The anodic oxidation of uranocene. Evidence for a reactive dication (original) (raw)
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339 - Electrochemical and enzymatic oxidation of 3,9-dimethyl uric acid
Bioelectrochemistry and Bioenergetics, 1980
Manuscript received October Sth rg7g The electrochemical oxidation of 3,g-dimethyl uric acid in aqueous solution has been studied between pH 3-3 and 5.8 at graphite electrodes. A single z e-r H+ oxidation voltammetric peak is observed corresponding to the formation of a very unstable cationic diimine intermediate-This reacts very rapidly with water to give an imino-alcohol intermediate. The latter intermediate may be observed as a U-V_-absorbing species (& = zgo nm between pH 3.3-S-8) and by means of its voltammetric reduction peak noted on cyclic voltammetry of 3,g-dimethyl uric acid. The location of the absorption spectrum of this imino-alcohol has been used to deduce its probable structure and the structures of imino-alcohol intermediates formed on o_xidation of other uric acid derivatives_ Hydration of the imino-alcohol gives the +,5-die? of 3,g-dimethyl uric acid which decomposes to the final reaction products_ The observed firstorder rate constant for the latter reaction between pH 3-3 and SS is 0.20 + O-05 s-r. _ O_xidation of 3.g-dimethyl uric acid in the presence of peroxidase and H,O, gives rise to an intermediate which has identical spectral and electrochemical properties and very similar kinetic properties to the imino-alcohol intermediate generated electrochemically. Accordingly, it appears that the electrochemical and pero_xidase-catalyzed oxidations of 3.g-dimethyl uric acid proceed via identical reaction mechanisms.
Investigation of the enzymic and electrochemical oxidation of uric acid derivatives
Biochimica et Biophysica Acta (BBA) - Enzymology, 1979
The electrochemical oxidation of a number of N-methylated uric acids at the pyrolytic graphite and gold electrodes has been compared to their enzymic oxidation with type VIII peroxidase and H~O~. Spectral, electroanalytical and kinetic evidence supports the conclusion that for all compounds the electrochemical and enzymic reactions proceed by identical mechanisms.
1989
5-Chloro-7-methyl-A4*9-isouric acid (11) has been chemically synthesized and shown to be rapidly converted to 5-hydroxy-7-methyl-A4~9-isouric acid (14) in aqueous buffers at ca. pH 7. The physical and chemical properties of 14 in solution have been elucidated. Electrochemical oxidation of 7-methyluric acid (10) at its first volt-etric oxidation peak forms a UV-absorbing intermediate. This intermediate exhibits physical and chemical properties which are identical to those of 14. These observations provide the first unequivocal evidence for the chemical structure of a UV-absorbing intermediate formed upon electrochemical oxidation of any purine.
Bioelectrochemistry and Bioenergetics, 1982
Electrochemical oxidation of uric acid in phosphate-containing supporting electrolytes between pH 3-9 at a reticulated vitreous carbon electrode in a thin-layer spectroelectrochemical cell leads to formation of U.V.-absorbing intermediate species. Electrochemical reduction of the intermediate-containing solution leads to the partial regeneration of uric acid. This behavior provides compelling evidence that an imine-alcohol is one of the U.V.-absorbing intermediate species since only this compound may be expected to be reduced to a species which can regenerate uric acid.
Electrochemical Activation and Functionalization of the Uranyl Ion
Interconversion of the oxidation states of uranium enables separations and reactivity schemes involving this element and contributes to technologies for recycling of spent nuclear fuels. The redox behaviors of uranium species impact these processes, but use of electrochemical methods to drive reactions of well-defined precursors and to obtain molecular insights into the outcomes has received less attention than it deserves. Here, we show that electro-reduction of the uranyl ion (UO22+) can be used to promote stepwise functionalization of the typically unreactive oxo groups with exogenous triphenylborane (BPh3) serving as a moderate electrophile. Parallel electroanalytical, spectrochemical, and chemical reactivity studies, supported by spectroscopic findings and structural data from X-ray diffraction analysis on key reduced and borylated products, demonstrate that our electrochemical approach largely avoids undesired cross reactions and disproportionation pathways; these conventional...
A comparison of the peroxidase-catalyzed and electrochemical oxidation of uric acid
Bioelectrochemistry and Bioenergetics, 1982
Horseradish peroxidase (type VIII) catalyzed and electrochemical oxidations of 2-thiouracil have been studied in phosphate buffer of pH 7.20 (JL==l.O M) at an ambient temperature of 25±2°C. The peroxidase catalyzed oxidation has been initiated by using hydrogen peroxide and electrooxidation carried out at pyrolytic graphite electrode. The UV-absorbing intermediates generated in both the oxidations have been characterized by voltammetry, spectrophotometry and by kinetics of decay and are found identical. Products of enzymic and electrochemical oxidations have been characterized by using GC-MS stuides. A tentative redox scheme has been proposed for the enzymic oxidation of 2-thiouracil and compared with that of electrooxidation and has also been found similar. Thus, it has been concluded that oxidation of 2-thiouracil by enzymic and electrochemical methods are, in a chemical sense, identical.
