Biomedical subjects

P Riesz

Publications and source records attributed to P Riesz.

At least 19 recordsLinked to original sources

PubMed2004

Enhanced ultrasound-induced apoptosis and cell lysis by a hypotonic medium.

PURPOSE: To test the hypothesis that non-lethal hypotonia will enhance ultrasound-induced cell killing in vitro and that the mechanism is mechanical in nature. MATERIALS AND METHODS: Hypotonic RPMI medium (146 mOsm) was used to induce non-lethal osmotic swelling of human myelomonocytic leukaemia U937 cells. Hypotonia for 10 min was started just before exposure to 1 MHz ultrasound at 0.5 or 1.0 Wcm(-2) for 10 min, or 5 min before exposure to 2.0 Wcm(-2) for 1 min. Surviving intact cells were then determined by the trypan blue dye exclusion test immediately after treatment. After 6-h incubation of the treated cells, early apoptosis and secondary necrosis were measured using a flow cytometer. Intracellular free calcium ion imaging by Fura-2 fluorescence and cellular ion scanning using a secondary ion mass spectrometer were also performed. RESULTS: Enhancement of ultrasound-induced cell lysis was observed at all intensities, and most prominently at 2.0 Wcm(-2), while apoptosis induction was significantly enhanced at intensities of 0.5 and 1.0 Wcm(-2), but not at 2.0 Wcm(-2). The enhanced cell lysis is attributed to the increased susceptibility of the cells to mechanical damage. This is consistent with previous reports describing the effects of mechanical stresses on cell membranes. Cellular ion scanning images also suggest that hypotonia has an effect on the membrane damage-and-repair mechanism of the cells. CONCLUSIONS: The results support the hypothesis that non-lethal hypotonia can enhance ultrasound-induced cell killing. These findings also suggest the 'sonomechanical' nature of the effects on the cells.

Apoptosis↗

PubMed2001

Sonochemistry of surfactants in aqueous solutions: an EPR spin-trapping study.

The surfactant properties of solutes play an important role in the sonochemistry and sonoluminescence of aqueous solutions. Recently, it has been shown, for relatively low molecular weight surfactants, that these effects can be correlated with the Gibbs surface excess of the solute. In the present study we investigate whether this correlation is valid for relatively high molecular weight surfactants and the mechanisms of surfactant decomposition during sonolysis. Sonolysis of argon-saturated aqueous solutions of nonvolatile surfactants [n-alkanesulfonates, n-alkyl sulfates, n-alkylammoniopropanesulfonates (APS), and poly(oxyethylenes) (POE)] was investigated by EPR and spin-trapping with 3,5-dibromo-4-nitrosobenzenesulfonate. Secondary carbon radicals (-.CH-), formed by abstraction reactions, were observed for all surfactants that were sonicated. The yield of primary carbon (-.CH(2)) and methyl (.CH(3)) radicals that are formed by pyrolysis is greatest for the zwitterionic (i.e., APS) and nonionic surfactants (i.e., POE). The yield of (-.CH-) radicals was measured following sonolysis of n-alkyl anionic surfactants [sodium pentanesulfonate (SPSo), sodium octanesulfonate (SOSo), sodium octyl sulfate (SOS), and sodium dodecyl sulfate (SDS)]. In the concentration range of 0-0.3 mM, the -.CH- radical yield increases in the order SDS approximately equal to SOS approximately equal to SOSo > SPSo. At higher concentrations, a plateau in the maximum (-.CH-) radical yield is reached for each surfactant, which follows the order SPSo > SOS approximately equal to SOSo > SDS; i.e., the radical scavenging efficiency increases with decreasing n-alkyl chain length. A similar trend was observed for the .CH(3) yield following sonolysis of a homologous series of n-alkyl APS surfactants. The results show that the Gibbs surface excess of certain nonvolatile surfactants does not correlate with the extent of decomposition following sonolysis in aqueous solutions. Instead, the decomposition of surfactants depends on their chemical structure and their ability to equilibrate between the bulk solution and the gas/solution interface of cavitation bubbles.

Alkanes↗

PubMed2001

Monomerization of photosensitizers by ultrasound irradiation in surfactant micellar solutions.

