Electrical conductivity of π-conjugated polymers with nitro substituents

π-Conjugated polymers bearing nitro substituent(s), e.g., poly(aryleneethynylene) (PAE) type polymers and poly(4,8-dinitroanthraquinone-1,5-diyl) P(4,8-NO₂-1,5-AQ), show semiconducting properties with electrical conductivities of an order of 10⁻⁷ to 10⁻⁶ S · cm⁻¹ at room temperature without special oxidation and reduction of the polymer. P(4,8-NO₂-1,5-AQ) shows a large shift of phase in alternating current (ac) measurements and a unique magnetism at low temperature.     

Merocyanine 540 Solubilized as an Ion Pair with Cationic Surfactant in Nonpolar Solvents: Spectral and Photochemical Properties

Merocyanine 540 (MC) is an anionic dye that is used to photopurge the bone marrow of leukemia cells. Under these conditions it is localized mostly in cell membranes, which may affect its photochemical reactivity. We investigated the photochemistry of MC dissolved as a hydrophobic ion pair with a hexadecyltrioctadecylammonium cation in cyclohexane, trimethylpentane and toluene as well as in propylene carbonate, CH3CN, C2H5OH and D2O. In organic solvents, the absorption and fluorescence spectra of MC were strongly red-shifted compared with aqueous solutions. The fluorescence was also more intense despite aggregation that occurred in some solvents. Aggregation strongly affects the spectral and photochemical properties of MC, especially in aliphatic hydrocarbons in which distinctive H-type aggregates are formed. Hydrophobic MC is a moderate photosensitizer of singlet molecular oxygen (1O2). The following values for 1O2 quantum yields were calculated based on 1O2 phosphorescence relative to 1O2 generation by Rose Bengal: approximately 0.12 in trimethylpenthane, approximately 0.13 in cyclohexane, 0.045 in EtOH, 0.039 in toluene, 0.007 in CH3CN and approximately 3 x 10(-4) in D2O. The H-aggregates of MC in cyclohexane and trimethylpentane are better 1O2 producers than monomeric MC. The above 1O2 quantum yields are corrected for self-quenching because MC is an efficient 1O2 quencher (17 x 10(7) M-1 s-1 in CH3CN, 6.8 x 10(7) M-1 s-1 in D2O, 5.2 x 10(7) M-1 s-1 in EtOH, and 1.4 x 10(7) M-1 s-1 in toluene). Merocyanine undergoes photodegradation, a solvent-dependent process that proceeds faster when the dye is aggregated. The initial photodegradation rate is much slower in organic solvents than in water, but photodegradation products accumulated during longer irradiation may increase the rate in most solvents. Higher photostability and better photosensitization by MC in hydrophobic nonpolar solvents suggest that the killing of leukemia cells via a photodynamic mechanism may operate mostly in cell membranes. In contrast, any cytotoxic products from photodecomposition may be important in hydrophilic cell compartments. Our data show the spectral and photochemical properties of MC in a pure hydrophobic environment.     

Vitamin B-sensitized photo-oxidation of dopamine

Abstract Kinetics and mechanism of the photo-oxidation of the natural catecholamine-type neurotransmitter dopamine (DA) has been studied in aqueous solution, under aerobic conditions, in the presence of riboflavin (Rf, vitamin B(2)) as a photosensitizer. Results indicate the formation of a weak dark complex Rf-DA, with a mean apparent association constant K(ass) = 30 m(-1), only detectable at DA concentrations much higher than those employed in photochemical experiments. An intricate mechanism of competitive reactions operates upon photoirradiation. DA quenches excited singlet and triplet states of Rf, with rate constants of 4.2 x 10(9) and 2.2 x 10(9) m(-1) s(-1), respectively. With the catecholamine in a concentration similar to that of dissolved molecular oxygen in air-saturated water, DA and oxygen competitively quench the triplet excited state of Rf, generating superoxide radical anion (O(2)(*-)) and singlet molecular oxygen (O(2)((1)Delta(g))) by processes initiated by electron and energy-transfer mechanisms, respectively. Rate constants values of 1.9 x 10(8) and 6.6 x 10(6) m(-1) s(-1) have been obtained for the overall and reactive (chemical) interaction of DA with O(2)((1)Delta(g)). The presence of superoxide dismutase increases both the observed rates of aerobic DA photo-oxidation and oxygen uptake, due to its known catalytic scavenging of O(2)(*-), a species that could revert the overall photo-oxidation effect, according to the proposed reaction mechanism. As in most of the catecholamine oxidative processes described in the literature, aminochrome is the DA oxidation product upon visible light irradiation in the presence of Rf. It is generated with a quantum yield of 0.05.     

