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1.
Ponnusamy Sami Natarajan Mariselvi Kandasamy Venkateshwari Murugesan Vairalakshmi Arunachalam Sarathi Kasi Rajasekaran 《Transition Metal Chemistry》2010,35(5):563-570
The kinetics of reduction of heteropoly 11-tungstovanadophosphate, [PVVW11O40]4−, (HPA1) and heteropoly 10-tungstodivanadophosphate, [PVVVVW10O40]5−, (HPA2) by thiourea has been investigated in HClO4/phthalate/acetate buffer solutions spectrophotometrically at 25 °C in aqueous medium. The stoichiometry of the reaction is
1:1 in both cases. The HPAs are converted into the corresponding one-electron reduced heteropoly blues, namely, [PVIVW11O40]5− and [PVIVVVW10O40]6−, and thiourea is oxidised to formamidine disulphide. The reaction shows first-order dependence in both [HPA] and [thiourea]
at constant pH. The rate–pH profile shows the participation of both the neutral and deprotonated forms of thiourea in the
reaction. The reaction proceeds through an outer sphere electron transfer mechanism in which activation-controlled electron
transfer is the rate-determining step. Self-exchange rate constants for the couples [PVVW11O40]4−/[PVIVW11O40]5−, [PVVVVW10O40]5−/[PVIVVVW10O40]6− and H2NCSNH2/H2NCS·+NH2 have been evaluated by Marcus theory. 相似文献
2.
Ponnusamy Sami Kandasamy Venkateshwari Natarajan Mariselvi Arunachalam Sarathi Kasi Rajasekaran 《Transition Metal Chemistry》2009,34(7):733-737
The rates of the electron transfer reaction of l-cysteine and thioglycolic acid with the polyoxometalate, [PVVW11O40]4−, have been measured spectrophotometrically in aqueous acid medium. The polyoxometalate oxidizes cysteine to cystine and thioglycolic
acid to dithioglycolic acid and gets reduced to heteropoly blue, [PVIVW11O40]5−. The order of the reaction with respect to oxidant is one, whereas the reaction shows second order dependence on the substrates.
The rate–pH profile shows that both the unionized and ionized thiol groups of the substrates are active species involved in
electron transfer. A suitable mechanism has been proposed for the title reaction based on the results of kinetic studies. 相似文献
3.
Guru C. Pradhan 《Transition Metal Chemistry》1992,17(5):443-445
The kinetics of the base hydrolysis ofcis-[Co(en)2(RNH2)-(SalH)]2+ (R=Me or Et; SalH=HOC6H4CO
2
−
) were investigated in aqueous ClO
4
−
in the 0.004–0.450 mol dm−3 [OH−] range, I=0.50 mol dm−3 at 30–40°C. The phenoxide species is hydrolysed via [OH−]-independent and [OH−]-dependent paths, the latter being first order in [OH−]. The high rate of alkali-independent hydrolysis of the phenoxide species is associated with high ΔH≠ and ΔS≠ values, in keeping with the SNICB mechanism involving an amido conjugate base generated by the phenoxide-assisted NH-deprotonation
of the coordinated amine. The [OH−]-dependent path also involves the conventional SN1 CB mechanism. The rate constant, k1, for the SNICB path exhibits a steric acceleration with the increasing size of the non-labile alkylamine, whereas the rate
constant, k2, for the SN1CB path shows a reverse trend.
TMC 2578 相似文献
4.
C. M. Varghese A. Shunmugasundaram R. Murugesan T. Jey Abalan 《Journal of Chemical Sciences》2002,114(1):75-82
Heteropoly blues of α-1,2 and α-1,4 isomers of [PV2W10O40]5−have been prepared by using the electrochemical technique. EPR spectra, measured as a function of temperature over a wide
range (20-300 K), are explicable in terms of electron-hopping processes in heteropoly blues. Temperature dependence of A∥of
the isomers suggest that the activation energy for electron hopping is greater for the α-1,4 isomer than the α-1,2 isomer.
