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Project Progress

1. Molecular Self-Organization

Studies in molecular self-organization continued to focus on amphiphilic molecules, which are molecules that possess both hydrophobic and hydrophilic regions. These molecules tend to self-organize spontaneously in an aqueous environment. Co-Investigators Hazen and Deamer continued their investigations of suites of molecules produced when an aqueous solution of pyruvate is subjected to hydrothermal conditions (250°C at 0.2 GPa). Their efforts involved identification of the lipid-like molecules that form vesicles in water.

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Postdoctoral Fellow Nicholas Platts continued to develop the “PAH world” model of life’s origins, based on the discotic self-organization of functionalized polycyclic aromatic hydrocarbon (PAH) molecules in an aqueous environment. In this model, a stack of PAHs becomes decorated at the edges with the bases of nucleic acids, which are linked into a genetic-type sequence. Platts has proposed this model as a precursor to the RNA world.

2. Molecular Selection and Organization on Mineral Surfaces

The group’s studies in molecular selection focused on problems related to what molecules are adsorbed selectively onto what mineral surfaces. Given the vast numbers of different mineral surfaces and different organic molecules of interest, a combinatoric approach is needed. Therefore, Postdoctoral Fellow Jake Maule, Doctoral Student Rebecca Martin, and Co-Investigators Steele, Vicenzi, and Hazen focused on the application of microarray technologies to apply small amounts of many different molecules to several different mineral surfaces in a single experiment. In recent experiments the team printed arrays of a suite of amno acids and pentose sugars onto feldspar, quartz, and calcite surfaces. The group’s principal objective was to refine procedures, both in printing arrays (Figure 2) and in analyzing those arrays using time-of-flight secondary ion mass spectrometry, or ToF-SIMS (Figure 3). A significant advance was the identification of mass fragments that allows them to distinguish between sugars and amino acids (Figure 4).

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Figure 3. A single 150-μm array spot of lysine on calcite imaged with ToF-SIMS. (A) Mass 42.96 ions from ⁴³Ca and ⁴²CaH (lysine masks the mineral surface so the spot appears dark). (B) Mass 43.04 C₂H₅N amino acid fragment.

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In addition to these studies of chiral selection, Collaborator Gözen Ertem continued studies of the formation of RNA oligomers on Na-montmorillonite, a clay mineral. She demonstrated the formation of phosphodiester bonds in the presence of this clay. Furthermore, Ertem found that the rates of formation of different oligomers differ significantly. Thus, only a limited number of oligomers could have formed on the early Earth, rather than equal amounts of all possible isomers.

Another project, undertaken by Doctoral Student Matthieu Galvez, focuses on the question “Why ribose?” By exposing various mineral surfaces to mixtures of ribose, arabinose, xylose and lyxose, and measuring differential adsorption, Galvez hopes to document a mechanism by which ribose may have been selectively concentrated on certain mineral surfaces.