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1.
One-electron oxidation of thionine has been studied using specific oxidizing radicals such as Cl−Tl(II) and N3 generated by pulse radiolysis of aqueous solutions. The semioxidized thionine exhibited threepK’s indicating four conjugate acid-base forms. N3 radicals were found to be less efficient in oxidizing thionine as compared to Cl
2
−
, Tl2+ and Tl(OH)+. The rate constants for electron abstraction from thionine by Cl
2
−
, Tl2+, Tl(OH)+, Tl(OH)2 and N3 were evaluated. The spectra of different protonated forms of semioxidized thionine and the extinction coefficients at λmax are presented. Reaction of OH radicals with thionine gave transient products whose spectra and acid-base properties were
different from those of semioxidized thionine. The rate constant for formation of the product transient agrees well with competition
kinetic value for reaction of OH with thionine reported earlier. 相似文献
2.
The reactions of e−
aq, H-atoms, OH radicals and some one electron oxidants and reductants were studied with dithio-oxamide (DTO) in aqueous solutions
using pulse radiolysis technique. The transient species formed by the reaction of e−
aq with DTO at pH 6.8 has an absorption band with λ
max at 380 nm and is reducing in nature. H-atom reaction with DTO at pH 6.8 also produced the same transient species. The semi-reduced
species was found to be neutral indicating that the electron adduct gets protonated quickly. However at pH 1, the species
produced by H-atom reaction had a different spectrum with λ
max at 360 and 520 nm. Reaction of acetone ketyl radicals and CO2
− radicals with DTO at pH 6.8 gave transient spectra which were identical to that obtained by e−
aq reaction. However at pH 1, the spectrum obtained by the reaction of acetone ketyl radicals with DTO was similar to that obtained
by H-atom reaction at that pH. The transient species formed by OH radical reaction with DTO in the pH range 1–9.2 also has
two absorption maxima at 360 and 520 nm. This spectrum was identical with the spectrum obtained by H-atom reaction at pH 1.
This means that all these radicals viz. OH, H-atom and (CH3)2COH radicals react with DTO at pH 1 by H-abstraction mechanism. The transient species produced was found to be sensitive to
the presence of oxygen. One-electron oxidizing radicals such as Br2
−· and SO4
−· radicals reacted with DTO at neutral pH to give the same species as produced by OH radical reaction having absorption maxima
at 360 to 520 nm. At acidic pHs, only Br2
−· and Cl2
−· radicals were able to oxidize DTO to give the same species as produced by OH radical reaction. The semioxidized species is
a resonance stabilized species with the electron delocalized over the-N-C-S bond. This species was found to be neutral and
non-oxidizing in nature. 相似文献
3.
Nature of the transient species formed during pulse radiolysis of thioacetamide in aqueous solutions
K. Kishore P. Dwibedy G. R. Dey D. B. Naik P. N. Moorthy 《Research on Chemical Intermediates》1998,24(1):35-45
Thioacetamide (TA) is an organic compound having thioamide group similar to that in thiourea derivatives. Its reactions with
eaq−, H-atom and OH radicals were studied using the pulse radiolysis technique at various pHs and the kinetic and spectral characteristics
of the transient species were determined. The initial adduct formed by the reaction of TA with OH radicals at pH 7 does not
absorb light in the 300–600 nm region but reacts with the parent compound to give a transient species with an absorption maximum
around 400 nm. At pH 0, the reaction of OH radicals with TA directly gives a similar transient species with absorption maximum
at 400 nm. Transient species formed by H-atom reaction with TA and pH 0 has no absorption in the 300–600 nm region but at
higher acidity a new transient species is formed which has absorption maximum at 400 nm. This transient absorption observed
in the case of both OH and H atom reaction with TA is ascribed to the formation of a resonance stabilized radical similar
to that obtained in the case of thiourea derivatives. The species produced by electron reaction viz. electron adduct was found to be a strong reductant and could reduce MV2+ with a high rate constant. H2S was produced as a stable product in the reaction of eaq− and its G-value was determined to be about 0.8. 相似文献
4.
