Involvement Of Singlet Oxygen Research Articles

Construction of CuO@CuS/PVDF composite membrane and its superiority for degradation of antibiotics by activation of persulfate

Antibiotics were frequently detected in influent of wastewater treatment plants (WTPs), which brought potential crisis to human beings and the environment. In this study, series of CuO@CuS nanocomposites were synthesized by co-precipitation combined with microwave treatment, which was employed to activate persulfate (PS) toward degrading tetracycline (TC). Results indicated that CuO@CuS with a molar ratio of 2:1 displayed the superior PS activation performance with TC removal efficiency. In order to further improve the recycle and utilization of nano-composites, CuO@CuS/PVDF membrane were constructed, leading to a greatly enhancement of TC removal efficiency (87.4%) within 3 h. Subsequently, physicochemical properties of CuO@CuS/PVDF membrane were characterized systematically. The effects of operating parameters, such as PS concentration, the initial pH value and co-existing ion on the CuO@CuS/PVDF-PS system were optimized in detail. The analysis results disclosed that when [PS] = 0.4 g/L, pH = 3, the system exhibited excellent degradation efficiency by elimination of contaminant solution. Furthermore, the enhanced mechanism of CuO@CuS/PVDF-PS system for organic pollutants elimination was proposed and confirmed, which was ascribed to the involvement of hydroxyl radical (·OH), sulfate radical (SO4·−) and singlet oxygen (1O2). Thence, the constructed membrane/PS system exhibited potential application in wastewater treatment.

Rapid transformation of H1-antihistamines cetirizine (CET) and diphenhydramine (DPH) by direct peroxymonosulfate (PMS) oxidation

With growing interest in advanced oxidation processes (AOPs), the number of research studies on peroxymonosulfate (PMS) mediated pollutant degradation has increased significantly due to its high radical generation potential upon activation. However, rare studies have focused on the non-radical based PMS reactions. In this study, degradation of model H1-antihistamines cetirizine (CET) and diphenhydramine (DPH) by unactivated PMS was investigated. Addition of scavengers to the reaction mixture ruled out the involvement of hydroxyl radical (OH), sulfate radical (SO4–), singlet oxygen (1O2) and superoxide anion radical (O2–), indicating direct PMS oxidation as the predominant reaction path. Such a mechanism was further supported by the N-oxide products identified by mass spectrometry and nuclear magnetic resonance (NMR) analyses. Solution pH had a pronounced influence on the degradation kinetics regardless the presence or absence of transition metal Fe(II). The highest species dependent second order rate constants were kHSO5-/DPH0 of 175 ± 15.9 M–1 s–1 and kHSO5-/CET- of 36.6 ± 0.16 M–1 s–1. The addition of 100 μM Fe(II) promoted OH mediated degradation of H1-antihistamines and their N-oxide products. This study demonstrated selective transformation with the potential for extensive degradation employing both the direct and catalytic PMS oxidative processes.

Effect of degree of β-chlorination on photocatalytic activity of meso-tetraphenylporphyrin under homogeneous and nanoscale heterogeneous conditions: Chlorination vs. bromination

