The effect of 1′,3,5,5′-tetramethyl-1′<Emphasis Type="Italic">H</Emphasis>-1,3′-bipyrazole on the corrosion of steel in 1.0 <Emphasis Type="SmallCaps">M</Emphasis> hydrochloric acid

The effect of some prepared compounds, namely 3,5-dimethyl-1H-pyrazole (P1), 3(5)-amino-5(3)-methylpyrazole (P2), and 1′,3,5,5′-tetramethyl-1′H-1,3′-bipyrazole (P3), on the corrosion behaviour of steel in 1.0 M hydrochloric acid solution as corrosive medium has been investigated at 308 K using weight-loss measurement, potentiodynamic polarisation, linear polarisation, and impedance spectroscopy (EIS). Generally, inhibition efficiency of the investigated compounds was found to depend on the concentration and nature of the inhibitor. P3 was a better inhibitor than P1 and P2, and its inhibition efficiency increased with increasing concentration of inhibitor, attaining 94% above 10⁻³  M. Potentiodynamic polarisation studies clearly reveal that P3 acts essentially as a cathodic inhibitor. E (%) values obtained from different methods are in reasonably good agreement. EIS measurements show an increase of transfer resistance with inhibitor concentration. Partial π-charge on atoms was calculated. Correlation between the highest occupied molecular orbital energy E _HOMO and inhibition efficiencies was sought. The temperature effect on the corrosion behaviour of steel in 1.0 M HCl without and with different concentrations of inhibitor P3 was studied in the temperature range 308 to 343 K. Thermodynamic data, for example heat of adsorption ( \Updelta H_\textads^° \Updelta H_{\text{ads}}^{^\circ } ), entropy of adsorption ( \Updelta S_\textads^° \Updelta S_{\text{ads}}^{^\circ } ) and free energy of adsorption ( \Updelta G_\textads^° \Updelta G_{\text{ads}}^{^\circ } ) were calculated by use of thermodynamic equations. Kinetic activation data, for example E _a, ΔH*, ΔS* and pre-exponential factor, were calculated, and are discussed. The inhibiting action of P3 on the corrosion of steel in 1–10 M hydrochloric acid was also studied by weight-loss measurement. The rate constant and reaction constant were calculated for the corrosion reactions. Adsorption of P3 on the steel surface in 1.0 M HCl follows the Langmuir isotherm model.     

Thermodynamic behavior of complexation process between benzo-15-crown-5 with Li+, Na+, K+, and NH4 + cations in acetonitrile–methanol binary media

The stability constants of 1:1 (M:L) complexes of benzo-15-crown-5 (B15C5) with Li⁺, Na⁺, K⁺ and NH₄ ⁺ cations, the Gibbs standard free energies ( $ \Updelta {\text{G}}_{\text{c}}^{ \circ } $ ), the standard enthalpy changes ( $ \Updelta {\text{H}}_{\text{c}}^{ \circ } $ ) and standard entropy changes ( $ \Updelta {\text{S}}_{\text{c}}^{ \circ } $ ) for formation of these complexes in acetonitrile–methanol (AN–MeOH) binary mixtures have been determined conductometrically. The conductance data show that the stoichiometry of the complexes formed between the macrocyclic ligand and the studied cations is 1:1 (M:L). In most cases, addition of B15C5 to solutions of these cations, causes a continuous increase in the molar conductivities which indicates that the mobility of complexed cations is more than the uncomplexed ones. The stability constants of the complexes were obtained from fitting of molar conductivity curves using a computer program, GENPLOT. The results show that the selectivity order of B15C5 for the metal cations changes with the nature and composition of the binary mixed solvent. The values of standard enthalpy changes ( $ \Updelta {\text{H}}_{\text{c}}^{ \circ } $ ) for complexation reactions were obtained from the slope of the van’t Hoff plots and the changes in standard entropy ( $ \Updelta {\text{S}}_{\text{c}}^{ \circ } $ ) were calculated from the relationship $ \Updelta {\text{G}}_{{{\text{c}},298.15}}^{ \circ } = \Updelta {\text{H}}_{\text{c}}^{ \circ } - 298.15\Updelta {\text{S}}_{\text{c}}^{ \circ } $ . A non-linear behavior was observed between the stability constants (log K_f) of the complexes and the composition of the acetonitrile–methanol (AN–MeOH) binary solution. The results obtained in this study, show that in most cases, the complexes formed between B15C5 and Li⁺, Na⁺, K⁺ and NH₄ ⁺ cations are both enthalpy and entropy stabilized and the values of these thermodynamic quantities change with the composition of the binary solution.     

