Formation Of Singlet Oxygen Research Articles

Solvent effects on the photooxidation of indolepyrazines

Photodestruction of 2-(pyrazin-2′-yl)-1H-indole and 2,5-di(1H-indol-2′-yl)pyrazine involves singlet oxygen generation and its rapid insertion into the indole ring with the formation of benzoxazinone derivatives: 2-(pyrazin-2-yl)-4H-3,1-benzoxazin-4-one and 2-[5-(1H-indol-2-yl)pyrazin-2-yl]-4H-3,1-benzoxazin-4-one. The quantum yield of this reaction strongly depends on the environment. It is definitely smaller in protic methanol than in aprotic acetonitrile or n-hexane. The observed effect of photostabilization is explained by formation of hydrogen bonded complexes between the chromophore and alcohol, which results in lower triplet formation efficiency and, in consequence, decrease of singlet oxygen formation quantum yield.Graphical abstract

Highly Charged Ru(II) Polypyridyl Complexes as Photosensitizer Agents in Photodynamic Therapy of Epithelial Ovarian Cancer Cells.

Ovarian cancer recurrence is frequent and associated with chemoresistance, leading to extremely poor prognosis. Herein, we explored the potential anti-cancer effect of a series of highly charged Ru(II)-polypyridyl complexes as photosensitizers in photodynamic therapy (PDT), which were able to efficiently sensitize the formation of singlet oxygen upon irradiation (Ru12+ and Ru22+) and to produce reactive oxygen species (ROS) in their corresponding dinuclear metal complexes with the Fenton active Cu(II) ion/s ([CuRu1]4+ and [Cu2Ru2]6+). Their cytotoxic and anti-tumor effects were evaluated on human ovarian cancer A2780 cells both in the absence or presence of photoirradiation, respectively. All the compounds tested were well tolerated under dark conditions, whereas they switched to exert anti-tumor activity following photoirradiation. The specific effect was mediated by the onset of programed cell death, but only in the case of Ru12+ and Ru22+ was preceded by the loss of mitochondrial membrane potential soon after photoactivation and ROS production, thus supporting the occurrence of apoptosis via type II photochemical reactions. Thus, Ru(II)-polypyridyl-based photosensitizers represent challenging tools to be further investigated in the identification of new therapeutic approaches to overcome the innate chemoresistance to platinum derivatives of some ovarian epithelial cancers and to find innovative drugs for recurrent ovarian cancer.

A Carbon Nanodot Based Near-Infrared Photosensitizer with a Protein-Ruthenium Shell for Low-Power Photodynamic Applications.

Near-infrared (NIR) light-activated photosensitization represents an encouraging therapeutic method in photodynamic therapy, especially for deep tissue penetration. In this context, two-photon activation, i.e., utilization of photons with relatively low energy but high photon flux for populating a virtual intermediate state leading to an excited state, is attractive. This concept would be highly advantageous in photodynamic therapy due to its minimal side effects. Herein, we propose that the combination of plasma protein serum albumin (HSA) containing several Ru complexes and NIR two-photon excitable carbon nanodots (Cdots), termed HSA-Ru-Cdots, provides several attractive features for enhancing singlet oxygen formation within the mitochondria of cancer cells stimulated by two-photon excitation in the NIR region. HSA-Ru-Cdot features biocompatibility, water solubility, and photostability as well as uptake into cancer cells with an endosomal release, which is an essential feature for subcellular targeting of mitochondria. The NIR two-photon excitation induced visible emission of the Cdots allows fluorescence resonance energy transfer (FRET) to excite the metal-to-ligand charge transfer of the Ru moiety, and fluorescence-lifetime imaging microscopy (FLIM) has been applied to demonstrate FRET within the cells. The NIR two-photon excitation is indirectly transferred to the Ru complexes, which leads to the production of singlet oxygen within the mitochondria of cancer cells. Consequently, we observe the destruction of filamentous mitochondrial structures into spheroid aggregates within various cancer cell lines. Cell death is induced by the long-wavelength NIR light irradiation at 810 nm with a low power density (7 mW/cm2), which could be attractive for phototherapy applications where deeper tissue penetration is crucial.

