Thermodynamic parameters and sorption of U(VI) on ACSD

This paper discusses the sorption properties for U(VI) by alginate coated CaSO₄·2H₂O sepiolite and calcined diatomite earth (Kieselguhr) (ACSD). The removal of U(VI) from aqueous solution by sorption onto ACSF in a single component system with various contact times, pH, temperatures, and initial concentrations of U(VI) was investigated. The sorption patterns of uranium on the composite adsorbent followed the Langmuir, Freundlich and Dubinin-Radushkhevic (D-R) isotherms. The Freundlich, Langmuir, and D-R models have been applied and the data correlated well with Freundlich model and that the sorption was physical in nature (sorption energy, E _a = 17.05 kJ/mol). The thermodynamic parameters such as variation of enthalpy ΔH, variation of entropy ΔS and variation of Gibbs free energy ΔG were calculated from the slope and intercept of lnK ₀ vs. 1/T plots. Thermodynamic parameters (ΔH _ads = 31.83 kJ/mol, ΔS _ads = 167 J/mol·K, ΔG ^o _ads (293.15 K) = −17.94 kJ/mol) showed the endothermic heat of sorption and the feasibility of the process. The thermodynamics of U(VI) ion/ACSD system indicates the spontaneous and endothermic nature of the process. It was noted that an increase in temperature resulted in a higher uranium loading per unit weight of the adsorbent.     

Adsorption of uranium(VI) onto <Emphasis Type="Italic">Ulva sp.</Emphasis>-sepiolite composite

Ulva sp. and sepiolite were used to prepare composite adsorbent. The adsorption of uranium(VI) from aqueous solutions onto Ulva sp.-sepiolite has been studied by using a batch adsorber. The parameters that affect the uranium(VI) adsorption, such as solution pH, initial uranium(VI) concentration, and temperature, have been investigated and the optimum conditions determined. The adsorption patterns of uranium on the composite adsorbent followed the Freundlich and Dubinin-Radushkevich (D-R) isotherms. The Freundlich, Langmuir, and Dubinin-Radushkevich (D-R) models have been applied and the data correlate well with Freundlich model. The sorption is physical in nature (sorption energy, E = 4.01 kJ/mol). The thermodynamic parameters such as variation of enthalpy ΔH, variation of entropy ΔS and variation of Gibbs free energy ΔG were calculated from the slope and intercept of lnK _d vs. 1/T plots. Thermodynamic parameters (ΔH _ads = −22.17 kJ/mol, ΔS _ads = −17.47 J/mol·K, ΔG ^o _ads (298.15 K) = −16.96 kJ/mol) show the exothermic heat of adsorption and the feasibility of the process. The results suggested that the Ulva sp-sepiolite composite adsorbent is suitable as a sorbent material for recovery and biosorption/adsorption of uranium ions from aqueous solutions.     

Complexation of [2.2]paracyclophane with β- and γ-cyclodextrins studied by HPLC and NMR

The NMR spectra of [2.2]paracyclophane with β- or γ-cyclodextrin in DMF-d₇ at room temperature do not show significant complexation, while HPLC of the complexes in mixed H₂O:alcohol solvents demonstrate complexation with different stoichiometries. At 243 K in DMF solution the H3 and H5 NMR signals of γ-cyclodextrin (but not β) exhibit complexation-induced chemical shifts denoting complex formation. According to HPLC, at room temperature the [2.2]paracyclophane complex with β-cyclodextrin in 20% H₂O:EtOH exhibits 1:2 stoichiometry with K ₁ = 1×10² ± 2, K ₂ = 9.0×10⁴ ± 2×10³ (K = 9×10⁶) while that with γ-cyclodextrin in 50% H₂O:MeOH exhibits 1:1 stoichiometry with K ₁ = 4×10³ ± 150 M⁻¹. Thermodynamic parameters for both complexes have been estimated from the retention time temperature dependence. For the β-cyclodextrin complexation at 25°C ΔG ⁰ _CD is −39.7 kJ mol⁻¹ while ΔH ⁰ _CD and ΔS ⁰ _CD are −88.2 kJ mol⁻¹ and −0.16 kJ mol⁻¹ K⁻¹. For γ-cyclodextrin, the corresponding values are ΔG ⁰ _CD = −20.5 kJ mol⁻¹, ΔH ⁰ _CD = −33.5 kJ mol⁻¹ and ΔS ⁰ _CD = −0.04 kJ mol⁻¹ K⁻¹.      