Thermodynamic study of metal corrosion and inhibitor adsorption processes in copper/N-1-naphthylethylenediamine dihydrochloride monomethanolate/nitric acid system: part 2

N-1-Naphthylethylenediamine dihydrochloride monomethanolate (N-NEDHME) was tested as a corrosion inhibitor for copper in 2 M HNO₃ solution using the standard gravimetric technique at 303–343 K. N-NEDHME acts as an inhibitor for copper in an acidic medium. Inhibition efficiency increases with increase in concentration of N-NEDHME but decreases with a rise in temperature. Thermodynamic parameters such as adsorption heat ( $ \Updelta H_{\text{ads}}^\circ $ ), adsorption entropy ( $ \Updelta S_{\text{ads}}^\circ $ ) and adsorption free energy ( $ \Updelta G_{\text{ads}}^\circ $ ) were obtained from experimental data of the temperature studies of the inhibition process at five temperatures ranging from 303 to 343 K. Kinetic parameters activation such as $ E_{a} $ , $ \Updelta H_{\text{a}}^\circ $ , $ \Updelta S_{\text{a}}^\circ $ and pre-exponential factors have been calculated and are discussed. Adsorption of N-NEDHME on the copper surface in 2 M HNO₃ follows the Langmuir isotherm model.     

Densities and Volumetric Properties of Binary Mixtures of Formamide with 1-Butanol, 2-Butanol, 1,3-Butanediol and 1,4-Butanediol at Temperatures between 293.15 and 318.15 K

The densities of binary mixtures of formamide (FA) with 1-butanol, 2-butanol, 1,3-butanediol, and 1,4-butanediol, including those of the pure liquids, over the entire composition range were measured at temperatures (293.15, 298.15, 303.15, 308.15, 313.15 and 318.15) K and atmospheric pressure. From the experimental data, the excess molar volume, V _m ^E, partial molar volumes, and , at infinite dilution, and excess partial molar volumes, and , at infinite dilution were calculated. The variation of these parameters with composition and temperature of the mixtures are discussed in terms of molecular interactions in these mixtures. The partial molar expansivities, and , at infinite dilution and excess partial molar expansivities, and , at infinite dilution were also calculated. The V _m ^E values were found to be positive for all the mixtures at each temperature studied, except for FA + 1-butanol which exhibits a sigmoid trend wherein V _m ^E values change sign from positive to negative as the concentration of FA in the mixture is increased. The V _m ^E values for these mixtures follow the order: 1-butanol < 2-butanol < 1,3-butanediol < 1,4-butanediol. It is observed that the V _m ^E values depend upon the number and position of hydroxyl groups in these alkanol molecules.     

Kinetics and Equilibria for Complex Formation between Palladium(II) and Chloroacetate

Kinetics and equilibria for the formation of a 1:1 complex between palladium(II) and chloroacetate were studied by spectrophotometric measurements in 1.00 mol HClO₄ at 298.2 K. The equilibrium constant, K, of the reaction

Mechanistic studies of the reaction of bis(2,4,6-tripyridyl 1,3,5-triazine)iron(II) with triazines

Bis(2,4,6-tripyridyl 1,3,5-triazine)iron(II), \textFe(\textTPTZ) ₂ ^{2 +} {\text{Fe(\text{TPTZ})}}_{ 2}^{{ 2 { + }}} reacts with 3-(2-pyridyl)-5,6-bis(4-phenyl-sulfonicacid)-1,2,4-triazine (PDTS) and 3-(4-(4-phenylsulfonicacid)-2-pyridyl)-5,6-bis(4-phenylsulfonic-acid)-1,2,4-triazine (PPDTS) to give \textFe(PDTS) ₃ ^4- {\text{Fe(PDTS)}}_{ 3}^{ 4- } and \textFe(PPDTS) ₃ ^7- {\text{Fe(PPDTS)}}_{ 3}^{ 7- } respectively. Both of these substitution reactions are fast and their kinetics were monitored by stopped-flow spectrophotometry in acetate buffers in the pH range of 3.6–5.6 at 25–45 °C. Both reactions are first order in \textFe(TPTZ) ₂ ^{2 +} {\text{Fe(TPTZ)}}_{ 2}^{{ 2 { + }}} and triazine, and pH has negligible effect on the rate. The kinetic data suggest that these reactions occur in an associative path and a mechanism is proposed considering both protonated and unprotonated forms of PDTS and PPDTS are very similar in reactivity. The kinetic and activation parameters have been evaluated.     

