共查询到20条相似文献,搜索用时 171 毫秒
1.
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
2.
The phenyl substituted acridine-1,8-dione (AD) dye reacts with (CH3)2*COH radicals with a bimolecular rate constant of 0.6 × 108 dm3 mol−1 s−1 in acidic aqueous-organic mixed solvent system. The transient optical absorption band (λmax = 465 nm, ɛ = 6.8 × 102 dm3 mol−1 cm−1) is assigned to ADH* formed on protonation of the radical anion. In basic solutions, (CH3)2*COH radicals react with a bimolecular rate constant of 4.6 × 108 dm3 mol−1 s−1 and the transient optical absorption band (λmax = 490 nm, ɛ = 10.4 × 103 dm3 mol−1 cm−1) is assigned to radical anion, AD*−, which has a pKa value of 8.0. The reduction potential value of the AD/AD*− couple is estimated to be between −0.99 and −1.15 V vs NHE by pulse radiolysis studies. The cyclic voltammetric studies showed
the peak potential close to −1.2 V vs Ag/AgCl. 相似文献
3.
E. P. Surovoi S. V. Bin N. V. Borisova 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2010,84(8):1401-1405
During the irradiation of WO3 films d = 7–160 nm thick by light at λ = 320 nm (I = (1.5–7) × 1015 quantum cm−2 s−1), absorption band at λ = 850 nm appeared along with absorption band edge shift to shorter waves. The subsequent irradiation
of samples at λ = 850 nm caused the disappearance of the longwave absorption band. The intrinsic absorption edge of WO3 films was determined (λ = 320 nm). The degree of transformations of WO3 films increased under atmospheric conditions as the intensity of incident light and the time of irradiation (1–140 min) grew
and as film thickness decreased. A mechanism of photochemical transformations of WO3 films was suggested. This mechanism included the generation of electron-hole pairs, the recombination of part of nonequilibrium
charge carriers, the formation of [eVa2+e] centers, and the isolation of photolysis products. 相似文献
4.
5.
The spectral and kinetic parameters of transient species generated in the irradiation of 6-ethoxy-2,2,4-trimethyl-8-nitro-1,2-dihydroquinoline
were examined by stationary and pulse photolysis in the solvents: heptane, acetonitrile, methanol, and ethanol. Upon excitation
of the long-wavelength absorption band (λex > 450 nm), a reversible photochemical reaction was revealed, and the spectral and kinetic parameters of three transient species
observed in the photolysis were characterized (λmax = 390, 400, and 420 nm (acetonitrile), k = 97, 500, and 2000 s−1, respectively). The absorption spectra and the rate constants of the decay of transient species are almost independent of
the medium polarity and the presence of oxygen in the system. The excited state generated during irradiation to the short-wavelength
absorption band (290 < λex < 350 nm) is inactive in the photochemical reaction and deactivates without the formation of transient species. The mechanism
of the reversible photochemical reaction is suggested, which involves the opening of the heterocycle N-C bond upon photoexcitation
of the long-wavelength absorption band and the thermal back reaction. 相似文献
6.
Dimethylgermylene and its Ge=Ge doubly bonded dimer, tetramethyldigermene, have been characterized directly in solution by
308-nm laser flash photolysis in n-hexane solution, as well as 254-nm photolysis in hydrocarbon glasses at t = 77 K. An absorption band maximum of λ
max ≈ 430 nm and molar absorption coefficient of ε ≈ 2,700 M−1 cm−1 have been shown to be attributable to low-temperature glasses, while the absorption band maximum of λ
max ≈ 480 nm and molar absorption coefficient of ε ≈ 2,400 M−1 cm−1 have been shown to be related to dimethylgermylene in n-hexane solution. The molar absorption coefficient of tetramethyldigermene (λ
max ≈ 380 nm) was determined to be ε ≈ 84,000 M−1 cm−1. The germylene is formed via (formal) cheletropic photocycloreversion of 7,7′-dimethylgerma-1,4,5,6-tetraphenyl-2,3-benzo-norbornadiene.
Tetramethyldigermene and 1,2,3,4-tetraphenylnaphthalene in the triplet state were formed, together with dimethylgermylene.
We attempted to explain the various contradictory interpretations of experimental data existing in the literature on this
reaction. 相似文献
7.
