NO3 Radicals Research Articles

Antiproliferative Activities of Lipophililic Fluoroquinolones- Based Scaffold Against a Panel of Solid and Liquid Cancer Cell Lines

Objectives:In this work, 9 lipophilic-acid chelating FQs (fluoroquinolones) comprising chelating groups have been prepared, characterized and screened for in vitro cytotoxicity, radical scavenging and antiinflammation propensities.Methods:Using sulforhodamine B colorimetric bioassay vs. cisplatin; FQs-inflicted reductions’ of viability against breast T47D and MCF7, Pancreatic PANC-1, colorectal HT29, HCT116, SW620, CACO2, SW480 and Leukaemia K562 cancer cell lines were examined in quadruplicates/dose/cell line. Parameters including potency, toxicity, and selectivity (potency/toxicity) have been reported along with DPPH- and NO- radicals’ scavenging capacities -as their molecular action mechanism- in comparison to ascorbic acid and indomethacin respectively. Using Griess assay in Lipopolysaccharide (LPS) prompted RAW264.7 macrophages; mitigation of inflammation was investigated. Results:nitroFQ 3b, unlike the rest of FQs in PANC1 and MCF7 cells, exhibited remarkably superior NO-radical scavenging/antiinflammation capacity to indomethacin with respective antiproliferative IC50 values (<50µM) 49 vs. cisplatin’s 122 and 6 vs. cisplatin’s 28 (p<0.01-0.001; n=4). Reduced FQ 4b of significantly dual DPPH-NO scavenging propensities exerted exceptionally substantial micromolar antiproliferation in colorectal cancer cells with respective antiproliferative IC50 values (<50µM) of HCT116 0.84< HT29 1.6<PANC1 5.7<SW620 9.2 vs. cisplatins’, (p<0.01-0.001; n=4). FQ 5a of superb NO radical reduction effect had antiproliferative IC50 value (<50µM) of 37.6 in PANC1 cells. In breast cancer T47D the ascending order of pronounced nano-micromolar antiproliferative IC50 values (<50µM) was 4d<3d<4a<4b<3b (0.009<0.59<10<15<41 vs. cisplatins’, p<0.01-0.001; n=4). Both 4d and 4b displayed both DPPH-NO radicals reduction –related cytotoxicities. NO radical scavengers 3d and 3b as well as DPPH radical scavenger 4a exerted highly appreciably relevant antineoplastic affinities. Conclusion:Acidic groups and C8-C7 ethylene diamine Chelation Bridge along with bulky dual halogenations can be substantially associated with molecular action mechanisms of FQs cytotoxicities, antioxidative and antiinflammation effects, collectively.

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This study investigated the radicals scavenging and erythrocyte membrane stabilizing properties of stem bark of A. altilis and leaf of S. alata. The plants were macerated in 80% EtOH/H2O at room temperature, evaporated under reduced pressure, lyophilized and partitioned to obtain n-hexane, DCM, EtOAc, n-BuOH and aqueous fractions respectively. In vitro radical scavenging and erythrocyte membrane stabilizing activities of extracts and fractions were carried out using colorimetric assay and hypotonicity and heat-induced haemolysis methods respectively. The results showed concentration-dependent radical scavenging activities. The EtOAc fractions of A. altilis and S. alata with IC50 values 0.68±0.07 and 1.55±0.38 mg/mL exhibited good NO radical scavenging properties and IC50 values of 0.25±0.05 and 0.49±0.13 mg/mL anti-lipid peroxidation activities, while the EtOAc and DCM fractions of A. altilis with IC50 2.22±0.05 and 3.67±0.19 mg/mL OH radical scavenging activities. The crude extracts, DCM and EtOAc fractions of both plants exhibited good protective activity on erythrocyte membrane in a dose-dependent manner compared with diclofenac. The results justify the ethnomedicinal use of the plants in polyhedral formulations for the management of oxidative stress-induced diseases.

Computational study of the reaction of C3H3 with HNCO and the decomposition of C4H4NO radicals

AbstractAb initio CCSD(T)/CBS(T,Q,5)//M06‐2X/aug‐cc‐pVTZ calculations have been applied to figure out the C4H4NO (isopropyl aminocarbonyl) potential energy surface (PES). The resulting energetics and molecular parameters of all species involved in the system have been then employed in the TST and RRKM/ME computations of temperature‐ and pressure‐dependent rate coefficients and product yields. The calculated results show that rate constants of the abstraction reactions C3H3 + HNCO → C3H4 + NCO are pressure‐independent while those of the addition reactions C3H3 + HNCO and the C4H4NO decomposition reactions were found to be pressure‐dependent. The calculated enthalpies of formation for species involved in the system are in good ageement with the available literature data. All the results of this work may provide a useful database source for the further study of this kind of reactions.

