The glass transition temperature of trehalose, sucrose, glucose, and fructose aqueous solutions h... more The glass transition temperature of trehalose, sucrose, glucose, and fructose aqueous solutions has been predicted as a function of the water content by using the free volume/percolation model (FVPM). This model only requires the molar volume of water in the liquid and supercooled regimes, the molar volumes of the hypothetical pure liquid sugars at temperatures below their pure glass transition temperatures, and the molar volumes of the mixtures at the glass transition temperature. The model is simplified by assuming that the excess thermal expansion coefficient is negligible for saccharide-water mixtures, and this ideal FVPM becomes identical to the Gordon-Taylor model. It was found that the behavior of the water molar volume in trehalose-water mixtures at low temperatures can be obtained by assuming that the FVPM holds for this mixture. The temperature dependence of the water molar volume in the supercooled region of interest seems to be compatible with the recent hypothesis on th...
Journal of the Chemical Society Faraday Transactions, 1997
Page 1. High-temperature wall-tube cell Design, characterization and results of mass transport ph... more Page 1. High-temperature wall-tube cell Design, characterization and results of mass transport phenomena Liliana N. Trevani,a Ernesto Calvoa¤ and Horacio R. Cortia,b¤ a Instituto de de los Materiales, Medio Ambiente y Facultad de Ciencias Qu mica F sica Energ a. ...
The properties of water clusters (H(2)O)(n) over a broad range of sizes (n=4-100) were studied by... more The properties of water clusters (H(2)O)(n) over a broad range of sizes (n=4-100) were studied by microcanonical parallel tempering Monte Carlo and replica exchange molecular dynamics simulations at temperatures between 20 and 300 K, with special emphasis in the understanding of relation between the structural transitions and dipole behavior. The effect of the water interaction potential was analyzed using six nonpolarizable models, but more extensive calculations were performed using the TIP4P-ice water model. We find that, in general, the dipole moment of the cluster increases significantly as the cluster melts, suggesting that it could be used to discriminate between the solidlike and liquidlike phases. The effect of a moderate electric field on the cluster heat capacity and total dipole moment was found to be negligible.
The diffusional mobility of disodium fluorescein has been measured in supercooled aqueous solutio... more The diffusional mobility of disodium fluorescein has been measured in supercooled aqueous solutions of trehalose, a widely used cryoprotectant disaccharide. The results were analyzed on the basis of the classical continuum hydrodynamic theory (Stokes-Einstein relationship) and compared with results for the diffusion and electrical conductivity of other ionic and nonionic solutes in trehalose and sucrose aqueous solutions. Disodium fluorescein obeys the classical model over a restricted range of inverse reduced temperatures, T g/ T, scaled by the glass transition temperature. Decoupling in neutral solutes takes place at higher values of T g/ T, while in ionic solutes it occurs all over the range of T g/ T studied, as observed for the water mobility in supercooled sugar solutions.
Journal of the Chemical Society Faraday Transactions, 1990
ABSTRACT Cluster theory of electrolytes has been used to study the contribution to the Helmholtz ... more ABSTRACT Cluster theory of electrolytes has been used to study the contribution to the Helmholtz energy, A, of clusters having up to four ions. The population distribution that minimizes A is dominated by neutral clusters. When solutions are sufficiently concentrated, redissociation ensues. We discuss the importance of the particular cluster definition adopted in determining the structure of the electrolyte in the entire concentration range. The comparison of the internal energy calculated by cluster theory to that obtained by simulations, shows a significant improvement over MSA, but the agreement with simulation results is only fair. The osmotic coefficients of two real aqueous electrolytes, NaCl at 573 K and MgSO4 at 373 K, have been used to assess the limitations of cluster theory when applied to real electrolyte systems. Possible extensions of cluster theory are discussed.
β-cyclodextrin-grafted dextrans with spacer arms of different length were employed to evaluate th... more β-cyclodextrin-grafted dextrans with spacer arms of different length were employed to evaluate the impact of supramolecular interactions on invertase activity. The modified dextrans were used as single additives or combined with trehalose in freeze-dried formulations containing invertase. Enzyme activity conservation was analyzed after freeze-drying and thermal treatment. The change of glass transition temperatures (Tg ) was also evaluated and related to effective interactions. Outstanding differences on enzyme stability were mainly related to the effect of the spacer arm length on polymer-enzyme interactions, since both the degree of substitution and the molecular weight were similar for the two polymers. This change of effective interactions was also manifested in the pronounced reduction of Tg values, and were related to the chemical modification of the backbone during oxidation, and to the attachment of the β-cyclodextrin units with spacer arms of different length on dextran. Th...
