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1.
Int J Mol Sci ; 21(19)2020 Sep 27.
Artigo em Inglês | MEDLINE | ID: mdl-32992497

RESUMO

We report the generation of gold nanoparticles (AuNPs) from the aqueous solution of chloro(2,2',2″-terpyridine)gold(III) ion ([Au(tpy)Cl]2+) through X-ray radiolysis and optical excitation at a synchrotron. The original purpose of the experiment was to investigate the photoinduced structural changes of [Au(tpy)Cl]2+ upon 400 nm excitation using time-resolved X-ray liquidography (TRXL). Initially, the TRXL data did not show any signal that would suggest structural changes of the solute molecule, but after an induction time, the TRXL data started to show sharp peaks and valleys. In the early phase, AuNPs with two types of morphology, dendrites, and spheres, were formed by the reducing action of hydrated electrons generated by the X-ray radiolysis of water, thereby allowing the detection of TRXL data due to the laser-induced lattice expansion and relaxation of AuNPs. Along with the lattice expansion, the dendritic and spherical AuNPs were transformed into smaller, raspberry-shaped AuNPs of a relatively uniform size via ablation by the optical femtosecond laser pulse used for the TRXL experiment. Density functional theory calculations confirm that the reduction potential of the metal complex relative to the hydration potential of X-ray-generated electrons determines the facile AuNP formation observed for [Au(tpy)Cl]2+.


Assuntos
Ouro/química , Nanopartículas Metálicas/química , Soluções/química , Água/química , Difração de Raios X/métodos , Elétrons , Compostos de Ouro/química , Terapia a Laser/métodos , Lasers , Tamanho da Partícula , Radiólise de Impulso/métodos , Síncrotrons , Raios X
2.
Free Radic Res ; 53(9-10): 1005-1013, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31514547

RESUMO

Pulse radiolysis was conducted to investigate: several fundamental reactions of a natural flavonoid, rutin, and its glycosylated form (αG-rutin) as a basis for their radiation protection properties; the reactions with •OH (radical scavenging) and dGMP radical, dGMP• (chemical repair), which was used as a model of initial and not yet stabilised damage on DNA. Three absorption peaks were commonly seen in the reactions of the flavonoids with •OH, showing that their reactive site is the common structure, i.e. aglycone. One among the three peaks was attributed to the flavonoid radical produced as a result of the removal of a hydrogen atom. The same peak was found in their reactions with dGMP•, showing that dGMP• is chemically repaired by obtaining a hydrogen atom supplied from the flavonoids. Such a spectral change due to the chemical repair was as clear as never reported. The rate constants of the chemical repair reaction were estimated as (9 ± 2)×108 M-1 s-1 and (6 ± 1)×108 M-1 s-1 for rutin and αG-rutin, respectively. The rate constants of the radical scavenging reactions towards •OH were estimated as (1.3 ± 0.3)×1010 M-1 s-1 and (1.0 ± 0.1)×1010 M-1 s-1 for rutin and αG-rutin, respectively. In addition, there was no obvious difference between rutin and αG-rutin, indicating that the glycosylation does not change early chemical reactions of rutin.


Assuntos
Radiólise de Impulso/métodos , Proteção Radiológica/métodos , Rutina/química , Flavonoides
3.
Chem Rev ; 119(6): 4413-4462, 2019 03 27.
Artigo em Inglês | MEDLINE | ID: mdl-30741537

