ATP- and redox-induced conformational changes in the activator of the radical enzyme 2-hydroxyisocaproyl-CoA dehydratase

A [4Fe–4S]¹⁺ cluster-containing protein activates 2-hydroxyisocaproyl-CoA dehydratase by an ATP-driven electron transfer. The activator has been proposed to change its conformation by MgATP similarly to nitrogenase Fe-protein. Iron chelation by bathophenanthroline removed the reduced [4Fe–4S]¹⁺ cluster from the activator in an ATP-dependent manner (rate, v = 0.128 ± 0.004 min⁻¹; K_m = 21 ± 1 μM); with ADP no chelation was observed (v < 0.001 min⁻¹). Chelation of the oxidised [4Fe–4S]²⁺ cluster occurred faster with ADP (v = 0.34 ± 0.05 min⁻¹) than with ATP (v = 0.132 ± 0.005 min⁻¹). The data indicate that reduction of the activator and binding of ATP induce conformational changes necessary to transfer the electron to the dehydratase. Interaction of both proteins promotes ATP hydrolysis (K_m = 0.5 ± 0.1 μM).     

Catalytic effect of CTAB on the interaction of dipeptide glycyl-tyrosine (Gly-Tyr) with ninhydrin

The effect of cationic micelles of cetyltrimethylammonium bromide (CTAB) on the interaction of dipeptide glycyl-tyrosine (Gly-Tyr) with ninhydrin under varying conditions has been studied spectrophotometrically at 70 °C and pH 5.0. The reaction followed first- and fractional-order kinetics with respect to [Gly-Tyr] and [ninhydrin], respectively. Increase in total concentration of CTAB from 0 to 70 × 10⁻³ mol dm⁻³ resulted in an increase in the pseudo-first-order rate constant (k_ψ) by a factor of ca. 3. Quantitative kinetic analysis of k_ψ − [CTAB] data was performed on the basis of pseudo-phase model of the micelles (proposed by Menger and Portnoy and developed by Bunton) and Piszkiewicz model. A possible mechanism has been proposed and the kinetic data have been used to evaluate the micellar binding constants K_S (268 mol⁻¹ dm³ for Gly-Tyr) and K_N (64 mol⁻¹ dm³ for ninhydrin).     

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.     

Determination of Henry’s constant using a photoacoustic sensor

We present a simple method for measuring Henry’s constant k_Hof ethanol using photoacoustic spectroscopy. At T =  298.1 K the measured value fork_H is (0.877  ±  0.039)kPa · kg · mol ^− 1. Our data show that Henry’s law is valid at ethanol molalities between 0.1mol · kg ^− 1 and 1.4 mol · kg ^− 1. The temperature dependence of Henry’s constant was carefully examined by measuring the ethanol vapour pressure of six different aqueous solutions between T =  273.1 K and T =  298.1 K. By analysing the gas phase concentration and applying Henry’s law, an ethanol molality of 0.864 mol · kg ^− 1in the liquid phase can be measured with an error of  ± 0.038mol · kg ^− 1. The detection limit of the photoacoustic sensor is a gaseous ethanol pressure of 10 ^− 3kPa. Ethanol molality changes as low as 1.10 ^− 3mol · kg ^− 1can be measured.     

Measurement of the (pressure,density, temperature) relation of two (methane + nitrogen) gas mixtures at temperatures between 240 and 400 K and pressures up to 20 MPa using an accurate single-sinker densimeter

Comprehensive (p, ρ, T) measurements on two gas mixtures of (0.9CH₄ + 0.1N₂) and (0.8CH₄ + 0.2N₂) have been carried out at six temperatures between 240 and 400 K and at pressures up to 20 MPa. A total of 108 (p, ρ, T) data for the first mixture and 134 for the second one are given. These measurements were performed using a compact single-sinker densimeter based on Archimedes’ buoyancy principle. The overall uncertainty in density ρ is estimated to be (1.5 · 10⁻⁴ · ρ + 2 · 10⁻³ kg · m⁻³) (coverage factor k = 2), the uncertainty in temperature T is estimated to be 0.006 K (coverage factor k = 2), and the uncertainty in pressure p is estimated to be 1 · 10⁻⁴·p (coverage factor k = 2). The equipment has been previously checked with pure nitrogen over the whole temperature and pressure working ranges and experimental results (35 values) are given and a comparison with the reference equation of state for nitrogen is presented.     