The absorption and fluorescence properties of pheophorbide-a, Sodium salt of pheophorbide-a and its long chain (C20H39) ester (Pheophytine) were investigated in air-saturated micellar aqueous solutions before and after ultrasound irradiation (48 kHz, 10 min). The absorption spectra changed depending on the surfactant; cetyltrimethyl ammonium bromide (CTAB) or sodium dodecyl sulfate concentrations. The formation of different molecular species in various micellar solutions was estimated from the analysis of the absorption spectra. The absorption bands resulted from an aggregated form of the chromophore present in 50 mM phosphate buffer and in pre-micellar solutions. The specific bands of the aggregate disappeared with a simultaneous increase of the bands of monomer in normal micellar solution. The fluorescence spectra, the lifetimes and the fraction of each component (with a characteristic lifetime) of the chromophore in the micellar solutions changed significantly before and after ultrasound irradiation although the changes in absorption spectra were small. The fluorescence emission band at 710 nm due to the aggregate almost disappeared in the pre-micellar solution after ultrasound irradiation. The fraction of the short-lifetime component estimated for the aggregates decreased 55% in H2O or 85% in 2 mM CTAB, however the long-lifetime components increased after the ultrasound treatment. From these fluorescence properties, it was concluded that the aggregated molecules were converted to a stable monomeric form by ultrasound. Extrapolation of these data to in vivo situations suggests that pretreatment of certain photosensitizers with ultrasound in micellar solutions may lead to increased efficiency of photodynamic therapy since only the monomers are photodynamically active.

Cetrimonium↗

PubMed2000

Evidence against singlet oxygen formation by sonolysis of aqueous oxygen-saturated solutions of Hematoporphyrin and rose bengal. The mechanism of sonodynamic therapy.

The possible role of singlet oxygen in the mechanism of sonodynamic therapy, the synergistic effect of ultrasound and certain sonosensitizers, was investigated. We used 4,4'-bis(1-p-carboxyphenyl-3- methyl-5-hydroxyl)-pyrazole (DRD 156), a sensitive new reagent which reacts specifically with singlet oxygen (1O2) but not with OH radicals, superoxide anion radicals or H2O2, to produce an EPR detectable signal. Sonolysis (48 kHz) of 90% D2O oxygen-saturated PBS solutions of Hematoporphyrin or Rose Bengal did not lead to the formation of detectable EPR signals of the semiquinone radical of DRD156. In contrast, the EPR signal of the semiquinone radical of DRD156 was observed during photoirradiation of Hematoporphyrin at 505 nm or of Rose Bengal at 544 nm. These results are inconsistent with a major role for singlet oxygen formation in the sonolysis of aqueous solutions of these compounds. An alternative mechanism for sonodynamic therapy involving peroxyl and alkoxyl radicals is discussed.

Electron Spin Resonance Spectroscopy↗

PubMed2000

Free radical intermediates in sonodynamic therapy.

Current understanding of the mechanism of sonodynamic action (i.e. the ultrasound-dependent enhancement of the cytotoxic action of certain drugs--sonosensitizers) with potential applications for cancer therapy is presented. The experimental evidence suggests that sonosensitization is due to the chemical activation of sonosensitizers inside or in the close vicinity of hot collapsing cavitation bubbles to form sensitizer-derived free radicals either by direct pyrolysis or due to reactions with .H and .OH radicals, formed by pyrolysis of water. These free radicals (mostly carbon-centered) react with oxygen to form peroxyl and alkoxyl radicals. Unlike .OH and .H, which are also formed by pyrolysis inside cavitation bubbles, the reactivity of alkoxyl and peroxyl radicals with organic components dissolved in biological media is lower and hence have higher probability of reaching critical cellular sites. Sonodynamic therapy appears to be a promising modality for cancer treatment since ultrasound can penetrate deep within the tissue and can be focused in a small region of tumor to chemically activate relatively non-toxic molecules (e.g. porphyrins) thus minimizing undesirable side effects.

Electron Spin Resonance Spectroscopy↗

PubMed1999

Effects of cysteamine and cystamine on the sonochemical accumulation of hydrogen peroxide--implications for their mechanisms of action in ultrasound-exposed cells.

