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1.
Veleeparambil M. Manoj Usha K. Aravind Hari Mohan Charuvila T. Aravindakumar 《Research on Chemical Intermediates》2011,37(8):1113-1122
The decomposition studies of S-nitrosothiols (RSNO) are important due to their potential role in vivo in connection with the storage and transport of nitric
oxide (•NO) within the body. Reactions of hydroxyl radicals (•OH) with a number of RSNOs (S-nitroso derivatives of N-acetyl-dl-penicillamine, l-cysteinemethylester, N-acetylcysteamine, and dl-penicillamine) in aqueous medium at neutral and acidic pH have been reported in the present study. Radiation chemical technique
(steady state and pulse radiolysis) has been utilized for the determination of the reaction rate constants, the end product
analyses, and the transient intermediate species. The rate constants for the reaction of •OH with the selected RSNOs were determined using a competition kinetic method with 2′-deoxy-d-ribose as the competitor. All the rate constants were found to be of the order of diffusion controlled (1010 M−1 s−1). The degradation yield of RSNOs was found to be quantitative (i.e., G(–RSNO) ≈ G(•OH)) at neutral and acidic pH. The major products of decomposition were the respective disulfide (RSSR) and nitrite (NO2
−). A good material balance is also obtained between the degradation yield and the formation of the products (i.e., G(–RSNO) ≈ G(RSSR) + G(NO2
−)). The major transient intermediate was the thiyl radical (RS•). Its intermediacy was confirmed by making use of the electron transfer reaction of 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonate)
(ABTS2−) to RS•, which results in the formation of ABTS•− having a transient absorption spectrum with λmax at 410 nm. Based on these results, a generalized reaction mechanism is deduced for the reaction of •OH with RSNO. 相似文献
2.
ZHU Hongping ZHANG Zhaoxia ZHAO Hongwei WANG Wenfeng & YAO Side . Shanghai Institute of Applied Physics Chinese Academy of Sciences Shanghai China . Graduate University of the Chinese Academy of Sciences Beijing China 《中国科学B辑(英文版)》2006,49(4):308-314
Reactive oxygen species (ROS) are generated dur- ing radiation, respiratory burst, normal metabolic processes and so on. There are enzymatic and non-enzymatic antioxidants such as superoxide dis- mutase (SOD), glutathione peroxidase (GSH-Px), vi- tamin E (VE) and carotenoids that can either inhibit or repair the ROS-induced damage. ROS is essential to maintain physiological homeostasis. However, exces- sive ROS give rise to oxidative damage to proteins, lipids and DNA which related t… 相似文献
3.
Damages induced by free radicals on human serum albumin (HSA), the most prominent protein in plasma, were investigated by
Raman spectroscopy. HSA underwent oxidative and reductive radical stress. Gamma-irradiation was used to simulate the endogenous
formation of reactive radical species such as hydrogen atoms (•H), solvated electrons (eaq−) and hydroxyl radicals (•OH). Raman spectroscopy was shown to be a useful tool in identifying conformational changes of the protein structure and specific
damages occurring at sensitive amino acid sites. In particular, the analysis of the S–S stretching region suggested the radical
species caused modifications in the 17 disulphide bridges of HSA. The concomitant action of eaq− and •H atoms caused the formation of cyclic disulphide bridges, showing how cystine pairs act as efficient interceptors of reducing
species, by direct scavenging and electron transfer reactions within the protein. This conclusion was further confirmed by
the modifications visible in the Raman bands due to Phe and Tyr residues. As regards to protein folding, both oxidative and
reductive radical stresses were able to cause a loss in α-helix content, although the latter remains the most abundant secondary
structure component. β-turns motifs significantly increased as a consequence of the synergic action of eaq− and •H atoms, whereas a larger increase in the β-sheet content was found following the exposure to •OH and/or •H attack. 相似文献
4.
The mechanisms of reactions between CC13OO• radical and quercetin, rutin and epigallocatechin gallate (EGCG) have been studied using pulse radiolytic technique. It is
suggested that the electron transfer reaction is the main reaction between CC13OO• radical and rutin, EGCG, but there are two main pathways for the reaction of CC13OO• radical with quercetin, one is the electron transfer reaction, the other is addition reaction. The reaction rate constants
were determined. It is proved that quercetin and rutin are better CC13OO• radical scavengers than EGCG. 相似文献
5.
