Two New Methods of Actinometry for Epr‐measurements

Moan, Johan Emelian; Høvik, B.; Wold, Einar

doi:10.1111/j.1751-1097.1979.tb07189.x

Cited by 15 publications

(8 citation statements)

References 3 publications

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“…Although TEMP has been used to detect the generation of singlet oxygen (Lion et af., 1976;Salvatore and Vorst, 1977;Moan et al, 1979), no further reference was made to the formation of TEMPO. Our studies provide evidence that TEMPO was indeed a reaction product of TEMP and lo2.…”

Section: Inset Is the Relationship Of Discussionmentioning

confidence: 99%

EPR STUDIES OF TRAPPED SINGLET OXYGEN (^lO₂) GENERATED DURING PHOTOIRRADIATION OF HYPOCRELLIN A

Zang

Zhang

Misra

1990

Photochem & Photobiology

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Hypocrellin A, a peryloquinone derivative, has recently been isolated from the sacs of the fungus Hypocrella bambusae. This pigment, in combination with phototherapy, has been used in human medicine to cure various skin diseases. The generation of singlet oxygen during photoirradiation of Hypocrellin A (HA) was detected as an oxidation product of a sterically hindered amine (tetramethylpiperidine oxide; TEMPO) by electron paramagnetic resonance (EPR) spectroscopic techniques. Azide inhibited the EPR signal intensity in a dose-dependent manner with a quenching rate constant of 3.86 x 10(8) M-1s-1 in ethanol. Deuterated solvents, known to increase the lifetime of singlet oxygen, augmented the EPR signal intensity. The rate of production of singlet oxygen was dependent not only upon the concentration of HA and the time of irradiation but also on the oxygen content of the reaction mixture. The hyperfine splitting constant (aN = 16.3 G) and g-value (g = 2.0056) of the photoproduct of TEMP-singlet oxygen and TEMPO were found to be identical. This indicates that the nitroxide species detected by EPR spectroscopy generated by reacting TEMP with photogenerated 1O2 is TEMPO. The rate constant (kT) for the reaction of singlet oxygen with TEMP to form TEMPO radical was found to be 5.3 x 10(5) M-1s-1.

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Section: Inset Is the Relationship Of Discussionmentioning

confidence: 99%

EPR STUDIES OF TRAPPED SINGLET OXYGEN (^lO₂) GENERATED DURING PHOTOIRRADIATION OF HYPOCRELLIN A

Zang

Zhang

Misra

1990

Photochem & Photobiology

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“…This setting represented a compromise between the ideals of high spectral resolution and fluence rates high enough for moderate rates of oxygen consumption. The fluence rate at the cell (2-30 Wlm' over the wavelength region investigated) was routinely measured using a Yellow Springs Instruments radiometer (Model 65-A), and periodically checked by actinometry using hematoporphyrin (Sigma) and 2,2.6,6-tetramethyl-4-piperidone (Aldrich) (Moan et al, 1979). The time required to collect data at each wavelength was typically 20 to 90 min.…”

Section: Sample Preparationmentioning

confidence: 99%

Photoinduced Oxygen Consumption in Melanin Systems. Action Spectra and Quantum Yields for Eumelanin and Synthetic Melanin

Sarna

Sealy

1984

Photochem & Photobiology

146

113

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Abstract— The first quantitative measurements of the wavelength dependence of oxygen consumption in systems containing eumelanin (from bovine eyes) and synthetic DOPA melanin are reported. Consumption of oxygen (considered to be a requirement for immediate pigment darkening) during irradiation of melanins with either visible or ultraviolet light was monitored using a spin probe nitroxide‐electron spin resonance spectroscopic approach. From initial rates of oxygen removal, quantum yields have been obtained over a wavelength range from 230 to 600 nm. Eumelanins are moderately effective in promoting oxygen consumption; quantum yields are low for irradiation with visible light, but increase sharply with light of shorter wavelengths. The absolute quantum yield for oxygen consumption is about 0.1% for natural melanin at 320 nm. The action spectrum is similar for both natural and synthetic melanins, indicating that the major chromophore responsible for oxygen consumption is the same for both kinds of material. This chromophore is not the major melanin chromophore responsible for absorption of visible light. The action spectrum also clearly differs from published action spectra for melanogenesis; however, the weak wavelength dependence for visible light is similar to that found for immediate pigment darkening. Catalase decreases the rate of oxygen consumption by 50%, confirming that hydrogen peroxide is the major molecular product of oxygen reduction. A Type I (free‐radical) mechanism evidently predominates: D2O and azide are shown to have only minor effects, ruling out any major contribution from a Type II (singlet‐oxygen) process to the overall oxygen consumption.

