- Comparison of the Electrochemical and Enzymic Oxidation of 1,3,7-Trimethyluric Acid at Solid Electrodes
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The electrochemical oxidation of 1,3,7-trimethyluric acid has been studied in phosphate buffers in the pH range 2.1-10.2 at solid electrodes. In cyclic voltammetry a single, well defined, pH-dependent oxidation peak was obtained at all of the three electrodes used. However, the reduction behavior of the oxidation product was different at pyrolytic graphite, glassy carbon (GCE), and platinum due to adsorption at PGE and GCE. The nature of the electrode reaction was established as EC, in which a charge transfer is followed by competitive chemical reactions. The formation of the same UV-absorbing intermediate and products and identical rate constants for the decay of the UV-absorbing intermediate indicated that the electrochemical oxidation of 1,3,7-trimethyluric acid proceeds by an identical mechanism at PGE, GCE, and Pt. The results of a peroxidase-catalyzed oxidation of 1,3,7-trimethyluric acid were compared with the electrochemical oxidation; it is concluded that both of the oxidations follow a similar pathway.
- Goyal, Rajendra Nath,Jain, Ajay Kumar,Jain, Neena
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- Microwave-assisted facile synthesis of dispiro 4-imino-1,3-dioxolanes
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The condensation reactions of isocyanides 1 with 1,3-dimethyl alloxan 2 to afford dispiro 4-imino-1,3-dioxolane heterocycles, in excellent yields under microwave irradiation, are reported.
- Teimouri, Mohammad Bagher
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- PHOTOPROXIMITY PROFILING OF PROTEIN-PROTEIN INTERACTIONS IN CELLS
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Photoactive probes and probe systems for detecting biological interactions are described. The photoactive probes include probes that combine both photocleavable and photoreactive moieties. The photoactive probe systems can include a first probe comprising a photocatalytic group and a second probe comprising a group that can act as a substrate for the reaction catalyzed by the photocatalytic group. The probes and probe systems can also include groups that can specifically bind to a binding partner on a biological entity of interest and a detectable group or a precursor thereof. The probes and probe systems can detect spatiotemporal interactions of proteins or cells. In some embodiments, the interactions can be detected in live cells. Also described are methods of detecting the biological interactions.
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Page/Page column 114; 117
(2021/04/01)
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- Kharasch reaction: Cu-catalyzed and non-Kharasch metal-free peroxidation of barbituric acids
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It was discovered that the Kharasch peroxidation of barbituric acids proceeds both with a Cu-catalyst and without a metal catalyst. Despite the presence of possible thermal-initiated side oxidation pathways, α-tert-butylperoxybarbiturates were selectively prepared from substituted barbituric acids and tert-butyl hydroperoxide.
- Bityukov, Oleg V.,Vil, Vera A.,Sazonov, George K.,Kirillov, Andrey S.,Lukashin, Nikita V.,Nikishin, Gennady I.,Terent'ev, Alexander O.
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supporting information
p. 920 - 924
(2019/02/27)
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- Catalytic Amine Oxidation under Ambient Aerobic Conditions: Mimicry of Monoamine Oxidase B
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The flavoenzyme monoamine oxidase (MAO) regulates mammalian behavioral patterns by modulating neurotransmitters such as adrenaline and serotonin. The mechanistic basis which underpins this enzyme is far from agreed upon. Reported herein is that the combination of a synthetic flavin and alloxan generates a catalyst system which facilitates biomimetic amine oxidation. Mechanistic and electron paramagnetic (EPR) spectroscopic data supports the conclusion that the reaction proceeds through a radical manifold. This data provides the first example of a biorelevant synthetic model for monoamine oxidase B activity.
- Murray, Alexander T.,Dowley, Myles J. H.,Pradaux-Caggiano, Fabienne,Baldansuren, Amgalanbaatar,Fielding, Alistair J.,Tuna, Floriana,Hendon, Christopher H.,Walsh, Aron,Lloyd-Jones, Guy C.,John, Matthew P.,Carbery, David R.
