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PubMed2004

Critical effect of hydrogen peroxide concentration in photochemical oxidative degradation of C.I. Acid Red 27 (AR27).

The photochemical decolorization of C.I. Acid Red 27 (AR27), an anionic monoazo dye, was studied in the UV/H2O2 process by using a batch reactor with a UV-C lamp emitting at 254 nm (30 W). The decolorization rate follows pseudo-first order kinetic with respect to the AR27 concentration. The results indicate that the apparent reaction rate constant in the UV/H2O2 process is a function of H2O2 concentration. In this work, a mathematical relation between the apparent reaction rate constant of the AR27 removal and used H2O2 was established. The applied amount of H2O2 was performed in two forms: (i) the light fraction absorbed by H2O2 in 254 nm, (ii) the initial concentration ratio of H2O2 to AR27. The results obtained from this mathematical model are in good agreement with experimental results.

Amaranth Dye↗

PubMed2005

Light-induced degradation of metsulfuron-methyl in water.

Photodegradation of metsulfuron-methyl, a sulfonylurea herbicide, has been investigated in aqueous solution at different pH and excitation wavelengths. The efficiency of the process has been evaluated through quantum yield determinations. The identification of the photoproducts indicates that the major photochemical pathway is initiated by C-S bond dissociation followed by involvement of water to yield the main final products; the behaviour in water is shown to differ markedly from that in an organic environment.

Arylsulfonates↗

PubMed2005

An overview of environmental hazards and exposure risk of hydrofluorocarbons (HFCs).

Hydrofluorocarbons (HFCs) are being used as replacements for chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) that cause significantly stratospheric ozone depletion and global warming. HFCs under commercial uses as cleaning solvents in the electronic components, blowing agent in the foamed plastics, refrigerant in the air conditioning units and refrigerators, fire suppression agent in the fire protection, propellant in the metered dose inhalers (MDIs), and dry etching agent in the semiconductor manufacturing. Among these HFCs, 1,1,1,2-tetrafluoroethane (HFC-134a) is the most widely used one. From the environmental, ecological, and health points of view, it is urgent to mitigate and control the emissions of these HFCs from a diversity of commercial applications and industrial processes. This article aims to introduce these HFCs in commercial uses and environmental hazards (i.e., global warming, photochemical potential, flammability safety, environmental partition and ecotoxicity). Further, the updated data on the human toxicity, occupational exposure and health risk of these HFCs (esp., HFC-134a) are addressed in this review paper.

Chlorofluorocarbons↗

PubMed2000

The heme synthesis and degradation pathways: role in oxidant sensitivity. Heme oxygenase has both pro- and antioxidant properties.

The heme biosynthetic and catabolic pathways generate pro- and antioxidant compounds, and consequently, influence cellular sensitivity to oxidants. Heme precursors (delta-aminolevulinic acid, porphyrins) generate reactive oxygen species (ROS), from autoxidation and photochemical reactions, respectively. Heme, an essential iron chelate, serves in respiration, oxygen transport, detoxification, and signal transduction processes. The potential toxicity of heme and hemoproteins points to a critical role for heme degradation in cellular metabolism. The heme oxygenases (HOs) provide this function and participate in cellular defense. This hypothesis emerges from the observation that the activation of HO-1 is an ubiquitous cellular response to oxidative stress. The reaction products of HO activity, biliverdin, and its subsequent metabolite bilirubin, have antioxidant properties. Furthermore, iron released from HO activity stimulates ferritin synthesis, which ultimately provides an iron detoxification mechanism that may account for long-term cytoprotection observed after HO induction. However, such models have overlooked potential pro-oxidant consequences of HO activity. The HO reaction releases iron, which could be involved in deleterious reactions that compete with iron reutilization and sequestration pathways. Indeed, the induction of HO activity may have both pro- and antioxidant sequelae depending on cellular redox potential, and the metabolic fate of the heme iron.

Aminolevulinic Acid↗

PubMed2002

Stabilization of inorganic nanocrystals by organic dendrons.

