Horacio R. Corti

Thermophysical Properties of Trehalose and Its Concentrated Aqueous Solutions

AbstractPurpose. To address the lack of fundamental thermophysical data for trehalose and its aqueous systems by measuring equilibrium and non-equilibrium properties of such systems. Methods/Results. Differential scanning calorimetry (DSC) and dynamic mechanical analysis were used to measure glass transition temperatures of trehalose and its solutions. X-ray diffractometry was used to verify the structure of amorphous trehalose. Controlled-stress rheometry was used to measure viscosity of several aqueous trehalose systems at ambient and sub-ambient temperatures. Over this temperature range, the density of these solutions was also measured with a vibrating tube densimeter. The equilibrium phase diagram of aqueous trehalose was determined by measuring the solubility and freezing point depression. Conclusions. Our solubility measurements, which have allowed long times for attainment of chemical equilibrium, are substantially different from those reported earlier that used different techniques. Our measurements of the glass transition temperature of trehalose are higher than reported values. A simple model for the glass transition is presented to describe our experimental observations.

High-Activity Mesoporous Pt/Ru Catalysts for Methanol Oxidation

High activity mesoporous Pt/Ru catalysts with 2D-hexagonal structure were synthesized using a triblock poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) copolymer (Pluronic F127) template. The normalized mass activities for the methanol oxidation reaction (MOR) of the Pt/Ru catalysts with a regular array of pores is higher than those reported for nanoparticulated Pt/Ru catalysts. Different kinetic parameters, as Tafel slope and activation energy, were obtained for the MOR on the mesoporous catalysts. Results indicated that catalysts performance depends on pore size. Mass activities and the CO2 conversion efficiency for large pore size mesoporous catalysts (10 nm) are greater than those reported for smaller pore size mesoporous catalysts with similar composition. The effect of pore size on catalysts performance is related to the greater accessibility of methanol to the active areas inside large pores. Consequently, the overall residence time of methanol increases as compared with mesoporous catalyst with small pores.

Water properties of food, pharmaceutical, and biological materials

Water properties of food, pharmaceutical, and biological materials , Water properties of food, pharmaceutical, and biological materials , کتابخانه مرکزی دانشگاه علوم پزشکی تهران

Distribution of solutes between coexisting steam and water

Abstract For a thorough description of aqueous systems with coexisting liquid-vapor phases, it is necessary to have a means of describing the concentration of solutes in the two-fluid phases over a wide temperature range. A general procedure is presented which allows the description of the distribution ratio of solutes at infinite dilution (KD) between water and steam over all the range of coexistence of the two-fluid phases. The procedure has been employed for many different solutes, e.g., nonreactive gases, reactive gases, nonionic, and ionic solutes. For the gaseous solutes a formulation is given which allows the calculation of KD over the complete temperature range with good precision

Viscosity of concentrated sucrose and trehalose aqueous solutions including the supercooled regime

The viscosity of aqueous solutions of sucrose and trehalose is analyzed over a wide range of concentrations and temperatures covering the normal liquid and supercooled liquid regions, close to the glass transition temperature. These sugar solutions are fragile systems whose viscosity exhibits temperature dependence with a large departure from Arrhenius behavior. A description of the temperature and concentration dependences of the solution viscosity is given in terms of a scaled Arrhenius representation, which adopts the reduced temperature Tg∕T as the state variable. A comparison with results obtained from other theoretical or semiempirical equations is also presented.

State diagrams for improving processing and storage of foods, biological materials, and pharmaceuticals (IUPAC Technical Report)

Supplemented temperature/composition phase diagrams include the non-equilibrium glass-transition temperature (Tg) curve and equilibrium ice-melting and solubility curves. The inclusion of the non-equilibrium curve allows one to establish relationships with the time coordinate and, thus, with the dynamic behavior of systems, provided that the thermal history of such systems is known. The objective of this report is to contribute to the potential applications of supplemented state diagrams for aqueous glass-formers, in order to describe the influence of water content, nature of vitrifying agents, and temperature on the physico-chemical properties of foods and biological and pharmaceutical products. These data are helpful to develop formulations, processing strategies, or storage procedures in order to optimize the stability of food ingredients and pharmaceutical formulations. Reported experimental data on phase and state transitions for several food and pharmaceutical systems were analyzed. Some methodological aspects and the effect of phase and state transitions on the main potential chemical reactions that can alter those systems during processing and/or storage are discussed.