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supporting information
p. 8997 - 9000
(2015/08/03)
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- Fenton chemistry of 1,3-dimethyluracil
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Hydroxyl radicals were generated in the Fenton reaction at pH 4 (Fe2+ + H2O2 → Fe3+ + ?OH + OH-, k ≈ 60 L mol-1 s-1) and by pulse radiolysis (for the determination of kinetic data). They react rapidly with 1,3-dimethyluracil, 1,3-DMU (k = 6 × 109 L mol-1 s-1). With H2O2 in excess and in the absence of O2, 1,3-DMU consumption is 3.3 mol per mol Fe2+. 1,3-DMUglycol is the major product (2.95 mol per mol Fe2+). Dimers, prominent products of ?OH-induced reactions in the absence of Fe2+/Fe3+ (Al-Sheikhly, M.; von Sonntag, C. Z. Naturforsch. 1983, 31b, 1622) are not formed. Addition of ?OH the C(5)-C(6) double bond of 1,3-DMU yields reducing C(6)-yl 1 and oxidizing C(5)-yl radicals 2 in a 4:1 ratio. The yield of reducing radicals was determined with tetranitromethane by following the buildup of nitroform anion. Reaction of 1 with Fe3+ that builds up during the reaction or with H2O2 gives rise to a short-chain reaction that is terminated by the reaction of Fe2+ with 2, which re-forms 1,3-DMU. In the presence of O2, 1.1 mol of 1,3-DMU and 0.6 mol of O2 are consumed per mol Fe2+ while 0.16 mol of 1,3-DMU-glycol and 0.17 mol of organic hydroperoxides (besides further unidentified products) are formed. In the presence of O2, 1 and 2 are rapidly converted into the corresponding peroxyl radicals (k = 9.1 × 108 L mol-1 s-1). Their bimolecular decay (2k = 1.1 × 109 L mol-1 s-1) yields ~22% HO2?/O2?- in the course of fragmentation reactions involving the C(5)-C(6) bond. Reduction of Fe3+ by O2?- leads to an increase in ?OH production that is partially offset by a consumption of Fe2+ in its reaction with the peroxyl radicals (formation of organic hydroperoxides, k ≈ 3 × 105 L mol-1 s-1; value derived by computer simulation).
- Theruvathu,Aravindakumar,Flyunt,Von Sonntag,Von Sonntag
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p. 9007 - 9014
(2007/10/03)
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- N,N-Dialkylalloxans - a new class of catalyst for dioxirane epoxidations
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N,N-Dimethyl- and N,N-dibenzylalloxans 1a and 1b have been prepared and used as novel dioxirane catalysts for the epoxidation of a range of di- and tri-substituted alkenes in good to excellent yield. The dibenzylalloxan 1b can be recovered in high yield with no evidence of catalyst decomposition.
- Carnell, Andrew J.,Johnstone, Robert A. W.,Parsy, Christophe C.,Sanderson, William R.
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p. 8029 - 8032
(2007/10/03)
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- Kinetics of Oxidation of Caffeine by Bromamine-B in HCl Medium
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Kinetics of oxidation of caffeine by sodium N-bromobenzenesulphonamide (bromamine-B; BAB) in HCl medium have been studied at 288 K. The rate shows a first order dependence on [BAB], fractional orders in [H+] and [Cl-] and is independent of [caffeine]. Addition of the reaction product, benzenesulphonamide and variation of ionic strength of the medium have no effect on rate. A decrease of the dielectric constant of the medium decreased the rate constant. The solvent isotope effect has been studied in D2O medium. Activation parameters have been evaluated from the Arrhenius plots. Mechanisms proposed and the derived rate laws are in agreement with the observed kinetics.
- Puttaswamy,Mayanna
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- Photosensitized Oxidation of Oxopurines by Rose Bengal
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Photosensitized oxidations of oxopurines (OP) as caffeine, theophylline, theobromine and 1,3,7-trimethyluric acid (TMU) by Rose Bengal were investigated. In all cases photooxidations occur by a type II mechanism. Reactive and nonreactive 1O2 quenching rate constants by OP were determined in different solvents. Based on the correlations of the rate constants with different solvent parameters (α, β, ET[30], AN, DN, π*, ∈), the initial formation of an exciplex between 1O2 and OP is proposed that evolves to a zwitterionic transition state. Some reaction products were characterized, among them 3-methyl-5-(methylamine)-1,5-dehydrohydantoin was obtained as the main photooxidation product of TMU. A reaction mechanism is proposed for the formation of this and other reaction products.
- Murgida, Daniel H.,Aramendia, Pedro F.,Erra Balsells, Rosa
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p. 467 - 473
(2007/10/03)
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- Oxidation of caffeine by sodium N-bromo-p-toluene sulphonamide in HCl medium
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Kinetics of oxidation of caffeine by sodium N-bromo-p-toluenesulphonamide (BAT) in HCl medium has been studied at 288 K. The rate shows a first order dependence on [BAT], fractional orders in [H+] and [Cl-] and is independent of [caffeine]. Addition of the reaction product, p-toluenesulphonamide and varying ionic strength of the medium have no effect on the rate. The rate constant decreases with decrease in the dielectric constant of the medium. The solvent isotope effect has been studied in D2O medium. Activation parameters have been evaluated from the Arrhenius plots. The proposed reaction mechanism and the derived rate laws are consistent with the observed kinetics.
- Puttaswamy,Mayanna
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p. 225 - 227
(2007/10/03)
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- Electrochemical behaviour of 5-(2-benzothiazolyl hydrazono)-1,3-dimethylbarbituric acid
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The electrochemical oxidation and reduction behaviour of 5-(2-benzothiazolyl hydrazono)-1,3-dimethyl barbituric acid has been studied in the pH range 3.0-11.0 at PGE and dropping mercury electrode.The electrochemical oxidation of hydrazones has not previously been studied in detail.The studies reported on hydrazones earlier deal with their reduction.The mechanisms of electrooxidation and electroreduction are suggested on the basis of spectral studies, coulometry and product identification.
- Malik, Wahid U.,Goyal, R. N.,Rajeshwari, Miss
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