- Facile synthesis of 1,2,3-tricarbonyls from 1,3-dicarbonyls mediated by cerium(IV) ammonium nitrate
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A mild and efficient protocol for the synthesis of vicinal tricarbonyl compounds from β-dicarbonyls in a single step using cerium(IV) ammonium nitrate as a catalytic oxidant is described. Ease of execution, wide substrate scope and the suitability for the synthesis of commercially important compounds like ninhydrin, alloxan and oxoline make this reaction particularly noteworthy.
- Sivan, Akhil,Deepthi, Ani
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supporting information
p. 1890 - 1893
(2014/03/21)
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- pH dependent photooxygenation of xanthine and uric acid
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Photooxygenation of xanthine and uric acid has been carried out by singlet oxygen in presence of methylene blue and rose bengal respectively in different media (neutral, acidic, alkaline) at different pH giving various products, which have been characterized by spectral data and elemental analysis.
- Jain, Shubha,Kushwah, Archana,Jaiswal, Anjna
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p. 1289 - 1293
(2013/01/15)
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- Catalytic strategies for sustainable oxidations
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Several catalytic protocols for the oxidation of hydro-soluble substrates are presented that employ totally inorganic and robust polyoxometalate-based catalysts as well as porphyrin sensi-tizers, fullerenes and hybrid conjugates. Strategies for the imple-mentation of the system stability and efficiency are discussed.
- Carraro, Mauro,Sartorel, Andrea,Scorrano, Gianfranco,Carofiglio, Tommaso,Bonchio, Marcella
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experimental part
p. 1971 - 1978
(2009/04/07)
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- Electrochemical oxidation of guanosine-5'-monophosphane at the pyrolytic graphite electrode
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The electrochemical oxidation of guanosine-5'-monophosphate has been investigated in phosphate containing supporting electrolytes at pH 2.5-10.8 at a pyropytic graphite electrode by cyclic sweep voltammetry, spectral studies, controlled potential electrolysis and related techniques. The initial course of the electrode reaction has been deduced to involve a pH dependent 4e, 4H+ oxidation to give a diimine species which undergoes a series of chemical reactions to give different products. The kinetics of the decay of the UV-absorbing intermediate generated during electrooxidation has been studied at different pH values and first-order rate constants for the disappearance of the UV-absorbing intermediate have been calculated. The electrooxidation of guanosine-5'-monophosphate has been found to be an EC reaction (electrode reaction followed by chemical reactions) in which charge transfer is followed by competitive chemical reactions. The ultimate products of oxidation, urea riboside phosphate, alloxan (pyrimidine-2,4,5,6-(1H,3H)-tetraone) and a dimer were characterized by IR. 1H NMR and mass spectrometry at pH 3.4. A detailed interpretation of the redox mechanism for the formation of these products is presented.
- Gohal, Rajendra N.,Puri, Bal K.,Jain, Neena
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p. 832 - 837
(2007/10/03)
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- Voltammetric and chronoamperometric investigations on the oxidation of 7-methylxanthine
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Electrooxidation of 7-methylxanthine has been studied at pyrolytic graphite electrode in phosphate to be buffers of pH 2.0-10.9. A well defined 4e, 4H+ oxidation peak was noticed and an unstable diimine is formed whose half life has been found to be 40 ms by chronoamperometry. The reaction has been identified as EC in which charge transfer is followed by chemical reactions. The products have been characterized by m.p., 1HNMR and mass spectrum and a tentative reaction mechanism for their formation is suggested.
- Goyal, Rajendra N.,Singhal, Naveen K.