RESUMO

Pulse radiolysis is a powerful method for generating highly reduced or oxidized species and free radicals. Combined with fast time-resolved spectroscopic measurement, we can monitor the reactions of intermediate species on time scales ranging from picoseconds to seconds. The application of pulse radiolysis to water generates hydrated electrons (eaq-) and specific radicals, rendering this technique useful for investigating a number of biological redox processes. The first pulse radiolysis redox investigations explored in this review involved intramolecular electron transfer processes in protein with multiple electron-accepting sites. Pulse radiolysis enabled direct monitoring of the internal electron transfer rates and the distribution of electrons within proteins. Structural information from X-ray data has allowed analysis of the rate constants and their activation parameters in relation to the mechanisms with current theoretical treatments. The second set of pulse radiolysis redox investigations explored here concerned the intermediates of enzyme reactions after redox reactions. Pulse radiolysis allowed the extremely rapid donation of electrons to a redox center in a protein. It makes it possible to observe the unstable intermediates after the reduction and the following subsequent steps. For example, the intermediates generated through the one-electron reduction of oxygenated hemoproteins, such as cytochrome P450 and nitric oxide synthase, were characterized. Interestingly, ligand exchange can occur upon the reduction of heme iron, in which different amino acid residues bind to heme in the ferrous and ferric states, respectively. We directly observed the ligand-switching intermediates of bacterial CooA, a CO sensor, and bacterial iron response regulator protein. These ligand exchange processes are physiologically important for regulating the electrode potential and effective formation of superoxide anion or HO•. The third set of pulse radiolysis redox investigations explored in this review concerns free-radical processes in biological systems. Free radicals are produced in cells and organisms in a variety of processes. The cell has developed special and very effective machinery for controlling and detoxifying reactive radicals. Radiation-generated radicals allow studies of the reactions between specific radicals and solutes, often revealing the mechanisms underlying the initial and subsequent reactions. The crucial contribution was made using pulse radiolysis techniques and knowledge of the identities, properties, and reactions of radicals. These radicals include superoxide (O2•-), nitric monoxide (NO•), ascorbate, urate, and protein radicals. This review focuses on the reactions of these radicals and their physiological functions.


Assuntos
Radicais Livres/química , Proteínas/química , Transporte de Elétrons , Flavoproteínas Transferidoras de Elétrons/química , Radical Hidroxila/química , Modelos Químicos , Modelos Moleculares , Oxirredução , Radiólise de Impulso/métodos , Água/química
4.
Chemistry ; 22(34): 12189-98, 2016 Aug 16.
Artigo em Inglês | MEDLINE | ID: mdl-27405246

RESUMO

Understanding electron-transfer processes is crucial for developing organoselenium compounds as antioxidants and anti-inflammatory agents. To find new redox-active selenium antioxidants, we have investigated one-electron-transfer reactions between hydroxyl ((.) OH) radical and three bis(alkanol)selenides (SeROH) of varying alkyl chain length, using nanosecond pulse radiolysis. (.) OH radical reacts with SeROH to form radical adduct, which is converted primarily into a dimer radical cation (>Se∴Se<)(+) and α-{bis(hydroxyl alkyl)}-selenomethine radical along with a minor quantity of an intramolecularly stabilized radical cation. Some of these radicals have been subsequently converted to their corresponding selenoxide, and formaldehyde. Estimated yield of these products showed alkyl chain length dependency and correlated well with their antioxidant ability. Quantum chemical calculations suggested that compounds that formed more stable (>Se∴Se<)(+) , produced higher selenoxide and lower formaldehyde. Comparing these results with those for sulfur analogues confirmed for the first time the distinctive role of selenium in making such compounds better antioxidants.


Assuntos
Álcoois/química , Antioxidantes/química , Cátions/química , Radical Hidroxila/química , Compostos Organosselênicos/química , Radiólise de Impulso/métodos , Enxofre/química , Transporte de Elétrons , Elétrons
5.
In Vivo ; 30(2): 119-21, 2016.
Artigo em Inglês | MEDLINE | ID: mdl-26912822

RESUMO

Cancer therapy by means of high-energy ions is very efficient. As a consequence of the linear-energy-transfer effect only a negligible part of the produced free radicals can escape combination processes to form molecular products and to cause undesired side processes. Positrons (e⁺) and γ-rays, generated by the nuclear interaction of high-energy ions in the medium, serve in monitoring the radiation dose absorbed by the tumor. However, due to the dipole nature of water molecules a small proportion of thermalized positrons (e⁺th) can become solvated (e⁺aq). Hence, they are stabilized, live longer and can initiate side reactions. In addition, positronium (Ps), besides solvated electrons (e⁺aq), can be generated and involved in the reaction mechanisms. For a better understanding of the reaction mechanisms involved and to improve cancer therapy, a time-resolved pulse radiolysis instrument using high-energy particles is discussed here. The proposed method is examined and recommended by CERN experts. It is planned to be realized at the MedAustron Radiation Therapy and Research Centre in Wiener Neustadt, Austria.