Phytochemicals and antioxidant potential of ginger (Zingiber officinale) and garlic (Allium sativum) extracts

Matured fresh root of Ginger (Zingiber officinale R.) and bulb of Garlic (Allium sativum L.) and their binary mixture were evaluated for phytochemicals and antioxidant potential using standard methods. The results of preliminary phytochemical screening of aqueous and ethanol extract of Ginger and Garlic showed the presence of some phytochemicals such as tannin, saponin, flavonoids, alkaloids, terpenoids, steroids and glycosides at various levels. The antioxidant activities of aqueous and ethanol extracts of ginger and garlic showed a total phenolic content mg/g of Ginger (6.432 and 14.176) Garlic (7.172 and 2.146), DPPH content Ginger (58.817 and 86.915) % Garlic (37.582 and 26.451), OH radicals ginger (85.358 and 87.694) garlic (83.956 and 79.751), Fe2+ chelation of ginger (4.584 and 43.444) garlic (7.961 and 53.984), NO radicals of ginger (74.894 and 12.658) garlic (58.966 and 86.392). However the antioxidant contents of the binary mixture of both aqueous and ethanol extracts of ginger and garlic (70:30) showed increased in all antioxidant properties. These implies that both aqueous and ethanol extracts of ginger and garlic possessed good phytochemicals and antioxidant potential which indicates that consumption of these two spices either separately or as a mixture could be encouraged especially for those suffering from any form of cardiovascular diseases.

A quantitative structure activity relationship (QSAR) model for predicting the rate constant of the reaction between VOCs and NO3 radicals

NO3 radical is one of the important oxidants used for the chemical degradation of Volatile organic compounds (VOCs). Thus, the derivation of rate constant (kNO3) is critical to understand the removal kinetics of VOCs. To better estimate the kNO3, a quantitative structure activity relationship (QSAR) model was established using the kNO3 of 189 VOCs and quantum chemical parameters. The optimal QSAR model can predict the kNO3 with its R2, q2, and Qext2 being 0.880, 0.872, and 0.861, respectively. The QSAR analysis results indicate that the energy of the highest occupied molecular orbital (EHOMO) and the maximum value of electrophilic Fukui index (f(−)x) are two intrinsic factors determining the kNO3. Additionally, the analysis of the correlation between kNO3 values and quantum chemical parameters shows that the gap energy between LUMO and HOMO (EGAP), the minimum value of free radical Fukui index (f (0)n), and the maximum value of bond order (BOx) also significantly affect kNO3. The validations of the optimal QSAR model confirm the high realizability, stability and accuracy, and the wide applicability of the derived model for predicting kNO3.

Barrier effect and wound healing activity of the medical device REF-FTP78 in the treatment of gastroesophageal reflux disease

REF-FTP78 is a class IIb medical device present on the market with different trade names and developed for the treatment of gastroesophageal reflux disease (GERD). This medical device is based on polysaccharides from Aloe Barbadensis and fucoidans from brown seaweeds, such as Undaria pinnatifida and Fucus vesiculosus, and aims to exert a protective effect on the esophageal mucosa against the noxious components of refluxate. The present study reports on the efficacy of REF-FTP78 devoting a particular attention to the barrier effect and wound healing properties, combined with antioxidant and anti-inflammatory activities. Film-forming properties and barrier effect were investigated on in vitro reconstructed human esophageal epithelium, through TEER measurement and evaluation of caffeine and Lucifer yellow permeability, and in an ex vivo swine model of esophageal mucosa damage. Antioxidant and anti-inflammatory properties were evaluated in terms of scavenging activity towards DPPH, ABTS and NO radicals and a wound healing assay was carried out to study the influence of the product on cell migration. The obtained results highlighted a significant barrier effect, with a reduction in caffeine penetration equal to 65.3%, the ability to both repair and prevent the damage caused by an acid insult, confirmed by a good transepithelial resistance for the tissue treated with the tested item, and the capacity to promote wound healing. Furthermore, the tested product showed good antioxidant and anti-inflammatory properties in the performed radical scavenging assays. These findings support the use of REF-FTP78 in the treatment of GERD.

