Synthesis and Photophysical Characterizations of Pyrroloquinolone Photosensitizers for Singlet Oxygen Production†

A series of pyrroloquinolone photosensitizers bearing different halogen substituents (Cl, Br, I) on the heterocyclic framework was studied. These structures were readily prepared through a multi-step synthetic sequence involving an oxidative protocol as an important step to access the quinolone framework. Spectroscopic characterizations and computational investigations were carried out to study the dyes before and after the oxidative step. Interestingly, the fluorescence emission was significantly reduced upon oxidation. In spite of a low photostability under UV light, the pyrroloquinolone photosensitizers proved effective to produce singlet oxygen. Higher singlet oxygen quantum yields were obtained with photosensitizers bearing halogen atoms with a higher atomic number.     

Effect of pressure on the oxidative cracking of C<Subscript>2</Subscript>—C<Subscript>4</Subscript> alkanes

The influence of pressure on the oxidative cracking of light alkanes C₂—C₄ was investigated. An elevated pressure reduces the temperature of oxycracking of light alkanes but with further increase in pressure the effect is reduced. The applied pressure decreases the temperature of the total conversion of oxygen while the maximum conversion of alkanes is not influenced. The pressure above atmospheric promotes oxidative cracking reactions but weakly affects thermal processes. At deep conversion of light alkanes, the selectivity towards main products is nearly invariable at the utilized pressures.     

Early recognition of oxidative degradation in polymers by chemiluminescence

Most common polymers degrade readily during normal use by reaction with oxygen. Rapid screening tests are requested by industry to characterise the oxidative stability of the materials. The chemiluminescence (CL) method, which is based on the fact that oxidation reactions of most organic materials, including polymers, are accompanied by weak emission of light, has the potential for being such a test. Selected examples of CL measurements, in a commercially available instrumentation, on different kind of materials and material formulations (as used in industrial applications) clearly indicate that the CL technique is capable of determining the relative oxidative stability of polymers at very early stages of degradation.     

Characteristics of pine wood oxidative pyrolysis: Degradation behavior,carbon oxide production and heat properties

Oxidative pyrolysis of pine wood was studied by thermogravimetric analysis (TGA) coupled with mass spectrometer (MS) and differential scanning calorimetry (DSC) methods. The effects of oxygen concentration on pyrolysis behavior, carbon oxide production and heat properties were investigated. Several parameters were defined to evaluate the oxygen influence. It was found that oxygen dramatically promotes the oxidative degradation and char oxidation rate. The reactivity index was found to be proportional to the oxygen concentration, which suggested that oxidative degradation reactions were under increasingly kinetic control in elevated oxygen concentration environments. Carbon oxides evolution properties were investigated. There are two releasing peaks in MS curves for oxidative condition comparing with one peak under inert condition. They are related with oxidative degradation and char oxidation, respectively. Both total amounts and rates of carbon oxides emission were found to increase with oxygen concentration. The cumulative emission ratio of CO to CO₂ first decreases then increases with oxygen concentration with 10% as turning point. It may be caused by different oxygen diffusion behaviors with variable oxygen concentrations. The absolute reaction heat value of oxidative pyrolysis (−7.23 MJ kg⁻¹, 5% O₂) is much larger than that of inert condition (+0.28 MJ kg⁻¹). Increasing of oxygen concentration results in an increase of heat emission. Comparing with pine wood low heat value, the net heat emission efficiencies under different oxygen concentrations (5%, 10%, 15%, 21%) are 39.73%, 44.84%, 68.90% and 78.41%, respectively.     

Highly efficient and photostable photosensitizer based on BODIPY chromophore

Photosensitizers are reagents that produce reactive oxygen species upon light illumination and are commonly used to study oxidative stress or for photodynamic therapy. There are many available photosensitizers, but most have limitations, such as low photostability, structural instability, or a limited usable range of solvent conditions. Here, we describe a novel photosensitizer scaffold (2I-BDP) based on the unique characteristics of the BODIPY chromophore (i.e., high extinction coefficient, high photostability, and insensitivity to solvent environment). 2I-BDP shows stronger near-infrared singlet oxygen luminescence emission and higher photostability than the well-known photosensitizer, Rose Bengal. Unlike other photosensitizers, this scaffold is widely applicable under various conditions, including lipophilic and aqueous environments. HeLa cells loaded with 2I-BDP could be photosensitized by light illumination, demonstrating that 2I-BDP is potentially useful as a reagent for cell photosensitization, oxidative stress studies, or PDT.     