Sorption behavior of Sn(II) onto Haro river sand from aqueous acidic solutions

The sorption behavior of Sn(II) onto Haro river sand has been examined with respect to nature of electrolyte, agitation time, dosage of sorbent and concentration of sorbate. Maximum sorption (95.5%) has been achieved from 0.034M hydrochloric acid solution after equilibrating sorbate (2·10⁻⁵M) and sorbent (50 mg) for 120 minutes at aV/W ratio of 90 cm³·g⁻¹. The kinetic data have been subjected to Morris-Weber and Lagergren equations. The kinetics of sorption proceeds a two stage process consisting of a relatively slow initial uptake followed by a much rapid increase in the sorption. The rate constant of intraparticle transport, K_d, comes out to be 8.75·10⁻⁸ mol·g⁻¹·min^−1/2 and the first order rate constant for sorption is 0.0416 min⁻¹. The sorption data of Sn(II) onto Haro river sand followed Langmuir, Freundlich and Dubinin-Radushkevich (D-R) type isotherms. The Langmuir constant,Q, related to sorption capacity and,b, related to sorption energy are computed to be 10.6±1.1 μmol·g⁻¹ and 1123±137 dm³·mol⁻¹, respectively. The D-R isotherm yields the values ofC _m=348±151 μmol·g⁻¹ and β=−0.01044±0.0008 mol²·kJ⁻² and ofE=6.9±0.3 kJ·mol⁻¹. In all three isotherms correlation factor (γ) is ≥0.99. The influence of common anions and cations on the sorption has been investigated. Zn(II), Mg(II), oxalate, Pb(II), Mn(II) and tartrate reduce the sorption significantly whereas Fe(II) causes substantial increase in the sorption. It is essential that all ions causing a decrease in the sorption of Sn(II) must be absent from the sorptive solution otherwise low sorption yields would result.     

Catalytic and Thermodynamic Characterization of Endoglucanase (CMCase) from <Emphasis Type="Italic">Aspergillus oryzae</Emphasis> cmc-1

Monomeric extracellular endoglucanase (25 kDa) of transgenic koji (Aspergillus oryzae cmc-1) produced under submerged growth condition (7.5 U mg⁻¹ protein) was purified to homogeneity level by ammonium sulfate precipitation and various column chromatography on fast protein liquid chromatography system. Activation energy for carboxymethylcellulose (CMC) hydrolysis was 3.32 kJ mol⁻¹ at optimum temperature (55 °C), and its temperature quotient (Q ₁₀) was 1.0. The enzyme was stable over a pH range of 4.1–5.3 and gave maximum activity at pH 4.4. V _max for CMC hydrolysis was 854 U mg⁻¹ protein and K _m was 20 mg CMC ml⁻¹. The turnover (k _cat) was 356 s⁻¹. The pK _a1 and pK _a2 of ionisable groups of active site controlling V _max were 3.9 and 6.25, respectively. Thermodynamic parameters for CMC hydrolysis were as follows: ΔH* = 0.59 kJ mol⁻¹, ΔG* = 64.57 kJ mol⁻¹ and ΔS* = −195.05 J mol⁻¹ K⁻¹, respectively. Activation energy for irreversible inactivation ‘E _a(d)’ of the endoglucanase was 378 kJ mol⁻¹, whereas enthalpy (ΔH*), Gibbs free energy (ΔG*) and entropy (ΔS*) of activation at 44 °C were 375.36 kJ mol⁻¹, 111.36 kJ mol⁻¹ and 833.06 J mol⁻¹ K⁻¹, respectively.     

