Photochemical Reactions Research Articles

Revealing the Influencing Factors of an Oxygenated Volatile Organic Compounds (OVOCs) Source Apportionment Model: A Case Study of a Dense Urban Agglomeration in the Winter

AbstractUnderstanding sources of oxygenated volatile organic compounds (OVOCs) in the atmosphere still has large uncertainties. In this study, an improved OVOC source apportionment model was developed by principal component analysis and multiple linear regression based on the online monitoring of nonmethane hydrocarbons (NMHCs) and OVOCs in a dense urban agglomeration in the winter. The modeled concentrations were in good agreement with the measured concentrations (R2 = 0.56–0.97). The concentrations of major OVOCs, except for 2‐methylacrolein, were greatly affected by anthropogenic sources (15.8%–76.8%) and secondary generation (0.0%–51.7%), while transport and natural sources contributed to 0.0%–26.8% and 0.0%–32.0%, respectively. The selection of isoprene as the natural tracer led to an underestimation of the OVOC species from primary emission and an overestimation from natural sources. In addition, photochemical reactions significantly reduced the simulation accuracy of the model for NMHCs in the afternoon, with the R2 of 0.60 ± 0.23, which was lower than the overall value of 0.82 ± 0.11. However, the R2 for OVOCs (0.83 ± 0.14) did not decrease significantly in the afternoon due to the compensation of secondary oxidation. Furthermore, the concentration gradient distribution of the species gradually changes from a normal distribution to an exponential normal distribution with a decrease in concentration, the accuracy of the model was influenced by the degree of matching between tracer and species concentration gradient as species concentration change. Developing models with additional tracers at different concentration levels may enhance the robustness of the OVOC source apportionment model without increasing its complexity.

Exposure to Ozone Downregulates Bcl-2 and Increases Executing Caspases-3 and -8 in the Hippocampus, Frontal Cortex, and Cerebellum of Rats.

Introduction Ozone (O3) is one of the most prevalent atmospheric pollutants, arising from a photochemical reaction between volatile organic compounds (VOC), nitrogen oxides (NOx), and sunlight.O3 triggers oxidative stress, resulting in lipid oxidation, inflammation, alterations in metabolic and cellular signaling, and potentially initiating cell death in vulnerable brain regions.Inflammation and oxidative stress are recognized for their ability to induce cell death, primarily through the apoptosis pathway, involving various proteins that participate in this process via two pathways: intrinsic and extrinsic. Objective This study aims to identify the expression of pro-apoptotic proteins and Bcl-2 in the frontal cortex, cerebellum, and hippocampus of rats exposed to O3 acutely. Methods Two groups of 20 Wistar rodents (250-300 g) were established. The control group (n=10) was exposed to unrestricted polluted air for 12 hours, while the experimental group (n=10) was exposed to 1 ppm of O3. After exposure, the animals were sacrificed for immunofluorescence and Western blot analysis. Using a t-test, the arbitrary units of pro-apoptotic proteins and Bcl-2 were compared between the two groups. Results Significant increases in caspase-8 and caspase-3 activation were found in the O3-exposedgroup compared to the control group, specifically in the frontal cortex, cerebellum, and hippocampus. Additionally, notable changes in Bcl-2 expression were observed in these brain regions. The TUNEL (terminal deoxynucleotidyl transferase dUTP nick end labeling) assay further indicated significant differences in immunopositivity between the groups in the same areas. However, intrinsic apoptotic proteins such as Bax, VDAC1, and cytochrome-c did not show significant differences between the groups within these structures. Western blotanalyses aligned with the immunofluorescence results, showing statistically significant concentrations of caspase-8 in the cerebellum, caspase-3 in the hippocampus, and Bcl-2 in the frontal cortex in the O3exposed group. Conversely, proteins like Bax, cytochrome-c, and VDAC1 did not exhibit significant differences in all analyzed structures. Conclusions This study demonstrates that acute exposure to 1 ppm of ozone can trigger neuronal apoptosis in the frontal cortex, hippocampus, and cerebellum of rats, primarily through the activation of the extrinsic apoptosis pathway via caspase-8 and caspase-3. Additionally, it causes a reduction in Bcl-2 expression, an essential antiapoptotic protein. Despite not observing the activation of intrinsic pathway proteins like BAX, VDAC, or cytochrome-c, the study suggests that chronic O3 exposure might promote cell death by activating this pathway, requiring further long-term research.

