Oxidation of aliphatic alcohols by triethylammonium chlorochromate in non-aqueous medium – A kinetic and mechanistic study

The oxidation of some aliphatic alcohols by triethylammonium chlorochromate (TriEACC) in dimethyl sulfoxide leads to the formation of the corresponding carbonyl compounds. The reaction is first order with respect to TriEACC. The reaction exhibited Michaelis–Menten type kinetics with respect to alcohol. The reaction is catalyzed by hydrogen ions. The hydrogen-ion dependence has the form: k_obs = a + b[H⁺]. The oxidation of [1,1-²H₂] ethanol (MeCD₂OH) exhibits a substantial primary kinetic isotope effect. Oxidation of aliphatic alcohol was studied in 19 different organic solvents. The solvent effect has been analysed using Kamlet’s and Swain’s multi-parametric equation. A suitable mechanism has been proposed.     

Buffer standards for the physiological pH of N-[2-hydroxy-1,1-bis(hydroxymethyl)ethyl]glycine (TRICINE) from T = (278.15 to 328.15) K

The pH values of two buffer solutions without NaCl and seven buffer solutions with added NaCl, having ionic strengths (I = 0.16 mol · kg⁻¹) similar to those of physiological fluids, have been evaluated at 12 temperatures from T = (278.15 to 328.15) K by way of the extended form of the Debye–Hückel equation of the Bates–Guggenheim convention. The residual liquid junction potentials (δE_j) between the buffer solutions of TRICINE and saturated KCl solution of the calomel electrode at T = (298.15 and 310.15) K have been estimated by measurement with a flowing junction cell. For the buffer solutions with the molality of TRICINE(m₁) = 0.06 mol · kg⁻¹, NaTRICINE(m₂) = 0.02 mol · kg⁻¹, and NaCl(m₃) = 0.14 mol · kg⁻¹, the pH values at T = 310.15 K obtained from the extended Debye–Hückel equation and the inclusion of the liquid junction correction are 7.342 and 7.342, respectively. These are in excellent agreement. The zwitterionic buffer TRICINE is recommended as a secondary pH standard in the region for clinical application.     

Kinetic spectrophotometric method for trace determination of thiocyanate based on its inhibitory effect

A kinetic spectrophotometric method for the determination of thiocyanate, based on its inhibitory effect on silver(I) catalyzed substitution of cyanide ion, by phenylhydrazine in hexacyanoferrate(II) is described. Thiocyanate ions form strong complexes with silver(I) catalyst which is used as the basis for its determination at trace level. The progress of reaction was monitored, spectrophotometrically, at 488 nm (λ_max of [Fe(CN)₅PhNHNH₂]^3?, complex) under the optimum reaction conditions at: 2.5 × 10^?3 M [Fe(CN)₆]^4?, 1.0 × 10^?3 M [PhNHNH₂], 8.0 × 10^?7 M [Ag⁺], pH 2.8 ± 0.02, ionic strength (μ) 0.02 M (KNO₃) and temperature 30 ± 0.1 °C. A linear relationship obtained between absorbance (measured at 488 nm at different times) and inhibitor concentration, under specified conditions, has been used for the determination of [thiocyanate] in the range of 0.8–8.0 × 10^?8 M with a detection limit of 2 × 10^?9 M. The standard deviation and percentage error have been calculated and reported with each datum. A most plausible mechanistic scheme has been proposed for the reaction. The values of equilibrium constants for complex formation between catalyst–inhibitor (K_CI), catalyst–substrate (K_s) and Michaelis–Menten constant (K_m) have been computed from the kinetic data. The influence of possible interference by major cations and anions on the determination of thiocyanate and their limits has been investigated.     

Study on the thermodynamic characteristics between fluoroquinolone and bovine serum albumin

The binding reactions of the fluoroquinolone with bovine serum albumin (BSA) were investigated by microcalorimetry. The thermodynamic parameters were measured with the help of spectroscopy in a Tris–HCl buffer solution (pH 7.0, made isotonic with sodium chloride) at T = 298 K. Microcalorimetric measurements show that the molar change of enthalpy Δ_rH_m is insignificant for the reaction, which may suggest that the interaction is governed mainly by entropy, and the interaction between the protein and the drugs is stronger. The results also reveal an entropy–enthalpy compensation relationship of the interaction.     

