Solubility of polyethers in hydrocarbons at low temperatures. A model for potential genetic backbones on warm titans.

Ethers are proposed here as the repeating backbone linking units in linear genetic biopolymers that might support Darwinian evolution in hydrocarbon oceans. Hydrocarbon oceans are found in our own solar system as methane mixtures on Titan. They may be found as mixtures of higher alkanes (propane, for example) on warmer hydrocarbon-rich planets in exosolar systems ("warm Titans"). We report studies on the solubility of several short polyethers in propane over its liquid range (from 85 to 231 K, or -188 °C to -42 °C). These show that polyethers are reasonably soluble in propane at temperatures down to ca. 200 K. However, their solubilities drop dramatically at still lower temperatures and become immeasurably low below 170 K, still well above the ∼ 95 K in Titan's oceans. Assuming that a liquid phase is essential for any living system, and genetic biopolymers must dissolve in that biosolvent to support Darwinism, these data suggest that we must look elsewhere to identify linear biopolymers that might support genetics in Titan's surface oceans. However, genetic molecules with polyether backbones may be suitable to support life in hydrocarbon oceans on warm Titans, where abundant organics and environments lacking corrosive water might make it easier for life to originate.

Synthesis of carbohydrates in mineral-guided prebiotic cycles.

One present obstacle to the "RNA-first" model for the origin of life is an inability to generate reasonable "hands off" scenarios for the formation of carbohydrates under conditions where they might have survived for reasonable times once formed. Such scenarios would be especially compelling if they deliver pent(ul)oses, five-carbon sugars found in terran genetics, and exclude other carbohydrates (e.g., aldotetroses) that may also be able to function in genetic systems. Here, we provide detailed chemical analyses of carbohydrate premetabolism, showing how borate, molybdate, and calcium minerals guide the formation of tetroses (C(4)H(8)O(4)), heptoses (C(7)H(14)O(7)), and pentoses (C(5)H(10)O(5)), including the ribose found in RNA, in "hands off" experiments, starting with formaldehyde and glycolaldehyde. These results show that pent(ul)oses would almost certainly have formed as stable borate complexes on the surface of an early Earth beneath a humid CO(2) atmosphere suffering electrical discharge. While aldotetroses form extremely stable complexes with borate, they are not accessible by pathways plausible under the most likely early Earth scenarios. The stabilization by borate is not, however, absolute. Over longer times, material is expected to have passed from borate-bound pent(ul)oses to a branched heptulose, which is susceptible to Cannizzaro reduction to give dead end products. We show how this fate might be avoided using molybdate-catalyzed rearrangement of a branched pentose that is central to borate-moderated cycles that fix carbon from formaldehyde. Our emerging understanding of the nature of the early Earth, including the presence of hydrated rocks undergoing subduction to form felsic magmas in the early Hadean eon, may have made borate and molydate species available to prebiotic chemistry, despite the overall "reduced" state of the planet.

2'-deoxycytidines carrying amino and thiol functionality: synthesis and incorporation by Vent (exo-) polymerase.

[reaction: see text] The synthesis of 2'-deoxycytidine nucleosides bearing amino and thiol groups appended to the 5-position of the nucleobase via a butynyl linker is described. The corresponding triphosphates were then synthesized from the nucleoside and incorporated into oligonucleotides by Vent (exo(-)) DNA polymerase. The ability of Vent (exo(-)) polymerase to amplify oligonucleotides containing these functionalized cytidine derivatives in a polymerase chain reaction (PCR) was demonstrated for the amino-functionalized derivative.