Assuntos
Elétrons , Raios gama , Íons/uso terapêutico , Neoplasias/radioterapia , Radiólise de Impulso/métodos , Humanos , Radiólise de Impulso/instrumentação
6.
Molecules ; 19(11): 19152-71, 2014 Nov 19.
Artigo em Inglês | MEDLINE | ID: mdl-25415477

RESUMO

The kinetics and spectral characteristics of the transients formed in the reactions of •OH and •N3 with quinoxalin-2(1H)-one (Q), its methyl derivative, 3-methylquinoxalin-2(1H)-one (3-MeQ) and pyrazin-2-one (Pyr) were studied by pulse radiolysis in aqueous solutions at pH 7. The transient absorption spectra recorded in the reactions of •OH with Q and 3-MeQ consisted of an absorption band with λmax = 470 nm assigned to the OH-adducts on the benzene ring, and a second band with λmax = 390 nm (for Q) and 370 nm (for 3-MeQ) assigned, inter alia, to the N-centered radicals on a pyrazin-2-one ring. The rate constants of the reactions of •OH with Q and 3-MeQ were found to be in the interval (5.9-9.7) × 109 M-1·s-1 and were assigned to their addition to benzene and pyrazin-2-one rings and H-abstraction from the pyrazin-2-one nitrogen. In turn, the transient absorption spectrum observed in the reaction of •N3 exhibits an absorption band with λmax = 350 nm. This absorption was assigned to the N-centered radical on the Pyr ring formed after deprotonation of the respective radical cation resulting from one-electron oxidation of 3-MeQ. The rate constant of the reaction of •N3 with 3 MeQ was found to be (6.0 ± 0.5) × 109 M-1·s-1. Oxidation of 3-MeQ by •N3 and Pyr by •OH and •N3 confirms earlier spectral assignments. With the rate constant of the •OH radical with Pyr (k = 9.2 ± 0.2) × 109 M-1·s‒1, a primary distribution of the •OH attack was estimated nearly equal between benzene and pyrazin-2-one rings.


Assuntos
Radicais Livres/química , Quinoxalinas/química , Benzeno/química , Elétrons , Concentração de Íons de Hidrogênio , Radical Hidroxila/química , Cinética , Nitrogênio/química , Oxirredução , Radiólise de Impulso/métodos
7.
Free Radic Res ; 48(11): 1300-10, 2014 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-25156684

RESUMO

Hypotaurine and cysteine sulfinic acid are known to be readily oxidized to the respective sulfonates, taurine and cysteic acid, by several oxidative agents that may be present in biological systems. In this work, the relevance of both the carbonate anion and nitrogen dioxide radicals in the oxidation of hypotaurine and cysteine sulfinic acid has been explored by the peroxidase activity of Cu,Zn superoxide dismutase (SOD) and by pulse radiolysis. The extent of sulfinate oxidation induced by the system SOD/H2O2 in the presence of bicarbonate (CO3(•-) generation), or nitrite ((•)NO2 generation) has been evaluated. Hypotaurine is efficiently oxidized by the carbonate radical anion generated by the peroxidase activity of Cu,Zn SOD. Pulse radiolysis studies have shown that the carbonate radical anion reacts with hypotaurine more rapidly (k = 1.1 × 10(9) M(-1)s(-1)) than nitrogen dioxide (k = 1.6 × 10(7) M(-1)s(-1)). Regarding cysteine sulfinic acid, it is less reactive with the carbonate radical anion (k = 5.5 × 10(7) M(-1)s(-1)) than hypotaurine. It has also been observed that the one-electron transfer oxidation of both sulfinates by the radicals is accompanied by the generation of transient sulfonyl radicals (RSO2(•)). Considering that the carbonate radical anion could be formed in vivo at high level from bicarbonate, this radical can be included in the oxidants capable of performing the last metabolic step of taurine biosynthesis. Moreover, the protective effect exerted by hypotaurine and cysteine sulfinate on the carbonate radical anion-mediated tyrosine dimerization indicates that both sulfinates have scavenging activity towards the carbonate radical anion. However, the formation of transient reactive intermediates during sulfinate oxidation by carbonate anion and nitrogen dioxide radical may at the same time promote oxidative reactions.


