Apparent Molar Enthalpies Research Articles

Thermochemistry on ephedrine hydrochloride and N-methylephedrine hydrochloride

The crystal structures of ephedrine hydrochloride and N-methylephedrine hydrochloride have been determined by X-ray crystallography. The molar enthalpies of dissolution of the two compounds with various molalities were measured at T = 298.15 K in distilled water by means of isoperibol solution-reaction calorimeter, respectively. According to the theory of Pitzer, the molar enthalpies of dissolution of the two compounds at infinite dilution, Δ s H m ∞ , and Pitzer’s parameters β MX ( 0 ) L , β MX ( 1 ) L , and C MX Φ L , were obtained. Then the values of apparent relative molar enthalpies ( Φ L ) , hydration heat, and relative partial molar enthalpies of the two compounds ( L ¯ 2 ) were derived from the experimental results of the enthalpies of dissolution of the two compounds. Finally, the ionic radius of the cations can be calculated from the data of the corresponding effective volume of the cations.

Thermochemical properties of 1,1-diamino-2,2-dinitroethylene (FOX-7) in dimethyl sulfoxide (DMSO)

The enthalpy of dissolution of 1,1-diamino-2,2-dinitroethylene (FOX-7) in DMSO was measured by means of a RD496-2000 Calvet microcalorimeter at 298.15 K. Empirical formulae for the calculation of the enthalpy of dissolution (Δ diss H), relative partial molar enthalpy (Δ diss H partial) and relative apparent molar enthalpy (Δ diss H apparent) were obtained from the experimental data of the enthalpies of dissolution of FOX-7 in dimethyl sulfoxide (DMSO). The dilution/crystallization kinetic behavior of FOX-7 in DMSO/water system was investigated and the kinetic equation describing the dilution/crystallization process was presented.

Enthalpies of dilution of aqueous mixed solutions of LiCl and Li2B4O7 at 298.15 K

The enthalpies of dilution, ΔdilHm, have been measured for LiCl+Li2B4O7+H2O system at T=298.15 K by using a RD496-III microcalorimeter. A suitable measurement method was used to obtain the better data of the enthalpies of dilution for the ternary mixing solutions to low concentrations. The relative apparent molar enthalpies, Lϕ, have been determined and the relationships between Lϕ and ionic strength I at different molal fractions of Li2B4O7 were obtained. The effect of the borate Li2B4O7 on the heat properties for the studied system was discussed.

Unusual Behavior of the Aqueous Solutions of Gemini Bispyridinium Surfactants: Apparent and Partial Molar Enthalpies of the Dimethanesulfonates

Apparent and partial molar enthalpies at 298 K of the aqueous solutions of cationic gemini surfactants 1,1'-didodecyl-2,2'-dimethylenebispyridinium dimethanesulfonate (12-Py(2)-2-(2)Py-12 MS); 1,1'-didodecyl-2,2'-trimethylenebispyridinium dimethanesulfonate (12-Py(2)-3-(2)Py-12 MS); 1,1'-didodecyl-2,2'-tetramethylenebispyridinium dimethanesulfonate (12-Py(2)-4-(2)Py-12 MS); 1,1'-didodecyl-2,2'-octamethylenebispyridinium dimethanesulfonate (12-Py(2)-8-(2)Py-12 MS); 1,1'-didodecyl-2,2'-dodecamethylenebispyridinium dimethanesulfonate (12-Py(2)-12-(2)Py-12 MS) were measured as a function of concentration and are here reported for the first time. They show a very peculiar behavior as a function of the spacer length, not allowing for the determination of a -CH 2- group contribution when this group is added to the spacer. The curve of the compound with a four-carbon-atom-long spacer lies between those of the compound with a spacer of 2 and 3 carbon atoms, instead of that below the latter, as expected. This surprising behavior, never found before in the literature and different from that found for the more popular m- s- m-type bisquaternary ammonium gemini surfactants, could be explained by a conformation change of the molecule, caused by stacking interactions between the two pyridinium rings, mediated by the counterion and appearing at an optimum length of the spacer. The hypothesis is also supported by the data obtained from the surface tension vs log c curves, showing that A min, the minimum area taken at the air-water interface by the molecule, is significantly lower for 12-Py(2)-4-(2)Py-12 MS than that of the other compounds of the same homologous series, and that the same compound has a greater tendency to form micelles instead of adsorbing at the air/water interface. The evaluation of the micellization enthalpies, by means of a pseudophase transition model, agrees with the exposed trends. These results confirm the great crop of information that can be derived from the study of the solution thermodynamics of aggregate systems and in particular from the curves of apparent and molar enthalpies vs concentration.

