Electrochemical nitrite reduction

Other researchers have reported electrochemical nitrite reduction using aquocobalamin " and water-insoluble metallo-phthalocyanines absorbed onto electrodes. Nyokong and coworkers found that the potential for catalytic nitrite reduction varied with metal in a series of metallo-phthalocyanine complexes adsorbed onto a glassy carbon electrode (GCE) in basic solutions, Cu(Pc) > Fe(Pc) > Ni(Pc) > Co(Pc) > Mn(Pc) > Zn(Pc). ... 

Kim, S. and G. Kwag (2002). Increased catalytic activity of iron phthalocyanine on the electrochemical nitrite reduction upon heat-treatment probed by x-ray absorption fine structure. Bull. Korean Chem. Soc. 23(1), 25-26. 

Electrochemical carboxylation of acetophenone with CO2 coupled with nitrite reduction proceeds by the controlled-potential electrolysis of CO2-saturated acetonitrile containing [Fe4S4 (SPh)4] , N02, PhCOCH3, and a dehydration... 

Star-shaped core with iron-sandwich units 2,987 4,527 = 2.0" 1.3" H2O (basic) Electrochemical aqueous nitrate and nitrite reduction [152]... 

The electrochemical behaviour of H2O in molten LiNOs-KNOs eutectic has been elucidated.Contrary to previous reports, electroreduction of H2O is coupled with nitrite reduction, probably involving an autocatalytic mechanism and an adsorbed intermediate. 

Figure 14.9 The application of porous PAN films and composites to the sensing of nitrite. Scale 7 gm (A) Porous film ofpoly(aniline) formed from the in situ electrochemical synthesis in the presence of WO nm polystyrene nanoparticle templates. (B) Enhanced electrocatalysis of concentrations of 50 gM nitrite in 0.7 M HCI at+ 50 mVvs. Ag/AgCI of the nanocomposite film (d) compared to classy carbon (a), pre-treatedglassy carbon (b) and bulk PANI [85]. (Reprinted with permission from Chemistry A European journal, Nanocomposite and nanoporous polyaniline conducting polymers exhibit enhanced catalysis of nitrite reduction by X. Luo, A.j. Killard and M.R. Smyth, 13, 2138-2143. Copyright (2007) Wiley-VCH)...

Choi, H.J., G. Kwag, and S. Kim (2001). Electrochemical and XAFS investigation of nitrite reduction by heat-treated fi-oxo derivative if iron phthalocyanin supported on high area carbon. J. Electtoanal. Chem. 508, 105-114. 

The electrochemical behavior of the electrodes modified with PPy nanowires was described as a chemical sensor [386,387]. The modified electrodes had good activity towards nitrite reduction. The electroreduction current depended linearly on the concentration of nitrite and increased with increasing the PPy thickness, acidity of electrolyte solution, temperature, and scan rate. In the range of 2.28 x 10 to 0.02 M, the nitrite concentrations could be accurately determined from the good linearity between the electroreduction current and the concentration of nitrite. 

A nitrite-sensitive material has been developed by Fabre et al. with a poly(iV-methylpyrrole) film incorporating a metal-substituted heteropolyanion [(H20)Fe XWn039]" (X = P, n = 4, or X = Si, n = 5) as a doping anion [38C1-382]. Such a film was electrochemically stable and exhibited an efficient elec-trocatalytic activity vis-a-vis the nitrite reduction. In contrast, poor results were obtained when PPy was used as the immobilization matrix [383, 384]. The key step of this electrocatalytic process was the formation of an iron-nitrosyl complex generated from the replacement of H2O initially coordinated to the iron center by an NO group, the reduction of which led to the catalytic conversion of NO2 into ammonium ions [385, 386]. The measured catalytic currents were linear with the nitrite concentration over the range 1 X 10 to 3 X 10 M [382]. Furthermore, anions such as NOJ,... 

Microelectronic technologies have also been used in nitrite biosensors and electrochemical sensors (Suzuki and Taura, 2001 Adhikari and Majumdar, 2004). Ameida et al. (2013) have also developed a method of electrochemical nitrite measurement by means of a gold working electrode covered with 1,2-diaminobenzene (DAB) integrated in a FIA system. This sensor helps improve selectivity, repeatability, stability, and sensitivity. A Nafion/lead-ruthenate pyrochlore electrode chemically modified for determination of NO2 oxidation and NO reduction based on AC-impedance spectroscopy and FIA has also been tested (Zen et al., 2000). Quan and Shin (2010) also tested an electrochemical nitrite biosensor based on co-immobilization of copper-containing nitrite reductase and viologen-modified chitosan (CHIT-V) on a glassy carbon electrode (GCE). 

Nitrate and nitrite originating from fertilizers are highly oxidizing species and their electrochemical reduction could be an option for denitrification. Cu-based MOFs and several POMOFs have shown substantial electrochemical activity for nitrite reduction, as expected from the catalytic properties of POM anions. A 3D... 