A series of hydrophilic organic dendron ligands was designed and synthesized for stabilizing high-quality semiconductor and noble metal nanocrystals. The focal point of the dendron ligands is chosen to be a thiol group which is a universal coordinating site for compound semiconductor and noble metal nanocrystals. The methods for binding these dendron ligands onto the surface of the nanocrystals are simple and straightforward. The thin, about 1-2 nm, but closely packed and tangled ligand shell provides sufficient stability for the "dendron-protected nanocrystals" to withstand the rigors of the coupling chemistry and the standard separation/purification techniques. The chemistry presented can be immediately applied for the development of a new generation of biomedical labeling reagents based on high-quality semiconductor nanocrystals. It also provides an alternative path to apply noble metal nanocrystals for developing sensitive detection schemes for chemical and biochemical purposes. The concept may further provide an optimal solution for many other problems encountered in nanocrystal-related research and development, for which the stability of the nanocrystals is a critical issue. Furthermore, the experimental results confirmed that the photochemical stability of colloidal semiconductor and noble metal nanocrystals is the key for developing reliable and reproducible processing chemistry for these nanocrystals.

Journal Article↗

PubMed2004

Reactivities of carboxyalkyl-substituted 1,4,5,8-naphthalene diimides in aqueous solution.

A series of water-soluble 1,4,5,8-naphthalene diimide derivatives has been prepared and their redox and photophysical properties characterized. From laser flash photolysis studies, the triplet excited state of N,N'-bis[2-(N-pyridinium)ethyl]-1,4,5,8-naphthalene diimide (NDI-pyr) was found to undergo oxidative quenching with the electron donors DABCO, tyrosine, and tryptophan as expected from thermodynamics. Interestingly, the reactivities of naphthalene diimides (NDI) possessing alpha- and beta-carboxylic acid substituents (R = -CH2COO-, -C(CH3)2COO-, and -CH2CH2COO-) were strikingly different. In these compounds, the transient produced upon 355 nm excitation did not react with the electron donors. Instead, this transient reacted rapidly (k > 10(8)-10(9) M-1 s-1) with known electron acceptors, benzyl viologen and ferricyanide. The transient spectrum of the carboxyalkyl-substituted naphthalimides observed immediately after the laser pulse was nearly identical to the one-electron-reduced form of 1,4,5,8-naphthalene diimide (produced independently using the bis-pyridinium-substituted naphthaldiimide). From our studies, we conclude that the transient produced upon nanosecond laser flash photolysis of NDI-(CH2)nCOO- is the species produced upon intramolecular electron transfer from the carboxylate moiety to the singlet excited state of NDI. In separate experiments, we verified that the singlet excited state of NDI-pyr does, indeed, react intermolecularly with acetate, alanine, and glycine. The process is further substantiated using thermodynamic driving force calculations. The results offer new prospects of the efficient photochemical production of reactive carbon-centered radicals.

Animals↗

PubMed2002

Oxidative stress-independent depletion of epidermal vitamin A by UVA.