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- Comparison of electrochemical and enzymic oxidation of 7,9-dimethyluric acid
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The oxidation of 7,9-dimethyluric acid has been studied in aqueous phosphate buffers in the pH range 2.3-10.0 at a variety of solid electrodes. The conjugate base is found as the electroactive species which on 2e, H+ oxidation gives an unstable diimine. The attack of water molecule on the diimine in a follow up chemical reaction gives a UV-absorbing intermediate which decomposes in a pseudo-first order reaction to give alloxan and 1,3-dimethylurea at pH 3.0 and 1,3-dimethylallantoin and 1,3-dimethyl-5-hydroxyhydantoin-5-carboxamide at pH 7.2. The electrochemical behaviour of dimethyluric acid at PGE, GCE and Ft electrodes is the same. A comparison of electrochemical behaviour with unsubstituted uric acid indicates that methyl groups at positions 7 and 9 shift the Ep towards less positive potential. However, the overall course of electrode reaction remains unchanged. The peroxidase catalysed oxidation of 7,9-dimethyluric acid also exhibites the same spectral and kinetic behaviour and hence it is concluded that electrochemical and enzymic oxidation proceed by an identical EC mechanism.
- Goyal, Rajendra N.,Singhal, Naveen
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p. 276 - 282
(2007/10/03)
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- Electrochemical and peroxidase catalysed oxidation of 9-β-D-ribofuranosyluric acid 5′-monophosphate
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The electrochemical oxidation of 9-β-D-ribofuranosyluric acid 5′-monophosphate (UA-9R-5′-P) in aqueous solution has been studied in the pH range 2.10-10.0. The evidence strongly indicates that UA-9R-5′-P is oxidized in a 2e-, 2H+ reaction to give an unstable diimine which subsequently decomposes. A UV absorbing intermediate is observed during electrooxidation which decays in a pseudo first-order reaction to give alloxan, urea and ribosyl phosphate at pH 3.0. Controlled potential electrolysis results in the transfer of 2.0 ± 0.2 electrons per molecule and three major products are obtained at pH 7.0; allantoin, 5-hydroxyhydantoin-5-carboxamide and D-ribose. Tentative reaction schemes are proposed to explain the formation of these products. Oxidation of UA-9R-5′-P in the presence of peroxidase and H2O2 also generates an intermediate which has spectral and kinetic properties identical to those of the intermediate generated electrochemically. Thus, it is believed that electrochemical and enzymic oxidation of UA-9R-5′-P proceed by identical reaction mechanisms.
- Goyal, Rajendra N.,Rastogi, Arshi
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p. 2423 - 2429
(2007/10/03)
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- Differential pulse voltammetric investigations of uric acid in aqueous and micelle systems
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Differential pulse voltammetric behaviour of uric acid has been studied in phosphate buffers of pH 2.3- 11.2 at glassy carbon electrode. A well-defined 2e, 2H+, pH-dependent oxidation peak has been noticed and the conjugate base found as the electroactive species. Cationic surfactants have been found to significantly affect the Ep and ip. At concentrations below CMC, the change in Ep is predominantly due to adsorption effects, whereas at concentrations above CMC electrocatalysis and micellar catalysis shifted the Ep towards less positive potentials. The voltammetric behaviour in the presence of surfactants indicates that the 2e oxidation proceeds in two le steps and the formation of cationic free radical is suggested. The products of electrode reaction have been found to be the same in aqueous and micelle systems.
- Goyal, Rajendra N.,Ahmad, Shakeel,Rastogi, Arshi
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p. 283 - 289
(2007/10/03)
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- Electrochemical and enzymic oxidation of 9-methyluric acid at solid electrodes
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The electrochemical oxidation of 9-methyluric acid has been studied in the pH range 2.0-11.3 at pyrolytic graphite, platinum and glassy carbon electrodes.The oxidation was found to occur in a single 2e-, H+ pH-dependent reaction at all the three electrodes.Adsorption complications were observed at the pyrolytic graphite and glassy carbon electrodes whereas no such behaviour was observed at platinum.The UV-spectral changes and the kinetics of the decay of the UV-absorbing intermediate generated during the reaction were found to be essentially the same at all the three electrodes.The peroxidase catalyzed oxidation of 9-methyluric acid was also found to be similar to the electrochemical oxidation.The products of oxidation were the same at all the electrodes suggesting thereby that adsorptive action at the surface of PGE and GCE did not affect the EC mechanism
- Goyal, Rajendra N.,Jain, Ajay K.,Jain, Neena
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p. 1055 - 1062
(2007/10/02)
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- Rate of Decomposition of Murexide in Mixed Solvents: An Indicator for Proton Activity
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The rate of decomposition of murexide depends strongly on the proton concentration.The observed rate constant correlates well with the relative permittivity of the solvent.This correlation is established by measurements in binary mixtures of water-dioxane and water-ethanol between 20 and 40 deg C and may be applied to the estimation of the proton concentration in the aqueous domains of microemulsions.