Subsequent elegant work by Lambert and coworkers61 has shown that, while under UHV conditions the electropumped Na is indistinguishable from Na adsorbed by vacuum deposition, under electrochemical reaction conditions the electrochemically supplied Na can form surface compounds (e.g. Na nitrite/nitrate during NO reduction by CO, carbonate during NO reduction by C2FI4). These compounds (nitrates, carbonates) can be effectively decomposed via positive potential application. Furthermore the large dipole moment of Na ( 5D) dominates the UWr and O behaviour of the catalyst-electrode even when such surface compounds are formed. 

The monovalent Co chemistry of amines is sparse. No structurally characterized example of low-valent Co complexed exclusively to amines is known. At low potentials and in non-aqueous solutions, Co1 amines have been identified electrochemically, but usually in the presence of co-ligands that stabilize the reduced complex. At low potential, the putative monovalent [Co(cyclam)]+ (cyclam = 1,4,8,11-tetraazacyclotetradecane) in NaOH solution catalyzes the reduction of both nitrate and nitrite to give mixtures of hydroxylamine and ammonia.100 Mixed N-donor systems bearing 7r-acceptor imine ligands in addition to amines are well known, but these examples are discussed separately in Section 6.1.2.1.3. 

To provide a model for nitrite reductases72 Karlin and co-workers characterized a nitrite-bound complex (226) (r = 0.05)214 In an endeavor to model nitrite reductase activity, Tanaka and co-workers prepared a few mononuclear complexes (227) (r = 0.74)215 (228) (r = 0.82),216 (229) (r = 0.97),217 (230) (r = 0.16),217 (231) (r = 0.07),217 and (232) (r = 0.43 and r = 0.53)217 and studied the electrochemical reduction of N02A As a part of their activity on modeling heme-copper terminal oxidases, Holm and co-workers prepared complex (233) (r = 0.96).218 Using a sterically hindered tris(pyridylmethyl)amine, Canary et al. prepared a complex (234) (r=1.00), studied its redox behavior, and discussed various factors that may contribute to the difference (higher potential for the new complex) in the redox potential of a Cu Cu1 couple between substituted and unsubstituted ligands.2 9... 

Studies on the electrochemical reduction of [(terpy)(bpy)Mnn(N02)]+ complexes (M = Ru, Os) have relevance for the catalytic conversion of nitrite to ammonia 336 337... 

In a related observation, reported by Tanaka et al. (81), the copper(II) complex Cu(tpa)2+ (tpa = tris[(2-pyridyl)methyl] amine) was shown to serve as a catalyst for the electrochemical reduction of nitrite to N20 and traces of NO in aqueous solution. NO and/or a copper nitrosyl complex would appear to be the likely intermediates in this process (81a). 

The potential for catalytic removal of nitrate was introduced in the late eighties and bears some similarity to the electrochemical process in as much as both involve stepwise reduction of the nitrogen oxidation state via formation of nitrites, ammonia and N2. As with the electrochemical process, the major drawback is the potential for formation of undesired products such nitrite and ammonium which must be depleted at more stringent levels than the nitrate itself... 

The investigation of electrochemical, electrocatalytic, and catalytic reduction of nitrite and nitrate have attracted much... 

Although molybdenum and tungsten enzymes carry the name of a single substrate, they are often not as selective as this nomenclature suggests. Many of the enzymes process more than one substrate, both in vivo and in vitro. Several enzymes can function as both oxidases and reductases, for example, xanthine oxidases not only oxidize purines but can deoxygenate amine N-oxides [82]. There are also sets of enzymes that catalyze the same reaction but in opposite directions. These enzymes include aldehyde and formate oxidases/carboxylic acid reductase [31,75] and nitrate reductase/nitrite oxidase [83-87]. These complementary enzymes have considerable sequence homology, and the direction of the preferred catalytic reaction depends on the electrochemical reduction potentials of the redox partners that have evolved to couple the reactions to cellular redox systems and metabolic requirements. 

The electrochemical transformation of a molybdenum nitrosyl complex [Mo(NO)(dttd)J [dttd = 1,2-bis(2-mercaptophenylthio)ethane] (30) is rather interesting (119). Ethylene is released from the backbone of the sulfur ligand upon electrochemical reduction. The resulting nitrosyl bis(dithiolene) complex reacts with O2 to give free nitrite and a Mo-oxo complex. Multielectron reduction of 30 in the presence of protons releases ethylene and the NO bond is cleaved, forming ammonia and a Mo-oxo complex (Scheme 15). The proposed reaction mechanism involves successive proton-coupled electron-transfer steps reminiscent of schemes proposed for Mo enzymes (120). 

The presence of N-N02 fragment in 1-nitropyrazole significantly facilitates the process of electrochemical reduction E m=-0.95, It" xn=-. 73 V (acetonitrile). The first wave corresponds to a one-electron irreversible transfer the second wave is approximately 3.5 times higher and shows sharp drop prior to background discharge (Scheme 3.36). Analysis of the dependence of 1-nitropyrazole reduction potentials on pH shows that the second wave corresponds to the reduction of the N02 anion (nitrite ion) formed [851],... 

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