β-Chlorination of meso-tetraphenylporphyrin, H2TPP leads to the formation of H2TPPClx (X = 2, 4, 6 and 8) with absorption bands in the range of 421–451 and 650–715 nm, for the Soret and Q(0,0) bands, respectively. H2TPPClx were used as photosensitizers for the aerobic photooxidation of cyclooctene under mild conditions and compared with that of the non-chlorinated porphyrin. The lowest degree of catalyst degradation was observed in the case of H2TPPCl2. H2TPPCl2 and H2TPPCl4 showed the highest photocatalytic activity among the series. In spite of the electron-withdrawing effects of the chlorine atoms, with the exception of H2TPPCl2, the chlorinated porphyrins showed a comparable oxidative degradation to that of H2TPP towards oxidative degradation. The preference of blue LED lamp over the red one shows that the absorption at the Soret band region of the chlorinated porphyrins is mainly responsible for the photosensitizer ability of the catalyst. In this regard, H2TPPCl2 and H2TPPCl4 which have the highest overlap with the emission bands of the blue LED lamp showed the highest photocatalytic activity than the other H2TPPClx and H2TPP. Also, control reactions performed in the presence of 1,3-diphenylisobenzofuran and 1,4-benzoquinone provided evidence for the involvement of singlet oxygen as the main reactive oxygen species in this reaction. Singlet oxygen quantum yields (φF) of H2TPPClx were smaller than that of the non-chlorinated porphyrin and decreased as H2TPPCl8 > H2TPPCl4 > H2TPPCl6 ≥ H2TPPCl2. H2TPPClx showed much higher photocatalytic activities than their brominated counterparts. Also, the φF values and oxidative stability of the chlorinated porphyrins were usually higher than those of the brominated porphyrins, with the same degree of β-halogenation. Protonation of H2TPPClx with weak and strong acids (HCOOH, CF3COOH and HCl), also their immobilization on a nano-structured acidic polymer (Amberlyst 15) were used to study the influence of core protonation on photocatalytic activity and oxidative stability of the chlorinated porphyrins.

A unique Si-doped carbon nanocatalyst for peroxymonosulfate (PMS) activation: insights into the singlet oxygen generation mechanism and the abnormal salt effect

The Si-engaged, carbon-activated peroxymonosulfate (PMS) system proceeding via the non-radical oxidation pathway involving singlet oxygen (1O2) represents a promising advanced oxidation process.

Synthesis, Structure, and Chemical Nuclease Activity of DNA with [Cu(dpq)(L–Met)Cl] · H2O

A new mononuclear copper complex [Cu(dpq)(L–Met)Cl] ⋅ H2O has been designed and synthesized using the phenanthroline derivative dipyridoquinoxaline (dpq). This complex has been characterized by element analysis and X-ray single crystal diffraction. The crystal structure of the complex belongs to a monoclinic system with space group C2/c. Binding of the complex to DNA has been investigated by absorption spectroscopy, fluorescence spectroscopy, and agarose gel electrophoresis. Spectrophotometric studies have showed that the mode of binding is intercalation with a binding constant Kb of 1.25 × 103 L mol–1. Additionally, the complex could quench an ethidium bromide-DNA complex. The apparent binding constant value for the complex is 1.89 × 10 5 L mol–1, which is slightly lower than the classical binding constant of 107 L mol–1. In addition, the quenching mechanism of the complex has been not static or dynamic. Agarose gel electrophoresis has shown that the complex cleaved circular pBR322 plasmid DNA to both nicked and linear forms; at higher concentrations and longer reaction times, the cutting results have been improved. The cleavage mechanism between the complex and plasmid DNA may involve singlet oxygen and hydroxyl radical as reactive oxygen species.

Formulation induces direct DNA UVA photooxidation. Part I. Role of the formulating cationic surfactant

Cetyltriethylammonium bromide (CTEAB) was considered as a cationic surfactant to form lipoplexes with DNA. In TRIS/HCl buffer, CTEAB self-assembles above its critical micelle concentration (CMC = 0.15 mM) into small spherical micelles as determined by complementary scattering techniques. This surfactant readily interacts with the supercoiled plasmid DNA pBR322 via electrostatics and hydrophobic interactions. Upon increasing surfactant concentration, successive phase transitions are observed from partial neutralization to full compaction of DNA as evidenced by agarose gel electrophoresis, tensiometry, pyrene fluorescence, UV–Vis absorbance and circular dichroism measurements. Under UVA radiation (λ ≥ 335 nm), we show that the presence of the surfactant increases photooxidized damage on DNA especially in the compacted state. A mechanistic study using selective scavengers shows the involvement of singlet oxygen in these oxidative processes due to the direct UVA absorption of DNA itself.

Synchro-Excited Free-Running Single Photon Counting: A Novel Method for Measuring Short-Wave Infrared Emission Kinetics.

