Triplet Oxygen Research Articles

Laser-induced singlet oxygen selectively triggers oscillatory mitochondrial permeability transition and apoptosis in melanoma cell lines

Singlet oxygen (1O2) is an electronically excited state of triplet oxygen which is less stable than molecular oxygen in the electronic ground state and produced by photochemical, thermal, chemical, or enzymatic activation of O2. Although the role of singlet oxygen in biology and medicine was intensively studied with photosensitisers, using of these compounds is limited due to toxicity and lack of selectivity. We generated singlet oxygen in the skin fibroblasts and melanoma cell lines by 1267 nm laser irradiation. It did not induce production of superoxide anion, hydrogen peroxide or activation of lipid peroxidation in these cells confirming high selectivity of 1267 nm laser to singlet oxygen. 1O2 did not change mitochondrial membrane potential (ΔΨm) in skin fibroblasts but induced fluctuation in ΔΨm and complete mitochondrial depolarisation due to opening permeability transition pore in B16 melanoma cells. 1267 nm irradiation did not change the percentage of fibroblasts with necrosis but significantly increased the number of B16 melanoma cells with apoptosis. Thus, singlet oxygen can induce apoptosis in cancer B16 melanoma cells by opening of mitochondrial permeability transition pore (PTP) but not in control fibroblasts.

Spin engineering of single-site metal catalysts

Single-site metal atoms (SMAs) on supports are attracting extensive interest as new catalytic systems because of maximized atom utilization and superior performance. However, rational design of configuration-optimized SMAs with high activity from the perspectives of fundamental electron spin is highly challenging. Herein, N-coordinated Fe single atoms are successfully distributed over axial carbon micropores to form dangling-FeN4 centers (d-FeN4). This unique d-FeN4 demonstrates much higher intrinsic activity toward oxygen reduction reaction (ORR) in HClO4 than FeN4 without micropore underneath and commercial Pt/C. Both theoretical calculation and electronic structure characterization imply that d-FeN4 endows central Fe with medium spin (t2g4 eg1), which provides a spin channel for electron transition compared with FeN4 with low spin. This leads to the facile formation of the singlet state of oxygen-containing species from triplet oxygen during the ORR, thus showing faster kinetics than FeN4. This work provides an in-depth understanding of spin tuning on SMAs for advanced energy catalysis.

Simulation of thermal field distribution in biological tissue and cell culture media irradiated with infrared wavelengths.

In recent years, there has been a growing interest in the singlet form of oxygen as a regulator of the physiological functions of cells. One of the ways to generate singlet oxygen is direct optical excitation of the triplet oxygen form. Since molecular oxygen weakly absorbs light, high power is required to obtain sufficient concentrations of singlet oxygen. However, the increase in the radiation power of laser can induce a local temperature increase around the laser spot. This may be critical considering the temperature governs every biological reaction within living cells, in particular. Here, the interaction of laser radiation of infrared wavelengths, generating singlet oxygen, with biological tissues and cell culture media was simulated. Using the COMSOL Multiphysics software, the thermal field distribution in the volume of skin, brain tissue and cell culture media was obtained depending on the wavelength, power and exposure time. The results demonstrate the importance of taking temperature into account when conducting experimental studies at the cellular and organismal levels.

Efficient catalysis of endogenous oxygen generation for MRI-guided synergistic photodynamic therapy by ternary nanostructure

Tumor hypoxic microenvironment is a crucial bottleneck limiting its clinical therapeutic efficacy. Therefore, how to design nano-drugs with clear structure and function based on the characteristics of the tumor microenvironment to overcome the hypoxia of tumors and achieve high-efficiency and low-toxicity treatment is an important strategy to solve the problem of tumor treatment. Herein, we design and synthesize a ternary nano-platform, Ce6-AuCeFe, with longan structure by a simple method to obtain Magnetic Resonance Imaging (MRI)-guided cascade reagent to enhance cancer Photodynamic therapy (PDT). The AuCeFe was synthesized via a one-pot reaction with controlled morphology and loaded with Ce6 to assist PDT. Ce6-AuCeFe was synthesized as a hybrid nanocatalyst model of glucose oxidase and peroxidase mimics because of its outstanding catalytic performance. As nontoxic glucose was continuously converted to abundant H2O2 by AuCeFe, the excess H2O2 was subsequently catalyzed by the peroxidase-like activity of AuCeFe to generate O2, which helped to alleviate the hypoxic tumor microenvironment. The mechanistic studies elucidate that the ternary nanoparticles facilitate triplet oxygen into singlet oxygen through energy transfer, which leads to highly toxic reactive oxygen species (ROS) production combined with PDT, achieving much desirable cancer cells killing effect under hypoxia conditions. Meanwhile, the degradation of Ce6-AuCeFe under tumor microenvironment also enhanced on T1 and T2-weighted MRI, indicating that Ce6-AuCeFe could be used as two-mode MRI contrast agents for precisely guiding in therapy. In summary, our study provides a novel strategy for tumor therapy by utilizing well-structured metal composites to achieve high-efficiency oxygen production, thereby overcoming the hypoxic tumor microenvironment.