K. Pietrucha L. Góra K. Burczak 《Journal of Radioanalytical and Nuclear Chemistry》1998,232(1-2):83-86
Hydroxyl radicals were generated radiolytically in N2O-saturated aqueous solutions of the aminoglycoside antibiotic, gentamycin. Using the pulse radiolysis technique, the rate
constant of OH radicals with gentamycin determined was 1.2·109 dm3·mol−1·s−1. Upon.OH attack a transient species with an absorption maximum at 270 nm is observed which decays by second-order kinetics within
the solute concentration range of 3.2·10−5 to 1·10−3mol·dm−3. Transient species undergoes transformation to a permanent product absorbing between 260 and 340 nm with maximum absorption
at 300 nm. Rate constant of the reaction of bimolecular decay of gentamycin radicals, k (Gen.+Gen.) was found to be ≈ 1.4·107 dm3·mol−1·s−1. 相似文献
5.
Rate constants for reactions of 2-pyridinol with one electron reductants, such ase
aq
−
and H atoms and one-electron oxidants, viz. OH, N3, Br
2
−
, C1
2
−
and O− have been determined at different pH values using the pulse radiolysis technique. From the corrected absorption spectra of
the product transient species, the extinction coefficients of these species at their respective absorption maxima have been
determined. The kinetics of decay of these transients have been investigated. ThepK
a values of transients formed bye
aq
−
and OH radical reactions have been estimated to be 7.6 and 3.5 respectively. Rate constants for electron transfer from semireduced
2-pyridinol to different electron acceptors have been determined. 相似文献
6.
Reactions of e−aq, OH radicals and H atoms were studied with n-allylthiourea (NATU) using pulse radiolysis. Hydrated electrons reacted with
NATU (k = 2.8×109 dm3 mol−1 s−1) giving a transient species which did not have any significant absorption above 300 nm. It was found to transfer electrons
to methyl viologen. At pH 6.8, the reduction potential of NATU has been determined to be −0.527 V versus NHE. At pH 6.8, OH radicals were found to react with NATU, giving a transient species having absorption maxima at 400–410
nm and continuously increasing absorption below 290 nm. Absorption at 400–410 nm was found to increase with parent concentration,
from which the equilibrium constant for dimer radical cation formation has been estimated to be 4.9×103 dm3 mol−1. H atoms were found to react with NATU with a rate constant of 5 × 109 dm3 mol−1 s−1, giving a transient species having an absorption maximum at 310 nm, which has been assigned to H-atom addition to the double
bond in the allyl group. Acetoneketyl radicals reacted with NATU at acidic pH values and the species formed underwent reaction
with parent NATU molecule. Reaction of Cl.−2 radicals (k = 4.6 × 109 dm3 mol−1 s−1) at pH 1 was found to give a transient species with λmax at 400 nm. At the same pH, reaction of OH radicals also gave transient species, having a similar spectrum, but the yield
was lower. This showed that OH radicals react with NATU by two mechanisms, viz., one-electron oxidation, as well as addition to the allylic double bond. From the absorbance values at 410 nm, it has been
estimated that around 38% of the OH radicals abstract H atoms and the remaining 62% of the OH radicals add to the allylic
double bond. 相似文献
7.
Salts ofN-(β-hydroxyalkyl)-N′-hydroxydiazeneN-oxides, RCH(OH)CH2N(O)=NO− M+ (R=Me, Pri, or But; and M=Li, Na, K, Ag, NH4, or Me4N), were prepared. Their alkylation with alkyl halides R′X (X=Cl, Br, or I) and dimethyl sulfate was studied. Generally, alkylation
afforded mixtures ofN-(β-hydroxyalkyl)-N′-alkoxydiazeneN-oxides RCH(OH)CH2N(O)=NOR′ andO-alkyl-N-(β-hydroxyalkyl)-N-nitrosohydroxylamines RCH(OH)CH2N(NO)OR′.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1996–2001, October, 1998. 相似文献
8.
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
9.