Design of polymeric carriers to enhance antimicrobial photodynamic inactivation

Mixed polymeric micelles are a promising tool for the design of nanocarriers with pharmaceutical properties. These micellar systems allow reversing numerous properties of lipophilic drugs. Particularly, when applied to transport photosensitizers (PSs), they give rise to a wide variety of nanophotosensitizers (nPSs). These compounds are used to inactivate numerous bacteria resistant to conventional antibiotics. This research proposes the development of new mixed micelles, with better properties than simple micelles, for the trapping of Neutral Red (NR) and its monobrominated derivative (NRBr). Based on the combination of Pluronic P-123 with Pluronic F-108, Pluronic L-61 and Tween 80, 15 binary micellar systems were obtained. These mixed micelles presented a single population of homogeneous particles, with a diameter less than 70 nm. Moreover, several mixed micelles show smaller CMC than the simple system. These properties are predictors of high micellar stability and good anti-dilution properties, favoring their drug delivery applications. For these reasons, were loaded with NR and NRBr, showing good encapsulation efficiency. The 30 new nPSs presented an adequate size for pharmaceutical use and markedly enhanced the photochemical reactivity of the free PSs. Many of the mixed micellar systems showed greater production of singlet oxygen than the simple micelles of Pluronic P-123. Furthermore, all micellar systems increased the chemical stability of NRBr, which degrades in pH 7.4 buffer solution. Finally, all nPSs presented greater phototoxic activity against methicillin-resistant Staphylococcus aureus than free PSs. The nPSs formed by P-123: F-108 (90:10) + NR, P-123: F-108 (90:10) + NRBr, P-123: L-61 (80:20) + NRBr and P −123: T80 (80:20) + NRBr caused greater photodynamic inactivation of the microorganism than simple P-123 micellar systems. These nPSs could be considered excellent candidates for application in the treatment of infections caused by bacteria resistant to antibiotics.

Sulfur Switches for Responsive Peptide Materials.

There is considerable recent interest in the synthesis and development of peptide-based materials as mimics of natural biological assemblies that utilize proteins and peptides to form organized structures and develop beneficial properties. Due to their potential compatibility with living organisms, synthetic peptide materials are also being developed for applications such as cell grafting, therapeutic delivery, and implantable diagnostic devices. One desirable feature for such applications is the ability to design materials that can respond to stimuli by changes in their structure or properties under biologically relevant conditions. Peptide and protein assemblies can respond to stimuli, such as changes in temperature, solution pH, ions present in media, or interactions with other biomacromolecules. An exciting area of emerging research is focused on how biology uses the chemistry of sulfur-containing amino acids as a means to regulate biological processes. These concepts have been utilized and expanded in recent years to enable the development of peptide materials with readily switchable properties.The incorporation of sulfur atoms in polypeptides, peptides, and proteins provides unique sites that can be used to alter the physical and biological properties of these materials. Sulfur-containing amino acid residues, most often cysteine and methionine, are able to undergo a variety of selective chemical and enzyme-mediated reactions, which can be broadly characterized as redox or alkylation processes. These reactions often proceed under physiologically relevant conditions, can be reversible, and are significant in that they can alter residue polarity as well as conformations of peptide chains. These sulfur-based reactions are able to switch molecular and macromolecular properties of peptides and proteins in living systems and recently have been applied to synthetic peptide materials. Naturally occurring "sulfur switches" can be reversible or irreversible and are often triggered by enzymatic activity. Sulfur switches in peptide materials can also be triggered in vitro using oxidation/reduction and alkylation as well as photochemical reactions. The application of sulfur switches to peptide materials has greatly expanded the scope of these switches due to the ability to readily incorporate a wide variety of noncanonical sulfur-containing synthetic amino acids.Sulfur switches have been shown to provide considerable potential to reversibly alter peptide material properties under mild physiologically relevant conditions. An important molecular feature of sulfur-containing amino acid residues was found to be the location of sulfur atoms in the side chains. The variation of sulfur atom positions from the backbone by single bond lengths was found to significantly affect polypeptide chain conformations upon oxidation-reduction or alkylation/dealkylation reactions. With the successful adaptation of sulfur switches to peptide materials, future studies can explore how these switches affect how these materials interact with biological systems. This Account provides an overview of the different types of sulfur switch reactions found in biology and their properties and the elaboration of these switches in synthetic systems with a focus on recent developments and applications of reversible sulfur switches in peptide materials.