Dynamics of Hydration of Alkylsulfonate Anions in Aqueous Solutions

The ¹⁷O-NMR spin-lattice relaxation times (T ₁) of water molecules in aqueous solutions of n-alkylsulfonate (C₁ to C₆) and arylsulfonic anions were determined as a function of concentration at 298 K. Values of the dynamic hydration number, (S^-) = n_h ^- (t_c^- /t_c⁰ - 1)(\mathrm{S}^{-}) = n_{\mathrm{h}}^{ -} (\tau_{\mathrm{c}}^{-} /\tau_{\mathrm{c}}^{0} - 1), were determined from the concentration dependence of T ₁. The ratios (t_c ^-/t_c⁰\tau_{\mathrm{c}}^{ -}/\tau_{\mathrm{c}}^{0}) of the rotational correlation times (t_c ^-\tau_{\mathrm{c}}^{ -} ) of the water molecules around each sulfonate anion in the aqueous solutions to the rotational correlation time of pure water (t_c⁰\tau_{\mathrm{c}}^{0}) were obtained from the n _DHN(S⁻) and the hydration number (n_h ^-n_{\mathrm{h}}^{ -} ) results, which was calculated from the water accessible surface area (ASA) of the solute molecule. The t_c ^-/t_c⁰\tau_{\mathrm{c}}^{ -}/\tau_{\mathrm{c}}^{0} values for alkylsulfonate anions increase with increasing ASA in the homologous-series range of C₁ to C₄, but then become approximately constant. This result shows that the water structures of hydrophobic hydration near large size alkyl groups are less ordered. The rotational motions of water molecules around an aromatic group are faster than those around an n-alkyl group with the same ASA. That is, the number of water–water hydrogen bonds in the hydration water of aromatic groups is smaller in comparison with the hydration water of an n-alkyl group having the same ASA. Hydrophobic hydration is strongly disturbed by a sulfonate group, which acts as a water structure breaker. The disturbance effect decreases in the following order: $\mbox{--} \mathrm{SO}_{3}^{-} > \mbox{--} \mathrm{NH}_{3}^{ +} > \mathrm{OH}> \mathrm{NH}_{2}$\mbox{--} \mathrm{SO}_{3}^{-} > \mbox{--} \mathrm{NH}_{3}^{ +} > \mathrm{OH}> \mathrm{NH}_{2}. The partial molar volumes and viscosity B _V coefficients for alkylsulfonate anions are linearly dependent on their n _DHN(S⁻) values.     

Thermochemistry of hydroxymethylphenol isomers

The standard (p° = 0.1 MPa) molar enthalpies of formation in the crystalline state of the 2-, 3- and 4-hydroxymethylphenols, $ {{\Updelta}}_{\text{f}} H_{\text{m}}^{\text{o}} ( {\text{cr)}} = \, - ( 3 7 7. 7 \pm 1. 4)\,{\text{kJ}}\,{\text{mol}}^{ - 1} $ , $ {{\Updelta}}_{\text{f}} H_{\text{m}}^{\text{o}} ( {\text{cr) }} = - (383.0 \pm 1.4) \, \,{\text{kJ}}\,{\text{mol}}^{ - 1} $ and $ {{\Updelta}}_{\text{f}} H_{\text{m}}^{\text{o}} ( {\text{cr)}} = - (382.7 \pm 1.4)\,{\text{kJ}}\,{\text{mol}}^{ - 1} $ , respectively, were derived from the standard molar energies of combustion, in oxygen, to yield CO₂(g) and H₂O(l), at T = 298.15 K, measured by static bomb combustion calorimetry. The Knudsen mass-loss effusion technique was used to measure the dependence of the vapour pressure of the solid isomers of hydroxymethylphenol with the temperature, from which the standard molar enthalpies of sublimation were derived using the Clausius–Clapeyron equation. The results were as follows: $ \Updelta_{\rm cr}^{\rm g} H_{\rm m}^{\rm o} = (99.5 \pm 1.5)\,{\text{kJ}}\,{\text{mol}}^{ - 1} $ , $ \Updelta_{\rm cr}^{\rm g} H_{\rm m}^{\rm o} = (116.0 \pm 3.7) \,{\text{kJ}}\,{\text{mol}}^{ - 1} $ and $ \Updelta_{\rm cr}^{\rm g} H_{\rm m}^{\rm o} = (129.3 \pm 4.7)\,{\text{ kJ mol}}^{ - 1} $ , for 2-, 3- and 4-hydroxymethylphenol, respectively. From these values, the standard molar enthalpies of formation of the title compounds in their gaseous phases, at T = 298.15 K, were derived and interpreted in terms of molecular structure. Moreover, using estimated values for the heat capacity differences between the gas and the crystal phases, the standard (p° = 0.1 MPa) molar enthalpies, entropies and Gibbs energies of sublimation, at T = 298.15 K, were derived for the three hydroxymethylphenols.     