Oxidative processing of light alkanes: State-of-the-art and prospects

Recent literature data on partial oxidation of light alkanes into syngas and oxidative coupling of methane into C₂ hydrocarbons are reviewed. The problems of these processes (high cost of pure oxygen; safety; activity, selectivity and stability of catalysts; temperature regime; coke formation and other by-products; insufficient level of methane transformation into ethane and ethylene) are considered. Possible solutions of these problems and prospects of practical use of light alkanes processing are discussed.     

Generation of Singlet Molecular Oxygen by Lipid Hydroperoxides and Nitronium Ion†

Singlet molecular oxygen is a reactive species involved in biological oxidative processes. The major cellular targets of singlet molecular oxygen are unsaturated fatty acids in the membrane, as well as nucleic acids and proteins. The aim of this study was to investigate whether lipids and commercial hydroperoxides generate singlet molecular oxygen, in presence of nitronium and activated nitronium ion. For this purpose, monomol light emitted in the near-infrared region (λ = 1270 nm) was used to monitor singlet molecular oxygen decay in different solvents, with different hydroperoxides and in the presence of azide. Direct measurements of the singlet molecular oxygen spectrum at 1270 nm recorded during the reaction between lipids and commercial hydroperoxides and nitronium ions unequivocally demonstrated the formation of this excited species.     

ELECTROCHEMICAL GENERATION OF SOLUTION LUMINESCENCE—III.: EFFECT OF OXYGEN ON QUANTUM YIELD AND KINETICS OF LUMINOL

Abstract -The growth and decay of light emission were examined for luminol as a funtion of oxygen concentration in aqueous alkaline solutions during and after the application of a controlled potential, square-wave electrochemical pulse. The results indicate that, in the rise portion of the light, the rate of electrochemical oxidation of luminol governs the light emission rate; while in the decay portion, the rate is first order and is independent of oxygen concentration. Quantum yields based on integration of the total light emitted also appear to be independent of oxygen above a threshold value. These results are consistent with evidence that the emitting state is an excited singlet.     

The oxyluminescence of polymers. A review

A review of the oxyluminescence of polymers is presented here. When polymers are heated in an air or oxygen atmosphere, they exhibit a low-level light emission called oxyluminescence (OL). This new phenomenon has been used to study the oxidative degradation of polymers as well as to evaluate stabilizer concentration and behavior. This review consists of the following: (a), OL intensity and spectral distribution; (b), mechanism of the OL process; (c), kinetics of OL; (d), OL in polymer stabilizer studies; (e), instrumentation; and (f), polymers studied by OL.     

Continuing damage to rat retinal DNA during darkness following light exposure

The damaging effects of visible light on the mammalian retina can be detected as functional, morphological or biochemical changes in the photoreceptor cells. Although previous studies have implicated short-lived reactive oxygen species in these processes, the termination of light exposure does not prevent continuing damage. To investigate the degenerative processes persisting during darkness following light treatment, rats were exposed to 24 h of intense visible light and the accumulation of DNA damage to restriction fragments containing opsin, insulin 1 or interleukin-6 genes was measured as single-strand breaks (ssb) on alkaline agarose gels. With longer dark treatments all three DNA fragments showed increasing DNA damage. Treatment of rats with the synthetic antioxidant dimethylthiourea prior to light exposure reduced the initial development of alkali-sensitive strand breaks and allowed significant repair of all three DNA fragments. The time course of double-strand DNA breaks was also examined in specific genes and repetitive DNA. Nucleosomal DNA laddering was evident immediately following the 24 h light treatment and increased during the subsequent dark period. The increase in the intensity of the DNA ladder pattern suggests a continuation of enzymatically mediated apoptotic processes triggered during light exposure. The protective effects of antioxidant suggests that the light-induced DNA degradative process includes both early oxidative reactions and enzymatic processes that continue after cessation of light exposure.     