Polymorphism of paracetamol

The thermodynamic relationship between crystal modifications of paracetamol was studied by alternative methods. Temperature dependence of saturated vapor pressure for polymorphic modifications of the drug paracetamol (acetaminophen) was mea sured and thermodynamic functions of the sublimation process calculated. Solution calorimetry was carried out for the two modifications in the same solvent. Thermodynamic parameters for sublimation for form I (monoclinic) were found: ΔG _sub²⁹⁸=60.0 kJ mol⁻¹; ΔH _sub²⁹⁸=117.9±0.7 kJ mol⁻¹; ΔS _sub²⁹⁸=190±2 J mol⁻¹ K⁻¹. For the orthorhombic modification (form II), the saturated vapor pressure could only be studied at 391 K. Phase transition enthalpy at 298 K, ΔH _tr²⁹⁸(I→II)=2.0±0.4 kJ mol⁻¹, was derived as the difference between the solution enthalpies of the noted polymorphs in the same solution (methanol). Based on ΔH _tr²⁹⁸ (I→II), differences between temperature dependencies of heat capacities of both modifications and the vapor pressure value of form II at 391 K, the temperature dependence of saturated vapor pressure and thermodynamic sublimation parameters for modification II were also estimated (ΔG _sub²⁹⁸=56.1 kJ mol⁻¹; ΔH _sub²⁹⁸=115.9±0.9 kJ mol⁻¹; ΔS _sub²⁹⁸=200±3 J mol⁻¹ K⁻¹). The results indicate that the modifications are monotropically related, which is in contrast to findings recently reported found by classical thermochemical methods.     

Adsorption syntax of Au(III) on unloaded polyurethane foam

The nature of adsorption behavior of Au(III) on polyurethane (PUR) foam was studied in 0.2M HCl aqueous solution. The effect of shaking time and amount of adsorbent were optimized for 3.16·10⁻⁵M solution of Au(III) in 0.2M HCl. The classical Freundlich and Langmuir adsorption isotherms have been employed successfully. The Freundlich parameters 1/n and adsorption capacityK are 0.488±0.016 and (1.40±0.22)·10⁻² mol·g⁻¹, respectively. The Langmuir constants of saturation capacityM and binding energyb are (1.66±0.08)·10⁻⁴mol·g⁻¹ and 40294±2947 l·g⁻¹, respectively, indicating the monolayer chemical sorption. The mean free energy (E) of adsorption of Au(III) on PUR foam has been evaluated using D-R isotherm and found to be 11.5±0.16 kJ·mol⁻¹ reflecting the ion exchange type of chemical adsorption. The effect of temperature on the adsorption has also been studied. the isosteric heat of adsorption was found to be 44.03±1.66 kJ·mol⁻¹. The thermodynamic parameters of ΔG, ΔH, ΔS and equilibrium constantK _c have been calculated. The negative values of ΔG, ΔH and ΔS support that the adsorption of Au(III) on PUR foam is spontaneous, exothermic and of ion exchange chemisorption. The nature of the Au(III) species sorbed on PUR foam have been discussed.     

Mechanism of Oxidation of <Emphasis Type="SmallCaps">L</Emphasis>-Cysteine by Hexachloroiridate(IV) — A Kinetic Study

The kinetics of oxidation of L-Cysteine in aqueous HClO₄ medium were studied using a one-equivalent oxidant, hexachloroiridate(IV). The reaction exhibits second-order dependence with respect to hexachloroiridate(IV) and first-order in cysteine. The rate decreases with increase in hydrogen ion concentration indicating that the zwitterionic form of cysteine is more reactive. Cysteic acid is identified as the product of oxidation. A suitable mechanism involving the formation of [IrCl₆]²⁻ – sulphur bonded intermediate is proposed. The activation parameters of the reaction are computed using the linear least squares method and the values of E_a and ΔS^# are found to be 27.97±1.82 kJ mol⁻¹ and −51.30±6.0 J K⁻¹mol⁻¹, respectively.     

Influence of cerium(IV) and manganese(II) on the oxidation of <Emphasis Type="Italic">D</Emphasis>-galactose by chromium(VI) in the presence of HClO<Subscript>4</Subscript>