ABSTRACT A B S T R A C T The electrical mobility of LiPF 6 in acetonitrile–dimethyl sulfoxide (AC... more ABSTRACT A B S T R A C T The electrical mobility of LiPF 6 in acetonitrile–dimethyl sulfoxide (ACN–DMSO) mixtures, a potential electrolyte in oxygen cathodes of lithium-air batteries, has been studied using a very precise conductance technique, which allowed the determination of the infinite dilution molar conductivity and association constant of the salt in the whole composition range. In the search for preferential Li + ion solvation, we also measured the electrical conductivity of tetrabutylammonium hexafluorophosphate (TBAPF 6), a salt formed by a bulky cation, over the same composition range. The results show a qualitative change in the curvature of the LiPF 6 molar conductivity composition dependence for ACN molar fraction (x ACN) $ 0.95, which was not observed for TBAPF 6 . The dependence of the measured Li/Li + couple potential with solvent composition also showed a pronounced change around the same composition. We suggest that these observations can be explained by Li + ion preferential solvation by DMSO in ACN–DMSO mixtures with very low molar fractions of DMSO. ã
Journal of the Chemical Society, Faraday Transactions, 1997
Page 1. High-temperature wall-tube cell Design, characterization and results of mass transport ph... more Page 1. High-temperature wall-tube cell Design, characterization and results of mass transport phenomena Liliana N. Trevani,a Ernesto Calvoa¤ and Horacio R. Cortia,b¤ a Instituto de de los Materiales, Medio Ambiente y Facultad de Ciencias Qu mica F sica Energ a. ...
The preparation and characterization of a monolithic mesoporous carbon structure, which could be ... more The preparation and characterization of a monolithic mesoporous carbon structure, which could be used as diffusion layer in PEM and DMPEM micro fuel cells, is d.
Journal of the Chemical Society, Faraday Transactions, 1990
ABSTRACT Cluster theory of electrolytes has been used to study the contribution to the Helmholtz ... more ABSTRACT Cluster theory of electrolytes has been used to study the contribution to the Helmholtz energy, A, of clusters having up to four ions. The population distribution that minimizes A is dominated by neutral clusters. When solutions are sufficiently concentrated, redissociation ensues. We discuss the importance of the particular cluster definition adopted in determining the structure of the electrolyte in the entire concentration range. The comparison of the internal energy calculated by cluster theory to that obtained by simulations, shows a significant improvement over MSA, but the agreement with simulation results is only fair. The osmotic coefficients of two real aqueous electrolytes, NaCl at 573 K and MgSO4 at 373 K, have been used to assess the limitations of cluster theory when applied to real electrolyte systems. Possible extensions of cluster theory are discussed.
Journal of the Chemical Society, Faraday Transactions, 1996
Page 1. Ionic association in asymmetric electrolytes Horacio R. Corti,'y... more Page 1. Ionic association in asymmetric electrolytes Horacio R. Corti,'yb** Daniel Laria"vb and Liliana N. Trevani' a Instituto de Quimica Fisica de Materiales, Medio Ambiente y Energia, Facultad de Ciencia Exactas y Naturales ...
Aqueous Systems at Elevated Temperatures and Pressures, 2004
... very dilute solutions where the ionion interactions can be neglected, the cross coefficient a... more ... very dilute solutions where the ionion interactions can be neglected, the cross coefficient aþ2 is zero and we obtain the following limiting expressions aiiziF2 l0i ¼ ð10: 23Þ nic2 D0¼RTF21z þ þ 1lz 2 l l0þl02 ðl0 þ þ l0 2 Þ ! : ð10: 24Þ Page 341. 328 HR Corti, LN Trevani and A ...
ABSTRACT The densities of aqueous solutions of lithium, sodium and potassium hydroxides were meas... more ABSTRACT The densities of aqueous solutions of lithium, sodium and potassium hydroxides were measured up to 3m (mol-kg–1) with a vibrating tube densimeter from 55 to 250C an at pressures close to saturation. The apparent molar volumes of the solutions were calculated and the infinite dilution values at each temperature and saturation pressure were obtained by extrapolation. The present data are compared with literature values (for LiOH and KOH below 75C and over the entire temperature range for NaOH) and with the predictions of a semiempirical model. It is concluded that the high temperature data for NaOH reported here improves the available experimental information on the volumetric properties of this system. The influence of ion association on the volumetric properties of LiOH solutions is also discussed.
