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At least 91 records · Page 5Linked to original sources
PubMed1995

Singlet oxygen-trapping reaction as a method of (1)O2 detection: role of some reducing agents.

The production of singlet oxygen by H2O2 disproportionation and via the oxidation of H2O2 by NaOCl in a neutral medium was monitored by spin trapping with 2,2,6,6 tetramethyl-4-piperidone (TMPone). The singlet oxygen formed in both reactions oxidized 2,2,6,6 tetramethyl-4-piperidone to give nitroxide radicals. However the production of nitroxide radicals was relatively small considering the concentrations of H2O2 and NaOCl used in the reaction systems. Addition of electron donating agents: ascorbate, Fe2+ and desferrioxamine leads to an increase in the production of nitroxide radicals. We assumed that a very slow step of the reaction sequence, the homolytic breaking of the O-O bond of N-hydroperoxide (formed as an intermediate product during the reaction of 1O2 with TMPone) could be responsible for the relatively small production of nitroxide radicals. Electron donating agents added to the reaction system probably raise the rate of the hydroperoxide decomposition by allowing a more rapid heterolytic cleavage of the O-O bond leading to a greater production of nitroxide radicals. The largest effect was observed in the presence of desferrioxamine. Its participation in this process is proved by the concomitant appearance of desferrioxamine nitroxide radicals. The results obtained demonstrate that the method proposed by several authors and tested in this study to detect singlet oxygen is not convenient for precise quantitative studies. The reactivity of TMPone towards O2.-/HO2. and .OH has been also investigated. It has been found that both O2.-/HO2. and .OH radicals formed in a phosphate buffer solution (pH 7.4, 37 degrees C), respectively by a xanthine-oxidase/hypoxanthine system and via H2O2 UV irradiation, do not oxidize 2,2,6,6 tetramethyl-4-piperidone to nitroxide radicals.

Ascorbic Acid↗
PubMed1992

[Synthesis and stereochemistry of potentially powerful analgesics: 2,4-m-diaryl substituted 3,7-diazabicyclo(3,3,1)nonan-9-one-1,5-diesters].

The 2,4-di-2-pyridyl- substituted 7-methyl-3,7-diazabicyclo[3.3.1] nonan-9-one-1,5-diester shows a reasonable kappa-agonistic activity in the mouse vas deferens test. -To enhance the analgetic activity derivatives with m-Cl-, m-CH3-, m-OCH3-, m-OH-, and m-NO2 substituted phenyl residues at C-2/4 were synthesized: From the condensation of benzaldehydes, methylamine, and oxoglutarate isomeric mixtures of piperidones were obtained, containing cis-ketone and -enol and trans-enol; the isomerisation reactions of these piperidones were observed in CDCl3 and CD3OD. The bicyclus resulting from the reaction of the piperidones with HCHO and methylamine exhibits conformational rigidity because the free rotation of the 2,4-aryl groups is hindered. The rotational barrier around the C-2-aryl-bond was shown to be 18 kcal/mol by analysis of variable temp. 1H-NMR spectra.

Analgesics↗
PubMed2005

Comparison between sonodynamic effect and photodynamic effect with photosensitizers on free radical formation and cell killing.

Although enhancement of ultrasound-induced cell killing by photodynamic reagents has been shown, the sonochemical mechanism in detail is still not clear. Here, comparison between sonodynamic effect and photodynamic effect with photosensitizers at a concentration of 10 microM on free radical formation and cell killing was made. When electron paramagnetic-resonance spectroscopy (EPR) was used to detect 2,2,6,6-tetramethyl-4-piperidone-N-oxyl (TAN) after photo-irradiation or sonication with 2,2,6,6-tetramethyl-4-piperidone (TMPD), the order of TAN formation in the photo-irradiated samples was as follows: rhodamine 6G (R6) > sulforhodamine B (SR) > hematoporphyrin (Hp) > rhodamine 123 (R123) > rose bengal (RB)>erythrosine B (Er) = 0; although there was time-dependent TAN formation when the samples were sonicated, no significant difference among these agents were observed. All these agents suppressed ultrasound-induced OH radical formation detected by EPR-spin trapping. Sensitizer-derived free radicals were markedly observed in SR, RB and Er, while trace level of radicals derived from R6 and R123 were observed. Enhancement of ultrasound-induced decrease of survival in human lymphoma U937 cells was observed at 1.5 W/cm(2) (less than inertial cavitation threshold) for R6, R123, SR and Er, and at 2.3 W/cm(2) for R6, R123, Er, RB and SR. On the other hand, photo-induced decrease of survival was observed for R6, Hp and RB at the same concentration (10 microM). These comparative results suggest that (1) (1)O(2) is not involved in the enhancement of ultrasound-induced loss of cell survival, (2) OH radicals and sensitizer-derived free radicals do not take part in the enhancement, and (3) the mechanism is mainly due to certain mechanical stress such as augmentation of physical disruption of cellular membrane by sensitizers in the close vicinity of cells and/or cavitation bubbles.