The Effect of Land Use Classification on the Gas‐Phase and Particle Composition of the Troposphere: Tree Species Versus Forest Type Information

AbstractRelationships between vegetation and air quality are intricate and still not fully understood. For regional air quality assessments, a better understanding of the diverse feedback mechanisms is crucial. The present article investigates the impact of land use data set detailedness on air quality predictions. Therefore, two different land use data sets were applied for simulations with COSMO‐MUSCAT for Germany in May 2014. One data set includes detailed information about tree species while the second one obtains generalized widely applied land use classes including mixed and coniferous forests. Moreover, we examined the role of agricultural NO soil emissions, agricultural biomass density enhancements, and model resolution. For a more comprehensive implementation of the secondary organic aerosol (SOA) formation, the SOA module was extended considering additional biogenic volatile organic compound (BVOC) precursor groups from isoprene, α‐pinene, limonene, and sesquiterpene oxidations. The model studies showed substantial differences in BVOC emission patterns between the two land use data sets. The application of detailed tree species information leads to complex BVOC emission patterns with high emission spots. In contrast, coarser forest information lead to standardized comprehensive emissions which result in 50% higher BVOC emissions. These differences affect both the atmospheric oxidizing potential and the production rates of SOA precursors. Land use induced regional differences (tree species minus forest information) in NOx (±2.5%), ozone (−2.5%), OH (±50%), NO3 radical (+70%) concentrations, and SOA (−60%) mass are modeled. Overall, the simulations demonstrate that detailed land use information, extended organic chemistry treatment, and high spatial resolution are mandatory for air quality assessments.

Bioactive phenolic compounds and organic acids in the decoction of fruits and leaves of Schinus areiraL

Leaf and fruit decoctions of Schinus areiraL. from northwest Argentina were investigated here. Phenolic compounds and organic acids were analyzed by HPLC. Antioxidant capacity and α-glucosidase inhibition were determined by using in vitrotests. The general toxicity was assessed against Artemia salinanauplii. Hyperoside and 3 O-caffeoylquinic acid in leaf decoctions; gallic acid and catechin in fruit decoction were the major phenolic compounds. Malic and citric acids were the main organic acid quantified in the leaf and fruit decoctions, respectively. Fruit decoction had a relatively important content of shikimic acid, precursor of Tamiflu. Leaf decoction presents a greater richness in bioactive compounds with antiradical activity against DPPH●, O2●-and ●NO radicals. S. areiraleaves and fruits had α-glucosidase inhibitory activity comparable to hyperoside and acarbose. Fruit decoction was not eco-toxic; leaf decoction showed significant eco-toxic activity and could be chosen for the search of other bioactive compounds with pharmacological activity.

Glory scattering in deeply inelastic molecular collisions.

For molecular collisions, the deflection of a molecule's trajectory provides one of the most sensitive probes of the interaction potential and there are general rules of thumb that relate the direction of deflection to precollision conditions. Following intuition, forward scattering results from glancing collisions, whereas near head-on collisions result in back scattering. Here we present the observation of forward scattering in inelastic processes that defies this common wisdom. For deeply inelastic collisions between NO radicals and CO or HD molecules, we observed forward scattering in fully resolved pair-correlated differential cross-sections, despite the low impact parameters that are needed to induce a sufficient energy transfer. We rationalized these findings by extending the textbook model of hard-sphere scattering-taking inelastic energy transfer into account-and attribute the forward scattering to glory-type trajectories caused by attractive forces. This phenomenon, which we refer to as hard-collision glory scattering, is predicted to be ubiquitous. We derive under which conditions hard-collision glory scattering occurs and retrospectively identify such behaviour in previously studied systems.

Emission of volatile organic compounds by plants on the floor of boreal and mid-latitude forests

The forests of the boreal and mid-latitude zones of the Northern Hemisphere are the largest source of reactive volatile organic compounds (VOCs), which have an important impact on the processes occurring in the atmospheric boundary layer. However, the composition of biogenic emissions from them remains incompletely characterized, as evidenced by the significant excess OH radical concentrations predicted by models in comparison with those observed under the forest canopy. The missing OH sink in the models may be related to the fact that they do not take into account the emission of highly reactive VOCs by vegetation on the forest floor. In this work, we report the results of laboratory determinations of the composition of VOCs emitted by representatives of different groups of plants that form the living soil cover (LSC) in the forests of the boreal and mid-latitude zones: bryophytes, small shrubs, herbaceous plants, and ferns. In the chromatograms of volatile emissions of all 11 studied plant species, 254 compounds with carbon atoms ranging in number from two to 20 were registered. All plants were characterized by the emission of terpenes, accounting for 112 compounds, and the second largest group (35 substances) was formed by carbonyl compounds. Both groups of compounds are characterized by high reactivity and are easily included in the processes of gas-phase oxidation with the participation of radicals HO, NO3 and ozone. These data indicate the importance of a thorough study of the so far disregarded source of VOCs, that is, the LSC in forests.

