Free Nitrogen Atom Research Articles

Exploring structural and optical properties of a new series of soft salts based on cyclometalated platinum complexes.

A series of nine new soft salts based on two platinum(II) complexes, namely ([Pt(C^N)(CN)2]-[Pt(C^N)(en)]+) (en = ethane-1,2-diamine), has been developed and synthesized. Their photophysical properties in both solution and the solid state were described. All soft salt complexes exhibit phosphorescence emission with PLQY in the solid state up to 0.36. Most of these materials displayed aggregation-induced emission (AIE) or aggregation-induced emission enhancement (AIEE) in water/DMSO solutions as the water ratio increased. Structure-property relationships were analyzed in relation to emission properties. The presence of the free nitrogen atoms in soft salt complexes with a C^N pyrimidine-based ligand allowed for reversible sensitivity to acidic vapors, resulting in the quenching of phosphorescence emission. Additionally, for selected soft salts, we described reversible vapochromism behaviour, making these new materials interesting for multi-detection purposes in anti-counterfeiting applications.

ДОСЛІДЖЕННЯ КОМПЛЕКСОУТВОРЕННЯ ПОЛІЕТИЛЕНІМІНУ З ЙОНАМИ МІДІ (ІІ), НІКЕЛЮ (ІІ), КОБАЛЬТУ (ІІ)

There is described the influence of polyethylenimine globule structure on complexation with copper (II), nickel (II) and cobalt (II) ions. There are determined the values of the coordination number with the change of the pH of the solution for the complexes of ethylenediamine, diethylenetriamine and polyethylenimine with metal ions. It is investigated that the complexation of these metal ions with low molecular weight amines passes through three stages and with PEI through two stages. It is shown that the content of free nitrogen atoms in PEI, which do not react with metal ions, increases with increasing concentration of PEI in solution. The number of monomer units associated with metal ions depends on the size of the globule of the macromolecule, as well as the reaction process. The complexation reaction in solution is determined by the diffusion of metal ions into the polymer globule. If the reaction takes place in a diffusion field at a low polymer concentration, the rate of complexation is proportional to the concentration of macromolecules and the concentration of metal ions in solution.

A Zn based two-dimensional metal-organic framework as a dual ion sensor in aqueous media.

Excess and shortage of some metal ions like Fe3+ ions in drinking water away from permissible levels can cause severe health threat. Similarly, chromium is found chiefly in a hexavalent form that also poses a threat to human health. Human beings and other living organisms are at greater risk of exposure to these toxic ions and other chemicals. Development of new, effective and fast sensors is the need of time. MOFs are nanoporous materials which have quite fast detection time and effective in sensing of various metal ions and hazardous chemicals. A Zn based two-dimensional is synthesized and applied for the sensing of Fe3+ and Cr2O72- ions. Due to the presence of free oxygen and nitrogen atoms, this MOF showed quite high sensitivity with Ksv value of 1.8×104 and 6.5×104 with a limit of detection (LOD) 2.5μM and 0.15μM for Fe3+ and Cr2O72-ions respectively. This study proved the two-dimensional MOF as excellent sensor for the detection of Fe3+ and Cr2O72- ions. This can be used as colorimetric sensor for these ions due to color changes visible to the naked eye.

C‒H activation of caffeine at triruthenium and triosmium centers

Reactions of caffeine with triruthenium and triosmium clusters are described. Caffeine reacts with [Ru3(CO)12] at 110°C to afford [Ru3(CO)10{µ,η1,κ1-C5N4(CH3)3O2}(µ-H)] (1) and [Ru3(CO)8{µ,η1,κ1-C5N4(CH3)3O2}2(µ-H)2] (2) which contain metalated caffeine ligand(s) formed via C‒H bond activation at imidazole ring carbon of caffeine. Similar reactions between caffeine and [Os3(CO)12] or [Os3(CO)10(µ-H)2] furnish only the osmium analogue of 1 namely [Os3(CO)10{µ,η1,κ1-C5N4(CH3)3O2}(µ-H)] (3). In all these products, the metalated caffeine ligand acts in bridging capacity using the free imidazole ring nitrogen and carbon atoms. Cluster 1 readily reacts with PPh3 at room temperature to yield mono- and bis-phosphine substituted derivatives [Ru3(CO)9(PPh3){µ,η1,κ1-C5N4(CH3)3O2}(µ-H)] (4) and [Ru3(CO)8(PPh3)2{µ,η1,κ1-C5N4(CH3)3O2}(µ-H)] (5), respectively. All the new clusters have been spectroscopically characterized together with single crystal X-ray diffraction studies of 1 and 3.