Quenching of singlet molecular oxygen (1O2) by azide anion in solvent mixtures.

The azide ion is a strong physical quencher of singlet molecular oxygen (1O2) and is frequently employed to show involvement of 1O2 in oxidation processes. Rate constants (k(q)) for the quenching of 1O2 by azide are routinely used as standards to calculate k(q) values for quenching by other substrates. We have measured k(q) for azide in solvent mixtures containing deuterium oxide (D2O), acetonitrile (MeCN), 1,4-dioxane, ethanol (EtOH), propylene carbonate (PC), or ethylene carbonate (EC), mixtures commonly used for many experimental studies. The rate constants were calculated directly from 1O2 phosphorescence lifetimes observed after laser pulse excitation of rose bengal (RB), used to generate 1O2. In aqueous mixtures with MeCN and carbonates, the rate constant increased nonlinearly with increasing volume of organic solvent in the mixtures. k(q) was 4.78 x 10(8) M(-1) s(-1) in D2O and increased to 26.7 x 10(8) and 27.7 x 10(8) M(-1) s(-1) in 96% MeCN and 97.7% EC/PC, respectively. However, in EtOH/D2O mixtures, k(q) decreased with increasing alcohol concentration. This shows that a higher solvent polarity increases the quenching efficiency, which is unexpectedly decreased by the proticity of aqueous and alcohol solvent mixtures. The rate constant values increased with increasing temperature, yielding a quenching activation energy of 11.3 kJ mol(-1) in D2O. Our results show that rate constants in most solvent mixtures cannot be derived reliably from k(q) values measured in pure solvents by using a simple additivity rule. We have measured the rate constants with high accuracy, and they may serve as a reliable reference to calculate unknown k(q) values.     

Photogeneration of the free radicals and singlet oxygen by chrysophanol from rheum

Chrysophanol (3-methyl-1,8-dihydroxyanthraqui-none) belongs to a family of anthraquinone pigmentsthat naturally exist in many kinds of plants, such asrheum, a Chinese herbal medicine growing abundantlyin China. Besides their biological activities, thesepigments are also well known as photosensitizers[1,2].Photosensitizers are able to photochemically producehighly reactive species, such as O2, O2 , ?OH, and 1 ??induce a series of damage to biologic…     

基于碘代Bodipy超分子聚合物的构筑和光物理性能研究

本文以对羟基苯甲醛和3-溴丙炔为原料,经过巯基-炔基点击化学反应成功合成了含有双四重氢键的2,6-二碘代-8-[4-(2-脲基-4[1H]-嘧啶酮)苯基]-氟化硼二吡咯甲川化合物(IBodipy-BisUPy),并对其进行了详细的结构表征以及紫外、荧光、瞬态吸收、低温磷光等光物理性质测试。I-Bodipy-BisUPy可通过四重氢键非共价键作用驱动形成超分子聚合物。重原子碘的存在促进了I-Bodipy-BisUPy从单重激发态向三重激发态的系间窜越,可在低温下呈现一个近红外磷光发射峰,其三重态的寿命为56.7μs。利用微乳法将超分子聚合物制备成纳米颗粒,ESR和对1,5-二羟基萘的光敏氧化性能测试表明此超分子聚合物纳米颗粒可在水中产生单重态氧(1O2),且能够实现对底物的光敏氧化。     

Excited-state dynamical behavior of 1,4-anthraquinone in a fluid solution.

The excited triplet-state transient time profiles of 1,4-anthraquinone (1,4-AQ) have been measured in a degassed CCl4 fluid solution at different temperatures near room temperature, together with the steady-state emission spectra, which consist of the S1(n, pi*) and weak S2(pi, pi*) fluorescence at room temperature, and of the T1(pi, pi*) phosphorescence at 77 K. Quantitative analysis of the T1 triplet decay profiles measured as a function of temperature provides estimates for the energy and rates that characterize the excited-state dynamical behavior of 1,4-AQ.     