Empirical and theoretical models of equilibrium and non-equilibrium transition temperatures of supplemented phase diagrams in aqueous systems (IUPAC Technical Report)

This paper describes the main thermodynamic concepts related to the construction of supplemented phase (or state) diagrams (SPDs) for aqueous solutions containing vitrifying agents used in the cryo- and dehydro-preservation of natural (foods, seeds, etc.) and synthetic (pharmaceuticals) products. It also reviews the empirical and theoretical equations employed to predict equilibrium transitions (ice freezing, solute solubility) and non-equilibrium transitions (glass transition and the extrapolated freezing curve). The comparison with experimental results is restricted to carbohydrate aqueous solutions, because these are the most widely used cryoprotectant agents. The paper identifies the best standard procedure to determine the glass transition curve over the entire water-content scale, and how to determine the temperature and concentration of the maximally freeze-concentrated solution.

Mobilities and ion-pairing in LiB(OH)4 and NaB(OH)4 aqueous solutions. A conductivity study

The conductivities of aqueous solutions of sodium borate at 25°C and lithium borate at various temperatures are reported. The conductivity of the B(OH)4− ion is 35.3 ±0.2 S-cm2-mole−1 at 25°C. The electrolytes are both associated, the lithium salt being more associated than the sodium salt. The mobilities and association constants obtained from the conductivity data agree with a model recently proposed for the H2O−B(OH)4− interactions. A discrepancy in the reported thermodynamic behavior of NaB(OH)4 aqueous solutions has been resolved by means of the association constants obtained in the present study. Thus the usefulness of the conductivity measurements to determine excess chemical potentials of binary electrolytes in dilute solution is again shown.

Direct Alcohol Fuel Cells

Fuel cells are strongly linked to renewable energies, particularly to the so-called “Hydrogen Economy”. For decades the development of fuel cells able to convert hydrogen and oxygen in electrical energy with water as unique byproduct has motivated huge activity in fundamental and applied electrochemistry. In this chapter we introduce the concept of methanol economy and discuss its status and perspectives. To be a reality the methanol and other alcohol economies depend on the development of alcohol feed fuel cells, whose components, operation modes and general performance are analyzed. 1.1 World Energy Consumption: Current Status and Tendencies The Stone Age did not end for lack of stone, and the oil age will end long before the world runs out of oil. Sheikh Ahmed Yamani (former Saudi Arabia’s Oil Minister) The world energy consumption at the beginning of this decade was 12 billion tonnes of oil equivalent (toe), and 87 % is generated by burning fossil fuels (oil 33.7 %, natural gas 23.6 % and coal 29.7 %) [1], which are non-renewable and increase the CO2 content of the atmosphere, considered as the major man-made H.R. Corti (*) Departamento de Fı́sica de la Materia Condensada, Centro Atómico Constituyentes, CNEA, and INQUIMAE (Universidad de Buenos Aires – CONICET), Buenos Aires, Argentina e-mail: hrcorti@cnea.gov.ar E.R. Gonzalez Instituto de Quı́mica de São Carlos-USP, São Carlos, SP, Brazil e-mail: ernesto@iqsc.usp.br 1 Toe is defined as the amount of energy released when one tonne of crude oil is burned. It is equivalent to 41.87 GJ or 11.63 MWh. H.R. Corti and E.R. Gonzalez (eds.),Direct Alcohol Fuel Cells: Materials, Performance, Durability and Applications, DOI 10.1007/978-94-007-7708-8_1,

Densities and partial molar volumes of aqueous solutions of lithium, sodium, and potassium hydroxides up to 250°C

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 250°C 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 75°C 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.