Hari Mohan 《Journal of Chemical Sciences》2002,114(6):749-758
In neutral aqueous solution of (phenylthio)acetic acid, hydroxyl radical is observed to react with a bimolecular rate constant
of 7.2 × 10-1 dm3 mol−s− and the transient absorption bands are assigned to•OH radical addition to benzene and sulphur with a rough estimated values of 50 and 40% respectively. The reaction of the•OH radical with diphenyl sulphide (k = 4.3 × 108 dm3 mol−1 s−1) is observed to take place with formation of solute radical cation, OH-adduct at sulphur and benzene with estimated values
of about 12, 28 and 60% respectively. The transient absorption bands observed on reaction of•OH radical, in neutral aqueous solution of 4-(methylthio)phenyl acetic acid, are assigned to solute radical cation (λmax = 550 and 730 nm), OH-adduct at sulphur (λmax = 360 nm) and addition at benzene ring (λmax = 320 nm). The fraction of•OH radical reacting to form solute radical cation is observed to depend on the electron-withdrawing power of substituted group.
In acidic solutions, depending on the concentration of acid and electron-withdrawing power, solute radical cation is the only
transient species formed on reaction of•OH radical with the sulphides studied. 相似文献
6.
Pulse radiolysis of resveratrol was carried out in aqueous solutions at pH ranging from 6.5 to 10.5. The one-electron oxidized
species formed by the N•3 radicals at pH 6.5 and 10.5 were essentially the same with λmax at 420 nm and rate constant varying marginally (k = (5−6.5) × 109 dm3 mol−1 s−1). The nature of the transients formed by NO•2, NO• radical reaction at pH 10.5 was the same as that with N•3, due to the similarity in decay rates and the absorption maximum. Reaction of •OH radical with resveratrol at pH 7 gives an absorption maximum at 380 nm, attributed to the formation of carbon centered
radical. The repair rates for the thymidine and guanosine radicals by resveratrol were approx. 1 × 109 dm3 mol−1 s−1, while the repair rate for tryptophan was lower by nearly an order of magnitude (k = 2 × 108 dm3 mol−1 s−1). The superoxide radical anion was scavenged by resveratrol, as well as by the Cu–resveratrol complex with k = 2 × 107 and 1.5 × 109 dm3 mol−1 s−1, respectively. Its reduction potential was also measured by cyclic voltammetry. 相似文献
7.
The •OH and the NO2
• radicals generated pulse radiolytically in N2O-saturated aqueous solution at pH 8–8.5 oxidize Mesna to form the corresponding thiyl radicals which on reaction with thiolate
ions form an RSSR•
− type of transient with λmax = 420 nm. The rate constants for the formation of these transients were determined. In the absence of O2 at pH=6, the RS• radicals formed show an absorption maximum at 360 nm and an ε=200±50 dm3 mol−1 cm−1. The rate constant k (•OH+RSH) was 6×109 dm3 mol−1 s−1 as determined from competition kinetics. In the presence of O2 the Mesna thiyl radical was seen to rapidly add oxygen to form an RSOO• type of species with λmax = 535 nm, ε=700±50 dm3 mol−1 cm−1 and k (RS•+O2)=1.3×108 dm3 mol−1 s−1. Both the RS• and the RSOO• radicals formed by the oxidation of Mesna were able to abstract H-atoms from ascorbate ions and k(RS• +AH−)=~k(RSOO•+AH−)=~6−7×108 dm3 mol−1 s−1-. Moderately strong oxidants like CCl3OO• and the (CH3)3CO• radicals, having a reduction potential of +1.4−1.6 V vs NHE were unable to oxidize Mesna. The results thus reflect on the
pro- and anti-oxidant properties of Mesna. 相似文献
8.
Alexander Konkin Frank Wendler Frank Meister Hans-Klaus Roth Albert Aganov Oliver Ambacher 《Cellulose (London, England)》2007,14(5):457-468
Degradation processes of N-methylmorpholine-N-oxide monohydrate (NMMO), cellulose and cellulose/NMMO solutions were studied by high performance liquid chromatography (HPLC)
and electron spin resonance (ESR) spectroscopy. Kinetics of radical accumulation processes under UV (λ = 248 nm) excimer laser
flash photolysis was investigated by ESR at 77 K. Beside radical products of cellulose generated and stabilized at low temperature,
radicals in NMMO and cellulose/NMMO solutions were studied for the first time in those systems and attributed to nitroxide
type radicals ∼CH2–NO•–CH2∼ and/or ∼CH2–NO•–CH3∼ at the first and methyl •CH3 and formyl •CHO radicals at the second step of the photo-induced reaction. Kinetic study of radicals revealed that formation and recombination
rates of radical reaction depend on cellulose concentration in cellulose/NMMO solutions and additional ingredients, e.g.,
Fe(II) and propyl gallate. HPLC measurements showed that the concentrations of ring degradation products, e.g., aminoethanol
and acetaldehyde, are determined by the composition of the cellulose/NMMO solution. Results based on HPLC are mainly maintained
by ESR that supports the assumption concerning a radical initiated ring-opening of NMMO. 相似文献
9.