Photopolymerization Pattern of New Methacrylate Cellulose Acetate Derivatives.

Polymeric photocrosslinked networks, of particular interest in the design of materials with targeted characteristics, can be easily prepared by grafting light-sensitive moieties, such as methacrylates, on polymeric chains and, after photochemical reactions, provide materials with multiple applications via photopolymerization. In this work, photopolymerizable urethane-methacrylate sequences were attached to free hydroxyl units of cellulose acetate chains in various proportions (functionalization degree from 5 to 100%) to study the properties of the resulting macromolecules and the influence of the cellulosic material structure on the double bond conversion degree. Additionally, to manipulate the properties of the photocured systems, the methacrylate-functionalized cellulose acetate derivatives were mixed with low molecular weight dimethacrylate derivatives (containing castor oil and polypropylene glycol flexible chains), and the influence of UV-curable composition on the photopolymerization parameters being studied. The achieved data reveal that the addition of dimethacrylate comonomers augmented the polymerization rates and conversion degrees, leading to polymer networks with various microstructures.

A Bound Exciton Resonance Modulated by Bulk and Localized Coherent Phonons in Double Perovskites.

Optically excited electronic excitations are coupled to the soft and polar halide perovskite lattice, generating coherent phonons after subpicosecond interband laser-excitation. In Ag-based halide double perovskites, Ag-vacancies can bind free excitons, resulting in a pronounced bound exciton resonance. Here, we report the detection of three modulation frequencies corresponding to coherent phonons in Ag-based double perovskite nanocrystals at distinct spectral positions at the bound exciton resonance. Two of them are found in oscillatory spectral shifts of the bound exciton resonance and are identified as Cs- and Br-related bulk phonons. Surprisingly, a third frequency is observed as an intensity modulation. We argue that this amplitude oscillation is a consequence of an optically generated vibronic wave packet localized at a Ag-vacancy. Consequently, the localized coherent phonon modulates the giant oscillator strength of the bound exciton. This optically induced and spatially localized lattice shaking could potentially be useful for initiating photochemical reactions with atomic precision.

Characteristics and Source Apportionment of Volatile Organic Compounds in an Industrial Area at the Zhejiang–Shanghai Boundary, China

As “fuel” for atmospheric photochemical reactions, volatile organic compounds (VOCs) play a key role in the secondary generation of ozone (O3) and fine particulate matter (PM2.5, an aerodynamic diameter ≤ 2.5 μm). To determine the characteristics of VOCs in a high-level ozone period, comprehensive monitoring of O3 and its precursors (VOCs and NOx) was continuously conducted in an industrial area in Shanghai from 18 August to 30 September 2021. During the observation period, the average concentration of VOCs was 47.33 ppb, and alkanes (19.64 ppb) accounted for the highest proportion of TVOCs, followed by oxygenated volatile organic compounds (OVOCs) (13.61 ppb), alkenes (6.92 ppb), aromatics (4.65 ppb), halogenated hydrocarbons (1.60 ppb), and alkynes (0.91 ppb). Alkenes were the predominant components that contributed to the ozone formation potential (OFP), while aromatics such as xylene, toluene, and ethylbenzene contributed the most to the secondary organic aerosol production potential (SOAFP). During the study period, O3, NOx, and VOCs showed significant diurnal variations. Industrial processes were the main source of VOCs, and the second largest source of VOCs was vehicle exhaust. While the largest contribution to OFP was from vehicle exhaust, the second largest contribution was from liquid petroleum gas (LPG). High potential source contribution function (PSCF) values were observed in western and southeastern areas near the sampling sites. The results of a health risk evaluation showed that the Hazard Index was less than 1 and there was no non-carcinogenic risk, but 1,3-butadiene, benzene, chloroform, 1,2-dibromoethane, and carbon tetrachloride pose a potential carcinogenic risk to the population.

Single-Component Photochemical Afterglow Near-Infrared Luminescent Nano-Photosensitizers: Bioimaging and Photodynamic Therapy.