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“…Prior to ESR measurements, photon fluence rates, at approximately 1 cm from the front of the cavity, were measured using a YSI Radiometer, Model 65A (Yellow Springs Instruments, Columbus, OH). The amount of light incident on the solution inside the ESR cavity was calculated by actinometry using hematoporphyrin and 2,2,6,6-tetramethyl-4-piperidine N-oxyl [20]. It was assumed that [~ = I 0 (l 10-'el), where Ia is the amount of light absorbed by S-nitrosothiol, I 0 is the amount of light incident on the sample, e is the molar extinction coefficient, c is the concentration of S-nitrosothiol, and 1 is the path length.…”

Section: Irradiation Procedures and Quantum Yield Measurementsmentioning

confidence: 99%

Photosensitized decomposition of S‐nitrosothiols and 2‐methyl‐2‐nitrosopropane Possible use for site‐directed nitric oxide production

et al. 1995

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Irradiation of S-nitrosoglutathione (GSNO) with light (A = 550 nm) resulted in the homolytie decomposition of GSNO to generate glutathionyl radical (GS-) and nitric oxide (-NO), which were monitored by ESR spectrometry. Inclusion of Rose Bengal (RB) resulted in a 9-fold increase in the quantum yield for • NO production and also an increase in the rate of thiyl radical formation. The bimolecular rate constant for the interaction of triplet RB with GSNO has been estimated to be approximately 1.2 x 109 M -1 s -I by competition with oxygen. Hematoporphyrin (liP) also enhanced the rate of" NO production by 2-3-fold. 2-Methyl-2-nitrosopropane (MNP) decomposed on irradiation (A = 660 nm) to form "NO and tert-butyl radical. Aluminum phthalocyanine tetrasulphonate enhanced the rate of decomposition of MNP by 10-fold. These studies show that photosensitizers enhance the release of" NO from donor compounds.

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Two New Methods of Actinometry for Epr‐measurements

Cited by 15 publications

References 3 publications

EPR STUDIES OF TRAPPED SINGLET OXYGEN (^lO₂) GENERATED DURING PHOTOIRRADIATION OF HYPOCRELLIN A

EPR STUDIES OF TRAPPED SINGLET OXYGEN (^lO₂) GENERATED DURING PHOTOIRRADIATION OF HYPOCRELLIN A

Photoinduced Oxygen Consumption in Melanin Systems. Action Spectra and Quantum Yields for Eumelanin and Synthetic Melanin

Photosensitized decomposition of S‐nitrosothiols and 2‐methyl‐2‐nitrosopropane Possible use for site‐directed nitric oxide production

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Two New Methods of Actinometry for Epr‐measurements

Cited by 15 publications

References 3 publications

EPR STUDIES OF TRAPPED SINGLET OXYGEN (lO2) GENERATED DURING PHOTOIRRADIATION OF HYPOCRELLIN A

EPR STUDIES OF TRAPPED SINGLET OXYGEN (lO2) GENERATED DURING PHOTOIRRADIATION OF HYPOCRELLIN A

Photoinduced Oxygen Consumption in Melanin Systems. Action Spectra and Quantum Yields for Eumelanin and Synthetic Melanin

Photosensitized decomposition of S‐nitrosothiols and 2‐methyl‐2‐nitrosopropane Possible use for site‐directed nitric oxide production

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EPR STUDIES OF TRAPPED SINGLET OXYGEN (^lO₂) GENERATED DURING PHOTOIRRADIATION OF HYPOCRELLIN A

EPR STUDIES OF TRAPPED SINGLET OXYGEN (^lO₂) GENERATED DURING PHOTOIRRADIATION OF HYPOCRELLIN A