DNA cleavage by UVA irradiation of NADH with dioxygen via radical chain processes

Efficient DNA cleaving-activity is observed by UVA irradiation of an O(2)-saturated aqueous solution of NADH (beta-nicotinamide adenine dinucleotide, reduced form). No DNA cleavage has been observed without NADH under otherwise the same experimental conditions. In the presence of NADH, energy transfer from the triplet excited state of NADH ((3)NADH*) to O(2) occurs to produce singlet oxygen ((1)O(2)) that is detected by the phosphorescence emission at 1270 nm. No quenching of (1)O(2) by NADH was observed as indicated by no change in the intensity of phosphorescence emission of (1)O(2) at 1270 nm in the presence of various concentrations of NADH. In addition to the energy transfer, photoinduced electron transfer from (3)NADH* to O(2) occurs to produce NADH(*+) and O(2)(*-), both of which was observed by ESR. The quantum yield of the photochemical oxidation of NADH with O(2) increases linearly with increasing concentration of NADH but decreases with increasing the light intensity absorbed by NADH. Such unusual dependence of the quantum yield on concentration of NADH and the light intensity absorbed by NADH indicates that the photochemical oxidation of NADH with O(2) proceeds via radical chain processes. The O(2)(*-) produced in the photoinduced electron transfer is in the protonation equilibrium with HO(2)(*), which acts as a chain carrier for the radical chain oxidation of NADH with O(2) to produce NAD(+) and H(2)O(2), leading to the DNA cleavage.     

Complexation properties of the crown ether-containing N-thiophosphorylated thiourea towards Ni(II)

Reaction of the deprotonated N-thiophosphorylated thiourea (4'-benzo-15-crown-5)NHC(S)NHP(S)(OiPr)(2) (HL) with NiCl(2) in aqueous EtOH leads to dark green [Ni(L-1,5-S,S')(2)]·2H(2)O crystals that were isolated by recrystallization from a mixture of CH(2)Cl(2) and n-hexane.     

Superoxide radical anion adduct of 5,5-dimethyl-1-pyrroline N-oxide (DMPO). 3. Effect of mildly acidic pH on the thermodynamics and kinetics of adduct formation

The nitrone, 5,5-dimethylpyrroline N-oxide (DMPO), is a commonly used spin trap for the detection of superoxide radical anion (O2*-) using electron paramagnetic resonance spectroscopy. This work investigates the reactivity of DMPO to O2*- in mildly acidic pH (5.0-7.0). Mild acidity is characteristic of acidosis and has been observed in hypoxic systems, e.g., ischemic organs and cancer cells. Although the established pKa for O2*- is 4.8, the pKa for DMPO is unknown. The pKa of the conjugate acid of DMPO was determined to be 6.0 using potentiometric, spectrophotometric, 1H and 13C NMR, and computational methods. 1H and 13C NMR were employed to investigate the site of protonation. An alternative mechanism for the spin trapping of O2*- in mildly acidic pH was proposed, which involves protonation of the oxygen to form the N-hydroxy imino cation and subsequent addition of O2*-. The exoergicity of O2*- addition to protonated DMPO was rationalized using density functional theory (DFT) at the PCM/B3LYP/6-31+G**//B3LYP/6-31G* level of theory.     

SPECTROSCOPIC STUDIES OF CUTANEOUS PHOTOSENSITIZING AGENTS–XV. ANTHRALIN and ITS OXIDATION PRODUCT 1,8-DIHYDROXYANTHRAQUINONE

The photochemistry (Type I and II) of anthralin and its photo-oxidation product 1,8-dihydroxyanthraquinone (1,8-DHAQ) has been studied in ethanol, acetonitrile and dimethylsulfoxide using spin-trapping and direct detection of singlet oxygen (1O2) luminescence techniques. In ethanol, where it exists in its neutral form (AN), anthralin does not undergo either Type I or II reactions upon UV-irradiation. In contrast, irradiation of anthralin in acetonitrile, a solvent in which anthralin is partially converted to its corresponding mono-anion (AN-), generates both superoxide and singlet oxygen. Irradiation of anthralin in dimethylsulfoxide, where the AN- form is present in substantial quantity, generates superoxide and solvent derived radicals but no detectable singlet oxygen. UV-irradiation of 1,8-DHAQ in ethanol and acetonitrile produces both superoxide and singlet oxygen in significant yields. In dimethylsulfoxide, on the other hand, only superoxide and solvent derived radicals are observed. The 1O2 quantum yield for AN- and 1,8-DHAQ in acetonitrile were determined to be 0.14 and 0.88 relative to rose bengal in the same solvent. These findings suggest that the AN photosensitization occurs via Type I and II pathways, is solvent dependent and involves AN- as well as its oxidation product 1,8-DHAQ, which is a more potent generator of both singlet oxygen and superoxide.     