- Barrabass, Susanne,Stickdorn, Katrin,Knoche, Wilhelm
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p. 637 - 642
(2007/10/02)
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- Analysis of oxidative cytosine products in DNA exposed to ionizing radiation
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From ionizing radiation studies, we have previously characterized a large number of modifications of cytosine and 2'-deoxycytidine which arise by way of hydroxyl radical or base radical cation reactions.However, it remains a great challenge today to detect and quantitate these lesions in DNA.In the present work, I have developed a method for the analysis of six oxidation products of cytosine in DNA using HF acid hydrolysis and gas chromatography/mass spectrometry with isotopic dilution.The analysis of gamma-irradiated DNA indicated that uracil 5,6-glycols 5-hydroxyuracil and 5-hydroxyhydantoin are the major stable decomposition products of cytosine residues, whereas alloxane and 1-carbamoyl-2-oxo-4,5-dihydroxy-imidazolidine are formed in comparatively lower yields.These results suggest that the major pathway of OH radical induced decomposition of cytosine in DNA involves initial deamination of intermediate 5-hydroxy-6-hydroperoxides. - Keywords: Oxidative DNA damage, mass spectrometry, isotopic dilution, mutagenesis.
- Wagner, J. R.
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p. 1280 - 1286
(2007/10/02)
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- Electrochemical and enzymatic oxidation of 7-methyluric acid
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The electrochemical oxidation of 7-methyluric acid has been studied in phosphate buffers (pH range 3.2-11.2) at pyrolytic graphite electrode.In linear and cyclic sweep voltammetry, 7-methyluric acid exhibited one well defined 2e, 2H(1+) pH dependent oxidation peak.The pseudo first order rate constants for the decay of UV absorbing intermediate have been calculated at different pH.At pH 3.2 products of electrooxidation were characterised to be alloxan and methyl urea whereas at pH 7.0 the major products of oxidation were found to be methylated allantoin and 1-methyl-5-hydroxyhydantoin-5-carboxamide.The enzymatic oxidation of 7-methyluric acid also indicated behaviour similar to electrochemical oxidation.Tentative EC mechanism for the oxidation has also been suggested.Key Words: purines / 7-methyluric acid / electrochemical oxidation
- Goyal, R. N.,Bansal, V.,Verma, M. S.
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p. 146 - 153
(2007/10/02)
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- Oxidation chemistry of 2,8-dihydroxyadenine at a pyrolytic graphite electrode
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The electrochemical oxidation of 2,8-dihydroxyadenine has been studied at a pyrolytic graphite electrode in the pH range 3.0-11.2.The oxidation of 2,8-dihydroxyadenine proceeds in a single 2e, 2H+ step to give the corresponding diimine, which on follow up chemical reactions gives allantoin at pH 7.5 and parabanic acid, alloxan and urea at pH 3.0.An EC mechanism for the electrochemical oxidation of 2,8-dihydroxyadenine has also been suggested.
- Goyal, R. N.,Mittal, Alok
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p. 852 - 856
(2007/10/02)
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- Oxidation Chemistry of Adenine and Hydroxyadenines at Pyrolytic Graphite Electrodes
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The electrochemical oxidation of adenine and hydroxyadenines has been studied in aqueous solutions in the pH range 3.0-11.2 using a pyrolytic graphite electrode.The initial course of the electrode reaction has been deduced to involve a 2e, 2H+ reaction to give 2- and not 8-hydroxyadenine, further oxidation of which gives 2,8-dihydroxyadenine and then diimine species which undergo a series of chemical reactions to give different products.The major products of oxidation at pH 3.0 and parabanic acid (imidazolidinetrione)> and at pH 7.0 have been isolated using HPLC and column chromatography and their structures elucidated by spectroscopic techniques.The probable EC mechanisms for their formation have also been suggested.