Molecular spin ladders self-assembly from [Ni(dmit)2]− building blocks: Syntheses,structures and magnetic properties

Two ion-pair compounds, consisting of 1-(4′-R-benzyl)pyridinium ([RBzPy]⁺, R = NO₂ (1) and Br (2)) and [Ni(dmit)₂]⁻ (dmit²⁻ = 2-thioxo-1,3-dithion-4,5-dithiolato), have been synthesized and structurally characterized. The anions of [Ni(dmit)₂]⁻ stack into dimers, which further construct into two-leg ladder through terminal S⋯S interactions in 1, lateral S⋯S interactions in 2. The weak H-bonding interactions of C–H⋯S were observed in 2, while only weak van de Waals interactions between anion and cations in 1. The magnetic susceptibilities measured in 2–300 K indicate AFM exchange interaction domination both two compounds. A peculiar magnetic transition at ∼100 K was observed in 1. An AFM ordering below ∼11 K was found in 2, and the best fit to magnetic susceptibility above 45 K in this compound, using a dimer model with s = 1/2, give rise to Δ/k_B = 36.1 K, zJ = −0.91 K, C = 3.2 × 10⁻³ emu K mol⁻¹ and χ₀ = −4.0 × 10⁻⁶ emu mol⁻¹ with g of 2.0 fixed.     

Pulse radiolysis of aqueous diphenyloxide

Pulse radiolysis of aqueous diphenyloxide (DPO) has been performed under various experimental conditions. The OH radicals react with DPO on various positions of the molecule with a rate constant, k=2.1×10¹⁰ l mol⁻¹ s⁻¹. The major reaction step appears to be a cleavage of the C–O bond of DPO resulting into C₆H₄OH (λ=285 nm) and C₆H₅O(λ=325 nm) radicals in addition to DPO–OH adducts. They disappear according to a second-order reaction. In the presence of air or in a gas mixture of N₂O:O₂=4:1 the DPO–OH adducts are scavenged by oxygen, resulting into peroxyl radicals, which are long-lived species. For the reaction of e_aq⁻ with DPO a rate constant, k=2×10¹⁰ l mol⁻¹ s⁻¹ was found.     

Noise and ac impedance analysis of ion transfer kinetics at the micro liquid/liquid interface

Fluctuation analysis was utilized to determine the TEA ion transfer kinetics across the water/1,2-dichloroethane interface. The obtained data were compared with those derived from electrochemical impedance spectroscopy experiments using the same electrolytic cell. The apparent standard rate constants k_s determined by these two techniques have a similar value. The average value k_s = 0.37 cm s^− 1 is comparable with the previously reported value k_s = 0.2 cm s^− 1. The experimental approach utilizing a thick wall glass micro-capillary to fix the interface exhibits a very small stray capacitance value, proving this system to be suitable for determining the kinetics of the fast ion transfer across a liquid/liquid interface. Application of a method employing a small perturbation signal prevents polarization of the inner capillary surface by current flowing through the cell. The induced polarization of the capillary can affect ion concentration at the interface due to electroosmosis and thus make the kinetic data evaluation difficult or erroneous.     

Thermodynamics of the oxidation–reduction reaction {2 glutathionered(aq) + NADPox(aq)=glutathioneox(aq) + NADPred(aq)}