Other parameters like stability of the blues and intra-molecular electron transfer rate constants are also evaluated using
EPR as the tool. 相似文献
5.
L. G. Detsuheva M. A. Fedotov L. I. Kuznetsova A. A. Vlasov V. A. Likholobov 《Russian Chemical Bulletin》1997,46(5):874-880
Unsaturated heteropolyanions (HPA) [PW11O39]7− stabilize TiIV hydroxo complexes in aqueous solutions (Ti: PW11 [PW11O39]7−⪯12, pH 1–3). Spectral studies (optical,17O and31P NMR, and IR spectra) and studies by the differential dissolution method demonstrated that TiIV hydroxo complexes are stabilized through interactions of polynuclear TiIV hydroxo cations with heteropolyanions [PW11TiO40
5− formed. Depending on the reaction conditions, hydroxo cations Ti
n−1O
x
H
y
m+ either add to oxygen atoms of the W−O−Ti bridges of the heteropolyanions to form the complex [PW11TiO40·Ti
n−1O
x
H
y
]
k−
(at [HPA]=0.01 mol L−1) or interact with TiIV of the heteropolyanions through the terminal o atom to give the polynuclear complexes [PW11O39Ti−O−Ti
n−1O
x
H
y
]q− (at [HPA]=0.2 mol L−1). When the complexes of the first type were treated with H2O2, TiIV ions added peroxo groups.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 914–920, May, 1997. 相似文献
6.
R. F. Vasil’ev V. D. Kancheva G. F. Fedorova D. I. Batovska A. V. Trofimov 《Kinetics and Catalysis》2010,51(4):507-515
Six antioxidants from the class of chalcones (ArOH), compounds from which flavonoids are obtained in nature, were studied.
The antiradical activity of chalcones and a number of related compounds was determined by a chemiluminescence method using
the scavenging of peroxide radicals ROO· + ArOH → ROOH + OAr· (with the rate constant k
7) in a model reaction of diphenylmethane (RH) oxidation. The structures and energies of the reagents and intermediates were
determined by semiempirical quantum chemical (PM3, PM6) calculations. 3,4-Dihydroxychalcone and caffeic acid, which have a
catechol structure, that is, two neighboring OH groups in phenyl ring B, exhibited high antioxidant activity (k
7 ≈ 107 l mol−1 s−1); this is consistent with the lowest bond strengths D(ArO-H) of 79.2 and 76.6 kcal/mol, respectively. The abstraction of a hydrogen atom by the ROO· radical is the main reaction path of these compounds; however, the low stoichiometric coefficients of inhibition (f = 0.3–0.7) suggest a contribution of secondary and/or side reactions of ArOH and OAr·. In the other chalcones, the ArO-H bond is stronger (D(ArO-H) = 83–88 kcal/mol) and the antioxidant activity is lower (k
7 = 104–105 l mol−1 s−1). 相似文献
7.
Two solid complexes, fac–[Cr(gly)3] and [Cr(gly)2(OH)]2, (where gly is glycinato ligand) were prepared and their acid-catalysed aquation products were identified. The structure
of [Cr(gly)3] was solved by X-ray diffraction, revealing a cationic 3D sublattice with perchlorate anions inside its cavities. Acid-catalysed
aquation of [Cr(gly)3] and [Cr(gly)2(OH)]2 leads to the same inert product, [Cr(gly)2(H2O)2]+, in a two-stages process. At the first stage, intermediate complexes, [Cr(gly)2(O–glyH)(H2O)]+ and [Cr(gly)2(H2O)–OH–Cr(gly)2(H2O)]+, are formed respectively. Kinetics of the first aquation stage of [Cr(gly)3] were studied in HClO4 solutions. The dependencies of the pseudo first-order rate constants on [H+] are as follows: k
obs1H = k
0 + k
1
K
p1[H+], where k
0 and k
1 are rate constants for the chelate-ring opening via spontaneous and acid-catalysed reaction paths, respectively, and K
p1 is the protonation constant. The proposed mechanism assumes formation of the reactive intermediate as a result of proton
addition to the coordinated carboxylate group of the didentate ligand. Some kinetic studies on the second reaction stage,
the one-end bonded glycine liberation, were also done. The obtained results were analogous to those for stage I. In this case,
the proposed reactive species are intermediates, protonated at the carboxylate group of the monodentate glycine. Base hydrolysis
of two complexes, [Cr(gly)2(O–gly)(OH)]− and [Cr(gly)2(OH)2]−, was studied in 0.2–1.0 M NaOH. The pseudo first-order rate constants, k
obsOH, were [OH−] independent in the case of [Cr(gly)2(O–gly)(OH)]−, whereas those for [Cr(gly)2(OH)2]− linearly depended on [OH−]. The reaction mechanisms were proposed, where the OH− -catalysed reaction path was rationalized in terms of formation of the reactive conjugate base, [Cr(gly)2(OH)(O)]2−, as a result of OH− ligand deprotonation. Activation parameters were determined and discussed. 相似文献
8.
