Experimental and computational thermochemistry of 1,4-benzodioxan and its 2-R derivatives

The standard molar energies of combustion, at T = 298.15 K, of crystalline 1,4-benzodioxan-2-carboxylic acid and 1,4-benzodioxan-2-hydroxymethyl were measured by static bomb calorimetry in an oxygen atmosphere. The standard molar enthalpies of sublimation, at T = 298.15 K, were obtained by Calvet microcalorimetry. These values were used to derive the standard molar enthalpies of formation of the compounds in the gas phase at T = 298.15 K: 1,4-benzodioxan-2-carboxylic acid ?(547.7 ± 3.0) kJ · mol^?1 and 1,4-benzodioxan-2-hydroxymethyl ?(374.2 ± 2.3) kJ · mol^?1.In addition, density functional theory calculations using the B3LYP hybrid exchange–correlation energy functional with extended basis sets, 6-311G⁷ and cc-pVTZ, have been performed for the compounds studied. We have also tested two more accurate computational procedures involving multiple levels of electron structure theory in order to get reliable estimates of the thermochemical parameters of the compounds studied. The agreement between experiment and theory gives confidence to estimate the enthalpies of formation of other 2-R derivatives of 1,4-benzodioxan (R = –CH₂COOH, –OH, –COCH₃, –CHO, –CH₃, –CN, and –NO₂).     

Calorimetric and computational study of 7-hydroxycoumarin

The standard (p° = 0.1 MPa) molar energy of combustion in oxygen, at T = 298.15 K, of 7-hydroxycoumarin was measured by static bomb calorimetry. The value of the standard molar enthalpy of sublimation was obtained by Calvet microcalorimetry and corrected to T = 298.15 K. Combining these results, the standard molar enthalpy of formation of the compound, in the gas phase, at T = 298.15 K, has been calculated, ?(337.5 ± 2.3) kJ · mol^?1. The values for the temperature of fusion, T_fusion, and for the fusion enthalpy, at T = T_fusion, are also reported.Additionally, high-level density functional theory calculations using the B3LYP hybrid exchange-correlation energy functional with extended basis sets, the MC3BB and MC3MPW methods and more accurate correlated computational techniques of the MCCM suite have been performed for the compound.The agreement between experiment and theory gives confidence to estimate the enthalpy of formation of the remaining hydroxycoumarins substituted in the benzene ring.     

Investigation of steam reforming of acetic acid to hydrogen over Ni–Co metal catalyst

Catalytic generation of hydrogen by steam reforming of acetic acid over a series of Ni–Co catalysts have been studied. The catalyst with the molar ratio of 0.25:1 between Ni and Co was superior to other catalysts. The effects of reaction temperature, liquid hourly space velocity (LHSV) and molar ratios of steam-to-carbon (S/C) were studied in detail over this catalyst. At T = 673 K, LHSV = 5.1 h⁻¹, S/C = 7.5:1, the catalyst exhibited the best performances. Acetic acid was converted completely to hydrogen, while H₂ selectivity reached up to 96.3% and CO₂ selectivity up to 98.1% was obtained, respectively. Ni–Co catalyst showed rather stable performances for the 70 h time-on-stream without any deactivation.     

Enhancing the rate capability of high capacity xLi2MnO3 · (1 − x)LiMO2 (M = Mn,Ni, Co) electrodes by Li–Ni–PO4 treatment

The rate capability of high capacity xLi₂MnO₃ · (1 ? x)LiMO₂ (M = Mn, Ni, Co) electrodes for lithium-ion batteries has been significantly enhanced by stabilizing the electrode surface by reaction with a Li–Ni–PO₄ solution, followed by a heat-treatment step. Reversible capacities of 250 mAh/g at a C/11 rate, 225 mAh/g at C/2 and 200 mAh/g at C/1 have been obtained from 0.5Li₂MnO₃ · 0.5LiNi_0.44Co_0.25Mn_0.31O₂ electrodes between 4.6 and 2.0 V. The data bode well for their implementation in batteries that meet the 40-mile range requirement for plug-in hybrid vehicles.     

