Prebiotic Synthesis of Protobiopolymers Under Alkaline Ocean Conditions

Abstract

Clasically, prebiotic chemistry has focused on the production and identification of simple organic molecules, many of them forming part of "intractable polymers" named tholins. In a previous work, we demonstrated that in experiments using an external energy source and inorganic carbon the aqueous aerosols improved the formation of hydrophilic tholins. Herein, we elucidate the role of pH (from 4 to 12) in prebiotic experiments using saline aqueous aerosols, spark discharges and an atmosphere containing CH(4). At all values of pH, the saline aqueous aerosols increased the production of a significant variety of carboxylic acids that could have been present in a primitive Krebs cycle. Moreover, the study for the first time of hydrophilic tholins by 2-D electrophoresis revealed that these are formed by a set of unexpected heavy polymeric species. The initial alkaline conditions significantly increased both the apparent molecular weight of polymeric species up to 80 kDa and their diversity. We propose the term of protobiopolymers to denote those polymeric species fractionated by 2-D electrophoresis since these are formed by biomolecules present in living systems and show diversity in length as well as in functional groups. Thus, aerosols formed in simulated alkaline ocean conditions could provide an optimal medium for the formation of the primeval materials that could be precursors to the emergence of life.

Prebiotic chemistry in neutral/reduced-alkaline gas-liquid interfaces

“…In the case of the spark discharge experiments using saline solutions or alkaline aqueous aerosols, a previous step of desalting is necessary before GC-MS analyses of the hydrophilic tholins . Thus, those were desalted by an ion exchange resin, and a F NH3 fraction and a F H2O fraction were obtained for experiments 3 and 4 according to the solvents used as eluants 9 . The relationship F N3H /F H2O (mg of freeze-dried ammoniacal fraction/mg of freeze-dried water fraction) was 0.75 and 1.08 for experiments 3 and 4 , respectively.…”

“…The syntheses of the hydrophilic and hydrophobic tholins via spark discharges experiments in an atmosphere of CH 4 + N 2 + H 2 and liquid water, aqueous aerosols or saline aqueous aerosols (experiments 1 – 4 , Table 1) are described in references 8 and 9 . New experiments were carried out following the methodology previously developed using a gas mixture CH 4 :NH 3 :H 2 (40:30:30) purchased from Air Liquid (experiments 5 – 8 , Table 1.…”

“…A few examples reported using water in the solid state (e.g. 6 ), and interestingly, in the last decade, the role of the aqueous aerosols in these types of experiments is being explored 7–9 . The possible importance of aerosols in the origin of life on the early Earth has been emphasized in recent years.…”

“…On the other hand, pure water was employed in the majority of Miller-type experiments, and the roles of salinity and pH have been rarely studied in this type of experiment 9,18–21 . Because salinity and pH are important physico-chemical parameters on a planetary scale and in local environments and since the right environment (in the case that this one was unique) for the emergence of life currently remains unknown, both parameters should be taken into account in Miller-type experiments.…”

Non-associative phase separation in an evaporating droplet as a model for prebiotic compartmentalization

“…Microdroplets have been demonstrated as prebiotically plausible reactors [1][2][3] . Microdroplet reactors facilitate thermodynamically unfavourable synthetic reactions in bulk solution, where one product molecule is formed from two or more reactant molecules with a high loss of entropy.…”