Kinetics and mechanism of oxidation of ferrocyanide by N-bromosuccinimide in aqueous acidic solution
Alaa Eldin M. Abdel-Hady 《Transition Metal Chemistry》2008,33(7):887-892
The kinetics of oxidation of ferrocyanide by N-bromosuccinimide (NBS) has been studied spectrophotometrically in aqueous acidic medium over temperature range 20–35 °C,
pH = 2.8–4.3, and ionic strength = 0.10–0.50 mol dm−3 over a range of [Fe2+] and [NBS]. The reaction exhibited first order dependence on both reactants and increased with increasing pH, [NBS], and
[Fe2+]. The rate of oxidation obeys the rate law: d[Fe3+]/dt = [Fe(CN)6]4–[HNBS+]/(k
2 + k
3/[H+]). An outer-sphere mechanism has been proposed for the oxidation pathway of both protonated and deprotonated ferrocyanide
species. Addition of both succinimide and mercuric acetate to the reaction mixture has no effect on the reaction rate under
the experimental conditions. Mercuric acetate was added to the reaction mixture to act as scavenger for any bromide formed
to ensure that the oxidation is entirely due to NBS oxidation. 相似文献
9.
Base hydrolysis of [Cr(ox)2(quin)]3− (where quin2− is N,O-bonded 2,3-pyridinedicarboxylic acid dianion) causes successive ligand dissociation and leads to a formation of a
mixture of oligomeric chromium(III) species, known as chromates(III). The reaction proceeds through [Cr(ox)(quin)(OH)2]3− and [Cr(quin)(OH)4]3− formation. Dissociation of oxalato ligands is preceded by the opening of the Cr-quin chelate-ring at the Cr–N bond. The kinetics
of the chelate-ring opening and the first oxalate dissociation were studied spectrophotometrically, within the lower energy
d–d band region at 0.4–1.0 M NaOH. The pseudo-first-order rate constants (k
obs0 and k
obs1) were calculated using SPECFIT software for an A → B → C reaction pattern. Additionally, kinetics of base hydrolysis of [Cr(ox)(quin)(OH)2]3− and cis-[Cr(ox)2(OH)2]3− were studied. The determined pseudo-first-order rate constants were independent of [OH−]. A mechanism is postulated that the reactive intermediate with the one-end bonded quin ligand, [Cr(ox)2(O-quin)(OH)]4−, formed in the first reaction stage, subsequently undergoes oxalates substitution. Kinetic parameters for the chelate-ring
opening and the first oxalate dissociation were determined. 相似文献
10.