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.     

Density functional study of small bimetallic Ag–Pd clusters

The geometric and electronic properties of small Ag_mPd_n clusters with m + n = 2–5 are studied within the framework of density functional theory in conjunction with two hybrid and one GGA exchange–correlation functional. For every composition, the global minimum is identified by using geometry optimization for a collection of initial structures. Results indicate that, for bimetallic tetramers and pentamers, the clusters shift from two-dimensional to three-dimensional structures with the addition of a second Pd atom. Ag₂Pd₂ is identified as the most stable tetramer by the calculation of the excess energy and second energy difference of bimetallic clusters. Concerning the fragmentation channels it is seen that the most favourable route in the majority of cases is via the evaporation of a single atom. Density of states calculations reveal that the increase of Pd content depletes the isolated s states close to the Fermi level, while at the same time shifts the d states to higher energies.     

Caractérisation par spectrométrie de masse MALDI–TOF de poly(isosorbide-éther)s cycliques et linéaires obtenus sous irradiation microondes

Characterisation of cyclic and linear poly(isosorbide-ether)s obtained under microwave irradiation by MALDI–TOF mass spectrometry. We studied the influence of the alkyl chain length and of the leaving group on the fraction of cyclic or linear poly(isosorbide-ether)s. A survey by MALDI–TOF MS showed that cyclic chains (C) are predominant when some short aliphatic chains are used (m = 4 or 6), whereas with longer chains (m = 8, 10 or 12), we noted that cyclic products were in a minority, whatever the leaving group (bromide or mesyl). Important non-thermal microwave effects have been demonstrated, notably a methanol-insoluble fraction of polyether considerably larger than the one obtained by conventional heating. These poly(isosorbide-ether)s have been characterized by RMN, MALDI–TOF, SEC, elementary analysis, and DSC. The survey of the thermal behaviour by DSC showed that the temperatures of fusion increase with the aliphatic chain's length (m = 12; T_f = 37 °C).     

(Liquid + liquid) equilibria of the (water + butyric acid + dodecanol) ternary system

(Liquid + liquid) equilibrium (LLE) data for the (water + butyric acid + dodecanol) ternary system have been determined experimentally at T = (298.2, 308.2 and 318.2) K. Complete phase diagrams were obtained by determining binodal curves and tie lines. The reliability of the experimental tie lines was confirmed by using the Othmer–Tobias correlation. The UNIFAC method was used to predict the phase equilibrium in the ternary system using the interaction parameters determined from experimental data of CH₃, CH₂, COOH, OH and H₂O functional groups. Distribution coefficients and separation factors were evaluated for the immiscibility region.     

Isothermal (vapour + liquid) equilibrium (VLE) for binary mixtures containing diethyl carbonate,phenyl acetate,diphenyl carbonate,or ethyl acetate

The isothermal (vapour + liquid) equilibrium (VLE) (P–T–x_i–y_i) was determined the binary systems of (ethyl acetate + diethyl carbonate) from T = (373.2 to 453.2) K, (ethyl acetate + phenyl acetate) at T = 373.2 K, and (diethyl carbonate + phenyl acetate) at T = 373.2 K, while the VLE (P–T–x_i) of three diphenyl carbonate-containing binary systems was also determined experimentally at temperatures from (373.2 to 453.2) K. The experimental results show no azeotrope formation and near ideal solution behaviour for each binary system. These new VLE (P–T–x_i–y_i) data have been passed by the point, area, and infinite dilution thermodynamic consistency tests. The Wilson-HOC, the NRTL-HOC, and the UNIQUAC-HOC models were applied to correlate the VLE results and the optimal values of the model parameters have been determined through data reduction. Comparable results were obtained from these three models.     

