When grown anaerobically on a succinate+nitrate (SN) medium, Paracoccus denitrificans forms the membrane-bound, cytoplasmically oriented, chlorate-reducing nitrate reductase Nar, while the periplasmic enzyme Nap is expressed during aerobic growth on butyrate+oxygen (BO) medium. Preincubation of SN cells with chlorate produced a concentration-dependent decrease in nitrate utilization, which could be ascribed to Nar inactivation. Toluenization rendered Nar less sensitive to chlorate, but more sensitive to chlorite, suggesting that the latter compound may be the true inactivator. The Nap enzyme of BO cells was inactivated by both chlorate and chlorite at concentrations that were at least two orders of magnitude lower than those shown to affect Nar. Partial purification of Nap resulted in insensitivity to chlorate and diminished sensitivity to chlorite. Azide was specific for SN cells in protecting nitrate reductase against chlorate attack, the protective effect of nitrate being more pronounced in BO cells. The results are discussed in terms of different metabolic activation of chlorine oxoanions in both types of cells, and limited permeation of chlorite across the cell membrane.

• MeSH
• chlorečnany metabolismus   farmakologie   MeSH
• chloridy metabolismus   farmakologie   MeSH
• dusičnany metabolismus   MeSH
• inhibitory enzymů metabolismus   farmakologie   MeSH
• kyselina jantarová metabolismus   MeSH
• nitrátreduktasa antagonisté a inhibitory   metabolismus   MeSH
• oxidace-redukce MeSH
• Paracoccus denitrificans enzymologie   metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• chlorečnany MeSH
• chloridy MeSH
• chlorite MeSH Prohlížeč
• dusičnany MeSH
• inhibitory enzymů MeSH
• kyselina jantarová MeSH
• nitrátreduktasa MeSH

Effect of platinum nanoparticle size on catalytic reduction of nitrate in liquid phase was examined under ambient conditions by using hydrogen as a reducing agent. For the size effect study, Pt nanoparticles with sizes of 2, 4 and 8 nm were loaded silica support. TEM images of Pt nanoparticles showed that homogeneous morphologies as well as narrow size distributions were achieved during the preparation. All three catalysts showed high activity and were able to reduce nitrate below the recommended limit of 50 mg/L in drinking water. The highest catalytic activity was seen with 8 nm platinum; however, the product selectivity for N2 was highest with 4 nm platinum. In addition, the possibility of PVP capping agent acting as a promoter in the reaction is highlighted.

• Klíčová slova
• Pt, environmental catalysis, hydrogenation, nanoparticles, nitrate reduction, platinum, wastewater, water treatment,
• Publikační typ
• časopisecké články MeSH

Chronic nitrogen inputs can alleviate N limitation and potentially impose N losses in forests, indicated by soil enrichment in 15 N over 14 N. However, the complexity of the nitrogen cycle hinders accurate quantification of N fluxes. Simultaneously, soil ecologists are striving to find meaningful indicators to characterise the "openness" of the nitrogen cycle. We integrate soil δ15 N with constrained ecosystem N losses and the functional gene potential of the soil microbiome in 14 temperate forest catchments. We show that N losses are associated with soil δ15 N and that δ15 N scales with the abundance of soil bacteria. The abundance of the archaeal amoA gene, representing the first step in nitrification (ammonia oxidation to nitrite), followed by the abundance of narG and napA genes, associated with the first step in denitrification (nitrate reduction to nitrite), explains most of the variability in soil δ15 N. These genes are more informative than the denitrification genes nirS and nirK, which are directly linked to N2 O production. Nitrite formation thus appears to be the critical step associated with N losses. Furthermore, we show that the genetic potential for ammonia oxidation and nitrate reduction is representative of forest soil 15 N enrichment and thus indicative of ecosystem N losses.

• MeSH
• amoniak MeSH
• Archaea genetika   MeSH
• denitrifikace MeSH
• dusičnany * MeSH
• dusík analýza   MeSH
• dusitany MeSH
• lesy MeSH
• mikrobiota * genetika   MeSH
• nitrifikace MeSH
• oxidace-redukce MeSH
• půda MeSH
• půdní mikrobiologie MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• amoniak MeSH
• dusičnany * MeSH
• dusík MeSH
• dusitany MeSH
• půda MeSH