Assuntos
Carbonatos/química , Cisteína/análogos & derivados , Radicais Livres/química , Dióxido de Nitrogênio/química , Radiólise de Impulso/métodos , Superóxido Dismutase/metabolismo , Taurina/análogos & derivados , Animais , Bovinos , Cromatografia Líquida de Alta Pressão , Cisteína/química , Espectroscopia de Ressonância de Spin Eletrônica , Eritrócitos/enzimologia , Peróxido de Hidrogênio/metabolismo , Oxidantes/metabolismo , Oxirredução , Peroxidases/metabolismo , Taurina/química , Tirosina/química
8.
Analyst ; 139(7): 1707-12, 2014 Apr 07.
Artigo em Inglês | MEDLINE | ID: mdl-24555180

RESUMO

Resazurin (RNO) reduction by hydrated electrons produces a fluorescent molecule: resorufin (RN). To take advantage of RN fluorescence, a novel setup is designed by implementing fluorescence detection induced by laser in a pulse radiolysis experiment. Time resolved fluorescence spectra were recorded with a fast gated intensified CCD camera during the reduction of RNO from µs to ms. Two 532 nm laser types have been used to describe the short µs range by a 5 ns Q-switch laser and the µs-ms range by a CW DPSS laser. By fitting the simulated model to the experimental data a second order rate constant of 10(9) M(-1) s(-1) was re-evaluated. This method should be considered in the near future in many in situ and real time measurements for evaluating radical production.


Assuntos
Lasers , Oxazinas/análise , Radiólise de Impulso/métodos , Espectrometria de Fluorescência/métodos , Xantenos/análise , Elétrons , Radicais Livres/química , Oxazinas/química , Oxirredução , Radiólise de Impulso/instrumentação , Espectrometria de Fluorescência/instrumentação , Xantenos/química
9.
Free Radic Res ; 47(12): 1046-53, 2013 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-24074186

RESUMO

The reaction of hydroxyl radicals ((•)OH) with Aß1-16 peptide was carried out using pulse radiolysis to understand the effect of oxidation of peptide on its copper-binding properties. This reaction produced oxidized, dimeric and trimeric Aß1-16 peptide species. The formation of these products was established with the help of fluorescence spectroscopy and mass spectrometry. The mass spectral data indicate that the major site of oxidation is at His6, while the site for dimerization is at Tyr10. Diethyl pyrocarbonate-treated Aß1-16 peptide did not produce any trimeric species upon oxidation with (•)OH. The quantitative chemical modification studies indicated that one of the three histidine residues is covalently modified during pulse radiolysis. The copper-binding studies of the oxidized peptide revealed that it has similar copper-binding properties as the unoxidized peptide. Further, the cytotoxicity studies point out that both oxidized and unoxidized Aß1-16 peptide are equally efficient in producing free radicals in presence of copper and ascorbate that resulted in comparable cell death.