Thermodynamics and Biological Properties of the Aqueous Solutions of New Glucocationic Surfactants

Thermodynamic properties of aqueous solutions of newly synthesized compounds, namely, N-[2-(beta-D-glucopyranosyl)ethyl]-N,N-dimethyl-N-alkylammonium bromides with hydrophobic tails of 12 (C12DGCB) and 16 (C16DGCB) carbon atoms, determined as a function of concentration by means of direct methods, are reported here. Dilution enthalpies, densities, and sound velocities were measured at 298 K, allowing for the determination of apparent and partial molar enthalpies, volumes, and compressibilities. Changes in thermodynamic quantities upon micellization were derived using a pseudophase-transition approach. From a comparison with the corresponding acetylated compounds N-[2-(2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosyl)ethyl]-N,N-dimethyl-N-dodecylammonium bromide (C12AGCB) and N-[2-(2,3,4,6-tetra-O-acetyl-beta-D-glucopyanosyl)ethyl]-N,N-dimethyl-N-hexadecylammonium bromide (C16AGCB), the role played in the micellization process by the acetylated glycosyl moiety was inferred: it enhances the hydrophobic character of the molecule and lowers the change in enthalpy of micelle formation by about 1.5 kJ mol(-1). By comparing the volume of C12DGCB with those of DEDAB and DTAB, the volumes taken up by the (beta- d-glucopyranosyl)ethyl and beta- d-glucopyranosyl groups were found to be 133 and 99 cm3 mol(-1), respectively. Regarding the interaction with DPPC membranes, it seems that the sugar moiety of the hexadecyl deacetylated compound gives rise to hydrogen bonds with the oxygen atoms of the lipid phosphates, shifting the phase transition of DPPC from a bilayer gel to a bilayer liquid crystal to lower temperatures. C16AGCB induces significantly greater changes than C16DGCB in the structure of liposomes, suggesting the formation of domains. The interaction is strongly enhanced by the presence of water. Neither compound interacts strongly with DNA or compacts it, as shown by EMSA assays and AFM images. Only C16AGCB is able to deliver little DNA inside cells when coformulated with DOPE, as shown by the transient transfection assay. This might be related to the ability of C16AGCB to form surfactant-rich domains in the lipid structure.

Solubilities of magnesium- l-ascorbate, calcium- l-ascorbate, magnesium- l-glutamate, magnesium- d-gluconate, calcium- d-gluconate, calcium- d-heptagluconate, l-aspartic acid, and 3-nitrobenzoic acid in water

The solubility in water of magnesium- l-ascorbate, calcium- l-ascorbate, magnesium- l-glutamate, magnesium- d-gluconate, calcium- d-gluconate, calcium- d-heptagluconate, l-aspartic acid, and 3-nitrobenzoic acid was determined in the 278.15 K to 343.15 K temperature range. The solubility of these compounds served to permit the evaluation of the apparent molar enthalpies of solution.

Description of dilution enthalpies and heat capacities for aqueous solutions within the MSA–NRTL model with ion solvation

The capability of the MSA–NRTL model to describe heat effects for binary aqueous electrolyte and nonelectrolyte solutions, with a relatively reduced number of parameters, is examined. The thermodynamic properties described include the osmotic coefficient, ϕ , the apparent relative molar enthalpy, Φ L , and the apparent molar heat capacity, Φ C P . The MSA–NRTL model consists of the mean spherical approximation (MSA) for the long-range electrostatic contribution to the Gibbs energy (for ionic solutions) and a local composition model, the non-random two-liquid (NRTL) model for the short-range contribution.

