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The interaction of histidine, cysteine, NO and nitrite with cobalt(II) N,N',N″,N‴-tetramethyltetra-3,4-tetrapyridinoporphyrazine ([Co^IItmtppa]⁴⁺) is reported. Metal-based autoreduction of [Co^IItmtppa]⁴⁺ occurs with the formation of the [Co^Itmtppa(-2)]³⁺ species in the presence of histidine and cysteine. Kinetic data for the auto reduction of [Co^IItmtppa]⁴⁺ in the presence of these amino acids gave the rate constants k_f = 2.1 × 10¹ and 2.8 dm³ mol^-1 s^-1, for cysteine and histidine, respectively. One molecule of NO or nitrite was found to coordinate to the [Co^IItmtppa]⁴⁺ species. The equilibrium and rate constants for the coordination of the nitric oxide were K = 2.3 × 10⁴dm³mol^-1 and k_f = 7.5 dm³mol^-1s^-1, respectively. The coordination of nitrite to [Co^IItmtppa]⁴⁺ occurred with an equilibrium constant of K = 2.0 × 10²dm³mol^-1 and a rate constant of k_f = 4.0 × 10^-3dm³mol^-1s^-1. There was no evidence for the coordination of two molecules of nitrite to the [Co^IItmtppa]⁴⁺ species.

The electrocatalytic reduction of nitrite on a dinuclear ruthenium phthalocyanine (RuPc)₂ modified electrode is studied, using cyclic voltammetry (cyclic voltammogram), rotating disc electrode (RDE) and ring-disc electrode (RRDE) techniques. The products of nitrite reduction are ammonia, nitrous oxide, and hydroxylamine. Depending on the experimental conditions, ammonia or nitrous oxide is formed as the main product. The initial step in the electroreduction of nitrite catalyzed by (RuPc)₂ is a one electron Ru^II / Ru^I process, followed by coordination of NO₂⁻ to the metal center. Formation of a nitrosyl complex prior to the electroreduction does not occur. A suitable mechanism is proposed by analyzing the rate equation and the Tafel slope.

Cobalt phthalocyanine (CoPc), cobalt tetracarboxy phthalocyanine (CoTCPc) and cobalt octacarboxy phthalocyanine (CoOCPc), adsorbed onto glassy carbon electrodes, have been used for the electrocatalytic detection of nitrite, L-cysteine and melatonin. The modified electrodes electrocatalytically detected nitrite around 800 mV vs.Ag|AgCl, a value less positive compared to that of an unmodified glassy carbon electrode (at 950 mV vs.Ag|AgCl) and also gave detection limits in the 10^-7 M range for nitrite detection. L-cysteine was detected by the modified electrodes at potentials between 0.50 to 0.65 V vs.Ag|AgCl, with L-cysteine detection limits also in the 10^-7 M range. The detection limits for melatonin ranged from 10^-7 to 10^-6 M. CoPc-modified electrodes displayed good separation of interferents (tryptophan and ascorbic acid) in the presence of melatonin. Analyses of commercial melatonin tablets using modified electrodes gave excellent agreement with manufacturer's value for all modified electrodes of this work.

We report on the electrodeposition of gold nanoparticles (AuNPs) on a glassy carbon electrode (GCE) followed by deposition of nickel tetrasulfonated phthalocyanine (NiTSPc) film by electropolymerization (poly-NiTSPc-GCE) to form Poly-NiTSPc/AuNPs-GCE. The presence of the gold nanoparticles caused a lowering of the anodic and cathodic peak separation (ΔE_p) of ferricyanide from 126 mV on poly-NiTSPc to 110 mV on poly-NiTSPc/AuNPs. The electrooxidation of nitrite improved on modified electrodes compared to GCE, with the latter giving E_p = 0.78 V and the modified electrodes gave E_p = 0.62 V or 0.61 V. Poly-NiTSPc/AuNPs-GCE had higher currents compared to poly-NiTSPc-GCE. This indicates the enhancement effect caused by the AuNPs. Electrochemical impedance spectroscopy and chronoamperometric studies also showed that poly-NiTSPc/AuNPs-GCE was a better electrocatalyst than poly-NiTSPc-GCE or AuNPs-GCE.