Assuntos
Peptídeos beta-Amiloides/química , Cobre/química , Fragmentos de Peptídeos/química , Sequência de Aminoácidos , Peptídeos beta-Amiloides/metabolismo , Peptídeos beta-Amiloides/toxicidade , Linhagem Celular Tumoral , Cobre/metabolismo , Humanos , Radical Hidroxila/química , Radical Hidroxila/metabolismo , Dados de Sequência Molecular , Oxirredução , Fragmentos de Peptídeos/metabolismo , Fragmentos de Peptídeos/toxicidade , Radiólise de Impulso/métodos , Espectrometria de Fluorescência , Espectrometria de Massas por Ionização e Dessorção a Laser Assistida por Matriz
10.
J Phys Chem A ; 117(42): 10801-10, 2013 Oct 24.
Artigo em Inglês | MEDLINE | ID: mdl-24070331

RESUMO

The diethyl carbonate, DEC, is an ester that is used as a solvent in Li-ion batteries, but its behavior under ionizing radiation was unknown. The transient optical absorption spectra, the decay kinetics, and the influence of various scavengers have been studied by using the picosecond laser-triggered electron accelerator ELYSE. In neat DEC, the intense near-IR (NIR) absorption spectrum is assigned to the solvated electron. It is overlapped in the visible range by another transient but longer-lived and less intense band that is assigned to the oxidized radical DEC(-H). The solvated electron molar absorption coefficients and radiolytic yield evolution from 25 ps, the geminate recombination kinetics, and the rate constants of electron transfer reactions to scavengers are determined. The radiolytic mechanism, indicating a certain radioresistance of DEC, is compared with that for other solvents.


Assuntos
Dietil Pirocarbonato/análogos & derivados , Radiólise de Impulso/métodos , Dietil Pirocarbonato/química , Cinética , Espectroscopia de Luz Próxima ao Infravermelho
11.
J Proteomics ; 92: 51-62, 2013 Oct 30.
Artigo em Inglês | MEDLINE | ID: mdl-23454334

RESUMO

The method of radiolysis is based upon the interaction of ionising radiation with the solvent (water). One can form the same free radicals as in conditions of oxidative stress ((•)OH, O2(•)(-), NO2(•)…). Moreover, the quantity of reactive oxygen (ROS) or nitrogen (RNS) species formed in the irradiated medium can be calculated knowing the dose and the radiation chemical yield, G, thus this method is quantitative. The use of the method of radiolysis has provided a wealth of data, especially about the kinetics of the oxidation by various free radicals and their mechanisms, the identification of transients formed, their lifetimes and the possibility to repair them by the so-called antioxidants. In this review we have collected the most recent data about protein oxidation that might be useful to a proteomic approach. This article is part of a Special Issue entitled: Posttranslational Protein modifications in biology and Medicine.


Assuntos
Processamento de Proteína Pós-Traducional , Proteômica/métodos , Radiólise de Impulso/métodos , Espécies Reativas de Nitrogênio/metabolismo , Espécies Reativas de Oxigênio/metabolismo , Animais , Humanos , Oxirredução
12.
Eur Biophys J ; 40(8): 947-57, 2011 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-21594746

RESUMO

The initial effect of nanosecond pulsed electric fields (nsPEFs) on cells is a change of charge distributions along membranes. This first response is observed as a sudden shift in the plasma transmembrane potential that is faster than can be attributed to any physiological event. These immediate, yet transient, effects are only measurable if the diagnostic is faster than the exposure, i.e., on a nanosecond time scale. In this study, we monitored changes in the plasma transmembrane potential of Jurkat cells exposed to nsPEFs of 60 ns and amplitudes from 5 to 90 kV/cm with a temporal resolution of 5 ns by means of the fast voltage-sensitive dye Annine-6. The measurements suggest the contribution of both dipole effects and asymmetric conduction currents across opposite sides of the cell to the charging. With the application of higher field strengths the membrane charges until a threshold voltage value of 1.4-1.6 V is attained at the anodic pole. This indicates when the ion exchange rates exceed charging currents, thus providing strong evidence for pore formation. Prior to reaching this threshold, the time for the charging of the membrane by conductive currents is qualitatively in agreement with accepted models of membrane charging, which predict longer charging times for lower field strengths. The comparison of the data with previous studies suggests that the sub-physiological induced ionic imbalances may trigger other intracellular signaling events leading to dramatic outcomes, such as apoptosis.