UVA-ketoprofen-induced hemoglobin radicals detected by immuno-spin trapping

Ketoprofen (3-benzoyl-alpha-methylbenzeneacetic acid, KP) is a widely used nonsteroidal anti-inflammatory drug (NSAID) that causes both phototoxicity and photoallergy. Here, we investigated the formation of hemoglobin radicals, in both purified hemoglobin and red blood cells (RBC), induced by ultraviolet A (UVA)-KP by using "immuno-spin trapping," a novel approach that combines the specificity of spin trapping with the sensitivity of antigen-antibody interactions. The methemoglobin (metHb) radicals react covalently with 5,5-dimethyl-1-pyrroline N-oxide (DMPO) to form nitroxyl radical adducts that are oxidized to the corresponding nitrone adducts, which in turn are specifically recognized by antiserum against DMPO nitrone. We found that the formation of nitrone adducts in metHb depended on the UVA dose, the KP concentration and the presence of DMPO, as determined by enzyme-linked immunosorbent assay and Western blotting. Adduct formation decreased when irradiation was carried out in the presence of catalase or nitrogen, suggesting that H2O2 plays a key role in KP-UVA-induced metHb radical formation. KP in the dark did not generate metHb radical-derived nitrone adducts, whereas UVA alone resulted in the formation of metHb radical-derived nitrone adducts that increased with UVA dose from 4 to 10 J/cm2. However, KP (25 and 200 microM) plus UVA (4 and 10 J/cm2) resulted in a significant increase in the formation of metHb radical-derived nitrone adducts as compared with UVA or KP alone, indicating that KP photosensitized the production of the metHb radicals in the presence of UVA. In contrast, no metHb radical-derived nitrone adduct was detected in the absence of DMPO, even though KP and UVA were present. We also detected the hemoglobin radical formation in RBC as well as in hemolysates. The endogenous antioxidants and exogenous reduced glutathione inhibited the protein radical formation. These studies have shown that the immuno-spin-trapping technique can be used to detect radical damage in proteins as a result of photosensitizing reactions. The successful detection of protein radical formation caused by KP photosensitization could help further understand the photoallergic effect of this NSAID.     

在光动力光疗中类卟啉稀土配合物光敏作用原初反应的特征: 产生自由基I型机制的ESR研究

本文用ESR方法研究了类卟啉稀土配合物[(CO2H-APPC)Gd]Cl2的光敏反应。用4-hydro-tetramethylpiperidine-N-oxide radical(4-hydro-TEMPO)作探针, 通过对其消自旋的作用, 证实[(CO2H-APPC)Gd]Cl2光敏反应中有阳离子自由基[(CO2H-APPC)Gd]^+产生, 加入还原剂可促使[(CO2H-APPC)Gd]^+生成。经由5, 5-Dimethyl-1-pyrrolineN-oxide(DMPO)对超氧阴离子(O2^-)和羟基自由基(.OH)的自旋捕捉及对该自旋加合物[DMPO-O2^-]和[DMPO-OH]的ESR测定, 证实有O2^-和.OH产生, 并用SOD清除O2^-和甲酸钠清除.OH的实验, 进一步证实O2^-和.OH的产生。上述结果说明[(CO2H-APPC)Gd]Cl2光敏反应存在着产生[(CO2H-APPC)Gd]^+和活性氧自由基的I型机制。     

Novel multifunctional organic semiconductor materials based on 4,8-substituted 1,5-naphthyridine: synthesis, single crystal structures, opto-electrical properties and quantum chemistry calculation

