In the present paper, the adsorption of amino acids (Ala, Met, Gln, Cys, Asp, Lys, His) on clays (bentonite, kaolinite) was studied at different pH (3.00, 6.00, 8.00). The amino acids were dissolved in seawater, which contains the major elements. There were two main findings in this study. First, amino acids with a charged R group (Asp, Lys, His) and Cys were adsorbed on clays more than Ala, Met and Gln (uncharged R groups). However, 74% of the amino acids in the proteins of modern organisms have uncharged R groups. These results raise some questions about the role of minerals in providing a prebiotic concentration mechanism for amino acids. Several mechanisms are also discussed that could produce peptide with a greater proportion of amino acids with uncharged R groups. Second, Cys could play an important role in prebiotic chemistry besides participating in the structure of peptides/proteins. The FT-IR spectra showed that the adsorption of amino acids on the clays occurs through the amine group. However, the Cys/clay interaction occurs through the sulfhydryl and amine groups. X-ray diffractometry showed that pH affects the bentonite interlayer, and at pH 3.00 the expansion of Cys/bentonite was greater than that of the samples of ethylene glycol/bentonite saturated with Mg. The Mössbauer spectrum for the sample with absorbed Cys showed a large increase ( approximately 20%) in ferrous ions. This means that Cys was able to partially reduce iron present in bentonite. This result is similar to that which occurs with aconitase where the ferric ions are reduced to Fe 2.5.

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Graphite microparticles (d50 6.20 μm) were oxidized by strong acids, and the resultant graphite oxide was thermally exfoliated to graphene oxide sheets (MPGO, C/O 1.53). Graphene oxide was treated with nonthermal plasma under a SO2 atmosphere at room temperature. The XPS spectrum showed that SO2 was inserted only as the oxidized intermediate at 168.7 eV in the S 2p region. Short thermal shocks at 600 and 400 °C, under an Ar atmosphere, produced reduced sulfur and carbon dioxide as shown by the XPS spectrum and TGA analysis coupled to FTIR. MPGO was also submitted to thermal reaction with SO2 at 630 °C, and the XPS spectrum in the S 2p region at 164.0 eV showed that this time only the nonoxidized episulfide intermediate was inserted. Plasma and thermal treatment produced a partial reduction of MPGO. The sequence of thermal reaction followed by plasma treatment inserted both sulfur intermediates. Because oxidized and nonoxidized intermediates have different reactivities, this selective insertion would allow the addition of selective types of organic fragments to the surface of graphene oxide.

Graphene oxide, MPGO, was obtained by oxidation of graphite microparticles by a H 2 SO 4 /KMnO 4 /H 2 O 2 mixture followed by thermal exfoliation. Non-thermal plasma treatment of MPGO under SO 2 atmosphere resulted in the insertion of the oxidized intermediates only. Refluxing this material in CS 2 (46°C) showed sulfur elimination and interconversion of the oxidized into non-oxidized intermediates with an energetic barrier of ΔG ‡ = 25.81 kcal mol À1 without decarboxylation. The episulfide content in modified MPGO increases with respect to the oxidized intermediates when increasing temperature. Modification of MPGO with SO 2 at 630°C presented exclusively the non-oxidized intermediate. These results support the hypothesis that there are two major reactions with different energetic demand in the SO 2 reduction on carbons: desulfurization and decarboxylation. The selectivity of thiolysis and aminolysis towards the intermediates inserted in the MPGO matrix allowed the aminothiolysis of a sample containing both intermediates with the insertion of the amino group on the episulfide site followed by an intramolecular thiolysis with double functionalization of the matrix.

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