Advances in modeling techniques for aqueous organic molecules at hydrothermal conditions: Searching for clues as to the chemical origins of life.

摘要

This dissertation seeks to address some of the basic problems involved in modeling the thermodynamics of infinitely dilute organic molecules at hydrothermal conditions and presents an equation of state for simple acyclic organic solutes. The proposed equation should allow accurate predictions to 630 K, an increase of roughly 150 degrees over earlier work. However, several of the predicted thermodynamic trends were unexpected. Free energy of formation calculations strongly suggested that at high temperature (T > 480 K) the existence of larger, more complex organic molecules was preferred over the existence of smaller, less complex organic molecules. These results are quite opposite to the situation at room temperature, where the existence of smaller organic solutes is preferred over large molecules. Similar trends were also found in the predicted organic aqueous solubilities. As an independent check of the free energy predictions, classical molecular dynamics calculations were conducted and the results were found to be in good agreement with the equation of state's predicted trends. Generally speaking, our results suggest that a hydrothermal medium is considerably more favorable for the chemical evolution of complex organic molecules (both in terms of the free energy of formation and aqueous solubility of a particular organic solute) than an aqueous solution at ambient conditions. These findings offer addition support for the high-temperature origin of life hypothesis. In addition, a novel new computational technique was developed, based solely on first principles, which should allow for relatively fast and accurate free energy predictions of bulk aqueous organics, helping to further eliminate some of the undesirable guess work out of empirically based thermodynamic modeling methods.