A synergistic study on the synthesis of juglone via photooxidation in a UV–Vis LED based photomicroreactor

Photochemical transformations are mobilized by traceless photons of narrow or broad visible light wavelength and have been proven as a green and sustainable synthesis route for organic compounds. However, most of such investigations were restricted to only parametric studies, lacking in examining a synergistic involvement of actinometric, kinetics and mass transfer mechanisms on product yield. To address this vital issue, we executed the synthesis of natural product juglone via the photooxidation of 1,5-dihydroxynapthalene (DHN) mediated through singlet oxygen, which was produced by triplet–triplet energy transfer from three porphyrin-based photosensitizers to triplet oxygen upon irradiation from UV–Vis LED. Compared to the other two photosensitizers, m-TcPP (meso-tetracarboxyphenylporphyrine) showed a higher molar extinction coefficient and remarkable energy transfer, resulting in higher DHN conversion and juglone yield. Full DHN conversion and 82% yield were obtained at the m-TcPP loading of 2.0 mol% and the residence time of 22.1 min. Actinometric investigation showed that the photon flux was significantly improved by rising m-TcPP and DHN concentrations. The maximum radiant power absorbed by the DHN photooxidation could reach 17.3% of the total input power of UV–Vis LED strip. The detailed reaction mechanism of the DHN photooxygenation was discussed through the Jablonski diagram and rate constants of intermediate steps were determined. A positive relationship between the photon flux and the apparent rate constant was found by rising m-TcPP concentration from 0.01 to 0.05 mM, while the rise in DHN concentration from 5.0 to 10.0 mM resulted in a negative correlation between these parameters. Consequently, a synergistic improvement of photon flux and apparent rate constant was necessitated to attain complete DHN conversion and high juglone yield.

Instability in the System of the Distant Post-AGB Star LS III +52°24 (IRAS 22023+5249)

The optical spectra of the B-supergiant LS III+52 24 (IRAS 22023+5249) obtained at the 6-meter telescope BTA with a resolution R$\ge$60000 in 2010-2021 revealed signs of wind variability and velocity stratification in the extended atmosphere. The H$\alpha$ and H$\beta$ lines have a P Cyg type profile; their wind absorption changes position in the range from $-270$ to $-290$ km/s. The intensity of the H$\alpha$ emission reaches record values with respect to the local continuum: I/Icont $\approx$70. The stationary radial velocity according to the positions of symmetric forbidden emissions and permitted metal emissions was taken as the systemic velocity Vsys=$-149.6\pm$0.6 km/s. Based on the positions of absorptions of NII and OII ions, a time variability of the radial velocity in the range from $-127.2$ to $-178.3$ km/s was found for the first time for this star. This variability indicates the possible presence of a companion and/or atmospheric pulsations. The change of the oxygen triplet profile OI 7775 A due to the occurrence of unstable emission was registered. The set of interstellar absorptions of the NaI D-lines profile in the range from $-10.0$ to $-167.2$ km/s is formed in the Local Arm and subsequent arms of the Galaxy. The distance to the star, d$\ge$5.3 kpc, combined with the high systemic velocity, indicates that the star is located in the Galaxy beyond the Scutum-Crux arm.

