Photochemical Transformations Research Articles

Photocatalytic Boryl Radicals Triggered Sequential B─N/C─N Bond Formation to Assemble Boron-Handled Pyrazoles.

Vinyldiazo compounds are one of the most important synthons in the construction of a cyclic ring. Most photochemical transformations of vinyldiazo compounds are mainly focusing on utilization of their C═C bond site, while reactions taking place at terminal nitrogen atom are largely unexplored. Herein, a photocatalytic cascade radical cyclization of LBRs with vinyldiazo reagents through sequential B─N/C─N bond formation is described. The reaction starts with the addition of LBRs (Lewis base-boryl radicals) at diazo site, followed by intramolecular radical cyclization to access a wide range of important boron-handled pyrazoles in good to excellent yields. Control experiments, together with detailed mechanism studies well explain the observed reactivity. Further studies demonstrate the utility of this approach for applications in pharmaceutical and agrochemical research.

Unveiling the Potential of Heterogeneous Catalysts for Molecular Solar Thermal Systems.

Solar energy utilization has gained considerable attention due to its abundance and renewability. However, its intermittent nature presents a challenge in harnessing its full potential. The development of energy storing compounds capable of capturing and releasing solar energy on demand has emerged as a potential solution. These compounds undergo a photochemical transformation that results in a high-energy metastable photoisomer, which stores solar energy in the form of chemical bonds and can release it as heat when required. Such systems are referred to as MOlecular Solar Thermal (MOST)-systems. Although the photoisomerization of MOST systems has been vastly studied, its back-conversion, particularly using heterogeneous catalysts, is still underexplored and the development of effective catalysts for releasing stored energy is crucial. Herein we compare the performance of 27 heterogeneous catalysts releasing the stored energy in an efficient Norbornadiene/Quadricyclane (NBD/QC) MOST system. We report the first benchmarking of heterogeneous catalysts for a MOST system using a robust comparison method of the catalysts' activity and monitoring the conversion using UV-Visible (UV-Vis) spectroscopy. Our findings provide insights into the development of effective catalysts for MOST systems. We anticipate that our assay will reveal the necessity of further investigation on heterogeneous catalysis.

Accelerated Electrophotocatalytic C(sp3)−H Heteroarylation Enabled by an Efficient Continuous‐Flow Reactor**

AbstractElectrophotocatalytic transformations are garnering attention in organic synthesis, particularly for accessing reactive intermediates under mild conditions. Moving these methodologies to continuous‐flow systems, or flow ElectroPhotoCatalysis (f‐EPC), showcases potential for scalable processes due to enhanced irradiation, increased electrode surface, and improved mixing of the reaction mixture. Traditional methods sequentially link photochemical and electrochemical reactions, using flow reactors connected in series, yet struggle to accommodate reactive transient species. In this study, we introduce a new flow reactor concept for electrophotocatalysis (EPC) that simultaneously utilizes photons and electrons. The reactor is designed with a transparent electrode and employs cost‐effective materials. We used this technology to develop an efficient process for electrophotocatalytic heteroarylation of C(sp3)−H bonds. Importantly, the same setup can also facilitate purely electrochemical and photochemical transformations. This reactor represents a significant advancement in electrophotocatalysis, providing a framework for its application in flow for complex synthetic transformations.

Accelerated Electrophotocatalytic C(sp3 )-H Heteroarylation Enabled by an Efficient Continuous-Flow Reactor.

Electrophotocatalytic transformations are garnering attention in organic synthesis, particularly for accessing reactive intermediates under mild conditions. Moving these methodologies to continuous-flow systems, or flow ElectroPhotoCatalysis (f-EPC), showcases potential for scalable processes due to enhanced irradiation, increased electrode surface, and improved mixing of the reaction mixture. Traditional methods sequentially link photochemical and electrochemical reactions, using flow reactors connected in series, yet struggle to accommodate reactive transient species. In this study, we introduce a new flow reactor concept for electrophotocatalysis (EPC) that simultaneously utilizes photons and electrons. The reactor is designed with a transparent electrode and employs cost-effective materials. We used this technology to develop an efficient process for electrophotocatalytic heteroarylation of C(sp3 )-H bonds. Importantly, the same setup can also facilitate purely electrochemical and photochemical transformations. This reactor represents a significant advancement in electrophotocatalysis, providing a framework for its application in flow for complex synthetic transformations.

