Modelling of protein solution properties
The research pursued in this work concentrates on modelling two protein solution properties: activity coefficients and solubility. While modelling protein solubility was the prime objective activity coefficients were considered first as deviation from ideal solution behaviour was expected to occur for protein containing systems. Activity coefficients of protein related compounds, amino acids and peptides, were studied first hypothesising that these compounds represent proteins and because activity coefficient data is documented for those compounds but not for proteins. The predictive UNIFAC model was studied but failed, which led to examination of the related UNIQUAC model. The objective of the work was the creation of a model base, which was achieved. This model base was then utilised for protein containing systems. Protein activity coefficient data was made available and could be successfully modelled using the established framework. Furthermore, the activity coefficient data was examined over different pH and temperature ranges, salt types and concentrations. A qualitative comparison of the data to protein solubility results of other researchers was pursued and used to confirm the model approach. Having demonstrated that protein solubility was qualitatively represented through protein activity coefficients a quantitative solubility approach was addressed next. For two protein systems the solubility behaviour was modelled successfully as a function of salt concentration and temperature. Findings of other researchers were integrated into the discussion of the model results while also the calculated protein activity coefficients were examined and a qualitative confirmation of the model was achieved. The models used in this study for the description of two protein solution properties, when applied to six different proteins over various pH and temperature ranges, salt types and concentrations showed qualitative and quantitative success. They should find application to many other protein systems.