Regulation of Irradiation‐Dependent Long‐Lived Room Temperature Phosphorescence by Controlling Molecular Structures of Chromophores and Matrix

AbstractLong‐lived room temperature phosphorescent (LRTP) materials have attracted widespread attention due to their unique luminescence phenomenon and application prospects in the fields of information encryption and bioimaging. However, achieving intelligent response LRTP from amorphous polymers under atmospheric conditions is fascinating but challenging. Here, a series of irradiation‐dependent LRTP systems with ultralong phosphorescent lifetime and high quantum yields are fabricated by a consuming triplet oxygen strategy, and the LRTP performance exhibits obvious chromophore structure and polymeric molecular weight dependence. By extending the UV irradiation time, the phosphorescence lifetime can be increased by hundreds of times, which can exceed 2 s. Experimental results prove that the molecular weight of the polymer matrix, the doping concentration, and the structure of the chromophore have a crucial influence on the stimulus‐response speed and phosphorescence properties of the materials. This kind of intelligent and irradiation‐dependent LRTP material has excellent application prospects in the field of multi‐level information encryption. This work will effectively promote the development of stimulus‐responsive LRTP materials under atmospheric conditions.

Photodegradation of tetracycline by asymmetrical zinc(II)phthalocyanines conjugated to cobalt tungstate nanoparticles

This work focused on syntheses of novel asymmetrically tetra substituted Zn phthalocyanines (ZnPc) each containing a single carboxyl group, with the other substituents bearing alkynyl (complex 1) and fluorine containing groups (complexes 2 and 3). The complexes were conjugated to cobalt tungstate nanoparticles and employed as efficient photocatalysts for degradation of tetracycline in water. ZnPc complexes and their conjugates showed good photophysical and photochemical properties behaviour with complex 1 giving higher triplet and singlet oxygen quantum yields compared to 2 and 3. Complex 1 showed higher activity towards the photodegradation of tetracycline compared to complexes 2 and 3, with higher kobs and initial rates for the former. The photocatalysis obeyed the Langmuir-Hinshelwood kinetic model.

A Perylenediimide-Based Zinc-Coordination Polymer for Photosensitized Singlet-Oxygen Generation

In the face of anthropogenic global warming the design and synthesis of materials, which enable energy transfer processes using sunlight as an energy source, are of high interest. Perylenediimides are a highly absorbing class of chromophores suitable for sunlight absorption and conversion. Therefore, metal–organic frameworks (MOFs) and coordination polymers (CPs) with incorporated organic perylene chromophores are highly interesting materials both for applied, but also fundamental, photophysical research. MOFs/CPs have the advantage of a modular adjustability of interchromophoric distances and angles, and the choice of metal nodes can be used to further tune the material towards the desired photophysical properties. In the present paper, we present a study using a reported organic perylenediimide (PDI) chromophore (H2tpdb) as a linker to be incorporated into coordination polymer and test towards applicability within the photochemical 1O2 generation. In detail, a novel zinc 2D -coordination polymer Zn(tpdb)(DMF)3 is reported, which is synthesized using a solvothermal synthesis with Zn(NO3)2 and a ditopic organic perylene linker. Both the linker and Zn-CP are fully characterized, including SC-XRD, showing a strong aggregation of tightly packed chromophores in the solid state. The photophysical properties are examined and discussed, including the observed shifts within the absorption spectra of the CP are compared to the linker in solution. These shifts are mainly attributed to the for PDIs known H-type aggregation and an additional charge transfer in the framework structure, causing a limited quantum yield of the emission. Finally, the photosensitization of triplet oxygen to singlet oxygen using 1,3-diphenylisobenzofurane (DBPF) as a trapping agent is investigated both for the free linker and the Zn-CP, showing that the perylene chromophore is an efficient photosensitizer and its activity can, in principle, be retained after its incorporation in the coordination polymer.

Autoxidation of Formaldehyde with Oxygen-A Comparison of Reaction Channels.

The autoxidation of formaldehyde through initiation by triplet oxygen is studied via two initial steps: (1) H-atom abstraction and (2) 3O2 addition reaction. The reaction energy profiles show that the reactions are thermodynamically and kinetically demanding. A comparison of the pathways of these initial reactions and the search for a less energy-demanding pathway is presented. The presence of a Brønsted acid has no effect on the energetics of the reaction, while the presence of a single water molecule catalyst enhances the initial reactions. The H-atom abstraction reaction from formaldehyde results in formyl and hydroperoxy radicals. These radicals on further reaction with the second equivalent of 3O2 lead to a CO + 2HO2 product channel. The 3O2 addition reaction to formaldehyde results in a triplet biradical intermediate which further leads to performic acid, the precursor in the synthesis of carboxylic acids from aldehydes. In the presence of water molecules, performic acid is formed in a single kinetic step, and this leads to a CO2 + OH + HO2 product channel upon subsequent reaction with 3O2 in a thermodynamically favorable reaction. The results show that the less established 3O2 addition reaction to aldehydes is a viable route for autoxidation in the absence of purpose-built initiators, in addition to the well-established H-atom abstraction route.