Influence of Hydrogen and Oxygen on Porous Silicon Light Emission

The effect of oxygen and hydrogen on the photoluminescence intensity of porous silicon was examined. The results indicate that the presence of oxygen is necessary for visible light emission. In contrast, high hydrogen passivation is unfavorable for visible light emission.     

Time Resolved Spectroscopic Characterization of a-C:H Deposition by Methane and Removal by Oxygen Inductively Coupled RF Plasma

The deposition of amorphous hydrogenated carbon thin films by inductively coupled radio frequency (IC RF) pure methane plasma and its subsequent removal by IC RF pure oxygen plasma have been studied within a cylindrical glass tube. Both processes were simultaneously monitored by optical emission spectroscopy, light transmission through thin film deposits, temperature of the discharge tube and total gas pressure measurements. Comparing the time evolution of all parameters, various stages of oxygen plasma cleaning process were established. The transitions between E-mode and H-mode of plasma induced by the presence of cleaning products impurities were observed and discussed.     

Reversible Photoactivated Phosphorescence of Gold(I) Arylethynyl Complexes in Aerated DMSO Solutions and Gels

Phosphorescence in fluid solutions at ambient temperature is usually quenched by molecular oxygen via energy transfer, and singlet oxygen is concomitantly sensitized. The long‐lived phosphorescence of a series of Au^I arylethynyl complexes with tunable emission energies in aerated dimethyl sulfoxide (DMSO) solutions can be completely and repeatedly switched on by controlled photoirradiation. A trace amount of DMSO oxidation by the sensitized singlet oxygen is proposed to lead to a depletion of molecular oxygen in the local microenvironment of the Au^I phosphor in the photoactivation processes. Harnessing the photoactivated phosphorescence and using UV light as a non‐contact pen, a writing–erasing–rewriting prototype has been demonstrated with a DMSO gel containing Au^I arylethynyl complexes.     

CROSS-LINKING OF MEMBRANE PROTEINS AND PROTOPORPHYRIN-SENSITIZED PHOTOHEMOLYSIS*

Abstract— Irradiation of protoporphyrin-sensitized red cells with blue light in the presence of oxygen alters many components of their membranes and eventually leads to hemolysis. Extensive cross-linking of membrane proteins can be observed before hemolysis occurs (Girotti, 1976).
Facile oxidative hemolysis can be achieved without observable cross-linking of membrane proteins upon incubation (37°C) of red cells containing membrane-bound 3ß-hydroxy-5α-hydroperoxy-△⁶-cholcstene. Thus, protein cross-linking is not obligatory for oxidative lysis. Deoxygenation by Ar bubbling strongly retards the light-induced increase in osmotic fragility and strongly inhibits eventual hemolysis of protoporphyrin-sensitized erythrocytes. However, similar reduction in oxygen concentration only partially inhibits cross-linking of membrane proteins. These results suggest that membrane protein cross-linking and photohemolysis are not coupled processes.     

OXYGEN CONSUMPTION AND LUMINESCENCE OF ISOLATED Porichthys PHOTOPHORES IN RESPONSE TO ADRENERGIC STIMULATIONS

Isolated photophores of Porichthys maintained in saline at 20_oC, consume oxygen at a mean rate of 115 ± 5 ± 10 ₃ nmol O₂ min₁ ( n = 165).
In the presence of 0.1 and 1 mM adrenalin or noradrenaline the photophore produces a fast peak of light followed by a slow luminescence. A large increase in oxygen consumption occurs prior to the fast light response and it remains slightly above the resting level during the following slow light emission.
When isolated photophores do not produce the fast peak of light(in response to isoprenalin or after treatment with phentolamine), there is only a slight transient increase of oxygen consumption. During the production of the slow luminescence the oxygen consumption remains close to the resting level.
A relationship between the oxygen consumption and the light emission during the fast luminescence has been found: it is suggested that most of the oxygen consumed could be involved in a triggering mechanism of light production.     