A novel paramagnetic coordination polymer, fabricated from Co(NCS)2 and 2-pyridinecarbaldehyde isonicotinoylhydrazone

We report on a mixed cobalt(II)/cobalt(III) heteroleptic coordination polymer of the salt-like structure {[(CoIIIL2)2CoII(NCS)2][CoII(NCS)4]}n∙a(solvent) (1∙a(solvent)), obtained by a reaction of Co(NCS)2 with 2-pyridinecarbaldehyde isonicotinoylhydrazone (HL). Complex 1∙a(solvent) contains 15.52% of solvent molecules, which fits to six molecules of EtOH per one [(CoIIIL2)2CoII(NCS)2][CoII(NCS)4] species, and the structure of the crystals can be assigned to the {[(CoIIIL2)2CoII(NCS)2][CoII(NCS)4]}n∙6EtOH composition. 1∙a(solvent) was found to be stable after drying at 80 °C for several days, yielding a solvent-free complex 1. The FTIR data of both structures supports the complete loss of solvents after drying, while the general framework remains intact. As evident from the comparison of the experimental X-ray powder diffraction data of 1 with the calculated powder pattern generated from the single crystal X-ray data of 1∙a(solvent), the former complex partially loses its crystallinity; however, the experimental powder pattern resembles the calculated one. Thus, the overall structure of 1 is similar to that of 1∙a(solvent). The crystal structure of 1∙a(solvent) is constructed from the V-shaped (CoIIIL2)+ cations, where the metal ion is N4S2-coordinated by two L. These (CoIIIL2)+ cations are interlinked through CoII(NCS)2 molecules by coordination via free 4-pyridyl nitrogen atoms, yielding a 1D polymeric cationic chain {[(CoIIIL2)2CoII(NCS)2]2+}n, which are interlinked into a 3D framework through a bunch of bifurcated (N)C–S⋯π(2-Py) and linear (NN)C–H⋯O non-covalent interactions. Due to such 3D aggregation, a half of rhombohedral cells are filled by the interlayered [CoII(NCS)4]2– anions, while the other half of cells is free from non-volatile species and filled with volatile solvent molecules, yielding 1D tubular voids, which occupy about 17% of unit cell volume. Direct current variable-temperature magnetic susceptibility measurements on a polycrystalline sample of 1∙a(solvent) were carried out in the temperature range 1.8–300 K. The magnetic behaviour of 1∙a(solvent) indicates the presence of magnetic anisotropy of the CoII ions and/or very weak intermolecular exchange interactions. The surface and pore properties of 1 and HL were calculated by N2 adsorption at 77 K. In addition, CO2 adsorption properties of 1 and HL at different temperatures were determined. It was found that 1 increased both textural and CO2 adsorption properties.

Effect of N,N,N′-trimethylpiperazinium (TMP+) cations on magnetic properties and dimerization of fullerenes in the (TMP+)(CoIIporphyrin)(C60−) salts

New salts of fullerene C60•− radical anions with N,N,N′-trimethylpiperazinium cations (TMP+) containing neutral cobalt(II) porphyrin molecules: {(TMP+)⋅CoIIOEP}⋅(C60•−)⋅2C6H4Cl2⋅C6H5CN (1) and (TMP+)3{CoIITMPP⋅(C60−)}2(C60•−) ⋅C6H4Cl2⋅C6H5CN (2) have been obtained (OEP and TMPP are octaethyl- or tetrakis(4-methoxyphenyl)porphyrins, respectively). In these salts the C60•− radical anions or the TMP+ cations with free nitrogen atom can coordinate to cobalt(II) porphyrins and form Co-C(C60−) or Co-N(TMP+) bonds. The properties of these salts and the possibility of fullerene dimerization depend on type of bonds formed. For example, TMP+ cations in 1 form coordination (TMP+)⋅CoIIOEP assemblies preserving free non-bonded C60•− radical anions. They are effectively coupled with S = 1/2 spins localized on CoIIOEP (Weiss temperature is −27 K and decrease of magnetic moment of 1 is observed below 150 K). Previously the {(MDABCO+)⋅CoIITMPP}2⋅(C60−)2⋅(C6H4Cl2)2.5⋅(C6H5CN)1.5 salt was obtained in which doubly-bonded (C60−)2 dimers were found. In contrast to this salt, TMP+ cations in 2 preserved uncoordinated allowing the formation of the Co-C(C60−) bond of 2.273(3) Å length in the diamagnetic σ-bonded CoIITMPP⋅(C60−) anions. In coordinated state, fullerene anions cannot dimerize in 2 in spite of that their mutual arrangement and short interfullerene distances are favorable for such dimerization. Thus, variation of cations in the (Cation+)(CoIIporphytin)(C60−) salts drastically affects their properties and allows one to control dimerization of fullerene anions.