Electron Spin Resonance Spectroscopy↗
PubMed2002

A novel free-radical ring contraction of a cyclic carbamate.

During a study on iodocyclocarbamation reactions of 2-styryl-4-piperidones, a novel ring contraction was observed. Iodocyclocarbamation of 2-styryl-4-piperidone 3 gave the bicyclic carbamate 4. Reduction of 4 under free-radical conditions effected a stereoselective ring contraction to provide oxazolidinone 6. A three-electron-three-center mechanism is proposed.

Aza Compounds↗
PubMed2006

Highly enantioselective access to primary propargylamines: 4-piperidinone as a convenient protecting group.

[reaction: see text] We report a highly enantioselective, catalytic three-component coupling of aldehydes, alkynes, and 4-piperidone hydrochloride hydrate to afford the corresponding tertiary propargylamines in useful yields. The selective cleavage of the piperidone protecting group using either ammonia/EtOH or a polymer-supported scavenger amine furnishes primary propargylamines.

Aldehydes↗
PubMed1975

Induction of erythroid differentiation in murine virus infected eythroleukemia cells by highly polar compounds.

Murine-virus-infected erythroleukemia cells cultured in a medium with dimethylsulfoxide or N,N-dimethylformamide are induced to differentiate to erythroid cells. A number of highly polar compounds have a similar effect in inducing erythroid differentiation of the virus-infected cells, as assayed by the appearance of hemoglobin. These compounds are 1-methyl-1-2-piperidone, N,N-dimethylacetamide, N-methylpyrrolidinone, N-methylacetamide, 2-pyrrolidinone, propionamide, pyridine-N-oxide, piperidone, N-methylformamide, acetamide, and triethylene glycol. It has been previously reported that dimethylsulfoxide must be present during DNA synthesis and, possibly, shortly therafter, to induce differentiation. These findings are consistent with the hypothesis that dimethylsulfoxide and related polar compounds act by changing the conformation of DNA or a DNA-protein complex, causing an alteration in transcription that leads to the expression of the program of erythroid differentiation.

Acetamides↗
PubMed1975

Tumorigenesis by oxygenated nitrosopiperidines in rats.

Three oxygenated N-nitrosopiperidines--nitroso-3-piperidinol, nitroso-4-piperidinol, and nitroso-4-piperidone--were prepared and given in drinking water at equivalent molar doses to Sprague-Dawley rats. All were potent carcinogens, 100% of the rats developed tumors in all treatment groups. Nitroso-3-piperidinol resembled nitrosopiperidine in inducing a high incidence of tumors of the nasal cavity and upper alimentary tract, and a few liver tumors. Nitroso-4-piperidinol and nitroso-4-piperidone caused a high incidence of tumors of the nasal cavity but very few tumors of the upper alimentary tract. After treatment with the 4-substituted compounds, a high incidence of liver tumors was observed in females but not in males.

Animals↗
PubMed2001

Ultraviolet irradiation of titanium dioxide in aqueous dispersion generates singlet oxygen.

We previously reported that irradiation of titanium dioxide (TiO2) in ethanol generates both singlet oxygen (1O2) and superoxide anion (O2*-) as measured by EPR spectroscopy. The present study describes the production of reactive oxygen species upon irradiation of TiO2 in aqueous suspension as determined by EPR spectroscopy using 2,2,6,6-tetramethyl-4-piperidone (4-oxo-TMP) and 5,5-dimethyl-pyrroline-N-oxide (DMPO). Photoproduction of 1O2 by suspended TiO2, detected as 2,2,6,6-tetramethyl-4-piperidone-N-oxyl (4-oxo-TEMPO), was measured in water and deuterium oxide (D2O) in the presence or absence of sodium azide (NaN3) and under air or argon atmospheres. Production of a DMPO-OH adduct was examined in 4-oxo-TMP containing medium in the presence or absence of dimethyl sulfoxide (DMSO). The signal for the DMPO spin adduct of superoxide anion was not observed in aqueous conditions. Kinetic analysis revealed that 1O2 was produced at the surface of irradiated TiO2 in aqueous suspension as was observed in ethanol. Kinetic analysis revealed that the formation of DMPO-OH adduct reflects oxidation of DMPO by 1O2 rather than the trapping of the hydroxyl radical produced by the reaction of photo-exited TiO2 and water. The production of large amounts of 1O2 by TiO2 in aqueous suspension as compared to those in ethanol and possible formation of hydroxyl radical in aqueous suspension but not in alcohol, suggest that irradiation of TiO2 in aqueous environments is biologically more important than that in non-aqueous media.

