Advancements in High-pressure Chemistry: Informing Biosignature Detection and Aqueous Salt Equilibria

Abstract

High-pressure chemistry is an interdisciplinary science concerned with the behavior of materials often above 100 megapascals (MPa). These conditions—thousands of times greater than atmospheric pressure—facilitate a variety of unique processes and phenomena otherwise inaccessible in the typical laboratory setting. Of note, high-pressure techniques can provide insights into the environments of the outer solar system. With the recent launch of the Europa Clipper (October 2024) and the Dragonfly rotorcraft to Titan (planned 2028), predictive information about icy ocean worlds is vital to both mission success and the search for life elsewhere in the Universe. This dissertation presents advancements in biosignature detection and the mapping of equilibria in salt-water binaries of interest to the chemistry and Earth and space science communities. The activity of an ice-binding peptide against a high-pressure, non-hexagonal phase of ice is evaluated, and the high-pressure melting curves of water ices in the presence of relevant ions for oceans of our solar system are determined. The former, inspired by the life-preserving mechanisms of organisms at boundary conditions on Earth, reveals that the growth of tetragonal ice VI and, by extension, other exotic ice polymorphs can be moderated by ice recrystallization inhibition (IRI) agents. A new method for performing splat assays at high pressure is developed, opening the door for comparable works on the habitability of icy worlds and ocean exoplanets. The latter provides fundamental, thermodynamic data characterizing the liquidus lines of water up to 1400 MPa and a three molal (mol/kg) concentration of magnesium sulfate, sodium sulfate, and magnesium chloride. Melting curves are compared to an ideal solution model extended to high pressures, with implications on the behavior of mixed systems and the subsurface oceans of icy worlds. The applications of and possibilities for high-pressure chemistry are endless, and I look forward to seeing future creative advancements in this burgeoning field of research.