A series of 4,8-substituted 1,5-naphthyridines (1a-1h) have been successfully synthesised by a Suzuki cross-coupling between 4,8-dibromo-1,5-naphthyridine (4) and the corresponding boronic acids (2a-2h) in the presence of catalytic palladium acetate in yields of 41.4-75.8% and have ben well characterized. They are thermally robust with high phase transition temperatures (above 186 °C). Compounds 1b, 1e and 1f crystallized in the monoclinic crystal system with the space groups P2(1)/c, P2(1)/c and P2(1)/n, respectively. All of them show the lowest energy absorption bands (λ(max)(Abs): 294-320 nm), revealing low optical band gaps (2.77-3.79 eV). These materials emit blue fluorescence with λ(max)(Em) ranging from 434-521 nm in dilute solution in dichloromethane and 400-501 nm in the solid state. 4,8-Substituted 1,5-naphthyridines 1a-1h have estimated electron affinities (EA) of (2.38-2.72 eV) suitable for electron-transport materials and ionization potentials (IP) of 4.85-5.04 eV facilitate excellent hole-injecting/hole-transport materials properties. Quantum chemical calculations using DFT B3LYP/6-31G* showed nearly identical the lowest unoccupied molecular orbitals (LUMO) of -2.39 to -2.19 eV and the highest occupied molecular orbitals (HOMO) of -5.33 to -6.84 eV. These results demonstrate the 4,8-substituted 1,5-naphthyridines 1a-1h with a simple architecture might be promising blue-emitting (or blue-green-emitting) materials, electron-transport materials and hole-injecting/hole-transport materials for applications for developing high-efficiency OLEDs.     

Photophysical and photochemical studies of 2-phenylbenzimidazole and UVB sunscreen 2-phenylbenzimidazole-5-sulfonic acid

The sunscreen agent 2-phenylbenzimidazole-5-sulfonic acid (PBSA) and its parent 2-phenylbenzimidazole (PBI) cause DNA photodamage via both Type-I and Type-II mechanisms when UVB irradiated. We have studied the photophysical and photochemical properties of these compounds and their ability to photogenerate reactive oxygen species including free radicals. PBI and PBSA exhibit both oxidizing and reducing properties in their excited state. The absorption and fluorescence properties of PBSA depend strongly upon pH, and hence the photochemistry of PBSA was studied in both neutral and alkaline solutions. PBSA showed strong oxidizing properties when UV irradiated in neutral aqueous solution (pH 7.4) in the presence of cysteine, glutathione and azide, as evidenced by the detection of the corresponding S-cysteinyl, glutathiyl and azidyl radicals with the aid of the spin trap, 5,5-dimethyl-1-pyrroline N-oxide (DMPO). However, when an aqueous anaerobic solution (pH 10) of PBSA and either nitromethane (NM) or 4-nitrobenzoic acid (4-NBA) were irradiated, the corresponding nitro anion radicals were observed. This finding suggests that both NM and 4-NBA are reduced by direct electron transfer from the excited state PBSA. During UV irradiation of an aerobic solution of PBSA, O2*- and *OH radical were generated and trapped by DMPO. Further, PBI (in ethanol) and PBSA (in ethylene glycol : water 2: 1 mixture) showed low temperature (77 K) phosphorescence (lambdamax = 443, 476 and 509 nm) and also an electron paramagnetic resonance half-field transition (deltaMs = +/-2), which is evidence for a triplet state. This triplet produced singlet oxygen (1O2) with quantum yields 0.07 and 0.04 in MeCN for PBI and PBSA, respectively. These studies demonstrate that UV irradiation of PBSA and PBI generates a variety of free radicals and active oxygen species that may be involved in the photodamage of DNA.     

Superoxide anion radical generation in the NaOH/H(2)O(2)/Fe(III) system: a spin trapping ESR study

