model. Intermediate products formed during CV degradation and the extent of mineralization were confirmed from MALDI-TOF-MS and TOC analysis, respectively. The turnover number (TON) and turnover frequency (TOF) were obtained as 2.45 × 10−6 mol per g and 6.81 × 10−10 mol per g per second. A promising reusability was achieved up to seven cycles. The ESP catalyst used in this study was characterized by SEM, FTIR, XRD, XPS, BET surface area analysis, UV–visible DRS, XRF, and pHZPC analyses. The present work offers a novel facile but selective route for CV degradation and opens up newer possibilities for eggshell waste utilization as catalyst.

Reaction of FeaqII with Peroxymonosulfate and Peroxydisulfate in the Presence of Bicarbonate: Formation of FeaqIV and Carbonate Radical Anions.

Many advanced oxidation processes (AOPs) use Fenton-like reactions to degrade organic pollutants by activating peroxymonosulfate (HSO5-, PMS) or peroxydisulfate (S2O82-, PDS) with Fe(H2O)62+ (FeaqII). This paper presents results on the kinetics and mechanisms of reactions between FeaqII and PMS or PDS in the absence and presence of bicarbonate (HCO3-) at different pH. In the absence of HCO3-, FeaqIV, rather than the commonly assumed SO4•-, is the dominant oxidizing species. Multianalytical methods verified the selective conversion of dimethyl sulfoxide (DMSO) and phenyl methyl sulfoxide (PMSO) to dimethyl sulfone (DMSO2) and phenyl methyl sulfone (PMSO2), respectively, confirming the generation of FeaqIV by the FeaqII-PMS/PDS systems without HCO3-. Significantly, in the presence of environmentally relevant concentrations of HCO3-, a carbonate radical anion (CO3•-) becomes the dominant reactive species as confirmed by the electron paramagnetic resonance (EPR) analysis. The new findings suggest that the mechanisms of the persulfate-based Fenton-like reactions in natural environments might differ remarkably from those obtained in ideal conditions. Using sulfonamide antibiotics (sulfamethoxazole (SMX) and sulfadimethoxine (SDM)) as model contaminants, our study further demonstrated the different reactivities of FeaqIV and CO3•- in the FeaqII-PMS/PDS systems. The results shed significant light on advancing the persulfate-based AOPs to oxidize pollutants in natural water.

Targeted Decomplexation of Metal Complexes for Efficient Metal Recovery by Ozone/Percarbonate

Traditional methods cannot efficiently recover Cu from Cu(II)-EDTA wastewater and encounter the formation of secondary contaminants. In this study, an ozone/percarbonate (O3/SPC) process was proposed to efficiently decomplex Cu(II)-EDTA and simultaneously recover Cu. The results demonstrate that the O3/SPC process achieves 100% recovery of Cu with the corresponding kobs value of 0.103 min-1 compared with the typical •OH-based O3/H2O2 process (81.2%, 0.042 min-1). The carbonate radical anion (CO3•-) is generated from the O3/SPC process and carries out the targeted attack of amino groups of Cu(II)-EDTA for decarboxylation and deamination processes, resulting in successive cleavage of Cu-O and Cu-N bonds. In comparison, the •OH-based O3/H2O2 process is predominantly responsible for the breakage of Cu-O bonds via decarboxylation and formic acid removal. Moreover, the released Cu(II) can be transformed into stable copper precipitates by employing an endogenous precipitant (CO32-), accompanied by toxic-free byproducts in the O3/SPC process. More importantly, the O3/SPC process exhibits excellent metal recovery in the treatment of real copper electroplating wastewater and other metal-EDTA complexes. This study provides a promising technology and opens a new avenue for the efficient decomplexation of metal-organic complexes with simultaneous recovery of valuable metal resources.

Simplified Multiple-Well Approach for the Master Equation Modeling of Blackbody Infrared Radiative Dissociation of Hydrated Carbonate Radical Anions.

Blackbody infrared radiative dissociation (BIRD) in a collision-free environment is a powerful method for the experimental determination of bond dissociation energies. In this work, we investigate temperature-dependent BIRD of CO3·-(H2O)1,2 at 250-330 K to determine water binding energies and assess the influence of multiple isomers on the dissociation kinetics. The ions are trapped in a Fourier-transform ion cyclotron resonance mass spectrometer, mass selected, and their BIRD kinetics are recorded at varying temperatures. Experimental BIRD rates as a function of temperature are fitted with rates obtained from master equation modeling (MEM), using the water binding energy as a fit parameter. MEM accounts for the absorption and emission of photons from black-body radiation, described with harmonic frequencies and infrared intensities from quantum chemical calculations. The dissociation rates as a function of internal energy are calculated by Rice-Ramsperger-Kassel-Marcus theory. Both single-well and multiple-well MEM approaches are used. Dissociation energies derived in this way from the experimental data are 56 ± 6 and 45 ± 3 kJ/mol for the first and second water molecules, respectively. They agree within error limits with the ones predicted by ab initio calculations done at the CCSD(T)/aug-cc-pVQZ//CCSD/aug-cc-pVDZ level of theory. We show that the multiple-well MEM approach described here yields superior results in systems with several low-lying minima, which is the typical situation for hydrated ions.