Reactions of radiolytically generated CO3
•− with some ferric heme proteins, catalase, cytochrome c, and horseradish peroxidase (HRP), were studied. Carbonate radical
anion oxidized amino acid residues of these proteins, but did not react directly with heme iron. HRP and catalase lost about
30% and 20% of their activity, respectively, after the reaction with 100 μM of CO3
•−. The rate constants of the reactions of CO3
•− with the investigated proteins measured by the pulse radiolysis method at pH 8–8.4 and 10 varied from 1.0 × 108 M−1 s−1 (for cytochrome c) to 3.7 × 109 M−1 s−1 (for catalase). 相似文献
10.
Tao Song Corey N. W. Lam Dominic C. M. Ng Galina Orlova Julia Laskin De-Cai Fang Ivan K. Chu 《Journal of the American Society for Mass Spectrometry》2009,20(6):972-984
The dissociation of [CuII(L)His]•2+ complexes [L=diethylenetriamine (dien) or 1,4,7-triazacyclononane (9-aneN3)] bears a strong resemblance to the previously reported behavior of [CuII(L)GGH]•2+ complexes. We have used low-energy collision-induced dissociation experiments and density functional theory (DFT) calculations
at the B3LYP/6-31+G(d) level to study the macrocyclic effect of the auxiliary ligands on the formation of His•+ from prototypical [CuII(L)His]•2+ systems. DFT revealed that the relative energy barriers of the same electron-transfer (ET) dissociation pathways of [CuII(9-aneN3)His]•2+ and [CuII(dien)His]•2+ are very similar, with the ET reactions of [CuII(9-aneN3)His]•2+ leading to the generation of two distinct His•+ species; in contrast, the proton transfer (PT) dissociation pathways of [CuII(9-aneN3)His]•2+ and [CuII(dien)His]•2+ differ considerably. The PT reactions of [CuII(9-aneN3)His]•2+ are associated with substantially higher barriers (>13 kcal/mol) than those of [CuII(dien)His]•2+. Thus, the sterically encumbered auxiliary 9-aneN3 ligand facilitates ET reactions while moderating PT reactions, allowing the formation of hitherto nonobservable histidine
radical cations. 相似文献
11.
E. T. Denisov 《Kinetics and Catalysis》2000,41(3):293-297
The experimental activation energies of the R• + O = CR1R2 and RO• + CH2 = CHR1 addition reactions are analyzed within the framework of the parabolic model of the bimolecular addition reaction. The activation
energy also depends on the dissociation energy of the forming C-O bond and on the reaction enthalpy: the higher the dissociation
energy, the higher the activation energy. The empirical relationshipr
e
J..D
e
= 0.97 x 10-13 m kJ.-1 mol is found for H•, Cl•, Br•
• and RO• radical addition to multiple C=C and C=O bonds (re is the distance between the peaks of the intersecting parabolic curves). This is due to the effect of the triplet repulsion
on radical addition. The interaction of polar groups and the steric effect also influence the activation energy. 相似文献
12.
Experimental data that support the hypothesis on the determining role of •OH radicals in the emergence of luminescence during the oxidation of U(IV) with atmospheric oxygen in aqueous HClO4 solutions have been obtained using the H2O2-FeSO4 system as a source of OH radicals. It has been found that brighter chemiluminescence (CL) is observed in the presence of
10−5 mol/l Fe2+ in a 5 × 10−4 mol/l U(IV) solution in 0.1 mol/l HClO4 compared with the FeSO4-free solution. The CL yield in the presence of Fe2+ (ηCL = 3.9 × 10−8) is 2.8 times that in the solution without iron (ηCL = 1.4 × 10−8). These results can be regarded as a further piece of evidence for the idea that the elementary event of the formation of
a CL emitter—electronically excited uranyl ion *(UO22+)—in radical chain U(IV) oxidation reactions is electron transfer from the uranoyl ion (UO2+) to the oxidant, the •OH radical. Thus, one of the main prerequisites for light emission during U(IV) oxidation reactions is a high generation efficiency
of •OH radicals and their easy access to the uranoyl UO2+ ion. 相似文献
13.