Isopiestic Determination of the Osmotic and Activity Coefficients of Li2SO4(aq) at T=298.15 and 323.15 K, and Representation with an Extended Ion-Interaction (Pitzer) Model

Isopiestic vapor-pressure measurements were made for Li2SO4(aq) from 0.1069 to 2.8190 mol⋅kg−1 at 298.15 K, and from 0.1148 to 2.7969 mol⋅kg−1 at 323.15 K, with NaCl(aq) as the reference standard. Published thermodynamic data for this system were reviewed, recalculated for consistency, and critically assessed. The present results and the more reliable published results were used to evaluate the parameters of an extended version of Pitzer’s ion-interaction model with an ionic-strength dependent third-virial coefficient, as well as those of the standard Pitzer model, for the osmotic and activity coefficients at both temperatures. Published enthalpies of dilution at 298.15 K were also analyzed to yield the parameters of the ion-interaction models for the relative apparent molar enthalpies of dilution. The resulting models at 298.15 K are valid to the saturated solution molality of the thermodynamically stable phase Li2SO4⋅H2O(cr). Solubilities of Li2SO4⋅H2O(cr) at 298.15 K were assessed and the selected value of m(sat.)=3.13±0.04 mol⋅kg−1 was used to evaluate the thermodynamic solubility product K s(Li2SO4⋅H2O, cr, 298.15 K) = (2.62±0.19) and a CODATA-compatible standard molar Gibbs energy of formation Δf G om (Li2SO4⋅H2O, cr, 298.15 K) = −(1564.6±0.5) kJ⋅mol−1.

The solvent extraction of zinc, cadmium and chromium from phosphoric acid solutions by tri- n butyl phosphate in kerosene diluent

In this paper, the solvent extraction of zinc(II), cadmium(II) and chromium(III) from phosphoric acid solutions by tri- n butyl phosphate (TBP) in kerosene as diluent was investigated. The distribution coefficients were determined and the results showed clearly a maximum values at 5.5 mol/L H 3PO 4 concentration and a minimum values at 1.0 mol/L H 3PO 4 concentration. The apparent standard molar enthalpies Δ H° for extraction of zinc(II), cadmium(II) and chromium(III) were found to be, respectively, 51.11, 45.43 and 59.87 kJ/mol which indicate the endothermic nature of the extraction process. The apparent standard entropies Δ S° were also determined 1.685 × 10 −3, 1.377 × 10 −3 and 1.961 × 10 −3 kJ/mol K. The apparent standard Gibbs free energies Δ G° of extraction of zinc(II), cadmium(II) and chromium(III) were consequently calculated. Based on the regression analysis of the data, the equations for prediction of the distribution coefficients D of zinc(II), cadmium(II) and chromium(III), respectively were obtained.

Thermodynamic properties of aqueous micellar solutions of some new acetylated gluco-cationic surfactants

Thermodynamic properties of the aqueous solutions of a newly synthesized homologous series of N-[2-(2,3,4,6-tetra- O-acetyl-β- d-glucopyranosyl)ethyl]- N, N-dimethyl- N-alkylammonium bromides with hydrophobic tails of 8, 12 and 16 carbon atoms, determined as a function of concentration by means of direct methods, are here reported for the first time. Dilution enthalpies, densities and sound velocities were measured at 298 K, allowing for the determination of apparent and partial molar enthalpies, volumes and compressibilities. Changes in thermodynamic quantities upon micellization were derived using a pseudo-phase transition approach. The trends of apparent and partial molar enthalpies versus m confirm the increase in global hydrophobicity of the molecule, already suggested by the value of the cmc of C 12AGCB, lower than that of DTAB, and show that, also in the case of surfactants with a bulky substitution on the polar head, the group contribution of the –CH 2– is additive both in the plateau (−1.3 kJ mol −1 group −1) and in the micellization enthalpy changes (−1.5 kJ mol −1 group −1). The determination of apparent molar volumes and compressibilities presents some experimental problems, due to the strong tendency of this class of surfactants to adsorb on the glass surfaces. Even so, the group contribution of the methylene group results as being additive and comparable to that of other cationic and anionic surfactants. From the comparison with DTAB, the volume of (2,3,4,6-tetra- O-acetyl-β- d-glucopyranosyl)ethyl group results as 291 cm 3 mol −1.