Cysteine Oxidation to Sulfenic Acid in APE1 Aids G-Quadruplex Binding While Compromising DNA Repair.

Apurinic/apyrimidinic endonuclease-1 (APE1) is a base excision repair (BER) enzyme that is also engaged in transcriptional regulation. Previous work demonstrated that the enzymatic stalling of APE1 on a promoter G-quadruplex (G4) recruits transcription factors during oxidative stress for gene regulation. Also, during oxidative stress, cysteine (Cys) oxidation is a post-translational modification (PTM) that can change a protein's function. The current study provides a quantitative survey of cysteine oxidation to sulfenic acid in APE1 and how this PTM at specific cysteine residues affects the function of APE1 toward the NEIL3 gene promoter G4 bearing an abasic site. Of the seven cysteine residues in APE1, five (C65, C93, C208, C296, and C310) were prone to carbonate radical anion oxidation to yield sulfenic acids that were identified and quantified by mass spectrometry. Accordingly, five Cys-to-serine (Ser) mutants of APE1 were prepared and found to have attenuated levels of endonuclease activity, depending on the position, while KD values generally decreased for G4 binding, indicating greater affinity. These data support the concept that cysteine oxidation to sulfenic acid can result in modified APE1 that enhances G4 binding at the expense of endonuclease activity during oxidative stress. Cysteine oxidation to sulfenic acid residues should be considered as one of the factors that may trigger a switch from base excision repair activity to transcriptional modulation by APE1.

Solvent Cage Concept for the Homolytic Fragmentation of the Peroxynitrite-CO2 Adduct, ONOOCO2.

The toxicity of peroxynitrite, ONOO-, is directed by carbon dioxide via the formation of the corresponding adduct, ONOOCO2-. Entity ONOOCO2- is believed to be a highly unstable compound that primarily decomposes to nitrate and carbon dioxide, but it also undergoes fractional homolysis to generate carbonate radical anion, CO3•-, and nitrogen dioxide, NO2•, in a so-called solvent (radical) cage reaction. Recently, Koppenol et al. reviewed their proposal that ONOOCO2- is a relatively long-lived intermediate, arguing that "the solvent cage as proposed is physically not realistic". To further address whether ONOOCO2- could be a long-lived species, bond dissociation enthalpies (BDE) were calculated by the composite reference method (SMD)W1BD. Anion ONOOCO2- can exist in two conformers, s-cis-gauche and s-trans-gauche with predicted gas-phase O-O BDEs of about 10.8 and 9.5 kcal mol-1, respectively. Therefore, both conformers should have very short lifetimes. The (SMD)W1BD method was also used to evaluate the thermodynamic parameters of interest, revealing that the homolytic decomposition of ONOOCO2- is the most reasonable pathway. Moreover, previously reported experimental chemically induced dynamic nuclear polarization data also support the intermediacy of the radical cage and the formation of products CO2 and NO3- at a total yield of about 70%. Because the solvent radical cage concept for the decay of ONOO- in the presence of CO2 is supported by a variety of spectrometric methods as well as by quantum chemical calculations at high levels of theory, it provides strong evidence against the "out-of-cage" construct. For clarification of the nature of the transient UV/vis absorption(s) between 600 and 700 nm, as observed by Koppenol et al., several experimental approaches are suggested.

UV/Sodium percarbonate for bisphenol A treatment in water: Impact of water quality parameters on the formation of reactive radicals

