Browsing by Author "Fernandes, Isa Cristiana Moreira"
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- Aminoácidos em solução aquosa contendo electrólitosPublication . Fernandes, Isa Cristiana Moreira; Pinho, SimãoRecentemente tem aumentado o interesse pelo conhecimento de propriedades termodinâmicas de soluções aquosas contendo aminoácidos e electrólitos. Neste trabalho mediu-se os valores experimentais da actividade da água em soluções aquosas contendo Glicina, ou DL-Alanina ou L-Serina, com sulfato de amónio a diferentes molalidades, a 298.15 K. Optou-se pelo método higrométrico para determinar a actividade da água usando o aparelho LabMASTER- w a da Novasina (com uma câmara controlada e uma precisão de ±0,001). Os valores de actividade da água foram utilizados para testar três metodologias teóricas diferentes: o modelo de Zdanovskii-Stokes-Robinson (ZSR), e sua a extensão, e a aproximação de Clegg-Seinfeld- Brimblecombe (CSB), comparando-as entre elas e com os valores obtidos experimentalmente. Determinaram-se os erros médios globais para os modelos de Zdanovskii-Stokes-Robinson, e sua extensão, e para o modelo de Clegg-Seinfeld-Brimblecombe, sendo 4.08%, 1.18% e 2.17%, respectivamente os valores obtidos. Usando apenas dois parâmetros ajustáveis, a extensão do modelo ZSR demonstrou melhores resultados na descrição da actividade da água neste tipo de sistemas. Recently the interest in knowledge of thermodynamic properties of aqueous amino acids solutions containing electrolytes has increased dramatically. In this work water activity ( ) w a in Glycine, DL-Alanine and L-Serine aqueous systems with ammonium sulfate, at 298.15 K, was measured. The LabMASTER- w a water activity instrument (with a controlled chamber and with an accuracy of ±0.001) was used to perform the measurements. The new experimental data was used to test three different theoretical approaches, the Zdanovskii- Stokes-Robinson (ZSR) its extension and the Clegg-Seinfeld-Brimblecombe (CSB) method, comparing them among themselves and with the new experimental data. The global mean deviation was estimated for each approach, the Zdanovskii-Stokes-Robinson (ZSR), its extension, and Clegg-Seinfeld-Brimblecombe (CSB) method, the values are 4.08%, 1.18% and 2.17%, respectively. Using only two adjustable parameters, the extension of ZSR model has shown better results in the description of water activity in these systems.
- Experimental and theoretical studies on water activity: aqueous solutions of amino acids with electrolytesPublication . Fernandes, Isa Cristiana Moreira; Vilarinho, Mário F.; Pinho, SimãoIn the recent past a considerable body of work has been published on the measurement of activity coefficients and solubility data in aqueous amino acid solutions containing electrolytes [1]. However, no information on water activity in this type of system has yet been published [2]. In this work water activity (aw) in DL-alanine, glycine or L-serine aqueous systems with ammonium sulfate, at 298.15 K, was measured. The LabMASTER-aw water activity instrument (Novasina, Switzerland) was used to perform the measurements. The instrument, with a controlled chamber temperature (± 0.2 K), shows high precision (± 0.001 aw units). The new experimental data was used to test different theoretical schemes such as Zdanovskii-Stokes-Robinson (ZSR) model [3] and its extension, or the Clegg-Seinfeld-Brimblecombe (CSB) approach [4], in the calculation of amino acid and electrolyte activity coefficients in those solutions. Comparisons between the different approaches are given.
- Water activity in aqueous amino acid solutions containing ammonium sulfate at 298.2 KPublication . Vilarinho, Mário F.; Fernandes, Isa Cristiana Moreira; Pinho, SimãoWater activity in aqueous solutions of DL-alanine, glycine, or L-serine, with ammonium sulfate, molality ranging from 0.5 to 5.0, have been measured at 298.2 K. The new experimental data was correlated using three different theoretical schemes such as Zdanovskii-Stokes-Robinson, its extension, or the Clegg-Seinfeld-Brimblecombe approach, with global average absolute deviations in the calculation of the osmotic coefficient of 3.46 %, 0.93 % and 1.95 %, respectively. The extended Zdanovskii-Stokes-Robinson method also enabled the prediction of unsymmetric molal activity coefficients of the electrolyte, in fair agreement with the experimental values found from literature measured by an electrochemical method. It is evidenced the usefulness of the experimental ternary data measured to extend the capabilities of thermodynamic models to higher salt and amino acid concentrations.