Inverse gas chromatography analysis of spruce fibers with different lignin content

Unbleached TMP spruce fibers were stepwise delignified by KMnO₄/H₂SO₄ and five partly delignified samples were obtained. Fibers were characterized in terms of carboxylic groups, lignin and hemicelluloses content. IGC measurements were performed in the untreated fibers and in the five delignified fiber samples, as well as in microcrystalline cellulose (MCC). Different parameters, such as the dispersive component of the surface free energy (g_s ^d \gamma_{{_{s} }}^{d} ), the free energy and the enthalpy of adsorption with nonpolar probes ( \Updelta G_a^d \Updelta G_{a}^{d} and \Updelta H_a^d \Updelta H_{a}^{d} , respectively), as well as the specific interactions with polar probes, quantified by the free energy and the enthalpy of adsorption ( \Updelta G_a^s \Updelta G_{a}^{s} and \Updelta H_a^s \Updelta H_{a}^{s} , respectively), were determined. The values of g_s ^d \gamma_{{_{s} }}^{d} and \Updelta G_a^d \Updelta G_{a}^{d} are for all samples lower than for pure cellulose and vary slightly with the amount of lignin. For small contents of lignin, the values of \Updelta G_a^s \Updelta G_{a}^{s} of the acidic probes decrease with the delignification whereas those of the basic probes increase, pointing to a rather acidic character of the fibers due to the increase of the relative amount of the carbohydrates. The values for MCC corroborate these findings. Despite the substantial variation in the carboxylic group content during delignification, no clear tendencies were detected regarding the affinity with the basic probes.     

Metallosurfactant Schiff base cobalt(III) coordination complexes. Synthesis,characterization, determination of CMC values and biological activities

Twelve surfactant Schiff base ligands were synthesized from salicylaldehyde and its chloro-, bromo- and methoxy- derivatives by condensation with long-chain aliphatic primary amines, and a number of mixed ligand cobalt(III) surfactant Schiff base coordination complexes of the type [Co(trien)A]²⁺ were synthesized from the corresponding dihalogeno complexes by ligand substitution. The Schiff bases and their complexes were characterized by physico-chemical and spectroscopic methods. The complexes form foams in aqueous solution upon shaking. The critical micelle concentration (CMC) values of the complexes in aqueous solution were obtained from conductance measurements. Specific conductivity data (at 303–323 K) served for the evaluation of the thermodynamics of micellization ( \Updelta G_\textm⁰ \Updelta G_{\text{m}}^{0} , \Updelta H_\textm⁰ \Updelta H_{\text{m}}^{0} , \Updelta S_\textm⁰ \Updelta S_{\text{m}}^{0} ). The complexes were tested for its antimicrobial activity.     

High speed liquid chromatography with small bore columns

Using a specially designed column system, we have systematically investigated the effect of mobile phase velocity on column efficiency. The performance of small bore columns operated at different linear velocities of mobile phase was examined for three different types of injection system. Using the value of H^∞/u or n^∞/t${}_{\text{r}}^{\text{º}}$ as a criterion of a high speed separation, we calculated values of n/t${}_{\text{r}}^{\text{º}}$ for different solutes according to the equation \documentclass{article}\pagestyle{empty}\begin{document}$ {{\rm n}\mathord{\left/ {\vphantom {{\rm n} {{\rm t}_{\rm r}^ \circ }}}\right. \kern-\nulldelimiterspace} {{\rm t}_{\rm r}^ \circ }} = {{{\rm n}^\infty } \mathord{\left/ {\vphantom {{{\rm n}^\infty } {{\rm t}_{\rm r}^ \circ }}} \right. \kern-\nulldelimiterspace} {{\rm t}_{\rm r}^ \circ }}\left({\frac{{1 + {\rm k'}}}{{{\rm k' + }\beta }}} \right)^2 $\end{document}; the results obtained are in agreement with the experimentally determined values. These systematic investigations culminated in the separation of seven compounds in less than 10 s; the respective chromatogram is shown.     