The glass transition temperature of trehalose, sucrose, glucose, and fructose aqueous solutions h... more The glass transition temperature of trehalose, sucrose, glucose, and fructose aqueous solutions has been predicted as a function of the water content by using the free volume/percolation model (FVPM). This model only requires the molar volume of water in the liquid and supercooled regimes, the molar volumes of the hypothetical pure liquid sugars at temperatures below their pure glass transition temperatures, and the molar volumes of the mixtures at the glass transition temperature. The model is simplified by assuming that the excess thermal expansion coefficient is negligible for saccharide-water mixtures, and this ideal FVPM becomes identical to the Gordon-Taylor model. It was found that the behavior of the water molar volume in trehalose-water mixtures at low temperatures can be obtained by assuming that the FVPM holds for this mixture. The temperature dependence of the water molar volume in the supercooled region of interest seems to be compatible with the recent hypothesis on th...
Journal of the Chemical Society Faraday Transactions, 1997
Page 1. High-temperature wall-tube cell Design, characterization and results of mass transport ph... more Page 1. High-temperature wall-tube cell Design, characterization and results of mass transport phenomena Liliana N. Trevani,a Ernesto Calvoa¤ and Horacio R. Cortia,b¤ a Instituto de de los Materiales, Medio Ambiente y Facultad de Ciencias Qu mica F sica Energ a. ...
The properties of water clusters (H(2)O)(n) over a broad range of sizes (n=4-100) were studied by... more The properties of water clusters (H(2)O)(n) over a broad range of sizes (n=4-100) were studied by microcanonical parallel tempering Monte Carlo and replica exchange molecular dynamics simulations at temperatures between 20 and 300 K, with special emphasis in the understanding of relation between the structural transitions and dipole behavior. The effect of the water interaction potential was analyzed using six nonpolarizable models, but more extensive calculations were performed using the TIP4P-ice water model. We find that, in general, the dipole moment of the cluster increases significantly as the cluster melts, suggesting that it could be used to discriminate between the solidlike and liquidlike phases. The effect of a moderate electric field on the cluster heat capacity and total dipole moment was found to be negligible.
The diffusional mobility of disodium fluorescein has been measured in supercooled aqueous solutio... more The diffusional mobility of disodium fluorescein has been measured in supercooled aqueous solutions of trehalose, a widely used cryoprotectant disaccharide. The results were analyzed on the basis of the classical continuum hydrodynamic theory (Stokes-Einstein relationship) and compared with results for the diffusion and electrical conductivity of other ionic and nonionic solutes in trehalose and sucrose aqueous solutions. Disodium fluorescein obeys the classical model over a restricted range of inverse reduced temperatures, T g/ T, scaled by the glass transition temperature. Decoupling in neutral solutes takes place at higher values of T g/ T, while in ionic solutes it occurs all over the range of T g/ T studied, as observed for the water mobility in supercooled sugar solutions.
Journal of the Chemical Society Faraday Transactions, 1990
ABSTRACT Cluster theory of electrolytes has been used to study the contribution to the Helmholtz ... more ABSTRACT Cluster theory of electrolytes has been used to study the contribution to the Helmholtz energy, A, of clusters having up to four ions. The population distribution that minimizes A is dominated by neutral clusters. When solutions are sufficiently concentrated, redissociation ensues. We discuss the importance of the particular cluster definition adopted in determining the structure of the electrolyte in the entire concentration range. The comparison of the internal energy calculated by cluster theory to that obtained by simulations, shows a significant improvement over MSA, but the agreement with simulation results is only fair. The osmotic coefficients of two real aqueous electrolytes, NaCl at 573 K and MgSO4 at 373 K, have been used to assess the limitations of cluster theory when applied to real electrolyte systems. Possible extensions of cluster theory are discussed.
β-cyclodextrin-grafted dextrans with spacer arms of different length were employed to evaluate th... more β-cyclodextrin-grafted dextrans with spacer arms of different length were employed to evaluate the impact of supramolecular interactions on invertase activity. The modified dextrans were used as single additives or combined with trehalose in freeze-dried formulations containing invertase. Enzyme activity conservation was analyzed after freeze-drying and thermal treatment. The change of glass transition temperatures (Tg ) was also evaluated and related to effective interactions. Outstanding differences on enzyme stability were mainly related to the effect of the spacer arm length on polymer-enzyme interactions, since both the degree of substitution and the molecular weight were similar for the two polymers. This change of effective interactions was also manifested in the pronounced reduction of Tg values, and were related to the chemical modification of the backbone during oxidation, and to the attachment of the β-cyclodextrin units with spacer arms of different length on dextran. Th...