Synthesis and spectroscopic properties of novel dipyrrole and tetrapyrrole-based photosensitizers with various biphenylyl substituents

Two series of novel pyrrole-based photosensitizers - sulfanyl porphyrazines, and BODIPY derivatives with different biphenylyl substituents such as fluorine atoms, cyano, or alkyloxycarbonyl groups, were synthesized, characterized, and subjected to broad spectroscopic studies. All tested compounds showed intensive light absorption, but only BODYPY derivatives exhibited emission properties. Moreover, iodinated BODIPYs revealed a significant heavy atom effect manifested by a red-shift of the absorption band by about 30 nm, about a 20-fold reduction in fluorescence intensity, and singlet oxygen generation efficiency increased 30–60 times compared to non-iodinated analogs. There was no correlation between the presence of peripheral fluorine atoms, cyano, or alkyloxycarbonyl groups and the absorption or emission properties. However, in both porphyrazines and BODIPYs, singlet oxygen formation was influenced by the substituents in the biphenylyl group. The compounds with cyano groups had the highest singlet oxygen generation ability and fluorine-analogs the lowest. Photodegradation studies revealed low or moderate decomposition of porphyrazines and non-iodinated BODIPYs with 5.9–18.8% of dyes degraded after 20 min of irradiation. However, the iodinated BODIPYs decomposed much faster, with the percentage of degradation in the range of 40.5–65.5%.

The Glycolysis-derived α-Dicarbonyl Metabolite Methylglyoxal is a UVA-photosensitizer Causing the Photooxidative Elimination of HaCaT Keratinocytes with Induction of Oxidative and Proteotoxic Stress Response Gene Expression†.

Cellular oxidative stress contributes to solar ultraviolet (UV) radiation-induced skin photoaging and photocarcinogenesis. Light-driven electron and energy transfer reactions involving non-DNA chromophores are a major source of reactive oxygen species (ROS) in skin, and the molecular identity of numerous endogenous chromophores acting as UV-photosensitizers has been explored. Methylglyoxal (MG), a glycolytic byproduct bearing a UV-active α-dicarbonyl-chromophore, is generated under metabolic conditions of increased glycolytic flux, associated with posttranslational protein adduction in human tissue. Here, we undertook a photophysical and photochemical characterization of MG substantiating its fluorescence properties (Stokes shift), phosphorescence lifetime, and quantum yield of singlet oxygen (1 O2 ) formation. Strikingly, upon UV-excitation (290 nm), a clear emission (around 490 nm) was observed (phosphorescence-lifetime: 224.2 milliseconds). At micromolar concentrations, MG acts as a UVA-photosensitizer targeting human HaCaT-keratinocytes inducing photooxidative stress and caspase-dependent cell death substantiated by zVADfmk-rescue and Alexa-488 caspase-3 flow cytometry. Transcriptomic analysis indicated that MG (photoexcited by noncytotoxic doses of UVA) elicits expression changes not observable upon isolated MG- or UVA-treatment, with upregulation of the proteotoxic (CRYAB, HSPA6) and oxidative (HMOX1) stress response. Given the metabolic origin of MG and its role in human pathology, future investigations should address the potential involvement of MG-photosensitizer activity in human skin photodamage.

Singlet oxygen generation for selective oxidation of emerging pollutants in a flow-by electrochemical system based on natural air diffusion cathode.

The decay of free radicals involved in side reactions is one of the challenges faced by electrochemical degradation of organic pollutants. To this end, a non-radical oxidation system was constructed by a natural air diffusion cathode (ADC) and a Ti-based dimensional stable anode coated by RuO2 (RuO2-Ti anode) for cathodic hydrogen peroxide activation by anodic chlorine evolution. The ADC fabricated by the carbon black of BP2000 produced a stable concentration of hydrogen peroxide of 339.94mg L-1 (current efficiency of 73.4%) without aeration, which was superior to the cathode made by the XC72 carbon black. The flow-by ADC-RuO2 system consisted of an ADC and a RuO2-Ti anode showed high selectivity to aniline (AN) compared to benzoate (BA) in a NaCl electrolyte, whose degradation efficiencies were 97.72% and 1.3%, respectively. Rapid degradations of a mixture of emerging pollutants and AN were also observed in the ADC-RuO2 system, with pseudo-first-order kinetic constants of 0.51, 1.29, 0.89, and 0.99min-1 for Bisphenol A (BPA), tetracycline (TC), sulfamethoxazole (SMX) and AN, respectively. Quenching experiments revealed the main reactive oxygen species for the pollutant degradation was singlet oxygen (1O2), which was also identified by the electron spin resonance (ESR) analysis. Finally, the steady-stable content of 1O2 was quantitatively determined to be 6.25 × 10-11M by the method of furfuryl alcohol (FFA) probe. Our findings provide a fast, low energy consumption and well controlled electrochemical oxidation method for selective degradation of organic pollutants. H2O2 generated on an air diffusion cathode by naturally diffused O2, reacts with ClO- produced from chloride oxidation on the RuO2-Ti anode to form singlet oxygen (1O2). The electrochemical system shows an efficient oxidation to electron-rich emerging pollutants including bisphenol A, tetracycline, sulfamethoxazole and aniline, but a poor performance on the electron-deficient compounds (e.g., benzoate).