Formation of free radical intermediates in a NaOH/H(2)O(2)/Fe(III) system has been studied by ESR spectroscopy in the presence of the spin trap 5,5-dimethy-1-pyrroline N-oxide (DMPO). DMPO/O(2(*) ) (-) and DMPO/(*)OH signals were simultaneously detected in this system, but only the DMPO/(*)OH signal could be observed in the absence of Fe(III). Effects of pH values and Fe(III) concentrations on the ESR signal intensities were investigated in detail. Formation of DMPO/O(2(*) ) (-) adduct was inhibited by the addition of superoxide dismutase (SOD), catalase or nitro blue tetrazolium (NBT), and by chelating the Fe(III) with some chelators, including ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), and desferrioxamine (DFO). Deoxygenation from the NaOH/H(2)O(2)/Fe(III) mixture had a slight effect on the formation of DMPO/O(2(*) ) (-). DMPO/O(2(*) ) (-) signal was also detected from the NaOH/H(2)O(2)/Fe(II) mixture, but it can be totally suppressed under anaerobic conditions. Considering the hydrolysis of Fe(III) into polymerization iron species with oxide phases in the alkaline medium, Fe(2)O(3) was directly suspended into a mixture of NaOH/H(2)O(2) for comparison. Fortunately, the presence of Fe(2)O(3) suspension was found to be of benefit to the production of DMPO/O(2(*) ) (-). Influence of aging time of hydrolytic iron species on the superoxide anion radical generation was also studied. These results suggest that the generation of O(2(*) ) (-) from the NaOH/H(2)O(2)/Fe(III) system was probably caused by the heterogeneous surface catalysis initiated by hydrolytic iron species.     

Spin trapping by 5,5-dimethylpyrroline-N-oxide in Fenton media in the presence of Nafion perfluorinated membranes: limitations and potential

Spin trapping by 5,5-dimethylpyrroline-N-oxide (DMPO) was used for the detection of radicals in Fenton media in the presence and absence of Nafion perfluorinated ionomers. For ethanol as solvent, the same types of spin adducts were detected in the presence or absence of Nafion. Solvent-derived adducts, DMPO/*OC2H5 and DMPO/*CH(OH)CH3, were identified, and their presence was rationalized by Fe(III)-catalyzed nucleophilic addition of ethanol to the spin trap and hydrogen abstraction by *OH radicals; oxygen radical adducts, DMPO/*O2(-) and DMPO/*OOH, were also detected. In Fenton media with methanol as solvent (and no Nafion), the DMPO/*O2(-) adduct dominated immediately after sample preparation, and a mixture consisting of DMPO/*OCH3, DMPO/*CH3, DMPO/*O2(-), and DMPO/*OOH adducts was detected after 30 min. In the presence of Nafion, only the adduct DMPO/*OH was detected. For water as solvent, only the DMPO/*OH adduct was detected, in both the absence and the presence of Nafion. The full hyperfine tensor components of this adduct were determined in Fenton media in the presence of Nafion with water and methanol as solvents. In Nafion/water exposed to the Fenton reagent at 358 K for 3 h, a DMPO adduct of a carbon-centered radical was also identified and assigned to a Nafion-derived fragment; its exact nature is under investigation. Variations of the 14N and Hbeta hyperfine splittings of a given adduct with the local polarity were key to the identification of some DMPO adducts, in particular DMPO/*O2(-). Both *OOH and O2*- adducts, with different 14N and Hbeta splittings, were detected simultaneously in some samples, for the first time in the spin trapping literature. Comparison with the results of a direct electron spin resonance study of Nafion exposed to the Fenton reagent indicated that spin trapping by DMPO can provide complementary information on the type of radicals present during Nafion degradation. The spin trapping approach described in this paper is limited, however, to systems that do not contain organic solvents.     

Singlet Oxygen–mediated Hydroxyl Radical Production in the Presence of Phenols: Whether DMPO–·OH Formation Really Indicates Production of ·OH?¶

The reaction of singlet oxygen (1O2) generated by ultraviolet-A (UVA)-visible light (lambda > 330 nm) irradiation of air-saturated solutions of hematoporphyrin with phenolic compounds in the presence of a spin trap, 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), gave an electron spin resonance (ESR) spectrum characteristic of the DMPO-hydroxyl radical spin adduct (DMPO-*OH). In contrast, the ESR signal of 5,5-dimethyl-2-pyrrolidone-N-oxyl, an oxidative product of DMPO, was observed in the absence of phenolic compounds. The ESR signal of DMPO-*OH decreased in the presence of either a *OH scavenger or a quencher of *O2 and under anaerobic conditions, whereas it increased depending on the concentration of DMPO. These results indicate both 1O2- and DMPO-mediated formation of free *OH during the reaction. When DMPO was replaced with 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline-N-oxide (DEPMPO), no DEPMPO adduct of oxygen radical species was obtained. This suggests that 1O2, as an oxidizing agent, reacts little with DEPMPO, in which a strong electron-withdrawing phosphoryl group increases the oxidation potential of DEPMPO compared with DMPO. A linear correlation between the amounts of DMPO-*OH generated and the oxidation potentials of phenolic compounds was observed, suggesting that the electron-donating properties of phenolic compounds contribute to the appearance of *OH. These observations indicate that 1O2 reacts first with DMPO, and the resulting DMPO-1O2 intermediate is immediately decomposed/reduced to give *OH. Phenolic compounds would participate in this reaction as electron donors but would not contribute to the direct conversion of 1O2 to *OH. Furthermore, DEPMPO did not cause the spin-trapping agent-mediated generation of *OH like DMPO did.     

