Solvation of nitrogen compounds in Titan’s seas, precipitates, and atmosphere

Stevenson, James; Fouad, Wael A.; Shalloway, David; Usher, D. A.; Lunine, Jonathan I.; Chapman, Walter G.; Clancy, Paulette

doi:10.1016/j.icarus.2015.04.019

Cited by 18 publications

(28 citation statements)

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“…The larger seas of Titan have been determined by radar sounding to be mostly methane with significant admixtures (∼10%) of ethane and nitrogen (27,28). Because HCN is mostly insoluble in such mixtures (29), it is unlikely that polymers will form there. Rather, it is more likely that the materials investigated herein may undergo reactions in tidal pools near the shores of seas and lakes, where geological activity, tidal effects associated with Titan's noncircular orbit, and changes in the hemispherical distribution of sunlight caused by ∼10…”

Section: Speculations On the Implications Of These Results For Life Wmentioning

confidence: 99%

Polymorphism and electronic structure of polyimine and its potential significance for prebiotic chemistry on Titan

Rahm

Lunine

Usher

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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The chemistry of hydrogen cyanide (HCN) is believed to be central to the origin of life question. Contradictions between Cassini-Huygens mission measurements of the atmosphere and the surface of Saturn's moon Titan suggest that HCN-based polymers may have formed on the surface from products of atmospheric chemistry. This makes Titan a valuable "natural laboratory" for exploring potential nonterrestrial forms of prebiotic chemistry. We have used theoretical calculations to investigate the chain conformations of polyimine (pI), a polymer identified as one major component of polymerized HCN in laboratory experiments. Thanks to its flexible backbone, the polymer can exist in several different polymorphs, which are relatively close in energy. The electronic and structural variability among them is extraordinary. The band gap changes over a 3-eV range when moving from a planar sheet-like structure to increasingly coiled conformations. The primary photon absorption is predicted to occur in a window of relative transparency in Titan's atmosphere, indicating that pI could be photochemically active and drive chemistry on the surface. The thermodynamics for adding and removing HCN from pI under Titan conditions suggests that such dynamics is plausible, provided that catalysis or photochemistry is available to sufficiently lower reaction barriers. We speculate that the directionality of pI's intermolecular and intramolecular =N-H … N hydrogen bonds may drive the formation of partially ordered structures, some of which may synergize with photon absorption and act catalytically. Future detailed studies on proposed mechanisms and the solubility and density of the polymers will aid in the design of future missions to Titan.hydrogen cyanide | prebiotic chemistry | Titan | polymers S aturn's moon Titan is a carbon-rich, oxygen-poor world with a wide range of organic compounds, atmospheric energy sources, and alkane liquid seas-all measured by the remarkably successful Cassini-Huygens mission (1). The extreme cold puts liquid water out of reach-buried 50-100 km below a frigid ice crust (2). The lack of liquid water and presence of liquid hydrocarbons makes Titan a unique "natural laboratory" for exploring potential nonterrestrial forms of prebiotic chemistry or, more speculatively, biochemistry, whose essential biopolymers would differ profoundly from terrestrial ones (3). Regardless of the specific chemistry involved, life requires polymorphic molecules that combine flexibility with the ability to form the organized metastable structures needed for function, adaptation, and evolution. This, almost certainly, requires extended molecules capable of intermolecular and intramolecular hydrogen bonding, but such bonds need not involve oxygen; nitrogen is a potential surrogate. Although =N-H . . . N bonds are weaker than those involving oxygen, their energies are large compared with thermal energy (kT ∼ 0.18 kcal/mol at Titan's low temperature, 90-94 K) and intermolecular and intramolecular bonds need not compete with the strong -O-H . ...