Victor Ryzhov Adrian K. Y. Lam Richard A. J. O’Hair 《Journal of the American Society for Mass Spectrometry》2009,20(6):985-995
In this work, we describe two different methods for generating protonated S-nitrosocysteine in the gas phase. The first method
involves a gas-phase reaction of protonated cysteine with t-butylnitrite, while the second method uses a solution-based transnitrosylation reaction of cysteine with S-nitrosoglutathione
followed by transfer of the resulting S-nitrosocysteine into the gas phase by electrospray ionization mass spectrometry (ESI-MS).
Independent of the way it was formed, protonated S-nitrosocysteine readily fragments via bond homolysis to form a long-lived
radical cation of cysteine (Cys•+), which fragments under collision-induced dissociation (CID) conditions via losses in the following relative abundance order:
•COOH ≫ CH2S > •CH2SH-H2S. Deuterium labeling experiments were performed to study the mechanisms leading to these pathways. DFT calculations were
also used to probe aspects of the fragmentation of protonated S-nitrosocysteine and the radical cation of cysteine. NO loss
is found to be the lowest energy channel for the former ion, while the initially formed distonic Cys•+ with a sulfur radical site undergoes proton and/or H atom transfer reactions that precede the losses of CH2S, •COOH, •CH2SH, and H2S. 相似文献
14.
Prashant V. Kamat Geneviève Sauvé Dirk M. Guldi Klaus -Dieter Asmus 《Research on Chemical Intermediates》1997,23(7):575-585
Pulse radiolysis and steady-state radiolysis experiments describing the radical and electron transfer reactions of C84 are reported here for the first time. C84 reacts readily with radiolytically generated chloromethyl (•CCl3) and trichloromethylperoxyl (CCl3OO•) radicals in CCl4. The formation of the radical adduct has been confirmed from its characteristic absorption in the UV (320 nm) and visible
(480 nm). Radical-induced oxidation in 1,2-dichloroethane (1,2-DCE) resulted in a short lived transient absorbing at 920 nm.
Reduction of C84 in toluene/2-propanol/acetone could be conveniently followed by formation of an absorption band with an absorption maximum
at 960 nm. 相似文献
15.
Radoslaw A. Wach Hisaaki Kudoh Maolin Zhai Yusa Muroya Yosuke Katsumura 《Journal of polymer science. Part A, Polymer chemistry》2005,43(3):505-518
Laser flash photolysis with excitation at 248 nm was used to study photochemically derived changes of carboxymethylcellulose (CMC) in aqueous solutions. Transient absorption spectra of solutions after photolysis revealed a broad band with a maximum of approximately 720 nm, which could be ascribed to the signal of the hydrated electron. The interaction of the hydrated electron with CMC was slow (<107 dm3 mol?1 s?1), but the OH radical, formed by the decomposition of H2O2, reacted with CMC at a high rate constant (9.5–11.0 × 108 dm3 mol?1 s?1). The rate constant of the reactions of CMC with hydroxyl radicals depended on the conformation of the macromolecules, which was determined by the pH of the solution. Transient absorption was recorded at a wavelength shorter than 370 nm for CMC solutions photolyzed in the presence of H2O2. As a result of OH attack, long‐lived radicals were formed on CMC. The recombination of macroradicals led to the formation of crosslinking bonds between side‐chain groups, and as a result of it an insoluble gel arose in low‐pH solutions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 505–518, 2005 相似文献
16.
Ravi Joshi Soumyakanti Adhikari Tulsi Mukherjee 《Research on Chemical Intermediates》2001,27(6):623-634
Using the technique of pulse radiolysis, redox studies of 3-azido-3-deoxythymidine (azidothymidine or AZT) with hydrated electron and hydroxyl radicals, generated in phosphate-buffered aqueous medium, are reported. The hydrated electron reacts with AZT (k = 1.9 × 1010 dm3 mol-1 s-1) to generate transients with absorption maxima at 300 and 340 nm. The hydroxyl radical adds to AZT to generate transients with absorption maxima at 310 and 365 nm, with formation rate constant of 9.0 × 109 dm3 mol-1 s-1 as observed at 310 and 365 nm. The secondary radical 6-hydroxy-5-yl-azidothymidine, formed in the reaction of AZT with hydroxyl radical, reacts with bilirubin to give a transient of bilirubin with bimolecular rate constant of 1.8 × 108 dm3 mol-1 s-1. In the reaction of hydroxyl radical with AZT/riboflavin pair, an . H atom transfer from riboflavin to the 6-hydroxy-5-yl-azidothymidine is observed. Reactions of OH-derived radicals of thymine with bilirubin and riboflavin are similar to that of AZT. Possible mechanisms are proposed for the observed reactions. 相似文献
17.
