Measuring the thermodynamic properties of adenine; towards a model for the origins of life

Models for the origin of life in hydrothermal environments require the thermodynamic data for aqueous adenine solutions. Apparent molar volumes were measured using a Anton Paar DMA 5000 densitometer and apparent molar heat capacities were measured using the cylinder cell Nano-DSC III 6300 nano-calorimeter from 10 to 90 °C. This calorimeter was compared to the capillary cell version using standard potassium chloride solutions and both were shown to yield equally accurate results. NMR spectroscopy was used to measure the self-association constants and enthalpies of self association up to 55 °C. The standard partial molar volumes and standard partial molar heat capacities for an adenine monomer dimer equilibrium mixture and adenine hydrochloride were measured from 15 to 90 °C, and for sodium adeninate from 10 to 40 °C. The New experimental data for the adenine species AdH2+, AdH, Ad-, and (AdH)2 used to derive parameter for the density model that can be used to calculate adenine equilibrium constants under hydrothermal conditions.