Visible Light-Induced Templated Metathesis of Peptide-Nucleic Acid Conjugates with a Diselenide Bridge.

The use of template molecules as chemical scaffolds that significantly influence the course of the reaction has recently been intensively studied. Peptide nucleic acids (PNA) are molecules that mimic natural nucleic acids. They are a promising matrix in such reactions because they possess high affinity and specificity in their interactions. The manner of PNA interaction is predictable based on sequence complementarity. Recently, we report the visible light-induced metathesis reaction in peptides containing a diselenide bond. Herein, we present an efficient and straightforward method of the visible light-driven diselenide-based metathesis of peptide-nucleic acid conjugates. Compared to a similar photochemical transformation in peptides, a significant increase in the metathesis efficiency was obtained due to the template effect.

Atmospheric Modelling of Photochemical Transformations of Pollutants: Impact of Weather Conditions and Diurnal Cycle (Case Study: Ust-Kamenogorsk, Kazakhstan)

In this study, the dispersal of atmospheric pollutants from point sources and their photochemical transformations are examined. The mass conservation principle underlies a system of differential equations formulated to describe the transfer and transformation processes, incorporating stoichiometric formulas and reaction rate constants. The atmospheric boundary layer model and the transport-transformation equation of pollutants are considered, integrating a specific parameter to assess the influence of anthropogenic heat sources and surface heterogeneity on pollutant dispersion. Using Ust-Kamenogorsk, an industrial city in Kazakhstan, as a case study, the model accounts for variations in photochemical transformations due to weather conditions, ambient temperature, and time of day. To facilitate numerical simulations of atmospheric pollution and visualize various scenarios, a software application package was created, incorporating photochemical transformations. The developed suite of applications has been verified with real data and benchmarked against contemporary software packages such as WRF and SILAM. Moving forward, the refined model aims to forecast air pollution patterns in industrial cities across Kazakhstan.

Recent Discovery, Development, and Synthetic Applications of Formic Acid Salts in Photochemistry

AbstractThe advancement of sustainable photoredox catalysis in synthetic organic chemistry has evolved immensely because of the development of versatile and cost‐effective reagents. In recent years, a substantial effort has been dedicated to exploring the utility of formic acid salts in various photochemical reactions. In this context, formates have demonstrated diverse capabilities, functioning as reductants, sources of carbonyl groups, and reagents for hydrogen atom transfer. Notably, the CO2⋅– radical anion derived from formate exhibits strong reductant properties for cleaving both C−X and C−O bonds. Moreover, these salts play a pivotal role in carboxylation reactions, further highlighting their significance in a variety of photochemical transformations. The ability of formates to serve as reductants, carbonyl sources, and hydrogen atom transfer reagents reveal exciting possibilities in synthetic organic chemistry. This minireview highlights an array of captivating discoveries, underscoring the crucial role of formates in diverse and distinctive photochemical methods, enabling access to a wide range of value‐added compounds.

Recent Discovery, Development, and Synthetic Applications of Formic Acid Salts in Photochemistry.

The advancement of sustainable photoredox catalysis in synthetic organic chemistry has evolved immensely because of the development of versatile and cost-effective reagents. In recent years, a substantial effort has been dedicated to exploring the utility of formic acid salts in various photochemical reactions. In this context, formates have demonstrated diverse capabilities, functioning as reductants, sources of carbonyl groups, and reagents for hydrogen atom transfer. Notably, the CO2 ⋅- radical anion derived from formate exhibits strong reductant properties for cleaving both C-X and C-O bonds. Moreover, these salts play a pivotal role in carboxylation reactions, further highlighting their significance in a variety of photochemical transformations. The ability of formates to serve as reductants, carbonyl sources, and hydrogen atom transfer reagents reveal exciting possibilities in synthetic organic chemistry. This minireview highlights an array of captivating discoveries, underscoring the crucial role of formates in diverse and distinctive photochemical methods, enabling access to a wide range of value-added compounds.