Thermal analysis of hypersonic flows of carbon dioxide and air in thermodynamic non-equilibrium

Numerical simulations of carbon dioxide and air flows are presented for the Mars Pathfinder experimental capsule configuration under hypersonic conditions. Despite the low density flows, it is shown that the medium can be modeled as a continuum and that a laminar flow approximation is valid. The finite volume method is used to solve the Navier-Stokes equations including Park’s two-temperature model for chemical dissociation and ionization. Results are presented in terms of heat flux distributions over the capsule surface and good agreement is observed between simulations and experimental data. Although freestream conditions are relatively similar for both gas mixtures, the different shock wave topologies and species dissociation profiles lead to changes with respect to thermal non-equilibrium, presented in terms of the translational-rotational and vibrational-electronic temperature modes. Ionization effects are also investigated for an air flow at more extreme conditions, with an even lower freestream density and higher Mach number. An assessment of chemical species models shows that ionization of free nitrogen and oxygen atoms in the air mixture must be accurately captured since it causes large variations in the thermal non-equilibrium process, substantially altering the surface heat flux.

Highly selective and sensitive detection towards cationic Cu2+ and Fe3+ contaminants via an In-MOF based dual-responsive fluorescence probe

Effective recognition and detection of heavy metal Cu2+ and Fe3+ ions from water are highly desirable because of their serious harms to human health and environmental safety. However, the existing detection techniques are still high cost, time-consuming and highly demanding for operators. As an alternative approach to address this issue, an indium-based MOF labeled as In-MOF of 1 with high water stability and opposite charges to Cu2+ and Fe3+ ions was successfully prepared and deployed as optical sensor to sense target analytes, according to our previous work. Prominently, this anionic framework exhibits high photoluminescence property and excellent fluorescence quenching response to target analytes with high selectivity, sensitivity and detection limits of 3.88 ppb for Cu2+, 4.2 ppb for Fe3+ ions, respectively, both of which have been confirmed to be ultro-low values among all reported MOFs-based photochemical sensors. Furthermore, the quick and accurate probing capability of 1 also has been proved even under the interference of dozens of anions or cations. The possible photoluminescence and fluorescence quenching mechanisms were studied in detail, revealing that rapid coordination reactions between free imidazole nitrogen and carboxyl oxygen atoms of the framework (Lewis basic sites) and the metal ions of Cu2+/Fe3+ (Lewis acid sites) should be proposed to be the key reason for high efficiency fluorescence quenching.

A pacs-type metal-organic framework based on [Cd3(OH)] clusters for effective C2H2/CO2 separation and fluorescent detection of TNP in water

Metal-organic frameworks (MOFs) have become a versatile platform for gas capture/separation and luminescent sensing of toxic pollutants, and the combination of both of these properties depends on the robust framework and pre-designed pore functionality which is critical to achieve the targeted applications. In this work, a novel Cd(II)-MOF {(NH2Me2)[Cd3 (μ3-OH) (tpt) (TZB)3](H2O)2 (1,4-dioxane)5}n (1, H2TZB ​= ​4-(1H-tetrazol-5-yl)benzoic acid, tpt ​= ​2,4,6-tri (pyridin-4-yl)-1,3,5-triazine) comprising of a {Cd3(OH)}5+ cluster-based unit (SBU) has been solvothermally formed from nitrogen-rich and highly fluorescent organic ligands. The porous structure 1 is composed of cages and segments which are affixed by high density of free nitrogen atoms. The activated Cd(II)-MOF (1a) exhibits a relative high C2H2 sorption capacity than that of CO2 which endows it with a C2H2/CO2 sorption selectivity of 7.26 ​at room temperature. Furthermore, complex 1 could behave as a luminescent sensor for highly discriminative detection of explosive 2,4,6-trinitrophenol (TNP) via remarkable fluorescence quenching (Ksv ​= ​6.16✕104 ​M−1).