- Goyal, Rajendra N.,Kumar, Anoop,Mittal, Alok
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p. 1369 - 1375
(2007/10/02)
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- Electrochemical oxidation of xanthine at solid electrodes
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The electrochemical oxidation of xanthine at glassy carbon electrode (GCE) and pyrolytic graphite electrode (PGE) has been studied in the pH range of 1.8-10.7 and found to proceed in a 4e, 4H(+) reaction via the formation of uric acid at both the electrodes.Cyclic voltammetric behaviour, spectral studies, observed first order rate constant and product identification clearly point out that xanthine initially oxidises in a 2e, 2H(+) reaction to give uric acid which on subsequent oxidation gives the final products.The first order decay of UV absorbing intermediate has been monitored and the products have been identified.A plausible mechanism is suggested on the basis of observed experimental behaviour.
- Goyal, R. N.
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p. 467 - 471
(2007/10/02)
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- Electrochemical Behaviour of 9-Methylxanthine at Glassy Carbon Electrode
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The electrochemical oxidation of 9-methylxanthine at a glassy carbon electrode has been examined in the pH range 1.9 - 10.00 by linear and cyclic sweep voltammetry, coulometry and spectral studies.The products of electrooxidation have been identified and a plausible mechanism is suggested.
- Goyal, R. N.
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p. 343 - 347
(2007/10/02)
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- Electrochemical oxidation of 8-methylxanthine at stationary pyrolyric graphite electrode
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Electrochemical oxidation of 8-methylxanthine has been investigated in phosphate buffers of pH range (1.35-10.71) using various techniques such as linear and cyclic sweep voltammetry, coulometry, controlled potential electrolysis and spectral studies.Linear and cyclic sweep voltammetry of 8-methylxanthine exhibit one well-defined 2e, 2H(+) oxidation peak (Ia).The first order rate constant for the disappearance of UV absorbing intermediate has been calculated.The products of controlled potential electrolysis have been separated in the pH range (1.35-4.57) and identified as alloxan and acetamidine.A tentative mechanism has been proposed to account for the observed experimental results.
- Goyal, R. N.,Kumar, Anoop
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p. 949 - 952
(2007/10/02)
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- On-line electrochemistry/thermospray/tandem mass spectrometry as a new approach to the study of redox reactions: the oxidation of uric acid.
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The electrochemical oxidation pathway of uric acid was determined by on-line electrochemistry/thermospray/tandem mass spectrometry. Intermediates and products formed as a result of electrooxidation were monitored as the electrode potential was varied. Several reaction intermediates have been identified and characterized by tandem mass spectrometry. The tandem mass spectrometric results provide convincing evidence that the primary intermediate produced during the electrooxidation of uric acid has a quinonoid diimine structure. The results indicate that once formed via electrooxidation, the primary intermediate can follow three distinct reaction pathways to produce the identified final products. The final electrochemical oxidation products observed in these studies were urea, CO2, alloxan, alloxan monohydrate, allantoin, 5-hydroxyhydantoin-5-carboxamide, and parabanic acid. The solution reactions that follow the initial electron transfer at the electrode are affected by the vaporizer tip temperature of the thermospray probe. In particular, it was found that at different tip temperatures either hydrolysis or ammonolysis reactions of the initial electrochemical oxidation products can occur. Most importantly, the results show that the on-line combination of electrochemistry with thermospray/tandem mass spectrometry provides otherwise difficult to obtain information about redox and associated chemical reactions of biological molecules such as the structure of reaction intermediates and products, as well as providing insight into reaction pathways.
- Volk,Yost,Brajter-Toth
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p. 1709 - 1717
(2007/10/02)
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