Time-resolved measurements of short-wave infrared (SWIR) photoluminescence on the submicrosecond to millisecond scale are needed for physical and chemical studies involving singlet oxygen, single-walled carbon nanotubes, and other samples with weak, slow emission. We present here an alternative to the common method of time-correlated single photon counting (TCSPC) that is well suited to indium gallium arsenide avalanche photodiode (APD) detectors operated in Geiger mode. In the new method, termed synchro-excited free-running single photon counting (SEFR-SPC), excitation pulses from inexpensive laser diodes (providing a variety of wavelengths) are synchronized to detection events from a free-running detector covering the 900 to 1700 nm range. In contrast to traditional TCSPC, data from this method can be rigorously corrected for pile-up distortions, allowing operation with high excitation powers and low repetition rates. A technique is described to extend the system's dynamic range to approximately 108. We also show that SEFR-SPC provides state-of-the-art sensitivity in the SWIR spectral region and that spectrally filtered kinetic data can offer additional insights. A six-step correction protocol has been developed and implemented as a LabVIEW program for very accurate acquisition of kinetic shapes. The SEFR-SPC method will be a valuable tool for studies of weak, long-lived emission sources.

Inside Cover: Optimization of the photodynamic inactivation of prions by a phthalocyanine photosensitizer: The crucial involvement of singlet oxygen (J. Biophotonics 8/2019)

Photodynamic inactivation of prions by disulfonated hydroxyaluminum phthalocyanine.Further details can be found in the article by Marie Kostelanska, Jaroslav Freisleben, Zdenka Backovska Hanusova, et al. (e201800430). image

Optimization of the photodynamic inactivation of prions by a phthalocyanine photosensitizer: The crucial involvement of singlet oxygen.

Prion disorders are fatal neurodegenerative diseases caused by the autocatalytic conversion of a natively occurring prion protein (PrPC ) into its misfolded infectious form (PrPTSE ). The proven resistance of PrPTSE to common disinfection procedures increases the risk of prion transmission in medical settings. Herein, we present the effective photodynamic inactivation (PDI) of prions by disulfonated hydroxyaluminum phthalocyanine (AlPcOH(SO3 )2 ) utilizing two custom-built red light sources. The treatment eliminates PrPTSE signal in infectious mouse brain homogenate with efficiency that depends on light intensity but has a low effect on the overall protein content. Importantly, singlet oxygen (O2 (1 Δg )) is the only species significantly photogenerated by AlPcOH(SO3 )2 , and it is responsible for the PDI of prions. More intensive light conditions show not only higher O2 (1 Δg ) production but also decreases in AlPcOH(SO3 )2 photostability. Our findings suggest that PDI by AlPcOH(SO3 )2 -generated O2 (1 Δg ) represents a promising approach for prion inactivation that may be useful in future decontamination strategies for delicate medical tools.

Contrasting photoreactivity of β2-adrenoceptor agonists Salbutamol and Terbutaline in the presence of humic substances

The photodegradation reactions of two typical β2-adrenoceptor agonists, salbutamol (SAL) and terbutaline (TBL), alone, and in the presence of Aldrich humic acid (AHA) or Suwannee River fulvic acid (SRFA) were investigated by steady-state photolysis experiments, laser flash photolysis (LFP), kinetic modeling and quantum calculation. AHA and SRFA (2–20 mgC L−1) accelerated the phototransformation of both SAL and TBL. For SAL, an inhibiting effect of oxygen on the photodegradation was observed that is fully consistent with the main involvement of excited triplet states of HS (3HS*). On the contrary, oxygen drastically enhanced the photodegradation of TBL showing that 3HS* were negligibly involved in the reaction. The involvement of singlet oxygen was also ruled out because of the low reaction rate constant measured between TBL and singlet oxygen. Quantum calculations were therefore performed to explore whether oxygenated radicals could through addition reactions explain the differences of reactivity of TBL and SAL in oxygen medium. Interestingly, calculations showed that in the presence of oxygen, the addition of phenoxyl on TBL led to the formation of adducts and to the loss of TBL while the same addition reaction on SAL partly regenerated the starting compound and at the end degraded SAL less efficiently. This study is of high relevance to understand the processes involved in SAL and TBL phototransformation and the photoreactivity of HS. Moreover, our findings suggest that TBL might be a promising probe molecule to delineate the role of oxygenated radicals.