Based on the observed cytoprotective effect of the intracellularly permeable radical scavenger cysteamine (+NH3CH2CH2SH) in cells exposed to ultrasound and the lack of protection by its oxidized cell-nonpermeable form, cystamine (+NH3CH2CH2S-SCH2CH2NH3+), it was suggested that inertial cavitation (the growth of small gas bubbles present in the liquid exposed to ultrasound and their subsequent violent collapse) and associated free radical production may occur intracellularly (Radiat. Res. 89:369; 1982). Here we demonstrate that high concentrations (> 10 mM) of the thiol cysteamine effectively lower H2O2 yields following ultrasound exposure in argon- and air-saturated phosphate buffered saline (PBS), while cystamine is less effective under argon and practically without effect in air-saturated PBS. Direct removal of H2O2 by cysteamine is the dominant mechanism while scavenging of the H2O2 precursors .OH and superoxide plays a lesser role. Since H2O2 is a known cytotoxic species capable of penetrating cells if produced extracellularly, these results offer an alternative hypothesis for the protective effect of cysteamine and the lack of protection by cystamine, based on their differential ability to lower ultrasound-dependent H2O2 yields, without the necessity of invoking intracellular cavitation.

Argon↗

PubMed1999

EPR characterization of free radical intermediates formed during ultrasound exposure of cell culture media.

Free radicals and/or hydrogen peroxide produced by exposure of cells to ultrasound are potentially cytotoxic and mutagenic. The formation and type of free radical species can be substantially modulated by the chemical composition of the media in which the ultrasound exposures of cells are carried out. In the current study, we examined the free radical intermediates formed during ultrasound exposure of a typical cell culture medium (RPMI-1640); the dominant free radicals that were identified by spin trapping were derived from the hydrophobic amino acids Trp, Leu, and Phe, and were formed by hydrogen abstraction from these amino acids. Compared to exposures in phosphate-buffered saline, the yield of *OH radicals and H2O2 was significantly reduced in the cell culture medium, glucose (the main organic component in the medium), and the hydrophobic amino acids (Trp, Phe, Tyr, Leu, Val, Met) being chiefly responsible for this effect. In contrast, other nonhydrophobic amino acids did not contribute significantly to the *OH or H2O2 decrease. These findings are consistent with the accumulation of hydrophobic solutes at the liquid-gas interface of the collapsing cavitation bubbles resulting in increased efficiency of radical scavenging.

Amino Acids↗

PubMed1998

Effect of gas-containing microspheres and echo contrast agents on free radical formation by ultrasound.

Stabilized microbubbles (microspheres) are widely used to enhance the contrast of ultrasound imaging. Our data provide direct evidence that the contrast agents, Levovist, PVC-AN (polyvinylidene chloride-acrylonitryl copolymer), and Albunex (compared to 5% human albumin), at concentrations comparable to those used for ultrasound imaging, enhance H2O2 production (through the superoxide-dependent pathway) in air-saturated aqueous solutions exposed to 47 kHz ultrasound above the cavitation threshold. These agents also act as scavengers of .H atoms and .OH radicals, thus lowering H2O2 formation (by recombination of .OH radicals) in argon-saturated solutions. EPR spin trapping also reveals that secondary radicals derived from the contrast agents are produced by reactions with .H and .OH which are formed by pyrolysis of water inside cavitation bubbles. In addition, the contrast agents themselves undergo pyrolysis reactions in the cavitation bubbles as demonstrated by formation of methyl radicals. Possible deleterious consequences of the formation of sonochemical intermediates may have to be assessed, particularly since some of the echo contrast agents have been shown to lower the cavitation threshold of diagnostic ultrasound. Unlike the microspheres formed from organic molecules, inorganic microspheres, Eccospheres, because of their stability and inert nature with respect to participation in free radical processes, appear to be suitable tools for enhancing the yields of aqueous sonochemical reactions.

Acrylic Resins↗

PubMed1997

Nitric oxide formation from hydroxylamine by myoglobin and hydrogen peroxide.

Hydroxylamine (HA), which is a natural product of mammalian cells, has been shown to possess vasodilatory properties in several model systems. In this study, HA and methyl-substituted hydroxylamines, N-methylhydroxylamine (NMHA) and N,N-dimethylhydroxylamine (NDMHA), have been tested for their ability to generate free diffusible nitric oxide (NO) in the presence of myoglobin (Mb) and hydrogen peroxide. A NO-specific conversion of 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (carboxy-PTIO) to 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl (carboxy-PTI), measured by electron spin resonance (ESR) spectroscopy, along with nitrite and nitrate production, was observed for HA but not for NMHA and NDMHA. ESR measurements at 77 K showed the formation of the ferrous nitrosyl myoglobin, Mb-NO, in the reaction mixtures containing Mb, H2O2 and HA. Our data also demonstrate that Mb-NO is an end product of the reaction pathway involving Mb, H2O2 and HA, rather than a reaction intermediate in the formation of NO. In summary, our results demonstrate a possible pathway of NO formation from HA, however, the significance of this mechanism for bioactivation of HA in vivo is unknown at the present time.