Reversible fluorescent switching properties of pyrene-substituted acylhydrazone derivatives toward mechanical force and acid vapor with aggregation-induced emission

Four pyrene-substituted acylhydrazone derivatives named PMBH ((E)-N'-(pyren-1-ylmethylene)benzohydrazide), PMPH ((E)-N'-(pyren-1-ylmethylene)picolinohydrazide), PMNH ((E)-N'-(pyren-1-ylmethylene)nicotinohydrazide) and PMIH ((E)-N'-(pyren-1-ylmethylene)isonicotinohydrazide) by functionalizing the phenyl ring and pyridyl ring with pyrene-substituted acylhydrazone moiety have been designed and synthesized, whose properties were investigated. All the four synthesized compounds exhibited favorable aggregation induced emission (AIE) features and reversible mechanofluorochromism (MFC) behaviour. Especially, the intense cyan emission of PMIH changed into orange-yellow emission with a 101 nm red-shift upon grinding. The MFC behavior was associated with the crystalline-amorphous phase transformation between the pristine and ground states, which was confirmed by the investigations of the power X-ray diffraction (PXRD), the differential scanning calorimetry (DSC) and field emission scanning electron microscopy (FESEM). Specifically, PMPH, PMNH and PMIH demonstrated remarkable and reversible acidofluorochromic response due to the presence of free nitrogen atom of pyridyl groups at the terminal position. The chosen approaches showed a new possibility for generating multi-stimuli responsive materials with modulated solid state properties.

IR-Laser Ablation of Potassium Cyanide: A Surprisingly Simple Route to Polynitrogen and Polycarbon Species.

Pulsed laser irradiation of solid potassium cyanide (KCN) produces, besides free nitrogen and carbon atoms, the molecular species KN and KC which are potential candidates for interstellar species of potassium. Additionally, N3, N3 −, KN3, C3, C3 −, and KC3 are produced and isolated in solid noble gases as well as in solid N2. Molecular potassium nitrene (KN) reacts with dinitrogen in neon and argon matrices after photochemical excitation (λ=470 nm) forming molecular end‐on (C ∞v) and side‐on (C 2v) potassium azide isomers. The side‐on isomer (C 2v) is thermodynamically favored at the CCSD(T)/ma‐def2‐TZVP level of theory. It can be obtained from the end‐on isomer by UV‐irradiation (λ=273 nm).

Devising Chemically Robust and Cationic Ni(II)-MOF with Nitrogen-Rich Micropores for Moisture-Tolerant CO2 Capture: Highly Regenerative and Ultrafast Colorimetric Sensor for TNP and Multiple Oxo-Anions in Water with Theoretical Revelation.

Metal-organic frameworks (MOFs) show distinctive superiority for carbon dioxide (CO2) capture and luminescent sensing of toxic pollutants over other materials, where combination of both of these properties together with improvement of hydrolytic stability and pore functionality is critical to environmental remediation applications. The Ni(II) framework [Ni2(μ2-OH)(azdc)(tpim)](NO3)·6DMA·6MeOH (CSMCRI-3) (tpim = 4,4',4″-(1H-imidazole-2,4,5-triyl)tripyridine, H2azdc = azobenzene-4,4'-dicarboxylic acid, DMA = dimethylacetamide, CSMCRI = Central Salt & Marine Chemicals Research Institute), encompassing cationic [Ni2(μ2-OH)(CO2)2] SBUs, is solvothermally synthesized from nitrogen-rich and highly fluorescent organic struts. The noninterpenetrated structure, containing free nitrogen atom affixed microporous channels, is stable in diverse organic solvents and weakly basic and acidic aqueous solutions. The activated MOF (3a) exhibits strong CO2-framework interaction and extremely selective CO2 adsorption over N2 (292.5) and CH4 (11.7). Importantly, water vapor exposure does not affect the surface area and/or multiple CO2 uptake-release cycles, signifying potential of the porous structure for long-term use under humid conditions. Aqueous-phase sensing studies illustrate extremely specific and ultrafast detection of explosive 2,4,6-trinitrophenol (TNP) via remarkable fluorescence quenching (KSV = 1.3 × 105 M-1), with a 0.25 ppm limit of detection (LOD). Furthermore, 3a serves as unique luminescent probe for highly discriminative and quick responsive detection of three noxious oxo-anions (Cr2O72-, CrO42-, MnO4-) in water via noteworthy turn-off responses and extreme low LODs (Cr2O72- 0.9; CrO42- 0.29; MnO4- 0.25 ppm). It is imperative to stress the outstanding reusability of the MOF toward multicyclic sensing of all four major water contaminants, alongside visible colorimetric changes upon individual analyte detection. Mechanistic insights in light of the electron transfer route together with density functional theory calculations portray the influence of pore functionalization in framework-analyte interactions, including alternation in energy levels, where varying degrees of contribution of energy transfer explicitly authenticates high quenching of the material.