In hairless mice, epidermal vitamin A (retinol and retinyl esters) is strongly decreased following a single exposure to UVB. Here, using the same mouse model, we studied the effects of UVA on epidermal vitamin A content, lipid peroxidation, and CRBP-I expression, as well as the putative prevention of vitamin A depletion or lipid peroxidation by topical alpha-tocopherol. An acute exposure to UVA completely depleted epidermal vitamin A with EC50 of 0.25 and 0.5 J per cm2 for retinyl esters and retinol, respectively; these values were 0.1 J per cm2 for both retinoids under UVB exposure. CRBP-I expression was increased 2-fold 8 h following UVA exposure (10 J per cm2), and this increase persisted for at least 16 h. A single UVA exposure induced a concentration-dependent epidermal lipid peroxidation (EC50 = 3.5 J per cm2) giving rise to 55.4 +/- 4.2 nmol lipid peroxides per g at 20 J per cm2, whereas UVB, up to 1 J per cm2, did not increase the basal concentration of 6.7 +/- 0.9 nmol lipid peroxides per g. On the other hand, topical menadione induced a concentration-dependent lipid peroxidation, but did not affect vitamin A content. Pretreatment with alpha-tocopherol (i) did not inhibit UV-induced vitamin A depletion, (ii) completely inhibited the increased lipid peroxidation induced by UVA or menadione, and (iii) accelerated reconstitution of epidermal vitamin A after UVB but not UVA induced depletion. Thus acute UVA induced both epidermal vitamin A depletion and lipid peroxidation, UVB induced only vitamin A depletion, and menadione induced only a lipid peroxidation; topical alpha-tocopherol prevented lipid peroxidation but not vitamin A depletion. These observations indicate (i) that CRBP-I neither provides protection to UVB- and UVA-induced epidermal vitamin A depletion, nor interferes significantly with reconstitution, and (ii) that the UV-induced vitamin A depletion and lipid peroxidation in mouse epidermis are unrelated processes. UV light does not destroy epidermal vitamin A through an oxidative stress but probably by a photochemical reaction in which UV radiations at about 325 nm give the corresponding activation energy.

Administration, Topical↗

PubMed2003

The development of substitute inks and controls for reducing workplace concentrations of organic solvent vapors in a vinyl shower curtain printing plant.

During the summer of 1994, football players at a practice field reported noxious odors in the area. Ohio Environmental Protection Agency (OEPA) investigations of industries surrounding the field included a printing facility producing vinyl shower curtains with screen-printed designs. Though not the source of the odor, they were discharging volatile organic compounds directly to the environs in violation of OEPA regulations. To achieve compliance they installed a catalytic oxidizer for treating discharged air. Due to high equipment costs, the capacity of the installed catalytic oxidizer resulted in a substantial reduction in discharged air flow rates and increased solvent vapor concentrations within the workplace. Vapor levels caused worker discomfort, prompting a request for assistance from the Ohio Bureau of Workers Compensation. The vapor concentrations were found to exceed NIOSH, OSHA, and ACGIH acceptable exposure levels. The workers were then required to wear organic vapor removing respirators full-time while printing as a temporary protective measure. The company requested NIOSH assistance in finding methods to reduce solvent vapor concentrations. NIOSH studies included the identification of the sources and relative magnitude of solvent emissions from the printing process, the design of controls for the emissions, and the development of substitute inks using non-photochemically reactive solvents. The new ink system and controls allowed OEPA removal of the requirement for the treatment of discharged air and substantial increases in dilution ventilation. Increased ventilation would permit reduction in worker exposures to less than 1/3 mixture TLV levels and removal of requirements for respirator usage. This solution was the result of a comprehensive review of all facets of the problem, including OEPA regulations. It also required cooperative work between the company and federal, state, and local governmental agencies.

Air Movements↗

PubMed1990

Adaptation of the Photosynthetic Apparatus in Maize Leaves as a Result of Nitrogen Limitation : Relationships between Electron Transport and Carbon Assimilation.

In maize (Zea mays L., cv Contessa), nitrogen (NO(3) (-)) limitation resulted in a reduction in shoot growth and photosynthetic capacity and in an increase in the leaf zeaxanthin contents. Nitrogen deficiency had only a small effect on the quantum yield of CO(2) assimilation but a large effect on the light-saturated rate of photosynthesis. Linear relationships persisted between the quantum yield of CO(2) assimilation and that of photosystem II photochemistry in all circumstances. At high irradiances, large differences in photochemical quenching and nonphotochemical quenching of Chl a fluorescence as well as the ratio of variable to maximal fluorescence (Fv/Fm) were apparent between nitrogen-deficient plants and nitrogen-replete controls, whereas at low irradiances these parameters were comparable in all plants. Light intensity-dependent increases in nonphotochemical quenching were greatest in nitrogen-deficient plants as were the decreases in Fv/Fm ratio. In nitrogen-deficient plants, photochemical quenching decreased with increasing irradiance but remained higher than in controls at high irradiances. Thermal dissipative processes were enhanced as a result of nitrogen deficiency (nonphotochemical quenching was elevated and Fv/Fm was lowered) allowing PSII to remain relatively oxidised even when carbon metabolism was limited via nitrogen limitation.