Animals↗

PubMed1997

Inhibition of rat and human cytochrome P4502E1 catalytic activity and reactive oxygen radical formation by nitric oxide.

Nitric oxide (NO) reacts with heme-containing enzymes, including certain isoforms of cytochrome P450. Cytochrome P4502E1 (CYP2E1) is induced by ethanol and plays an important role in the toxicity of ethanol and other hepatotoxins. CYP2E1 is also very effective in generating reactive oxygen intermediates such as superoxide radical and H2O2, oxidizing ethanol to the 1-hydroxyethyl radical, and has a high NADPH oxidase activity. The effect of NO on CYP2E1 catalytic activity and generation of reactive oxygen intermediates was evaluated. Incubating liver microsomes isolated from rats treated with pyrazole to induce high levels of CYP2E1, with gaseous NO or NO released from a variety of NO donors such as SNAP, DEA/NO, spermine/NO, and GSNO, resulted in a loss of CYP2E1 catalytic activity with specific substrates such as p-nitrophenol or dimethylnitrosamine. Trapping of NO with hemoglobin resulted in protection of CYP2E1 activity against the inactivation by NO. There was no effect by analogues of the donors which do not release NO nor was there any effect by NO on NADPH-cytochrome P450 reductase activity. Inactivation of CYP2E1 by NO was not prevented by superoxide dismutase or catalase, suggesting that superoxide, H2O2, or peroxynitrite were not responsible for the actions of NO. The inactivated CYP2E1 was not degraded nor did it lose its epitope sites as shown by Western blot analysis. Associated with loss of CYP2E1 catalytic activity was a decrease in the formation of superoxide radical and H2O2, in microsomal lipid peroxidation catalyzed by low, but not high concentration of iron, and in consumption of NADPH. Oxidation of ethanol to the 1-hydroxyethyl radical was also inhibited by NO. ESR experiments indicated the formation of stable heme-NO complexes with CYP2E1. NO appears to compete with O2 and CO for binding to CYP2E1 as incubation with gaseous NO, or NO donors inhibited formation of the characteristic CO binding spectrum of P450. Microsomes isolated from a stably transfected HepG2 cell line expressing only CYP2E1 were also inactivated by NO, validating interaction of NO with this isoform of P450. These results indicate that NO inhibits CYP2E1 catalytic activity and generation of reactive radical intermediates. NO may prevent toxicity of agents which require bioactivation by P450 isoforms such as CYP2E1 and in generation of reactive intermediates by CYP2E1.

Animals↗

PubMed1997

Sonodynamic toxicity of gallium-porphyrin analogue ATX-70 in human leukemia cells.

Low concentrations (> or = 1 microM) of the gallium-porphyrin analogue ATX-70 significantly enhanced cellular toxicity in human leukemia HL-525 cells exposed to 50 kHz ultrasound. The mechanism of this ATX-70-dependent sonosensitization is unknown, but we have established the requirement of extracellular localization of ATX-70 molecules for sonosensitization. Short-lived toxic intermediates produced from ATX-70 by ultrasound are implicated in the mechanism, since no cytotoxicity was found when medium containing ATX-70 was sonicated and subsequently added to the cells. However, we were unable to demonstrate the existence of radical intermediates by EPR spin trapping with the nitroso spin trap, DBNBS, and ATX-70-dependent sonotoxicity could not be ameliorated by the addition of up to 70 mM POBN and DMPO spin traps during ultrasound exposure.

Cell Death↗

PubMed1996

Peroxyl radical formation in aqueous solutions of N,N-dimethylformamide, N-methylformamide, and dimethylsulfoxide by ultrasound: implications for sonosensitized cell killing.