Mechanism of thermolysis of hydrazino-dinitroethylenes

Promising energetic materials – 1,1-diamino-2,2-dinitroethylene (DADNE) derivatives, in which one or two hydrogen atoms are replaced by –NH2 group, were studied by quantum-chemical calculations using hybrid functional PBE0 with cc-pVDZ basis set and coupled cluster method CCSD with aug-cc-pVDZ basis set. A number of thermolysis primary steps were investigated and it was shown that the addition of –NH2 group leads to a change in the mechanism of rate-limiting step. The main channels for DADNE are transfer of hydrogen to carbon and various transformations of aci-forms; for hydrazino derivatives hydrogen transfer to carbon is the only main channel and the following transformations are NO2 radical separation and transfer of another one hydrogen atom to an oxygen and elimination of HNO2 molecule.

Single and sequential double ionization of NO radical in intense laser fields.

We examine the dependences of the single and double ionization probabilities of NO radical on the angle between the NO axis and the laser polarization direction in an intense laser field (790nm, 100fs, 1-10 × 1014 W/cm2) and show that the double ionization is enhanced when the NO axis is parallel to the laser polarization direction. We reveal that the angular dependence of the sequential double ionization probability is determined by the shape of the 5σ orbital of NO+ from which the second photoelectron is emitted in the ionization from NO+ to NO2+. We also reveal that the fast oscillation in the probability of the tunnel ionization of NO originating from a coherent superposition of the two spin-orbit components in the electronic ground X2Π state is described well based on the molecular Ammosov-Delone-Krainov (MO-ADK) theory in which the time evolution of the electron density distribution of the 2π orbital is taken into account.

Comparative Antioxidant, Anti-Acetylcholinesterase and Anti-α-Glucosidase Activities of Mediterranean Salvia Species.

Salvia species have a cosmopolitan distribution and comprise several well-known plants valuable for pharmaceutical and food industries due to their recognized medicinal, food flavouring, and preservative properties. The present study aimed to evaluate and compare the biological activities of seven wild-growing Salvia species from the Mediterranean area (S. fruticosa, S. glutinosa, S. nemorosa, S. officinalis, S. pratensis, S. sclarea, S. verticillata). All studied ethanolic leaf extracts exhibited significant DPPH and NO radical scavenging ability, lipid peroxidation inhibition, and reducing power, as well as moderate iron-chelating properties. Together with S. officinalis and S. fruticosa, S. verticillata showed anti-acetylcholinesterase activity, while S. glutinosa was also found to possess the ability to inhibit α-glucosidase. Total flavonoid (0.37–0.90%), phenolic acid (3.55–12.44%), tannin (1.22–2.60%), and anthocyanin contents (0.03–0.08%) were determined in Salvia leaves. Rosmarinic acid was the predominant hydroxycinnamic acid in all studied sage plants, ranging from 9400 to 38,800 μg/g. The correlation study showed a strong relationship between biological activities and contents of total phenolic acids, total tannins, and rosmarinic acid, indicating their significant contribution to the efficiency of tested Salvia species. Our results highlighted Mediterranean sage plants as rich sources of potent antioxidant, neuroprotective, and hypoglycemic agents which are worthy of further research.

Analysis of emissions-driven changes in the oxidation capacity of the atmosphere in Europe