Fluoride affinities of fluorinated alanes

The fluoride affinities of fluorinated alanes, AlH_mF_3?m (m = 1–3) were measured using energy-resolved collision-induced dissociation of fluorinated aluminate anions. The AlH_mF_4?m^? anions were formed by reaction of dimethylethylamine-alane with fluoride ion and F₂. From the measured bond dissociation energies, the fluoride affinities of fluorinated alanes are determined to be 93.2 ± 3.1, 97.5 ± 4.0, and 108.6 ± 3.7 kcal/mol for m = 3, 2, and 1, respectively. The fluoride affinities are in good agreement with the theoretical calculations at the CCSD(T)/CBS and B3LYP/6-31 + G* levels of theory. The increased Lewis acidity of more fluorinated alanes is attributed to increased positive charge density on the aluminum.     

Crystal growth and magnetic properties of the new iridates Ln1−xNa1+xIrO4 (Ln = Gd–Er,Y; x = 0.04–0.25)

We report the single crystal structures and magnetic properties of a series of lanthanide-containing iridates, Ln_1−xNa_1+xIrO₄ (Ln = Gd–Er, Y; x = 0.04–0.26) grown from a mixed sodium and cesium hydroxide flux. The compounds crystallize in the hexagonal space group P-62m (#189) with lattice parameters ranging from a = 9.3872(2)–9.4596(3) Å and c = 3.1512(1)–3.2030(2) Å and are structurally related to other iridium oxides. The oxidation state of iridium ranges from +4.08 (Gd) to +4.50 (Er). Magnetic susceptibility measurements reveal the existence of antiferromagnetic correlations below 15 K.     

Thermochemistry of the biochemical reaction: { pyrophosphate(aq) + H2O(l) = 2 phosphate(aq)}

Calorimetric enthalpies of reaction have been measured for the overall biochemical reaction{pyrophosphate(aq)  +  H₂O(l)  =  2phosphate (aq)} . The reaction was catalyzed by alkaline phosphatase and, to simplify the thermochemistry, was carried out in the absence of Mg ^2 + (aq). Measurements were performed with phosphate buffer ( pH  =  7.19 and 7.94), PIPES buffer ( pH  =  7.13), and HEPES buffer ( pH  =  7.86). The results of these measurements were analyzed by using an equilibrium model. These calculations lead to the standard molar enthalpy changeΔ_rH_m^o =  − (17.3  ±  0.6)kJ·mol ^− 1 (temperature T =  298.15 K and ionic strengthI =  0) for the reference reaction{HP₂O₇^3 − (aq)  +  H₂O(l)  =  2HPO₄^2 − (aq)  +  H ⁺ (aq)} . Values of the apparent equilibrium constantK^′ for the overall biochemical reaction from the literature were also analyzed by using the equilibrium model in order to obtain what is believed to be a reliable value for the equilibrium constantK =  4.7 · 10 ^− 4 for the reference reaction. The values ofK and Δ_rH_m^o for the reference reaction have been used together with values from the CODATA tables to calculate standard molar formation properties for the pyrophosphate species.     

Buffer standards for the physiological pH of the zwitterionic compound of 3-(N-morpholino)propanesulfonic acid (MOPS) from T = (278.15 to 328.15) K

This paper reports the pH values of five NaCl-free buffer solutions and 11 buffer compositions containing NaCl at I = 0.16 mol · kg⁻¹. Conventional pa_H values are reported for 16 buffer solutions with and without NaCl salt. The operational pH values have been calculated for five buffer solutions and are recommended as pH standards at T = (298.15 and 310.15) K after correcting the liquid junction potentials. For buffer solutions with the composition m₁ = 0.04 mol · kg⁻¹, m₂ = 0.08 mol · kg⁻¹, m₃ = 0.08 mol · kg⁻¹ at I = 0.16 mol · kg⁻¹, the pH at 310.15 K is 7.269, which is close to 7.407, the pH of blood serum. It is recommended as a pH standard for biological specimens.     

Direct electrochemistry study of glucose oxidase on Pt nanoparticle-modified aligned carbon nanotubes electrode by the assistance of chitosan–CdS and its biosensoring for glucose

Aligned carbon nanotubes (ACNTs) electrode has been developed for the direct protein electrochemistry and enzyme-biosensor study involving two types of nanoparticles. Pt nanoparticles (Pt_nano) were electro-modified on the ACNTs’ each tube, greatly increasing the electrode surface area for locating protein and also its electronic transfer ability. Glucose oxidase (GOD) with chitosan (CS) and CdS nanoparticles electrochemically coated on each tube of ACNTs–Pt_nano by the electrodeposition reaction of CS when pH value passing its pKa. The CdS nanoparticles between ACNTs electrode and GOD have stimulated the GOD’s direct electron transfer during its redox reaction of FAD/FADH₂. The CS–GOD–CdS/ACNTs–Pt_nano electrode also offer sensitive response to the substrate of glucose with detection limit of 46.8 μM (S/N = 3) and apparent Michaelis–Menten constant of 11.86 mM.     