The dimeric unit [La(H2O)4(m-PO3C6H4COOH)(m-PO2(OH)C6H4COOH)(m-PO(OH)2C6H4COOH)]2 as building block of layered hybrid material

A new hybrid organic–inorganic material with the structural formula unit [La(H₂O)₄(m-PO₃C₆H₄COOH)(m-PO₂(OH)C₆H₄COOH)(m-PO(OH)₂C₆H₄COOH)]₂ (or [La(H₂O)₄C₂₁H₁₈O₁₅P₃]₂) has been synthesized under hydrothermal condition from La(NO₃)₃·6H₂O and 3-phosphonobenzoic acid (m-PO(OH)₂–C₆H₄–COOH) which is a rigid organic precursor possessing two types of functional groups: phosphonic acid and carboxylic acid. The two units of the produced hybrid are linked together by hydrogen bonds leading to a layered framework composing of by a repetition of inorganic and organic slices. The organic layers consist of dimeric units made of two meta-phosphono-benzoic acid linked together by hydrogen bonds involving their COOH groups. Two kinds of dimeric units are observed: PO₃C₆H₄COOH?HOOCC₆H₄PO(OH)₂, present 2 times in the structure, and PO₂(OH)C6H4COOH?HOOCC₆H₄PO₂(OH). The material crystallises in a monoclinic cell (C2/c (15) space group) with the following parameters: a = 42.515(4) Å, b = 7.4378(6) Å, c = 20.307(2) Å, β = 118.031(6)°, V = 5668.2(9) Å³, Z = 4, density = 1.908 g/cm³.     

Experimental and computational thermochemistry of the dihydroxypyridine isomers

The standard (p^∘ = 0.1 MPa) molar enthalpy of formation for crystalline 2,3-dihydroxypyridine was measured, at T = 298.15 K, by static bomb calorimetry and the standard molar enthalpy of sublimation, at T = 298.15 K, was obtained using Calvet microcalorimetry. These values were used to derive the standard molar enthalpy of formation of 2,3-dihydroxypyridine in gaseous phase, at T = 298.15 K, –(263.9 ± 4.6) kJ · mol⁻¹.Additionally, high-level density functional theory calculations using the B3LYP hybrid exchange-correlation energy functional with extended basis sets have been performed for all dihydroxypyridine isomers to determine the thermochemical order of stability of these systems. The agreement between experiment and theory for the 2,3-dihydroxypyridine isomer gives confidence to the estimates of the enthalpies of formation concerning the other five isomers. It is found that the enthalpic increment for the dihydroxy substitution of pyridine is equal to the sum of the respective enthalpic increment of the monosubstituted pyridines.     

Activity coefficients of glycine in aqueous electrolyte solutions: experimental data for (H2O + KCl + glycine) atT = 298.15 K and (H2O + NaCl + glycine) atT = 308.15 K

Electrochemical cells with two ion-selective electrodes against a single-junction reference electrode were used to obtain the activity coefficients of glycine in aqueous electrolyte solutions. Activity coefficient data were presented for {H₂O  +  KCl (m_S)  +  glycine (m_A)}, and {H₂O  +  NaCl (m_S)  +  glycine (m_A)} atT =  298.15 K and T =  308.15 K, respectively. The results show that the presence of an electrolyte and the nature of its cation have a significant effect on the activity coefficient of glycine in aqueous electrolyte solutions and, in turn, on the method of separation from its culture media. The results of the mean ionic activity coefficients of KCl were compared with those values reported in the literature, which were obtained by the isopiestic method. It was found that the method applied in this study provides accurate activity coefficient data. The effect of temperature on the mean ionic activity coefficient of NaCl in presence of glycine was also investigated.     

Thermodynamics of the ternary systems: (water + glycine,l-alanine and l-serine + di-ammonium hydrogen citrate) from volumetric,compressibility, and (vapour + liquid) equilibria measurements

