Fertility after photodynamic inactivation of bacteria in extended boar semen.

Antimicrobial resistance is an increasing challenge in semen preservation of breeding animals, especially in the porcine species. Bacteria are a natural component of semen, and their growth should be inhibited to protect sperm fertilizing capacity and the female's health. In pig breeding, where semen is routinely stored at 17°C in the liquid state, alternatives to conventional antibiotics are urgently needed. Photodynamic inactivation (PDI) of bacteria is a well-established tool in medicine and the food industry but this technology has not been widely adopted in semen preservation. The specific challenge in this setting is to selectively inactivate bacteria while maintaining sperm integrity and functionality. The aim of this study was to test the principle of PDI in liquid stored boar semen using the photosensitizer 5,10,15,20-tetrakis(N-methyl-4-pyridyl)-21H,23H-porphine (TMPyP) and a white light LED-setup. In the first step, photophysical experiments comprising singlet oxygen phosphorescence kinetics of TMPyP and determination of the photosensitizer triplet time revealed a sufficiently high production of reactive singlet oxygen in the Androstar Premium semen extender, whereas seminal plasma acted as strong quencher. In vitro experiments with extended boar semen showed that the established PDI protocol preserves sperm motility, membrane integrity, DNA integrity, and mitochondrial activity while efficiently reducing the bacteria below the detection limit. A proof-of-concept insemination study confirmed the in vivo fertility of semen after photodynamic treatment. In conclusion, using the PDI approach, an innovative tool was established that efficiently controls bacteria growth in extended boar and maintains sperm fertility. This could be a promising contribution to the One Health concept with the potential to reduce antimicrobial resistance in animal husbandry.

Phase-activity relationship of MnO2 nanomaterials in periodate oxidation for organic pollutant degradation.

Manganese dioxide (MnO2), renowned for its abundant natural crystal phases, emerges as a leading catalyst candidate for the degradation of pollutants. The relationship between its crystal phase and catalytic activity, particularly for periodate activation, has remained both ambiguous and contentious. This study delineates the influence of various synthetic MnO2 phase structures on their capabilities in catalyzing periodate-assisted pollutant oxidation. Five distinct MnO2 phase structures (α-, ß-, γ-, δ-, and ε-MnO2) were prepared and evaluated to activate periodate and degrade pollutants, following the sequence: α-MnO2 > γ-MnO2 > ß-MnO2 > ε-MnO2 > δ-MnO2. Through quenching experiments, electron paramagnetic resonance tests, and in situ electrochemical studies, we found an electron transfer-mediated process drive pollutant degradation, facilitated by a highly reactive metastable intermediate complex (MnO2/PI*). Quantitative structure-activity relationship analysis further indicated that degradation efficiency is strongly associated with both the crystal phase and the Mn (IV) content, highlighting it as a key active site. Moreover, the α-MnO2 phase demonstrated exceptional recycling stability, enabling an effective pollutant removal in a continuous flow packed-bed reactor for 168 h. Thus, α-MnO2/PI proved highly effective in mineralizing organic pollutants and reducing their toxicities, highlighting its significant potential for environmental remediation.

Self-Assembled BODIPY@Au Core-Shell Structures for Durable Neuroprotective Phototherapy.

BODIPY analogs are promising photosensitizers for molecular phototherapy; however, they exhibit high dark cytotoxicity and limited singlet oxygen generation capacity. In this study, we developed self-assembled core-shell nanophotosensitizers by linking a bipyridine group to BODIPY (Bpy-BODIPY) and promoting J-aggregation on gold nanourchins. This design enhances photostability and reduces the energy gap between the lowest singlet excited state and the lower triplet state, facilitating efficient singlet oxygen production. Notably, Bpy-BODIPY@Au significantly suppresses tau protein aggregation and enhances neuroprotective action, even in the presence of a phosphatase inhibitor. This work broadens the application of BODIPY chemistry to nanoagents for neuroprotective therapy.