The kinetics and mechanism of the oxidation of D-galactose by chromium(VI) in the absence and presence of cerium(IV) and manganese(II) were studied spectrophotometrically in aqueous perchloric acid media. The reaction is first order in both [D-galactose] and [H⁺]. The cerium(IV) inhibits the oxidation path, whereas manganese(II) catalyzes the reactions. The observed inhibitory role of cerium(IV) suggests the formation of chromium(IV) as an intermediate. In the manganese(II) catalyzed path, the D-galactose-manganese(II) complex was considered to be an active oxidant. In this path, the complex forms a ternary chromate ester with chromium(IV) which subsequently undergoes acid catalyzed redox decomposition (one-step three-electron transfer: Indian J. Chem., 2004, vol. 42A, p. 1060; Colloids and Surfaces, 2001, vol. 193, p. 1) in the rate determining step. On the basis of kinetic data, the mechanism of D-galactose oxidation is proposed for parent, the manganese(II) catalyzed and cerium(IV) — inhibited reactions. The activation parameters E _a = 59 kJ ΔH ^# = 57 kJ mol⁻¹, and ΔS ^# = −119 J K⁻¹ mol⁻¹ are calculated and discussed. Reaction products are also examined. Published in Russian in Kinetika i Kataliz, 2009, Vol. 50, No. 1, pp. 90–95. This article was submitted by the authors in English.     

Stationary points on the energy hypersurface of the reaction O3 + H•→ [•O3H]* ⇆ O2 + •OH and thermodynamic functions of •O3H at G3MP2B3, CCSD(T)-CBS (W1U) and MR-ACPF-CBS levels of theory

The relative enthalpies, ΔH^o (0) and ΔH^o (298.15), of stationary points (four minimum and three transition structures) on the ^•O₃H potential energy surface were calculated with the aid of the G3MP2B3 as well as the CCSD(T)–CBS (W1U) procedures from which we earlier found mean absolute deviations (MAD) of 3.9 kJ mol⁻¹ and 2.3 kJ mol⁻¹, respectively, between experimental and calculated standard enthalpies of the formation of a set of 32 free radicals. For CCSD(T)-CBS (W1U) the well depth from O₃ + H^• to trans-^•O₃H, ΔH^o_well(298.15) = −339.1 kJ mol⁻¹, as well as the reaction enthalpy of the overall reaction O₃ + H^•→O₂ + ^•OH, Δ_rH^o(298.15) = −333.7 kJ mol⁻¹, and the barrier of bond dissociation of trans-^•O₃H → O₂ + ^•OH, ΔH^o(298.15) = 22.3 kJ mol⁻¹, affirm the stable short-lived intermediate ^•O₃H. In addition, for radicals cis-^•O₃H and trans-^•O₃H, the thermodynamic functions heat capacity C^o_p(T), entropy S^o (T), and thermal energy content H^o(T) − H^o(0) are tabulated in the range of 100 − 3000 K. The much debated calculated standard enthalpy of the formation of the trans-^•O₃H resulted to be Δ_fH^o(298.15) = 31.1 kJ mol ⁻¹ and 32.9 kJ mol ⁻¹, at the G3MP2B3 and CCSD(T)-CBS (W1U) levels of theory, respectively. In addition, MR-ACPF-CBS calculations were applied to consider possible multiconfiguration effects and yield Δ_fH^o(298.15) = 21.2 kJ mol ⁻¹. The discrepancy between calculated values and the experimental value of −4.2 ± 21 kJ mol⁻¹ is still unresolved. Note added in proof: Yu-Ran Luo and J. Alistair Kerr, based on the discussion in reference 12, recently presented an experimental value of Δ_fH^o(298.15) = 29.7 ± 8.4 kJ mol⁻¹ in the 85th edition of the CRC Handbook of Chemistry and Physics (in progress).     

The standard enthalpy of formation of silver pivalate

The standard enthalpy of combustion of crystalline silver pivalate, (CH₃)₃CC(O)OAg (AgPiv), was determined in an isoperibolic calorimeter with a self-sealing steel bomb, Δ_c H ⁰ (AgPiv, cr)= −2786.9±5.6 kJ mol⁻¹. The value of standard enthalpy of formation was derived for crystalline state: Δ_f H ⁰(AgPiv,cr)= −466.9±5.6 kJ mol⁻¹. Using the enthalpy of sublimation, measured earlier, the enthalpy of formation of gaseous dimer was obtained: Δ_f H ⁰(Ag₂Piv₂,g)= −787±14 kJ mol⁻¹. The enthalpy of reaction (CH₃)₃CC(O)OAg(cr)=Ag(cr)+(CH₃)₃CC(O)O^.(g) was estimated, Δ_r H ⁰=202 kJ mol⁻¹.     