Microcalorimetry, spectrophotometry, and high-performance liquid chromatography (h.p.l.c.) have been used to conduct a thermodynamic investigation of the glutathione reductase catalyzed reaction {2 glutathione_red(aq) + NADP_ox(aq)=glutathione_ox(aq) + NADP_red(aq)}. The reaction involves the breaking of a disulfide bond and is of particular importance because of the role glutathione_red plays in the repair of enzymes. The measured values of the apparent equilibrium constant K^′ for this reaction ranged from 0.5 to 69 and were measured over a range of temperature (288.15 K to 303.15 K), pH (6.58 to 8.68), and ionic strength I_m (0.091 mol · kg⁻¹ to 0.90 mol · kg⁻¹). The results of the equilibrium and calorimetric measurements were analyzed in terms of a chemical equilibrium model that accounts for the multiplicity of ionic states of the reactants and products. These calculations led to values of thermodynamic quantities at T=298.15 K and I_m=0 for a chemical reference reaction that involves specific ionic forms. Thus, for the reaction {2 glutathione_red⁻(aq) + NADP_ox³⁻(aq)=glutathione_ox²⁻(aq) + NADP_red⁴⁻(aq) + H⁺(aq)}, the equilibrium constant K=(6.5±4.4)·10⁻¹¹, the standard molar enthalpy of reaction Δ_rH^o_m=(6.9±3.0) kJ · mol⁻¹, the standard molar Gibbs free energy change Δ_rG^o_m=(58.1±1.7) kJ · mol⁻¹, and the standard molar entropy change Δ_rS^o_m=−(172±12) J · K⁻¹ · mol⁻¹. Under approximately physiological conditions (T=311.15 K, pH=7.0, and I_m=0.25 mol · kg⁻¹ the apparent equilibrium constant K^′≈0.013. The results of the several studies of this reaction from the literature have also been examined and analyzed using the chemical equilibrium model. It was found that much of the literature is in agreement with the results of this study. Use of our results together with a value from the literature for the standard electromotive force E^o for the NADP redox reaction leads to E^o=0.166 V (T=298.15 K and I=0) for the glutathione redox reaction {glutathione_ox²⁻(aq) + 2 H⁺(aq) + 2 e⁻=2 glutathione_red⁻(aq)}. The thermodynamic results obtained in this study also permit the calculation of the standard apparent electromotive force E^′o for the biochemical redox reaction {glutathione_ox(aq) + 2 e⁻=2 glutathione_red(aq)} over a wide range of temperature, pH, and ionic strength. At T=298.15 K, I=0.25 mol · kg⁻¹, and pH=7.0, the calculated value of E^′o is −0.265 V.     

Specific ion effects on the surface tension and surface potential of aqueous electrolytes

The phenomena of electrolytes affecting the surface tension of aqueous solutions and producing measurable surface potentials are reviewed in the light of recent studies of them. The factual information presented includes the molar ionic surface tension increments k_i = lim(c_i → 0)(dσ / dc_i) of many ions and the surface potential increments ∆ χ = χ_E − χ_W of electrolytes involving the cations H⁺, Na⁺, K⁺, and NH₄⁺ and various anions. Gaps in the data that invite filling and inconsistencies in reported data are pointed out. Correlations of k_i with several properties of the ions that should be relevant to their specific effects: their sizes, quantities representing their polarizabilities, their effects on the structure of the water and the binding of water molecules by them, are presented. Correlations of the surface potential increment ∆ χ with the electrolyte surface tension increments and with the differences between the cation and anion increments are shown. Models recently proposed for the rationalization of the observed phenomena and relevant theoretical developments are shown and discussed. The paradox of hydrogen ions not promoting significant charge separation at the interface but yielding large surface potentials is emphasized.     

Solubilities of l-glutamic acid, 3-nitrobenzoic acid,p-toluic acid,calcium-l-lactate,calcium gluconate,magnesium-dl-aspartate,and magnesium-l-lactate in water

Solubilities of l -glutamic acid, 3-nitrobenzoic acid, p -toluic acid, calcium-l -lactate, calcium gluconate, magnesium- dl -aspartate, and magnesium- l -lactate in water were determined in the temperature range 278 K to 343 K. The apparent molar enthalpies of solution at T =  298.15 K as derived from these solubilities areΔ_solH_m (l -glutamic acid,m_sat =  0.0565 mol · kg ^− 1)  =  30.2 kJ · mol ^− 1,Δ_solH_m (3-nitrobenzoic acid, m =  0.0188 mol · kg ^− 1)  =  28.1 kJ · mol ^− 1, Δ_solH_m( p - toluic acid, m =  0.00267 mol · kg ^− 1)  =  23.9 kJ · mol ^− 1,Δ_solH_m (calcium- l -lactate tetrahydrate,m =  0.2902 mol · kg ^− 1)  =  25.8 kJ · mol ^− 1,Δ_solH_m (calcium gluconate, m =  0.0806 mol · kg ^− 1)  =  22.1 kJ · mol ^− 1, Δ_solH_m(magnesium-dl -aspartate tetrahydrate, m =  0.1469 mol · kg ^− 1)  =  11.5 kJ · mol ^− 1, andΔ_solH_m (magnesium- l -lactate trihydrate,m =  0.3462 mol · kg ^− 1)  =  3.81 kJ · mol ^− 1.     

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.     