Theoretical and experimental studies of the spin trapping of inorganic radicals by 5,5-dimethyl-1-pyrroline N-oxide (DMPO). 2. Carbonate radical anion

Previous studies have shown that the enzyme-mediated generation of carbonate radical anion (CO(3)(.-)) may play an important role in the initiation of oxidative damage in cells. This study explored the thermodynamics of CO(3)(.-) addition to 5,5-dimethyl-1-pyrroline N-oxide (DMPO) using density functional theory at the B3LYP/6-31+G(**)//B3LYP/6-31G* and B3LYP/6-311+G* levels with the polarizable continuum model to simulate the effect of the bulk dielectric effect of water on the calculated energetics. Theoretical data reveal that the addition of CO(3)(.-) to DMPO yields an O-centered radical adduct (DMPO-OCO2) as governed by the spin (density) population on the CO(3)(.-). Electron paramagnetic resonance spin trapping with the commonly used spin trap, DMPO, has been employed in the detection of CO(3)(.-). UV photolysis of H(2)O(2) and DMPO in the presence of sodium carbonate (Na(2)CO(3)) or sodium bicarbonate (NaHCO(3)) gave two species (i.e., DMPO-OCO(2) and DMPO-OH) in which the former has hyperfine splitting constant values of a(N) = 14.32 G, a(beta)-Eta = 10.68 G, and a(gamma-H) = 1.37 G and with a shorter half-life compared to DMPO-OH. The origin of the DMPO-OH formed was experimentally confirmed using isotopically enriched H(2)(17)O(2) that indicates direct addition of HO(.) to DMPO. Theoretical studies on other possible pathways for the formation of DMPO-OH from DMPO-OCO(2) in aqueous solution and in the absence of free HO(.) such as in the case of enzymatically generated CO(3)(.-), show that the preferred pathway is via nucleophilc substitution of the carbonate moiety by H(2)O or HO(-). Nitrite formation has been observed as the end product of CO(3)(.-) trapping by DMPO and is partly dependent on the basicity of solution. The thermodynamic behavior of CO(3)(.-) in the aqueous phase is predicted to be similar to that of the hydroperoxyl (HO(2)(.)) radical.     

Room-temperature long-lived triplet excited states of naphthalenediimides and their applications as organic triplet photosensitizers for photooxidation and triplet-triplet annihilation upconversions

Naphthalenediimide (NDI) derivatives with 2,6- or 2,3,6,7-tetrabromo or amino substituents were prepared. N,N'-dialkyl-2,6-dibromo NDI (compound 2) and N,N'-dialkyl-2,3,6,7-tetrabromo NDI (compound 4) show phosphorescence emission at 610 or 667 nm, respectively. Phosphorescence was never observed for NDI derivatives. Conversely, N,N'-dialkyl-2,6-dibromo-3,7-diamino NDI (compound 5) shows strong absorption at 526 nm and fluorescence at 551 nm, and no phosphorescence was observed. However, nanosecond time-resolved transient difference absorption spectroscopy confirmed that the triplet excited state of 5 was populated upon photoexcitation. 2,3,6,7-Tetraamino NDI (6) shows fluorescence, and no triplet excited state was populated upon excitation. The compounds were used as singlet oxygen ((1)O(2)) photosensitizers for the photooxidation of 1,5-dihydroxylnaphthalene (DHN). We found that 5 is more efficient than the conventional photosensitizer, such as Ir(ppy)(2)(bpy)[PF(6)]. The compounds were also used as organic triplet photosensitizers for triplet-triplet annihilation based upconversions. An upconversion quantum yield up to 18.5% was observed.