Methylthiazolyl Tacn Ligands for Copper Complexation and Their Bifunctional Chelating Agent Derivatives for Bioconjugation and Copper-64 Radiolabeling: An Example with Bombesin.

We present here the synthesis of two new bifunctionalized azachelators, no2th-EtBzNCS and Hno2th1tha, as bioconjugable analogues of two previously described di- and trimethylthiazolyl 1,4,7-triazacyclononane (tacn) ligands, no2th and no3th, for potential uses in copper-64 (64Cu) positron emission tomography imaging. The first one bears an isothiocyanate group on the remaining free nitrogen atom of the tacn framework, while the second one presents an additional carboxylic function on one of the three heterocyclic pendants. Their syntheses required regiospecific N-functionalization of the macrocycles. In order to investigate their suitability for in vivo applications, a complete study of their copper(II) chelation was performed. The acid-base properties of the ligands and their thermodynamic stability constants with copper(II) and zinc(II) cations were determined using potentiometric techniques. Structural studies were conducted in both solution and the solid state, consolidated by theoretical calculations. The kinetic inertness in an acidic medium of both copper(II) complexes was determined by spectrophotometry, while cyclic voltammetry experiments were performed to evaluate the stability at the copper(I) redox state. UV-vis, NMR (of the zinc complexes), electron paramagnetic resonance spectroscopy, and density functional theory studies showed excellent agreement between the solution structures of the complexes and their crystallographic data. These investigations unambiguously prove that these bifunctional derivatives display similar coordination properties as their no2th and no3th counterparts, opening the door to targeted bioapplications. The no2th-EtBzNCS and Hno2th1tha ligands were then conjugated to a bombesin antagonist peptide for targeting the gastrin-releasing peptide receptor (GRPr). To highlight the potential of the two chelators for radiopharmaceutical development, the 64Cu-radiolabeling properties, in vitro stability, and binding affinity to GRPr of the corresponding bioconjugates were determined. Altogether, the results of this work warrant the further development of 64Cu-based radiopharmaceuticals comprising our novel bifunctional chelators.

Base-Free and Acceptorless Dehydrogenation of Alcohols Catalyzed by an Iridium Complex Stabilized by a N,N,N-Osmaligand

The preparation of a N,N,N-osmaligand, its coordination to iridium to afford an efficient catalyst precursor, and the catalytic activity of the latter in dehydrogenation reactions of hydrogen carriers based on alcohols are reported. Complex OsH2Cl2(PiPr3)2 (1) reacts with 3-(2-pyridyl)pyrazol to give the osmium(II) complex 2H, which contains an acidic hydrogen atom. Deprotonation of the latter by the bridging methoxy groups of the dimer [Ir(μ-OMe)(η4-COD)]2 (COD = 1,5-cyclooctadiene) leads to Ir(2)(η4-COD) (3), where osmaligand 2 has a free-nitrogen atom. Iridium complex 3 catalyzes the dehydrogenation of secondary and primary alcohols to ketones and aldehydes or esters, respectively, and the dehydrogenation of diols to lactones. Cyclooctatriene is detected during the catalysis by GC-MS, suggesting that the true catalyst of the reactions is a dihydride IrH2(2)-species with osmaligand 2 acting as N,N,N-pincer. The presence of a phenyl group in the substrates favors the catalytic processes. The dehydrogenat...

