In the recent decades, antibacterial peptides have occupied a strategic position for pharmaceutical drug applications and became subject of intense research activities since they are used to strengthen the immune system of all living organisms by protecting them from pathogenic bacteria. This work proposes a simple and easy statistical/computational method through a peptide polarity index measure by which an antibacterial peptide subgroup can be efficiently identified, that is, characterized by a high toxicity to bacterial membranes but presents a low toxicity to mammal cells. These peptides also have the feature not to adopt to an alpha-helicoidal structure in aqueous solution. The double-blind test carried out to the whole Antimicrobial Peptide Database (November 2011) showed an accuracy of 90% applying the polarity index method for the identification of such antibacterial peptide groups.

Clay minerals are considered important to chemical evolution processes due to their properties, ancient origin, and wide distribution. To extend the knowledge of their role in the prebiotic epoch, the adsorption sites of adenine, adenosine, AMP, ADP, ATP, Poly A, uracil, uridine, UMP, UDP, UTP and Poly U on sodium montmorillonite are investigated. X-ray diffraction, ultraviolet and infrared spectroscopy studies indicate that these molecules distribute into the interlamellar channel and the edge of the clay crystals. Monomers are adsorbed predominantly in the interlamellar channel, whereas polymers adsorb along the crystal edges. Such behavior is discussed mainly in terms of bulk pH, pK(a) of the adsorbate, and Van der Waals interactions.

A hydrothermal system is an environment where there is a flow of hot fluids beneath and up to the surface of the Earth. Hydrothermal vents are systems whose heat source is the underlying magma or hot water generated by convection currents due to high thermal gradients. Hydrothermal fossil deposits have also been recognized in impact craters. Besides Earth, the other place in the Solar System that shows evidence of past impact-induced hydrothermal systems is Mars. The circulation of hydrothermal solutions and interaction with country rocks leads to the precipitation of different mineral phases. In fact, hydrothermal vents, due to their characteristics (redox potential, abundance of organic matter and the presence of certain minerals), have been proposed as places where chemical evolution could have occurred. In this article, a review of hydrothermal environments (submarine, subaerial and impact-induced) and their advantages and disadvantages as primitive environments is presented. Thus far, the synthesis of organic compounds in simulation experiments has been achieved, although the role of prebiotic processes in these environments is still ill-defined. The conditions accompanying white vents are perhaps the best suited for the synthesis of organic molecules; however, this synthesis could have also occurred around black vents, where favorable temperature gradients are present.

Abstract. 0 2 -free aqueous solutions of 0.05 mol dm -3 rmmonium bicarbonate were studied after receiving vnrious doses of so Co gammas (0.001-170 Mrd) or krd pulses of 10 MeV electrons. Formate, oxalate, formaldehyde and an unidentified polymer (M W 14000-16000 daltons) were found to be the main radiolytic products. A large initial yield of formate in the Y-radiolysis, G(HC00 -) = 2.2, is due to the reaction CO* + HCO7 t HC00~ + CO3. The efficiency of organic synthesis within the large dose range studied is low and is explained by efficient pathways to the reformation of bicarbonate, where the reaction

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This paper describes the possible effects of ionizing radiation arising from long-lived soluble radionuclides within clays, in particular 40K, at the epoch of the emergence of life on Earth. The free dispersion of soluble radionuclides constitutes an effective in situ irradiation mechanism that might have acted upon adsorbed nucleic bases and their derivatives on clays, inducing chemical changes on these organic molecules. Several types of well documented reactions for radiolysis of nucleic acid bases and their derivatives are known, even at low doses (i.e., 0.1 Gy). For example, estimates with a dose rate calculated from 40K from deep sea clays at 3.8 Ga ago, indicates that over a period of 1000 years the amount of organic material transformated is 1.8 X 10(-7) moles/kg-clay. Although ionizing radiation may also induce synthetic reactions with prebiological interest, all in all these considerations indicate that nucleic acid bases and their derivatives adsorbed on clays were exposed for long periods to degradation conditions. Such situation promotes decomposition of organic molecules rather than protection of them and enhancement of farther polymerization, as it has been usually taken for granted.

Any proposed model of Earth's primitive environments requires a combination of geochemical variables. Many experiments are prepared in aqueous solutions and in the presence of minerals. However, most sorption experiments are performed in distilled water, and just a few in seawater analogues, mostly inconsistent with a representative primitive ocean model. Therefore, it is necessary to perform experiments that consider the composition and concentration of dissolved salts in the early ocean to understand how these variables could have affected the absorption of organic molecules into minerals. In this work, the adsorption of adenine, adenosine, and 5'AMP onto Namontmorillonite was studied using a primitive ocean analog (4.0 Ga) from experimental and computational approaches. The order of sorption of the molecules was: 5'AMP > adenine > adenosine. Infrared spectra showed that the interaction between these molecules and montmorillonite occurs through the NH group. In addition, electrostatic interaction between negatively charged montmorillonite and positively charge N1 of these molecules could occur. Results indicate that dissolved salts affect the sorption in all cases; the size and structure of each organic molecule influence the amount sorbed. Specifically, the X-ray diffraction patterns show that dissolved salts occupy the interlayer space in Na-montmorillonite and compete with organic molecules for available sites. The adsorption capacity is clearly affected by dissolved salts in thermodynamic terms as deduced by isotherm models. Indeed, molecular dynamic models suggest that salts are absorbed in the interlamellar space and can interact with oxygen atoms exposed in the edges of clay or in its surface, reducing the sorption of the organic molecules. This research shows that the sorption process could be affected by high concentration of salts, since ions and organic molecules may compete for available sites on inorganic surfaces. Salt concentration in primitive oceans may have strongly affected the sorption, and hence the concentration processes of organic molecules on minerals.