Indirect photolysis of cysteine and thiourea in the presence of metal ions in the aquatic environment

In this work are presented the studies on the photochemical transformations of TU (thiourea) and Cys (cysteine) with the addition of Cu(II) or Fe(III) ions to the system. So both thiols, TU, and Cys, have been subjected to induced photolysis with OH radicals, generated during irradiation of H2O2 with different artificial light sources in the presence of the Cu(II) and Fe(III) ions. Based on the results obtained, it was found that when Cu(II) or Fe(III) ions are added to the system, the oxidation rate of the thiols goes up a lot. It has been found that TU and, even more effectively, Cys bind the ions of the studied metals into stable complex compounds. It has been shown that the oxidation rates of the thiols depend also on the irradiation sources' radiation intensity and emission spectrum.

Chemodynamics of Polycyclic Aromatic Hydrocarbons and Their Alkylated and Nitrated Derivatives in the Yellow Sea and East China Sea.

The occurrence of continuously released polycyclic aromatic hydrocarbons (PAHs) in marginal seas is regulated by hydrological and biogeochemical processes; however, scarce knowledge is about their derivatives in marine environments. In this study, the dissolved and particulate PAHs and their alkylated/nitrated derivatives (A-PAHs/N-PAHs) in surface seawater of the southwestern Yellow Sea (YS) and northwestern East China Sea (ECS) during September 2022 were comprehensively discussed. Results confirm higher levels of Σ26PAHs (9.3-70 ng/L) and Σ43A-PAHs (13-76 ng/L) than Σ20N-PAHs (0.80-6.6 ng/L). The spatial heterogeneity of contaminants was regulated by substantial riverine runoff and ocean currents. Lagrangian Coherent Structure analysis further revealed the existence of a transport barrier at the shelf break of the southwestern YS where contaminants hardly crossed and tended to accumulate. The relationship between dissolved compounds and chlorophyll a indicated both biodegradation and the biological pump contributed to the depletion of PAHs and A-PAHs from surface seawater while the biological pump was the major driver for N-PAHs, despite their complicated water-particle partition behavior due to variations in physicochemical properties in the presence of nitro groups. Source identification demonstrated that pyrogenic and petrogenic sources dominated the YS and ECS, respectively, while photochemical transformations appeared more active in the YS.

X-ray induced Coulomb explosion imaging of transient excited-state structural rearrangements in CS2

Structural imaging of transient excited-state species is a key goal of molecular physics, promising to unveil rich information about the dynamics underpinning photochemical transformations. However, separating the electronic and nuclear contributions to the spectroscopic observables is challenging, and typically requires the application of high-level theory. Here, we employ site-selective ionisation via ultrashort soft X-ray pulses and time-resolved Coulomb explosion imaging to interrogate structural dynamics of the ultraviolet photochemistry of carbon disulfide. This prototypical system exhibits the complex motifs of polyatomic photochemistry, including strong non-adiabatic couplings, vibrational mode couplings, and intersystem crossing. Immediately following photoexcitation, we observe Coulomb explosion signatures of highly bent and stretched excited-state geometries involved in the photodissociation. Aided by a model to interpret such changes, we build a comprehensive picture of the photoinduced nuclear dynamics that follows initial bending and stretching motions, as the reaction proceeds towards photodissociation.

Characterizing water-soluble brown carbon in fine particles in four typical cities in northwestern China during wintertime: integrating optical properties with chemical processes

