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Query: KEGG:D01931 (TiO2)
 11,320 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Photoexcited TiO2 particles can drive various chemical reactions due to their strong oxidizing and reducing ability. To investigate the possible use of this effect for cancer treatment, the antitumor activity of photoexcited TiO2 particles was studied in vitro and in vivo. HeLa cells cultured in vitro were completely killed in the presence of TiO2 (50 micrograms/ml) with 10-min UV irradiation by a 500-W-Hg lamp. In contrast, very little cell death was observed from TiO2 treatment without UV irradiation. Photoexcited TiO2 particles also significantly suppressed the growth of HeLa cells implanted in nude mice, compared with those receiving TiO2 alone or UV irradiation alone. The cell death caused by photoexcited TiO2 particles was significantly protected in the presence of L-tryptophan and catalase. These molecules are quenchers of hydroxyl radicals and scavengers of hydrogen peroxide, respectively, suggesting that the cells were killed by the OH. and H2O2 produced from photoexcited TiO2 particles.
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PMID:Induction of cytotoxicity by photoexcited TiO2 particles. 155 37

In vitro studies of titanium and TiO2 as well as other metals were carried out to investigate the role of these metals in the inflammatory response through the Fenton reaction. The TiOOH matrix formed traps the superoxide radical, so that no or very small amounts of free hydroxyl radicals are produced. Ellipsometry and spin trapping with spectrophotometry and electron spin resonance (ESR) were used to study the interaction between Ti and H2O2. Spectrophotometry results indicated that Ti, Zr, Au and Al are low free OH-radical producers. We propose a new model for the titanium-tissue interface where the oxidized titanium surface is covered with a hydrated TiOOH matrix after the inflammatory reaction. This matrix is suggested to possess good ion exchange properties, and extracellular components may interact with the Ti(IV)-H2O2 compound before matrix formation. The TiOOH matrix is formed when the H2O2 coordinated to the Ti(IV)-H2O2 complex is decomposed to water and oxygen. Superoxide (O2-) may be bound therein. The oxide layer initially present may be partly reformed to a TiOOH matrix due to the interaction with hydrogen peroxide.
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PMID:Titanium-hydrogen peroxide interaction: model studies of the influence of the inflammatory response on titanium implants. 254 19

Hydroxyl radicals formed from hydrogen peroxide during an inflammatory response are potent agents for cellular deterioration. The behaviour of implanted material in terms of its ability to sustain or stop free radical formation may be therefore very important. In vitro studies of titanium which is known to be biocompatible and osseointegrates into human bone were carried out. In our model studies, the production of free radicals from H2O2 at Ti and TiO2 surfaces was measured by spin trapping techniques. Our findings suggest that there is no sustained hydroxyl radical production at a titanium (oxide) surface. We propose that this is due to the quenching of the Fenton reaction through both trapping and oxidation of superoxide radicals in a TiOOH adduct.
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PMID:Interaction between hydrogen peroxide and titanium: a possible role in the biocompatibility of titanium. 270 98

Electrochemical measurements, x-ray photoelectron spectroscopy, and scanning tunneling microscopy have been used to study the effect of hydrogen peroxide on the passivity of titanium in a phosphate-buffered saline (PBS) solution. The results indicate that the passive film formed in the PBS solution--with and without addition of H2O2--may be described with a two-layer structure model. The inner layer has a structure close to TiO2 whereas the outer layer consists of hydroxylated compounds. The introduction of H2O2 in the PBS solution broadens the hydroxylate-rich region, probably due to the formation of a Ti(IV)-H2O2 complex. Furthermore, the presence of H2O2 results in enhanced dissolution of titanium and a rougher surface on a microscopic scale. Finally, a dark pigmentation (blue color) is observed when titanium has been exposed--for several weeks--to PBS with additions of H2O2.
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PMID:Electrochemical and XPS studies of titanium for biomaterial applications with respect to the effect of hydrogen peroxide. 812 22

A comparative degradation study of endosulfan spiked at 35 micrograms/l in water using photocatalysis with (FeCl3/H2O2)/(TiO2/H2O2) and photolysis using either a xenon arc lamp and/or sunlight was performed. After irradiation the water samples were preconcentrated using C18 solid-phase disk extraction and analysis by gas chromatography-electron capture and mass spectrometric detection. Endosulfan sulphate was found in the photodegradation studies. Endosulfan showed high stability in water when it was exposed to sunlight and xenon are lamp, but by means of photocatalysis with FeCl3/H2O2, TiO2/H2O2, the degradation was very fast with half lives varying from 59-98 min. The degradation kinetics followed a first order reaction and the R.S.D. of rate constants, for n = 3, varied from 4-17%. The stability of endosulfan on C18 Empore disks has been determined at 20 degrees C, 4 degrees C and -20 degrees C for periods up to 3 months. Endosulfan was not degraded on C18 Empore disks. Ground water samples from south of Spain (Almeria) were monitored during 1 year. The compounds alpha-, beta- and endosulfan sulphate were detected at concentration values varying from 0.5-540 ng/l.
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PMID:Application of C18 disks followed by gas chromatography techniques to degradation kinetics, stability and monitoring of endosulfan in water. 958 81

