Electrochemical Characteristics of Nitro-Heterocyclic Compounds of Biological Interest IV. Lifetime of the Metronidazole Radical Anion

Electrochemical studies on metronidazole using mixed aqueous/dimethylformamide (DMF) solvents have allowed us to generate the one-electron addition product, the nitro radical anion, RNO^-₂. Cyclic volt-ammetric techniques have been employed to study the tendency of RNO^-₂ to undergo further chemical reaction. The return-to-forward peak current ratio. ip/ip_f. was found to increase towards unity with increasing DMF content of the medium, indicating the extended lifetime of RNO^-₂. Second order kinetics for the decay of RNO^-₂ were established at all DMF concentrations examined. Extrapolation has allowed the rate constant and a first half-life of 8.4 × 10⁴dm²/mol-sec and 0.059 seconds respectively, to be determined for the decay of RNO^-₂ in a purely aqueous media. This is impossible by direct electrochemical measurement in water. due to a different reduction mechanism, giving the hydroxylamine derivative in a single 4-electron step. The application of the technique to other nitro-aromatic compounds is discussed.     

Electrochemical Characteristics of Nitro-Heterocyclic Compounds of Biological Interest IV. Lifetime of the Metronidazole Radical Anion

Electrochemical studies on metronidazole using mixed aqueous/dimethylformamide (DMF) solvents have allowed us to generate the one-electron addition product, the nitro radical anion, RNO^?₂. Cyclic volt-ammetric techniques have been employed to study the tendency of RNO^?₂ to undergo further chemical reaction. The return-to-forward peak current ratio. ip/ip_f. was found to increase towards unity with increasing DMF content of the medium, indicating the extended lifetime of RNO^?₂. Second order kinetics for the decay of RNO^?₂ were established at all DMF concentrations examined. Extrapolation has allowed the rate constant and a first half-life of 8.4 × 10⁴dm²/mol-sec and 0.059 seconds respectively, to be determined for the decay of RNO^?₂ in a purely aqueous media. This is impossible by direct electrochemical measurement in water. due to a different reduction mechanism, giving the hydroxylamine derivative in a single 4-electron step. The application of the technique to other nitro-aromatic compounds is discussed.     

Electrochemical Characteristics of Nitroheterocyclic Compounds of Biological Interest VI. The Misonidazole Radical Anion

The addition of four aprotic solvents to misonidazole in an aqueous buffer system has been examined electrochemically. Qualitatively they all result in separation of the initial irreversible 4 electron reduction step into two stages, the RNO₂/RNO₂· and RNO₂· /RNHOH couples respectively. Despite some difficulties in achieving measurements for the discrete RNO₂/RNO₂· without interference from the following reduction step, it was clear that the various aprotic solvents influenced the lifetime of the RNO₂· species to different degrees. Resolution of the two processes was best achieved using a water-acetone system and this has been employed to study the lifetimes of the misonidazole radical anion as a function of acetone content and drug concentration. Analysis of the cyclic voltammetric response showed a second order decay pathway, in line with the metronidazole system studied under similar conditions. This has been compared with results from pulse radiolysis work, which suggested a first order reaction of unknown pathway for 2-nitroimidazole radical anions.     

The effect of 5-substitution on the electrochemical behavior and antitubercular activity of PA-824

Nitroimidazole PA-824 is part of an exciting new class of compounds currently undergoing clinical evaluation as novel TB therapeutics. The recently elucidated mechanism of action of PA-824 involves reduction of the nitroimidazole ring and subsequent nitric oxide release. The importance of this compound and its unique activity prompted us to explore how substitution of the nitroimidazole ring would affect electrochemical reduction and antitubercular activity. We prepared analogs of PA-824 with bromo, chloro, cyano, and amino substituents in the 5-position of the aromatic ring. We found that substitution of the imidazole ring greatly influences reduction and the stability of the corresponding nitro radical anion. Further, the antitubercular activities of the bromo and chloro analogs may indicate that an alternate nitroreductase pathway within Mycobacterium tuberculosis exists.     

三硝基甲苯致白内障机理及其在晶状体内代谢的研究

在建立TNT大鼠白内障的基础上,用HPLC分析了晶状体内TNT及其代谢产物,并用ESR及NBT方法检测了TNT在晶状体内的代谢过程所产生的自由基。结果表明,慢性染毒24个月的大鼠白内障晶状体内含有TNT原形和4氨基2,6二硝基甲苯代谢产物,以及在体外与正常晶状体微粒体孵育可产生TNT硝基阴离子自由基和超氧阴离子自由基。上述结果提示,TNT可进入晶状体内,在其还原代谢过程中产生硝基阴离子自由基中间产物,在有氧条件下进而产生超氧阴离子自由基,这可能是TNT导致白内障的启动因素。     

Electrochemical Studies of Tirapazamine: Generation of the One-Electron Reduction Product

The electrochemical properties of the benzotriazine di-N-oxide, tirapazamine (SR4233), and the mono-and zero-N-oxides, SR4317 and SR4330 respectively, have been investigated in dimethylformamide and acetonitrile. The voltammetry of tirapazamine is complicated, with up to 6 reduction steps being identified, depending on the solvent. Both SR4317 and SR4330 show two reduction steps. The first reduction of all three compounds is a reversible or quasi-reversible step, which is assigned to a 1-electron addition. Cyclic voltammetric studies show that the anion radical product is stable, although the tirapazamine 1-electron addition product shows a tendency to participate in a chemical following reaction. Subsequent reduction steps are all highly irreversible in nature. The 2nd electron transfer of SR4317 results in the formation of the free base, SR4330, which is identified voltammetrically. Comparison is made with the voltammetric behaviour of quinoline and quinoline-oxide.     