Journal Article↗

PubMed2007

Mass-independent sulfur isotopic compositions in stratospheric volcanic eruptions.

The observed mass-independent sulfur isotopic composition (Delta33S) of volcanic sulfate from the Agung (March 1963) and Pinatubo (June 1991) eruptions recorded in the Antarctic snow provides a mechanism for documenting stratospheric events. The sign of Delta33S changes over time from an initial positive component to a negative value. Delta33S is created during photochemical oxidation of sulfur dioxide to sulfuric acid on a monthly time scale, which indicates a fast process. The reproducibility of the results reveals that Delta33S is a reliable tracer to chemically identify atmospheric processes involved during stratospheric volcanism.

Journal Article↗

PubMed2002

PAH degradation by UV/H2O2 in perfluorinated surfactant solutions.

Polycyclic aromatic hydrocarbons (PAHs) solubilized in perfluorinated surfactant (PFS) solutions were degraded by direct photolysis and UV/H2O2 process. The subsequent recovery and reuse of these surfactant solutions were also demonstrated. Phenanthrene and pyrene were selected as representative PAHs and an anionic PFS: ammonium perfluorooctanoate (APFO) was used. In our experiments, micellar APFO solutions retarded the phenanthrene photolysis and enhanced the pyrene photolysis. The results indicate that the photochemical reactivity of compound in micelles is strongly dependent on specific properties of the solubilizate, possibly due to the different excited state behaviors of compound. UV/H2O2 process exhibits a greatly enhanced rate of PAH photolysis in both water and APFO compared to direct photolysis. indicating that hydroxyl radicals may be generated or penetrated at the sites of PAHs solubilized in the micelles. Additionally. a smaller rate enhancement by UV/H2O2 in micelles than in water suggests that micelles provide some degree of protection from hydroxyl radical attack. The possibility of recovery and reuse of PFS has been demonstrated by measuring the solubilizing capacity of APFO after direct photolysis and UV/H2O2 process. Overall, this study demonstrates UV/H2O2 process can be an effective treatment method for not only PAH degradation but also surfactant recovery and reuse.

Fluorine Compounds↗

PubMed2006

Effect of photochemical treatment on the biocompatibility of a commercial nonionic surfactant used in the textile industry.

The degradability of surfactants is a frequent and complex issue arising both at domestic as well as industrial treatment facilities. The present paper describes a laboratory study conducted to elucidate the photochemical and biochemical treatability of a nonionic, alkyl polyethylene ether-based surfactant formulation commonly used in the textile preparation stage. The application of H(2)O(2)/UV-C advanced photochemical oxidation appeared to be a suitable treatment alternative and 90% COD removal (COD(0) approximately 500 mg/L) could be achieved under optimized process conditions. A significant COD removal efficiency (74%) could also be reached after biodegradation (final COD=135 mg/L) of the surfactant; however, necessitated an acclimation period of at least 6 weeks for the achievement of steady-state conditions. H(2)O(2)/UV-C treatment efficiency was seriously retarded upon elevation of the initial COD to around 1000 mg/L, resulting in 46% COD and 38% TOC removal after 120 min photochemical oxidation (H(2)O(2,0)=1020 mg/L; pH(0)=9.1). The BOD(5)/COD ratio increased from 0.23 to 0.31 after the application of H(2)O(2)/UV-C revealing that photochemical pretreatment may have a positive effect on the ultimate biodegradation of the nonionic surfactant. Although the time required for activated sludge treatment to reach steady-state conditions could be reduced to 3 weeks for the photochemically pretreated surfactant formulation biochemical COD removal efficiency dramatically decreased from 74% to 39% for the nonionic surfactant being subjected to H(2)O(2)/UV-C pretreatment (ultimate COD after activated sludge treatment=265 mg/L).

