Hydrolysis of Laboratory Made Tholins in Aqueous Solutions: Implications for Prebiotic Chemistry on Titan

Details Hydrolysis of Laboratory Made Tholins in Aqueous Solutions: Implications for Prebiotic Chemistry on Titan Hydrolysis of Laboratory Made Tholins in Aqueous Solutions: Implications for Prebiotic Chemistry on Titan

Sep 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008dps....40.3409n&link_type=abstract

American Astronomical Society, DPS meeting #40, #34.09; Bulletin of the American Astronomical Society, Vol. 40, p.458

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Laboratory experiments that simulate the reactions occurring in Titan's thick nitrogen-methane atmosphere produce complex organic precipitates known as tholins. Tholins have the general formula CxHyNz, and are spectrally similar to Titan's haze. When placed in liquid water, specific water soluble compounds in the tholins have been shown to produce oxygenated organic species with activation energies in the range of 60 ± 10 kJ mol-1 and half-lives between 0.3 and 17 days at 273 K (Neish et al. 2008). Oxygen incorporation into such materials - a necessary step towards the formation of biological molecules - is therefore fast compared to the freezing of impact melts and cryolavas on Titan.
The rates quoted above are for reactions occurring in pure liquid water. The composition of impact melts and lavas on Titan are not likely to be pure water, but rather contain a few percent ammonia. Tobie et al. (2005) predict that Titan has a subsurface water layer with an ammonia concentration of 14 wt. % in the present era. The presence of ammonia would likely change the reaction rates and yields of the hydrolysis reactions of tholins. We have therefore extended our work to include the measurement of tholin hydrolysis rate coefficients in ammonia-water solutions. In this work, tholins were synthesized from a 0.98 N2/0.02 CH4 atmosphere in a high voltage AC flow discharge reactor, and dissolved in a 13 wt. % ammonia-water solution. Rates were determined by monitoring intensity changes of select species over time using high resolution FT-ICR MS. Comparisons between rates of similar species observed at different pH will be presented.
This work was supported by the NASA Exobiology Program. C. Neish was supported by an NSERC Postgraduate Scholarship.

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