Engineering H2O2 and O2 Self‐Supplying Nanoreactor to Conduct Synergistic Chemiexcited Photodynamic and Calcium‐Overloaded Therapy in Orthotopic Hepatic Tumors (Adv. Healthcare Mater. 20/2022)

Photodynamic Therapies In article 2201613 by Chia-Hao Su, Chen-Sheng Yeh, and co-workers, the concept of self-supplying H2O2 and O2 is presented by an all-in-one nanoreactor to process H2O2 and O2 generation, chemiluminescence resonance energy transfer (CRET) activated by the generated H2O2, and energy-transfer to excite photosensitizer resulting in singlet oxygen formation. This allows the conduction of an external light-fee CRET-mediated photodynamic therapy, ushering in a new era in light-based therapeutic interventions.

Oxidative decomposition mechanisms of lithium carbonate on carbon substrates in lithium battery chemistries

Lithium carbonate plays a critical role in both lithium-carbon dioxide and lithium-air batteries as the main discharge product and a product of side reactions, respectively. Understanding the decomposition of lithium carbonate during electrochemical oxidation (during battery charging) is key for improving both chemistries, but the decomposition mechanisms and the role of the carbon substrate remain under debate. Here, we use an in-situ differential electrochemical mass spectrometry-gas chromatography coupling system to quantify the gas evolution during the electrochemical oxidation of lithium carbonate on carbon substrates. Our results show that lithium carbonate decomposes to carbon dioxide and singlet oxygen mainly via an electrochemical process instead of via a chemical process in an electrolyte of lithium bis(trifluoromethanesulfonyl)imide in tetraglyme. Singlet oxygen attacks the carbon substrate and electrolyte to form both carbon dioxide and carbon monoxide—approximately 20% of the net gas evolved originates from these side reactions. Additionally, we show that cobalt(II,III) oxide, a typical oxygen evolution catalyst, stabilizes the precursor of singlet oxygen, thus inhibiting the formation of singlet oxygen and consequent side reactions.

Enhanced degradation of sulfamethoxazole by non-radical-dominated peroxymonosulfate activation with Co/Zn co-doped carbonaceous catalyst: Synergy between Co and Zn

Bimetallic catalysts are often used for peroxymonosulfate (PMS) activation in recent years due to the synergistic effects between two different metal species. However, the synergy between Zn and other transition metal in PMS activation are rarely studied because of the ease of evaporation of Zn species at high temperature. In this work, a Co/Zn co-doped carbonaceous catalyst derived from ZIF-67@ZIF-8 (Z67@8D) was prepared successfully by the core-shell replacement strategy, and used to activate PMS for sulfamethoxazole (SMX) degradation. Due to the co-existence of Co/Zn species (e.g., Co/Zn-N site), Z67@8D showed a much higher catalytic activity than that of Z8D, Z67D, and several commercial oxides. Importantly, the CoZn synergy was deeply revealed by combining experiments and density functional theory (DFT) calculations, in which Zn could adjust the electron distribution of Co, reducing the PMS adsorption energy and thus enhancing PMS decomposition and singlet oxygen (1O2) formation. Moreover, formed ZnO and graphitic structure of Z67@8D could also promote the catalytic activity. In addition, the good stability and reusability, universal applicability, and high environmental robustness of Z67@8D were demonstrated. Our findings may provide a new insight into the Zn-based bimetallic catalysts for PMS activation and pollutant degradation.

Red Wine Inspired Chromophores as Photodynamic Therapy Sensitizers.