Mid-infrared (4000-400 cm−1) absorption and Raman (4000-95 cm−1) spectra of the series of geometrically frustrated materials, botallackite-structure basic copper halides, α-Cu2(OH)3Cl and α-Cu2(OH)3Br polycrystalline samples were first, to the best of our knowledge, measured, respectively, to study the corresponding relationship between their vibrational spectral properties and crystal microstructures. Through the comparative analysis to the four spectra, the authors have definitely assigned or tentatively suggested the vibrational modes of hydroxyl groups in the trimeric hydrogen bond environment (OH)3 Cl/Br, and atomic units O-Cu-O, Cu-O and Cl/Br-Cu-Cl/Br, etc. These results can be propitious to the low temperature spectral property of α-Cu2(OH)3Cl and α-Cu2(OH)3Br which must help to understand the underlying physics of their exotic geometric frustration phenomena at low temperatures. 相似文献
10.
R. G. Gasanov 《Russian Chemical Bulletin》2000,49(1):46-49
The rate constants for reactions of Cl abstraction from CCl4 by CCl3CH2·CHR radicals and Br abstraction from CCl3CH2CHBrR (R=Bun, AcO, OCNC4H8, CN) by·Re(CO)5 radicals were determined by ESR spectroscopy using spin trapping technique. Replacement of H atoms at the C(β) atom by O
or N atoms reduces the reactivity of the radicals in the reactions of Cl abstraction from CCl4 by approximately an order of magnitude. The presence of two polar groups at the C(β) atom results in appreciable decrease
in the strength of the C−Br bond in CCl3CH2CHBrR adducts.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 45–48, January, 2000. 相似文献
11.
R. G. Gasanov 《Russian Chemical Bulletin》1990,49(1):46-49
The rate constants for reactions of Cl abstraction from CCl4 by CCl3CH2·CHR radicals and Br abstraction from CCl3CH2CHBrR (R=Bun, AcO, OCNC4H8, CN) by·Re(CO)5 radicals were determined by ESR spectroscopy using spin trapping technique. Replacement of H atoms at the C(β) atom by O
or N atoms reduces the reactivity of the radicals in the reactions of Cl abstraction from CCl4 by approximately an order of magnitude. The presence of two polar groups at the C(β) atom results in appreciable decrease
in the strength of the C−Br bond in CCl3CH2CHBrR adducts.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 45–48, January, 2000. 相似文献
12.
Puspalata Rajesh G. R. Dey D. B. Naik K. Kishore 《Research on Chemical Intermediates》2008,34(1):53-65
Reactions of 2- and 3-nitro anilines (2- and 3-NA) with eaq−, H-atoms and one-electron reductants have been studied using pulse radiolysis in aqueous solutions. Reactions of eaq− were found to be quite fast with both 2-NA and 3-NA resulting in their corresponding semi-reduced species which are reducing
in nature. Reduction potentials for 2-NA/2-Na•′ have been estimated to be approx. −0.56 Vvs. NHE and that for 3-NA/3-NA•− was found to be between −0.185 V and −0.45 Vvs. NHE. Semi-reduced 2-NA has main absorption peak at 300 nm with a shoulder in the 350 nm region and a broad weak band in
the 470–500 nm region, whereas semi-reduced 3-NA possesses an absorption peak at 520 nm. Reducing radicals such as (CH3)2 C•OH and CO2•− reacted with 2-NA, producing semi-reduced species, whereas reactions of these radicals with 3-NA produced their corresponding
radical-adduct species. 相似文献
13.
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
14.
The pulse radiolysis of FA and FA:water solutions was studied in the absence and presence of redox indicator 1,1′-dimethyl-4,4′-bipyridinium
dichloride (methyl viologen, MV2+). The experiments performed in the presence of MV2+ have provided strong support to the idea that the first species obtained from the reaction of esol− and •OH with FA produces radicals that show reactivity towards the MV2+. Both the radicals on reaction with MV2+ results in the appearance of the well-known intense blue MV•+ radical absorption signal (λmax = 395 nm, λmax = 605 nm). The intermediate radicals formed during radiolysis were used to generate silver nanoparticles. 相似文献
15.
The stoichiometric equilibrium constants, K
3
*
, for the formation of CuX
3
2−
from CuX
2
−
+X− where X=Cl and Br, have been determined from spectral measurements. The measurements were made in NaCl and NaBr solutions
from I=0.5 to 6.0m at 5, 25 and 45°C. The measured constants were extrapolated to infinite dilution using the Pitzer equations.
The Pitzer parameters, β0, β1 and Cφ, for the interaction of Na+ with CuX
2
−
and CuX
3
2−
are briefly discussed. 相似文献
16.