Enhanced Photodynamic Therapy for Neurodegenerative Diseases: Development of Azobenzene-Spiropyran@Gold Nanoparticles for Controlled Singlet Oxygen Generation.

The development of durable photosensitizers is pivotal for advancing phototherapeutic applications in biomedicine. Here, we introduce a core-shell azobenzene-spiropyran structure on gold nanoparticles, engineered to enhance singlet oxygen generation. These nano-photosensitizers exhibit increased structural stability and thermal resistance, as demonstrated by slowed O-N-C bond recombination dynamics via in-situ Raman spectroscopy. Notably, the in-situ formation of merocyanine and a light-induced compact shell arrangement extend its half-life from 47 minutes to over 154 hours, significantly boosting singlet oxygen output. The nano-photosensitizer also shows high biocompatibility and notably inhibits tau protein aggregation in neural cells, even with phosphatase inhibitors. Further, it promotes dendritic growth in neuro cells, doubling typical lengths. This work not only advances chemical nanotechnology but also sets a foundation for developing long-lasting phototherapy agents for treating neurodegenerative diseases.

Investigation of singlet-oxygen-responsive genes in the cyanobacterium Synechocystis PCC 6803.

Singlet oxygen (1O2) is an important reactive oxygen species whose formation by the type-II, light-dependent, photodynamic reaction is inevitable during photosynthetic processes. In the last decades, the recognition that 1O2 is not only a damaging agent, but can also affect gene expression and participates in signal transduction pathways has received increasing attention. However, contrary to several other taxa, 1O2-responsive genes have not been identified in the important cyanobacterial model organism Synechocystis PCC 6803. By using global transcript analysis we have identified a large set of Synechocystis genes, whose transcript levels were either enhanced or repressed in the presence of 1O2. Characteristic 1O2 responses were observed in several light-inducible genes of Synechocystis, especially in the hli (or scp) family encoding HLIP/SCP proteins involved in photoprotection. Other important 1O2-induced genes include components of the Photosystem II repair machinery (psbA2 and ftsH2, ftsH3), iron homeostasis genes isiA and idiA, the group 2 sigma factor sigD, some components of the transcriptomes induced by salt-, hyperosmotic and cold-stress, as well as several genes of unknown function. The most pronounced 1O2-induced upregulation was observed for the hliB and the co-transcribed lilA genes, whose deletion induced enhanced sensitivity against 1O2-mediated light damage. A bioreporter Synechocystis strain was created by fusing the hliB promoter to the bacterial luciferase (lux), which showed its utility for continuous monitoring of 1O2 concentrations inside the cell.

Controlled Photooxidation via Singlet Oxygen Generation by Triplet Harvesting in a Heavy Atom Free Pure Organic Dithienylethene-Naphthalene Diimide.

Noninvasive control over the reversible generation of singlet oxygen (1O2) has found the enormous practical implications in the field of biomedical science. However, metal-free pure organic emitters, connected with a photoswitch, capable of generating "on-demand" 1O2 via triplet harvesting remain exceedingly rare; therefore, the utilization of these organic materials for the reversible control of singlet oxygen production remains at its infancy. Herein, an ambient triplet mediated emission in quinoline-dithienylethene (DTE)-core-substituted naphthalene diimide (cNDI) derivative is unveiled via delayed fluorescence. The quinoline-DTE-cNDI triad displayed enhanced photoswitching efficiency via double FRET mechanism.  It was found to have direct utilization in controlled photosensitized organic transformations via efficient generation of singlet oxygen (yield ΦΔ ~ 0.73). The designed molecule exhibits a long-lived emission (τ ∼ 1.1 µs) and very small singlet-triplet splitting (ΔSET) of 0.13 eV empowering it to display delayed fluorescence. Comprehensive steady state and time-resolved emission spectroscopy (TRES) analyses along with DFT calculations offer detailed understandings into the excited-state manifolds of organic compound and energy transfer (ET) pathways involved in 1O2 generation.