Hydroxypyranoflavylium (HPF) cations are synthetic analogs possessing the same basic chromophore as the pyranoanthocyanins that form during the maturation of red wine. HPF cations absorb strongly in the visible spectral region, and most are fluorescent, triplet-sensitize singlet oxygen formation in solution and are strong photooxidants, properties that are desirable in a sensitizer for photodynamic therapy (PDT). The results of this study demonstrate that several simple HPF dyes can indeed function as PDT sensitizers. Of the eight HPF cations investigated in this work, four were phototoxic to a human cervical adenocarcinoma cell line (HeLa) at the 1-10 μmol dm-3 level, while only one of the eight compounds showed noticeable cytotoxicity in the dark. Neither a Type I nor a Type II mechanism can adequately rationalize the differences in phototoxicity of the compounds. Colocalization experiments with the most phototoxic compound demonstrated the affinity of the dye for both the mitochondria and lysosomes of HeLa cells. The fact that relatively modest structural differences, e.g., the exchange of an electron-donating substituent for an electron-withdrawing substituent, can cause profound differences in the phototoxicity, together with the relatively facile synthesis of substituted HPF cations, makes them interesting candidates for further evaluation as PDT sensitizers.

Lanthanum Doped Zinc Molybdate: Antibacterial and Photo-Catalysis Properties

This study investigates unique and specific properties of the lanthanum based zinc molybdate nanocomposite material. The lanthanum zinc molybdate nanocomposite material was synthesized using a simple and low cost “co-precipitation” method. The synthesized nano materials had structural, vibrational and morphological properties, determined by X-ray diffraction, fourier-transform infrared spectroscopy and field emission scanning electron microscopy. The synthesized nanomaterial was characterised using a range of techniques. X-ray diffraction was used to determine a particle size of 65.7 nm of the disc shaped hexagonal particle. Further characterisation was done using UV-visible spectroscopy and band gap energy analysis. The band gap value was found to be 3.58 eV. The nanocomposite also exhibited antibacterial activity against bacterial strains of Escherichia coli and Staphylococcus aureus. In the presence of light and air, nanoparticles of lanthanum zinc molybdate nanocomposite were found to inhibit the growth of Escherichia coli due to generation of singlet oxygen and hydrogen oxide radical. However, the same was not observed for S. aureus. Photocatalytic property of lanthanum zinc molybdate nanocomposite was determined using an aqueous solution of methylene blue dye. lanthanum zinc molybdate nanocomposite showed photo-degradation due to the formation of singlet oxygen and hydrogen oxide radical. Complete decolourization of blue colour of the of methylene blue solution at 6 pH was attained, using 40.0 mg lanthanum zinc molybdate nanocomposite, with a constant time interval. With time, the activity of lanthanum zinc molybdate nanocomposite was also found to decrease due to the formation of a hydrogen oxide layer on the surface of the nano material. This could be washed off with ethanol and distilled water. After drying, the catalytic nano particle could be reused for another reaction.

Unexpected Boost in Activity of a Cu(I) Photosensitizer by Stabilizing a Transient Excited State.

In this study, we present a slight but surprisingly successful structural modification of the previously reported heteroleptic Cu(I) photosensitizer Cubiipo ([(xantphos)Cu(biipo)]PF6; biipo = 16H-benzo-[4',5']-isoquinolino-[2',1':1,2]-imidazo-[4,5-f]-[1,10]-phenanthrolin-16-one). As a key feature, biipo bears a naphthalimide unit at the back, which is directly fused to a phenanthroline moiety to extend the conjugated π-system. This ligand was now altered to include two additional methyl groups at the 2,9-positions at the phenanthroline scaffold. Comparing the novel Cudmbiipo complex to its predecessor, ultrafast transient absorption spectroscopy reveals the efficient suppression of a major deactivation pathway by stabilization of a transient triplet state. Furthermore, quantitative measurements of singlet oxygen evolution in solution confirmed that a larger fraction of the excited-state population is transferred to the photocatalytically active ligand-centered triplet 3LC state with a much longer lifetime of ∼30 μs compared to Cubiipo (2.6 μs). In addition, Cudmbiipo was compared with the well-established reference complex Cubcp ([(xantphos)Cu(bathocuproine)]PF6) in terms of its photophysical and photocatalytic properties by applying time-resolved femto- and nanosecond absorption, step-scan Fourier transform infrared (FTIR), and emission spectroscopies. Superior light-harvesting properties and a greatly enhanced excited-state lifetime with respect to Cubcp enable Cudmbiipo to be more active in exemplary photocatalytic applications, i.e., in the formation of singlet oxygen and the isomerization of (E)-stilbene.