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Section: Speculations On the Implications Of These Results For Life Wmentioning

confidence: 99%

Polymorphism and electronic structure of polyimine and its potential significance for prebiotic chemistry on Titan

Rahm

Lunine

Usher

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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“…We determined that a disagreement of the order of about a factor of ten remains acceptable. Recently Stevenson et al (2015b) concentrated their experimental efforts on nitrogen compounds. As a general trend, they found HCN and CH 3 CN less soluble than what we found.…”

Section: Discussionmentioning

confidence: 99%

Structure of Titan’s evaporites

Cordier

Cornet

Barnes

et al. 2016

Icarus

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Numerous geological features that could be evaporitic in origin have been identified on the surface of Titan. Although they seem to be water-ice poor, their main properties -chemical composition, thickness, stratification-are essentially unknown. In this paper, which follows on a previous one focusing on the surface composition (Cordier et al., 2013b), we provide some answers to these questions derived from a new model. This model, based on the up-to-date thermodynamic theory known as "PC-SAFT", has been validated with available laboratory measurements and specifically developed for our purpose. 1-D models confirm the possibility of an acetylene and/or butane enriched central layer of evaporitic deposit. The estimated thickness of this acetylene-butane layer could explain the strong RADAR brightness of the evaporites. The 2-D computations indicate an accumulation of poorly soluble species at the deposit's margin. Among these species, HCN or aerosols similar to tholins could play a dominant role. Our model predicts the existence of chemically trimodal "bathtub rings" which is consistent with what it is observed at the south polar lake Ontario Lacus. This work also provides plausible explanations to the lack of evaporites in the south polar region and to the high radar reflectivity of dry lakebeds.

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“…We found that the energetic benefits in the dilute limit of solvation are similar for all three liquids, as well as to the results in which the addition of ethane to methane leads to small changes. 15 Note, however, that the saturated mole fraction of ACN is significantly higher in ethane than in methane. 29 (The lateral shifts between the curves are due to the different molar volumes of each simulated liquid and are irrelevant in interpreting the thermodynamics.)…”

Section: Molecular Dynamics Resultsmentioning

confidence: 98%

“…In addition, we expect including polarization effects will lead to slightly less solvation stability, as this would emphasize the difference between polar and non-polar interactions. 15 However, this would not affect the solvation mechanism.…”

Section: Molecular Dynamics Resultsmentioning

confidence: 99%

“…14 This method allowed us to investigate energetics through the interface, rather than only the solvation difference between the bulk vapor and bulk liquid states. 15 The results suggest that small alkane molecules in liquids at cryogenic temperatures surround small ACN clusters such that ACN aggregates do not separate into individual molecules in this environment.…”

Section: Theoretical and Simulation Methodsmentioning

confidence: 95%

See 1 more Smart Citation

Acetonitrile cluster solvation in a cryogenic ethane-methane-propane liquid: Implications for Titan lake chemistry

Corrales

Trumbo

et al. 2017

The Journal of Chemical Physics

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The atmosphere of Titan, Saturn's largest moon, exhibits interesting UV-and radiation-driven chemistry between nitrogen and methane, resulting in dipolar, nitrile-containing molecules. The assembly and subsequent solvation of such molecules in the alkane lakes and seas found on the moon's surface are of particular interest for investigating the possibility of prebiotic chemistry in Titan's hydrophobic seas. Here we characterize the solvation of acetonitrile, a product of Titan's atmospheric radiation chemistry tentatively detected on Titan's surface [H. B. Niemann et al., Nature 438, 779-784 (2005)], in an alkane mixture estimated to match a postulated composition of the smaller lakes during cycles of active drying and rewetting. Molecular dynamics simulations are employed to determine the potential of mean force of acetonitrile (CH 3 CN) clusters moving from the alkane vapor into the bulk liquid. We find that the clusters prefer the alkane liquid to the vapor and do not dissociate in the bulk liquid. This opens up the possibility that acetonitrile-based microscopic polar chemistry may be possible in the otherwise nonpolar Titan lakes.

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Solvation of nitrogen compounds in Titan’s seas, precipitates, and atmosphere

Cited by 18 publications

References 83 publications

Polymorphism and electronic structure of polyimine and its potential significance for prebiotic chemistry on Titan

Polymorphism and electronic structure of polyimine and its potential significance for prebiotic chemistry on Titan

Structure of Titan’s evaporites

Acetonitrile cluster solvation in a cryogenic ethane-methane-propane liquid: Implications for Titan lake chemistry

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