Abstract. Brown carbon (BrC) aerosol could impact atmospheric radiative forcing and play a crucial role in atmospheric photochemistry. In this study, fine particulate matter (PM2.5) filter samples were collected synchronously in four major cities in northwestern China during the winter season (December 2019–January 2020): Lanzhou (LZ), Xining (XN), Yinchuan (YC), and Ürümqi (UR), which are represented as energy-producing and heavy manufacturing cities in China. The primary aim of the study is to explore the optical properties, sources, and chemical processes of water-soluble BrC (WS-BrC). The average mass absorption efficiency at 365 nm (MAE365) of WS-BrC at these four cities was 1.24 ± 0.19 m2 g−1 (XN), 1.19 ± 0.12 m2 g−1 (LZ), 1.07 ± 0.23 m2 g−1 (YC), and 0.78 ± 0.16 m2 g−1 (UR). The properties of WS-BrC were further investigated by an acid–base titration experiment. The results showed that the MAE365 values in all cities increased with higher pH values (2–11), while the fluorescence intensities of water extracts fluctuated with pH values, being stronger under both highly acidic and basic conditions. The sensitivity to pH variation was most pronounced in the WS-BrC samples from YC and LZ, indicating the important contribution of acid or base functional group compounds in these locations. Additionally, the study revealed significant photo-enhancement (LZ) or photo-bleaching (YC and UR) phenomena of WS-BrC in different cities. These results suggest that the sources and/or chemical processes of WS-BrC varied among the cities. The sources and chemical processes of WS-BrC were further explored by a combination of parallel factor analysis (PARAFAC) on excitation–emission matrix (EEM) spectra of WS-BrC and positive matrix factorization analysis (PMF) on high-resolution mass spectra of water-soluble organic aerosol (WSOA). Six PARAFAC components were identified, including three humic-like substances (HULIS; two less oxygenated (LO) HULIS and one highly oxygenated (HO) HULIS), two protein-like or phenol-like substances (PLS), and one undefined substance. Four PMF factors were identified, including a water-soluble primary OA (WS-POA), a less oxidized oxygenated OA associated with coal combustion-induced WSOA (LO-OOA), and two highly oxidized oxygenated OAs resulting from photochemical oxidation and aqueous-phase oxidation transformations (HO-OOA1 and HO-OOA2). WS-POA was determined to be the most significant source of light absorption, accounting for 30 %–60 % based on multiple linear regression models, and it showed a significant correlation with PLS and LO-HULIS components. The loss of light absorption of WS-POA was found to occur through its conversion to LO-OOA and HO-OOAs through photochemical or aqueous reactions, with HO-OOAs being significantly correlated with the HO-HULIS component. These processes can be clearly illustrated by integrating optical properties and chemical composition using a Van Krevelen diagram and an EEM plot.

Photocatalyst‐Free Visible‐Light‐Promoted C‐3‐Alkylation of Indoles through C−H Functionalizations of N,N‐Dialkylanilines

AbstractVisible‐light, an environmentally benign and sustainable energy source, is considered an ideal condition for green chemical synthesis especially through C−H functionalization which has been a major focus for the synthesis of organic molecules in the last two decades. Here, we report a visible‐light driven photocatalyst‐free C‐3‐alkylation of indoles via C−H functionalizations of N,N‐dialkylanilines. When N,N‐dialkylaniline is reacted with various substituted indoles in DMSO solvent in an open reaction vessel at room temperature (r.t.) under the irradiation of a Compact Fluorescent Light (CFL, 27 W), C‐3‐alkylation of indoles occurs. The yield of the resulting product is up to 96 %. This photochemical transformation offers several advantages such as catalyst‐free, aerial oxygen as the sole oxidant, visible‐light promoted, and tolerable for various functional groups in indoles.

PHOTOCHEMICAL TRANSFORMATION OF DISSOLVED ORGANIC MATTER AND BEHAVIOR OF METALS IN THE WATERS OF THE SOUTHERN TAIGA BOG COMPLEX, WESTERN SIBERIA