Long afterglow luminescence-guided photodynamic therapy (PDT) performs advantages of noninvasiveness, spatiotemporal controllability, and higher signal to noise ratio. Photochemical afterglow (PCA) system emitting afterglow in an aqueous environment is highly suitable for biomedical applications, but still faces the challenges of poor tissue penetration depth and responsive sensitivity. In this work, two novel compounds, Iso-TPA and ABEI-TPA, are designed and synthesized to integrate the PCA system as a single component by coupling near-infrared(NIR) photosensitizers with singlet oxygen cache units, respectively. Both compounds emit NIR afterglow based on photochemical reaction. ABEI-TPA exhibits higher photoluminescence quantum efficiency with nonconjugated linkage, while Iso-TPA with conjugated linkage possesses better reactive oxygen species generation efficiency to achieve stronger PCA and effective PDT, which is ascribed to stronger intramolecular charge transfer effect of Iso-TPA. Iso-TPA nanoparticles can achieve effective long-lasting NIR afterglow in vivo bioimaging up to 120 s with higher imaging resolution and outstanding PDT efficacy of tumor, exhibiting promising potential on bioimaging and therapy.

Characteristics and impacts of fine particulates from the largest power plant plume in Taiwan

In this study, the impact of the coal-fired Taichung Power Plant (TPP) plume in Taiwan during an observation experiment from Oct. 31 to Nov. 22, 2021, is simulated. We used the WRF/CMAQ and HYSPLIT models to analyze the changes in the PM2.5 concentration and the contribution percentage of major PM2.5 species along the forward trajectory of the TPP plume. Twenty trajectories with high PM2.5 concentrations above the chimney are divided into three types: transport to inland (TI), northeast monsoon transport southward (NMTS), and transport to sea (TS). The first kind, which exhibits mostly windy cases, is more harmful to people. Moreover, the largest proportion of the plume when it first exits the stack is SO42− (sulfate), which slightly decreases over time. The proportions of OM (organic matter) and NO3− (nitrate) slightly increased, and the proportion of NH4+ (ammonium ions) increased but not significantly. With the generation of low volatility/semi-volatile SOA (secondary organic aerosol), the proportion of OM significantly increases along the trajectory. Daytime photochemical reactions increase the radical concentrations, leading to an increase in the generation of low volatility/semi-volatile SOA and thus an increase in the proportion of OM. However, the proportion of NO3− in the smoke plume is smaller than that in other major PM2.5 species. Near the chimney, ANO3 (nitrate) accounts for a larger proportion of NO3− than HNO3 (nitrate acid). Furthermore, a sensitivity test shows that the height of the TPP that is reduced from 250 m to 150 m can have less effect on the environment.

Diel variation of seawater volatile organic compounds, DMSP-related compounds, and microbial plankton inside and outside a tropical coral reef ecosystem

Biogenic volatile organic compounds (VOCs) play key roles in coral reef ecosystems, where, together with dimethylated sulfur compounds, they are indicators of ecosystem health and are used as defense strategies and infochemicals. Assessment and prediction of the exchange rates of VOCs between the oceans and atmosphere, with implications for atmospheric reactivity and climate, are hampered by poor knowledge of the regulating processes and their temporal variability, including diel cycles. Here, we measured the variation over 36h of the concentrations of DMSPCs (dimethylsulfoniopropionate (DMSP)-related compounds, namely DMSP, dimethylsulfoxide, acrylate, dimethylsulfide, and methanethiol as dimethyl disulfide) and VOCs (COS, CS2, isoprene, the iodomethanes CH3I and CH2ClI, and the bromomethanes CHBr3 and CH2Br2), in surface waters inside the shallow, northern coral-reef lagoon of Mo’orea (French Polynesia) and 4 km offshore, in the tropical open ocean. Comparisons with concurrent measurements of sea surface temperature, solar radiation, biogeochemical variables (nutrients, organic matter), and the abundances and taxonomic affiliations of microbial plankton were conducted with the aim to explain interconnections between DMSPCs, VOCs, and their environment across diel cycles. In open ocean waters, deeper surface mixing and low nutrient levels resulted in low phytoplankton biomass and bacterial activity. Consequently, the diel patterns of VOCs were more dependent on photochemical reactions, with daytime increases for several compounds including dissolved dimethylsulfoxide, COS, CS2, CH3I, and CH2ClI. A eukaryotic phytoplankton assemblage dominated by dinoflagellates and haptophytes provided higher cell-associated DMSP concentrations, yet the occurrence of DMSP degradation products (dimethylsulfide, dimethyl disulfide) was limited by photochemical loss. Conversely, in the shallow back reef lagoon the proximity of seafloor sediments, corals and abundant seaweeds resulted in higher nutrient levels, more freshly-produced organic matter, higher bacterial activity, and larger algal populations of Mamiellales, diatoms and Cryptomonadales. Consequently, DMSP and dimethylsulfoxide concentrations were lower but those of most VOCs were higher. A combination of photobiological and photochemical processes yielded sunny-daytime increases and nighttime decreases of dimethylsulfide, dimethyl disulfide, COS, isoprene, iodomethanes and bromomethanes. Our results illustrate the important role of solar radiation in DMSPC and VOC cycling, and are relevant for the design of sampling strategies that seek representative and comparable measurements of these compounds.