Thermochemistry of 2-Aminopyridine (C<Subscript>5</Subscript>H<Subscript>6</Subscript>N<Subscript>2</Subscript>)(s)

The molar enthalpies of solution of 2-aminopyridine at various molalities were measured at T=298.15 K in double-distilled water by means of an isoperibol solution-reaction calorimeter. According to Pitzer’s theory, the molar enthalpy of solution of the title compound at infinite dilution was calculated to be D_solH_m^￥ = 14.34 kJ·mol^-1\Delta_{\mathrm{sol}}H_{\mathrm{m}}^{\infty} = 14.34~\mbox{kJ}\cdot\mbox{mol}^{-1}, and Pitzer’s ion interaction parameters b_MX^(0)L, b_MX^(1)L\beta_{\mathrm{MX}}^{(0)L}, \beta_{\mathrm{MX}}^{(1)L}, and C_MX^fLC_{\mathrm{MX}}^{\phi L} were obtained. Values of the relative apparent molar enthalpies ( ^φ L) and relative partial molar enthalpies of the compound ([`(L)]₂)\bar{L}_{2}) were derived from the experimental enthalpies of solution of the compound. The standard molar enthalpy of formation of the cation C₅H₇N₂ ⁺\mathrm{C}_{5}\mathrm{H}_{7}\mathrm{N}_{2}^{ +} in aqueous solution was calculated to be D_fH_m^o(C₅H₇N₂⁺,aq)=-(2.096±0.801) kJ·mol^-1\Delta_{\mathrm{f}}H_{\mathrm{m}}^{\mathrm{o}}(\mathrm{C}_{5}\mathrm{H}_{7}\mathrm{N}_{2}^{+},\mbox{aq})=-(2.096\pm 0.801)~\mbox{kJ}\cdot\mbox{mol}^{-1}.     

Studies on electron transfer reactions: reduction of heteropoly 10-tungstodivanadophosphate by <Emphasis Type="SmallCaps">l</Emphasis>-cysteine in aqueous acid medium

l-cysteine undergoes facile electron transfer with heteropoly 10-tungstodivanadophosphate, [ \textPV^\textV \textV^\textV \textW _{1 0} \textO _{4 0} ]^{5 -} , \left[ {{\text{PV}}^{\text{V}} {\text{V}}^{\text{V}} {\text{W}}_{ 1 0} {\text{O}}_{ 4 0} } \right]^{5 - } , at ambient temperature in aqueous acid medium. The stoichiometric ratio of [cysteine]/[oxidant] is 2.0. The products of the reaction are cystine and two electron-reduced heteropoly blue, [PV^IVV^IVW₁₀O₄₀]⁷⁻. The rates of the electron transfer reaction were measured spectrophotometrically in acetate–acetic acid buffers at 25 °C. The orders of the reaction with respect to both [cysteine] and [oxidant] are unity, and the reaction exhibits simple second-order kinetics at constant pH. The pH-rate profile indicates the participation of deprotonated cysteine in the reaction. The reaction proceeds through an outer-sphere mechanism. For the dianion ⁻SCH₂CH(NH₃ ⁺)COO⁻, the rate constant for the cross electron transfer reaction is 96 M⁻¹s⁻¹ at 25 °C. The self-exchange rate constant for the ^- \textSCH₂ \textCH( \textNH₃ ⁺ )\textCOO ^- \mathord

An investigation of the decomposition of the intermediate ions produced by electron-impact. II—[C7H7]+ ions from several halogenotoluenes

The structure and decomposition of the [C₇H₇]⁺ ions produced by electron-impact from o-, m- and p-chlorotoluene, o-, m- and p-bromotoluence, and p-iodotoluence, have been investigated. By determining the relative abundance of normal and metastable ions, these [C₇H₇]⁺ ions at electron energy of 20 eV are shown to be so-called ‘tropylium ions’. The amount of the internal energy of the [C₇H₇]⁺ ion estimated by the relative ion abundance ratios, ? [C₅H₅]⁺/[C₇H₇]⁺ and m*/[C₇H₇]⁺ for the decomposition \documentclass{article}\pagestyle{empty}\begin{document}$ [{\rm C}_{\rm 7} {\rm H}_{\rm 7}]^ + \mathop \to \limits^{m^* } [{\rm C}_{\rm 5} {\rm H}_{\rm 5}]^ + + {\rm C}_{\rm 2} {\rm H}_{\rm 2} $\end{document}, is in the order iodotoluene > bromotoluene > chlorotoluene. The heats of formation of the activated complexes for the reaction \documentclass{article}\pagestyle{empty}\begin{document}$ [{\rm C}_{\rm 7} {\rm H}_{\rm 7}]^ + \mathop \to \limits^{m^* } [{\rm C}_{\rm 5} {\rm H}_{\rm 5}]^ + + {\rm C}_{\rm 2} {\rm H}_{\rm 2} $\end{document} were estimated. The values suggest that the decomposing [C₇H₇]⁺ ions from various halogenotoluenes are identical in structure.     