K. B. Petrushenko I. K. Petrushenko V. I. Smirnov N. V. Zorina E. Yu. Shmidt 《Russian Chemical Bulletin》2010,59(4):779-783
The electronic absorption spectra of radical cations of dipyrroles with a phenylene bridge were studied by laser flash photolysis
and quantum chemical methods. Intense absorption bands of the radical cations in the visible region (λmax ≈ 500 nm, εmax > 2 · 104 L mol−1 cm−1) are caused by excitation of electrons from single occupied MOs to the LUMO. In the near IR region, calculations predict
additional, relatively intense (f≈ 0.27–0.29) electronic transitions associated with excitation of electrons from low-lying MOs to the single occupied MO. 相似文献
8.
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
9.
The reaction of the · OH radical with the oxalate ion in an acidic aqueous solution was studied by pulse radiolysis. The rate
constant for the reaction of formation of the radical HOOC-COO·(λmax = 250 nm, ɛ = 1800 L mol−1 cm−1) is (5.0±0.5)·107 L mol−1 s−1. In the reaction with the hydrogen ion (k = 1.1·107 L mol−1 s−1), the radical HOOC-COO· is transformed into a nonidentified radical designated arbitrarily as H+(HOOC-COO)· (λmax = 260 nm, ɛ = 4000 L mol−1 cm−1).
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1165–1167, June, 2008. 相似文献
10.
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
11.
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
12.
I. P. Romm A. A. Malkov S. A. Lebedev V. V. Levashova T. M. Buslaeva 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2011,85(2):248-253
The electronic absorption spectra of palladium(II) diacetate (PDA) complexes with phosphines and sulfides (D) with the composition
Pd(OAc)2 · 2D (1: 2) contain an intense charge transfer band at λmax ∼ 300 nm (ɛ ∼ 15 000) and do not absorb in the region of 400 nm. Polynuclear compounds such as PDA trimer [Pd(OAc)2]3, trimer complexes with D, and four- and six-membered palladium metallocyclic compounds formed in the interaction of PDA with
mercaptans absorb at longer wavelengths. The electronic absorption spectra of all the palladium polynuclear compounds (clusters)
contain bands at λmax ∼ 400 nm (ɛ ∼ 1000). The appearance of these bands in the spectra of palladium clusters is evidence of the formation of chemical
bonds between neighboring Pd atoms, although Pd…Pd distances substantially exceed the sum of the covalent radii of palladium
atoms. 相似文献
13.
R. G. Bulgakov Yu. G. Ponomareva Z. S. Muslimov F. G. Valyamova R. A. Sadykov R. F. Tuktarov 《Russian Chemical Bulletin》2007,56(2):211-219
Fullerenyl radicals (FR) RC60
· and chemiluminescence (CL) are generated in the presence of O2 in C60—R3Al (R = Et, Bui) solutions in toluene (T = 298 K). The FR are formed due to the addition of the R· radical, which is an intermediate of R3Al autooxidation, to C60. Mass spectroscopy and HPLC were used to identify EtnC60Hm (n, m = 1–6), EtpC60 (p = 2–6), and dimer EtC60C60Et as stable products of FR transformations. As found by ESR, the EtC60
· radical (g = 2.0037) is also generated by photolysis of solutions obtained after interaction in the (C60— R3Al)—O2 system. In the presence of dioxygen, the FR is not oxidized but yields complexes with O2, which appear as broadening of the ESR signals. Chemiluminescence arising in the (C60—R3Al)—O2 system is much brighter (I
max = 1.86·108 photon s−1 mL−1) than the known background CL (I
max = 6.0·106 photon s−1 mL−1) for the autooxidation of R3Al and is localized in a longer-wavelength spectral region (λmax = 617 and 664 nm). This CL is generated as a result of energy transfer from the primary emitter 3CH3CHO* to the products of FR transformation: RnC60Hm, RpC60, and EtC60C60Et.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 205–213, February, 2007. 相似文献
14.
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
15.