INDUCTION OF A TRANSIENT ENHANCEMENT OF LOW LEVEL CHEMILUMINESCENCE IN INTACT LEAVES BY ANAEROBIC TREATMENT

Intrinsic low level chemiluminescence of dark adapted intact leaves exhibits a transient enhancement of light emission when ambient air is replaced with an anaerobic atmosphere. Re establishing aerobic conditions gives rise to a complex kinetic behavior of the light emission in the post-anoxic phase. Metabolic changes within the leaf are suggested to be responsible for this phenom enon, where intactness of the leaf is found to be of crucial importance. Leaf homogenate showed nearly oxygen independent chemiluminescence. In contrast, low level chemiluminescence of UV-light damaged leaves and of chloroplast preparations was inhibited by oxygen depletion. Spectral analyses of the ultraweak light emission from the intact leaf indicates that in both aerobic and anaerobic cases, the source of the ultraweak light is the same. The similarity to the spectrum of delayed fluorescence also obtained from the leaf suggests that chlorophyll is the light emitting species.     

Peroxidase Activity May Play a Role in the Cytotoxic Effect of Indole Acetic Acid*

Peroxidase activity in neutrophils is higher than in thioglycollate macrophages, while in lymphocytes this enzyme activity is very low. Indole-3-acetic acid is oxidized by peroxidase and the role of this enzyme in the cytotoxic effect of the compound was evaluated by measuring oxygen consumption, light emission and cell death in neutrophils, macrophages and lymphocytes. The increase in light emission, oxygen consumption and rate of cell death in cells cultured in the presence of indole-3-acetic acid presented a direct correlation with the peroxidase activity of the cells as follows: neutrophils > thioglycollate macrophages > resident macrophages > lymphocytes. Indeed, in lymphocytes that possess very low peroxidase activity, indole-3-acetic acid did not result in an increase in light emission or oxygen consumption and it was not cytotoxic.     

氧化偶联共聚合制备主链含β-萘烷基醚的红色发光聚合物

用氧化偶联聚合法合成了主链上含β-萘烷基醚和吡啶、二烷基芴、二苯乙烯和均四甲苯的聚合物.用FT-IR和1H NMR表征了聚合物的结构.广角X射线衍射表明共聚物的结构都是非晶态的.用UV-V is表征了共聚物的吸收特征.聚合物的荧光光谱表明,含有β-萘烷基醚和吡啶的聚合物在溶液中表现为红光发射材料.含有β-萘甲醚和二苯乙烯的共聚物为黄橙光发射,通过改变单体含量也可实现红光发射.含有β-萘甲醚和二烷基芴的聚合物固体有望成为白光发射材料.     

The emission thermophotometry (ETP) of some amino acids

The emission thermophotometry (ETP) curves of ten selected amino acids were determined in a flowing oxygen atmosphere. Most of the ETP curves contained a single emission peak in the 230–350°C temperature range; several of the curves contained multiple peaks and/or shoulder peaks. The light emission varied in intensity for each amino acid, but in most cases was at a very low level. The origin of the light emission process is not known but it is probably due to the presence of unstable pyrolysis products.     

Tailoring the charge carrier dynamics in ZnO nanowires: the role of surface hole/electron traps

Post-fabrication thermal-annealed ZnO nanowires (NWs) in an oxidizing (or a reducing) ambient were investigated using transient photoluminescence and X-ray photoelectron spectroscopy. Our findings reveal an ultrafast hole-transfer process to the surface adsorbed oxygen species (e.g., O(2)(-)) occurring within a few hundred picoseconds (ps) in the air-annealed samples; and an ultrafast electron-transfer process to charged oxygen vacancies (i.e., V(O)(2+)) occurring within tens of ps in the H(2)-annealed samples. Contrary to the common perception that the band edge emission (BE) dynamics are strongly influenced by the carrier trapping to the green emission related defect states (i.e., V(Zn)), these above processes compete effectively with the ZnO BE. Hole trapping by ionized V(Zn), which occurs in an ultrashort sub-ps-to-ps timescale (and hence limits its effective hole capture radius), however, has less influence on the BE dynamics. Importantly, our findings shed new light on the photoinduced charge transfer processes that underpins the novel properties of enhanced photocatalytic activity, photovoltaic performance, and photoconductivity response of ZnO NWs, thereby suggesting a strategy for tailoring the ultrafast carrier dynamics in ZnO NW-based devices.