Chemiexcitation-Triggered Photosensitizer Activation for Photooxidation of Aß1-42 Aggregates.

Oxidative degradation of the pathogenic amyloid-ß-peptide (Aß) aggregation is an effective and promising method to treat Alzheimer's disease under light irradiation. However, the limited penetration of external light sources into deep tissues has hindered the development of this treatment. Therefore, we have designed an unprecedented chemiluminescence-initiated photodynamic therapy system to replace external laser irradiation, primarily composed of d-glucose-based polyoxalate (G-poly(oxalate)), the novel photosensitizer (BD-Se-QM), and bis [2,4,5-trichloro-6-(pentoxy-carbonyl) phenyl] ester. BD-Se-QM possesses excellent singlet oxygen (1O2) generation efficiency and the ability to photooxidize Aß1-42 aggregates under white light. G-poly(oxalate) not only helps the nanosystem to cross the blood-brain barrier but also has sufficient oxalate ester groups to significantly enhance the efficiency of chemiluminescence resonance energy transfer. The oxalate ester groups in BD-Se-QM/NPs can chemically react with H2O2 to produce high-energy intermediates that activate BD-Se-QM, which can generate 1O2 to inhibit Aß1-42 aggregates and also promote microglial uptake of Aß1-42, reducing the Aß1-42-induced neurotoxicity. The chemically stimulated nanoplatform not only solves the drug delivery problem but also eliminates the need for external light sources. We anticipate that this chemically excited nanosystem could also be used for targeted delivery of other small molecule drugs.

Hormetic Response of Photosystem II Function Induced by Nontoxic Calcium Hydroxide Nanoparticles.

In recent years, inorganic nanoparticles, including calcium hydroxide nanoparticles [Ca Ca(OH)2 NPs], have attracted significant interest for their ability to impact plant photosynthesis and boost agricultural productivity. In this study, the effects of 15 and 30 mg L-1 oleylamine-coated calcium hydroxide nanoparticles [Ca(OH)2@OAm NPs] on photosystem II (PSII) photochemistry were investigated on tomato plants at their growth irradiance (GI) (580 µmol photons m-2 s-1) and at high irradiance (HI) (1000 µmol photons m-2 s-1). Ca(OH)2@OAm NPs synthesized via a microwave-assisted method revealed a crystallite size of 25 nm with 34% w/w of oleylamine coater, a hydrodynamic size of 145 nm, and a ζ-potential of 4 mV. Compared with the control plants (sprayed with distilled water), PSII efficiency in tomato plants sprayed with Ca(OH)2@OAm NPs declined as soon as 90 min after the spray, accompanied by a higher excess excitation energy at PSII. Nevertheless, after 72 h, the effective quantum yield of PSII electron transport (ΦPSII) in tomato plants sprayed with Ca(OH)2@OAm NPs enhanced due to both an increase in the fraction of open PSII reaction centers (qp) and to the enhancement in the excitation capture efficiency (Fv'/Fm') of these centers. However, the decrease at the same time in non-photochemical quenching (NPQ) resulted in an increased generation of reactive oxygen species (ROS). It can be concluded that Ca(OH)2@OAm NPs, by effectively regulating the non-photochemical quenching (NPQ) mechanism, enhanced the electron transport rate (ETR) and decreased the excess excitation energy in tomato leaves. The delay in the enhancement of PSII photochemistry by the calcium hydroxide NPs was less at the GI than at the HI. The enhancement of PSII function by calcium hydroxide NPs is suggested to be triggered by the NPQ mechanism that intensifies ROS generation, which is considered to be beneficial. Calcium hydroxide nanoparticles, in less than 72 h, activated a ROS regulatory network of light energy partitioning signaling that enhanced PSII function. Therefore, synthesized Ca(OH)2@OAm NPs could potentially be used as photosynthetic biostimulants to enhance crop yields, pending further testing on other plant species.