The apparent molar volumes and isentropic compressibility of glycine, l-alanine and l-serine in water and in aqueous solutions of (0.500 and 1.00) mol · kg^?1 di-ammonium hydrogen citrate {(NH₄)₂HCit} and those of (NH₄)₂HCit in water have been obtained over the (288.15 to 313.15) K temperature range at 5 K intervals at atmospheric pressure from measurements of density and ultrasonic velocity. The apparent molar volume and isentropic compressibility values at infinite dilution of the investigated amino acids have been obtained and their variations with temperature and their transfer properties from water to aqueous solutions of (NH₄)₂HCit have also been obtained. The results have been interpreted in terms of the hydration of the amino acids. In the second part of this work, water activity measurements by the isopiestic method have been carried out on the aqueous solutions of {glycine + (NH₄)₂HCit}, {alanine + (NH₄)₂HCit}, and {serine + (NH₄)₂HCit} at T = 298.15 K at atmospheric pressure. From these measurements, values of vapour pressure, osmotic coefficient, activity coefficient and Gibbs free energy were obtained. The effect of the type of amino acids on the (vapour + liquid) equilibrium of the systems investigated has been studied. The experimental water activities have been correlated successfully with the segment-based local composition Wilson model. Furthermore, the thermodynamic behaviour of the ternary solutions investigated has been studied by using the semi-ideal hydration model and the linear concentration relations have been tested by comparing with the isopiestic measurements for the studied systems at T = 298.15 K.     

Thermodynamics of the cell Pt | H2(p)| HCl (m)| AgCl| Ag and primary medium effects upon HCl in (glycerol + water) solvents

The electromotive force (e.m.f.)E of the cellPt|H₂(p)|HCl(m) in Z|AgCl|Ag in {glycerol (G)  +  water (W)} solvents, Z  =  (G  +  W), up to glycerol mass fraction w_G =  0.7 has been measured within the temperature range from 273.15 K to 313.15 K at HCl molalities up to 0.1mol · kg ^− 1. On this basis, the standard molar e.m.f. E_m ^∘ values pertaining to such solvent mixtures have been obtained, and have been combined with sparse literature data for optimization. At glycerol mass fractions up tow_G ≈  0.5, at constant temperature,E_m ^∘  shows a linear dependence on the glycerol mole fractionx_G and, in parallel, E_c ^∘ (on the amount-of-substance concentration scale) shows linear dependence on the glycerol volume fractionϕ_G . The primary medium effect upon HCl, defined as the difference (E_c ^∘ )_W −  (E_c ^∘ )_Z, has been considered as a function of the water volume fraction ϕ_Win terms of Feakins and French’s theory: this would lead to a primary hydration number n(hydr)  =  2.4 for HCl, in good agreement with previous results obtained with solvents other than (glycerol  +  water). In this connection, some basic methodological aspects are discussed. Ancillary values of the densities ρ_Zof the relevant solvent mixtures, which were hitherto unavailable and are necessary for the data processing leading toE_m ^∘  , have also been measured.     

(p, Vm, T) and phase equilibrium measurements for a natural gas-like mixture using an automated isochoric apparatus

We have developed an automatic apparatus for measuring phase equilibrium and (p, V_m, T) properties of gas mixtures in our laboratory. Based upon the isochoric method, the apparatus can operate at temperatures ranging from 100 K to 500 K at pressures up to 35 MPa, and yield absolute results in fully automated operation. Temperature measurements are accurate to 0.01 K and pressure measurements are accurate to 0.002 MPa. The isochoric method utilizes pressure versus temperature measurements along an isomole (near isochore) and detects phase boundaries by locating the change in the slope of the isomoles.We also have developed a strategy that allows us, when using the above isochoric method together with a second apparatus capable of isothermal density measurements, to collect derived densities that are competitive in accuracy with those of the densimeter, but with a procedure and design that is easy to automate. We present data on a natural gas-like mixture. The experimental data indicate that prediction of the dew point curve with current equations of state is unreliable.     

Determination of erythromycins in fermentation broth using liquid phase extraction with back extraction combined with high performance liquid chromatography

