Komatiites as Complex Adsorption Surfaces for Amino Acids in Prebiotic Environments, a Prebiotic Chemistry Essay

Understanding Titan's Prebiotic Chemistry: Synthesizing Amino Acids Through Aminonitrile Alkaline Hydrolysis

Titan is an ocean world with a plethora of organic material in its atmosphere and on its surface, making it an intriguing location in the search for habitable environments beyond Earth. Settled aerosols will mix with transient surface melts following cryovolcanic eruptions and impact events, driving hydrolysis reactions and prebiotic chemistry. Previous studies have shown that the hydrolysis of laboratory-synthesized Titan organics leads to the production of amino acids and other prebiotic molecules. The exact molecular structure of Titan aerosols remains unclear, yet aminonitriles have been hypothesized to be among the organic components. This laboratory study tested three reaction pathways that could potentially lead to the formation of amino acids: aminoacetonitrile → glycine, 2-aminopropanenitrile → alanine, and 4-aminobutanenitrile → γ-aminobutyric acid. Liquid chromatography mass spectrometry (LCMS) is used to quantify the abundance of amino acids over a 6-month period. We conclude that ammonia plays a key role in the synthesis of amino acids from aminonitriles, while the inclusion of salts (1 wt %) and minerals (25 mg/mL) did not have a significant effect on amino acid formation compared to ammonia. Rate constants (k) for alkaline hydrolysis of the aminonitriles were calculated. Our results suggest that if Titan's surface melts have a composition, including at least 5% ammonia in water, and if aminonitriles are present in Titan's organic aerosols, then amino acids will likely form. These results are highly relevant to the Dragonfly mission to Titan, which will sample impact melt material at Selk crater to search for prebiotic molecules.

Did Salts in Seawater Play an Important Role in the Adsorption of Molecules on Minerals in the Prebiotic Earth? The Case of the Adsorption of Thiocyanate onto Forsterite-91

Thiocyanate may have played as important a role as cyanide in the synthesis of several molecules. However, its concentration in the seas of the prebiotic Earth could have been very low. Thiocyanate was dissolved in two different seawaters: a) a composition that comes close to the seawater of the prebiotic Earth (seawater-B, Ca2+ and Cl-) and b) a seawater (seawater-A, Mg2+ and SO42-) that could be related to the seas of Mars and other moons in the solar system. In addition, forsterite-91 was a very common mineral on the prebiotic Earth and Mars. Two important results are reported in this work: 1) thiocyanate adsorbed onto forsterite-91 and 2) the amount of thiocyanate adsorbed, adsorption thermodynamic, and adsorption kinetic depend on the composition of the artificial seawater. For all experiments, the adsorption was thermodynamically favorable (ΔG < 0). The adsorption data fitted well in the Freundlich and Langmuir-Freundlich models. When dissolving thiocyanate in seawater 4.0-A-Gy and seawater 4.0-B-Gy, the adsorption of thiocyanate onto forsterite-91 was ruled by enthalpy and entropy, respectively. As shown by n values, the thiocyanate/foraterite-91 system is heterogeneous. For all kinetic data, the pseudo-first-order model presented the best fit. The constant rate for thiocyanate dissolved in seawater 4.0-A-Gy was twice that compared to thiocyanate dissolved in seawater 4.0-B-Gy or ultrapure-water. The interaction between thiocyanate and Fe2+ of forsterite-91 was with the nitrogen atom of thiocyanate. In the presence of thiocyanate, sulfate interacts with forsterite-91 as an inner-sphere surface complex, and without thiocyanate as an outer-sphere surface complex.

The pH dependent surface charging and points of zero charge. X. Update

Surfaces are often characterized by their points of zero charge (PZC) and isoelectric points (IEP). Different authors use these terms for different quantities, which may be equal to the actual PZC under certain conditions. Several popular methods lead to results which are inappropriately termed PZC. This present review is limited to zero-points obtained in the presence of inert electrolytes (halides, nitrates, and perchlorates of the 1st group metals). IEP are reported for all kinds of materials. PZC of metal oxides obtained as common intersection points of potentiometric curves for 3 or more ionic strengths (or by means of equivalent methods) are also reported, while the apparent PZC obtained by mass titration, pH-drift method, etc. are deliberately neglected. The results published in the recent publications and older results overlooked in the previous compilations by the same author are reported. The PZC/IEP are accompanied by information on the temperature and on the nature and concentration of supporting electrolyte (if available). The references to previous reviews by the same author allow to compare the newest results with the PZC/IEP of similar materials from the older literature.