Terephthalic acid: A dosimeter for the detection of hydroxyl radicals in vitro

Barreto, José C.; Smith, Gregory S.; Strobel, Nathaniel H. P.; McQuillin, Pamela A.; Miller, Thomas A.

doi:10.1016/0024-3205(94)00925-2

Cited by 282 publications

(188 citation statements)

References 11 publications

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“…The 3% (vol/vol) isopropanol was evaporated in air from the Nafion solution for 12 h before starting the measurements to ensure complete isopropanol evaporation. Additional Na-MnO 2 samples were resuspended in 0.1 M TPA, a hydroxyl radical trap (41), and measured on the EOS setup. The samples were measured in 1-mm path-length quartz cuvettes and stirred with a magnetic stir bar or recirculated in a flow-through cuvette.…”

Section: Methodsmentioning

confidence: 99%

Rate and mechanism of the photoreduction of birnessite (MnO ₂ ) nanosheets

Marafatto

Strader

Gonzalez-Holguera

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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The photoreductive dissolution of Mn(IV) oxide minerals in sunlit aquatic environments couples the Mn cycle to the oxidation of organic matter and fate of trace elements associated with Mn oxides, but the intrinsic rate and mechanism of mineral dissolution in the absence of organic electron donors is unknown. We investigated the photoreduction of δ-MnO 2 nanosheets at pH 6.5 with Na or Ca as the interlayer cation under 400-nm light irradiation and quantified the yield and timescales of Mn(III) production. Our study of transient intermediate states using time-resolved optical and X-ray absorption spectroscopy showed key roles for chemically distinct Mn(III) species. The reaction pathway involves (i) formation of Jahn-Teller distorted Mn(III) sites in the octahedral sheet within 0.6 ps of photoexcitation; (ii) Mn(III) migration into the interlayer within 600 ps; and (iii) increased nanosheet stacking. We propose that irreversible Mn reduction is coupled to hole-scavenging by surface water molecules or hydroxyl groups, with associated radical formation. This work demonstrates the importance of direct MnO 2 photoreduction in environmental processes and provides a framework to test new hypotheses regarding the role of organic molecules and metal species in photochemical reactions with Mn oxide phases. The timescales for the production and evolution of Mn(III) species and a catalytic role for interlayer Ca 2+ identified here from spectroscopic measurements can also guide the design of efficient Mn-based catalysts for water oxidation.manganese oxide | photoreduction | band-gap excitation | pump-probe spectroscopy | water oxidation M anganese is a key element in environmental processes, catalytic materials, and biological systems due to its rich redox chemistry and ability to form species with a high oxidizing potential. Photochemical processes can enhance significantly the cycling of Mn between the +4, +3, and +2 valence states (1-3). Photoreduction of Mn(IV) is the first step in the reductive dissolution of birnessite minerals in the euphotic zone of marine and lacustrine environments (4-6). This process couples the biogeochemical cycle of Mn to the redox cycling of carbon and trace metals associated with Mn oxide phases. In addition, the greater role of Mn(IV) photoreduction relative to microbial Mn(II) oxidation leads to the predominance of dissolved over particulate Mn in the photic zone of natural waters (1). Thermodynamic calculations predict that direct photoexcitation of Mn oxides in water by visible light will lead to net metal reduction over a wide range of environmentally relevant pH values (7). However, experimental evidence of direct photoexcitation of MnO 2 and subsequent photoreduction of Mn(IV) in the absence of organic electron donors is currently lacking. Experimental studies on the photochemical cycling of Mn have incorporated natural organic ligands that can enhance metal reduction via multiple pathways (5,8,9). These studies have identified aqueous Mn(II) as a reaction end product but have not inve...

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Section: Methodsmentioning

confidence: 99%

Rate and mechanism of the photoreduction of birnessite (MnO ₂ ) nanosheets

Marafatto

Strader

Gonzalez-Holguera

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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“…b) Terephtalic acid (TPA) (para-carboxy benzoate) was used as a hydroxyl radical specific fluorescent probe in control experiments without atria in the organ bath. Terephthalic acid (non-fluorescent) can be hydroxylated by hydroxyl radicals to yield a fluorescent product (monohydroxyterephthalate) (Barreto et al 1995), which can be determined quantitatively. TPA (10 mM) was dissolved in the normal buffer solution (pH 7.5) and constant currents of 5, 15 and 30 mA, respectively, were applied for periods of 75 s. The fluorescense was measured with a Shimadzu RF-5001 PC spectrofluorometer (excitation 312 nm, emission 426 nm).…”

Section: Methodsmentioning

confidence: 99%

The influence of oxidative stress on various inotropic responses in isolated rat left atria