The kinetics of the oxidation of promazine and chlorpromazine by hexaimidazolcobalt(III) were studied in the presence of a
large excess of cobalt(III) and H+ ions using u.v.–vis. spectroscopy ([CoIII] = (1–6) × 10−3 m, [ptz] = (2.5–10) × 10−5 m, [H+] = 0.05–0.8 m, I = 1.0 m (H+, Na+, Cl−), T = 333–353 K, l = 1 cm). In each case, the reversible reaction leads to formation of cobalt(II) species and a stable cationic radical. A
linear dependence of the pseudo-first-order rate constant (kobs) on [CoIII] with a non-zero intercept was established for both phenothiazine derivatives. A marked difference in the observed reaction
rate for promazine and chlorpromazine is associated with the difference in its ability to undergo oxidation and is consistent
with a trend in the redox potential changes for these reductants. The activation parameters for reactions studied were determined.
Mechanistic consequences of all the results are discussed. 相似文献
11.
Ewa Kita Hasan Marai Lisiak Michał Miłosz Jasiński Tomasz Drewa 《Transition Metal Chemistry》2010,35(2):177-184
Base hydrolysis of [Cr(ox)2(pda)]3− (where pda is N,O-bonded 2,4- and 2,5- pyridinedicarboxylic acid dianion) causes successive ligand dissociation and leads
to formation of a mixture of oligomeric chromium(III) species, known as chromates(III). The main reaction path proceeds through
[Cr(ox)(pda)(OH)2]3− and [Cr(pda)(OH)4]3− complexes. The kinetics of the first oxalate dissociation was studied spectrophotometrically, within the lower energy d–d
band region, at 0.4–1.0 M NaOH. The character of spectroscopic changes was consistent with a consecutive reaction model, where
the chelate-ring opening and the one-end bonded oxalato liberation are the first and the second reaction stages. The pseudo-first
order rate constants (k
obs0 and k
obs1) were calculated using SPECFIT software for an A → B → C reaction pattern. Additionally, kinetics of base hydrolysis of [Cr(ox)3]3− were studied. The calculated rate constants were independent of [OH
−
]. Kinetic parameters for the chelate-ring opening and the first oxalate dissociation were determined. Effect of the [Cr(ox)2(pda)]3− and [Cr(2,4-pda)3]3− complexes on 3T3 fibroblasts proliferation was studied. The results manifested low cytotoxicity of these complexes, which
makes them promising candidates for dietary supplements. 相似文献
12.
Joanna Wiśniewska 《Transition Metal Chemistry》2007,32(6):811-815
The kinetics of the electron-transfer reactions between promazine (ptz) and [Co(en)2(H2O)2]3+ in CF3SO3H solution ([CoIII] = (2–6) × 10−3
m, [ptz] = 2.5 × 10−4
m, [H+] = 0.02 − 0.05 m, I = 0.1 m (H+, K+, CF3SO
3
−
), T = 288–308 K) and [Co(edta)]− in aqueous HCl ([CoIII] = (1 − 4) × 10−3
m, [ptz] = 1 × 10−4
m, [H+] = 0.1 − 0.5 m, I = 1.0 m (H+, Na+, Cl−), T = 313 − 333 K) were studied under the condition of excess CoIII using u.v.–vis. spectroscopy. The reactions produce a CoII species and a stable cationic radical. A linear dependence of the pseudo-first-order rate constant (k
obs) on [CoIII] with a non-zero intercept was established for both redox processes. The rate of reaction with the [Co(en)2(H2O)2]3+ ion was found to be independent of [H+]. In the case of the [Co(edta)]− ion, the k
obs dependence on [H+] was linear and the increasing [H+] accelerates the rate of the outer-sphere electron-transfer reaction. The activation parameters were calculated as follows:
ΔH
≠ = 105 ± 4 kJ mol−1, ΔS
≠ = 93 ± 11 J K−1mol−1 for [Co(en)2(H2O)2]3+; ΔH
≠ = 67 ± 9 kJ mol−1, ΔS
≠ = − 54 ± 28 J K−1mol−1 for [Co(edta)]−. 相似文献
13.