Photocatalytic Generation of Singlet Oxygen by Graphitic Carbon Nitride for Antibacterial Applications.

Carbon-based functional nanocomposites have emerged as potent antimicrobial agents and can be exploited as a viable option to overcome antibiotic resistance of bacterial strains. In the present study, graphitic carbon nitride nanosheets are prepared by controlled calcination of urea. Spectroscopic measurements show that the nanosheets consist of abundant carbonyl groups and exhibit apparent photocatalytic activity under UV photoirradiation towards the selective production of singlet oxygen. Therefore, the nanosheets can effectively damage the bacterial cell membranes and inhibit the growth of bacterial cells, such as Gram-negative Escherichia coli, as confirmed in photodynamic, fluorescence microscopy, and scanning electron microscopy measurements. The results from this research highlight the unique potential of carbon nitride derivatives as potent antimicrobial agents.

Oncogenic and telomeric G-quadruplexes: Targets for porphyrin-triphenylphosphonium conjugates.

DNA chains with sequential guanine (G) repeats can lead to the formation of G-quadruplexes (G4), which are found in functional DNA and RNA regions like telomeres and oncogene promoters. The development of molecules with adequate structural features to selectively stabilize G4 structures can counteract cell immortality, highly described for cancer cells, and also downregulate transcription events underlying cell apoptosis and/or senescence processes. We describe here, the efficiency of four highly charged porphyrins-phosphonium conjugates to act as G4 stabilizing agents. The spectrophotometric results allowed to select the conjugates P2-PPh3 and P3-PPh3 as the most promising ones to stabilize selectively G4 structures. Molecular dynamics simulation experiments were performed and support the preferential binding of P2-PPh3 namely to MYC and of P3-PPh3 to KRAS. The ability of both ligands to block the activity of Taq polymerase was confirmed and also their higher cytotoxicity against the two melanoma cell lines A375 and SK-MEL-28 than to immortalized skin keratinocytes. Both ligands present efficient cellular uptake, nuclear co-localization and high ability to generate 1O2 namely when interacting with G4 structure. The obtained data points the synthesized porphyrins as promising ligands to be used in a dual approach that can combine G4 stabilization and Photodynamic therapy (PDT).

Cobalt germanium hydroxides with asymmetric electron distribution and surface hydroxyl groups for superb catalytic degradation performances.

Peroxymonosulfate (PMS)-based advanced oxidation processes (AOPs) are attractive approaches for solving the global problem of water pollution, due to the generation of highly-active reactive oxygen species (ROS). Therefore, highly-efficient PMS activation is crucial for promoting the catalytic degradation of environmental pollutants. Here, bimetallic CoGeO2(OH)2 nanosheets with abundant surface hydroxyl groups (CGH) were synthesized via a simple hydrothermal route for PMS activation and degradation of various organic contaminants for the first time. The abundant surface hydroxyl groups (≡Co-OH/≡Ge-OH) could promptly initiate PMS to generate highly-active species: singlet oxygen (1O2), sulfate radicals (SO4·-) and hydroxyl radicals (HO•), while the asymmetric electron distribution among Co-O-Ge bonds derived from the higher electronegativity of Ge than Co further enhances the quick electron transfer to promote the redox cycle of Co2+/Co3+ and Ge2+/Ge4+, thereby achieving an outstanding catalytic capability. The optimal catalyst exhibits nearly 100 % catalytic degradation performance of dyes (Methylene blue, Rhodamine B, Methyl orange, Orange II, Methyl green) and antibiotics (Norfloxacin, Bisphenol A, Tetracycline) over a wide pH range of 3-11 and under different coexisting anion conditions (Cl-, HCO3-, NO3-, HA), suggesting the excellent adaptability for practical usage. This study could potentially lead to novel perspectives on the remediation of water areas such as groundwater and deep-water areas.