Sonodynamic therapy, which refers to a synergistic effect of drugs and ultrasound, is a promising new modality for cancer treatment. The sonodynamic effect was found for a number of structurally unrelated compounds, and the underlying mechanisms are still unknown. Recently, Jeffers et al. (J. Acoust. Soc. Am. 97:669-676; 1995) have shown that the sonodynamic action of nontoxic concentrations of N,N-dimethylformamide (DMF), N-methyl formamide (MMF), and dimethylsulfoxide (DMSO) combined with ultrasound, on killing of cultured HL-60 human promyelocytic leukemia cells, and attributed this toxic effect to unknown short lived reactive species produced from these solutes by ultrasonic cavitation. Using the spin trap 3,5-dibromo-4-nitrosobenzene sulfonate (DBNBS) in nitrogen-saturated aqueous solutions of DMF, MMF, or DMSO exposed to 50 kHz ultrasound, we detected formation of .CH3 and .CH2N(CH3)CHO radical adducts for DMF, mostly .CH2NHCHO adducts for MMF, and .CH3 adducts for DMSO. These radicals were formed either by reactions of the solutes with ultrasound-generated .H and .OH radicals (such as .CH2R-type radicals in DMF and MMF, and .CH3 radicals in DMSO), or by direct pyrolysis of the weak bonds in the solute molecules (e.g., .CH3 radicals from DMF). In air-saturated sonicated solutions these carbon centered radicals were converted to the corresponding peroxyl radicals and spin trapped with 5,5-dimethyl-1-pyrroline-N-oxide (DMPO); .OOCH2N(CH3)CHO radicals were identified in DMF, .OOCH2NHCHO radicals in MMF, and .OOCH3 radicals in DMSO solutions. We suggest that these radical species by virtue of their longer lifetimes and higher selectivity, compared to .OH radicals, which are also formed in sonicated solutions, are the species responsible for sonodynamic cell killing by the combined effect of ultrasound with DMF, MMF, or DMSO.

Benzenesulfonates↗

PubMed1996

Sonolysis of ubiquinone in aqueous solutions. An EPR spin-trapping study.

Free radical formation in aqueous solutions of ubiquinone (coenzyme Qo) induced by ultrasound was studied by EPR and spin trapping with 3,5-dibromo-4-nitrosobenzene sulphonate. When aqueous solutions of ubiquinone were sonicated with 50-kHz ultrasound in the presence of argon or nitrogen, radicals formed by addition of.OH or.H to the double bonds of the ubiquinone ring and methyl radicals were observed as the major spin adducts. The methyl radicals were formed by pyrolysis of ubiquinone. These radicals led to the degradation of ubiquinone. The reduced from of ubiquinone, ubiquinol, was formed by sonication in the presence of argon, and its formation was prevented by addition of native but not of denatured superoxide dismutase. Sodium formate, which scavenges .OH to form CO2-., enhanced ubiquinol formation but partially inhibited the degradation of the ubiquinone ring. No ubiquinol was formed in nitrogen- or oxygen-saturated solutions under our conditions. These results indicate that ubiquinol was formed by reduction of ubiquinone by O2-., which was generated by the sonolysis of argon-saturated water.

Benzenesulfonates↗

PubMed1996

EPR spin trapping study of the decomposition of azo compounds in aqueous solutions by ultrasound: potential for use as sonodynamic sensitizers for cell killing.

Sonodynamic therapy, a promising new approach to cancer treatment, is based on synergistic cell killing by combination of certain drugs (sonosensitizers) and ultrasound. Although the mechanism of sonodynamic action is not understood, the role of free radicals produced from sonosensitizers by ultrasound is implicated. In this work, we studied formation of free radicals during the decomposition of several water-soluble azo compounds by 50 kHz ultrasound in aqueous solutions. Using the spin trap 3,5-dibromo-4-nitrosobenzene sulfonate (DBNBS) tertiary carbon-centered radicals from 2,2'-azobis (N,N'-dimethyleneisobutyramidine) dihydrochloride (VA-044), 2-(carbamoylazo)-isobutyronitrile (V-30), and 2,2'-azobis (2-amidinopropane) dihydrochloride (AAPH) and .CH3 radicals from 1,1'-azobis (N,N'-dimethylformamide) (ADMF) were detected in argon-saturated solutions and the corresponding oxygen-centered radicals (alkoxyl and peroxyl) from VA-044, V-30, and AAPH were identified using the spin trap 5,5'-dimethyl-1-pyrroline-N-oxide (DMPO) in aerated sonicated solutions. No free radicals from 4,4'-dihydroxyazobenzene-3,3'-dicarboxylic acid, disodium salt (DHAB) could be found in either system. While VA-044 and AAPH could also be readily decomposed by heat (42.5 degrees C and 80 degrees C), V-30 decomposition only occurred in the ultrasound-exposed solutions. The most likely mechanism of decomposition of azo compounds by ultrasound is their thermolysis in the heated shell of the liquid surrounding cavitating bubbles driven by ultrasound and/or by pyrolysis inside these bubbles. Experiments using scavengers of .OH and .H, which are produced by sonolysis in aqueous solutions, demonstrated that these radicals are not involved in the ultrasound-mediated radical production from the azo compounds. Due to the known cytotoxic potential of free radicals produced from azo compounds, the use of these compounds as ultrasound sensitizers appears to be a promising approach for sonodynamic cell killing.