Assuntos
Membrana Celular/efeitos da radiação , Campos Eletromagnéticos , Células Jurkat/efeitos da radiação , Potenciais da Membrana/efeitos da radiação , Radiólise de Impulso/métodos , Imagens com Corantes Sensíveis à Voltagem/métodos , Técnicas de Cultura de Células , Relação Dose-Resposta à Radiação , Condutividade Elétrica , Corantes Fluorescentes , Humanos , Espectrometria de Fluorescência
13.
Phys Rev Lett ; 106(11): 118101, 2011 Mar 18.
Artigo em Inglês | MEDLINE | ID: mdl-21469899

RESUMO

Single strand breaks are induced in DNA plasmids, pBR322 and pUC19, in aqueous media exposed to strong fields generated using ultrashort laser pulses (820 nm wavelength, 45 fs pulse duration, 1 kHz repetition rate) at intensities of 1-12 TW cm(-2). The strong fields generate, in situ, electrons and radicals that induce transformation of supercoiled DNA into relaxed DNA, the extent of which is quantified. Introduction of electron and radical scavengers inhibits DNA damage; results indicate that OH radicals are the primary (but not sole) cause of DNA damage.


Assuntos
Quebras de DNA de Cadeia Dupla/efeitos da radiação , DNA/efeitos da radiação , Radical Hidroxila/efeitos adversos , Plasmídeos/efeitos da radiação , Radiólise de Impulso/métodos , Elétrons/efeitos adversos , Sequestradores de Radicais Livres/química , Radicais Livres/efeitos adversos , Raios Infravermelhos , Lasers , Água/química
14.
J Phys Chem A ; 115(5): 718-25, 2011 Feb 10.
Artigo em Inglês | MEDLINE | ID: mdl-21192707

RESUMO

Nanosecond laser flash photolysis employing transient detection of emission and absorption in combination with pulse radiolysis and quantum theory has been employed to shed light into the kinetics, quantum yields, and mechanisms of the deactivation of the first excited singlet state of 1- and 2-thionaphthols (NpSH(S(1))). In contrast to thiophenols (ArSH(S(1))), the results revealed that the decay of the first excited singlet state of 1- and 2-thionaphthols (NpSH(S(1))) is governed by radiationless internal conversion (Φ(IC) = 0.29-0.46; 0.016-0.190) and intersystem crossing (Φ(ISC) = 0.14-0.15; 0.4-0.6), respectively, with pronounced S-H photodissociation (Φ(D) = 0.40-0.55; 0.35-0.40). Fluorescence as a deactivation channel plays a minor role (Φ(F) = 0.001-0.010; 0.010-0.034). Quantum chemical calculations helped in understanding the formation of naphthylthiyl radicals and rationalizing the differences in the efficiency of intersystem crossing of the 1- and 2-thionaphthol systems.


Assuntos
Radicais Livres/química , Naftóis/química , Fenóis/química , Fotólise , Radiólise de Impulso/métodos , Espectrometria de Fluorescência/instrumentação , Compostos de Sulfidrila/química , Algoritmos , Fluorescência , Isomerismo , Cinética , Lasers , Luz , Estrutura Molecular , Fotoquímica/métodos , Teoria Quântica
15.
J Radiat Res ; 52(1): 15-23, 2011.
Artigo em Inglês | MEDLINE | ID: mdl-21139328

RESUMO

A comparative study using the pulse radiolysis technique was carried out to investigate transient absorption spectra and rate constants for the reactions of (•)OH and N(3)(•) with edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one) and its four analogue compounds, 1,3-dimethyl-2-pyrazolin-5-one, 3-methyl-1-(pyridin-2-yl)-2-pyrazolin-5-one, 1-phenyl-3-trifluoromethyl-2-pyrazolin-5-one and 1-(4-chlorophenyl)-3-methyl-2-pyrazolin-5-one. The results showed that, unlike reaction mechanisms previously proposed, the phenyl group of edaravone played an important role in the reaction with (•)OH and OH adducts to the phenyl group were formed. Quantum chemical calculations also strongly supported this attribution and suggested that the most favorable site for attacks by (•)OH is the ortho position of the phenyl group. Moreover, the rate constants for the reactions of edaravone and its analogues towards (•)OH and N(3)(•) were about 8.0 × 10(9), and 4.0 × 10(9) dm(3) mol(-1) s(-1), respectively. Edaravone displayed higher reactivity compared to the others, in contrast to a previous report in which 3-methyl-1-(pyridin-2-yl)-2-pyrazolin-5-one showed the highest reactivity towards (•)OH.