ABSTRACT A B S T R A C T The electrical mobility of LiPF 6 in acetonitrile–dimethyl sulfoxide (AC... more ABSTRACT A B S T R A C T The electrical mobility of LiPF 6 in acetonitrile–dimethyl sulfoxide (ACN–DMSO) mixtures, a potential electrolyte in oxygen cathodes of lithium-air batteries, has been studied using a very precise conductance technique, which allowed the determination of the infinite dilution molar conductivity and association constant of the salt in the whole composition range. In the search for preferential Li + ion solvation, we also measured the electrical conductivity of tetrabutylammonium hexafluorophosphate (TBAPF 6), a salt formed by a bulky cation, over the same composition range. The results show a qualitative change in the curvature of the LiPF 6 molar conductivity composition dependence for ACN molar fraction (x ACN) $ 0.95, which was not observed for TBAPF 6 . The dependence of the measured Li/Li + couple potential with solvent composition also showed a pronounced change around the same composition. We suggest that these observations can be explained by Li + ion preferential solvation by DMSO in ACN–DMSO mixtures with very low molar fractions of DMSO. ã
Journal of the Chemical Society, Faraday Transactions, 1997
Page 1. High-temperature wall-tube cell Design, characterization and results of mass transport ph... more Page 1. High-temperature wall-tube cell Design, characterization and results of mass transport phenomena Liliana N. Trevani,a Ernesto Calvoa¤ and Horacio R. Cortia,b¤ a Instituto de de los Materiales, Medio Ambiente y Facultad de Ciencias Qu mica F sica Energ a. ...
The preparation and characterization of a monolithic mesoporous carbon structure, which could be ... more The preparation and characterization of a monolithic mesoporous carbon structure, which could be used as diffusion layer in PEM and DMPEM micro fuel cells, is d.
Journal of the Chemical Society, Faraday Transactions, 1990
ABSTRACT Cluster theory of electrolytes has been used to study the contribution to the Helmholtz ... more ABSTRACT Cluster theory of electrolytes has been used to study the contribution to the Helmholtz energy, A, of clusters having up to four ions. The population distribution that minimizes A is dominated by neutral clusters. When solutions are sufficiently concentrated, redissociation ensues. We discuss the importance of the particular cluster definition adopted in determining the structure of the electrolyte in the entire concentration range. The comparison of the internal energy calculated by cluster theory to that obtained by simulations, shows a significant improvement over MSA, but the agreement with simulation results is only fair. The osmotic coefficients of two real aqueous electrolytes, NaCl at 573 K and MgSO4 at 373 K, have been used to assess the limitations of cluster theory when applied to real electrolyte systems. Possible extensions of cluster theory are discussed.
Journal of the Chemical Society, Faraday Transactions, 1996
Page 1. Ionic association in asymmetric electrolytes Horacio R. Corti,'y... more Page 1. Ionic association in asymmetric electrolytes Horacio R. Corti,'yb** Daniel Laria"vb and Liliana N. Trevani' a Instituto de Quimica Fisica de Materiales, Medio Ambiente y Energia, Facultad de Ciencia Exactas y Naturales ...
Aqueous Systems at Elevated Temperatures and Pressures, 2004
... very dilute solutions where the ionion interactions can be neglected, the cross coefficient a... more ... very dilute solutions where the ionion interactions can be neglected, the cross coefficient aþ2 is zero and we obtain the following limiting expressions aiiziF2 l0i ¼ ð10: 23Þ nic2 D0¼RTF21z þ þ 1lz 2 l l0þl02 ðl0 þ þ l0 2 Þ ! : ð10: 24Þ Page 341. 328 HR Corti, LN Trevani and A ...
ABSTRACT The densities of aqueous solutions of lithium, sodium and potassium hydroxides were meas... more ABSTRACT The densities of aqueous solutions of lithium, sodium and potassium hydroxides were measured up to 3m (mol-kg–1) with a vibrating tube densimeter from 55 to 250C an at pressures close to saturation. The apparent molar volumes of the solutions were calculated and the infinite dilution values at each temperature and saturation pressure were obtained by extrapolation. The present data are compared with literature values (for LiOH and KOH below 75C and over the entire temperature range for NaOH) and with the predictions of a semiempirical model. It is concluded that the high temperature data for NaOH reported here improves the available experimental information on the volumetric properties of this system. The influence of ion association on the volumetric properties of LiOH solutions is also discussed.
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