Anthropogenic emissions in Europe have been gradually reduced thanks to a combination of factors, including restrictive regulation and policy implementation, fuel switching, technological developments, and improved energy efficiencies. Many measures have been specifically introduced to meet the annual and hourly limit value of NO2 for the protection of human health, mainly targeting traffic emissions. Due to NOX reduction policies in Europe, NO2 levels have generally declined, but O3 concentrations have been found to increase. This phenomenon would cause changes in the oxidant capacity of the atmosphere, altering the concentration of tropospheric oxidants in urban areas.The Community Multiscale Air Quality (CMAQ) modelling system has been used to study concentration changes of NO2, O3 and the main radicals in Europe between 2007 and 2015 for two months representatives of winter and summer conditions (January and July). In addition to describing the general situation in Europe, variations in pollutants along with NOX emission changes over 67 large European cities have been analysed by means of statistical methods.NOX emissions and NO2 concentrations decreased in both seasons during the period in all the selected cities. In most of them O3 concentrations increased in winter but decreased in summer. The concentration of the OH radical, the main oxidant during the daytime, shows an increase in winter. This is also the case for the main cities in summer although we found a general decrease in continent for this season. The NO3 radical, the main night-time oxidant, was found to increase in winter and decrease in summer. HNO3 shows a concentration decline in both seasons. The studied cities are classified in five groups by means of k-mean clustering procedure. We identified five groups with specific patterns, suggesting that the oxidant capacity of the European urban atmospheres has reacted differently to NOX emission abatement policies.

Mass spectrometry based fragmentation patterns of nitrosamine compounds.

Nitrosamines are a class of mutagenic substances that can display high carcinogenic potential. New chemical entities may have the potential to form unique nitrosamines specific to the drug substance. It is therefore essential to understand the gas-phase fragmentation behavior of nitrosamine compounds to enable the development of analytical methods to characterize novel nitrosamine compounds. The gas-phase fragmentation behavior of eight model nitrosamine compounds representing the common substructures seen in many small molecule pharmaceutical compounds was studied with positive electrospray ionization tandem mass spectrometry (ESI-MS/MS). The fragmentation patterns of these compounds under various collision parameters available in commercially available mass spectrometers were studied. Protonated nitrosamine compounds produced diagnostic fragment ions upon MS/MS. Three primary structure-dependent fragmentation pathways were observed. The first pathway involves the loss of 30 Da which corresponds to the loss of the NO radical from the protonated nitrosamine compound (Group 1). The second and third fragmentation pathways, which have not been reported for nitrosamine compounds, proceed via the loss of H2 O from the protonated nitrosamine compound (Group 2), and elimination and a loss of 46 Da (loss of NH2 NO) from the nitrosamine compound (Group 3). Results presented in this work provide an overview of the gas-phase fragmentation patterns of nitrosamine compounds and may be useful in identifying novel nitrosamine compounds in complex matrices.

Atmospheric Reactivity of Methoxyphenols: A Review

Methoxyphenols emitted from lignin pyrolysis are widely used as potential tracers for biomass burning, especially for wood burning. In the past ten years, their atmospheric reactivity has attracted increasing attention from the academic community. Thus, this work provides an extensive review of the atmospheric reactivity of methoxyphenols, including their gas-phase, particle-phase, and aqueous-phase reactions, as well as secondary organic aerosol (SOA) formation. Emphasis was placed on kinetics, mechanisms, and SOA formation. The reactions of methoxyphenols with OH and NO3 radicals were the predominant degradation pathways, which also had significant SOA formation potentials. The reaction mechanism of methoxyphenols with O3 is the cycloaddition of O3 to the benzene ring or unsaturated C═C bond, while H-abstraction and radical adduct formation are the main degradation channels of methoxyphenols by OH and NO3 radicals. Based on the published studies, knowledge gaps were pointed out. Future studies including experimental simulations and theoretical calculations of other representative kinds of methoxyphenols should be systematically carried out under complex pollution conditions. In addition, the ecotoxicity of their degradation products and their contribution to SOA formation from the atmospheric aging of biomass-burning plumes should be seriously assessed.

Aryl Hydrocarbon Receptor Activation by Benzo[a]pyrene Prevents Development of Septic Shock and Fatal Outcome in a Mouse Model of Systemic Salmonella enterica Infection.

This study focused on immunomodulatory effects of aryl hydrocarbon receptor (AhR) activation through benzo[a]pyrene (BaP) during systemic bacterial infection. Using a well-established mouse model of systemic Salmonella enterica (S.E.) infection, we studied the influence of BaP on the cellular and humoral immune response and the outcome of disease. BaP exposure significantly reduced mortality, which is mainly caused by septic shock. Surprisingly, the bacterial burden in BaP-exposed surviving mice was significantly higher compared to non-exposed mice. During the early phase of infection (days 1–3 post-infection (p.i.)), the transcription of proinflammatory factors (i.e., IL-12, IFN-γ, TNF-α, IL-1β, IL-6, IL-18) was induced faster under BaP exposure. Moreover, BaP supported the activity of antigen-presenting cells (i.e., CD64 (FcγRI), MHC II, NO radicals, phagocytosis) at the site of infection. However, early in infection, the anti-inflammatory cytokines IL-10 and IL-22 were also locally and systemically upregulated in BaP-exposed S.E.-infected mice. BaP-exposure resulted in long-term persistence of salmonellae up to day 90 p.i., which was accompanied by significantly elevated S.E.-specific antibody responses (i.e., IgG1, IgG2c). In summary, these data suggest that BaP-induced AhR activation is capable of preventing a fatal outcome of systemic S.E. infection, but may result in long-term bacterial persistence, which, in turn, may support the development of chronic inflammation.