Reported herein is an investigation of the impact of water quality parameters on the formation of carbonate radical anion (CO3•−) and hydroxyl radical (HO•) in UV/sodium percarbonate (UV/SPC) system versus in UV/hydrogen peroxide (UV/H2O2) system for bisphenol A (BPA) degradation in water. Pathways of CO3•− oxidation of BPA were proposed in this study based on the evolution of direct transformation products of BPA. Observed in this study, the degradation of BPA in the UV/SPC system was slower than that in the UV/H2O2 system in the secondary effluents collected from a local wastewater treatment plant due to the significant impact of coexisting constituents in the matrices on the former system. Single water quality parameter (e.g., solution pH, common anion, or natural organic matter) affected radical formations and BPA degradation in the UV/SPC system in a way similar to that in the UV/H2O2 system. Namely, the rise of solution pH decreased the steady state concentration of HO• resulting in a decrease in the observed pseudo first-order rate constant of BPA (kobs). Chloride anion and sulfate anion played a negligible role over the examined concentrations; nitrate anion slightly suppressed the reaction at the concentration of 20 mM; bicarbonate anion decreased the steady state concentrations of both CO3•− and HO• exerting significant inhibition on BPA degradation. Different extents of HO• scavenging were observed for different types of natural organic matter in the order of fulvic acid > mixed NOM > humic acid. However, the impact was generally less pronounced on BPA degradation in the UV/SPC system than that in the UV/H2O2 system due to the existence of CO3•−. The results of this study provide new insights into the mechanism of CO3•− based oxidation and new scientific information regarding the impact of water quality parameters on BPA degradation in the sytems of UV/SPC and UV/H2O2 from the aspect of reactive radical formation, which have reference value for UV/SPC application in wastewater treatment.

DFT investigation on the carbonate radical formation in the system containing carbon dioxide and hydroxyl free radical

A density functional theory (DFT) study was performed to explore the reaction mechanisms of CO2-containing systems(CO2,HCO3−,H2CO3) with hydroxyl radical using UM06-2X/aug-cc-pVTZ for geometry optimization and UCCSD(T)-F12/cc-pVDZ-F12 for electronic energies, the effect of solvation is considered using the implicit solvent model with two explicit water molecule. The final transformation of hydroxyl radical into carbonate anion radical by reaction with CO2-containing system was studied. The energy barriers, Gibbs free energy, reaction enthalpy changes and reaction rate constants for reaction of CO2-containing systems by hydroxyl radical are calculated. The results show that the reaction of hydroxyl with HCO3− has the lowest energy barrier (5.6 kcal/mol) and maximum reaction rate constant (7.60 × 107dm3mol−1s−1). However, the reaction of hydroxyl radical with CO2 has the highest energy barrier (20.3 kcal/mol) and the minimum reaction rate constant (8.88 × 10−10 dm3mol−1s−1) respectively. The equilibrium constant and rate ratio were calculated by the concentration ratio and free energy of the two conformations of H2CO3 in aqueous solution. The results show that the cc conformation of carbonate has a little higher reaction energy barrier and a higher reaction rate than ct conformation. ∙HCO3 generated by the reaction of CO2 and H2CO3 with hydroxyl radical is further dissociated in aqueous solution to form carbonate radical anion. The calculated free energy of the dissociation process is −2.5 kcal/mol and pKa is −1.9, indicating that HCO3− is a strong acid. Therefore, hydroxyl radicals are spontaneously converted to carbonate radical anions in CO2-containing systems.

Lipid oxidation that is, and is not, inhibited by vitamin E: Consideration about physiological functions of vitamin E

Lipids are oxidized in vivo by multiple oxidizing species with different properties, some by regulated manner to produce physiological mediators, while others by random mechanisms to give detrimental products. Vitamin E plays an important role as a physiologically essential antioxidant to inhibit unregulated lipid peroxidation by scavenging lipid peroxyl radicals to break chain propagation independent of the type of free radicals which induce chain initiation. Kinetic data suggest that vitamin E does not act as an efficient scavenger of nitrogen dioxide radical, carbonate anion radical, and hypochlorite. The analysis of regio- and stereo-isomer distribution of the lipid oxidation products shows that, apart from lipid oxidation by CYP enzymes, the free radical-mediated lipid peroxidation is the major pathway of lipid oxidation taking place in humans. Compared with healthy subjects, the levels of racemic and trans,trans-hydro (pero)xyoctadecadienoates, specific biomarker of free radical lipid oxidation, are elevated in the plasma of patients including atherosclerosis and non-alcoholic fatty liver diseases. α-Tocopherol acts as a major antioxidant, while γ-tocopherol scavenges nitrogen dioxide radical, which induces lipid peroxidation, nitration of aromatic compounds and unsaturated fatty acids, and isomerization of cis-fatty acids to trans-fatty acids. It is essential to appreciate that the antioxidant effects of vitamin E depend on the nature of both oxidants and substrates being oxidized. Vitamin E, together with other antioxidants such as vitamin C, contributes to the inhibition of detrimental oxidation of biological molecules and thereby to the maintenance of human health and prevention of diseases.