Accelerated photochemical reactions at oil-water interface exploiting melting point depression.

Water can accelerate a variety of organic reactions far beyond the rates observed in classical organic solvents. However, using pure water as a solvent introduces solubility constraints that have limited the applicability of efficient photochemistry in particular. We report here the formation of aggregates between pairs of arenes, heteroarenes, enamines, or esters with different electron affinities in an aqueous medium, leading to an oil-water phase boundary through substrate melting point depression. The active hydrogen atoms in the reactants engage in hydrogen bonds with water, thereby accelerating photochemical reactions. This methodology realizes appealingly simple conditions for aqueous coupling reactions of complex solid molecules, including complex drug molecules that are poorly soluble in water.

Tailoring Hot-Carrier Distributions of Plasmonic Nanostructures through Surface Alloying.

Alloyed metal nanoparticles are a promising platform for plasmonically enabled hot-carrier generation, which can be used to drive photochemical reactions. Although the non-plasmonic component in these systems has been investigated for its potential to enhance catalytic activity, its capacity to affect the photochemical process favorably has been underexplored by comparison. Here, we study the impact of surface alloy species and concentration on hot-carrier generation in Ag nanoparticles. By first-principles simulations, we photoexcite the localized surface plasmon, allow it to dephase, and calculate spatially and energetically resolved hot-carrier distributions. We show that the presence of non-noble species in the topmost surface layer drastically enhances hot-hole generation at the surface at the expense of hot-hole generation in the bulk, due to the additional d-type states that are introduced to the surface. The energy of the generated holes can be tuned by choice of the alloyant, with systematic trends across the d-band block. Already low surface alloy concentrations have a large impact, with a saturation of the enhancement effect typically close to 75% of a monolayer. Hot-electron generation at the surface is hindered slightly by alloying, but here a judicious choice of the alloy composition allows one to strike a balance between hot electrons and holes. Our work underscores the promise of utilizing multicomponent nanoparticles to achieve enhanced control over plasmonic catalysis and provides guidelines for how hot-carrier distributions can be tailored by designing the electronic structure of the surface through alloying.

Photochemical processes to cellular DNA damage by UV radiation of different wavelengths: biological consequences

UV radiation of sunlight induces in cellular DNA of different organisms photochemical reactions, which may lead to the development of series biological responses to arising lesions, including apoptosis, mutagenesis, and carcinogenesis. The chemical nature and the amount of DNA lesions depend on the wavelength of UV radiation. Photons of UV radiation in the region B (UVB, 290–320 nm) cause the production of two main defects, namely, cyclobutane pyrimidine dimers and, with a less yield, pyrimidine (6-4) pyrimidone photoproducts; their formation is the result of the direct UVB photon absorption by DNA bases. Photons of UV radiation in the region A (UVA, 320–400 nm) induce only cyclobutane dimers that can be formed by triplet-triplet energy transfer from cellular chromophores, absorbing photons of this UV region, to DNA thymine bases. UVA is much more effective than UVB in the sensitized oxidatively lesion formation in DNA such as single strand breaks and oxidized bases; among those, 8-oxo-dihydroguanine is the most frequent since it can be produced from several oxidation processes. In recent years, multiple papers, reporting novel, more detailed information about molecular mechanisms of photochemical reactions underlying the formation of different lesions in DNA were published. The present review mainly aims at summarizing and analyzing data contained in these publications, particularly regarding oxidative reactions that are initiated by reactive oxygen species and radicals generated by potential endogenous photosensitizers such as pterins, riboflavin, protoporphyrin IX, NADH, and melanin. The role of specific DNA photoproducts in genotoxic processes induced in living systems by UV radiation of different wavelengths, including human skin carcinogenesis, is discussed.