The polyaniline (PANI) base was ball-milled with silver nitrate in the solid state. Samples were prepared at various mole ratios of silver nitrate to PANI constitutional units ranging from 0 to 1.5 for three processing times, 0, 5, and 10 min. The emeraldine form of PANI was oxidized to pernigraniline, and the silver nitrate was reduced to metallic silver. Nitric acid is a byproduct, which may protonate the residual emeraldine and pernigraniline. The changes occurring in the structure of PANI are discussed on the basis of Fourier transform IR and Raman spectroscopies. Raman spectra revealed the formation of pernigraniline salt. The reaction between the two nonconducting components, emeraldine base and silver nitrate, produced a mixture of two conducting components, emeraldine or pernigraniline nitrate and metallic silver. The accompanying conductivity changes were determined. The increase in the conductivity of the original base, 10(-9) S cm(-1), up to 10(-2) S cm(-1) was found to depend on the mole ratio of silver nitrate to PANI base and on the processing time of the components in the ball mill.

• MeSH
• aniliny chemie   MeSH
• časové faktory MeSH
• chemické modely MeSH
• dusičnan stříbrný chemie   MeSH
• elektrická vodivost MeSH
• kyslík chemie   MeSH
• organická chemie metody   MeSH
• polymery chemie   MeSH
• Ramanova spektroskopie metody   MeSH
• spektroskopie infračervená s Fourierovou transformací metody   MeSH
• stříbro chemie   MeSH
• testování materiálů MeSH
• transmisní elektronová mikroskopie metody   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• aniline MeSH Prohlížeč
• aniliny MeSH
• dusičnan stříbrný MeSH
• kyslík MeSH
• polyaniline MeSH Prohlížeč
• polymery MeSH
• stříbro MeSH

The process of electrochemical treatment of a solution after strong basic anion exchanger regeneration was studied. The goal of the study was to reduce the nitrate content in the solution to allow its use in a closed loop. Diaphragmless, flow-through cells in a recirculation mode with and without a fluidizing bed of inert particles in the interelectrode space equipped with copper (Cu) cathodes and activated titanium anodes were used. The temperature was maintained at 20 degrees C. To assess the influence of recirculation of the regenerant solution on the quality of the treated water, the effect of the addition of copper ions to the solution, postelectrolysis cathode treatment, and enhanced mass transfer on the electrolysis results with respect to current efficiency and residual nitrate and nitrite concentration were investigated using an artificial solution. On the basis of the experimental results, a laboratory-scale unit for selective nitrate removal was designed and constructed that integrated ion exchange and electrochemical cell to one assembly. The process of recirculation of regenerant solution was tested using groundwater.

• MeSH
• amoniak analýza   MeSH
• chromatografie iontoměničová MeSH
• čištění vody přístrojové vybavení   metody   MeSH
• dusičnany chemie   MeSH
• elektrochemie * MeSH
• iontová výměna MeSH
• měď analýza   MeSH
• oxidace-redukce MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• srovnávací studie MeSH
• Názvy látek
• amoniak MeSH
• dusičnany MeSH
• měď MeSH

We synthesize p-type TiO2 nanotubes that allow band-gap adjustment by quantum confinement. These tubes therefore enable reductive photocatalytic reactions that are not thermodynamically possible on classic titania photocatalysts. Here, we demonstrate the direct photocatalytic nitrate reduction to ammonia without any need of hole scavengers. The quantum confinement effect (and thus the thermodynamic driving force) can be controlled by the thickness of the nanotube walls. Notably, the use of Pt single atoms as cocatalysts decorated on the TiO2 nanotubes additionally offers a superior ammonia production and a remarkable enhanced selectivity compared to Pt nanoparticles. Overall, the work not only highlights the potential of size-controlled modifications of electronic properties in extending the utility of a most classical photocatalyst but also exemplifies its use in technologically relevant reactions.

• Klíčová slova
• Photocatalytic nitrate reduction, Pt single atoms, Quantum confinement, p‐type titanium dioxide,
• Publikační typ
• časopisecké články MeSH

The process of selective nitrate removal from drinking water by means of ion exchange was studied. A commercial strong base anion exchanger with triethylammonium (-N+Et3) functional groups was used in the bicarbonate (HCO3-) and carbonate (CO3(2-)) form. The aim of this study was to optimize ion-exchanger regeneration in view of the subsequent electrochemical reduction of nitrates in the spent regenerant solution. The effects of ion-exchanger form, concentration of regenerant solution, and presence of nitrates, chlorides, and sulphates in the regenerant solution were studied. The strong base anion exchanger in HCO3- form that was investigated was able to treat 270 bed volumes of model water solution containing 124 mg dm(-3) nitrates. To achieve adequate regeneration of the saturated anion exchanger, it is necessary to use approximately 30 bed volumes of fresh 1-M sodium bicarbonate (NaHCO3) regenerant solution. The presence of residual 50-mg dm(-3) nitrates in the regenerant solution, treated by electrolysis, resulted in an increase in the dose of regenerant solution to 35 bed volumes and a decrease in the subsequent sorption run of approximately 13%. The volume of applied regenerant solution was high, but the consumption of NaHCO3 for regeneration was low.

