Partial molar volumes of amino acids in aqueous MgSO4 solutions between 278.15 and 308.15 K

• Autor(a) principal: Mota, Ana Carolina Costa
• Data de Publicação: 2014
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10198/11602
• topic: Partial molar volumes; Amino acids; Hydration numbers; Electrolyte

The main objective of this work is to contribute to the understanding of the molecular interactions between ions and protein groups in aqueous solutions, using amino acids as model compounds, by determining the partial molar volumes of glycine, L-alanine, DL-2-aminobutyric acid and L-valine in aqueous magnesium sulphate solutions. The densities of aqueous solutions of magnesium sulphate (0.1, 0.3, 0.7 and 1.0) mol·kg-1 containing the selected amino acids were measured at (278.15, 288.15, 298.15 and 308.15) K, using a digital density meter. After, the partial molar volumes at infinite di-lution of the amino acids were calculated, and then used to obtain the corresponding transfer volumes and hydration numbers. The dehydration effect on the studied amino acids was observed, increasing temperature or salt molality. The positive values of ∆trVmA suggest that the interactions ion/hydrophilic group (zwitterionic centers) are predominant, and applying the method-ology proposed by Friedman and Krishnan (1973), it was concluded that they are main-ly pairwise. Regarding the alkyl chain effect, the increase of the hydrophobic part of amino acids (glycine > L-alanine > DL-2-aminobutyric > L-valine) does not result in a decreasing trend of the partial molar volumes of transfer. To further analyse the alkyl chain effect of the amino acids, a group contribution meth-od was successfully applied to model the partial molar volumes data. The contribution of the zwitterionic (NH3+, COO-) groups to the value of the standard partial molar vol-ume predominates and increases with increasing magnesium sulphate concentration; in general, the contribution of the alkyl groups is much smaller, having a very weak de-creasing trend with increasing salt molality.