Axial O Atom-Modulated Fe(III)-N4 Sites for Enhanced Cascade Catalytic 1O2-Induced Tumor Therapy.

The rational construction of efficient hypoxia-tolerant nanocatalysts capable of generating singlet oxygen (1O2) without external stimuli is of great importance for tumor therapy. Herein, uniformly dispersed and favorable biosafety profile graphitic carbon nitride quantum dots immobilized with Fe-N4 moieties modulated by axial O atom (denoted as O-Fe-N4) are developed for converting H2O2 into 1O2 via Russell reaction, without introducing external energy. Notably, O-Fe-N4 performs two interconnected catalytic properties: glutathione oxidase-mimic activity to provide substrate for subsequent 1O2 generation, avoiding the blunting anticancer efficacy by glutathione. The O-Fe-N4 catalyst demonstrates a specific activity of 79.58 U mg-1 at pH 6.2, outperforming the most reported Fe-N4 catalysts. Density functional theory calculations demonstrate that the axial O atom can effectively modulate the relative position and electron affinity between Fe and N, lowering the activation energy, strengthening the selectivity, and thus facilitating the Russell-type reaction. The gratifying enzymatic activity stemming from the well-defined Fe-N/O structure can inhibit tumor proliferation by efficiently downregulating glutathione peroxidase 4 activity and inducing lipid peroxidation. Altogether, the O-Fe-N4 catalyst not only represents an efficient platform for self-cascaded catalysis to address the limitations of 1O2-involved cancer treatment but also provides a paradigm to enhance the performance of the Fe-N4 catalyst.

Optimal Oxophilicity at the Fe-Nx Interface Enhances the Generation of Singlet Oxygen for Efficient Fenton-Like Catalysis.

In the pursuit of efficient singlet oxygen generation in Fenton-like catalysis, the utilization of single-atom catalysts (SACs) emerges as a highly desired strategy. Here, a discovery is reported that the single-atom Fe coordinated with five N-atoms on N-doped porous carbon, denoted as Fe-N5/NC, outperform its counterparts, those coordinated with four (Fe-N4/NC) or six N-atoms (Fe-N6/NC), as well as state-of-the-art SACs comprising other transition metals. Thus, Fe-N5/NC exhibits exceptional efficacy in activating peroxymonosulfate for the degradation of organic pollutants. The coordination number of N-atoms can be readily adjusted by pyrolysis of pre-assembly structures consisting of Fe3+ and various isomers of phenylenediamine. Fe-N5/NC displayed outstanding tolerance to environmental disturbances and minimal iron leaching when incorporated into a membrane reactor. A mechanistic study reveals that the axial ligand N reduces the contribution of Fe-3d orbitals in LUMO and increases the LUMO energy of Fe-N5/NC. This, in turn, reduces the oxophilicity of the Fe center, promoting the reactivity of *OO intermediate-a pivotal step for yielding singlet oxygen and the rate-determining step. These findings unveil the significance of manipulating the oxophilicity of metal atoms in single-atom catalysis and highlight the potential to augment Fenton-like catalysis performance using Fe-SACs.

Toggling the Oxygen Affinity between Anthracenes and Naphthalenes.

We present the design of an anthracenyl⎯naphthyl (ANT⎯NAPH) dyad and its application as a luminescent 4-stage photo switch. Both segments can individually react with singlet oxygen to switch off an optical response. In their initial form the larger ANT component reacts significantly faster and thus an ANTO2⎯NAPH stage is turned on, observed by optical response of the remaining NAPH. To reduce its reactivity, ANT is substituted with two pyridine rings. This concept is first investigated and quantified on ANT and NAPH as separated molecules. Upon protonation the reaction of ANT becomes significantly slower. For the three possible pyridyl isomers this effect increases along the order meta

A BODIPY-Ferrocene Conjugate for the Combined Photodynamic Therapy and Chemodynamic Therapy with Improved Antitumor Efficiency.