Photophysical Details and O2-Sensing Analysis of a Eu(III) Complex in Polymer Composite Nanofibers Prepared by Electrospinning.

An as-synthesized Eu(III) complex, denoted as Eu(N-DPNQ)(TTD)3, was prepared and characterized, and the antenna mechanism between these ligands and central metal emitter was studied. Here DPNQ means 10-ethyl-10H-indolo [2′,3':5,6]pyrazino[2,3-f][1,10]phenanthroline and TTD is 4,4,4-trifluoro-1-(thiophen-2-yl)butane-1,3-dione. We find that Eu(N-DPNQ)(TTD)3 emission intensity dependents on oxygen concentration, and O2-sensing skill of Eu(N-DPNQ)(TTD)3 in polymer composite nanofibers of poly (vinylpyrrolidone) (PVP) prepared by electrospinning is investigated. Results reveal that the emission quenching of Eu(N-DPNQ)(TTD)3 is caused by the ground state (triplet) oxygen quenching on antenna ligands triplet state. The Eu(N-DPNQ)(TTD)3 doped composite nanofiber with a loading level of 6 wt% exhibits the best result with sensitivity of 2.43 and response time of 10 s, along with linear response.

Theoretical studies of the reactions of methyl ethyl ether with hydrogen atom, triplet oxygen atom and methyl radical

An analysis of reaction mechanisms and kinetics of the CH3OC2H5 + H, CH3OC2H5 + CH3• and CH3OC2H5 + O(3P) reactions has been examined. The M06-2X/cc-pVTZ level of theory has been used to calculate the geometries of all species and the standard reaction Gibbs free energy was calculated at the same theory. Fifteen reaction channels have been described, including the H-abstraction channels and CH3-transfer channels. Electronic energies were refined by CCSD(T)/CBS method and the rate coefficients were calculated using CVT/SCT method. For the title reactions, the H-abstraction channels from the CH2 group were identified as major reaction channels.

Empirical DFT Model to Predict Triplet Quantum Yield Through Singlet Oxygen Yields

AbstractTriplet photosensitizers can be used for a variety of applications, including photocatalysis, OLEDs, and photodynamic therapy. Excited triplet states can be quenched by triplet oxygen to make singlet oxygen. Often the singlet oxygen quantum yield (Φ▵) is used as a lower approximation for the triplet yield. Unpredictable effects of even minor structural changes can drastically alter the Φ▵ and complicate the design of new triplet photosensitizers. The most common strategy to increase Φ▵ is to incorporate heavy atoms, promoting the “heavy atom effect”. However, the position and the identity of the heavy atom greatly influences the Φ▵. We have created a predictive model that correlates calculated natural atomic orbital composition of the heavy atom(s) contributing to the frontier molecule orbitals of a photosensitizer with the experimental Φ▵. The model, derived from several fluorescein derivatives, provides a calculated Φ▵ in agreement with the experimental values for a variety of well‐known photosensitizers, including rhodamine dyes, fluorescein derivatives, and octahedral metal complexes.

Electronic couplings for singlet oxygen photosensitization and its molecular orbital overlap description

The reaction of triplet fusion, also named triplet-triplet annihilation, has attracted a lot of research interests because of its wide applications in photocatalytic, solar cells, and bioimaging. As for the singlet oxygen photosensitization, the reactive singlet oxygen species are generated through the energy transfers from photosensitizer (PS) to ground triplet oxygen molecule. In this work, we computed the electronic coupling for singlet oxygen photosensitization using the nonadiabatic coupling from the quantum chemical calculation. Then we utilized the molecular orbital (MO) overlaps to approximate it, where the MOs were computed from isolated single molecules. As demonstrated with quantitative results, this approach well describes the distribution of the coupling strength as the function of the intermolecular distance between the sensitizer and O2, providing us a simple but effective way to predict the coupling of triplet fusion reactions.

Photochromic Coordination Compound: Oxygen-Assisted Photoinduced Color Change for Triplet Oxygen Detection.