Ion-pair formation in the outer-sphere electron transfer reactions between tris-(1, 10) phenanthroline iron(II) and the halopentacyanocobaltate(III) complexes in aqueous acidic solutions

The kinetics of the reactions between Fe(phen) ₃ ²⁺ [phen = tris–(1,10) phenanthroline] and Co(CN)₅X³⁻ (X = Cl, Br or I) have been investigated in aqueous acidic solutions at I = 0.1 mol dm⁻³ (NaCl/HCl). The reactions were carried out at a fixed acid concentration ([H⁺] = 0.01 mol dm⁻³) and the second-order rate constants for the reactions at 25 °C were within the range of (0.151–1.117) dm³ mol⁻¹ s⁻¹. Ion-pair constants K _ip for these reactions, taking into consideration the protonation of the cobalt complexes, were 5.19 × 10⁴, 3.00 × 10² and 4.02 × 10⁴ mol⁻¹ dm⁻³ for X = Cl, Br and I, respectively. Activation parameters measured for these systems were as follows: ΔH* (kJ K⁻¹ mol⁻¹) = 94.3 ± 0.6, 97.3 ± 1.0 and 109.1 ± 0.4; ΔS* (J K⁻¹) = 69.1 ± 1.9, 74.9 ± 3.2 and 112.3 ± 1.3; ΔG* (kJ) = 73.7 ± 0.6, 75.0 ± 1.0 and 75.7 ± 0.4; E _a (kJ) = 96.9 ± 0.3, 99.8 ± 0.4, and 122.9 ± 0.3; A (dm³ mol⁻¹ s⁻¹) = (7.079 ± 0.035) × 10¹⁶, (1.413 ± 0.011) × 10¹⁷, and (9.772 ± 0.027) × 10²⁰ for X = Cl, Br, and I respectively. An outer – sphere mechanism is proposed for all the reactions.     

Kinetics and mechanism of thermal polymerization of hexafluoropropylene under high pressures

The basic kinetic parameters of thermal polymerization of hexafluoropropylene, namely, general rate constants, degree of polymerization, and their temperature and pressure dependences in the range of 230–290 °C and 2–12 kbar (200–1200 MPa) were determined. The activation energy (E _act = 132±4 kJ mol⁻¹) and activation volume (ΔV ₀ ^≠ = −27±1 cm³ mol⁻¹) were calculated. The activation energy of thermal initiation of polymerization was estimated. The reaction scheme based on the assumption about a biradical mechanism of polymerization initiation was proposed.     

Kinetic study of the promazine oxidation to promazine 5-oxide by trisoxalatocobaltate(III) in basic aqueous media

The kinetics of the oxidation of promazine by trisoxalatocobaltate(III) were studied in the presence of a large excess of the cobalt(III) in tris buffer solution using u.v.–vis spectroscopy ([Co^III] = (0.6 − 2) × 10⁻³ M, [ptz] = 6 × 10⁻⁵ M, pH = 6.6–7.8, I = 0.1 M (NaCl), T = 288−308 K, l = 1 cm). The reaction proceeds via two consecutive reversible steps. In the first step, the reaction leads to formation of cobalt(II) species and a stable cationic radical. In the second step, cobalt(III) is reduced to cobalt(II) ion and a promazine radical is oxidized to the promazine 5-oxide. Linear dependences of the pseudo-first-order rate constants (k ₁ and k ₂) on [Co^III] with a non-zero intercept were established for both redox processes. Rates of reactions decreased with increasing concentration of the H⁺ ion indicating that the promazine and its radical exist in equilibrium with their deprotonated forms, which are reactive reducing species. The activation parameters for reactions studied were as follows: ΔH^≠ = 44 ± 1 kJ mol⁻¹, ΔS^≠ = −100 ± 4 JK⁻¹ mol⁻¹ for the first step and ΔH^≠ = 25 ± 1 kJ mol⁻¹, ΔS^≠ = −169 ± 4 J K⁻¹ mol⁻¹ for the second step, respectively. Mechanistic consequences of all the results are discussed.     