• MeSH
• anionty analýza   MeSH
• chromatografie iontoměničová MeSH
• čištění vody přístrojové vybavení   metody   MeSH
• dusičnany chemie   MeSH
• elektrochemie * MeSH
• hydrogenuhličitany chemie   MeSH
• iontová výměna MeSH
• kvartérní amoniové sloučeniny chemie   MeSH
• měď analýza   MeSH
• oxidace-redukce MeSH
• spektrofotometrie atomová MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• srovnávací studie MeSH
• Názvy látek
• anionty MeSH
• dusičnany MeSH
• hydrogenuhličitany MeSH
• kvartérní amoniové sloučeniny MeSH
• měď MeSH
• triethylammonium cation MeSH Prohlížeč

A new method of determination of nitrate was developed, utilizing the nitrate reductase activity of Paracoccus denitrificans in which a further reduction of nitrate is blocked either by a mutation affecting formation of cytochromes c or by inhibition of the electron flow to nitrite reductase by mucidin. After deproteinization of the sample with zinc acetate the nitrite produced is determined colorimetrically.

• MeSH
• dusičnany analýza   metabolismus   MeSH
• dusitany metabolismus   MeSH
• mutageneze MeSH
• nitrátreduktasa MeSH
• nitrátreduktasy metabolismus   MeSH
• nitritreduktasy genetika   metabolismus   MeSH
• Paracoccus denitrificans genetika   metabolismus   MeSH
• stabilita enzymů MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• dusičnany MeSH
• dusitany MeSH
• nitrátreduktasa MeSH
• nitrátreduktasy MeSH
• nitritreduktasy MeSH

A comparative examination of reduced methyl [MV·](+) and benzyl [BV·](+) viologens (as artificial electron donors for quantitative estimation of the respiratory periplasmic (Nap) and membrane-embedded (Nar) nitrate reductases) using a newly constructed nap mutant strain of Paracocccus denitrificans was done. The activity with [MV·](+) was high in whole-cell assays, confirming that this compound donates electrons to Nar. Initial rates of the more lipophilic [BV·](+) were considerably lower, which was interpreted to be caused by an inhibition of the active transport of nitrate into the cells. Anionophoric activity of [BV·](+) was detectable but too low to effectively circumvent the inhibition of nitrate transporter.

• MeSH
• analýza jednotlivých buněk MeSH
• bakteriální proteiny chemie   genetika   metabolismus   MeSH
• benzylviologen metabolismus   MeSH
• dusičnany metabolismus   MeSH
• kinetika MeSH
• nitrátreduktasa chemie   genetika   metabolismus   MeSH
• oxidace-redukce MeSH
• Rhodobacteraceae chemie   enzymologie   genetika   MeSH
• transport elektronů MeSH
• Publikační typ
• časopisecké články MeSH
• hodnotící studie MeSH
• práce podpořená grantem MeSH
• Názvy látek
• bakteriální proteiny MeSH
• benzylviologen MeSH
• dusičnany MeSH
• nitrátreduktasa MeSH

Applying electrochemical nitrate reduction reaction (NO3RR) to produce ammonia offers a sustainable alternative to the energy-intensive Haber-Bosch process, which is crucial for clean energy and agricultural applications. While 2D MXenes hold great promise as electrocatalysts for NO3RR, their application for ammonia production remains underexplored. This study combines experimental and theoretical approaches to evaluate the catalytic performance of a series of MXenes with different central metal atoms for NO3RR. Among the materials studied (Ti3C2Tx, Ti3CNTx, Ti2CTx, V2CTx, Cr2CTx, Nb2CTx, and Ta2CTx), Ti3-based MXenes exhibit superior faradaic efficiency, ammonia yield rate, and stability. Density functional theory calculations offer further insights explaining the structure-activity-based observations. This research establishes a foundation for future studies aimed at leveraging MXenes for electrochemical nitrate reduction for green synthesis of ammonia.

• Klíčová slova
• 2D materials, catalysis, electrochemistry,
• Publikační typ
• časopisecké články MeSH