Calibration in isothermal titration calorimetry: Heat and cell volume from heat of dilution of NaCl( aq)

An isothermal titration calorimeter of the perfusion type (MicroCal model VP-ITC) is calibrated using the heat of dilution of NaCl in water. The relative apparent molar enthalpy function ( L ϕ) for NaCl( aq) varies strongly and nonlinearly with concentration in the low-concentration region (<0.2 M) that is sampled easily and extensively in a single program of injections of NaCl solution into water. This nonlinearity makes it possible to calibrate with respect to two quantities: the measured heat and the active cell volume. The heat factor is determined with typical standard error 0.003; its value in the current case is 0.987. The cell volume factor is 0.93 but is quite sensitive to possible systematic errors in the temperature and in the literature values for L ϕ. Both correction factors are closely tied to the delivered volume from the injection syringe, which required a correction factor of 0.973, attributed to an instrumental gear ratio error. Temperature calibration of the instrument showed a small offset of 0.12 K at the temperature 25 °C of the experiments, but the error increased to more than 1 K at 46 °C. The experiments were not able to distinguish clearly between mixing algorithms that assume instantaneous mixing on injection and those that assume instantaneous injection followed by mixing; however, examination of these algorithms has revealed an error in a program widely used to analyze isothermal titration calorimetry data.

Thermodynamics of reactions catalyzed by d-hydantoinase and N-carbamoyl- d-amino acid hydrolase

Microcalorimetry and high-performance liquid chromatography have been used to conduct a thermodynamic investigation of several biochemical reactions catalyzed by the enzymes d-hydantoinase and N-carbamoyl- d-amino acid hydrolase. Values of apparent equilibrium constants K′ and calorimetrically determined molar enthalpies of reaction Δ r H m(cal) were measured for the following d-hydantoinase catalyzed reactions: hydantoin(aq) + H 2O(l) = ureidoacetic acid(aq); 5,6-dihydrouracil(aq) + H 2O(l) = 3-ureidopropanoic acid(aq); 5-phenylhydantoin(aq) + H 2O(l) = 5-phenyl d-carbamoylate(aq); and 5-(4-hydroxyphenyl)hydantoin(aq) + H 2O(l) = 5-(4-hydroxyphenyl) d-carbamoylate(aq). Calorimetric measurements, in which both d-hydantoinase and N-carbamoyl- d-amino acid hydrolase were present, were performed on the following reactions: 5-phenylhydantoin(aq) + 3 H 2O(l) = d-phenylglycine(aq) + carbon dioxide(aq) + ammonia(aq); and (4-hydroxy)-phenylhydantoin(aq) + 3H 2O(l) = d-(4-hydroxyphenyl)glycine(aq) + carbon dioxide(aq) + ammonia(aq). A chemical equilibrium model was then used to calculate thermodynamic property values (equilibrium constants K, standard molar enthalpies of reaction Δ r H m ∘ , standard molar Gibbs free energies of reaction Δ r G m ∘ , and standard molar entropies of reaction Δ r S m ∘ ) for chemical reference reactions that correspond to the overall biochemical reactions that were studied experimentally. In several cases, we also provided estimated property values based on data for structurally similar reactions. The results can be used together with the chemical equilibrium model to calculate values of K′, the standard apparent molar Gibbs free energy change Δ r G m ′ ∘ , the standard apparent molar enthalpy change Δ r H m ′ ∘ , changes in binding of the proton Δ r N(H +), and the position of equilibrium for the several overall biochemical reactions considered in this study over a reasonably wide range of temperature, pH, and ionic strength.

Actinomycin D binds to single stranded DNA oligomers which contain double GTC triplets

The present work carried out a study on the interactions between Actinomycin D (ActD) and some single-stranded DNA oligomers, which contain double GTC triplets separated by TTT sequence. The interactions of drugs with DNA oligomers were investigated by UV, circular dichroism (CD) spectroscopy and isothermal titration calorimetry (ITC). The results indicate that ActD binds to the single stranded DNA oligomers in the fold back binding model as supported by added A/T base at DNA strand terminal which facilitates the formation of hairpin. The apparent binding constant K b, the apparent binding molar enthalpy Δ H 0 and other thermodynamic data were obtained. The binding affinities are sequence dependent and related to the length of DNA strand. And the higher molar binding enthalpy indicates that the binding process is enthalpy driven.

