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Publication Date

Summer 2013

Degree Type

Thesis - Campus Access Only

Degree Name

Master of Science (MS)




Daryl Eggers

Subject Areas

Chemistry; Biophysics


Guanidine hydrochloride (GuHCl) at 6 M concentration is a typical agent for denaturing proteins. According to most theoretical discussions, GuHCl denatures by directly binding to the protein, but the working hypothesis is that secondary solutes may influence protein structure by altering the properties of bulk water. The goal of this project was to determine the change in free energy of bulk water in the presence of GuHCl. It was hypothesized that GuHCl increases the free energy of water and shift reaction equilibria toward the unfavored state. For this purpose, isothermal titration calorimetry and pressure perturbation calorimetry techniques were used to measure ΔH and Δ(TΔS) values, respectively, for different concentrations of GuHCl relative to pure water at the same temperature. In addition, the solubility of cyclic diglycine (DKP) in GuHCl solution was measured in an attempt to relate the hydration of the peptide backbone to the thermodynamics of protein unfolding. Some experiments were repeated with other guanidinium salts, using two anions from opposite ends of the Hofmeister series in place of chloride. In general, no conclusions could be drawn from the calorimetry experiments, but the DKP solubility results supported the hypothesis that changes in the free energy of bulk water underlie the observed changes in reaction equilibria.