Automated in-solution protein digestion using a commonly available high-performance liquid chromatography autosampler

The bleaching of the pyrogallol red (PGR) dye mediated by superoxide anion radicals () generated from the xanthine/xanthine oxidase system (X/XO) was studied by UV-visible spectrophotometry. The absorption band (at 540 nm) of PGR quickly decreased in the presence of X/XO, implying an efficient reaction of with PGR. The process was unaffected by catalase (CAT), but completely abolished by superoxide dismutase (SOD). A mechanism of the reaction involving the consumption of one PGR molecule by two to generate one molecule of H₂O₂ is proposed. PGR was used as a probe to estimate the rate of generation in redox cycling reactions of a series of nitro compounds mediated by rat liver microsomes. The consumption of PGR induced by the redox cycling of nitrofurantoin was totally eliminated by the addition of SOD but unaffected by CAT. The initial rate of consumption of PGR mediated by the redox cycling of others nitro derivatives follows the order:furazolidindione>nitrofurantoin>nifurtimox>benznidazole>chloramphenicol.We concluded that PGR can be used as a probe to estimate the release of from enzymatic systems or from the redox cycling of nitro compounds.     

Electrochemical Characteristics of Nitro-Heterocyclic Compounds of Biological Interest. II. Nitrosochloramphenicol

The electrochemical Characteristics of nitrosochloramphenicol have been studied in aqueous buffer systems (pH 7.1) using direct current (d.c.) and differential pulse polarography. cyclic voltammetry and coulometric techniques. Up to 4 charge-transfer steps can be identified. The first reduction step is reversible both chemically and electrochemically. the charge-transfer product showing no tendency to undergo further reaction on the electrochemical time-scale. In contrast, the second reduction step is irreversible, with the product undergoing a fast following reaction to yield a redox-active species which was detected by cyclic voltammetry. From the data and by comparison with related systems. two reduction mechanisms are possible and are discussed.     

Electrochemical Characteristics of Nitro-Heterocyclic Compounds of Biological Interest. II. Nitrosochloramphenicol

The electrochemical Characteristics of nitrosochloramphenicol have been studied in aqueous buffer systems (pH 7.1) using direct current (d.c.) and differential pulse polarography. cyclic voltammetry and coulometric techniques. Up to 4 charge-transfer steps can be identified. The first reduction step is reversible both chemically and electrochemically. the charge-transfer product showing no tendency to undergo further reaction on the electrochemical time-scale. In contrast, the second reduction step is irreversible, with the product undergoing a fast following reaction to yield a redox-active species which was detected by cyclic voltammetry. From the data and by comparison with related systems. two reduction mechanisms are possible and are discussed.     

Electrochemical,UV-Visible and EPR studies on nitrofurantoin: Nitro radical anion generation and its interaction with glutathione

This paper deals with the reactivity of the nitro radical anion electrochemically generated from nitrofurantoin with glutathione. Cyclic voltammetry (CV) and controlled potential electrolysis were used to generate the nitro radical anion in situ and in bulk solution, respectively and cyclic voltammetry, UV-Visible and EPR spectroscopy were used to characterize the electrochemically formed radical and to study its interaction with GSH.

By cyclic voltammetry on a hanging mercury drop electrode, the formation of the nitro radical anion was possible in mixed media (0.015M aqueous citrate/DMF, 40/60, pH 9) and in aprotic media. A second order decay of the radicals was determined, with a k₂ value of 201 and 111M^-1 s^-1, respectively. Controlled potential electrolysis generated the radical and its detection by cyclic voltammetry, UV-Visible and EPR spectroscopy was possible. When glutathione (GSH) was added to the solution, an unambiguous decay in the signals corresponding to a nitro radical anion were observed and using a spin trapping technique, a thiyl radical was detected.

Electrochemical and spectroscopic data indicated that it is possible to generate the nitro radical anion from nitrofurantoin in solution and that GSH scavenged this reactive species, in contrast with other authors, which previously reported no interaction between them.     

心肌肌钙蛋白Ⅰ的分子印迹电化学生物传感器

应用分子印迹技术,以邻苯二胺和对苯二酚为功能单体,心肌肌钙蛋白Ⅰ(cTnI)为模板分子,在pH 7.0磷酸盐缓冲液中,利用循环伏安法在玻碳电极表面聚合形成了分子印迹膜.该分子膜对cTnI有特异性识别作用,在0.01～2.00 μg/mL的范围内,cTnI的浓度与氧化峰电流的变化呈线性关系,检测下限为2 ng/mL,响应时间为15 min.该分子印迹传感器具有制备简单、特异性及稳定性好等优点.     