Calorimetric and volumetric data of salting of albumin from human serum using NaCl solutions

Apparent molar volume and enthalpy changes for mixing NaCl (aq.) with albumin from human serum (aq.) are experimentally determined (25°C). Calorimetric experiments were carried out in an LKB 10700-2 calorimeter, whereas volumetric measurements were realized using an Anton Paar 60/602 densimeter. The density measurements were made after 1 and 24 h of the dissolution in the buffer (pH 4.2). The relation between the changes of the enthalpy and apparent molar volumes vs. molality of NaCl were determined. The obtained data are discussed together with data obtained previously for bovine albumin and hen egg lysozyme solutions with NaCl, Li2SO4 and (NH4)2SO4 salts of various concentration. As results correlations between the changes of enthalpy of salting and apparent molar volumes vs. molality of salts were made.

Thermodynamics of aqueous solutions of dodecyldimethylethylammonium bromide

The thermodynamic properties of the aqueous solutions of dodecyldimethylethylammonium bromide (DEDAB) were determined as a function of concentration by means of direct methods. Dilution enthalpies at 298 and 313 K, densities and sound velocities at 298 K were measured, allowing the determination of apparent and partial molar enthalpies, volumes, heat capacities and compressibilities. Changes in thermodynamic quantities upon micellization were derived using a pseudo-phase transition approach. These data allow for the determination of the effect of the CH 2 group, when added to the polar head of alkyltrimethylammonium bromides. The properties mainly affected by this addition are the enthalpies and, as a consequence, the entropies. The lowering of the charge density on the quaternary nitrogen due to the inductive effect of the ethyl group, greater than that of the methyl one, raises the plateau value of apparent and molar enthalpy by a quantity similar to that due to the removing of a methylene group from the hydrophobic chain. This effect does not play a great role in the value of the cmc (i.e. on the free energy of micelle formation), since the small decrease in cmc of DEDAB compared to DTAB reflects the increase in the overall hydrophobicity of the molecule. Volumes of DEDAB are greater than those of DTAB by about 15 cm 3 mol −1, both at infinite dilution and at micellar phase, a value in agreement with that generally accepted for a methylene group. The trends of apparent molar heat capacities and compressibilities vs m are the same as for DTAB: in fact, these quantities are related to the number of water molecules involved in the hydrophobic processes in solution, not very greatly affected by the substitution of a methyl group by an ethyl one on the polar head. In summary, this substitution affects to a significant extent the first derivatives of the free energy, but does not affect the second derivatives.

Studies on enthalpy of solution for ionic liquid: The system of 1-methyl-3-ethylimidazolium tetrafluoroborate (EMIBF 4)

The molar solution enthalpies of ionic liquids (IL) EMIBF 4 (1-methyl-3-ethylimidazolium tetrafluoroborate), EMIC (1-methyl-3-ethylimidazo-lium chloride) and ionic solid NaBF 4 at various molalities were determined by the solution-reaction isoperibol calorimeter in water at 298.15 K. In terms of a Debye–Hückel limiting term, the molar solution enthalpies of EMIBF 4, EMIC and NaBF 4 at infinite dilution, Δ s H m ° , were obtained. Then the values of apparent relative molar enthalpy were calculated. Hydration heat of both cation EMI + and anion BF 4 − was discussed. In terms of values of Δ s H m ° , the reaction heat of NaBF 4 + EMIC → EMIBF 4 + NaCl was estimated.