The chemical reduction of nitrate or nitrite species by zero-valent iron nanoparticle (ZVIN) in aqueous solution and related reaction kinetics or mechanisms using fine structure characterization were investigated. Experimentally, ZVIN of this study was prepared by borohydride reduction method at room temperature. The morphology of as-synthesized ZVIN shows that the nearly ball and ultrafine particles ranged of 20–50 nm were observed with FE-SEM analysis. The kinetic model of nitrites or nitrates reductive reaction by ZVIN is proposed as a pseudo-first-order kinetic equation. The nitrite and nitrate removal efficiencies using ZVIN were found 65–83% and 51–68%, respectively, based on three different initial concentrations. By using XRD patterns, the quantitative relationship between nitrite and Fe(III) or Fe(II) becomes similar to the one between nitrate and Fe(III) in the ZVIN study. The possible reason is linked with a faster nitrite reduction by ZVIN. In fact, the occurrence of the relative faster nitrite reductive reaction suggested that the passivation of the ZVIN have a significant contribution to iron corrosion. The XANES spectra show that the nitrites or nitrates reduce to N₂ while oxidizing the ZVIN to Fe₂O₃ or Fe₃O₄ electrochemically. It is also very clear that decontamination of nitrate or nitrite species in groundwater via the in-situ remediation with a ZVIN permeable reactive barrier would be environmentally attractive.

Nutrients, such as nitrate, nitrite, and phosphorus, are common contaminants in many aquatic systems in the United States. Ammonia and nitrate are both regulated by the drinking water standards in the US primarily because excess levels of nitrate might cause methemoglobinemia. Phosphorus might become sources of the eutrophication problems associated with toxic algae in the freshwater bodies. Toxic algal blooms can cause severe acute and chronic public health problems. Chemical reduction of nitrate by using zero-valent iron started as early as 1964, and considerable research reports relating to this technology to nanomaterial were extensively reported in 1990s making the use of nanoscale zero-valent iron (NZVI) particles for nitrate removal become one of the most popular technologies in this field. The purpose of the present study was to examine the potential of integrating green sorption media, such as sawdust, limestone, tire crumb, and sand/silt, with two types of nanoparticles, including NZVI and Titanium Dioxide (TiO₂), for nitrate removal in an engineering process. The study consists of running packed bed column tests followed by the addition of NZVI and TiO₂ to improve nitrate and phosphorus removal efficiency. Preliminary results in this paper show that the potential and advanced study may support the creation of design criteria of stormwater and groundwater treatment systems for water reuse in the future.

In the present work, maghemite nanoparticles (MNP) was synthesized by a simplified method and then modified by sodium dodecyl benzene sulfonate (NaDBS) for the removal of nitrite from aqueous solution. The prepared nanoparticles were characterized by Scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). The SEM image and XRD analysis showed that the average particle size and crystallite of the maghemite nanopaticles are ca. 32.7 nm and 33.5 nm, respectively. Different parameters namely, pH of the adsorption solution, adsorbent dosage and spectrophotometric reagents were optimized. Spectrophotometric determination of nitrite in an optimized condition showed that the MNP is able to deplete over 88% of nitrite from the initial solution. Moreover, dynamic adsorption study per se confirmed the shortest necessary contact time (ca. 6 min) in the adsorption process of nitrite which is quite encouraging from a practical and industrial point of view. The kinematic study revealed that the nitrite adsorption is a pseudo-first-order process. In addition, two different models (Freundlich- and kinetic-type model) were developed for the adsorbent dosage effect on nitrite adsorption. A Freundlich-type model manifested high coefficients of regression, indicating its robustness.

Exfoliation/restacking route was utilized to investigate layer-by-layer self-assembly of FeTMPyP/TaWO₆ [5, 10, 15, 20-tetrakis (N-methylpyridinium-4-yl) porphyrinato iron (III)] nanocomposite in this paper. The colloidal suspension of ${\text{TaWO}}_6^{-}$ nanosheet was tested by Zeta potential and proved to be in a well-dispersed statement. Analysis technologies such as X-ray diffraction Scanning electron microscope (SEM) infrared UV-Vis were used to characterize the final product. The results showed that FeTMPyP molecules were introduced into the lamellar space of host material successfully. The electrochemical behaviors of FeTMPyP-TaWO₆ nanocomposite were tested by cyclic voltammetry method, and the nanocomposite showed excellent electrocatalytic properties to the oxidation of nitrite with the anodic peak shifts from 0.122 to 0.860V. Besides, the detection limit of nitrite can be calculated to be $7.2\times 10^{-5}$M with the concentration of nitrite ranging from 0.1 to 3.61mM by different pulse voltammetry (DPV) analyzation.

The synthesis and reactivity of uranium complexes supported by a bis(aryloxide) cyclam ligand are surveyed. The hemilability of this ligand proved to be particularly appropriate to stabilize highly reactive uranium(III) and uranium(IV) complexes that were able to activate different unsaturated molecules. Of note are the reductive cleavage of azobenzene with the unprecedented formation of a trans-bis(imido) uranium(VI) complex and its reaction with carbon dioxide to generate a trans-oxido-imido uranium(VI) complex and phenyl isocyanate. The formation of a trans-dioxido uranium(VI) (uranyl) complex was also observed in the reaction of uranium(IV) complexes with sodium nitrite. Quantum chemical computations and solution ¹⁵N NMR spectroscopy were employed to evaluate bond covalency in the three {E=U=E}²⁺ complexes (E = O, NR).