The Ability of Functionalized Fullerenes and Surface‐Modified TiO2 Nanoparticles to Photosensitize Peroxidation of Lipids in Selected Model Systems

Photochemical properties of a new class of inorganic nanoparticles, namely a cationic C60 fullerene substituted with three quaternary pyrrolidinium groups (BB6) and a surface-modified nanocrystalline TiO2 with bromopyrogallol red (Brp@TiO2 ) were examined for their effectiveness in photogenerating singlet oxygen and free radicals. In particular, their ability to photosensitize peroxidation of unsaturated lipids was analyzed in POPC:cholesterol liposomes and B16 mouse melanoma cells employing a range of spectroscopic and analytical methods. Because melanoma cells typically are pigmented, we examined the effect of melanin on the photosensitized peroxidation of lipids in liposomes and B16 melanoma cells, mediated by BB6 and Brp@TiO2 nanoparticles. The obtained results suggest that peroxidation of unsaturated lipids, photosensitized by BB6 occurs mainly, although not exclusively, via Type II mechanism involving singlet oxygen. On the other hand, if surface-modified TiO2 is used as a photosensitizer, Type I mechanism of lipid peroxidation dominates, as indicated by the predominant formation of the free radical-dependent cholesterol oxidation products. The protective effect of melanin was particularly evident when BB6 was used as a photosensitizer, suggesting that melanin could efficiently interfere with Type II processes.

Just Add Luminol to Turn the Spotlight on Radziszewski Amidation.

Radziszewski amidation, namely the peroxide-mediated conversion of nitriles into amides, is a chemiluminescent reaction involving singlet oxygen. Its increasing relevance in green chemistry and analytical chemistry makes it an important subject to be discussed in advanced chemistry courses. To turn the attention of lecturers, teachers, and students toward this reaction, the history of its discovery as well as its practical applications is discussed. Moreover, a simple and effective experiment to demonstrate the chemiluminescent properties of Radziszewski amidation is provided.

Unveiling the important roles of coexisting contaminants on photochemical transformations of pharmaceuticals: Fibrate drugs as a case study

Pharmaceuticals are a group of ubiquitous emerging pollutants, many of which have been shown to undergo efficient photolysis in the environment. Photochemically produced reactive intermediates (PPRIs) sensitized by the pharmaceuticals in sunlit natural waters may induce photodegradation of coexisting compounds. In this study, the roles of coexisting contaminants on the phototransformation of pharmaceuticals were unveiled with the fibrate drugs gemfibrozil (GMF), fenofibrate (FNF), and fenofibric acid (FNFA) as model compounds. GMF undergoes initial concentration dependent photodegradation due to the involvement of singlet oxygen (1O2) initiated self-sensitized photolysis, and undergoes pH dependent photodegradation due to dissociation and hydroxyl radical (OH) generation. The decarboxylated intermediates of GMF and coexisting FNFA significantly accelerated the photodegradation of GMF. The promotional effects of the decarboxylated intermediates are attributed to generation of PPRIs, e.g. 1O2, superoxide (O2−), that subsequently react with GMF. Besides, FNFA can also promote the photodegradation of GMF through the electron transfer reaction from ground state GMF to excited state FNFA, leading to the formation of decarboxylated intermediates. The formed intermediates can subsequently also facilitate GMF photodegradation. The results presented here provided valuable novel insights into the effects of coexisting contaminants on the photodegradation of pharmaceuticals in polluted waters.