Link for citation: Raudina T.V., Smirnov S.V., Istigechev G.I., Pokrovsky O.S. Photochemical transformation of dissolved organic matter and behavior of metals in the waters of the southern taiga bog complex, Western Siberia. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 9, рр. 182-193. In Rus. The relevance. Dissolved organic matter is one of the largest biologically available sources of carbon in terrestrial and aquatic ecosystems, and its dynamics are critical to local and global carbon cycles. Destruction of organic matter during migration determines the biological cycle of elements and their stability. Important processes that lead to the transformation or removal of the dissolved organic matter are bio- and photodegradation. To date, enough research has been carried out to study the composition of humic substances, forms of metals, and the processes of migration of organo-mineral compounds in natural waters of the taiga zone, Western Siberia. Work is underway to study the dissolved organic carbon bioavailability, but the mechanisms of its photochemical transformations in different seasons of the year have not been studied. At the same time, photochemical mineralization of dissolved organic compounds largely regulates the biogeochemical cycles of elements by changing their bioavailability, the intensity of carbon dioxide emission from surface waters into the atmosphere, and the removal of dissolved trace elements through precipitation and coagulation. The main aim is to assess changes in the chemical composition and the rate of the dissolved organic matter and dissolved metals removal in the waters of the southern taiga bog complex (Western Siberia) under the sunlight exposure on a spatio-temporal scale. Objects: soil waters within different bog landscapes (open sedge-sphagnum fen, tall ryam (pine-shrub-sphagnum phytocenosis with high pine trees), and waterlogged mixed forest) of the Bakchar bog complex located in the southeastern part of the Ob-Irtysh interfluves, the Vasyugan plain. The waters were taken at a depth by digging a pit (40´40 cm area, 40 cm depth), which allowed the surrounding gravitational water to fill it up to the depth of 10–20 cm. The sampling took place during two field period in 2020 (June and October). Methods. pH, water temperature, specific conductivity (Cond) and dissolved oxygen were measured using a multiparameter instrument (WTW MULTI 3430 SET). The dissolved organic carbon was measured by a high-temperature thermic oxidation method using a Shimadzu TOC-LCPN analyzer, with an uncertainty of 2 %. The absorbance was measured at wavelengths up to 800 nm, 1 nm step using quartz 10 mm cuvette on a Cary-50 spectrophotometer. Major cations (Ca, Mg, Na, K), Si, and trace metals were determined with an ICP-MS Agilent CE 7500 with In and Re as internal standards and three various external ones. In the photodegradation experimental design, we followed the methodology which is sunlight exposure of sterile filtered (0,2 μm) samples in quartz reactors in the outdoor pool. Results. The authors revealed the influence of photodegradation on the qualitative and quantitative composition of dissolved organic substances and the behavior of metals in water samples of bog landscapes of the taiga zone of Western Siberia on spatiotemporal scales. It was established that from 3 to 30 % of the dissolved organic carbon can be removed from soil water under the influence of sunlight with maximum values in early June. At the same time, in autumn, despite the decrease in the amount of solar radiation, the photodegradable DOC can also reach 10–12 %. In general, there is a decrease in the percentage of the dissolved organic carbon loss in the waters in the row fen>ryam>forest. The dissolved organic carbon removal can be associated both with the transition of a part into an inorganic form, and with the destruction of high-molecular organic substances. A significant change (p<0.05) in the optical parameters is noted, which is consistent with the behavior of the dissolved organic matter during photolysis. In addition, under the influence of insolation, the transformation of organo-mineral compounds occurs, which leads to a change in the forms of metals. The greatest losses relative to control were observed for rare earth elements (Y, La, Ce, Pr, Nd), as well as Ti, V, which in some cases reach 70 % (more significant in fen waters). These trace elements show behavior similar to dissolved organic carbon, Al and Fe, which confirms the importance of organic and organo-Fe-Al-colloids determining the behavior of most elements in acidic waters with a high content of organic matter.

Sunlight-induced degradation of COVID-19 antivirals arbidol in natural aquatic environments: Mechanisms, pathways and toxicity

Insights into COVID-19 antivirals’ environmental fate and ecological risk are urgently required due to their increasing concentrations in aquatic environments, which have rarely been studied. Herein, we first investigated the photochemical transformation and the resulting alterations in toxicity of arbidol, an antiviral drug with relatively higher toxicity. The photolysis of arbidol was rapid with a rate constant of 0.106 min−1 due to its superior ultraviolet light absorption, in which the direct photolysis was predominated with a contribution of 91.5%. Despite its substantial photolysis, only 14.45% of arbidol was mineralized after 100 min, implying that arbidol and its products might have a long-term impact on aquatic environment. It was inferred that arbidol was photolyzed mainly via the loss of thiophenol, bromine, and alkylamine, based on twelve photolytic products identified. Notably, the experimental results demonstrated that the photolysis process increased the acute toxicity of arbidol, and the toxicity prediction indicated that the ecotoxicity of two photolytic products was very high with LC50 values below 0.1 mg/L. Due to the co-effect of multiple constituents, the photolytic rate observed in wastewater treatment plant effluent and in river water was comparable to that in ultra-pure water, while it was slightly enhanced in lake water. The presence of dissolved organic matter suppressed arbidol photolysis, while NO3− exhibited a promotion effect. These results would be of great significance to assess the fate and risk of COVID-19 antivirals in natural aquatic environments.