Infrared spectroscopy of difference and combination bands of the NO3 radical and anharmonicity analysis

The 2ν3-ν4 difference bands of 14NO3 and 15NO3 have been observed in the 1643.6 cm−1 and 1622.0 cm−1 region, respectively, and analyzed to determine molecular constants in the v3 = 2 state. The present paper also reports re-analysis of high-resolution spectra of the 15NO3 radical from 2000 to 2500 cm−1, which have been reported previously without vibrational assignments [J. Phys. Chem. A 114(2010), 980]. Three bands at 2004, 2128, and 2492 cm−1 are analyzed as the ν1 + ν3, 2ν3, and ν1 + ν3 + ν4 bands, including perturbations from nearby states. All vibrational states of 14NO3 and 15NO3 so far observed by infrared spectroscopy and laser induced fluorescence (LIF) are analyzed by using a vibrational energy matrix including cubic and quartic anhamonic effects, to determine anharmonicity constants and eigenvector coefficients. The first-order Coriolis coupling constants Cζ and the effective spin–orbit interaction constants aeff are calculated by using the eigenvector coefficients and compared with the observed values.

Atmospheric oxidation capacity and ozone pollution mechanism in a coastal city of southeastern China: analysis of a typical photochemical episode by an observation-based model

Abstract. A typical multi-day ozone (O3) pollution event was chosen to explore the atmospheric oxidation capacity (AOC), OH reactivity, radical chemistry, and O3 pollution mechanism in a coastal city of southeastern China, with an observation-based model coupled to the Master Chemical Mechanism (OBM-MCM). The hydroxyl radical (OH) was the predominant oxidant (90 ± 25 %) for daytime AOC, while the NO3 radical played an important role in AOC during the nighttime (72 ± 9 %). Oxygenated volatile organic compounds (OVOCs; 30 ± 8 %), NO2 (29 ± 8 %), and CO (25 ± 5 %) were the dominant contributors to OH reactivity, accelerating the production of O3 and recycling of ROx radicals (ROx = OH + HO2 + RO2). Photolysis of nitrous acid (HONO, 33 ± 14 %), O3 (25 ± 13 %), formaldehyde (HCHO, 20 ± 5 %), and other OVOCs (17 ± 2 %) was a major ROx source, which played an initiation role in atmospheric oxidation processes. Combined with regional transport analysis, the reasons for this O3 episode were the accumulation of local photochemical production and regional transport. The results of sensitivity analysis showed that volatile organic compounds (VOCs) were the limiting factor of radical recycling and O3 formation, and the 5 % reduction of O3 would be achieved by decreasing 20 % anthropogenic VOCs. Controlling emissions of aromatics, alkenes, and alkanes with ≥4 carbons was beneficial for ozone pollution mitigation. The findings of this study provide significant guidance for emission reduction and regional collaboration for future photochemical pollution control in the relatively clean coastal cities of China and similar countries.

SO2-enhanced nitrate photolysis on TiO2 minerals: A vital role of photochemically reactive holes

In this study, we investigated the nitrate photolysis on photoactive TiO2 particles in the presence of SO2 through theoretic DFT calculation and in situ DRIFTS analysis, and found that in a clean atmosphere nitrate was oxidized to •NO3 radicals by the holes generated on the surface of TiO2 under solar irradiation, followed reactive nitrogen species generation via •NO3 radicals reduction by photoinduced electrons. After shifting to the SO2-polluted environment, •NO3 radicals preferentially reacted with abundant sulfites to significantly increase nitrogen species formation, the online measured concentrations of NOx and HONO increased by approximately 2-fold and 6-fold respectively in comparison with clean atmosphere. These results demonstrate that photogenerated holes play a key role in nitrate photolysis on photoactive mineral dusts with or without the coexistence of SO2, providing new insights into the source of NOx and HONO in complex air polluted areas during the daytime.