Mechanism of the electroreduction of Ni (II) ions on mercury electrodes catalyzed by pyridine and its derivatives: nicotinamide, <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-diethylnicotinamide and nicotine: concept of parallel heterogeneous catalytic reactions

The theory of the polarographic catalytic currents (mechanism CE) has been developed for the system: Ni²⁺-L-X^p− where L: pyridine (Py), nicotinamide (NA), N,N-diethylnicotinamide (DEN), nicotine (NC) and X^p−: NO⁻ ₃, AcO⁻, HPO²⁻ ₄ . The theory is based on the kinetic parallel heterogeneous catalytic reactions:

Large Carbon Cluster Anions Generated by Laser Ablation of Graphene

The formation of large even-numbered carbon cluster anions, \textC_\textn ^- {\text{C}}_{\text{n}}^{ - } , with n up to 500 were observed in the mass spectra generated by laser ablation of graphene and graphene oxide, and the signal intensity of the latter is much weaker than that of the former. The cluster distributions generated from graphene can be readily altered by changing the laser energy and the accumulation period in the FT - ICR cell. By choosing suitable experimental conditions, weak signals of odd-numbered anions from \textC₁₂₅ ^- {\text{C}}_{{125}}^{ - } to \textC₂₁₁ ^- {\text{C}}_{{211}}^{ - } , doubly charged anions from \textC₇₀^{2 -} {\text{C}}_{{70}}^{{2 - }} to \textC₂₃₀^{2 -} {\text{C}}_{{230}}^{{2 - }} and triply charged cluster anions from \textC₈₀^{3 -} {\text{C}}_{{80}}^{{3 - }} to \textC₂₂₄^{3 -} {\text{C}}_{{224}}^{{3 - }} can be observed. Tandem MS was applied to some selected cluster anions. Though no fragment anions larger than \textC₂₀ ^- {\text{C}}_{{20}}^{ - } can be observed by the process of collisional activation with N₂ gas for most cluster ions, several cluster anions can lose units of C₂, C₄, C₆ or C₈ in their collision process. The differences in their dissociation kinetics and structures require further calculations and experimental studies.     

Solubility Measurements of Crystalline NiO in Aqueous Solution as a Function of Temperature and pH

Results of solubility experiments involving crystalline nickel oxide (bunsenite) in aqueous solutions are reported as functions of temperature (0 to 350 °C) and pH at pressures slightly exceeding (with one exception) saturation vapor pressure. These experiments were carried out in either flow-through reactors or a hydrogen-electrode concentration cell for mildly acidic to near neutral pH solutions. The results were treated successfully with a thermodynamic model incorporating only the unhydrolyzed aqueous nickel species (viz., Ni²⁺) and the neutrally charged hydrolyzed species (viz., Ni(OH)₂⁰)\mathrm{Ni(OH)}_{2}^{0}). The thermodynamic quantities obtained at 25 °C and infinite dilution are, with 2σ uncertainties: log₁₀K_s0^o = (12.40 ±0.29),\varDelta_rG_m^o = -(70. 8 ±1.7)\log_{10}K_{\mathrm{s0}}^{\mathrm{o}} = (12.40 \pm 0.29),\varDelta_{\mathrm{r}}G_{m}^{\mathrm{o}} = -(70. 8 \pm 1.7) kJ⋅mol⁻¹; \varDelta_rH_m^o = -(105.6 ±1.3)\varDelta_{\mathrm{r}}H_{m}^{\mathrm{o}} = -(105.6 \pm 1.3) kJ⋅mol⁻¹; \varDelta_rS_m^o = -(116.6 ±3.2)\varDelta_{\mathrm{r}}S_{m}^{\mathrm{o}} =-(116.6 \pm 3.2) J⋅K⁻¹⋅mol⁻¹; \varDelta_rC_p,m^o = (0 ±13)\varDelta_{\mathrm{r}}C_{p,m}^{\mathrm{o}} = (0 \pm 13) J⋅K⁻¹⋅mol⁻¹; and log₁₀K_s2^o = -(8.76 ±0.15)\log_{10}K_{\mathrm{s2}}^{\mathrm{o}} = -(8.76 \pm 0.15); \varDelta_rG_m^o = (50.0 ±1.7)\varDelta_{\mathrm{r}}G_{m}^{\mathrm{o}} = (50.0 \pm 1.7) kJ⋅mol⁻¹; \varDelta_rH_m^o = (17.7 ±1.7)\varDelta_{\mathrm{r}}H_{m}^{\mathrm{o}} = (17.7 \pm 1.7) kJ⋅mol⁻¹; \varDelta_rS_m^o = -(108±7)\varDelta_{\mathrm{r}}S_{m}^{\mathrm{o}} = -(108\pm 7) J⋅K⁻¹⋅mol⁻¹; \varDelta_rC_p,m^o = -(108 ±3)\varDelta_{\mathrm{r}}C_{p,m}^{\mathrm{o}} = -(108 \pm 3) J⋅K⁻¹⋅mol⁻¹. These results are internally consistent, but the latter set differs from those gleaned from previous studies recorded in the literature. The corresponding thermodynamic quantities for the formation of Ni²⁺ and Ni(OH)₂⁰\mathrm{Ni(OH)}_{2}^{0} are also estimated. Moreover, the Ni(OH)₃ ^-\mathrm{Ni(OH)}_{3}^{ -} anion was never observed, even in relatively strong basic solutions (m_{OH ^-} = 0.1m_{\mathrm{OH}^{ -}} = 0.1 mol⋅kg⁻¹), contrary to the conclusions drawn from all but one previous study.     