Azo Compounds↗

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↗

PubMed1993

Photosensitized formation of ascorbate radicals by riboflavin: an ESR study.

The riboflavin-sensitized photooxidation of ascorbate ion (HA-) to ascorbate radical (A.-) was followed by electron spin resonance (ESR) spectroscopy in conjunction with oxygen depletion measurements. In air-saturated aqueous media, steady-state amounts of A.- are rapidly established upon irradiation. The ESR signal disappears within a few seconds after the light is extinguished--more slowly under constant irradiation as oxygen is depleted. No photooxidation was observed in deaerated media. Similar results were obtained with other flavins and when ascorbyl palmitate was substituted for HA-. The effect of added superoxide dismutase, catalase, desferrioxamine, and singlet oxygen scavengers (NaN3 and tryptophan) was studied, as was replacement of water by D2O and saturation with O2. The results are indicative of ascorbate free radical production via direct reaction between ascorbate ion and triplet riboflavin in the presence of O2. While the presence of superoxide ion tends to reduce the steady-state concentration of A.-, competition from the reaction of HA- with singlet oxygen is less apparent in this system (at HA- > or = 1 mM) than in the previously studied aluminum phthalocyanine tetrasulfonate-photosensitized reaction.

Ascorbic Acid↗

PubMed1993

Sonochemistry of acetone and acetonitrile in aqueous solutions. A spin trapping study.

The 50 kHz sonolysis of argon-saturated water-acetone and water-acetonitrile mixtures was studied by EPR and spin trapping with 3,5-dibromo-4-nitrosobenzenesulfonate over a wide range of solvent composition. For both systems a single maximum was observed for the spin adduct yield of methyl radicals and of the radicals formed by H-abstraction from acetone and acetonitrile. These results combined with previous studies of water-methanol and water-ethanol mixtures indicate that the greater the vapor pressure of the volatile organic component, the lower the concentration of organic solute at which the maximum radical yield occurs. Methyl radicals from acetone are formed by C-C bond scission in the collapsing argon bubbles. For acetonitrile, C-H bond scission at high temperature is followed by H-addition to the triple bond and the decomposition of this intermediate radical to form methyl radicals. Since Anbar has shown (Science 161, 1343, 1961) that sonoluminescence and acoustic cavitation occur during the impact of liquid water on water with linear velocities similar to those of collapsing ocean waves, the sonochemistry of nitriles is of interest to chemical evolution studies.

Acetone↗

PubMed1992

Photosensitized formation of ascorbate radicals by chloroaluminum phthalocyanine tetrasulfonate: an electron spin resonance study.

The chloroaluminum phthalocyanine tetrasulfonate sensitized photooxidation of ascorbic acid to ascorbate radical (A.-) was followed by electron spin resonance (ESR) spectroscopy. In air saturated aqueous media, steady-state amounts of A.- are rapidly established upon irradiation. The ESR signal disappears within a few seconds after the light is extinguished--more slowly under constant irradiation as oxygen is depleted. No photooxidation was observed in deaerated media. The effect of added superoxide dismutase, catalase, desferrioxamine, and singlet oxygen scavengers (NaN3 and tryptophan) was studied, as was replacement of water by D2O and saturation with O2. The results are indicative of free radical production by direct reaction between ascorbate ion and sensitized phthalocyanine (a Type I mechanism) in competition with the (Type II) reaction of HA- with singlet oxygen, a reaction which does not produce ascorbate radical intermediates.

Ascorbic Acid↗