Detection of oxygen though color change is highly desirable for rapid qualitative analysis like the case of pH test papers. This work demonstrates 3O2-assisted photoinduced color change of a new photochromic coordination compound [Zn(4-aminopyridine)2Cl2] (ZnaPyCl), which represents the first photochromic compound with a selective 3O2 detection ability. The compound underwent photoinduced intraligand charge separation and formed a stable diradical-like triplet species in the solid state or in frozen solution, accompanied by conversion of triplet oxygen to singlet oxygen.

Controlling SARS-COV 2 by triplet oxygen molecules, spinning bubbles and other spinors- a hypothesis

Controlling SARS-COV 2 by triplet oxygen molecules, spinning bubbles and other spinors- a hypothesis

Photodynamic therapy characteristics of phthalocyanines in the presence of boron doped detonation nanodiamonds: Effect of symmetry and charge

The synthesis, photophysicochemical and photodynamic therapy (PDT) activities of benzothiazole substituted zinc phthalocyanine (Pc): 1 (asymmetrically substituted and composed of no charges), 2 (asymmetrically substituted and composed of three positive charges), and 3 (symmetrically substituted and composed of four positive charges), are presented. The triplet and singlet oxygen quantum yields were highest for complex 2 showing the importance of asymmetry and charge. The complexes are covalently and non-covalently linked to B doped detonation nanodiamonds (B@DNDs) to yield nanohybrids (B@DNDs-1, B@DNDs-2, B@DNDs-3). The presence of B@DNDs, asymmetry and positive charge resulted in improved PDT with the lowest cell viability being observed for B@DNDs-2 at 5%. The cell viability ranged from 5% to 7% for the nanohybrids compared to 19–26% for Pcs alone.

Red haloBODIPYs as theragnostic agents: The role of the substitution at meso position

Three different molecular designs based on BODIPY dye have been proposed as photosensitizers (PSs) for photodynamic therapy (PDT) by the inclusion of halogen atoms (Iodine) at 2,6-positions and with extended conjugation at 3, 5-positions and varying the substitution at meso position. The synthesis is described and their main photophysical features including singlet oxygen production and triplet states were characterized by absorption and fluorescence spectroscopy (steady-state and time-correlated) and nanosecond transient absorption spectroscopy. The results were compared with the commercial Chlorin e6. The three new red-halogen-BODIPYs showed a great balance between singlet oxygen generation (ΦΔ≥0.40) and fluorescence (Φfl≥0.22) for potential application on PDT, and particularly in theragnosis. In vitro experiments in HeLa cells were done to study their performance and to elucidate the best potential candidate for PDT.

Oxygen evolution in spin-sensitive pathways

The overall performance of water electrolysis suffers from the high kinetic barrier in the oxygen evolution reaction (OER) at the anode. Considerable effort has been made on the fundamental understandings of the reaction mechanisms of OER. Recently, the attention has been given to the OER on magnetic catalysts, which is believed being able to promote the kinetics of an OER process from singlet reactants to triplet oxygen. The process in principle involves spin selective electron transfer. Here, we discuss the effects of spin in OER based on the recent advances and summarize our recently proposed mechanisms of the OER in spin-sensitive pathways under the lattice oxygen oxidation mechanism, the interaction of two M−O entity mechanism, and the adsorbate evolution mechanism.

Computational Study of Photochemical Relaxation Pathways of Platinum(II) Complexes.

A series of functional platinum(II) complexes (Pt1-Pt3), which present high activity in four-photon absorption, in vivo imaging, and precise cancer therapy, as previously reported by the experimental work of Zhang et al. (Inorg. Chem. 2021, 60, 2362-2371), are computationally investigated in the article. We find that after the complex goes through four-photon absorption to the S1 state, it undergoes intersystem crossing to the T2 state and eventually reaches the T1 state through internal conversion. On the T1 state, both radiative and nonradiative decay to S0 exit. The radiative decay forms the basis for the phosphorescence imaging in tissues as reported in the original paper. In addition, the nonradiative decay can simultaneously generate cytotoxic singlet oxygen by the excited energy transfer process, also known as triplet oxygen's quenching of triplet states. We conclude that the phosphorescence property as well as the photosensitizer character jointly bring high activity of in vivo imaging and photodynamic therapy to these complexes.