Thermochemistry of paracetamol

Combustion calorimetry, Calvet-drop sublimation calorimetry, and the Knudsen effusion method were used to determine the standard (p ^o = 0.1 MPa) molar enthalpies of formation of monoclinic (form I) and gaseous paracetamol, at T = 298.15 K: \Updelta_\textf H_\textm^\texto ( \textC ₈ \textH ₉ \textO ₂ \textN,\text cr I ) = - ( 4 10.4 ±1. 3)\text kJ  \textmol ^{- 1} \Updelta_{\text{f}} H_{\text{m}}^{\text{o}} \left( {{\text{C}}_{ 8} {\text{H}}_{ 9} {\text{O}}_{ 2} {\text{N}},{\text{ cr I}}} \right) = - ( 4 10.4 \pm 1. 3){\text{ kJ}}\;{\text{mol}}^{ - 1} and \Updelta_\textf H_\textm^\texto ( \textC ₈ \textH ₉ \textO ₂ \textN,\text g ) = - ( 2 80.5 ±1. 9)\text kJ  \textmol ^{- 1} . \Updelta_{\text{f}} H_{\text{m}}^{\text{o}} \left( {{\text{C}}_{ 8} {\text{H}}_{ 9} {\text{O}}_{ 2} {\text{N}},{\text{ g}}} \right) = - ( 2 80.5 \pm 1. 9){\text{ kJ}}\;{\text{mol}}^{ - 1} . From the obtained \Updelta_\textf H_\textm^\texto ( \textC ₈ \textH ₉ \textO ₂ \textN,\text cr I ) \Updelta_{\text{f}} H_{\text{m}}^{\text{o}} \left( {{\text{C}}_{ 8} {\text{H}}_{ 9} {\text{O}}_{ 2} {\text{N}},{\text{ cr I}}} \right) value and published data, it was also possible to derive the standard molar enthalpies of formation of the two other known polymorphs of paracetamol (forms II and III), at 298.15 K: \Updelta_\textf H_\textm^\texto ( \textC ₈ \textH ₉ \textO ₂ \textN,\text crII ) = - ( 40 8.4 ±1. 3)\text kJ  \textmol ^{- 1} \Updelta_{\text{f}} H_{\text{m}}^{\text{o}} \left( {{\text{C}}_{ 8} {\text{H}}_{ 9} {\text{O}}_{ 2} {\text{N}},{\text{ crII}}} \right) = - ( 40 8.4 \pm 1. 3){\text{ kJ}}\;{\text{mol}}^{ - 1} and \Updelta_\textf H_\textm^\texto ( \textC ₈ \textH ₉ \textO ₂ \textN,\text crIII ) = - ( 40 7.4 ±1. 3)\text kJ  \textmol ^{- 1} . \Updelta_{\text{f}} H_{\text{m}}^{\text{o}} \left( {{\text{C}}_{ 8} {\text{H}}_{ 9} {\text{O}}_{ 2} {\text{N}},{\text{ crIII}}} \right) = - ( 40 7.4 \pm 1. 3){\text{ kJ}}\;{\text{mol}}^{ - 1} . The proposed \Updelta_\textf H_\textm^\texto ( \textC ₈ \textH ₉ \textO ₂ \textN,\text g ) \Updelta_{\text{f}} H_{\text{m}}^{\text{o}} \left( {{\text{C}}_{ 8} {\text{H}}_{ 9} {\text{O}}_{ 2} {\text{N}},{\text{ g}}} \right) value, together with the experimental enthalpies of formation of acetophenone and 4′-hydroxyacetophenone, taken from the literature, and a re-evaluated enthalpy of formation of acetanilide, \Updelta_\textf H_\textm^\texto ( \textC ₈ \textH ₉ \textON,\text g ) = - ( 10 9. 2 ± 2. 2)\text kJ  \textmol ^{- 1} , \Updelta_{\text{f}} H_{\text{m}}^{\text{o}} \left( {{\text{C}}_{ 8} {\text{H}}_{ 9} {\text{ON}},{\text{ g}}} \right) = - ( 10 9. 2\,\pm\,2. 2){\text{ kJ}}\;{\text{mol}}^{ - 1} , were used to assess the predictions of the B3LYP/cc-pVTZ and CBS-QB3 methods for the enthalpy of a isodesmic and isogyric reaction involving those species. This test supported the reliability of the theoretical methods, and indicated a good thermodynamic consistency between the \Updelta_\textf H_\textm^\texto \Updelta_{\text{f}} H_{\text{m}}^{\text{o}} (C₈H₉O₂N, g) value obtained in this study and the remaining experimental data used in the \Updelta_\textr H_\textm^\texto \Updelta_{\text{r}} H_{\text{m}}^{\text{o}} calculation. It also led to the conclusion that the presently recommended enthalpy of formation of gaseous acetanilide in Cox and Pilcher and Pedley’s compilations should be corrected by ~20 kJ mol⁻¹.     