Unraveling the photochemical reactivity of dissolved organic matter in the Yangtze river estuary: Integrating incubations with field observations

Dissolved organic matter (DOM) sustains a substantial part of the organic matter transported seaward in large estuaries, where photochemical reactions significantly influence its transformation and fate. Irradiation experiments can provide valuable information on the photochemical reactivity (photo-labile, photo-resistant, and photo-product) of molecules. However, previous research paid less attention to exploring the controls of the initial DOM chemistry to irradiation experiments and examining the applicability of their further integration with field research. Here, we conducted irradiation experiments for samples from the freshwater and seawater endmember of the Yangtze River Estuary (YRE), which receives organic matter transport from the largest river in China, the Yangtze River. Molecules that occurred before and after irradiation experiments were characterized by the Fourier transform ion cyclotron resonance mass spectrometry. Results show that both post-irradiation samples have the lower aromaticity degree and reduced oxidation state, while the freshwater endmember sample exhibits more dramatic changes, indicating the controls of parent molecules to the effect of irradiation experiments. Integrating with the “molecular matching” approach, we compared the molecules occurring in field samples with the classified molecules (photo-resistant, photo-labile, and photo-product) acquired from performed irradiation experiments and correlated the relative intensity of photochemical reactivity types with salinity. When applying results from different experiments to conduct “molecular matching”, the photo-resistant and photo-labile relative intensity possess consistently positive and negative trends with increasing salinity, respectively. This suggests their reliability for molecular matching applications, while the inconsistent trends for the photo-product relative intensity with salinity suggest its uncertainty in assessing the photo-induced effects. Moreover, the molecular composition within the photochemical reactivity types in field samples also evolved along the salinity gradient and showed similar trends with the DOM changes after experimental irradiation. Despite various factors influencing estimations, it is revealed that a fraction of aromatic molecules and majority of carboxyl-rich alicyclic molecules considered with biologically persistent nature in the YRE freshwater zone are simultaneously not susceptible to photochemical transformation to potentially constitute a long-term marine carbon sink. This study emphasizes the importance and limitations of the combination of field research and laboratory-controlled experiments to provide a better understanding of the crucial role of photochemical reactions in affecting carbon cycling in large estuaries.

Distribution of organochlorine pesticides (OCPs) in surface-mixed layer water and intertidal sediments of Lagos lagoon, Gulf of Guinea

Organochlorinated pesticides (OCPs) were analysed in intertidal sediments and surface-mixed layer water of Lagos lagoon in Nigeria in order to elucidate the contamination levels, sources and distribution characteristics, and potential human and ecological health risks associated with exposures to OCPs. The total ∑ OCPs in sediments ranged from 222.35 to 2585.30 μg/kg dw, with a mean concentration range between 13.08 and 172.35 μg/kg dw, respectively. The most dominant OCP compounds in the sediments were dichlorodiphenylethanes (40%), chlors (26%), cyclodienes (17%), HCHs (9%), and endos (8%). The concentration (μg/kg) of individual ∑OCP groups in sediment decreased in the following order: ∑ dichlorodiphenylethanes > ∑ Chlors > ∑ Cyclodienes > ∑ HCHs > ∑ Endos. The ∑ OCPs in water ranged from 23.63 (mean concentration: 1.97 ng/L) to 172.05 ng/L (mean concentration: 13.23 ng/L). Dichlorodiphenylethanes (46%), cyclodienes (21%), chlors (14%), HCHs (12%), and endos (7%) were the most prevalent OCP compounds in investigated water samples. These locations are pollution hotspots for potential wastes arising from industrial effluents, heavy shipping activities, municipal wastes and discharges of transformer oil from abandoned power generation and transmission facilities. The total composition and β-, γ- and δ-HCH isomeric ratios suggest recent anthropogenic introduction of the HCHs into the lagoonal ecosystem compared to historical deposits. Dichlorodiphenylethanes (p,p′-DDD, p,p′-DDE, and methoxychlor) were ubiquitous except p,p′-DDT. Results indicate historical inputs of technical DDT with considerable biodegradation and photochemical transformations. Generally, the ∑ chlors in sediments and surface-mixed layer water samples decreased following heptachlor > heptachlor epoxide > α-Chlordane > γ-Chlordane. The α-chlordane/γ-chlordane ratios indicate a mix of recent commercial and historical chlordane contamination sources. Concentrations of most OCPs significantly exceeded sediment quality guidelines suggesting that toxicity to benthic-dwelling faunas is estimated to be likely.

