Modeling the complicated chemical reactions in the interstellar medium and surface materials of Titan is nontrivial. Since both the atmosphere and the surface are rich in organic molecules, the chemistry may have important implications for the origin of biomolecules. Prebiotic synthesis of DNA nucleobases from simple molecules such as formamide has been known for more than half a century. In this study, new free radical pathways leading to the synthesis of guanine, hypoxanthine, purine, and adenine have been studied using density functional theory (B3LYP with the 6-311G(d,p) basis set). The pathways of the selected nucleobases demonstrate the importance of free radicals in the production of useful biomolecules under conditions appropriate for the interstellar medium or on Titan. The pathways may be universal in nature and proceed without solvent requirements. Calculations indicate that radical pathways yield lower reaction barriers as compared to previously reported pathways. Overall, these results suggest that the chemistry on Titan's surface and/or the growth of organic particulates in the haze layers in Titan's atmosphere likely involve free radicals. The mechanisms demonstrate that important prebiotic precursors can be predicted. The reaction sequences reported here may lead to the production and build-up of molecules with prebiotic relevance.

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SummaryIn comprehensive two-dimensional gas chromatography (GC6GC), two capillary columns are connected in series through an interface known as a "thermal modulator". This device transforms effluent from the first capillary column into a series of sharp injection-like chemical pulses suitable for high-speed chromatography on the second column. Dramatic increases in the resolving power, sensitivity, and speed of the gas chromatograph result. This paper describes the development of a robust and reliable thermal modulator for GC6GC.

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