Vanadium(V)-substituted Keggin-type heteropolyoxotungstophosphates as electron transfer and antimicrobial agents: oxidation of glutathione and sensitization of MRSA towards β-lactam antibiotics

Glutathione (GSH) undergoes facile electron transfer with vanadium(V)-substituted Keggin-type heteropolyoxometalates, [ \textPV^\textV \textW _{1 1} \textO _{4 0} ] ^{4 -} [ {\text{PV}}^{\text{V}} {\text{W}}_{ 1 1} {\text{O}}_{ 4 0} ]^{{ 4 { - }}} (HPA1) and [ \textPV^\textV \textV^\textV \textW _{1 0} \textO _{4 0} ] ^{5 -} [ {\text{PV}}^{\text{V}} {\text{V}}^{\text{V}} {\text{W}}_{ 1 0} {\text{O}}_{ 4 0} ]^{{ 5 { - }}} (HPA2). The kinetics of these reactions have been investigated in phthalate buffers spectrophotometrically at 25 °C in aqueous medium. One mole of HPA1 consumes one mole of GSH and the product is the one-electron reduced heteropoly blue, [ \textPV^\textIV \textW _{1 1} \textO ₄₀ ] ^5- [ {\text{PV}}^{\text{IV}} {\text{W}}_{ 1 1} {\text{O}}_{ 40} ]^{ 5- } . But in the GSH-HPA2 reaction, one mole of HPA2 consumes two moles of GSH and gives the two-electron reduced heteropoly blue [ \textPV^\textIV \textV^\textIV \textW ₁₀ \textO ₄₀ ] ^7- [ {\text{PV}}^{\text{IV}} {\text{V}}^{\text{IV}} {\text{W}}_{ 10} {\text{O}}_{ 40} ]^{ 7- } . Both reactions show overall third-order kinetics. At constant pH, the order with respect to both [HPA] species is one and order with respect to [GSH] is two. At constant [GSH], the rate shows inverse dependence on [H⁺], suggesting participation of the deprotonated thiol group of GSH in the reaction. A suitable mechanism has been proposed and a rate law for the title reaction is derived. The antimicrobial activities of HPA1, HPA2 and [ \textPV^\textV \textV^\textV \textV^\textV \textW ₉ \textO _{4 0} ] ^{6 -} [ {\text{PV}}^{\text{V}} {\text{V}}^{\text{V}} {\text{V}}^{\text{V}} {\text{W}}_{ 9} {\text{O}}_{ 4 0} ]^{{ 6 { - }}} (HPA3) against MRSA were tested in vitro in combination with vancomycin and penicillin G. The HPAs sensitize MRSA towards penicillin G.