Peters

Pfaffendorf

Zwieten

1997

Naunyn-Schmiedeberg's Arch Pharmacol

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The effects of free radicals, generated by electrolysis of a physiological salt solution, on various inotropic responses to drugs in isolated rat left atria were studied. Evidence for the generation of hydroxyl radicals was obtained from an appropriate fluorimetric assay. The amount of free radicals produced by electrolysis of the medium proved current-dependent. Exposure of isolated rat left atria to the medium which had been subjected to electrolysis caused a current-dependent decrease in contractile force. Oxidative stress, as a result of the electrolysis of the medium, caused altered inotropic responses to extra cellular Ca2+ (pD2 control group: 2.62 +/- 0.06 vs. 2.44 +/- 0.07 electrolysis group), sodium withdrawal (rise in contractile force control group: 1.73 +/- 0.19 mN vs. 0.48 +/- 0.21 mN electrolysis group) and lowering of stimulation frequency. The response to isoprenaline was diminished in atria subjected to oxidative stress and led to a rightward shift of the concentration response curves (pD2 control group: 7.56 +/- 0.10 vs. 6.77 +/- 0.11 electrolysis group). In addition, the inotropic responses to forskolin (pD2 control group: 6.17 +/- 0.12 vs. < 4.5 electrolysis group) and dibutyryl cAMP (rise in contractile force caused by 1 x 10(-5) M db-cAMP in control group: 2.15 +/- 0.01 mN vs. 1.21 +/- 0.10 mN electrolysis group) proved blunted as well. Measurement of the adenylyl cyclase activity revealed that free radicals attenuated the basal (by 11.1%) and forskolin stimulated (155.0 +/- 5.1 vs. 48.0 +/- 1.8 pmol cAMP/mg prot./min for control and electrolysis group respectively) activity of the adenylyl cyclase. DMSO, a well known hydroxyl radical scavenger, was able to abolish the free radical-induced decrease in the response to isoprenaline. Surprisingly, addition of alpha-adrenoceptor agonists to atria subjected to electrolysis-generated free radicals led to a rapid decrease in contractile force. DMSO was unable to counteract the negative intropic effect of methoxamine in atria subjected to oxidative stress. This negative inotropic response to alpha-adrenoceptor agonists in atria subjected to electrolysed medium is unlikely to be the direct result of phospholipase C or protein kinase C activation. Angiotensin II (which stimulates PLC, as well) did not reduce contractile force and chelerythrine (a PKC inhibitor) was unable to counteract the negative inotropic effect of the adrenoceptor agonists. In addition, the negative inotropic effect of methoxamine proved insensitive to 10(-6) M phentolamine and 10(-5) M doxazosin, which indicates an alpha-adrenoceptor independent mechanism. From this study we conclude that free radicals alter responses to various inotropic stimuli. These alterations may be the result of injured contractile elements, transporter molecules and molecules involved in signal transduction. Addition of alpha-adrenoceptor agonists after oxidative stress leads to a alpha-adrenoceptor. PLC and PKC independent decrease in contractile force.

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“…1). TPA has been used for the measurement of hydroxyl radicals by fluorometry (Fang et al, 1996;Mark et al, 1998;Barreto et al, 1995;Qu et al, 2000;Saran and Summer, 1999), however, there is no report on the HPLC separation-detection of HTPA to assay hydroxyl radicals.…”

Section: Introductionmentioning

confidence: 99%

An HPLC assay of hydroxyl radicals by the hydroxylation reaction of terephthalic acid

Li¹,

Abe²,

Nagasawa³

et al. 2004

Biomedical Chromatography

121

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An HPLC assay for hydroxyl radicals is described. The hydroxyl radical was trapped by terephthalic acid (non-fluorescent), and 2-hydroxyl terephthalic acid (fluorescent) was quantitated by HPLC-fluorescence detection. At a terephthalic acid concentration of 4.25 mmol/L, the hydroxyl radical formed in the Fenton reaction was successfully assayed in the concentration range of hydrogen peroxide of 2.5-50 micro mol/L, where the concentration of Fe(II) was 50 micro mol/L. The fluorescence of 2-hydroxy terephthalate was stable at 24 h, and its detection limit by this method was 5 nmol/L (100 fmol).

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Terephthalic acid: A dosimeter for the detection of hydroxyl radicals in vitro

Cited by 282 publications

References 11 publications

Rate and mechanism of the photoreduction of birnessite (MnO ₂ ) nanosheets

Rate and mechanism of the photoreduction of birnessite (MnO ₂ ) nanosheets

The influence of oxidative stress on various inotropic responses in isolated rat left atria

An HPLC assay of hydroxyl radicals by the hydroxylation reaction of terephthalic acid

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Terephthalic acid: A dosimeter for the detection of hydroxyl radicals in vitro

Cited by 282 publications

References 11 publications

Rate and mechanism of the photoreduction of birnessite (MnO 2 ) nanosheets

Rate and mechanism of the photoreduction of birnessite (MnO 2 ) nanosheets

The influence of oxidative stress on various inotropic responses in isolated rat left atria

An HPLC assay of hydroxyl radicals by the hydroxylation reaction of terephthalic acid

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Product

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Rate and mechanism of the photoreduction of birnessite (MnO ₂ ) nanosheets

Rate and mechanism of the photoreduction of birnessite (MnO ₂ ) nanosheets