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.

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.

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Hydrogen cyanide (HCN), an important precursor of organic compounds, is widely present in extraterrestrial environments. HCN is also readily synthesized in prebiotic simulation experiments. To gain insight into the radiation chemistry of one of the most important and highly versatile constituents of cometary ices, we examined the behavior of over-irradiated frozen and liquid HCN solutions under ionizing radiation. The samples were exposed to gamma radiation at a dose range from 0 up to 419 kGy. Ultraviolet spectroscopy and gas chromatography were used to follow the process. The analyses confirmed that gamma-ray irradiation of liquid HCN solutions generates several organic products. Many of them are essential to life; we verified the presence of carboxylic acids (some of them members of the Krebs cycle) as well as free amino acids and urea. These are the first studies to reveal the presence of these compounds in experiments performed at low temperatures and bulk irradiation. Organic material was produced even at low temperatures and low radiation doses. This work strongly supports the presumption that, as a parent molecule, HCN played a central essential role in the process of chemical evolution on early Earth, comets, and other extraterrestrial environments.