Acetate Counterions Research Articles

Synthesis of MnS/MnO Decorated N, S‐Doped Carbon Derived from a Mn(II)‐Coordinated Polymer for the Catalytic Oxidation of H2O2 and Bisphenol A

AbstractA way to synthesize a Mn2+‐ coordinated polymer precursor ligated by sulfur atoms with acetate counter ions (Mn‐DTOGA) is proposed, which is achieved by an imine formation reaction between dithiooxamide and glutaraldehyde in the presence of manganese (II) acetate. MnS/MnO decorated N, S‐doped carbon nanoparticles (MnS/O‐SNC) are then prepared by calcination of the Mn ion‐coordinated polymer for the practical applications of catalytic reactions. The Mn‐DTOGA and MnS/O‐SNC structures prepared at different temperatures (700, 800, and 900 °C) are characterized using various physical and electrochemical and chemical analyses. The nanoparticles prepared at 900 °C reveal the best performance for the catalytic oxidation of Hydrogen peroxide (H2O2) and bisphenol A. The decomposition potentials of H2O2 (1.0 mm) and bisphenol A (100.0 µm) on the catalyst modified electrode are observed to be +0.40 and +0.15 V (versus Ag/AgCl), respectively. It is observed that the catalytic performances to the oxidation reactions are mainly related to MnO decorated outside the SNC particles compared to MnS formed inside the particles. The electrode reveals a wide dynamic range with the low detection limits for H2O2 (0.08 (±0.02) µm) and bisphenol A (0.17 (±0.04) µm). This study will provide essential clues for the future catalyst design.

Photoinduced Processes in Lysine-Tryptophan-Lysine Tripeptide with L and D Tryptophan.

Optical isomers of short peptide Lysine-Tryptophan-Lysine (Lys-{L/D-Trp}-Lys) and Lys-Trp-Lys with an acetate counter-ion were used to study photoinduced intramolecular and intermolecular processes of interest in photobiology. A comparison of L- and D-amino acid reactivity is also the focus of scientists' attention in various specialties because today, the presence of amyloid proteins with D-amino acids in the human brain is considered one of the leading causes of Alzheimer's disease. Since aggregated amyloids, mainly Aβ42, are highly disordered peptides that cannot be studied with traditional NMR and X-ray techniques, it is trending to explore the reasons for differences between L- and D-amino acids using short peptides, as in our article. Using NMR, chemically induced dynamic nuclear polarization (CIDNP) and fluorescence techniques allowed us to detect the influence of tryptophan (Trp) optical configuration on the peptides fluorescence quantum yields, bimolecular quenching rates of Trp excited state, and the photocleavage products formation. Thus, compared with the D-analog, the L-isomer shows a greater Trp excited state quenching efficiency with the electron transfer (ET) mechanism. There are experimental confirmations of the hypothesis about photoinduced ET between Trp and the CONH peptide bond, as well as between Trp and another amide group.

Tertiary amine-bisquaternary ammonium functionalized polyacrylonitrile fiber for catalytic synthesis of pyran-annulated heterocycles

Polyacrylonitrile fiber supported bisquaternary ammonium salts with varying interchain quaternary ammonium (QA) to tertiary amine (TA) ratio, counter ions and linker groups were prepared and characterized by TGA, FTIR, XPS, XRD, SEM, EA and water contact angle. The functionalized fibers were used to catalyze three-component reaction (3CR) and tandem deacetalization-3CR for the synthesis of pyrano[4,3-b]pyrans, pyrano[3,2-c]chromenes and pyrano[3,2-c]quinolines in ethanol-water mixture. Under varying reaction conditions such as time, temperature, catalyst amount and solvents, the catalytic ability of the prepared fiber catalyst was investigated. Under the optimum conditions, the bisquaternary ammonium fiber with acetate counter ion and an interchain QA to TA ratio of 1:1 (PANBQAcF) showed the best catalytic activity among the prepared fiber catalysts, and it can be used for 10 runs consecutively with only a slight depreciation in catalytic activity. Interestingly, PANBQAcF can efficiently catalyze tandem deacetalization-Knoevenagel reaction and the relevant novel tandem deacetalization-3CRs for the synthesis of pyran-annulated heterocycles. In the tandem deacetalization reactions, the acetate ion plays an important role of facilitating proton transfer, which makes PANBQAcF a cooperative and reusable heterogeneous catalyst.

Aggregation Behavior of Structurally Similar Therapeutic Peptides Investigated by 1H NMR and All-Atom Molecular Dynamics Simulations.

Understanding of peptide aggregation propensity is an important aspect in pharmaceutical development of peptide drugs. In this work, methodologies based on all-atom molecular dynamics (AA-MD) simulations and 1H NMR (in neat H2O) were evaluated as tools for identification and investigation of peptide aggregation. A series of structurally similar, pharmaceutically relevant peptides with known differences in aggregation behavior (D-Phe6-GnRH, ozarelix, cetrorelix, and degarelix) were investigated. The 1H NMR methodology was used to systematically investigate variations in aggregation with peptide concentration and time. Results show that 1H NMR can be used to detect the presence of coexisting classes of aggregates and the inclusion or exclusion of counterions in peptide aggregates. Interestingly, results suggest that the acetate counterions are included in aggregates of ozarelix and cetrorelix but not in aggregates of degarelix. The peptides investigated in AA-MD simulations (D-Phe6-GnRH, ozarelix, and cetrorelix) showed the same rank order of aggregation propensity as in the NMR experiments. The AA-MD simulations also provided molecular-level insights into aggregation dynamics, aggregation pathways, and the influence of different structural elements on peptide aggregation propensity and intermolecular interactions within the aggregates. Taken together, the findings from this study illustrate that 1H NMR and AA-MD simulations can be useful, complementary tools in early evaluation of aggregation propensity and formulation development for peptide drugs.

Impact of counterions on micelle formation and polymerization of 11-acryloyloxyundecyltrimethylammonium surfactants

New surfactants based on the cationic monomer 11-acryloyloxyundecyltrimethylammonium with counterions bromide, nitrate, acetate, camphorsulfonate, 4-toluenesulfonate, trifluoroacetate were obtained in this work. In most cases counterions change the critical micelle concentration by 2–3 times (being compared with bromide) except sample with acetate counterions (in this case critical micelle concentration increases by an order of magnitude). Substitution of bromide for hydrophobic counterions (toluenesulfonate, trifluoroacetate, camphorsulfonate) does not lead to expected transformation of spherical micelles to long wormlike micelles. The polymerization of such monomers occurs according to the microemulsion mechanism involving micelles of monomers. • New surface-active monomers with various counterions have been obtained. • Hydrophobic counterions don't lead spherical to long wormlike micelles transition. • The degree of polymerization of formed polymers depend on counterions. • The surfactant with acetate has a maximum CMC value from the studied substances.

Counterion of Chitosan Influences Thermodynamics of Association of siRNA with a Chitosan-Based siRNA Carrier.

The work aimed to compare quality of a siRNA carrier prepared with chitosan of two different sources having similar degree of deacetylation and molecular weights. Differences were analyzed from thermodynamic characteristics of interactions with siRNA. The siRNA carrier (chitosan-coated poly(isobutylcyanoacrylate) nanoparticles) was prepared with home-prepared, CSLab, and commercial, CSCom, chitosans. Chitosan counterion was identified and chitosans CSCommod1 and CSCommod2 were obtained from CSCom exchanging counterion with that found on CSLab. Carrier quality was checked considering the size, zeta potential and siRNA association capacity by gel electrophoresis. Thermodynamic parameters of interactions between siRNA and chitosans in solution or immobilized at the carrier surface were determined by isothermal titration calorimetry(ITC). CSLab and CSCommod2 having a high content of acetate counterion associated better siRNA than CSCom and CSCommod1 which counterion included mainly chloride. ITC measurements indicated that siRNA interactions with chitosan and the siRNA carrier were driven by entropic phenomena including dehydration, but thermodynamic parameters of interactions clearly differed according to the nature of the counterion of chitosan. The influence of chitosan counterions was interpreted considering their different lyotropic character. Association of siRNA with our siRNA carrier was influenced by the nature of counterions associated with chitosan. Driven by entropic phenomena including dehydration, interactions were favored by acetate counterion. Although more work would be needed to decipher the influence of the counterion of chitosan during association with siRNA, it was pointed out as a new critical attribute of chitosan to consider while formulating siRNA carrier with this polysaccharide.

Formulation Composition and Process Affect Counterion for CSP7 Peptide.

Counterions commonly remain with peptides in salt form after peptide purification. In animal and human studies, acetate counterions are a safer and more acceptable choice for peptides than others (e.g., trifluoroacetate counterions). Various salt forms of caveolin-1 scaffolding domain (CSP7) affect counterion volatilization. The development of lyophilized formulations containing volatile compounds is a challenge because these compounds sublimate away during the process. This work aims to investigate the effect of excipients and lyophilization parameters on the preservation of volatile compounds after lyophilization. The peak areas obtained from 1H and 19F NMR spectra were used to calculate the molar ratio of counterions to CSP7. We found that the pH modifier excipient had the greatest impact on the loss of counterions. By optimizing the molar ratio of bulking agent to CSP7, volatile compounds can be preserved after lyophilization. Higher chamber pressure during lyophilization can lower the sublimation rate of volatile compounds. Moreover, the loss of volatile compounds affects the stability of CSP7 due to the pH shift of reconstituted solutions, thereby causing peptide aggregation. The optimization of the formulation and processing helps preserve volatile compounds, thus minimizing the pH change of reconstituted solutions and maintaining the stability of peptide.

Synthesis and structural characterization of dinuclear Zinc(II) and Europium(III) complexes based on a bis-hydrazone ligand

A C2-symmetrical N,O-Schiff base ligand containing two hydrazone units has been synthesized and structurally characterized. The solid state structure as determined by single-crystal X-ray diffraction analysis reveals the presence of both intramolecular and intermolecular hydrogen bonds which lead to the formation of a C1-symmetrical conformation as well as a novel one-dimensional (1-D) helical hydrogen-bonded network. The reactions of this bis-hydrazone ligand with zinc(II) and europium (III) salts under appropriate conditions resulted in dinuclear mono-ligand zinc and tri-ligand europium complexes, respectively. The complexes were characterized by NMR spectroscopies, mass spectrometry and elemental analysis. The zinc complex has been further structurally determined by X-ray crystallography. In its solid state structure, the ligand is doubly deprotonated incorporating two zinc(II) cores that are bridged with both phenol-O group and acetate counterions. The solution electronic absorption and emission properties were characterized for both the ligand and zinc complex.

Self-Assembled Networks of Short and Long Chitin Nanoparticles for Oil/Water Interfacial Superstabilization.

Highly charged (zeta potential ζ = +105 mV, acetate counterions) chitin nanoparticles (NCh) of three different average aspect ratios (∼5, 25, and >60) were obtained by low-energy deconstruction of partially deacetylated chitin. The nanoparticles were effective in reducing the interfacial tension and stabilized the oil/water interface via network formation (interfacial dilatational rheology data) becoming effective in stabilizing Pickering systems, depending on NCh size, composition, and formulation variables. The improved interfacial wettability and electrosteric repulsion facilitated control over the nanoparticle’s surface coverage on the oil droplets, their aspect ratio and stability against coalescence during long-term storage. Emulsion superstabilization (oil fractions below 0.5) occurred by the microstructuring and thickening effect of NCh that formed networks at concentrations as low as 0.0005 wt %. The ultrasound energy used during emulsion preparation simultaneously reduced the longer nanoparticles, producing very stable, fine oil droplets (diameter ∼1 μm). Our findings indicate that NCh surpasses any reported biobased nanoparticle, including nanocelluloses, for its ability to stabilize interfaces at ultralow concentrations and represent a step-forward in efforts to fully replace surfactants in multiphase systems.

Acidic Gases Separation from Gas Mixtures on the Supported Ionic Liquid Membranes Providing the Facilitated and Solution-Diffusion Transport Mechanisms.

Nowadays, the imidazolium-based ionic liquids containing acetate counter-ions are attracting much attention as both highly selective absorbents of the acidic gases and CO2 carriers in the supported ionic liquid membranes. In this regard, the investigation of the gas transport properties of such membranes may be appropriate for better understanding of various factors affecting the separation performance and the selection of the optimal operating conditions. In this work, we have tested CH4, CO2 and H2S permeability across the supported ionic liquid membranes impregnated by 1-butyl-3-methylimidazolium acetate (bmim[OAc]) with the following determination of the ideal selectivity in order to compare the facilitated transport membrane performance with the supported ionic liquid membrane (SILM) that provides solution-diffusion mechanism, namely, containing 1-butyl-3-methylimidazolium tetrafluoroborate (bmim[BF4]). Both SILMs have showed modest individual gases permeability and ideal selectivity of CO2/CH4 and H2S/CH4 separation that achieves values up to 15 and 32, respectively. The effect of the feed gas mixture composition on the permeability of acidic gases and permeselectivity of the gas pair was investigated. It turned out that the permeation behavior for the bmim[OAc]-based SILM toward the binary CO2/CH4, H2S/CH4 and ternary CO2/H2S/CH4 mixtures was featured with high acidic gases selectivity due to the relatively low methane penetration through the liquid phase saturated by acidic gases.

An unexpected μ4-oxido-bridged tetranuclear Cu(II) inverse coordination complex of a heptadentate bis(pyrazolyl)methane-based ligand: Synthesis, structure, spectroscopic properties, and catecholase activity

A new tetranuclear copper(II) complex, {But-C6H2(O)[CH = N-CH2-CH(pz)2]2}2Cu4(μ4-O)(OAc)4 (L2Cu4(μ4-O)(OAc)4, pz = pyrazolyl ring) has been prepared from the condensation reaction of 4-tert-butyl-2,6-diformylphenol with two equivalents of bis(pyrazolyl)ethanamine moieties in the presence of two equivalents of copper(II) acetate. The complex has been characterized by X-ray diffraction studies in solid state, as well as by UV–Vis, IR, and ESI spectroscopies. The structure of this inverse coordination complex consists of a central oxygen ion surrounded by four copper(II) cations residing in the corners of a distorted tetrahedron; the remaining coordination sites of the Cu2+ ions are filled by imine donors and acetate counter-ions, leaving the bis(pyrazolyl)methane donor groups uncoordinated to the copper(II) centers. In contrast to the solid-state structure, this compound was found to be dinuclear in solution, LCu2(OAc)2(OH). The complex catalyzes the oxidation of 3,5-di-tert-butylcatechol (DTBC) and 4-tert-butylcatechol (TBC) to their corresponding quinones. The catalytic mechanism was investigated using DTBC as a substrate, and it was found that the oxidation reaction occurs via two different pathways, one involving molecular oxygen and the other hydrogen peroxide as oxidants.

Effect of particle shape and size on the morphology and optical properties of zinc oxide synthesized by the polyol method

In this study we prepared zinc oxide (ZnO) nanoparticles using the polyol method with zinc acetate and/or sodium acetate in a propylene glycol medium with varied hydrolysis reaction time (10, 60 and 300 min). It was observed that the hydrolysis reaction time and the concentration of acetate ions had a strong effect on the morphology and size of ZnO nanoparticles (NPs). X-ray diffraction (XRD) patterns revealed that all samples crystalized in the typical ZnO wurtzite structure and Rietveld refinement was used to characterize the structure and to suggest a preferential growth. Fourier transformed infrared spectroscopy (FTIR) was performed and showed the typical ZnO band, no impurity signals, as well as differences in A1 and E1 vibration modes due to different crystal growth in the structure. Raman scattering was carried out to determine the defects in the structure of ZnO, such as interstitial oxygen and oxygen vacancies. Transmission electron microscope (TEM) images revealed that ZnO NPs size and shape are strongly dependent on the hydrolysis reaction time and addition of acetate counter ions, respectively. The change in shape and size has also affected the optical properties, such as the optical bandgap (Eg) of ZnO NPs and their florescence.

Coordination compounds of 4,5,6,7-tetrahydro-1H-indazole with Cu(II), Co(II) and Ag(I): structural, antimicrobial, antioxidant and enzyme inhibition studies

Coordination behavior of 4,5,6,7-tetrahydro-1H-indazole (H-Ind) with Cu(II), Co(II), and Ag(I) was studied. The ligand affords complexes bearing different geometries depending upon the metal and anion present in the starting salts. Five compounds with different structural perspectives, trans-[CuCl2(H-Ind)4] (1), trans-[CuBr2(H-Ind)4] (2), trans-[Cu(CH3COO)2(H-Ind)2] (3), trans-[CoCl2(H-Ind)4] (4), and [Ag(H-Ind)2]NO3 (5), were obtained. The ligand adopts tetrahydro-1H-indazole isomeric form in Cu(II) and Co(II) complexes and with Ag(I) ion the same ligand adopts tetrahydro-2H-indazole form. In the case of sterically demanding acetate counter ion in contrast to Cl or Br, the Cu(II) ion accepts two equivalents of the ligand and four-coordinated square planar complex was obtained. With AgNO3, the expected complex was obtained. The yield of reactions was >80% and all complexes were obtained as crystalline material from the reaction mixtures. Their structures were determined by X-ray diffraction and all complexes were tested for antibacterial (Enterobacter sakazkii, Escherichia coli, Staphylococcus aureus, Klebsiella pneumoniea), antifungal (Aspergillus flavus, Aspergillus fumegatus, Aspergillus nigar, Fusarium oxysporium), and antioxidant (2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid (ABTS) and 2,2-diphenyl-1-picrylhydrazyl (DPPH)) activities. The same were also tested as inhibitors against acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) .

Determination of effective charges and ionic mobilities of polycationic antimicrobial peptides by capillary isotachophoresis and capillary zone electrophoresis.

Capillary ITP (CITP) and CZE were applied to the determination of effective charges and ionic mobilities of polycationic antimicrobial peptides (AMPs). Twelve AMPs (deca- to hexadecapeptides) containing three to seven basic amino acid residues (His, Lys, Arg) at variable positions of peptide chain were investigated. Effective charges of the AMPs were determined from the lengths of their ITP zones, ionic mobilities, and molar concentrations, and from the same parameters of the reference compounds. Lengths of the ITP zones of AMPs and reference compounds were obtained from their CITP analyses in cationic mode using leading electrolyte (LE) composed of 10mMNH4 OH, 40mMAcOH (acetic acid), pH 4.1, and terminating electrolyte (TE) containing 40mMAcOH, pH 3.2. Ionic mobilities of AMPs and singly charged reference compounds (ammediol or arginine) were determined by their CZE analyses in the BGE of the same composition as the LE. The effective charges numbers of AMPs were found to be in the range 1.65-5.04, i.e. significantly reduced as compared to the theoretical charge numbers (2.86-6.99) calculated from the acidity constants of the analyzed AMPs. This reduction of effective charge due to tightly bound acetate counterions (counterion condensation) was in the range 17-47% depending on the number and type of the basic amino acid residues in the AMPs molecules. Ionic mobilities of AMPs achieved values (26.5-38.6)×10-9 m2 V-1 s-1 and in most cases were in a good agreement with the ratio of their effective charges and relative molecular masses.

Low-Temperature Water–Gas Shift Reaction over Au Supported on Anatase in the Presence of Copper: EXAFS/XANES Analysis of Gold–Copper Ion Mixtures on TiO2

Cu-modified Au/TiO2 (anatase, 200 m2/g) has been prepared by the incipient-wetness technique with introduction of the modifier either before or after Au loading. Such catalysts gave higher catalytic activities for the water–gas shift (WGS) reaction when compared to the unmodified catalysts mainly because of the existence of a synergetic interaction between Cu and Au, as the activities of both Cu/TiO2 and Au/TiO2 are lower than that of the bimetallic system. The WGS activities of both the as-prepared Au/TiO2 and a Au–Cuc/TiO2 catalyst were found to be high and stable. The presence of nitrates on Cuc–Au/TiO2 was found to be detrimental to the activity of Au on TiO2, as a result of the poisoning of Au and enhanced Au agglomeration by NO2 formed during reaction. The activities of Au/TiO2 catalysts modified with Cu-containing acetate counterions were found to decrease during the first 30 min on stream, reaching a constant value of (45 ± 2)%. However, when the poisoning by the acetate anion was eliminated through calcination, the activity increased compared to those of the Au/TiO2 catalysts. An increase in Cu loading was found to lower the activity of Au as a result of the loss of the interaction between the Au and the support interface. The XANES spectra of uncalcined as-prepared catalysts exhibited a pre-edge feature (due to the 1s-to-3d transition) characteristic of Au in a tetrahedral environment. The water–gas-shift-treated sample showed a reduction in the intensity of the white line, indicating a reduction of Au (a partial reduction of Au3+ to Au+/Au0). The XANES spectrum of calcined Cuc–Au/TiO2 (0.44 wt % Cu/3.74 wt % Au) confirmed that Cu exists as ions (Cu+/Cu2+) before and during the WGS reaction. The Au catalyst was not stable and continuously deactivated with time, and the white-line region showed a decrease in peak intensity during use. An increase in gold activity on Cu2+-modified TiO2 was achieved because at least 90% of the gold was reduced to the zero-valent state whereas most of the stabilizing metal (Cu2+) remained in the ionic state. We concluded that the addition of a stabilizing metal in ionic form during the preparation of the Au–Cuc/TiO2 system has marked effects in improving the initial dispersion of the reduced gold and also in helping to maintain a highly dispersed state of gold during use. The atomic ratio of stabilizing metal ions to gold metal plays a crucial role in maximizing the dispersion/stabilizing effects. The formation of bimetallic particles was not detected by EXAFS data analysis. The observed effects can be interpreted as a mutual influence of gold and copper ions and reduced species of gold and copper because of their competion for ion-exchange sites. It is unclear at present how this is achieved. However, EXAFS data analysis of both metals suggests that it is not due to a direct interaction between Au and Cu. In contrast to the results for the WGS reaction, copper was found to show no promotional effect on low-temperature CO oxidation or on preferential CO oxidation (PROX) in excess hydrogen.

Synthesis and properties of protic hydroxylic ionic liquids with two types of basic centers in their composition

1-((3-(1H-imidazol-1-yl)propyl)amino)-3-butoxypropan-2-ol with two types of nitrogenous centers and variable basicity was synthesized by reaction of butyl glycidyl ether with 1-(3-aminopropyl)imidazole. Ethanesulfonic acid was used for equimolar and complete neutralization of the obtained compound to produce hydroxylic ionic liquids. N-acetyl derivatives of the given liquid with ethanesulfonate and acetate counterions were also synthesized. According to 1H NMR spectroscopy, equimolarly neutralized compounds are characterized by a rapid migration of protons between the basic centers using the mechanisms of intermolecular and intramolecular transfer with a predominance of the latter at higher temperatures. Fully protonated ionic liquids are characterized by a low glass transition temperature (−60.9°С) and a high conductivity 5.45·10−4S/cm at 20°C under anhydrous conditions. Notably, there is an absence of determined correlation between the glass transition temperature or conductivity and the value of the viscosity of the ILs.

Influence of Anion Hydrophilicity on the Conformation of a Hydrophobic Weak Polyelectrolyte Brush

The conformation of a hydrophobic, weak cationic poly(2-diisopropylamino)ethyl methacrylate (PDPA) brush was studied using neutron reflectometry as a function of aqueous solution pH, ionic strength, and anion identity. In pH 4, 10 mM potassium nitrate the brush is highly charged, resulting in an extended, dilute conformation; at pH 9 the uncharged brush collapses to a single, dense layer. The brush response to added salt at constant pH (4.5) for varying concentrations of the potassium salts of acetate, nitrate, and thiocyanate revealed ion-specific conformations of the brush. At low ionic strength (0.1 mM) the brush was collapsed, independent of salt identity, while at higher ionic strengths (up to 500 mM) the conformation was dependent on counterion identity. The brush exhibited extended conformations in the presence of kosmotropic acetate counterions, while collapsed conformations were retained in the presence of strongly chaotropic thiocyanate counterions. The brush showed a richer set of behaviors in ...

Dual Role of Acetate in Copper(II) Acetate Catalyzed Dehydrogenation of Chelating Aromatic Secondary Amines: A Kinetic Case Study of Copper‐Catalyzed Oxidation Reactions

Copper(II) acetate is a frequent empirical choice of the copper source in copper(II)‐mediated redox reactions. The effect of the acetate counterion appears crucial but has not been adequately investigated. Herein, we report that copper(II) acetate catalyzes the aerobic dehydrogenation of chelating aromatic secondary amines. The chemoselectivity of acetate and chelating amines in this reaction provides a unique opportunity for a mechanistic study. The progression of this homogeneous reaction is monitored by using electron paramagnetic resonance spectroscopy, UV/Vis absorption spectroscopy, and manometry. The kinetic dependence on the amine substrate, copper(II), and acetate counterion, together with the results of kinetic isotope and substituent effect experiments, suggests that acetate acts both as a bridging ligand of a dinuclear catalytic center for mediating two‐electron transfer steps and as a base in the turnover‐limiting C–H bond‐cleavage step. Upon including 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) as a surrogate base, DBU and acetate act in a complementary manner to enable a rapid, catalytic dehydrogenation reaction of a chelating secondary amine substrate. Finally, the contrasting reactivities between copper(II) acetate (promoting two‐electron transfer) and copper(II) perchlorate (promoting single‐electron transfer) underscores how a counterion could completely alter the mechanistic pathway of a copper‐mediated oxidation reaction.

Refluxing Synthesis and Characterization of ZnO Nanopowders from Different Zinc Salts

In this article, ZnO nanopowders formed from different zinc salts such as acetate, nitrate and sulphate were prepared via homogeneous precipitation followed by refluxing route. Several analytic techniques such as XRD, TEM, and UV-Vis were used to make characterizations of the as-synthesized samples. The results showed that ZnO nanopowders prepared from the sulphate and nitrate salts have merely close crystalline size values, and a smaller crystalline size was obtained for the ZnO formed from acetate counter ions. The band gap of the samples synthesized with the counter ions (CH3COO-, NO3-, and SO42-) were 3.05 ± 0.02, 3.14 ± 0.02 and 3.16 ± 0.02, respectively.

Ionic-pair effect on the phosphorescence of ionic iridium(III) complexes

The synthesis and characterization of two water soluble ionic iridium(III) complexes containing hydrophilic acetate counterions is presented. The complexes exhibit one of the highest phosphorescence quantum yields reported up to now in water solution. The influence of the counterion position on the photophysical properties was highlighted through investigations in several polar solvents and in the crystalline solid state.