Surface charges and interfaces: implications for mineral roles in prebiotic chemistry

There exists an extensive literature on the possible roles of minerals in the prebiotic stages of the chemical evolution of life (Bernal 1951, Cairns-Smith 1982, Wächtershäuser 1992, Vieyra et al. 1995, Tessis et al. 1999, see Lahav (1994) for a review). Among the original proposals, minerals have been considered in: (a) processes that would discriminate molecular chirality; (b) condensation reactions of biomolecular precursors; (c) prebiotic catalysis; (d) biochemical templates; and (e) autocatalytic metabolism. In this communication it is emphazised the complex properties of both surface reactions and interfaces between minerals and aqueous solutions simulating Archean scenarios. The properties of pyrite surface net charge and of its interface with a solution simulating primitive seawater are discussed and their implications to the autocatalytic model (Wächtershäuser 1988a 1992) are presented in order to demonstrate their relevance. The proposed roles of iron-sulfide minerals (mainly pyrite) as physical support for primitive bidimensional metabolism and chiral discriminator (Wächtershäuser 1988a, Huber & Wächtershäuser 1998) are revised. It is shown that: (a) the net surface charge can be modulated by the pyrite-aqueous solution interface; (b) mononucleotides attachment to pyrite require a cationic bridge; and (c) direct absorption of acetate - a molecule proposed as carbon source in primitive aqueous environments - also modulates the interface properties and would have masked pyrite's bulk structure. These results indicate that physicochemical changes of mineral surfaces - caused by environments simulating Archean aqueous scenarios - should be taken into account in the proposals of mineral prebiotic roles

Nascimento de outra ruralidade The birth of another rurality

ESTE ARTIGO procura mostrar que Lefebvre (1970) e Kayser (1972, 1990) estavam errados sobre o destino da ruralidade. Evidências empíricas sobre o caso da Itália não confirmam as conjeturas extremas sobre "completa urbanização" ou "renascimento rural". E uma espécie de hermenêutica dessas duas hipóteses ajuda a fundamentar a terceira, que pretende superá-las.<br>THIS ARTICLE argues that Lefebvre (1970) and Kayser (1972, 1990) were both mistaken about the destiny of rurality. Empirical evidences from Italy do not confirm extreme conjectures on "complete urbanization" or "rural renaissance". And a kind of hermeneutics of these two hypothesis helps to build upon a third which intends to surpass them