Predicting Gibb's free energy changes for chemical processes: interaction of cations with poly-?-glutamate

Stephanie Mann

Document Type Dissertation/Thesis


The study of PGG was initially begun as a free energy perturbation srudy to determine if PGG preferred to be associated with one cation over another. The cations studied were Na+, K+, and Ca2+, with hopes of also expanding this study to Mg2+. Free energy perturbation was used to calculate the change in Gibbs free energy for the PGG associated with these cations. The studies were not completely conclusive, but seem to indicate that although PGG would prefer Ca2+ in an enthalpicly driven reaction, it would prefer Na+ with regards to entropy. Trial studies conducted on the acetate anion show that acetate prefers Ca2+ with regards to entropy and enthalpy. This indicates that PGG has some unique properties compared to comparable acetate solutions. To understand the enthalpic and entropic origins of the properties of PGG we did srudies of the radius of gyration, solvation shell ordering, ion pair types, and Hooke's law. These studies indicate that PGG has the most freedom of motion when associated with potassium and the least flexibility when associated with calcium.