Polyaniline nanotubes for impedimetric triglyceride detection

Polyaniline nanotubes (PANI-NT) based film electrophoretically deposited onto indium–tin–oxide (ITO) coated glass plate has been utilized for covalent immobilization of lipase (LIP), via glutaraldehyde (Glu), for triglyceride detection using impedimetric technique. It is shown that fatty acid molecules produced during triglyceride hydrolysis result in change in charge transfer resistance (R_CT) of PANI-NT film with varying triglyceride concentration. LIP/Glu/PANI-NT/ITO bioelectrode has linearity as 25–300 mg dL^?1, sensitivity as 2.59 × 10^?3 KΩ^?1 mg^?1 dL, response time as 20 s and regression coefficient as 0.99. A low value of apparent Michaelis–Menten constant (～0.62 mM) indicates high enzyme affinity to tributyrin. The LIP/Glu/PANI-NT/ITO bioelectrode has been utilized to estimate triglyceride in serum samples.     

Apparent molar volumes and apparent molar heat capacities of aqueous adonitol,dulcitol, glycerol,meso-erythritol,myo-inositol,d-sorbitol,and xylitol at temperatures from (278.15 to 368.15) K and at the pressure 0.35 MPa

Apparent molar volumes V_ϕ were determined for aqueous adonitol, dulcitol, glycerol, meso-erythritol, myo-inositol, d-sorbitol, and xylitol at temperatures from (278.15 to 368.15) K and at the pressure 0.35 MPa, and apparent molar heat capacities C_p,ϕ of the same solutions were determined at temperatures from (278.15 to 363.15) K at the same pressure. Molalities m/(mol · kg⁻¹) of the solutions were in the range (0.02 ⩽ m ⩽ 3.2) for adonitol, (0.02 ⩽ m ⩽ 0.15) for dulcitol, (0.02 ⩽ m ⩽ 5.0) for glycerol, (0.02 ⩽ m ⩽ 3.0) for meso-erythritol, (0.02 ⩽ m ⩽ 0.5) for myo-inositol, (0.02 ⩽ m ⩽ 2.0) for d-sorbitol, and (0.02 ⩽ m ⩽ 2.7) for xylitol. A vibrating tube densimeter was used to obtain solution densities and a fixed-cell temperature scanning calorimeter was used to obtain heat capacities. Values of V_ϕ and C_p,ϕ for these sugar alcohols are discussed relative to one another and compared to values from the literature, where available.     

Direct electrochemistry of myoglobin based on DNA accumulation on carbon ionic liquid electrode

Poly-anionic deoxyribonucleic acid (DNA) was accumulated on the positively charged surface of carbon ionic liquid electrode (CILE) with N-butylpyridinium hexafluorophosphate (BPPF₆) as binder, and then myoglobin (Mb) was immobilized onto the DNA film by electrostatic interaction to form Mb/DNA/CILE electrode. The direct electrochemistry of Mb was then investigated in detail. A pair of well-defined, quasi-reversible cyclic voltammetric peaks of Mb was obtained with the formal potentials (E⁰′) at ?0.304 V (vs. SCE) in phosphate buffer solution (PBS, pH 7.0). The Mb/DNA/CILE electrode showed excellent electrocatalytic activity to H₂O₂ and trichloroacetic acid (TCA) in the range of 1.0–160 μmol/L and 0.5–40.0 mmol/L, respectively. The apparent Michaelis–Menten constants (K_M) toward H₂O₂ and TCA were calculated as 0.42 and 0.82 mmol/L. So, the DNA/CILE had potential to study other proteins.     

Catalase-conjugated liposomes encapsulating glucose oxidase for controlled oxidation of glucose with decomposition of hydrogen peroxide produced