Oxidative thermal degradation of LDPE and the determination of some thermodynamic quantities

The pyrolysis of polyolefin wastes is one of the possible ways to obtain chemical feedstocks. In this work, the thermal degradation of low density polyethylene, (LDPE), which is a major product within plastics, was investigated in a semi-batch reactor system. First-order rate kinetics approach was chosen and reaction rate coefficients, k, and some thermodynamic quantities determined such as activation energy, reaction enthalpy, free activation enthalpy, and entropy of degradation of LDPE for different air flow rates. We found that the maximum value of some thermodynamic quantities, such as reaction rate coefficient is 0.0243 min⁻¹ at 600 mL min⁻¹ air flow rate and the free activation enthalpy (ΔG^≠) is 148.66 kJ mol⁻¹ at 450 mL min⁻¹ air flow rate and the reaction enthalpy (ΔH^≠) is 57.65 J mol⁻¹ at 623 K temperature conditions. Moreover, we found that the oxidative degradation of LDPE is not spontaneous and has lower energy necessary (for degradation) than non-oxidative degradation processes.     

Crystal structures and magnetic properties of complexes of M(NO3)2; M = MnII,CoII, NiII,and CuII,with pyridine ligands carrying an aminoxyl radical

Four complexes of M(NO₃)₂(4NOPy-OMe)₂, (4NOPy-OMe = 4-(N-tert-butyloxylamino)-2-(methoxymethylenyl)pyridine, and M = Mn^II, 1; Co^II, 2; Ni^II, 3; Cu^II, 4), were prepared and fully characterized. X-ray single crystal analysis reveals that four complexes are isostructural. The molecular structures are distorted octahedral in which the methoxy oxygen atoms coordinate to the metal ion by trans-configuration while the pyridyl nitrogen atoms and the nitrate oxygen atoms coordinate by cis-configuration. The magnetic properties of all complexes were investigated by SQUID magneto/susceptometry. Temperature dependence of the molar magnetic susceptibilities in the temperature range of 2–300 K indicated that the magnetic coupling between aminoxyl radicals and metal ion was antiferromagnetic in the complex 1 and were ferromagnetic in the complexes 2–4. The quantitative analysis based on the spin Hamiltonian, H = −2J(S₁S_M + S_MS₂) yielded the best fit as J/k_B = −13.4 ± 0.1 K, g = 1.94 ± 0.002, and θ = −0.78 ± 0.02 K for the complex 1, J/k_B = 48.7 ± 2.1 K, g = 2.07 ± 0.02, and θ = −2.83 ± 0.41 K for the complex 3 (the data in the temperature range 300–50 K were used), and J/k_B = 57.0 ± 1.2 K, g = 2.002 ± 0.004, and θ = −9.8 ± 0.1 K for the complex 4.     

The molar enthalpies of solution and vapour pressures of saturated aqueous solutions of some cesium salts

Vapour pressures of water over saturated solutions of cesium chloride, cesium bromide, cesium nitrate, cesium sulfate, cesium formate, and cesium oxalate were determined as a function of temperature. These vapour pressures were used to evaluate the water activities, osmotic coefficients and molar enthalpies of vapourization. Molar enthalpies of solution of cesium chloride, Δ_solH_m(T = 295.73 K; m = 0.0622 mol · kg⁻¹) = (17.83 ± 0.50) kJ · mol⁻¹; cesium bromide, Δ_solH_m(T = 293.99 K; m = 0.0238 mol · kg⁻¹) = (26.91 ± 0.59) kJ · mol⁻¹; cesium nitrate, Δ_solH_m(T = 294.68 K; m = 0.0258 mol · kg⁻¹) = (37.1 ± 2.3) kJ · mol⁻¹; cesium sulfate, Δ_solH_m(T = 296.43 K; m = 0.0284 mol · kg⁻¹) = (16.94 ± 0.43) kJ · mol⁻¹; cesium formate, Δ_solH_m(T = 295.64 K; m = 0.0283 mol · kg⁻¹) = (11.10 ± 0.26) kJ · mol⁻¹ and Δ_solH_m(T = 292.64 K; m = 0.0577 mol · kg⁻¹) = (11.56 ± 0.56) kJ · mol⁻¹; and cesium oxalate, Δ_solH_m(T = 291.34 K; m = 0.0143 mol · kg⁻¹) = (22.07 ± 0.16) kJ · mol⁻¹ were determined calorimetrically. The purity of the chemicals was generally greater than 0.99 mass fraction, except for HCOOCs and (COOCs)₂ where purities were approximately 0.95 and 0.97 mass fraction, respectively. The uncertainties are one standard deviations.     