Fast and Selective Heavy Metal Removal by a Novel Metal‐Organic Framework Designed with In‐Situ Ligand Building Block Fabrication Bearing Free Nitrogen

Fast and effective adsorbents for the selective removal of HgII and PbII ions were prepared by the reaction of Zn(NO3 )2 ⋅6H2 O, H2 BDC, and N1 ,N2 -bis(pyridin-4-ylmethylene) ethane-1,2-diamine (L) that yields an unprecedented two-dimensional layer-based supramolecular framework, {Zn(BDC)(L*)}⋅DMF (TMU-40), by solvothermal reaction. The formation of this framework involved an in situ C=C coupling of L to L* [L*=5,6-di(pyridin-4-yl)-1,2,3,4-tetrahydropyrazine]. As L* contains free nitrogen atoms, direct reaction of L* and metals led to metallated products. Post-synthetic modification of this novel MOF (TMU-40) with H2 O2 gives a new framework (O-TMU-40) by same structure and different ligand, which also bears free nitrogen atoms. FTIR spectra, TGA analysis, X-ray diffraction, Zeta Potential analysis and 1 H NMR spectroscopy were used to characterize the prepared frameworks. The TMU-40 and O-TMU-40 frameworks were used for heavy-metal removal from aqueous solutions. Maximum adsorption values of 269 mg g-1 for HgII with TMU-40 and 215 mg g-1 for PbII with O-TMU-40 were achieved in 10 min at 298 Kwithout changes in the pH of the adsorption medium with pseudo-second order kinetics based on the Langmuir model. The extremely fast kinetics of TMU-40 means this adsorbent can reduce heavily contaminated water containing HgII concentrations of 40 ppm down to the acceptable limit of 2 ppb.

Experimental and theoretical studies on vanadium bromoperoxidase activity of alkyne arm dioxidovanadium(V) complex: Crystal structure, spectral studies, and DFT calculations

The alkyne arm bearing dioxidovanadium(V) complex was synthesized by the reaction of vanadium sulphate, 1-[2-hydroxy-4-(prop-2-yn-1-yloxy)phenyl]ethanone and propane-1,2-diamine. The synthesized complex was characterized by various spectral techniques and its structure was determined using single-crystal X-ray diffraction analysis. Vanadium centre has square-pyramidal based geometry with an axial oxido ligand and the equatorial positions are occupied by another oxido ligand and phenolato oxygen, imine nitrogen and free amine nitrogen atoms. DFT and TD-DFT calculations were examined to identify the electronic structure, and electronic transitions of the complex observed in the absorption spectra. The percentage of intermolecular interactions in the crystal structure has been evaluated by 3D Hirshfeld surfaces and 2D fingerprint plots. The CH⋯π and intermolecular interactions of the complex were examined using Bader’s theory of QTAIM by ADF 2017. The dioxidovanadium(V) complex mimics as an efficient vanadium-dependent bromoperoxidase towards the bromination of phenol red in acetonitrile medium at room temperature.

Effect of Pyridyl Substitution on Chemical and Photochemical Water Oxidation by [Ru(terpyridine)(bipyridine)(OH2)]2+ Scaffolds

The complexes [Ru(2‐py‐tpy)(bpy)(OH2)][PF6]2 (1; bpy = 2,2′‐bipyridine), [Ru(3‐py‐tpy)(bpy)(OH2)][PF6]2 (2), and [Ru(4‐py‐tpy)(bpy)(OH2)][PF6]2 (3; n‐py‐tpy = 4′‐(n‐pyridyl)‐2,2′:6′,2′′‐terpyridine, n = 2–4), as electronic modifications of the [Ru(tpy)(bpy)(OH2)][PF6]2 scaffold, have been synthesized and characterized thoroughly by several spectroscopic methods. All three complexes were employed as catalysts for chemical and photochemical water oxidation. The free nitrogen atom of the pyridine ring in catalysts 1–3 is protonated at pH 1 and acts as an electron‐withdrawing group. For 2, the meta‐nitrogen atom has a larger withdrawing effect compared with those of 1 and 3, as the positive charge (δ+) is delocalized only at the carbon atoms. However, the positive charge (δ+) is distributed among the nitrogen and carbon atoms of the pyridine ring for the ortho‐ and para‐nitrogen atoms in 1 and 3, respectively. Electrochemical and manometry studies revealed that 1 and 3 are better catalysts owing to the weaker electron‐withdrawing effects than that for 2. All of these complexes also act as efficient catalysts towards the photo‐oxidation of water in pH 6.5 phosphate buffer at 20 °C in the presence of [Ru(bpy)3]2+ as a photosensitizer and Na2S2O8 as a sacrificial electron acceptor.