Antioxidants↗
PubMed1991

Effect of ultrasound and ionizing radiation on a sterically hindered cyclic secondary amine: an ESR study.

The possible use of 2,2,6,6-tetramethyl-4-piperidone (TMPone) for the detection of singlet oxygen was investigated by gamma radiolysis and sonolysis of oxygen-saturated aqueous solutions. Formation of 2,2,6,6-tetra-methyl-4-piperidone-N-oxyl (TAN) was observed with both gamma radiolysis and sonolysis with a similar dependence on the concentration of TMPone up to 20 mM and a strong dependence on pH. In oxygen-saturated solutions the sonolysis of TMPone leads to the formation of the cyclic hydroxylamine (approx. 30% of the yield of TAN) while radiolysis does not. In the low pH range (5-6.5) and at high concentrations of OH radical scavengers (azide or formate), TAN is produced by sonolysis but not by radiolysis. Sonolysis of argon-saturated solutions of TMPone produces methyl radicals due to the high-temperature regions of the collapsing cavitation bubbles. The methyl radicals were detected by ESR (electron spin resonance) and spin trapping with 3,5-dibromo-2,6-dideuterio-4-nitroso-benzene sulfonate. Since the reaction of singlet oxygen with TMPone is also strongly dependent on pH, it does not seem likely that TMPone could be used for the detection of singlet oxygen in sonochemistry.

Cobalt Radioisotopes↗
PubMed1995

Effect of gallium-porphyrin analogue ATX-70 on nitroxide formation from a cyclic secondary amine by ultrasound: on the mechanism of sonodynamic activation.

Sonodynamic therapy is a promising new modality for cancer treatment based on the synergistic effect on tumor cell killing by combination of a drug (typically a photosensitizer) and ultrasound. The mechanism of sonodynamic action was suggested to involve photoexcitation of the sensitizer by sonoluminescent light, with subsequent formation of singlet oxygen. In this work we studied the aqueous sonochemical reactions of the gallium-porphyrin derivative ATX-70, one of the most active sonodynamic agents found, using 50 kHz ultrasound. The experiments were carried out in the presence of 2,2,6,6-tetramethyl-4-piperidone hydrochloride (TMP), which reacts with singlet oxygen or .OH radicals to give the EPR-detectable nitroxide 2,2,6,6-tetramethyl-4-piperidone-N-oxyl (TMP-NO). Recently it has been suggested that the enhancement of TMP-NO yields in the presence of aqueous solutions of ATX-70 exposed to ultrasound was evidence for the formation of singlet oxygen in the system. Our results show that the surfactant cetyltrimethylammonium bromide (CTAB) can mimic the ATX-70-induced increase in the TMP-NO signal, but it fails to reproduce the behavior of ATX-70 in D2O: while the yields of TMP-NO in the presence of ATX-70 increase in D2O, the opposite effect was found with the surfactant CTAB. However, our data show that the increased TMP-NO yields in D2O are paralleled by an increased concentration of ATX-70 dimer, a form that is inactive in the photochemical generation of singlet oxygen. Our finding that the ATX-70-dependent enhancement of the TMP-NO signal was highest at approximately 20% O2, in both N2/O2 and argon/O2 mixtures, and decreased with increasing oxygen concentration is not compatible with the singlet oxygen mechanism. Finally, our results on the temperature dependence of the ATX-70-induced formation of TMP-NO are not consistent with the photochemical excitation of ATX-70 by sonoluminescent light: the ATX-70-dependent enhancement of TMP-NO signal increased with temperature in the range 10-25 degrees C, while the intensity of sonoluminescence of aqueous solutions both in multiple-bubble fields and in single-bubble experiments is known to decrease with increasing temperature.

Antineoplastic Agents↗