The catalase-conjugated liposome encapsulating glucose oxidase (CLG) was prepared for developing a novel liposomal system for glucose oxidation with controllable enzyme activities. The catalase molecules were conjugated to the surface of liposome with 100 nm in mean diameter through coupling with the membrane-incorporated 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-(glutaryl) (NGPE) at its mole fraction f_G of 0.05 or 0.15. The average number of enzyme molecules per CLG with f_G of 0.15 was 8.7 for glucose oxidase and 6.5 for catalase. The CLG-catalyzed oxidation of glucose was performed at 40 °C for prolonged period up to 99 h. The CLG with f_G of 0.15 gave larger oxidation rate than that with f_G of 0.05. In the fed-batch oxidation of glucose catalyzed by the former CLG, the stable oxidation rate was observed for 75 h with negligible accumulation of H₂O₂ produced because of the durable catalytic actions of the liposomal enzymes. The oxidation rate of the CLG reaction increased to 1.1 mM-glucose/(h mM-lipid) at the acidic pH in the internal phase of liposome and the neutral pH in the external one corresponding to the optimal pH conditions for the activities of glucose oxidase and catalase, respectively. The oxidation rate catalyzed by the CLG could be controlled by adding sublytic concentrations of cholate to increase permeability of the liposome membrane to glucose. The catalase-conjugated liposomal system is potentially utilized for controlling the rate of reactions catalyzed by a variety of oxidases.     

Study of bromide salts solubility in the (m1NaBr + m2MgBr2)(aq) system at T = 323.15 K. Thermodynamic model of solution behavior and (solid + liquid) equilibria in the (Na + K + Mg + Br + H2O) system to high concentration and temperature

The bromide minerals solubility in the mixed system (m₁NaBr + m₂MgBr₂)(aq) have been investigated at T = 323.15 K by the physico-chemical analysis method. The equilibrium crystallization of NaBr·2H₂O(cr), NaBr(cr), and MgBr₂·6H₂O(cr) has been established. The solubility-measurements results obtained have been combined with all other experimental equilibrium solubility data available in literature at T = (273.15 and 298.15) K to construct a chemical model that calculates (solid + liquid) equilibria in the mixed system (m₁NaBr + m₂MgBr₂)(aq). The solubility modeling approach based on fundamental Pitzer specific interaction equations is employed. The model gives a very good agreement with bromide salts equilibrium solubility data. Temperature extrapolation of the mixed system model provides reasonable mineral solubility at high temperature (up to 100 °C). This model expands the previously published temperature variable sodium–potassium–bromide and potassium–magnesium–bromide models by evaluating sodium–magnesium mixing parameters. The resulting model for quaternary system (Na + K + Mg + Br + H₂O) is validated by comparing solubility predictions with those given in literature, and not used in the parameterization process. Limitations of the mixed solution models due to data insufficiencies at high temperature are discussed.     

Propriétés catalytiques de la montmorillonite intercalée au titane dans l'oxydation de l'alcool allylique (E)-hex-2-én-1-ol

Catalytic properties of Ti-pillared montmorillonite for the epoxidation of (E)-hex-2-en-1-ol allylic alcohol. The present work is relative to the epoxidation of allylic alcohols by a well-characterised Ti-pillared montmorillonite (Ti-PILC) prepared by intercalating polymeric Ti cations formed by partial hydrolysis of TiCl₄ with HCl. The interlayer distance, the specific surface area and thermal stabilities of the resulting pillared clays depend mainly on the pH of the pillaring solution. For a ratio H⁺/Ti = 0.24, the Ti-PILC shows a basal spacing of 2,6 nm and a specific surface area of 316 m²·g^–1, stable up to 773 K. In the conversion of isopropanol, this Ti-PILC shows a Lewis type acidity and a low redox activity. It catalyses the oxidation of allylic alcohol (E)-hex-2-en-1-ol with tert-butyl hydroperoxide in the presence of diethyl tartrate. The yield and nature of the final products depend on the reaction temperature and catalyst activation: no epoxidation could be obtained with non calcined samples. With a solid calcined in air at 773 K and then converted to a Ti-PILC, the main product is hexenoic acid for a reaction below 273 K, while the epoxide of the allylic alcohol is formed with 50 % yield at 298 K. This yield is comparable to that reported for the same substrate for polymer supported Ti(IV) catalysts.     

Investigation on electro-catalytic oxidation properties of carbon nanotube–Ce-modified PbO2 electrode and its application for degradation of m-nitrophenol

In this work a carbon nanotube–Ce-modified PbO₂ (CNT–Ce–PbO₂) electrode was prepared by electrodeposition method, and compared with pure PbO₂, Ce–PbO₂, and CNT–PbO₂ electrodes. The direct and indirect oxidation capacities of prepared electrodes in electro-catalytic oxidation processes were investigated by cyclic voltammetry and hydroxyl radical production tests, respectively. The electro-catalytic activity of electrodes was examined by electro-catalytic oxidation of a model pollutant of m-nitrophenol (m-NP). Besides, high-performance liquid chromatography (HPLC) was also employed to identify the products resulting from the electro-catalytic oxidation of m-NP and the degradation mechanism of m-NP was proposed. Results show that the CNT–Ce–PbO₂ anode has higher direct and indirect oxidation capacities than pure PbO₂, Ce–PbO₂, and CNT–PbO₂ anodes. In the electro-catalytic oxidation of m-NP, the m-NP can be oxidized and degraded at all anodes, and the oxidation reactions of m-NP follow first-order kinetics. m-NP and TOC removal efficiencies are about 0.987 and 0.622 after electrolysis of 120 min and a maximum first-order rate constant of 0.036 min⁻¹ is achieved at the CNT–Ce–PbO₂ anode, which are obviously higher than those of the other three kinds of anodes.     