Temperature effected sorption of europium(III) onto 1-(2-pyridylazo)-2-naphthol impregnated polyurethane foam

Summary The sorption of Eu(III) ions onto PAN loaded PUF has been optimized and investigated under the influence of various temperatures, i.e., 303, 313 and 323 K. Maximum retention (>96%) of Eu(III) ions (1.79^. 10^-5M) onto PAN loaded PUF (7.75 mg^. ml^-1) was achieved after 30-minute equilibration time from pH 7 buffer solution. The variation of sorption with temperature yields the thermodynamic parameters ΔH=79±2 kJ^. mol^-1, ΔS=276±7 kJ^. mol^-1. K^-1and ΔG=-1.4±0.1 kJ^. mol^-1at 298 K. The positive value of enthalpy and negative free energy show endothermic and spontaneous nature of sorption, respectively. The sorption data followed Freundlich, Dubinin-Radushkevich (D-R) and Langmuir isotherms at all the three given temperatures. The Freundlich constant 1/n=0.70, 0.62 and 0.55 and sorption capacities C_m=10.8 mmol^. g^-1, 6.1 mmol^. g^-1and 4.4 mmol^. g^-1, respectively, decreased with increasing temperature. Similarly, the sorption capacities of D-R isotherm X_m=197.6 μmol^. g^-1, 201.2 μmol^. g^-1and 137.4 μmol^. g^-1, also decreased with temperature. However, the sorption free energy E=10.2 kJ^. mol^-1, 11.2 kJ^. mol^-1and 12.7 kJ^. mol^-1, increased with temperature. The monolayer coverage (Q) computed from Langmuir isotherm was 11.1±0.6 μmol^. g^-1and remains constant at all the three temperatures investigated. However, the binding energy constant bincreased with temperature. The relationship of bwith temperature and differential heat of adsorption (ΔH_diff) have been evaluated and discussed.     

Molar heat capacities and standard molar enthalpy of formation of 2-amino-5-methylpyridine

The heat capacities (C _p,m) of 2-amino-5-methylpyridine (AMP) were measured by a precision automated adiabatic calorimeter over the temperature range from 80 to 398 K. A solid-liquid phase transition was found in the range from 336 to 351 K with the peak heat capacity at 350.426 K. The melting temperature (T _m), the molar enthalpy (Δ_fus H _m⁰), and the molar entropy (Δ_fus S _m⁰) of fusion were determined to be 350.431±0.018 K, 18.108 kJ mol⁻¹ and 51.676 J K⁻¹ mol⁻¹, respectively. The mole fraction purity of the sample used was determined to be 0.99734 through the Van’t Hoff equation. The thermodynamic functions (H _T-H _298.15 and S _T-S _298.15) were calculated. The molar energy of combustion and the standard molar enthalpy of combustion were determined, ΔU _c(C₆H₈N₂,cr)= −3500.15±1.51 kJ mol⁻¹ and Δ_c H _m⁰ (C₆H₈N₂,cr)= −3502.64±1.51 kJ mol⁻¹, by means of a precision oxygen-bomb combustion calorimeter at T=298.15 K. The standard molar enthalpy of formation of the crystalline compound was derived, Δ_r H _m⁰ (C₆H₈N₂,cr)= −1.74±0.57 kJ mol⁻¹.     

Saturated Vapor Pressure of Iridium(III) Acetylacetonate

The temperature dependency of the saturated vapor pressure of Ir(acac)₃ has been measured by the method of calibrated volume (MCV), the Knudsen method, the flow transpiration method, and the membrane method. The thermodynamic parameters of phase transition of a crystal to gas were calculated using each of these methods, and the following values of ΔH _T ⁰ (kJ mol⁻¹) and ΔS _T ⁰ (J mol⁻¹K⁻¹), respectively, were obtained: MCV: 101.59, 156.70; Knudsen: 130.54, 224.40; Flow transpiration: 129.34, 212.23; Membrane: 95.45, 149.44 Coprocessing of obtaining data (MCV, flow transportation method and Knudsen method) at temperature ranges 110−200°C as also conducted:ΔH _T ⁰ =127.9±2.1 (kJ mol⁻¹ ); ΔS _T ⁰ =215.2±5.0 (J mol⁻¹ K⁻¹ ). This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermodynamic investigation of room temperature ionic liquid