UV Laser-Induced Photodecomposition of Matrix-Isolated Salicylhydroxamic Acid: Identification of New Isocyanate Complexes.

Photochemical reactions of salicylhydroxamic acid were induced using tunable UV laser radiation followed by FTIR spectroscopy. Four pairs of co-products were experimentally found to appear in the photolysis: C6H4(OH)NCO⋯H2O (1), C6H4(OH)C(O)N⋯H2O (2), C6H4(OH)2⋯HNCO (3), and C6H4(OH)NHOH⋯CO (4). The comparison of the theoretical spectra with the experimental ones allowed us to determine the structures of the complexes formed in the matrices. The mechanisms of the reaction channels leading to the formation of the photoproducts were proposed. It was concluded that the first step in the formation of the complexes (1), (2), and (3) was the scission of the N-O bond, whereas the creation of complex (4) was due to cleavage of the C-N bond.

Twisted Intramolecular Charge-Transfer State Addition to Electron-Poor Olefins.

When electron-rich arylpyrrolinium salts are irradiated with ultraviolet light in the presence of Michael acceptors, the pyrrolinyl and aryl fragments add to the activated and polarized double bond in a regioselective manner, forming two C-C bonds and fragmenting the substrate. In this paper, we present a model for this intriguing reaction, supported by spectroscopy and computational analyses, and provide evidence for rectifying previously misassigned structures. We postulate that the photochemical reaction is inefficient because the reaction between the twisted intramolecular charge-transfer state and the olefin competes with fluorescence from this state upon photon absorption. We also discuss the practical advantages of performing this photochemical reaction in a continuous flow setup. Additionally, we explore several subsequent reactions that allow us to further modify the products of the photochemical step, ultimately leading to the creation of new chemical structures.

Synthesis and Biological Evaluation of Novel Amino and Amido Substituted Pentacyclic Benzimidazole Derivatives as Antiproliferative Agents.

Newly designed pentacyclic benzimidazole derivatives featuring amino or amido side chains were synthesized to assess their in vitro antiproliferative activity. Additionally, we investigated their direct interaction with nucleic acids, aiming to uncover potential mechanisms of biological action. These compounds were prepared using conventional organic synthesis methodologies alongside photochemical and microwave-assisted reactions. Upon synthesis, the newly derived compounds underwent in vitro testing for their antiproliferative effects on various human cancer cell lines. Notably, derivatives 6 and 9 exhibited significant antiproliferative activity within the submicromolar concentration range. The biological activity was strongly influenced by the N atom's position on the quinoline moiety and the position and nature of the side chain on the pentacyclic skeleton. Findings from fluorescence, circular dichroism spectroscopy, and thermal melting assays pointed toward a mixed binding mode-comprising intercalation and the binding of aggregated compounds along the polynucleotide backbone-of these pentacyclic benzimidazoles with DNA and RNA.

Comprehensive study on air-quality impacts from chemical plant flare emissions under planned or emergency shutdown operations†

Chemical plant shutdown (CPS) operations will employ a flare system to combust waste, unwanted, and off-spec gases dumped from process units to protect the plant safety and the local community. However, the incomplete combustion of flare source under CPS operations including plant planned shutdown (PPS) and plant emergency shutdown (PES) will cause considerable air pollution events. Hitherto, quantitative studies on both primary (CO and NO2) and secondary (ozone) pollutant impacts induced by CPS flaring are still lacking. In this paper, the dynamic effect of flare emissions from two types of CPS (PPS and PES) on ambient air-quality impacts will be systematically and quantitatively studied. The study integrates the dynamic process simulation via Aspen Plus Dynamics with the regional air-quality modelling via Comprehensive Air-quality Model with extensions (CAMx). Case studies indicated that the primary pollutants from flare emissions will be significantly diluted due to the atmospheric transportation, and the maximum concentrations of CO and NO2 can respectively reach 119.0 and 11.0 ppb under PPS, and 47.5 and 4.5 ppb under PES. Meanwhile, the increasing height of the flaring stack will decrease CO and NO2 concentrations but increase the ozone concentration under CPS. Furthermore, CPS in daytime periods will greatly promote ozone generations due to the enhanced photochemical reactions under solar radiation. The maximum 1-hr and 8-hr ozone increment can be 16.6 and 7.1 ppb under PPS while 10.7 and 3.3 ppb under PES, respectively. Besides, the decreasing of flare destruction and removal efficiency will increase ozone and CO under PES.