Molecular and optical signatures of photochemical transformation of dissolved organic matter: Nonnegligible role of suspended particulate matter in urban river

Natural dissolved organic matter (DOM) is one of the Earth's dynamic carbon pools and a key intermediate in the global carbon cycle. Photochemical processes potentially affect DOM composition and activity in surface water. Suspended particulate matter (SPM) is the integral component of slow-moving rivers, and holds the potential for photochemical reactivity. To further investigate the influence of SPM on DOM photochemical transformation, this study conducted experiments comparing samples with and without SPM irradiated under simulated sunlight. Surface water samples from slow-moving urban rivers were collected. DOM optical characteristics and molecular features obtained by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) were investigated. Photolabile DOM was enriched in unsaturated and highly aromatic terrestrial substances. Photoproduced DOM had low aromaticity and was dominated by saturated aliphatics, protein-like substances, and carbohydrates. Study results indicated that the presence of SPM had a nonnegligible impact on the molecular traits of DOM, such as composition, molecular diversity, photolability, and bioavailability during photochemical reactions. In the environment affected by SPM, molecules containing heteroatoms exhibit higher photosensitivity. SPM promotes the photochemical transformation of a wider range of chemical types of photolabile DOM, particularly nitrogen-containing compounds. This study provides an essential insight into the more precise simulation of photochemical reactions of DOM influenced by SPM occurring in natural rivers, contributing to our understanding of the global carbon cycle from new theoretical perspectives.

Chemical and oxidative properties of fine particulate matter from near-road traffic sources

The toxicity associated with the fine particulate matter (PM2.5) has not been well studied, particularly in relation to the emissions from on-road vehicles and other sources in low- and middle-income countries such as India. Thus, a study was conducted to examine the oxidative potential (OP) of PM2.5 at a roadside (RS) site with heavy vehicular traffic and an urban background (BG) site in Mumbai using the dithiothreitol (DTT) assay. Simultaneous gravimetric PM2.5 was measured at both sites and characterized for carbonaceous constituents and water-soluble trace elements and metals. Results depicted higher PM2.5, elemental carbon (EC), and organic carbon (OC) concentrations on the RS than BG (by a factor of 1.7, 4.6, and 1.2, respectively), while BG had higher water-soluble organic carbon (WSOC) levels (by a factor of 1.4) and a higher WSOC to OC ratio (86%), likely due to the dominance of secondary aerosol formation. In contrast, the measured OPDTTv at RS (8.9 ± 5.5 nmol/min/m3) and BG (8.1 ± 6.4 nmol/min/m3) sites were similar. However, OPDTTv at BG was higher during the afternoon, suggesting the influence of photochemical transformation on measured OPDTTv at BG. At RS, OC and redox-active metals (Cu, Zn, Mn, and Fe) were significantly associated with measured OP (p < 0.05), while at BG, WSOC was most strongly associated (p < 0.05). The coefficient of divergence (COD) for PM2.5, its chemical species, and OPDTTv was >0.2, indicating spatial heterogeneity between the sites, and differences in emission sources and toxicity. The estimated hazard index (HI) was not associated with OPDTTv, indicating that current PM2.5 mass regulations may not adequately capture the health effects of PM2.5. The study highlights the need for further studies examining PM2.5 toxicity and developing toxicity-based air quality regulations.

Effect of pulsed light on curcumin chemical stability and antioxidant capacity.

Curcumin is the major bioactive component in turmeric with potent antioxidant activity. Little is known about how pulsed light (PL) technology (an emerging non-thermal food processing technology relying on high intensity short duration flashes of light) can affect the chemical stability and antioxidant capacity of curcumin. This study found that PL treatment of fluence levels from 0 to 12.75 J/cm2 produced a fluence-dependent reduction in curcumin content. These results paralleled the production of a tentative curcumin dimer, identified as a potential photochemical transformation product. PL-treated curcumin at relatively higher fluence levels decreased chemical-based ORAC and ABTS antioxidant capacity, relative to control (P < 0.05). This contrasted the effect observed to increase coincidently both intracellular antioxidant capacity (e.g., DCFH-DA (P < 0.05)) and GSH/GSSG ratio (P < 0.05), respectively, in cultured differentiated Caco-2 cells. In conclusion, the application of PL on curcumin results in photochemical transformation reactions, such as dimerization, which in turn, can enhance biological antioxidant capacity in differentiated Caco-2 cells.