Studies of Thermochemical Properties of a New Ionic Liquid Prepared by Mixing 1-Methyl- 3-Pentylimidazolium Chloride with InCl3

A new ionic liquid, PMIInCl4, was prepared by mixing 1-methyl-3-pentylimidazolium chloride (PMIC) with InCl3. The molar enthalpies of solution of PMIC and PMIInCl4 in water to form solutions at various molalities were determined at 298.15 K using an isoperibol calorimeter. Using Pitzer's electrolyte solution model, the molar enthalpies of solution of PMIC and PMIInCl4 at infinite dilution, Δsol H^m, and Pitzer's ion-interaction parameters βMX(0)L, βMX(1)L and CMXϕL, were derived. The values of the apparent relative molar enthalpy L and relative partial molar enthalpy of the solutes (PMIC and PMIInCl4), \(\bar{L}_{2}\), were subsequently calculated. Using the values of Δsol H^m of PMIC, PMIInCl4 and InCl3, the enthalpy change, Δr<H=−38.19kJ·;mol-1, was calculated for the reaction PMIC + InCl3 → PMIInCl4

Excess molar enthalpies and volumes of binary mixtures of nonafluorobutylmethylether with ketones at T = 298.15 K

Excess molar enthalpies, H m E , and volumes, V m E , were reported for binary mixtures of {nonafluorobutylmethylether, (FBME, C 4F 9OCH 3) + 2-propanone, or + 2-butanone, or + 3-pentanone} at 298.15 K. Results of H m E and V m E were positive over a whole range of concentrations for all the mixtures. The magnitude was in order: 2-propanone > 3-pentanone > 2-butanone for H m E and 3-pentanone > 2-butanone = 2-propanone for V m E at the maximum point. However, the difference in the maximum values of H m E and V m E by the increase in the number of carbon atoms in the ketones, n C is not so large. From these results, partial molar quantities ( H m , i E , ∞ , V m , i E , ∞ , and V m , i ∞ ) of the i component at infinite dilution, and apparent molar enthalpies of solvation, Δ solv H i of the i component were evaluated. The dependence of these thermodynamic quantities on the n C were discussed in consideration of various kinds of intermolecular interactions in pure component liquids and solutions.

Enthalpy change and mechanism of oxidation of o-phenylenediamine by hydrogen peroxide catalyzed by horseradish peroxidase

The hydrogen peroxide-oxidation of o-phenylenediamine (OPD) catalyzed by horseradish peroxidase (HRP) at 37 °C in 50 mM phosphate buffer (pH 7.0) was studied by calorimetry. The apparent molar reaction enthalpy with respect to OPD and hydrogen peroxide were −447 ± 8 kJ mol −1 and −298 ± 9 kJ mol −1, respectively. Oxidation of OPD by H 2O 2 catalyzed by HRP (1.25 nM) at pH 7.0 and 37 °C follows a ping–pong mechanism. The maximum rate V max (0.91 ± 0.05 μM s −1), Michaelis constant for OPD K m,S (51 ± 3 μM), Michaelis constant for hydrogen peroxide K m, H 2 O 2 (136 ± 8 μM), the catalytic constant k cat (364 ± 18 s −1) and the second-order rate constants k +1 = (2.7 ± 0.3) × 10 6 M −1 s −1 and k +5 = (7.1 ± 0.8) × 10 6 M −1 s −1 were obtained by the initial rate method.

Ratio of entropy to enthalpy in thermal transitions in biological tissues

Thermal transitions in biological tissues that have been reported in the literature are summarized in terms of the apparent molar entropy (DeltaS) and molar enthalpy (DeltaH) involved in the transition. A plot of DeltaS versus DeltaH for all the data yields a straight line, consistent with the definition of free energy, DeltaG=DeltaH+TDeltaS. Various bonds may be involved in cooperative bond breakage during thermal transitions; however, for the sake of description, the equivalent number of cooperative hydrogen bonds can be cited. Most of the tissue data behave as if 10 to 20 hydrogen bonds are cooperatively broken during coagulation, with one transition, the expression of heat shock protein, involving 90 cooperative hydrogen bonds. The data are consistent with DeltaS=a+bDeltaH, where a=-327.5 J(mol K) and b=31.47 x 10(-4) K(-1). If each additional hydrogen bond adds 19 x 10(3) Jmol to DeltaH, then each additional bond adds 59.8 J(mol K) to DeltaS. Hence, the dynamics of irreversible thermal transitions can be described in terms of one free parameter, the apparent number of cooperative hydrogen bonds broken during the transition.