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
17.
Reaction rate constants for the reactions of 3-pyridinol with oxidizing radicals viz. OH, N3, Br
2
–
, Cl
2
–
, SO
4
–
and O– have been determined in aqueous solutions at different, pH's. Absorption spectra of the product transient species have been recorded in the 320–600 nm region. In the alkaline region (pH 13) the N3 reaction product decays in two steps and O– does not bring about one-electron oxidation. Similarly, at neutral pH, SO
4
–
does not cause selective one-electron oxidation of 3-pyridinol. 相似文献
18.
E. T. Denisov 《Russian Chemical Bulletin》1998,47(11):2110-2116
A parabolic model of bimolecular radical reactions was used for analysis of the hydrogen transfer reactions of ketyl radicals:
>C·OH+R1COR2→>C=O+R1R2C·OH. The parameters describing the reactivity of the reagents were calculated from the experimental data. The parameters
that characterize the reactions of ketyl and alkyl radicals as hydrogen donors with olefins and with carbonyl compounds were
obtained: >C·OH+R1CH=CH2→>C=O+R1C·HCH3; >R1CH=CH2+R2C·HCH2R3→R2C·HCH3+R2CH=CHR3. These parameters were used to calculate the activation energies of these transformations. The kinetic parameters of reactions
of hydrogen abstraction by free radicals and molecules (adelhydes, ketones, and quinones) from the C−H and O−H bonds were
compared.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2178–2184, November, 1998. 相似文献
19.
Dorota Swiatla-Wojcik 《Research on Chemical Intermediates》2009,35(4):519-530
The effect of pH and associated ionic strength on the primary yields in the radiolysis of pressurised water has been assessed
by diffusion-kinetic calculations for temperatures in the range 100–300°C. Account has been taken for ionic strength I up to 0.1 mol kg−1, assuming that the counter ions of H+ in acid solutions and of OH− in base solutions have unit charge. In acid solutions, the H+ ions react with e−
aq. The decrease in G(e−
aq) and the increase in G(H) with decreasing pH becomes substantial for [H+] ≥ 1 × 10−4 m, but the primary yields of oxidising species are almost constant. In alkaline solutions, the OH− anions affect the spur chemistry of radiation-generated protons and hydroxyl radicals for [OH−] ≥ 1 × 10−4 m. The scavenging of H atoms and hydrogen peroxide becomes significant for [OH−] ≥ 1 × 10−2 m. The total yields G(OH) + G(O−) and G(H2O2) + G(HO2
−) are independent of base concentration below 0.01 m. In more alkaline solutions, G(OH) + G(O−) increases, whereas G(H2O2) + G(HO2
−) decreases with increasing [OH−]. Calculations showed the substantial yield of the reaction O− + e−
aq in 0.1 m base solution. Spur chemistry in alkaline hydrogenated water is not affected by the presence of H2 if less than 0.001 m of hydrogen is added. 相似文献
20.
At near neutral pH (approx. 5.5), the OH-adduct of chlorogenic acid (CGA), formed on pulse radiolysis of N2O-saturated aqueous CGA solutions (λ
max = 400 and 450 nm) with k = 9 × 109 dm3 mol−1 s−1, rapidly eliminates water (k = 1 × 103 s−1) to give a resonance-stabilized phenoxyl type of radical. Oxygen rapidly adds to the OH-adduct of CGA (pH 5.5) to form a
peroxyl type of radical (k = 6 × 107 dm3 mol−1 s−1). At pH 10.5, where both the hydroxyl groups of CGA are deprotonated, the rate of reaction of · OH radicals with CGA was
essentially the same as at pH 5.5, although there was a marked shift in the absorption maximum to approx. 500 nm. The CGA
phenoxyl radical formed with more specific one-electron oxidants, viz., Br
2
·−
and N
3
·
radicals show an absorption maximum at 385 and 500 nm, k ranging from 1–5.5 × 109 dm3 mol−1 s−1. Reactions of other one-electron oxidants, viz., NO
2
·
, NO· and CCl3OO· radicals, are also discussed. Repair rates of thymidine, cytidine and guanosine radicals generated pulse radiolytically at
pH 9.5 by CGA are in the range of (0.7–3) × 109 dm3 mol−1 s−1. 相似文献