Nannochloropsis oceanica (Eustigmatophyceae) mutants resistant to rose bengal demonstrate high tolerance to oxygen

ABSTRACT The genus Nannochloropsis (Eustigmatophyceae), including N. oceanica, has attracted considerable interest, due to its ability to accumulate high levels of lipids. Under large-scale cultivation outdoors, cells are exposed to a combination of high oxygen and light irradiance conditions that may promote photoinhibition, so selecting strains able to tolerate oxidative stress is desirable. Rose bengal (RB) reacts with oxygen to form singlet oxygen in the presence of light. Therefore, RB can be a very useful tool for testing the sensitivity of algae to oxidative stress and thus identify strains capable of photosynthesis under oxidative stress. In this study, two mutants of N. oceanica, RB2 and RB113, which are resistant to high concentrations of rose bengal, were phenotypically characterized for their sensitivity to high oxygen concentrations. Both strains exhibited levels of catalase and ascorbate peroxidase 1.5- and 3-fold higher, respectively, than the wild type. In addition, the synthesis of carotenoids was lower than in the wild type, indicating lower oxidative stress. These results were confirmed by chlorophyll fluorescence measurements, which indicated a lower sensitivity of the photosynthetic apparatus of the mutants, especially of RB2, even in the presence of H2O2. The results support the hypothesis that resistance to rose bengal may also induce resistance to high dissolved oxygen stress. The ability shown by the mutants to perform photosynthesis more efficiently under high oxygen stress than the wild type makes them promising candidates for outdoor cultures.

Anthraquinone-Based Metal-Organic Frameworks as a Bifunctional Photocatalyst for C-H Activation.

Metal-organic frameworks (MOFs) have gained attention as multifunctional catalytic platforms, allowing us to gain important insights into synergistically activating both C-H bonds and oxygen for improving oxidation. Herein, by ingenious incorporation of anthraquinone, we report an anthraquinone-based MOF as a bifunctional heterogeneous photocatalytic platform to simultaneously activate inert C(sp3)-H bonds and oxygen for C-H bond oxidation. Making use of the rigid framework with the fixation and isolation effect, both a great chemical stability and bifunctional synergistic photocatalytic effects were obtained through the immobilization of anthraquinone into a MOF. Importantly, while decorating two carboxyl groups on anthraquinone, the carbonyl groups of anthraquinone photosensitizers were not involved in coordinating the self-assembly and orderly arranged on the wall of channels that were constructed through a π-π interaction between the anthraquinone moieties in the adjacent layers, which was beneficial to form and stabilize the excited-state radical intermediates in the molecule-fenced channels, and the close proximity between the catalytic sites and the substrates to abstract a hydrogen atom from the substrate through the hydrogen atom transfer process aimed at activating the inertness of C-H bonds. Moreover, high-density-distributed anthraquinone dyes in the confined channels would activate oxygen to form singlet oxygen (1O2) through an energy transfer pathway, further promoting inert C(sp3)-H bond oxidation efficiency. Under visible light irradiation, this anthraquinone-based MOF was successfully applied to explore activation and oxidation of a series of substrates containing benzylic C(sp3)-H bonds in the presence of air or oxygen to produce the corresponding carbonyl products. This bifunctional photocatalytic platform based on a heterogeneous MOF provides an available catalytic avenue to develop a scalable and sustainable synthetic strategy using green and sustainable oxygen as the potent oxidant.

Effect of intermittency factor on singlet oxygen and PGE2 formation in azulene-mediated photodynamic therapy: A preliminary study

In photodynamic therapy, intermittent irradiation modes that incorporate an interval between pulses are believed to decrease the effect of hypoxia by permitting an interval of re-oxygenation. The effect of the irradiation intermittency factor (the ratio of the irradiation pulse time to the total irradiation time) on singlet oxygen formation and inflammatory cytokine production was examined using azulene as a photosensitizer. Effects of difference intermittency factor on singlet oxygen formation and inflammatory cytokine were examined. Azulene solutions (1/10 μM) were irradiated with a 638-nm 500 mW diode laser in fractionation (intermittency factor of 5 or 9) or continuous mode using 50 mW/cm2 at 4 or 8 J/cm2. Singlet oxygen measurement was performed using a dimethyl anthracene probe. Peripheral blood mononuclear cells (PBMC) were stimulated by 10 ng/ml rhTNF-α for 6 h, before addition of 1 and 10 μM azulene solutions and irradiation. PGE2 measurement was undertaken using a human PGE2 ELISA kit. Kruskal-Wallis with Dunn Bonferroni test was used for statistical analyses at p < 0.05.Irradiation of 1 μM azulene+4 J/cm2+intermittency factor of 9 increased singlet oxygen 3-fold (p < 0.0001). Irradiation of 10 μM azulene at either 4 J/cm2+intermittency of 9 or 8 J/cm2+intermittency factor of 5 reduced PGE2 expression in PBMCs to non-inflamed levels. Thus, at 50 mW/cm2, 10 μM azulene-mediated photodynamic therapy with a high intermittency factor and a low energy density generated sufficient singlet oxygen to suppress PGE2 in Inflamed PBMCs.

