Interaction between Macromolecules, Inorganic Salts and Small Organic Molecules

Solutes are present within aqueous systems in almost every area of research. The term solute can include salts, small organic molecules, proteins and any other chemical that can be dissolved. Understanding how solutes influence the properties of each other and medium they are dissolved in is of paramount importance if a system is to be fully understood, but the extent to which solutes perturb their medium is often overlooked. The aim of this research project was to use analytical techniques such as differential scanning calorimetry, pressure perturbation calorimetry and terahertz spectroscopy to better understand the mechanism by which water and solutes influence protein stability. Experimental results suggest that Hofmeister ions influence protein stability at higher salt concentrations by modulating the free energy required to hydrate the newly exposed core of the protein. Destabilising ions reduce the free energy required to hydrate the protein core and stabilising ions increase the free energy. At low salt concentrations salts influence protein stability to a small degree by interacting electrostatically with proteins. Pressure perturbation calorimetry studies suggested that Hofmeister ions are able to influence water dynamics at elevated temperatures through their electric field. These findings support the hypothesis that ions are able to stabilise proteins by competing for water with the unfolding protein through an electrostatic interaction. Coherent synchrotron radiation in the terahertz region of the electromagnetic spectrum was able to detect an extended hydration layer around bovine serum albumin. These findings supported other terahertz spectroscopy experiments that also detected extended hydration layers around proteins and suggests that water around protein molecules is more complex than a single layer of water molecules.