Photodynamic therapy (PDT) can destroy tumor cells by generating singlet oxygen (1O2) under light irradiation, which is limited by the hypoxia of the neoplastic tissue. Chemodynamic therapy (CDT) can produce toxic hydroxyl radical (•OH) to eradicate tumor cells by catalytic decomposition of endogenous hydrogen peroxide (H2O2), the therapeutic effect of which is highly dependent on the concentration of H2O2. Herein, we propose a BODIPY-ferrocene conjugate with a balanced 1O2 and •OH generation capacity, which can serve as a high-efficiency antitumor agent by combining PDT and CDT. The ferrocene moieties endow the as-prepared conjugates with the ability of chemodynamic killing of tumor cells. Moreover, combined PDT/CDT therapy with improved antitumor efficiency can be realized after exposure to light irradiation. Compared with the monotherapy by PDT or CDT, the BODIPY-ferrocene conjugates can significantly increase the intracellular ROS levels of the tumor cells after light irradiation, thereby inducing the tumor cell apoptosis at low drug doses. In this way, a synergistic antitumor treatment is achieved by the combination of PDT and CDT.

Contribution of oxidation reactions to photo-induced damage to cellular DNA.

This review article is aimed at providing updated information on the contribution of immediate and delayed oxidative reactions to the photo-induced damage to cellular DNA/skin under exposure to UVB/UVA radiations and visible light. Low-intensity UVC and UVB radiations that operate predominantly through direct excitation of the nucleobases are very poor oxidizing agents giving rise to very low amounts of 8-oxo-7,8-dihydroguanine and DNA strand breaks with respect to the overwhelming bipyrimidine dimeric photoproducts. The importance of these two classes of oxidatively generated damage to DNA significantly increases together with a smaller contribution of oxidized pyrimidine bases upon UVA irradiation. This is rationalized in terms of sensitized photooxidation reactions predominantly mediated by singlet oxygen together with a small contribution of hydroxyl radical that appear to also be implicated in the photodynamic effects of the blue light component of visible light. Chemiexcitation-mediated formation of "dark" cyclobutane pyrimidine dimers in UVA-irradiated melanocytes is a recent major discovery that implicates in the initial stage, a delayed generation of reactive oxygen and nitrogen species giving rise to triplet excited carbonyl intermediate and possibly singlet oxygen. High-intensity UVC nanosecond laser radiation constitutes a suitable source of light to generate pyrimidine and purine radical cations in cellular DNA via efficient biphotonic ionization.

Mesoporous Vinylene-Linked Covalent Organic Frameworks with Heteroatom-Tuned Crystallinity and Photocatalytic Behaviors.

Owing to its prominent π-delocalization and stability, vinylene linkage holds great merits in the construction of covalent organic frameworks (COFs) with promising semiconducting properties. However, carbon-carbon double bond formation reaction always exhibits relatively low reversibility, unfavorable for the formation of high crystalline frameworks through self-error correction and assembling processes. In this work, we report a heteroatom-tuned strategy to build up a series of two-dimensional (2D) vinylene-linked COFs by Knoevenagel condensation of an electron-deficient methylthiazolyl-based monomer with different triformyl substituted (hetero-)aromatic derivatives. The resulting COFs show high-quality periodic mesoporous structures with high surface areas. Embedding heteroatoms into the backbones enables significantly improving their crystallinity, and finely tailoring their semiconducting structures. Upon visible light stimulation, one of the as-prepared COFs with donor-π-acceptor structure could deliver a nearly seven-fold increase in the catalytic activity of hydrogen generation as compared with the other two. Meanwhile, in combination with high crystallinity and the matched conduction band energy level, such kind of COFs can be able to selectively generate singlet oxygen and superoxide radicals in a high ratio of up to 30:1, allowing for catalyzing aerobic thioanisole oxidation in distinctly tunable activities through the substituent electronic effect of the substrates.