Protoporphyrin IX Associated with Visible Light for the Treatment of Trichophyton rubrum Causing Onychomycosis - An Updated Review

Systemic medications used during the treatment of onychomycosis caused by Trichophyton rubrum may have relapse, making them costly and insignificant for the patient. Photodynamic therapy (PDT) is an advantageous therapeutic option for disease control, mainly due to the absence of risk of microbial resistance. The action of PDT is combined by three elements: photosensitizer (PS), visible light (VL) and molecular oxygen, leading to the formation of reactive oxygen species (ROS) or singlet oxygen formation (1O2), both ROS (type I mechanism) as 1O2 (type II mechanism) induce damage and death to microbial cells. This research was proposed as a study through a non-systematic review, to investigate the action of PS "Protoporphyrin IX" (Pp IX) associated with visible light on T. rubrum, contemplating clinical and relevant data regarding the treatment of onychomycosis by PDT. PubMed survey was conducted from June 2021 to April 2022. The research strategy included clinical trials, randomized trials, systematic reviews, meta-analyses and reviews in English. Pp IX has affinity for T. rubrum, which is justified by the incorporation of Pp IX into the cell membrane, which led to inhibition by LV irradiation. Thus, the photodynamic process of Pp IX may lead to cell death by type I and II mechanisms. The data found are promising, however, new studies in vitro and in vivo are suggested, since few studies have been found related to the theme.

Electrochemical Characterization of Ionic Dynamics Resulting from Spin Conversion of Water Isomers

Para- and ortho-isomers of water have different chemical and physical properties. Excitations by magnetic field, laser emission or hydrodynamic cavitation are reported to change energetic levels and spin configurations of water molecules that in turn change macroscopically measurable properties of aqueous solutions. Similar scheme is also explored for dissolved molecular oxygen, where physical excitations form singlet oxygen with different spin configurations and generate a long chain of ionic and free-radical reactions. This work utilizes electrochemical impedance spectroscopy (EIS) to characterize ionic dynamics of proposed spin conversion methods applied to dissolving of carbon dioxide CO2 and hydrogen peroxide H2O2 in pure water excited by fluctuating weak magnetic field in μT range. Measurement results demonstrate different ionic reactivities and surface tension effects triggered by excitations at 10−8 J/mL. The CO2- and O2-related reaction pathways are well distinguishable by EIS. Control experiments without CO2/H2O2 input show no significant effects. Dynamics of electrochemical impedances and temperature of fluids indicates anomalous quasi-periodical fluctuations pointing to possible carbonate-induced cyclic reactions or cyclical spin conversion processes. This approach can underlie the development of affordable electrochemical sensors operating with spin conversion technologies with applications in quantum biology, biophysics, and material science.

Mechanical Insights into Activation of Peroxides by Quinones: Formation of Oxygen-Centered Radicals or Singlet Oxygen.

In this work, the mechanism of the activation of peroxides by quinones has been investigated through quantum chemical calculations. Hydrogen peroxide (H2O2), peroxomonosulfate (PMS), peracetic acid (PAA), and CH3OOH were chosen as the model peroxides and p-benzoquinone (p-BQ) and tetrachloro-1,4-benzoquinone (TCBQ) as the model quinones. The nucleophilic attack of peroxides can occur on the carbonyl and olefinic carbons of quinones. For p-BQ, the nucleophilic attack of HO2-, CH3OO-, PMS, and PAA might prefer to occur on the carbonyl carbons, which have more positive atomic charges. Then, further transformation could not be induced from the addition of HO2- and CH3OO- to p-BQ. Comparatively, singlet oxygen (1O2) could be generated in the cases of PMS and PAA. For TCBQ, the chlorine atoms cause the olefinic carbons to carry more positive atomic charges, and then, HO2- preferred to add to the olefinic carbons, which might induce the formation of the hydroxyl radical (•OH). The activation of PMS by TCBQ was similar to that by p-BQ, with the kinetical feasibility of 1O2 formation. These findings may provide some theoretical insights into the reaction of peroxides with quinones, especially into the interconnection between the substitutes and the formation of oxygen-centered radicals (e.g., •OH) and 1O2.