Assuntos
Antipirina/análogos & derivados , Sequestradores de Radicais Livres/química , Sequestradores de Radicais Livres/efeitos da radiação , Modelos Químicos , Antipirina/química , Antipirina/efeitos da radiação , Simulação por Computador , Edaravone , Radical Hidroxila/química , Radical Hidroxila/efeitos da radiação , Nitrogênio/química , Nitrogênio/efeitos da radiação , Radiólise de Impulso/métodos
16.
Arch Biochem Biophys ; 504(1): 100-3, 2010 Dec 01.
Artigo em Inglês | MEDLINE | ID: mdl-20678468

RESUMO

Time-resolved pulse radiolysis investigations reported herein show that the carotenoids ß-carotene, lycopene, zeaxanthin and astaxanthin (the last two are xanthophylls--oxygen containing carotenoids) are capable of both reducing oxidized guanosine as well as minimizing its formation. The reaction of the carotenoid with the oxidized guanosine produces the radical cation of the carotenoid. This behavior contrasts with the reactions between the amino acids and dietary carotenoids where the carotenoid radical cations oxidized the amino acids (tryptophan, cysteine and tyrosine) at physiological pH.


Assuntos
Carotenoides/metabolismo , Dieta , Guanosina/metabolismo , Radiólise de Impulso/métodos , Transporte de Elétrons , Cinética , Nucleosídeos/metabolismo
17.
J Phys Chem A ; 114(32): 8271-7, 2010 Aug 19.
Artigo em Inglês | MEDLINE | ID: mdl-20666479

RESUMO

One-electron redox reactions of cyclic selenium compounds, DL-trans-3,4-dihydroxy-1-selenolane (DHS(red)), and DL-trans-3,4-dihydroxy-1-selenolane oxide (DHS(ox)) were carried out in aqueous solutions using nanosecond pulse radiolysis, and the resultant transients were detected by absorption spectroscopy. Both *OH radical and specific one-electron oxidant, Br(2)(*-) radical reacted with DHS(red) to form similar transients absorbing at 480 nm, which has been identified as a dimer radical cation (DHS(red))(2)(*+). Secondary electron transfer reactions of the (DHS(red))(2)(*+) were studied with 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS(2-)) and superoxide (O(2)(*-)) radicals. The bimolecular rate constants for the electron transfer reaction between (DHS(red))(2)(*+) with ABTS(2-) was determined as 2.4 +/- 0.4 x 10(9) M(-1) s(-1). From this reaction, the yield of (DHS(red))(2)(*+) formed on reaction with *OH radical was estimated in the presence of varying phosphate concentrations. (DHS(red))(2)(*+) reacted with O(2)(*-) radical with a bimolecular rate constant of 2.7 +/- 0.1 x 10(9) M(-1) s(-1) at pH 7. From the same reaction, the positive charge on (DHS(red))(2)(*+) was confirmed by the kinetic salt effect. HPLC analysis of the products formed in the reaction of (DHS(red))(2)(*+) with O(2)(*-) radicals showed formation of the selenoxide, DHS(ox). In order to know if a similar mechanism operated during the reduction of DHS(ox), its reactions with e(aq)(-) were studied at pH 7. The rate constant for this reaction was determined as 5.6 +/- 0.9 x 10(9) M(-1) s(-1), and no transient absorption could be observed in the wavelength region from 280 to 700 nm. It is proposed that the radical anion (DHS(ox))(*-) formed by a one-electron reduction would get protonated to form a hydroxyl radical adduct, which in presence of proton donors, would undergo dehydration to form DHS(*+). Evidence for this mechanism was obtained by converting DHS(*+) to (DHS(red))(2)(*+) with the addition of DHS(red) to the same system. Quantum chemical calculations provided supporting evidence for some of the redox reactions.