I. A. Mochalov A. N. Lapshin V. A. Nadtochenko V. A. Smirnov N. F. Goldshleger 《Russian Chemical Bulletin》2006,55(9):1598-1604
Axial coordination of fullerenopyrrolidine bearing the donor imidazolyl group, cis-3-(4-imidazolylphenyl)-1-(pyridin-2-yl)[60]fullereno[1,2-c]pyrrolidine (C60∼Im), with zinc meso-tetraphenylporphyrinate (ZnTPP) in an o-dichlorobenzene solution affords a non-covalently bonded donor-acceptor dyad ZnTPP-C60∼Im. The photochemical behavior of the ZnTPP-C60∼Im complex was studied by fluorescence (excitation at λ = 420 nm) and laser kinetic spectroscopy (excitation at λ = 532 nm,
12 ns). The formation constant of the 1: 1 porphyrin-fullerenopyrrolidine complex determined from quenching of ZnTPP fluorescence
assuming static intracomplex quenching is 1.6·104 L mol−1. Absorption spectra of the excited states in the system consisting of ZnTPP and Im∼C60 (ZnTPP/C60∼Im) were measured in solution from 380 to 1000 nm. The quenching constant of the triplet-excited ZnTPP with fullerenopyrrolidine
C60∼Im was determined. The results obtained indicate the formation of the triplet exciplex {PL}* ⇌ {Pδ+…Lδ−} in the ZnTPP/C60∼Im system upon laser photolysis.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1541–1547, September, 2006. 相似文献
16.
M. V. Sultanbaev S. S. Ostakhov Sh. Kh. Gantsev F. A. Khalilullin V. P. Kazakov 《High Energy Chemistry》2010,44(5):383-386
A spectral-luminescent study of the keto-enol tautomerism of 5-fluorouracil (FU) has been performed. A discrepancy between
the absorption and fluorescence (FL) excitation spectra of aqueous FU solutions (pH 7) has been established. Photoexcitation
at the long-wavelength band (340 nm) of the FU excitation spectrum made it possible to detect the fluorescence of its dienol
tautomer (λmax = 440 nm). The quenching of tryptophan fluorescence (K = 15 × 103 l/mol) and blood fluorescence by 5-fluorouracil has been investigated. 相似文献
17.
The formation of neutral Tl2 (λmax = 390 nm) and Tl4 (λmax = 360 nm) clusters in dilute aqueous solutions of Tl2SO4 containing formate ions was found by pulse radiolysis. The rate constants for the recombination of Tl0 atoms and Tl2 clusters are equal to 1.5·1010 L mol−1 s−1 and 1.0·1010Lmol−1 s−1 (±30%), respectively, and the extinction coefficient of Tl2 at 390 nm is −6.0·103 L mol−1 cm−1
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2367–2369, December, 1999. 相似文献
18.
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
19.
Pulse radiolysis of 2-Mercaptobenzothiazole (2-MBT) has been undertaken in aqueous solution. The semi-oxidized species formed
at pH 4.5 due to the reaction of OH•, Br2
•− and N3
• and at pH 10.5 with OH• yielded a spectrum with λmax = 348 and 595 nm. These semi-oxidized species were able to oxidize phenothiazine drugs (Eo⋟0.8 V). Reducing species such as eaq
−, CO2
•− and H• atoms react with 2-MBT resulting in the formation of a transient having λmax = 350 nm and reducing in nature. Kinetic and spectroscopic data of interest are reported. 相似文献
20.
N. Sh. Lebedeva R. S. Kumeev G. A. Al’per E. V. Parfenyuk A. S. Vashurin T. V. Tararykina 《Journal of solution chemistry》2007,36(6):793-801
For the first time the interactions between zinc(II)tetra-4-alkoxybenzoyloxiphthalocyanine (Zn(4—O—CO—C6H4—OC11H23)Pc) and 1,4-diazabicyclo[2.2.2]octane (DABCO) in o-xylene and chloroform have been studied by calorimetric titration and NMR and electron absorption spectroscopic methods.
It has been found that in o-xylene at concentrations of Zn(4—O—CO—C6H4—OC11H23)Pc higher than 6×10−4 mol⋅L−1
π–π dimers species are formed (λ
max= 685 nm). Additions of DABCO to the solution up to mole ratio 1 : 8 (Zn(4—O—CO—C6H4—OC11H23)Pc : DABCO) lead to a shift of the aggregation equilibrium towards monomer species due to formation of monoligand axial complexes.
Further increasing the DABCO concentration results in formation of Zn(4—O—CO—C6H4—OC11H23)Pc—DABCO—Zn(4—O—CO—C6H4—OC11H23)Pc sandwich dimers (λ
max= 675 nm). 相似文献