Superoxide dismutase activity and electrochemical study of the binuclear [Cu(TSA)2py]2 complex

The superoxide dismutase-mimetic activity and the electrochemical behavior of the binuclear complex [Cu(TSA)₂py]₂ is reported. The complex exhibits a marked SOD activity in the nitroblue tetrazolium assay. Its redox response is in agrement with two copper atoms partially coupled through the carboxylate moieties. The electrode reactions lie in the range of the superoxide/peroxide and oxygen/superoxide couples. This fact is indicative that this complex can act as catalyst for the SOD reaction.     

Electrochemical activity of an Fe(III)-reducing bacterium, Shewanella putrefaciens IR-1, in the presence of alternative electron acceptors

Cyclic voltammetry demonstrated that cells of Shewanella putrefaciens grown under anaerobic conditions without nitrate were electrochemically active. The electrochemical activity was inactivated reversibly by exposure to air, but not by nitrate. Lactate and an applied potential at +200 mV against an Ag/AgCl reference electrode restored the electrochemical activity. These findings can be used to improve the performance of a mediator-less microbial fuel cell using electrochemically active bacteria in the presence of nitrate.     

Micelle-supported electroenzymology: Succinate dehydrogenation by escherichia coli fumarate reductase in decylubiquinone and octyl glucoside micelles

The concept of micelle-supported electroenzymology is demonstrated using a system consisting of the membrane enzyme Escherichia coli fumarate reductase (FRD), the amphiphilic coenzyme analogue decylubiquinone (DU), the micelle-forming surfactant n-octyl glucoside (OG), and a gold electrode. The OG micelles provide a hydrophobic, membrane mimetic medium for FRD and DU to exchange electrons while the gold electrode serves to regenerate DU. When succinate is presented to the FRD/DU/OG micelle system, electroenzymatic oxidation of succinate to fumarate occurs as evidenced using cyclic voltammetry. DU is shown to be the only electroactive species in the system; and as increasing amounts of succinate are added, the expected increase in the peak anodic (oxidative) current and decrease in the peak cathodic (reductive) current are observed. The peak anodic current approaches a limiting value with succinate concentration in qualitative agreement with simple Michaelis-Menten enzyme kinetics. When the strong competitive inhibitor oxaloacetate is added, enzymatic oxidation of succinate is inhibited as indicated by no change in the peak anodic and cathodic currents with increasing succinate concentration. (c) 1993 John Wiley & Sons, Inc.     

Variability of the Fenton reaction characteristics of the EDTA, DTPA, and citrate complexes of iron

The common metal chelation agents, DTPA and EDTA are often used as models for physiological low-molecular weight iron complexes in biochemical studies, or for common biochemical protocols. In the biochemical literature there are apparent conflicts as to whether EDTA and DTPA are pro-oxidant or antioxidant additives. This apparent conflict is puzzling since in chemical systems Fe^IIEDTA and Fe^IIDTPA are well known Fenton reaction reagents. In this investigation we examined the voltammetric characteristics of the iron complexes of EDTA, DTPA, and citrate and the effect of the ligand:metal ratio (L:M) on the electrocatalytic (EC') waves that result from reduction of H₂O₂ by this complex. At a ratio of 1:1, the cyclic voltammetric waves of the complexes indicate the presence of a reversible species corresponding to the Fe^II/IIIL couple, along with a second irreversible reduction peak. The second irreversible voltammetric peak decreases at higher L:M ratios for EDTA and citrate. The 1:1 iron complexes of EDTA, DTPA, and citrate clearly induce the catalytic reduction of H₂O₂. In the presence of a greater than 100 fold excess of H₂O₂ relative to iron, higher L:M ratios greatly reduced the catalytic EC' wave compared to the 1:1 ratios. At H₂O₂:Fe ratios less than 50, the L:M ratio has very little effect of the EC' current. These observations may explain the apparent discrepancies in the biochemical literature. Addition of EDTA or DTPA may enhance oxidative processes if the L:M is low (less than unity), whereas rates of on-going oxidative processes may decrease if that ratio, along with the relative amount of H₂O₂, are both high (excess ligand). The impact of this study is of particular importance given the widespread use of these ligands in biochemical studies.     

Enzymatic synthesis and various properties of poly(catechol)

Poly(catechol) was prepared by using peroxidase as a catalyst in two types of solvent systems: an aqueous dioxane solution and a reverse micellar solution. Peroxidases derived from two sources, horseradish (HRP) and soybean (SBP), were employed as catalyst. The structure of the prepared polymer was elucidated by infrared analysis. Enzymatically prepared film of poly(catechol) at a Pt electrode was subjected to cyclic voltammetric studies in aqueous HCl medium and phosphate buffer pH 6.5. Thermal studies of the polymer were performed by thermogravimetric analysis. The iodine-labelled polymers showed low electrical conductivity in the range of 10⁻⁶ to 10⁻⁹ S cm⁻¹. The magnetic susceptibility and surface morphological property of the polymer were also studied.