Photo-induced antibacterial activity of a porphyrin derivative isolated from the harmful dinoflagellate Heterocapsa circularisquama

The dinoflagellate Heterocapsa circularisquama is highly toxic to bivalves. However, significant toxicity to finfish species has not been reported. We previously found that H. circularisquama has light-dependent haemolytic agents. Purification and chemical structural analyses revealed that the haemolytic agent H2-a is a porphyrin derivative, which exhibits light-dependent cytotoxicity toward tumour cells. To clarify the biological activity of H2-a further, its antibacterial activities against Gram-positive and Gram-negative bacteria were investigated in this study. A fraction (F5) equivalent to H2-a purified from the methanol extract of H. circularisquama showed potent light-dependent bactericidal activity toward Staphylococcus aureus, and the activity was concentration- and light illumination time-dependent; however, Escherichia coli was highly resistant to F5. Electron microscopic observation suggested that F5 induces morphological changes in S. aureus in a light-dependent manner. Further analysis using other bacterial species showed that the Gram-positive bacterium Bacillus subtilis was more sensitive than the Gram-negative bacteria Pseudomonas aeruginosa and Vibrio alginolyticus. These results indicate that F5 is a photo-induced antibacterial agent with relatively higher specificity to Gram-positive bacteria. Iodometric assay suggested that singlet oxygen was generated from light-illuminated F5. Histidine, a specific singlet oxygen scavenger, markedly inhibited the photosensitising antibacterial activity of F5 against S. aureus, suggesting the involvement of singlet oxygen in antibacterial activity. The antibacterial spectrum of F5 was evidently different from that of 5,10,15,20-tetra (N,N,N-trimethylanilinium) porphyrin tetratosylate, a commercially available porphyrin compound with antibacterial activity. Our results demonstrate that H. circularisquama has a novel antibacterial photosensitiser, a porphyrin derivative, with relatively higher specificity to Gram-positive bacteria. To the best of our knowledge, this is the first study to discover a porphyrin derivative with antibacterial activity in marine microalga.

Singlet Oxygen and the Origin of Oxygen Functionalities on the Surface of Carbon Electrodes

AbstractThe generation of oxygen‐containing functionalities on pristine carbon surfaces is investigated and shown to be light sensitive, specifically to infra‐red radiation. A mechanistic route involving singlet oxygen, 1O2, is proposed and evidenced.

Singlet Oxygen and the Origin of Oxygen Functionalities on the Surface of Carbon Electrodes.

The generation of oxygen-containing functionalities on pristine carbon surfaces is investigated and shown to be light sensitive, specifically to infra-red radiation. A mechanistic route involving singlet oxygen, 1 O2 , is proposed and evidenced.

Degradation of atrazine in soil by dielectric barrier discharge plasma – Potential singlet oxygen mediation

Dielectric barrier discharge (DBD) was used for the first time to remediate atrazine-polluted soil in a plane-to-grid plasma reactor operating with air at atmospheric pressure. It was established that atrazine degradation efficiency is an increasing function of applied voltage and discharge frequency. The degradation efficiency of atrazine in dry soil reached as high as 86.9% and 98.1% after 60 min of plasma treatment, starting from initial pollutant concentrations of 100 and 10 mg/kg, respectively. Low soil moisture content (5–10%) was found to enhance atrazine degradation in the DBD reactor in comparison to dry soil conditions. Atrazine mineralization after 60 min of treatment was 65.5% as confirmed by total organic carbon (TOC) analysis. The degradation profile of atrazine under DBD treatment was assessed using Fourier transform infrared spectroscopy (FTIR) and ultra-performance liquid chromatography-mass spectrometry (UPLC-MS). Several degradation pathways of atrazine were identified in addition to those previously reported with OH, H2O2, or O3 as the main oxidizing agents. The detected degradants included des-ethyl atrazine, hydroxy atrazine and de-ethylated oligomers of atrazine with the isopropyl group being largely preserved. An atrazine degradation mechanism under DBD conditions is proposed that is consistent with the intermediates identified and supports the dominant involvement of singlet oxygen in initiating the degradation under DBD conditions.