Insight into Speciation and Electrochemistry of Uranyl Ions in Deep Eutectic Solvents
The Journal of Physical Chemistry B, 2019
11 Understanding the speciation of metal ions in heterogeneous hydrogen bonded deep eutectic 12 solvents (DES) has immense importance for their wide range of applications in green 13 technology, environmental remediation and nuclear industry. Unfortunately, the fundamental 14 nature of the interaction between DES and actinide ions is almost completely unknown. In the 15 present work, we outline the speciation, solvationmechanism and redox chemistry of uranyl ion 16 (UO 2 2+) in DES consisting of choline chloride (ChCl) and urea as the hydrogen-bond donor. 17 Electrochemical and spectroscopic techniques along with the molecular dynamics(MD) 18 simulations have provided a microscopic insight into the solvation and speciation of UO 2 2+ ion in 19 DESand also on associated changes in physical composition of the DES. The hydrogen bonded 20 structure of DES plays an important role on the redox behavior of UO 2 2+ ion due to its strong 21 complexation with DES components. X-ray absorption spectroscopy (XAS) and MD simulations 22 showed strong covalent interactions of uranyl ions with the constituents of DES which lead to 23 rearrangement of the hydrogen bonding network in it without formation of any clusters or 24 aggregations. This, in turn, stabilizes the most unstable pentavalent uranium (UO 2 +) in the DES. 25 MD analysis also highlights the fact that numbers of H-bonds are reduced in thepresence 26 ofuranyl nitrate irrespective of the presence water with respect to pristineReline, whichsuggests 27 high stability of the formed complexedspecies.The effect of added water upto 20 v/v% on 28 speciation is insignificant for DES but the presence of water influences the redox chemistry of 29 UO 2 2+ ion considerably. The fundamental findings of the present work would have far reaching
Electrochemical and peroxidase-catalysed oxidation of 1-methyluric acid
Bioelectrochemistry and Bioenergetics, 1997
Electrochemical and peroxidase-catalyzed oxidation of epinephrine (EPI) has been studied. In the electrochemical studies a single well-defined, 4e, 4H + , pH-dependent oxidation peak was observed in square wave and cyclic sweep voltammetry at edge plane pyrolytic graphite electrode. In the reverse sweep a redox couple was observed. The decay of the UV-absorbing intermediate generated and the first-order rate constants were calculated at different pH and were found to be ∼6.3 × 10 −3 s −1 . The detection limit and sensitivity are found to be 17 × 10 −8 M and 2.325 A M −1 respectively. At pH 7.2, the electro-oxidation product was characterized using NMR and DEPT studies as leucoadrenochrome. The peroxidase-catalyzed oxidation was carried out using horseradish peroxidase and initiated by adding H 2 O 2 . The identical spectral changes, rate constants and product formed during electrochemical and enzymatic oxidation suggest that the same intermediate species is generated during both the oxidations. A tentative pathway for the oxidation of EPI has been suggested. It is concluded that the electrochemical and peroxidase-catalyzed oxidation of EPI proceed by an identical pathway.
Electrochemical oxidation of 9β-D-ribofuranosyluric acid in basic solution
Journal of Electroanalytical Chemistry and Interfacial Electrochemistry
The electrochemical oxidation of 9-b-D-ribofuranosyhnic acid (UA-9-R) has been studied at the pyrolytic graphite electrode at pH 9.2. The peak I, reaction is a 2 e-l H+ quasi-reveriible process giving an unstable quinonoid which is rapidly attacked by water to give one and perhaps two tertiary alcohol intermediates. In the absence of phosphate these intermediates decompose to give a mixture of S-hydroxyhydantoin-S-carboxamide-3-tiboside, ribose and 4-amino4carboxy-2,5-diketo-imidawle. In the presence of phosphate the putative tertiary alcohol intermediate undergoes a ring contraction to an electrooxidiible bicylic carboxylic acid which decomposes to an allantoin riboside. The carboxylic acid is partially responsible for the second, more positive oxidation peak of UA4-R (peak II,) and in a 2 e-l H+ reaction gives l-hydroxy-2,4,6,8-tetraaul-3,7-dioxo-5-ene-bicycl~3,3.O)-~t~e4~boside. A stable, peak I, product also contributes to the peak II, reaction. It is speculated that this species is a phosphorylated derivative of the bicyclic carboxylic acid. At pH 9.2, in the presence of phosphate, type VIII peroxidase is capable of oxidizing UA-9-R in a reaction chemically equivalent to the peak I, electrochemical process.
Comparison of electrochemical and enzymic oxidation of 1,3-dimethyluric acid
Bioelectrochemistry and Bioenergetics, 1998
Electrochemical oxidation of 1,3-dimethyluric acid has been studied in phosphate buffers of pH 2.3-10.3 at pyrolytic graphite electrode. The conjugate base has been found as the electroactive species and a single well-defined oxidation peak was observed. The presence of methyl groups have been found to shift E of uric acid towards less positive potential by 30-40 mV. The products of p electrooxidation were separated by HPLC at pH 3.0 and were characterized as 1,3-dimethylalloxan and urea. At pH 7.0, the major product Ž. was 5-hydroxyhydantoin-5-N-methyl carboxamide. The spectral studies during enzymic oxidation of 1,3-dimethyluric acid generated UV-absorbing intermediate similar to electrooxidation and the rate of decay was found to be same in both the cases. The electrochemical and enzymic oxidations appear to proceed by an identical mechanism. q 1998 Elsevier Science S.A.