Photodegradation of chlorothalonil was studied in deionized and ground water with sunlight and Suntest apparatus, with and without FeCl3/H2O2 and TiO2/H2O2. After irradiation of the water samples spiked at 28-100 micrograms/l of chlorothalonil, the water solutions were preconcentrated using solid-phase disk extraction with C18 and analyzed by gas chromatography-electron capture and gas chromatography-mass spectrometric detection. The degradation products identified by GC-MS were: trichloro-1,3-dicyanobenzene, dichloro-1,3-dicyanobenzene and chloro-1,3-dicyanobenzene. The degradation kinetics followed a first order reaction and the R.S.D. of rate constants, for n = 3, varied from 2 to 14%. Halflives varied between 0.7 and 101 h. The stability of chlorothalonil on C18 Empore disks was also investigated at 20 degrees C, 4 degrees C and -20 degrees C for periods of up to 3 months. Chlorothalonil was not degraded on C18 Empore disks.
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PMID:Photodegradation and stability of chlorothalonil in water studied by solid-phase disk extraction, followed by gas chromatographic techniques. 981 95

The role of hydroxyl radicals on the degradation of lignins during a cellulosic pulp bleaching process including a photocatalytic stage, was assessed using peroxyformic acid lignins EL1 and REL1 and two phenolic niphenyl lignin models 1 and 2. The irradiations were performed in the absence of photocatalyst TiO2 and H2O2 (condition a), in the presence of TiO2 (condition b) and in the presence of H2O2 (condition c). The experiments were conducted in alkaline (pH approximately 11) aqueous ethanol solutions with oxygen bubbling. The relative phenolic content of the irradiated solutions, which is indicative of the involvement of hydroxyl radicals, was determined by ionization absorption spectroscopy. The results obtained show that the catalyzed reaction involves both degradation of the phenolate groups by electron transfer and hydroxylation of the lignin aromatic structure. Benzyl alcohol structural elements in sodium borohydride reduced lignin REL1 and compound 2 were also found as good trapping agents for the hydroxyl radicals. The degradation of EL1 was studied by measuring its fluorescence emission by comparison to the fluorescence of compound 2. The emission spectra indicate that some biphenyl phenolate anions in EL1 are reacting under UV/visible irradiation and some others, probably polyphenolic chromophores emitting less fluorescence, are formed.
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PMID:Photocatalytic degradation of lignin and lignin models, using titanium dioxide: the role of the hydroxyl radical. 1066 53

Results are reported for a comparative photodegradation study of atrazine and desethylatrazine in water using TiO2/H2O2, FeCl3/H2O2, and photolysis. Deionized water and ground water spiked with atrazine or desethylatrazine at 36 micrograms/L were irradiated by using a xenon arc lamp and/or sunlight. After irradiation, the water samples containing the spiked pesticides were preconcentrated by using C18 solid-phase extraction disks and analyzed by gas chromatography with nitrogen-phosphorus and mass spectrometric detection. A relative percentage of 7% desethylatrazine was detected in samples removed after 20 and 4 min of sensitized photodegradation with TiO2 and Fe3+, respectively. Atrazine and desethylatrazine did not degrade when solar irradiation (in winter) and deionized water were used. Atrazine degraded faster than desethylatrazine when a xenon arc lamp or sunlight plus FeCl3 was used, with half-lives varying from 5 to 11 min and from 19 to 26 min, respectively. In other photodegradation experiments, the degradation of atrazine was slightly higher than that of desethylatrazine. This study shows that desethylatrazine has slightly higher stability than atrazine in environmental water samples; this stability accounts for the frequent detection of desethylatrazine together with atrazine in natural waters.
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PMID:Comparative photodegradation study of atrazine and desethylatrazine in water samples containing titanium dioxide/hydrogen peroxide and ferric chloride/hydrogen peroxide. 1069 4

In the last decade advanced oxidation processes (AOPs) have been gaining importance for destruction of waste as cleaner methods enabling conversion of organic contaminants to harmless species. Photodegradation processes in the presence of hydrogen peroxide (H2O2), ozone (O3) and titanium dioxide (TiO2) are most frequently offered for wastewater treatment. The novel gas-sparged reactor equipped with UV lamp proved to be an efficient system for photochemical degradation. In this investigation 80 ppm aqueous solution of phenol was treated for 40 minutes. 13% of phenol was eliminated in the UV/air system and 73% in the UV/H2 O2/air system at 80 l/min air flowrate. Air sparging did not result in phenol removal with the gas phase.
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PMID:H2O2/UV/air oxidation of organic contaminants in the gas-sparged cyclone reactor. 1094 87

A comparative study is made of 12 methods of chemical oxidation applied to degrading p-hydroxybenzoic acid in aqueous solution. The oxidation processes tested were: UV, O3, UV/TiO2, O3/Fe2+, O3/H2O2, O3/UV, UV/H2O2, H2O2/Fe2+, H2O2/Fe2+/O3, UV/H2O2/O3, H2O2/Fe2+/UV and O3/UV/H2O2/Fe2+. The 12 processes were ranked by reactivity. In a kinetic study, the overall kinetic rate constant was split up into three components: direct oxidation by UV irradiation (photolysis), direct oxidation by ozone (ozonation), and oxidation by free radicals (mainly OH*).
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PMID:Comparison of the degradation of p-hydroxybenzoic acid in aqueous solution by several oxidation processes. 1110 Jul 85


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