Process Improvement of Biogas Production from Anaerobic Co-digestion of Cow Dung and Corn Husk

A study of organic loading rate (OLR) and effect of NaOH concentration on the pretreatment stage of corn husk (CH) was conducted by Face-Centered Central Composite Design (CCF) to improve the biogas production. Three levels of OLR at 25.0 g VS · L⁻¹ · d⁻¹ (OLR₂₅), 35.0 g VS · L⁻¹ · d⁻¹ (OLR₃₅), and 45.0 g VS · L⁻¹ · d⁻¹ (OLR₄₅) were performed with NaOH pretreatment concentration of CH at 25.0% (N₂₅), 35.0% (N₃₅), and 45.0% (N₄₅) (w/w). The optimum production of biogas at 67.6 mL · min⁻¹ with methane concentration of 63.4% has been obtained at the application of OLR at 43.6 g VS · L⁻¹ · d⁻¹ and NaOH concentration at 33% (w/w).     

Short chain lead (II) alkanoates as ionic liquids and glass formers: A d.s.c., X-ray diffraction and FTIR spectroscopy study

Three members of the lead (II) n-alkanoates (from etanoate to n-butanoate) have been synthesized, purified and studied by d.s.c., X-ray diffraction, and FTIR spectroscopy. Lead (II) acetate, propanoate, and butanoate present only a melting transition at T = (452.6, 398.2, and 346.5) K, with Δ_fH = (16.0, 13.1, and 15.6) kJ · mol⁻¹, and Δ_fS = (35.3, 32.8, and 45.1) J · mol⁻¹ · K⁻¹, respectively. These temperature data correct to a great extent the historical values reported in the literature. These three members readily quench into a glass state. Their corresponding T_g values are (314.4, 289.0, and 274.9) K, respectively, measured by d.s.c. at a heating rate of 5 K · min⁻¹.     

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.     

Photo-induced degradation of some flavins in aqueous solution

The blue-light induced photo-degradation of FMN, FAD, riboflavin, lumiflavin, and lumichrome in aqueous solution at pH 8 is studied by measurement of absorption coefficient spectral changes due to continuous excitation at 428 nm. The quantum yields of photo-degradation determined are ϕ_D(riboflavin, pH 8) ≈ 7.8 × 10⁻³, ϕ_D(FMN, pH 5.6) ≈ 7.3 × 10⁻³, ϕ_D(FMN, pH 8) ≈ 4.6 × 10⁻³, ϕ_D(FAD, pH 8) ≈ 3.7 × 10⁻⁴, ϕ_D(lumichrome, pH 8) ≈ 1.8 × 10⁻⁴, and ϕ_D(lumiflavin, pH 8) ⩽ 1.1 × 10⁻⁵. In a mass-spectroscopic analysis, the photo-products of FMN dissolved in water (solution pH is 5.6) were identified to be lumichrome and the lumiflavin derivatives dihydroxymethyllumiflavin, formyllumiflavin, and lumiflavin-hydroxy-acetaldehyde. An absorption and emission spectroscopic characterisation of the primary photoproducts of FMN at pH 8 is carried out.     

The investigation of thermodynamic parameters of kinetic reaction between o-phenylenediamine and gold (III)

A visible spectrophotometric method has been developed for the reaction kinetics of o-phenylenediamine in the presence of gold (III). The method is based on the measurement of the absorbance of the reaction o-phenylenediamine and gold (III). Optimum conditions for the reaction were established as pH 6 at λ = 466 nm.When the reaction kinetic of o-phenylenediamine by gold (III) was investigated, it was observed that the following rate formula was found as ln (A/A₀) = −kt, according to absorbance measurements. The activation energy E_a and Arrhenius constant A were calculated from the Arrhenius equation as 1.009 kJ · mol⁻¹ and 3.46 · 10⁻² s⁻¹, respectively. Other activation thermodynamic parameters, entropy, ΔS (J · mol⁻¹ · K⁻¹), enthalpy, ΔH (kJ · mol⁻¹), Gibbs free energy, ΔG (kJ · mol⁻¹) and equilibrium constant, K_e were calculated at T = (283.2, 303.2, 323.2, and 343.2) K. The study was exothermic due to the decrease of entropy and was a non-spontaneous process during activation.