The molar heat capacities of the room temperature ionic liquid 1-butylpyridinium tetrafluoroborate (BPBF₄) were measured by an adiabatic calorimeter in temperature range from 80 to 390 K. The dependence of the molar heat capacity on temperature is given as a function of the reduced temperature X by polynomial equations, C _p,m [J K⁻¹ mol⁻¹]=181.43+51.297X −4.7816X ²−1.9734X ³+8.1048X ⁴+11.108X ⁵ [X=(T−135)/55] for the solid phase (80–190 K), C _p,m [J K⁻¹ mol⁻¹]= 349.96+25.106X+9.1320X ²+19.368X ³+2.23X ⁴−8.8201X ⁵ [X=(T−225)/27] for the glass state (198–252 K), and C _p,m[J K⁻¹ mol⁻¹]= 402.40+21.982X−3.0304X ²+3.6514X ³+3.4585X ⁴ [X=(T−338)/52] for the liquid phase (286–390 K), respectively. According to the polynomial equations and thermodynamic relationship, the values of thermodynamic function of the BPBF₄ relative to 298.15 K were calculated in temperature range from 80 to 390 K with an interval of 5 K. The glass transition of BPBF₄ was observed at 194.09 K, the enthalpy and entropy of the glass transition were determined to be ΔH _g=2.157 kJ mol⁻¹ and ΔS _g=11.12 J K⁻¹ mol⁻¹, respectively. The result showed that the melting point of the BPBF₄ is 279.79 K, the enthalpy and entropy of phase transition were calculated to be ΔH _m = 8.453 kJ mol⁻¹ and ΔS _m=30.21 J K⁻¹ mol⁻¹. Using oxygen-bomb combustion calorimeter, the molar enthalpy of combustion of BPBF₄ was determined to be Δ_c H _m⁰ = −5451±3 kJ mol⁻¹. The standard molar enthalpy of formation of BPBF₄ was evaluated to be Δ_f H _m⁰ = −1356.3±0.8 kJ mol⁻¹ at T=298.150±0.001 K.     

Syntheses, characterization and solid state thermal studies of N-propyl-1,2-diaminoethane (L) and N-isopropyl-1,2-diaminoethane (L′) complexes of nickel(II) nitrite: X-ray single crystal structure of trans-[NiL2(NO2)2]

Linkage isomers trans-bis(N-propyl-1,2-diaminoethane)dinitronickel(II) (brown, 1), trans-bis(N-isopropyl-1,2-diaminoethane)dinitritonickel(II) (blue-violet, 2a) and trans-bis(N-isopropyl-1,2-diaminoethane)dinitronickel(II) (brown, 2b) have been synthesized from solution and X-ray single crystal structure analysis of complex (1) has been performed. Simultaneous TG-DTA analyses reveal that complex (1) exhibits two successive phase transitions before to undergo decomposition (initial temperature of decomposition, Ti = 215 °C). The first one is reversible (82–98 °C; ΔH = 1.75 kJ mol⁻¹ for heating and 93–77 °C; ΔH = −1.65 kJ mol⁻¹ for cooling) and the second one is irreversible endothermic (135–150 °C kJ mol⁻¹; ΔH = 1.80 kJ mol⁻¹) phase transition. No visual color changes are observed in any of the two transitions. The causes related to the first phase transition remain unexplored. However, on the basis of IR spectral studies the second phase transition is supposed to be due to conformational changes of the diamine chelate rings. On the other hand, complexes (2a) and (2b) undergo decomposition without showing any phase transition [Ti = 185 and 195 °C for (2a) and (2b), respectively].     

Study on the thermodynamic properties of cholesterol

The standard molar enthalpy of combustion of cholesterol was measured at constant volume. According to value of Δ_r U _m^θ(−14358.4±20.65 kJ mol⁻¹), Δ_r H _m^θ(−14385.7 kJ mol⁻¹) of combustion reaction and Δ_f H _m^θ(2812.9 kJ mol⁻¹) of cholesterol were obtained from the reaction equation. The enthalpy of combustion reaction of cholesterol was also estimated by the average bond enthalpies. By design of a thermo-chemical recycle, the enthalpy of combustion of cholesterol were calculated between 283.15∼373.15 K. Besides, molar enthalpy and entropy of fusion of cholesterol was obtained by DSC technique.