Singlet oxygen involved electrochemical disinfection by anodic oxidation of H2O2 in the presence of Cl−

Due to its potential applications in decentralized water treatment systems, electrochemical synthesis of H2O2 for water decontamination has been widely investigated in recent years. In this study, it is found that the anodic oxidation of the residual H2O2 in the presence of Cl− can be an efficient electrochemical disinfection technology to guarantee the microbiological safety of the treated water. H2O2 can be oxidized by HOCl generated at the anode to form singlet oxygen (1O2). 1O2 has been recognized as an important disinfectant in solar disinfection (SODIS) but it has not yet been reported in electrochemical disinfection. The generation of 1O2 was directly confirmed by the detection of 1O2 monomol emission using a near infrared imaging system. The concentration of 1O2 can reach up to 1.64 pM in the anodic oxidation of H2O2 with Cl−. 1O2 plays an important role in Escherichia coli (E. coli) inactivation, and HOCl only plays a subordinate role in the presence of 1 mM H2O2 due to its low concentration. For example, by adding up the inactivation of E. coli by sole H2O2 and micro-concentration HOCl together only attribute to about 2 log in 60 min but 1O2 itself can account for about 3 log. Besides, the formation of the chlorinated disinfection by-products (Cl-DBPs) was mitigated considerably benefited from the fast reduction of HOCl by H2O2. These findings have potential implications for H2O2-based decentralized water treatment systems and provide a novel strategy for electrochemical disinfection because electrochlorination is having the same problems that chlorination has.

Cobalt(III) Complexes for Light-Activated Delivery of Acetylacetonate-BODIPY, Cellular Imaging, and Photodynamic Therapy.

Cobalt(III) complexes [Co(TPA)(L1)](ClO4)2 (1), [Co(4-COOH-TPA)(L1)](ClO4)2 (2), [Co(TPA)(L2)]Cl2 (3), and [Co(4-COOH-TPA)(L2)]Cl2 (4) having acetylacetonate-linked boron-dipyrromethene ligands (L1, acac-BODIPY; L2, acac-diiodo-BODIPY) were prepared and characterized, and their utility as bioimaging and phototherapeutic agents was evaluated (TPA, tris-(2-pyridylmethyl)amine; 4-COOH-TPA, 2-((bis-(2-pyridylmethyl)amino)methyl)isonicotinic acid). HL1, HL2, and complex 1 were structurally characterized by X-ray crystallography. Complexes 1 and 2 on photoactivation or in a reducing environment (excess GSH, ascorbic acid, and 3-mercaptopropionic acid) released the acac-BODIPY ligand. They exhibited strong absorbance near 501 nm (ε ∼ (5.2-5.8) × 104 M-1 cm-1) and emission bands near 513 nm (ΦF ∼ 0.13, λex = 490 nm) in dimethyl sulfoxide (DMSO). Complexes 3 and 4 with absorption maxima at ∼536 and ∼538 nm (ε ∼ (1.2-1.8) × 104 M-1 cm-1), respectively, afforded high singlet oxygen quantum yield (ΦΔ ∼ 0.79) in DMSO. Complexes 1-4 showed Co(III)-Co(II) redox responses near -0.2 V versus saturated calomel electrode (SCE) in dimethylformamide (DMF)-0.1 M tetrabutylammonium perchlorate (TBAP). The photocleavage of pUC19 DNA by complex 4 revealed the formation of both singlet oxygen and superoxide anion radicals as the reactive oxygen species (ROS). Confocal fluorescence microscopy showed the selective accumulation of complex 1 in the endoplasmic reticulum (ER) in A-549 cells. Complex 4 exhibited a high phototherapeutic index value (PI > 7000) in HeLa cancer cells (IC50 ∼ 0.007 μM in visible light of 400-700 nm, total dose ∼5 J cm-2). The ancillary ligands in the complexes demonstrated a structure-activity relationship and modulated the Co(III)-Co(II) redox potential, the complex solubility, acac-BODIPY ligand release kinetics, and phototherapeutic efficacy.