Kinetics and mechanism of bromide ions oxidation by cerium(IV) in sulphuric acid solutions revisited
Anna Katafias 《Transition Metal Chemistry》2006,31(7):907-911
Kinetics of Br− anion oxidation by cerium(IV) species in aqueous H2SO4 solutions have been reexamined. The rate of reaction was determined spectrophotometrically based on a factor analysis of
the absorbance – time data collected in the wavelength range 318–390 nm – the region characteristic for the cerium(IV) sulphato
complexes. The data fit very well to a pseudo-first order dependence under a large molar excess of the reductant. The rate
law of the form –d[CeIV]/dt = k[CeIV][Br–]2 has been obtained at constant H2SO4 concentration and ionic strength I = 2 m. The pseudo-first order rate constant decreases with an [H2SO4] increase from 0.1 to ca. 0.4 m range, then increases for higher [H2SO4]. The apparent activation parameters have been calculated from the third order rate constants k for different [H2SO4]. 相似文献
14.
Pd(II) complexes and twelfth-series heteropoly acids (HPA) H9[PMo6V6O40] and H3[PMo12O40] supported on silica gel oxidize benzene and toluene at 95°C. The formation of methyldiphenylmethane in the oxidation of
toluene on HPA/SiO2 and (PdCl2−HPA)/SiO2 catalysts, KIE>1 for the toluene/toluene-d8 pair, and greater rate for toluene than for benzene are in accord with a one-electron transfer mechanism.
L. M. Litvinenko Institute of Physical Organic and Coal Chemistry, National Academy of Sciences of Ukraine, 70 R. Lyuksemburg
ul., Donetsk 340114, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 35, No. 4, pp. 249–252, July–August,
1999. 相似文献
15.
The kinetics of oxidation of L-Alanine (Ala) by N-bromophthalimide (NBP) was studied in the presence of an anionic surfactant, sodium dodecyl sulfate, in acidic medium at
308 K. The rate of reaction was found to have first-order dependence on [NBP], fractional order dependence on [Ala] and inverse
fractional order dependence on [H+]. The addition of reduced product of the oxidant [Phthalimide] has decreased the rate of reaction. The rate of reaction increased
with increase in inorganic salts concentration i.e., [Cl−] and [Br−], whereas a change in ionic strength of the medium and [Hg(OAc)2] had no effect on oxidation velocity. The rate of reaction decreased with a decrease in dielectric constant of the medium.
CH3CN was identified as the main oxidation product of the reaction. The various activation parameters have been computed and
suitable mechanism consistent with the experimental findings has also been proposed. The micelle-binding constant has been
calculated.
Published in Russian in Kinetika i Kataliz, 2009, Vol. 50, No. 3, pp. 386–396.
The article is published in the original. 相似文献
16.
Ponnusamy Sami Kandasamy Venkateshwari Natarajan Mariselvi Arunachalam Sarathi Kasi Rajasekaran 《Transition Metal Chemistry》2010,35(2):137-142
l-cysteine undergoes facile electron transfer with heteropoly 10-tungstodivanadophosphate,
[ \textPV\textV \textV\textV \textW 1 0 \textO 4 0 ]5 - , \left[ {{\text{PV}}^{\text{V}} {\text{V}}^{\text{V}} {\text{W}}_{ 1 0} {\text{O}}_{ 4 0} } \right]^{5 - } , at ambient temperature in aqueous acid medium. The stoichiometric ratio of [cysteine]/[oxidant] is 2.0. The products of the
reaction are cystine and two electron-reduced heteropoly blue, [PVIVVIVW10O40]7−. The rates of the electron transfer reaction were measured spectrophotometrically in acetate–acetic acid buffers at 25 °C.
The orders of the reaction with respect to both [cysteine] and [oxidant] are unity, and the reaction exhibits simple second-order
kinetics at constant pH. The pH-rate profile indicates the participation of deprotonated cysteine in the reaction. The reaction
proceeds through an outer-sphere mechanism. For the dianion −SCH2CH(NH3
+)COO−, the rate constant for the cross electron transfer reaction is 96 M−1s−1 at 25 °C. The self-exchange rate constant for the
- \textSCH2 \textCH( \textNH3 + )\textCOO - \mathord