Industrial Waste↗

PubMed2003

Light directed gene transfer by photochemical internalisation.

Numerous gene therapy vectors, both viral and non-viral, are taken into the cell by endocytosis, and for efficient gene delivery the therapeutic genes carried by such vectors have to escape from endocytic vesicles so that the genes can further be translocated to the nucleus. Since endosomal escape is often an inefficient process, release of the transgene from endosomes represents one of the most important barriers for gene transfer by many such vectors. To improve endosomal escape we have developed a new technology, named photochemical internalisation (PCI). In this technology photochemical reactions are initiated by photosensitising compounds localised in endocytic vesicles, inducing rupture of these vesicles upon light exposure. The technology constitutes an efficient light-inducible gene transfer method in vitro, where light-induced increases in transfection or viral transduction of more than 100 and 30 times can be observed, respectively. The method can potentially be developed into a site-specific method for gene delivery in vivo. This article will review the background for the PCI technology, and several aspects of PCI induced gene delivery with synthetic and viral vectors will be discussed. Among these are: (i) The efficiency of the technology with different gene therapy vectors; (ii) use of PCI with targeted vectors; (iii) the timing of DNA delivery relative to the photochemical treatment. The prospects of using the technology for site-specific gene delivery in vivo will be thoroughly discussed, with special emphasis on the possibilities for clinical use. In this context our in vivo experience with the PCI technology as well as the clinical experience with photodynamic therapy will be treated, as this is highly relevant for the clinical use of PCI-mediated gene delivery. The use of photochemical treatments as a tool for understanding the more general mechanisms of transfection will also be discussed.

Animals↗

PubMed2004

Beta-lactam-forming photochemical reactions of N-trimethylsilylmethyl- and N-tributylstannylmethyl-substituted alpha-ketoamides.

Two mechanisms have been proposed for the beta-lactam-forming photochemical reactions of alpha-ketoamides. One, suggested by Aoyama, involves excited-state H-atom abstraction while the other, put forth by Whitten, follows a sequential SET-proton-transfer route. The photochemical properties of N-trimethylsilylmethyl- and N-tributylstannylmethyl-substituted alpha-ketoamides were explored in order to gain information about the mechanism of this process and to develop a regioselective method for beta-lactam formation. The results of this effort show that (1) photoreactions of N-trimethylsilylmethyl-substituted alpha-ketoamides proceed by competitive H-atom abstraction and sequential SET-desilylation pathways and (2) a sequential SET-destannylation pathway is preferentially followed in photochemical reactions of the tributylstannylmethyl-substituted alpha-ketoamides.

Amides↗

PubMed2006

Dendritic aggregation of oligothiophene during desorption of 2,5-diiodothiophene multilayer and topography-induced alignment of oligothiophene nanofibers.

The multilayer desorption behavior of 2,5-diidothiophene and the dendritic aggregation of photochemical reaction products during the desorption of 2,5-diiodothiophene multilayers have been studied. Like many other aromatic compounds, 2,5-diiodothiophene shows a multilayer desorption behavior different from the typical zeroth-order kinetics, a metastable desorption peak growth at approximately 220 K followed by a thick multilayer peak growth at approximately 235 K. Traditionally, these desorption behaviors have been attributed to the formation of three-dimensional clusters. This paper provides the direct evidence of this clustering process by producing nondesorbing photoreaction products in the multilayer and by imaging their clusters after the multilayer desorption. Oligothiophene species are produced via photochemical reactions of 2,5-diiodothiophene during the multilayer deposition at approximately 180 K in ultrahigh vacuum (UHV). Upon heating the multilayer to room temperature, the oligothiophene species forms into fibrous aggregates with a fractal dimension varying from 1.37 to 1.81 depending on their surface concentration. Using a topographical alteration of the substrate with a repeating pattern, these oligothiophene fibers can be aligned to a certain direction. This may allow in-situ fabrication of aligned conjugated polymer fibers directly on a target substrate.

