Abstract
The presence of amino acids in diverse extraterrestrial materials has suggested that amino acids are widespread in our solar system, serving as a common class of components for the chemical evolution of life. However, there are a limited number of parameters available for modeling amino acid polymerization at mineral–water interfaces, although the interfacial conditions inevitably exist on astronomical bodies with surface liquid water. Here, we present a set of extended triple-layer model parameters for aspartate (Asp) and aspartyl-aspartate (AspAsp) adsorptions on two-line ferrihydrite, anatase, and γ-alumina determined based on the experimental adsorption data. By combining the parameters with the reported thermodynamic constants for amino acid polymerization in water, we computationally demonstrate how these minerals impact the AspAsp/Asp equilibrium over a wide range of environmental conditions. It was predicted, for example, that two-line ferrihydrite strongly promotes Asp dimerization, leading to the AspAsp/Asp ratio in the adsorbed state up to 41% even from a low Asp concentration (0.1 mM) at pH 4, which is approximately 5 × 107 times higher than that attainable without mineral (8.5 × 10−6%). Our exemplified approach enables us to screen wide environmental settings for abiotic peptide synthesis from a thermodynamic perspective, thereby narrowing down the geochemical situations to be explored for life’s origin on Earth and Earth-like habitable bodies.
Highlights
Following the discoveries of thousands of exoplanetary systems [1,2], a significant effort is being devoted to the laboratory simulation of the formation and oligomerization of biologically relevant compounds on a planetary surface, thereby evaluating the possibility and architecture of life to exist [3,4,5]
We demonstrated a thermodynamic approach to evaluate the impact of mineral surfaces on amino acid polymerization using ferrihydrite, anatase, and γalumina as the minerals for Asp adsorption and dimerization
An important step is determining the key interfacial mechanisms controlling Asp and AspAsp adsorptions, thereby enabling the prediction of the adsorption constants for any mineral–Asp combinations based on a limited number of known constants
Summary
Following the discoveries of thousands of exoplanetary systems [1,2], a significant effort is being devoted to the laboratory simulation of the formation and oligomerization of biologically relevant compounds on a planetary surface, thereby evaluating the possibility and architecture of life to exist [3,4,5]. Amino acids are frequently targeted compounds for several reasons: (1) they are major building blocks for Earth’s life, (2) they have been synthesized in numerous experiments simulating primordial geochemical events [6], (3). They are representative soluble organic matter in extraterrestrial materials (carbonaceous chondrites and comets) [7,8], and (4) they facilitate various organic/inorganic reactions possibly crucial to life’s origin [9,10]. At the mineral–water interface, amino acids exhibit considerably different polymerization reactivities from those in aqueous solution [11,12] This phenomenon has long been studied in the prebiotic chemistry context, its parameterization for geo- and astrochemical modeling applications remains limited. The extrapolation of the results to those at naturally prevalent conditions, 0–50 ◦ C for the early Archean ocean [14], is always difficult owing to the occurrence of side reactions (e.g., decomposition) and the kinetic complexity of mineral–water–solute interactions [15]
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