Liquid phase extraction with back extraction (LPE-BE) combined with high performance liquid chromatography-diode array detection (HPLC-DAD) was applied for the extraction and determination of erythromycin A, B and C in fermentation broths. According to this procedure, the fermentation broth with the adjustment pH at a fixed value of 10 was first mixed with organic solvent (V_broth/V_org = 1.0). After shaking, the mixture was separated into two phases by microfuging at 13,000 rpm for 15 min. Then back extraction was performed into the acidic aqueous phase with pH 5.0 (V_org/V_aq = 1.0). After centrifugation at 3000, the two phases were separated and 50 μL of the acidic aqueous phase was injected into the HPLC. The effects of different variables such as the nature of extraction solvent and the pH of samples and buffer were investigated. At the most appropriate conditions, dynamic linear ranges of 0.5–8, 0.1–0.9 and 0.1–0.9 mg mL⁻¹ and limits of detection of 0.03, 0.003 and 0.002 mg mL⁻¹ were obtained for erythromycin A, B and C, respectively. Relative standard deviations (RSDs) of the proposed method were less than 9.5%. The mean recoveries were 99.5%. The proposed method is simple and sensitive with highly clean-up effect and it can be used for monitoring the progress of erythromycin fermentation.     

Magnetic properties of hybrid organo-inorganic copper(II) oxovanadate(V) phosphate and phosphonate bridged systems

The hybrid organo-inorganic compounds [Cu₄(bipy)₄V₄O₁₁(PO₄)₂]nH₂O (n ∼ 5) (1), [Cu₂(phen)₂(PO₄)(H₂PO₄)₂(VO₂) · 2H₂O] (2) and [Cu₂(phen)₂(O₃PCH₂PO₃)(V₂O₅) (H₂O)]H₂O (3) which present different bridging forms of the phosphate/phosphonate group, show different bulk magnetic properties. We herein analyze the magnetic behaviour of these compounds in terms of their structural parameters. We also report a theoretical study for compound (1) assuming four different magnetic exchange pathways between the copper centres present in the tetranuclear unit. For compound (1) the following J values were obtained J₁ = +3.29; J₂ = −0.63; J₃ = −2.23; J₄ = −46.14 cm⁻¹. Compound (2) presents a Curie–Weiss behaviour in the whole range of temperature (3–300 K), and compound (3) shows a maximum for the magnetic susceptibility at 64 K, typical for antiferromagnetic interactions. These data where fitted using a model previously reported in the literature, assuming two different magnetic exchange pathways between the four copper(II) centres, with J₁ = −30.0 and J₂ = −8.5 cm⁻¹.     

Isothermal compressibility and internal pressure studies of some non-electrolytes in aqueous solutions at low temperatures

The experimental data of density (ρ) and sound velocity (u) in the temperature range (275.15 to 293.15) K have been obtained for the systems (dioxane + water), (dimethylformamide + water), (tetrahydrofuran + water), and (acetonitrile + water). The specific heat (C_p) data for the above systems have been obtained at T = 279.15 K. The data obtained are used to calculate the derived parameters of adiabatic compressibility (β_S), at T = 275.15 K to T = 283.15 K, isothermal compressibility (β_T), and internal pressure (P_i) at T = 279.15 K for different concentrations. The solute properties: apparent molar volume (ϕ_V), apparent molar expansivity (ϕ_E), and apparent molar compressibility (ϕ_KS) have been studied and the limiting values for these properties are reported. The variation in apparent molar properties with concentration and the corresponding temperature and pressure effects are discussed in terms of hydrophobic hydration (–H bonding interaction) and hydrophobic interaction (non-polar group solute–solute association in water). It is noted that the internal pressure of solutions is quite insensitive in the region of solute–solute association, while its variation with concentration in the dilute region is sensitive in contrast to the aqueous alcohol solutions. The molecular interactions also exhibit individualistic behaviour and are much dependent on structural alterations in water structure.     

Low-temperature thermodynamic properties of Ir(C5H7O2)3: Connection of entropy with the molecule volume for tris-acetylacetonates of metals

The heat capacity of Ir(C₅H₇O₂)₃ has been measured by the adiabatic method within the temperature range (5 to 305) K. The thermodynamic functions (entropy, enthalpy, and reduced Gibbs free energy) at 298.15 K have been calculated using the obtained experimental heat capacity data. A connection has been found between the entropy and the volume of the elementary crystalline cell for β-acetylacetonates of some metals. The reasons for this interdependence are discussed. The values of entropies at T = 298.15 K have been calculated for all the metal acetylacetonates on which there are structural data.