Journal Article↗

PubMed2003

Photochemical properties of kynurenine pathway metabolites and indoleamines.

Photochemical damages to the biological system may occur through photodynamic action in the presence of photosensitive molecules. Photodynamic action contains the following processes; 1) photosensitisation and/or 2) electron transfer, in which singlet oxygen and superoxide radical production for each in the presence of oxygen molecules. We have studied those processes after the absorption of light by kynurenine pathway metabolites and indoleamine derivatives. We found that kynurenine and 3-hydroxykynurenine generate superoxide radical after electron transfer from their excited state molecules to oxygen molecules, and superoxide makes reduction reaction. On the other hand, it was found that kynurenic acid, melatonin, 5-methoxytryptamine and 5-methoxytryptophol work as photosensitisers with the detection of singlet oxygen production by using the N, N-dimethyl-4-nitrosoaniline bleaching method, while xanthurenic acid, serotonin and N-acetylserotonin generate no detectable amount of singlet oxygen. We have determined the photochemical quantum yields of singlet oxygen production for those photosensitisers, in which quantum yields are not so high except kynurenic acid (f3 = 0.101). In view of the multiple roles played by their metabolites in various systems, these results are relevant to taking into consideration of their photoeffect in the presence of light.

In Vitro Techniques↗

PubMed2006

Harnessing the energy of molecular recognition in a nanomachine having a photochemical on/off switch.

6A-Deoxy-6A-(N-methyl-3-phenylpropionamido)-beta-cyclodextrin operates as a molecular machine, where the amide group serves as a torsion bar to harness the work output resulting from extraction of 1-adamantanol and consequent complexation of the aryl substituent by the cyclodextrin, when the latter behave as the piston and cylinder, respectively, of a molecular pump. At 25 degrees C, the complexation changes the ratio of the amide (Z)- and (E)-isomers from 2.4:1 to 25:1, on which basis the work performed on the amide bond is calculated to be 1.4 kcal mol-1. trans-6A-Deoxy-6A-(N-methylcinnamido)-beta-cyclodextrin and the cis isomer function as a more advanced version of the machine, with the alkene moiety serving as a photochemical on/off switch. Irradiation at 300 nm converts the trans cinnamide to the cis isomer, while the reverse process occurs at 254 nm. With the cis isomer there is little interaction of the phenyl group with the cyclodextrin cavity, so in that mode the machine is turned off. By contrast, complexation of the aryl substituent by the cyclodextrin occurs with the trans cinnamide and changes the ratio of the amide (Z)- and (E)-isomers from 2.6:1 to 100:1. Consequently, in this mode the machine is turned on, and the work harnessed by the amide bond is 2.1 kcal mol-1.

Journal Article↗

PubMed2005

A non-terrestrial 16O-rich isotopic composition for the protosolar nebula.

The discovery in primitive components of meteorites of large oxygen isotopic variations that could not be attributed to mass-dependent fractionation effects has raised a fundamental question: what is the composition of the protosolar gas from which the host grains formed? This composition is probably preserved in the outer layers of the Sun, but the resolution of astronomical spectroscopic measurements is still too poor to be useful for comparison with planetary material. Here we report a precise determination of the oxygen isotopic composition of the solar wind from particles implanted in the outer hundreds of nanometres of metallic grains in the lunar regolith. These layers of the grains are enriched in 16O by >20 +/- 4 per thousand relative to the Earth, Mars and bulk meteorites, which implies the existence in the solar accretion disk of reactions--as yet unknown--that were able to change the 17O/16O and 18O/16O ratios in a way that was not dependent strictly on the mass of the isotope. Photochemical self-shielding of the CO gas irradiated by ultraviolet light may be one of these key processes, because it depends on the abundance of the isotopes, rather than their masses.

Carbon Monoxide↗