Solutions of 80 mM benzophenone (BP) and up to 14 mM p-terphenyl (TP) in the ionic liquid methyltributylammonium bis[(trifluoromethyl)sulfonyl]imide
(R4NNTf2) have been investigated by nanosecond pulse radiolysis. The resulting transient absorption spectra of pulse-irradiated argon
saturated solutions correspond to the formation of several intermediates derived from BP and TP: benzophenone radical anion
[(C6H5)2CO]•− (BP•−) converted after ~20 μs into ketyl radicals (C6H5)2C•OH (BP•H), a hydrogen adduct to the phenyl ring of benzophenone C6H5COC6H6•, p-terphenyl triplet excited state 3TP*, and traces of TP radical ions. 3TP* was formed in two steps, the first immediately during the pulse and the second in pseudo-first order process with a second
order reaction rate constant calculated from TP concentration dependence: k = ~2 × 108 dm3 mol−1 s−1. 相似文献
18.
Specific features of the kinetics of alkane and alkylbenzene oxidation with HOONO formed in the H2O2-NaNO2 system (pH 4.27) are quantitatively explained assuming the simultaneous occurrence of reactions in the gas and liquid phases.
A model of the kinetic distribution method is developed and verified that accounts for the equilibrium distribution of a substrate
and a reagent between phases and their interaction in both phases. Relative rate constants for the oxidation ofn-alkanes (C3-C8), isobutane, cyclopentane, cyclohexane, benzene, and alkylbenzenes are measured over a wide range of the volume ratios of
the gas and liquid phases (λ = Vg/V1). Relative rate constants for the oxidation of alkanes in the gas phase and alkylbenzenes in gas and solution were determined.
Similarity in substrate selectivities and kinetic isotope effects of the gasphase reactions of alkanes and arenes with peroxynitrous
acid and•OH radicals suggest that hydroxyl radical or the ˙OH...NO2 radical pair is an active species in the gas phase. In solution, alkylbenzenes react nonselectively with HOONO, as well as
with ˙OH radicals. In contrast to the liquid-phase oxidation of arenes, the liquidphase oxidation of all alkanes under study
insignificantly contribute (5–15%) to the overall rate of the substrate consumption. 相似文献
19.
Medha Rele B. S. Patro S. Adhikari G. P. Kalena S. Chattopadhyay T. Mukherjee 《Journal of Chemical Sciences》2002,114(6):739-747
The free radical scavenging properties and possible antioxidant activity of 1,3-diphenylpropane-1,3-dione (1) are reported.
Pulse radiolysis technique was employed to study the one-electron oxidation of 1 with various radicals viz. CCl3O2
•, N3
• and•OH in homogeneous aqueous solution. All these radicals reacted with 1 under ambient conditions at almost diffusion controlled
rates producing transient species with an absorption maximum around 420 nm that decayed at first order rates. The transient
absorption peak was shifted in the case of CCl3OO• radical reaction with 1 due to change in the polarity of the medium. Formation of a stable product with a broad absorption
band starting from 400 nm and cut off at 230 nm was observed in the oxidation of 1 with•OH and•N3 radicals. In a biological system also, 1 showed significant inhibitory activity against Fe2+-mediatedlipidperoxidation. Based on these observations, a suitable mechanism for the oxidation of 1 has been proposed. 相似文献
20.
Kinetics of formation and recombination of radicals formed by quenching of the triplet state of 4-carboxybenzophenone (CB)
with para-substituted phenol derivatives RC6H4OH (R = OMe, H, Cl, Br, I) in aqueous solutions was studied by nanosecond laser photolysis. At pH ≥ 5.4, quenching proceeds
with high rate constants ((1–3)⋅109 L mol−1 s−1) through electron transfer to form the radical anion CB⋅− and radical cation RC6H4OH⋅+. The latter is transformed into the phenoxyl radical within ≤10 ns. At pH ≤ 8, the CB⋅− radical anion is protonated in a phosphate buffer with the rate constant increasing from 4⋅106 to 15⋅106 s−1 with a decrease in the pH from 8 to 5.4. The yield of radicals decreases from 100 to 13% as the atomic weight of halogen
in the RC6H4OH molecule increases due to an increase in the probability of recombination of the primary triplet radical pair in the solvent
cage and partial intersystem crossing in an encounter complex (3CB, RC6H4OH). The effect of heavy atom is also observed in the kinetics of volume recombination of the radicals, the magnitude of effect
corresponds to the acceleration of the primary recombination of the triplet radical pair.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1397–1402, June, 2005. 相似文献