Kinetics of Squalene Quenching Singlet Oxygen and the Thermal Degradation Products Identification.

Squalene has been proven to possess various bioactive functions that are widely present in vegetable oils. A more comprehensive understanding of the reaction behavior of squalene under oxidative conditions was achieved by studying its antioxidant capacity and thermal degradation products. The total singlet oxygen quenching rate constant (kr + kq) of squalene was 3.8 × 107 M-1 s-1, and both physical and chemical quenching mechanisms equally contribute to the overall singlet oxygen quenching. Fourteen degradation products of squalene were identified at 180 °C by using gas chromatography-mass spectrometry (GC-MS). Combining with DFT calculations, the thermal degradation pathway of squalene was proposed: the aldehydes, ketones, and alcohols, and epoxy compounds were formed by the homolytic cleavage of squalene hydroperoxides to form alkoxy radicals, followed by ß-scission of the alkoxyl radicals at adjacent C-C bonds or intramolecular cyclization.

Fluorinated high-valent Sn(IV) porphyrins show remarkable photodynamic activity in cancer cells.

In recent years, Sn(IV) porphyrins have proven to be excellent choice as photosensitizers for photodynamic therapy. This work reports the synthesis, characterization and photodynamic activity of four high-valent fluorinated Sn(IV) porphyrins having different numbers of F-atoms in the peripheral of meso-phenyl groups viz. (Dichloro)meso-tetrakis(4-fluorophenylporphyrinato)stannic(IV), [Sn(IV)FTPP(Cl)2] or Sn1; (Dichloro)meso-tetrakis(2,4-difluorophenylporphyrinato)stannic(IV), [Sn(IV)2,4-FTPP(Cl)2] or Sn2; (Dichloro)meso-tetrakis(2,6-difluorophenylporphyrinato)stannic(IV), [Sn(IV)2,6-FTPP(Cl)2] or Sn3 and (Dichloro)meso-tetrakis(4-trifluoromethylphenylporphyrinato)stannic(IV), [Sn(IV)CF3TPP(Cl)2] or Sn4. The solid-state structure of Sn1 has been determined by single crystal X-ray diffraction analysis. The increasing number of F-atoms attached to the meso-phenyl positions of the porphyrin framework results in increase of their lipophilicity, singlet oxygen quantum yield (ΦΔ) and photocytotoxicity in A549 (human lung adenocarcinoma cells), MCF-7 and MDA-MB-231 (human breast adenocarcinoma) cells. Sn4 predominantly localize in the mitochondria of A549 cells. The light-induced cell death by the Sn(IV) porphyrins in A549 cells occur primarily via apoptosis.

Indirect photodegradation of typical pyrrolizidine alkaloids in water induced by triplet states of dissolved organic matter.

The occurrence of pyrrolizidine alkaloids (PAs) in the aquatic environment has received growing attention due to their persistent mutagenicity and carcinogenicity. In this study, the photooxidation processes of four representative PAs (senecionine, senecionine N-oxide, europine, and heliotrine) in the presence of dissolved organic matter (DOM) were investigated. The excited triplet DOM (3DOM*) was demonstrated to play a dominant role in the phototransformation of PAs. The observed degradation rates of PAs largely depended on the DOM concentration. Alkaline conditions and the presence of HCO3-/CO32- were conducive to the photodegradation. Based on kinetic modeling, the second-order reaction rate constants of PAs with 3DOM* were predicted to be (1.7∼5.3)×108 M-1 s-1, nearly two orders of magnitude higher than those with singlet oxygen (1O2). The monoester structure and electron-withdrawing substituent (e.g., -O atom) substantially affected the one-electron oxidation potential of PAs, which dictates the reaction rates of PAs with 3DOM*. Finally, a tentative degradation pathway of PAs was proposed, involving the formation of an N-centered radical cation through one-electron transfer, which then likely deprotonated and further oxidized to more persistent and toxic phototransformation products with an added oxygen atom into the pyrrole ring.