Evolución orgánica y diseño inteligente

Depto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasTRUEpu

Selective Chiral Symmetry Breaking during Crystallization: Parity Violation or Cryptochiral Environment in Control?

We have attempted to check experimentally whether the parity violating energy difference (PVED) between enantiomers is ultimately responsible for any bias in the final homochirality of crystals, after suitable autocatalytic amplification. When two equivalent (50-50) chiral populations of L- and D-crystals (of either NaClO3 or NaBrO3) generated independently are mixed and undergo dissolution-crystallization, one of the chiral populations disappears randomly in an irreversible autocatalytic competition process that nurtures the other population. If enough experiments are carried out with this 50-50 mixture of chiral crystals, a random distribution of solutions with final L- or D- crystals is obtained in total. However, when the two populations of L- and D-crystals are generated together in the same solution and undergo a dissolution-crystallization process, a nonrandom distribution of the final handedness among different homochiral solutions is obtained. This selective symmetry breaking is sporadic although always in the same direction; thus, we discard any explanation based on PVED effects. We conclude that the result represents an experimental demonstration of selective chiral symmetry breaking on a macrocopic level brought about by cryptochiral environmental impurity

On the microstructure, growth pattern and original porosity of belemnite rostra: insights from calcitic Jurassic belemnites

Calcitic belemnite rostra are usually employed to perform paleoenvironmental studies based on geochemical data. However, several questions, such as their original porosity and microstructure, remain open, despite they are essential to make accurate interpretations based on geochemical analyses. This paper revisits and enlightens some of these questions. Petrographic data demonstrate that calcite crystals of the rostrum solidum of belemnites grow from spherulites that successively develop along the apical line, resulting in a “regular spherulithic prismatic” microstructure. Radially arranged calcite crystals emerge and diverge from the spherulites: towards the apex, crystals grow until a new spherulite is formed; towards the external walls of the rostrum, the crystals become progressively bigger and prismatic. Adjacent crystals slightly vary in their c-axis orientation, resulting in undulose extinction. Concentric growth layering develops at different scales and is superimposed and traversed by a radial pattern, which results in the micro-fibrous texture that is observed in the calcite crystals in the rostra. Petrographic data demonstrate that single calcite crystals in the rostra have a composite nature, which strongly suggests that the belemnite rostra were originally porous. Single crystals consistently comprise two distinct zones or sectors in optical continuity: 1) the inner zone is fluorescent, has relatively low optical relief under transmitted light (TL) microscopy, a dark-grey color under backscatter electron microscopy (BSEM), a commonly triangular shape, a “patchy” appearance and relatively high Mg and Na contents; 2) the outer sector is non-fluorescent, has relatively high optical relief under TL, a light-grey color under BSEM and low Mg and Na contents. The inner and fluorescent sectors are interpreted to have formed first as a product of biologically controlled mineralization during belemnite skeletal growth and the non-fluorescent outer sectors as overgrowths of the former, filling the intra- and inter-crystalline porosity. This question has important implications for making paleoenvironmental and/or paleoclimatic interpretations based on geochemical analyses of belemnite rostra. Finally, the petrographic features of composite calcite crystals in the rostra also suggest the non-classical crystallization of belemnite rostra, as previously suggested by other authors. © 2016, Universidad Complutense de Madrid. All rights reserved

On the Physical Basis of Asymmetry and Homochirality

Mirror symmetry breaking is ubiquitous in our visible universe taking place in elementary particles, atoms, and molecules. Molecular chirality is not biogenic in itself, although its detection is often considered a biosignature, a conjecture inferred from the fact that we do not know life devoid of homochirality. The question of whether there is a connection between the cosmic preference for one enantiomer, as imposed by the weak force, and the single chirality displayed on Earth is vividly debated. This article gives a glimpse on the origin of asymmetry from a cosmological perspective and on physical transformations that lead to an enantiomeric imbalance, leaving chemical reactions essentially aside. These processes are more plausible as sources of prebiotic chirality than asymmetric amplifications requiring unnatural substrates and conditions and fighting against racemization. The latter may actually be a friend, not foe, and a driving force for enantioselection

Salt crystallization in porous construction materials I Estimation of crystallization pressure

The crystallization process of soluble salts inside the natural and artificial porous materials partially immersed in different saline solutions has been studied. This procedure is used to simulate the conditions of exposure to salt weathering in which foundations and lower walls of building structures are within the zone of capillary rise of saline ground water, Crystallization pressures that can develop in the samples, which are a function of the pore size and salt solution interfacial tension, have been calculated and are compared with experimental values of the materials tensile strength, since both these parameters allow the prediction of porous materials behaviour against salt weathering

Evidence of gully formation by regional groundwater flow in the Gorgonum–Newton region (Mars)

The discovery of gullies on Mars suggests liquid water activity near the surface of the planet in recent times. Since liquid water is unstable under the present-day P–T martian conditions, the formation mechanisms of the gullies, and the source of the putative water, have been a matter of debate for the last years. To provide new insights into these matters, we have approached the problem studying the gullies in relation to their regional setting. A major point in our study relates to the geographic orientation of gullies, an aspect that has been previously regarded as a crucial matter in different models, and has profound implications regarding their origin. We present a comprehensive and detailed survey of the Gorgonum–Newton region, and a study of the Dao and Nirgal Vallis regions. The survey was carried out with the aid of 965 high-resolution MOC images (752 for Gorgonum–Newton, 102 for Nirgal Vallis and 111 for Dao Vallis regions), and MOLA-derived DEMs.We found that gullies display a clear regional pattern, geographically and topographically consistent with a decreasing regional slope. We interpret the results in terms of the existence of several groundwater flow systems operating at different scales, which ultimately may have led to gully formation by seepage at the slopes of craters and canyons. We suggest that aquifers discharging at gully systems may have recharged from the surface, in response to the melting of young partially eroded ice-rich deposits

Estudio comparativo de los mecanismos de crecimiento de cristales de yeso en geles de TMS, Sílice y Agar

Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEpu

Desarrollo ontogénico y morfologías internas en sistemas abiertos difusión-reacción

Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEpu

Teaching Protein Crystallization by the Gel Acupuncture Method

Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEpu