Effect of the Composition of Ethanol–Water Mixtures on the Properties of Oxide (Zn-Zr-Si) and Zeolitic (Ta/SiBEA) Catalysts in the Production of 1,3-Butadiene

Theoretical and Experimental Chemistry - The reasons for the deactivating effect of water on the conversion of ethanol to 1,3-butadiene in the presence of Zn-Zr(La)-Si oxide and Cu(Ag, Zn)/Ta/SiBEA...     

Effect of the Halogen Dopant (F–, Cl–) on the Transport Properties of Proton Conductors Based on Ba4In2Zr2O11

Russian Journal of Electrochemistry - The effect of F– and Cl– doping on the transport properties of the proton conductor Ba4In2Zr2O11 was analyzed. The halogen-substituted phases were...     

The Effect of Concentration Parameters on Complexation in the Iron(0)–Iron(II)–Glycine–Water System

The processes of formation of iron(II) complexes in aqueous glycine solutions in the pH range of 1.0–8.0 at 298 K and ionic strength of 1 mol/L (NaClO₄) are studied using Clark and Nikolskii’s oxidation potential method. The type and number of coordinated ligands, the nuclearity, and the total composition of the resulting complexes are determined. The following complex species are formed in the investigated system: [Fe(OH)(H₂O)₅]⁺, [FeHL(H₂O)₅]²⁺, [Fe(HL)(OH)(H₂O)₄]⁺, [Fe(OH)₂(H₂O)₄]⁰, [Fe₂(HL)₂(OH)₂(H₂O)₈]²⁺, and [Fe(HL)₂(H₂O)₄]²⁺. Their formation constants are calculated by the successive iterations method using Yusupov’s theoretical and experimental oxidation function. The model parameters of the resulting coordination compounds are determined.     

Catalytic Spectrophotometric Determination of Bromide Based on the Diphenylcarbazide–Chromium(VI)–Iodate Reaction

A new catalytic spectrophotometric method for the determination of bromide is proposed. Diphenylcarbazide reacts with chromium(VI) ions in an acid medium to give a violet complex. The method is based on the bromide-catalyzed oxidation of this violet complex by iodate followed by measuring the color change at = 542 nm spectrophotometrically. The reaction starts after an induction period. Bromide ions catalyze this reaction, so that the induction period is decreased by the addition of Br^–. The derivative of the absorbance with respect to time was calculated. The maximum absorbance difference (A _m) and thetime taken to reach the maximum difference (t _m) were measured from the derivative curve. These values are used as the measured parameters for bromide determination. Under optimum conditions bromide can be determined in the range of 0.5–8 g/mL. The detection limit is 0.25 g/mL, and the relative standard deviation for ten replicate measurements of 1 g/mL of bromide is 1.57%. The method was applied to the determination of bromide in the Persian Gulf water.     

Electrochemical Synthesis of Fe–Cu Composites Based on Copper(II) Ferrite and Their Electrocatalytic Properties

Russian Journal of Electrochemistry - Copper(II) ferrite is synthesized by the co-precipitation method in the absence and in the presence of polyvinyl alcohol which is followed by thermally...     

Kinetic Determination of Iodide Traces Based on the Manganese(III) Metaphosphate–Arsenic(III) Reaction in the Presence of Orthophosphoric Acid

The kinetics of the iodide-catalyzed Mn(III) metaphosphate–As(III) reaction was studied in the presence of orthophosphoric acid. The reaction rate was followed spectrophotometrically at 516nm. It was established that orthophosphoric acid increased the reaction rate and that the extent of the non-catalytic reaction was extremely small. A kinetic equation was postulated and the apparent rate constant calculated. The dependence of the reaction rate on temperature was investigated and the energy of activation and other kinetic parameters determined. Iodide was determined under the optimal experimental conditions in the range 0.6–2.5ng·mL^–1 with a relative standard deviation of up to 6.7% and a detection limit of 0.12ngmL^–1. The effect of foreign ions on the accuracy of the determinations was also investigated.     

Studies on the Structure, Properties of Ferroaluminophosphate Molecular Sieve (FAPO-5) and Chemical State of Iron in the FAPO-5 Molecular Sieve

The pure Ferroaluminophosphate molecular sieve(FAPO-5) was synthesized by hydrothermal crystallization. The crystal structure of FAPO-5 was studied via XRD, electron probe energy dispersion analysis, Mossbauer spectroscopy, EPR, XPS and IR, the parameters of unit cell and chemical composition of FAPO-5 were determined. The result has that the structure of FAPO-5 is AlPO -5 type and Fe2+ Fe3+ are incorporated into the framework of FAPO-5 molecular sieve. In addition, the chemical state of iron in FAPO-5 molecular sieve were studied and the adsorption properties, surface acidity and thermal stability were also investigated.     

Electrochemical Properties of Membranes Based on Complexes Tetraphenylporphyrin–Ions of Group IIIB Metals (Al,Ga, In,Tl)

Porphyrins and related compounds (metalloporphyrins, phthalocyanines, etc.), owing to their unique complexing properties, are used ever more frequently as membrane-active components in membranes of ion-selective electrodes. The work examines electrochemical properties of membranes containing tetraphenylporphyrins (TPP) of metals of group IIIB of the periodic table (Al, Ga, In, Tl) and solvents-plasticizers of various nature, specifically, esters of phthalic, adipic, and sebacic acids and orthonitrophenyloctyl ether. The nature of the central atom of the metal determines the character of dependence of E on pH of solutions under study; it also defines the decrease in the slope of the SCN^– function occurring in the series AlTPP TlTPP and the change in the function sign for membranes containing TlTPP. For all the membranes, the selectivity sequences are determined by the method of individual solutions. The variation in K ^sel in the series Al Tl conforms to the other derived characteristics.     

Synthesis, Crystal Structure and Luminescent Properties of the Indium(Ⅲ) Complex Based on 2,6-Bis(1-phenylbenzimidazol-2-yl)pyridine

The complex [In(bpbp)Cl3]·H2O, where bpbp is 2,6-bis(1-phenylbenzimidazol- 2-yl)-pyridine (bpbp), was synthesized and characterized by X-ray single-crystal structure analysis. For the complex: C31H21Cl3InN5·H2O, Mr = 702.71, monoclinic, space group, P21/n, a = 9.3918(10), b = 21.024(2), c = 14.5323(15), β = 96.938(2)°, V = 2848.4(5)3, Z = 4, Dc = 1.639 g/cm3, λ = 0.71073, μ(MoKα) = 1.147 mm-1, F(000) = 1408, S = 1.00, R = 0.0430 and wR = 0.1438 for 4620 observed reflections with Ⅰ > 2σ(Ⅰ). It is a neutral complex. The In(Ⅲ) ion adopts a distorted trigonal bipyramidal geometry coordinated by three nitrogen atoms of the ligand and three chlorine atoms. The complex emits blue luminescence with emission peaks at 430 nm in the solid state.     

Influence of the Length of the Alanine Spacer on the Acidic–Basic Properties of the Ac–Lys–(Ala) n –Lys–NH2 Peptides (n?=?0, 1, 2, …, 5)

By using the potentiometric titration method, we have determined the pK _a values of the two terminal lysine groups in six alanine-based peptides differing in the length of the alanine chain: Ac?CLys?CLys?CNH₂ (KK), Ac?CLys?CAla?CLys?CNH₂ (KAK), Ac?CLys?CAla?CAla?CLys?CNH₂ (KAK2), Ac?CLys?CAla?CAla?CAla?CLys?CNH₂ (KAK3), Ac?CLys?CAla?CAla?CAla?CAla?CLys?CNH₂ (KAK4), and Ac?CLys?CAla?CAla?CAla?CAla?CAla?CLys?CNH₂ (KAK5) in aqueous solution. For each compound, the model of two stepwise acid?Cbase equilibria was fitted to the potentiometric-titration data. As expected, the pK _a values of the lysine groups increase with increasing length of the alanine spacer, which means that the influence of the electrostatic field between one charged group on the other decreases with increasing length of the alanine spacer. However, for KAK3, the pK _a1 value (8.20) is unusually small and pK _a2 (11.41) is remarkably greater than pK _a1, suggesting that the two groups are close to each other and, in turn, that a chain-reversal conformation is present for this peptide. Starting with KAK3, the differences between pK _a1 and pK _a2 decrease; however, for the longest peptide (KAK5), the values of pK _a1 and pK _a2 still differ by about 1 unit, i.e., by more than the value of log₁₀ (4)?=?0.60 that is a limiting value for the pK _a difference of dicarboxylic acids with increasing methylene-spacer length. Consequently, some interactions between the two charged groups are present and, in turn, a bent shape occurs even for the longest of the peptides studied.     

The Influence of Di-(2-Ethylhexyl)Phosphoric Acid on the Properties of Microemulsion in the Sodium Di-(2-Ethylhexyl)Phosphate–Di-(2-ethylhexyl)Phosphoric Acid–Decane–Water System

It has been shown that the presence of small amounts of di-(2-ethylhexyl)phosphoric acid (below 6 mol % in the mixture of surfactants) in a sodium di-(2-ethylhexyl)phosphate–di-(2-ethylhexyl)phosphoric acid–decane–water system widens the region of microemulsion existence with respect water and decreases the slope of the dependence of hydrodynamic droplet diameter of on water-to-sodium di-(2-ethylhexyl) phosphate molar ratio. At di-(2-ethylhexyl)phosphoric acid concentrations in its mixture with sodium di-(2-ethylhexyl)phosphate higher than 6 mol %, the fraction of water bound with ions in microemulsion droplets decreases, the region of microemulsion existence narrows, specific conductance decreases, and the slope of the dependence of the hydrodynamic droplet diameter of on the water-to-sodium di-(2-ethylhexyl) phosphate molar ration increases.     

The Influence of C(sp3)H–Selenium Interactions on the 77Se NMR Quantification of the π-Accepting Properties of Carbenes

Selenium NMR has become a standard tool for scaling the π-accepting character of carbenes. Herein, we highlight that non-classical hydrogen bonding (NCHB), likely resulting from hyperconjugation, can play a significant role in the carbene–selenium ⁷⁷Se NMR chemical shift, thus triggering a non-linear behavior of the Se-Scale.     

Synthesis,Crystal Structure and Electrochemistry Properties of an Iron(Ⅲ) Complex Based on the 3,5-Pyridinedicarboxylate and Water Ligands

Reaction of 3,5-pyridine-dicarboxylic acid(3,5-PydcH2) with iron salt in hydrothermal condition results in the formation of a three-dimensional self-assembly network formulated as [C14H14Fe2N2O12]n,and it has been structurally characterized by elemental analysis,IR spectra and X-ray diffraction.It crystallizes in the monoclinic system,space group C2/c with a=9.9633(15),b=12.0942(18),c=7.4297(11) and β=105.822o.The units of Fe2(pydc)2·2H2O are linked into a one-dimensional structure via the chelate carboxylate groups from the 3,5-pyridine-dicarboxylate.The interlayer hydrogen bonding interactions result in a three-dimensional supramolecular architecture.In the complex,the Fe(Ⅲ) ion displays a slightly distorted pentagonal bipyramidal geometry with seven coordination numbers.Cyclic-voltammetry measurement reveals the oxidation and reduction processes for the complex are quasi-reversible in nature.     

Origin of the Aggregation-Induced Phosphorescence of Platinum(II) Complexes: The Role of Metal–Metal Interactions on Emission Decay in the Crystalline State

Discerning the origins of the phosphorescent aggregation-induced emission (AIE) from Pt(II) complexes is crucial for developing the broader range of photo-functional materials. Over the past few decades, several mechanisms of phosphorescent AIE have been proposed, however, not have been directly elucidated. Herein, we describe phosphorescence and deactivation processes of four class of AIE active Pt(II) complexes in the crystalline state based on experimental and theoretical investigation. These complexes show metal-to-ligand and/or metal−metal-to-ligand charge transfer emission in crystalline state with different heat resistance against thermal emission quenching. The calculated energy profiles including the minimum energy crossing point between S₀ and T₁ states were consistent with the heat resistant properties, which provided the mechanism for AIE expression. Furthermore, we have clarified the role of metal-metal interaction in AIE by comparing two computational models.     

Based on the Second Virial Coefficient (A2) to Study Effect of the Synergistic Action of Solvent and External Electric Field on the Solution Behavior and Film’s Condensed State Structure

Chinese Journal of Polymer Science - The solventnatures are crucial to deeply reveal solution behavior of macromolecular chains, physical essence of condensed state structures formation of the film...     

Complexation of Dioxovanadium(V) with D-(-)-Quinic Acid at Different Ionic Strengths Using Different Models Based on the Debye-Hückel Theory

The complex formation reaction between the dioxovanadium(V) cation $\mathrm{VO}_{2}^{+}$ and D-(-)-quinic acid {(1R,3R,4S,5R)-(-)-1,3,4,5-tetrahydroxycyclohexane-1-carboxylic acid} has been studied in aqueous solutions. The UV data and the values of the derived conditional stability constants are presented and discussed in the light of one stoichiometric model for the reaction at T=298?K and different ionic strengths (0.10 to 1.00)?mol?dm^?3 of sodium chloride. Speciation diagrams and dissociation constants were obtained on the basis of UV spectroscopic measurements and potentiometric titrations, respectively. Our results show that one complex species, VO₂L, exists in solution in the pH range of about 1.00 to 3.00. The parabolic, Specific Ion Interaction Theory (SIT), and extended Debye-Hückel type (EDH) models successfully describe the ionic strength dependence of the stability constants. A comparison with literature data is also reported.     

Electrochemical Determination of Copper(II) in Water Samples Using a Novel Ion-Selective Electrode Based on a Graphite Oxide–Imprinted Polymer Composite

A novel copper(II)-selective electrode based on graphite oxide/imprinted polymer composite was developed for the electrochemical monitoring of copper(II) (Cu²⁺) ions. The electrode exhibited highly selective potentiometric response to Cu²⁺ with respect to common alkaline, alkaline earth and heavy metal cations. The composite composition studies indicated that the most suitable composite composition performing the most promising potentiometric properties was 20.0% ionophore (Cu²⁺-ion imprinted polymer), 10.0% paraffin oil, 5.0% multiwalled carbon nanotubes, and 65.0% graphite oxide. The fabricated electrode exhibited a linear response to Cu²⁺ over the concentration range of 1.0?×?10^??6–1.0?×?10^??1?M (correlation coefficient of 0.9998) with a sensitivity of 26.1?±?0.9?mV decade^??1. The detection limit of the fabricated electrode was determined to be 4.0?×?10^??7?M. The electrode worked well in the pH range of 4.0–8.0. The electrode had stable, reversible and fast potentiometric response (3?s). In addition, the electrode had a lifetime of more than 1 year. The analytical applications of the proposed electrode were performed using as an indicator electrode for the potentiometric titration of Cu²⁺ with ethylene diamine tetraacetic acid solution and for the determination of Cu²⁺ of spiked river, dam, and tap water samples. The obtained results for potentiometric titration and water samples were satisfactory.     

Syntheses,Structures and Luminescent Properties of Cd(Ⅱ)/Zn(Ⅱ) Coordination Polymers Based on the Flexible 4-Substituted Bis(1,2,4-triazole) Ligand

Two new cadmium(Ⅱ) and zinc(Ⅱ) coordination polymers, {[Cd(btre)0.5-(mip)(H_2O)_2]·H_2O}n(1) and [Zn(btre)(mip)]n(2), were synthesized at room temperature condition and characterized by IR spectra, elemental analyses, single-crystal and powder X-ray diffractions(btre = 1,2-bis(1,2,4-triazol-4-yl)ethane, H2 mip = 5-methyl-1,3-benzenedicarboxylic acid). Complex 1 belongs to the triclinic system, P1 space group, with a = 8.9830(6), b = 10.0579(6), c = 10.2479(9) ?, α = 98.837(6), β = 115.975(8), γ = 106.370(6)°, V = 756.30(11) ?~3 and Z = 2; complex 2 crystallizes in monoclinic, space group P21/c, with a = 7.0332(3), b = 14.9947(7), c = 15.9689(7) ?, β = 97.1170(10)°, V = 1671.12(13) ?~3 and Z = 4. Compounds 1 and 2 based on the same N/O-donor ligands show different structures. The one-dimensional chains of 1 are further linked by hydrogen bonding and π-π interactions to yield a three-dimensional supramolecular structure. The two-dimensional(6,3) networks of 2 are further extended into a 3D framework via π-π interactions. Thermal stabilities and luminescence of 1 and 2 were investigated.