Physicochemical properties of bactericidal plasma-treated water

Plasma-treated water (PTW), i.e. distilled water (DW) exposed to low-temperature atmospheric pressure helium plasma, exhibited strong bactericidal activity against Escherichia coli in suspension even within a few minutes of preparation. This effect was enhanced under acidic conditions. The bactericidal activity of PTW was attenuated according to first-order kinetics and the half-life was highly temperature dependent. The electron spin resonance (ESR) signal of an adduct of the superoxide anion radical () was detected in an aqueous solution using a spin-trapping reagent mixed with PTW, and adding superoxide dismutase to the PTW resulted in a loss of the bactericidal activity and weakening of the ESR adduct signal of in the spin-trapping. These results suggest that plays an important role in imparting bactericidal activity to PTW. Moreover, molecular nitrogen was required both in the ambient gas and in the DW used to prepare the PTW. We, therefore, suggest that the reactive molecule in PTW with bactericidal effects is not a free reactive oxygen species but nitrogen atom(s)-containing molecules that release , such as peroxynitrous acid (ONOOH) or peroxynitric acid (O2NOOH). Considering the activation energy for degradation of these species, we conclude that peroxynitric acid stored in PTW induces the bactericidal effect.

HIGH TEMPERATURE GAS NITRIDING TREATMENT OF AISI 430 USING LOW AND HIGH PURITY NITROGEN GAS

The properties of stainless steels can be improved by high temperature gas nitriding (HTGN) treatment. The improving of their properties are obtained from nitrogen atom which diffuse into stainless steel. Nitrogen gas is the main source of nitrogen atom on the HTGN treatment. Generally, these treatment use high purity of nitrogen gas. The aim of this research is to investigate the effect of nitrogen gas purity on the HTGN treatment for AISI 430. Stainless steel AISI 430 plate 2 mm thick was processed by HTGN treatment. The specimens was exposed at nitrogen gas atmosphere at temperature 1200oC and held for 2 hours prior quenching in water. The treatment used industrial/welding grade (99.5%) as low nitrogen gas purity and ultra high purity (UHP) grade (99.999%) as high nitrogen gas purity. The vickers micro-hardness test was conducted to evaluate the hardness distribution from surface into middle section of the specimens before and after treatment. Light optical microscope was applied to examine the microstructure of specimens after treatment. Metallographic examination shows both treatments using low and high purity gas have the same grain size. However HTGN treatment using low purity of nitrogen gas produces hardness slightly lower than the high purity. This is due the high content of impurity of the low purity gas that reduces the partial pressure of nitrogen gas. Another effect of impurity is the reaction between nitrogen gas and its impurity especially oxygen gas. These reactions reduce the amount of free nitrogen atom which diffuses on the stainless steel.

Consecutive introduction of Ag(i)to an anionic homoleptic Co(iii) complex: variable Ag(i) coordination mode

Although the pyridine-2,6-diamide ligand is widely reported, coordination chemistry of the analogous pyrazine-2,6-diamide ligand has not been reported to date. To study the complexation behavior, we have synthesized N,N′-dibenzylpyrazine-2,6-dicarboxamide and the heterometallic complexes were in a stepwise manner. After dimerisation with Co(III) complexation, two ring nitrogen atoms are freely available. These two free pyrazine nitrogen atoms were studied for their coordination with Ag(I), resulting in three heterometallic complexes, C40H34AgCoN8O5, C42H38Ag3CoN10O11 and C42H53AgCoN9O13. The mode of coordination could be controlled by varying the metal to ligand ratio and varying the counter anion. Moreover, we found conditions that make the ligand to either coordinate or not coordinate to Ag+. Some of these complexes also display the rare organometallic (C–Ag) bond.