Transformations of S-substituted 5,7-dimethyl-4а,5а-diphenyl-3-thioxoperhydroimidazo[4,5-e]-1,2,4-triazin-2-ones under treatment of 1,2-benzoquinones and photochemical properties of reaction products

For the first time 5,7-di-tert-butyl-1,3-dimethyl-3a,9a-diphenyl-3,3a-dihydro-1H-benzo[5,6][1,4]dioxino[2,3-d]imidazol-2(9aH)-one 13 and complex 9 of 4,6-di-tert-butyl-3-nitrobenzene-1,2-diol with 1,3-dimethyl-4,5-diphenyl-1H-imidazol-2(3H)-one 10a were prepared by the reactions of 3-alkylthio-5,7-dimethyl-4a,7a-diphenyl-4a,5,7,7a-tetrahydro-1H-imidazo[4,5-e]-1,2,4-triazin-6(4H)-ones with 3,5-di-tert-butyl-1,2-benzoquinone 1 and 4,6-di-tert-butyl-3-nitro-1,2-benzoquinone 2, respectively. Photochemical transformations of compounds 9 and 10a as well as products of its photooxygenation involving singlet oxygen under UV irradiation: urea 16, isomeric 1,3-dimethyl-4,5-diphenylimidazolidin-2-ones 17 and 17′, and compound 18 were studied by the spectral-kinetic method. Data on the absorption and fluorescence properties of synthesized compounds and their photoproducts were obtained.

An efficient and simple tool for assessing singlet oxygen involvement in the photo-oxidation of conjugated materials

Upon exposure to photooxidative conditions, organic materials are susceptible to undergo degradation via processes involving radical oxygen species and/or reaction with singlet oxygen (1O2). In this frame, the work herein presents a new and straightforward methodology to clarify the role of highly-reactive 1O2 in the photodegradation mechanism of conjugated materials applied in organic electronics. The general methodology consists in the comparison of the infrared signatures of the conjugated materials after the materials are exposed to photooxidative and thermooxidative conditions and in situ generated 1O2. The methodology was validated by analysing the behaviour of four donor materials commonly used in organic solar cells. Analysis of the degradation mechanism of these materials allowed exemplifying the three possible case scenarios, namely (1) both 1O2 and radical oxygen species are involved in the general photooxidation mechanism of the studied material, (2) the material is unreactive towards 1O2 and thus this species plays no role in the photooxidation process, and (3) the conjugated material is reactive towards chemically produced 1O2 but this species is not the main responsible for the photooxidative degradation of the material. In the latter two cases, a free-radical oxidation process accounts for the photooxidation of the investigated materials. The results derived from this simple, yet enlightening, methodology provide fundamental understanding about the degradation pathways of conjugated materials, which is a key point to develop not only efficient but also stable organic electronic devices.

Activation of peroxymonosulfate by phenols: Important role of quinone intermediates and involvement of singlet oxygen

In this study, the kinetics of reactions of peroxymonosulfate (PMS) with ten model phenols (including phenol, methylphenols, methoxyphenols, and dihydroxybenzenes) were examined. The oxidation kinetics of these phenols by PMS except for catechol and resorcinol showed autocatalysis in alkaline conditions (pH 8.5 and 10), due to the contribution of singlet oxygen (1O2) produced from PMS activation by quinone intermediates formed from their phenolic parents. The oxidation rates of ortho- and meta-substituted methylphenols and methoxyphenols by PMS were much higher than their para-substituted counterparts under similar conditions. This was attributed to the relatively low yields of quinone intermediates from para-substituted phenols. SMX could be efficiently degraded by PMS in the presence of phenols which showed great autocatalysis when they individually reacted with PMS, and the addition of methanol in excess had negligible influence suggesting that 1O2 rather than hydroxyl radical and sulfate radical played an important role. Transformation of SMX by 1O2 underwent three pathways including hydroxylation of aniline ring, oxidation of aromatic amine group to generate nitro-SMX, and oxidative coupling to generate azo-SMX and hydroxylated azo-SMX. These results obtained in this work improve the understanding of in situ chemical oxidation using PMS for remediation of subsurface, where phenolic and quinonoid moieties are ubiquitous.