Carbonate anion photolyzed by solar radiation or combined with peracetic acid to form reactive species for dye degradation

The carbonate anion radical (CO3•−) has a high oxidative capacity and is therefore used for the degradation of persistent environmental contaminants. In this sense, this work aimed to evaluate combinations to obtain this radical, such as Na2CO3 with solar radiation or peracetic acid (PAA), using the efficiency of the degradation of methylene blue as a parameter to evaluate the performance of the process. The combination of PAA + Na2CO3 showed the ability to degrade the dye without the presence of solar radiation, but with a low reaction speed. The dye degradation process involving PAA + Na2CO3 follows a first-order kinetic model. This behavior can be explained by the formation of singlet oxygen from the reaction between CH3COOO− and OH−. In photolyzed processes with solar radiation, the presence of CO32− was the main factor for the degradation of the dye; consequently, the reactants PAA and acetic acid, which have greater protonation capacity of the CO32− to HCO32− anion, reduced the degradation efficiency. The formation of CO3•− is spontaneous when the carbonate anion CO32− is in contact with the radicals •OH, CH3C(O)O• and CH3C(O)OO•. Another important behavior was the degradation of the dye in the Na2CO3 + solar radiation process due to the excitation of colored dissolved organic matter (CDOM) (dye) to CDOM* in the triplet state and subsequent formation of singlet oxygen.

A review on percarbonate-based advanced oxidation processes for remediation of organic compounds in water

Sodium percarbonate (SPC) is considered a potential alternative to liquid hydrogen peroxide (H2O2) in organic compounds contaminated water/soil remediation due to its regularly, transportable, economical, and eco-friendly features. The solid state of SPC makes it more suitable to remediate actual soil and water with a milder H2O2 release rate. Apart from its good oxidative capacity, alkaline SPC can simultaneously remediate acidized solution and soil to the neutral condition. Conventionally, percarbonate-based advanced oxidation process (P-AOPs) system proceed through the catalysis under ultraviolet ray, transition metal ions (i.e., Fe2+, Fe3+, and V4+), and nanoscale zero-valent metals (iron, zinc, copper, and nickel). The hydroxyl radical (•OH), superoxide radical (•O2−), and carbonate radical anion (•CO3−) generated from sodium percarbonate could attack the organic pollutant structure. In this review, we present the advances of P-AOPs in heterogeneous and homogeneous catalytic processes through a wide range of activation methods. This review aims to give an overview of the catalysis and application of P-AOPs for emerging contaminants degradation and act as a guideline of the field advances. Various activation methods of percarbonate are summarized, and the influence factors in the solution matrix such as pH, anions, and cations are thoroughly discussed. Moreover, this review helps to clarify the advantages and shortcomings of P-AOPs in current scientific progress and guide the future practical direction of P-AOPs in sustainable carbon catalysis and green chemistry.

Using sodium percarbonate to suppress vertically distributed filamentous cyanobacteria while maintaining the stability of microeukaryotic communities in drinking water reservoirs

The increasing frequency and intensity of blooms of toxin- and taste & odour-producing filamentous cyanobacteria in water sources is a growing global issue. Compared to the common spherical Microcystis genus, the removal of filamentous cyanobacteria is more difficult in drinking water treatment plants; hence, abatement and control of the occurrence and proliferation of harmful filamentous cyanobacteria within drinking water sources is important for water supply. In this study, the solid sodium percarbonate (SPC), Na2CO3·1.5H2O2, was used as an algaecide to eliminate the cyanobacteria distributed throughout the water column in the surface and bottom layer of a reservoir serving as a drinking water source. Results showed that although the oxidation capacity of SPC was higher in the surface water due to the higher light intensity than in the bottom water, 3.0 mg/L SPC can still suppress the harmful cyanobacteria in the bottom water after 36 h because the carbonate ion generated by SPC decomposition can act as an activator of H2O2 to generate many reactive oxygen species — including superoxide radicals, carbonate radical anions, and hydroxyl radicals — even in the light-limited environment. The obtained inactivation rates for the main cyanobacteria in this reservoir followed the order: Pseudanabaena limnetica > Raphidiopsis curvata > Cylindrospermopsis raciborskii. 3.0 mg/L SPC has a slight impact on microeukaryotic communities according to the 18S rRNA gene sequencing, while 6.0 mg/L SPC changed the composition of eukaryotic phytoplankton and zooplankton clearly. Eukaryotic co-occurrence networks showed that although the network of eukaryotic plankton in treated surface water was more compact and clustered, stability of microeukaryotes in the treated surface water was lower than for the treated bottom water, owing to the higher oxidation capacity of SPC in the surface water. The results above not only have important implications for full-scale control of harmful cyanobacteria in drinking water sources, especially filamentous cyanobacteria with vertical distributions, but also help to ensure the health and stability of the whole aquatic ecosystem.

Hydroxyl radical is a significant player in oxidative DNA damage in vivo.

Recent publications have suggested that oxidative DNA damage mediated by hydroxyl radical (˙OH) is unimportant in vivo, and that carbonate anion radical (CO3˙-) plays the key role. We examine these claims and summarize the evidence that ˙OH does play a key role as an important member of the reactive oxygen species (ROS) in vivo.