Transient Absorption Spectroscopic Investigation of the Photocyclization-Deprotection Reaction of 3',5'-Dimethoxybenzoin Fluoride.

The 3',5'-dimethoxybenzoin (DMB) system has been widely investigated as a photoremovable protecting group (PRPG) for the elimination of various functional groups and has been applied in many fields. The photolysis of DMB fluoride leads to a highly efficient photocyclization-deprotection reaction, resulting in a high yield of 3',5'-dimethoxybenzofuran (DMBF) in a MeCN solution, while there is a competitive reaction that produces DMB in an aqueous solution. The yield of DMB increased as the volume ratio of water increased. To understand the solvent effect of the photolysis of selected DMB-based compounds, a combination of femtosecond to nanosecond transient absorption spectroscopies (fs-TA and ns-TA), nanosecond time-resolved resonance Raman spectroscopy (ns-TR3) and quantum chemical calculation was employed to study the photophysical and photochemical reaction mechanisms of DMB fluoride in different solutions. Facilitated by the bichromophoric nature of DMB fluoride with electron-donating and -withdrawing chromophores, the cyclized intermediates could be found in a pure MeCN solution. The deprotection of a cyclic biradical intermediate results in the simultaneous formation of DMBF and a cyclic cation species. On the other hand, in aqueous solution, fs-TA experiments revealed that α-keto cations could be observed after excitation directly, which could easily produce the DMB through the addition of a hydroxyl within 8.7 ps. This work provides comprehensive photo-deactivation mechanisms of DMB fluoride in MeCN and aqueous conditions and provides critical insights regarding the biomedical application of DMB-based PRPG compounds.

Avoiding Oxygen Removal for Photochemical Reactions – towards Water as the Solvent

AbstractOxygen removing protocols have long been the standard approach to perform photoreactions. By encapsulating photosensitizers and reactants in tailored supramolecular assemblies, preservation of photoreactivity even in the presence of molecular oxygen can be observed. Herein, we showcase some of the solutions that could render time‐consuming oxygen removal redundant in photochemical synthesis. A focus has been dedicated to aqueous solutions of supramolecular assemblies as potential reaction media. They present an attractive solution possibly useful not only for synthetic photochemical transformations, but also for water purification, bio‐applications or biocatalysis. The included media are membranes, hydrogels, deep eutectic solvents and peptide assemblies.

Pollution Characteristics，Sources，and Secondary Generation of Organic Acids in PM2.5 in Zhengzhou

Organic acids in atmospheric particulate matter are widely involved in various physical and chemical reactions in the atmosphere and contribute greatly to the formation of secondary organic aerosols and haze pollutions. Therefore， the concentration distribution characteristics， sources， and secondary formation of organic acids in particulate matter are of great significance for further investigation of organic aerosols and their secondary transformation. Fine particulate matter （PM2.5） samples were collected in Zhengzhou， and three types of organic acids， including dicarboxylic acids， fatty acids， and resin acids， were analyzed to explore their species distribution， seasonal variations， source contribution， and secondary generation. Malonic acid （di-C3） and succinate acid （di-C4） were the most abundant in the identified dicarboxylic acids， which showed obvious seasonal variations in the order of summer > autumn > winter > spring. Fatty acids had the highest concentration in winter and the lowest concentration in spring， showing obvious bimodal advantages， with the most abundant compounds being palmitic acid and stearic acid （C18）. Principal component analysis and multiple linear regression （MLR） were used to analyze the source of organic acids in PM2.5 in Zhengzhou； the results showed that 35% of the organic acids came from combustion and traffic sources， 24% from cooking sources， 23% from secondary formation， and 17% from natural sources. The ratios of the selected marker species （i.e.， di-C3 / di-C4， F/M， and C18：1 / C18） were used as tracers for the secondary formation of the organic aerosol and its aging process. The results showed that the photochemical reaction was intense in summer， and the proportion of organic aerosol aging or secondary production was high， whereas the photochemical reaction was weak in winter， and the aging degree of organic aerosol was low. Correlation analysis and MLR were used in combination to quantify the relative contribution of gas-phase oxidation and liquid-phase oxidation to dicarboxylic acid formation， and the results showed that gas-phase oxidation played a dominant role in the sampling period （accounting for 58%）， especially in summer （61%）.