Assuntos
Elétrons , Compostos Heterocíclicos com 1 Anel/química , Compostos Organosselênicos/química , Radiólise de Impulso/métodos , Cromatografia Líquida de Alta Pressão , Radical Hidroxila/química , Modelos Moleculares , Conformação Molecular , Oxirredução , Teoria Quântica
19.
J Hazard Mater ; 172(2-3): 1185-92, 2009 Dec 30.
Artigo em Inglês | MEDLINE | ID: mdl-19699577

RESUMO

Polyphenols, like gallic acid (GA) released in the environment in larger amount, by inducing some unwanted oxidations, may constitute environmental hazard: their concentration in wastewater should be controlled. Radiolytic degradation of GA was investigated by pulse radiolysis and final product techniques in dilute aqueous solution. Subsidiary measurements were made with 3,4,5-trimethoxybenzoic acid (TMBA) and 3,4,5-trihydroxy methylbenzoate (MGA). The hydroxyl radical and hydrogen atom intermediates of water radiolysis react with the solute molecules yielding cyclohexadienyl radicals. The radicals formed in GA and MGA solutions in acid/base catalyzed water elimination decay to phenoxyl radicals. This reaction is not observed in TMBA solution. The hydrated electron intermediate of water decomposition adds to the carbonyl oxygen, the anion thus formed protonates on the ring forming cyclohexadienyl radical or on the carbonyl group forming carbonyl centred radical. The GA intermediates formed during reaction with primary water radicals in presence of oxygen transform to non-aromatic molecules, e.g., to aliphatic carboxylic acids.


Assuntos
Ácido Gálico/efeitos da radiação , Substâncias Perigosas , Radiólise de Impulso/métodos , Flavonoides , Radicais Livres/química , Ácido Gálico/química , Resíduos Industriais/prevenção & controle , Fenóis , Polifenóis , Soluções , Água , Poluentes Químicos da Água/química , Poluentes Químicos da Água/efeitos da radiação
20.
J Am Chem Soc ; 130(44): 14772-7, 2008 Nov 05.
Artigo em Inglês | MEDLINE | ID: mdl-18841971

RESUMO

The dynamics of electron adducts of 2'-deoxynucleotides and oligonucelotides (ODNs) were measured spectroscopically by nanosecond pulse radiolysis. The radical anions of the nucleotides were produced within 10 ns by the reaction of hydrated electrons (e(aq)(-)) and were protonated to form the corresponding neutral radicals. At pH 7.0, the radical anion of deoxythymidine (dT(*-)) was protonated to form the neutral radical dT(H)(*) in the time range of microseconds. The rate constant for the protonation was determined as 1.8 x 10(10) M(-1) s(-1). In contrast, the neutral radical of dC(H)(*) was formed immediately after the pulse, suggesting that the protonation occurs within 10 ns. The transient spectra of excess electrons of the double-stranded ODNs 5'-TAATTTAATAT-3' (AT) and 5'-CGGCCCGGCGC-3' (GC) differed from those of pyrimidine radicals (C and T) and their composite. In contrast, the spectra of the electron adducts of the single-stranded ODNs GC and AT exhibited characteristics of C and T, respectively. These results suggest that, in duplex ODNs, the spectral intermediates of G-C and A-T anions complex were formed. On the microsecond time scale, the subsequent changes in absorbance of the ODN AT had a first-order rate constant of 4 x 10(4) s(-1), reflecting the protonation of T.


Assuntos
DNA/química , Pareamento de Bases , Nucleotídeos de Desoxiadenina/química , Nucleotídeos de Desoxicitosina/química , Nucleotídeos de Desoxiguanina/química , Concentração de Íons de Hidrogênio , Oligonucleotídeos/química , Radiólise de Impulso/métodos , Timidina/química
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