Esterification of (RS)-Ibuprofen by native and commercial lipases in a two-phase system containing ionic liquids

Four commercially available lipases and two native lipases from Aspergillus niger AC-54 and Aspergillus terreus AC-430 were used for the resolution of (RS)-Ibuprofen in systems containing the ionic liquids [BMIM][PF₆] and [BMIM][BF₄]. The lipases showed higher conversion in a two-phase system using [BMIM][PF₆] and isooctane compared to that in pure isooctane. Although the best enzyme was a commercially available lipase from Candida rugosa (E = 8.5), another native lipase, produced in our laboratory, from A. niger gave better enantioselectivity (E = 4.6) than the other lipases tested (E = 1.9–3.3.). After thorough optimization of several reaction conditions (type and ratios of isooctane/ionic liquid, amount of enzyme, and reaction time), the E-value of A. niger lipase (15% w/v) could be duplicated (E = 9.2) in a solvent system composed of [BMIM][PF₆] and isooctane (1:1) after 96 h of reaction.     

Evidence of an odd–even effect on the thermodynamic parameters of odd fluorotelomer alcohols

A phase transition study, including vapour pressure determinations of odd fluorotelomer alcohols {oFTOH; CF₃(CF₂)_nCH₂OH, with n = 5 to 9}, is reported in order to explore the effect of the successive introduction of –CF₂– groups into the molecule on the thermodynamic properties related to (solid + liquid, solid + gas, and liquid + gas) equilibria. An odd–even effect on the thermodynamic parameters of fusion and sublimation was observed in the homologous series of odd fluorotelomer alcohols indicating an increase of the stability in the crystal packing for the members with an odd number of carbon atoms. The vaporization parameters of o-FTOH were compared with the literature data for their alkane analogues and the results showed a higher volatility of liquid fluorotelomer alcohols than their congeners. The higher molecular conformation restriction of perfluorinated alcohols and/or the higher molar mass seems to contribute to their higher entropy of vaporization which drives the volatility of the 1H,1H-perfluorinated alcohols.     

Dual-signal anodic stripping voltammetric determination of trace arsenic(III) at a glassy carbon electrode modified with internal-electrolysis deposited gold nanoparticles

A glassy carbon electrode (GCE) modified with internal-electrolysis deposited gold nanoparticles (AuNPs_ied) was applied to sensitively and selectively detect As(III) by anodic stripping linear sweep voltammetry (ASLSV). The AuNPs_ied/GCE was prepared based on the redox replacement reaction between a supporting-electrolyte-free aqueous HAuCl₄ and a copper sheet in saturated KCl separated by a salt bridge. Under optimum conditions (0.5 M aqueous H₂SO₄, 300-s preconcentration at − 0.4 V), the ASLSV peak current for the As(0)–As(III) oxidation responded linearly to As(III) concentration from 0.02 to 3 μM with a limit of detection (LOD) of 0.9 nM (0.07 μg L^− 1) (S/N = 3), while that for the As(III)–As(V) oxidation was linear with As(III) concentration from 0.02 to 1 μM with a LOD of 4 nM (0.3 μg L^− 1) (S/N = 3). An appropriate high-scan-rate for ASLSV can enhance both the sensitivity and signal-to-noise ratio. This method was applied for analyses of As(III) in real water samples.     

Copper diazine spin ladders: Synthesis,structure and magnetic analyses of Cu(2-methylthiopyrazine)Br2

The reaction of copper(II) bromide with 2-methylthiopyrazine (meSpz) in THF/CH₂Cl₂ gave crystals of [Cu(meSpz)Br₂]_n. The compound crystallizes in the monoclinic space group C2/m: a = 13.754(6) Å, b = 6.825(2) Å, c = 9.731(4) Å, β = 104.598(8)°. The structure comprises ladders where the rungs of the ladder are formed by bridging bromide ions and the rails are formed by bridging meSpz molecules. Magnetic susceptibility data over the range 1.8–325 K was fit to a strong-rung ladder model resulting in J/k_rung = ?39.79(17) K and J/k_rail = ?18.0(4) K.