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Diaz-Hernandez J.L.,IFAPA Camino de Purchil | Lopez-Galindo A.,Instituto Andaluz Of Ciencias Of La Tierra
Atmospheric Environment | Year: 2011

Particulate matter suspended in air mainly consists of a complex, multiphase system. Its nature is largely mineral at a global scale, and it has a significant physicochemical impact on the Earth's atmosphere and on biogeochemical cycles. These mineral phases come mainly from windblown soil processes, mostly from great deserts. Despite their importance, the behaviour of their airborne components in time and space is not well known. This study found that the rate of mineral deposition over an annual cycle in the south-eastern Iberian Peninsula was 26.03 g m-2 yr-1, with maxima in spring and summer. Using powder X-Ray diffraction techniques, this value has been broken down as follows (in g m-2 yr-1): quartz (4.90), dolomite (3.36), calcite (3.28), micas (2.97), smectites (2.10), halite (1.84), kaolinite (1.82), sulphates (1.28), amorphous matter (1.15), feldspars (0.18) and graphite (0.17). Although quartz normally is the major individual component of solid particles in the atmosphere-carbonates (calcite + dolomite) can exceed quartz, and phyllosilicates can total as much as carbonates. Clay minerals correlate well with salts (sulphates and halite), and there is an antagonistic relation between sulphates and calcite. Amorphous matter consists of a mixture of metal oxides and organic compounds, among others. Graphite, a net anthropogenic constituent of atmospheric dust, only represents minor quantities. The behavioural differences of the minerals are due to their different reactivity, based on their intrinsic properties of specific surface area, deliquescence, swelling and water retention capacity, and the presence of metallic and exchangeable cations. Smectites seem to play an essential role in the atmospheric processing of SO2 and in secondary sulphate genesis. © 2011 Elsevier Ltd.

Ingles-Prieto A.,University of Granada | Ibarra-Molero B.,University of Granada | Delgado-Delgado A.,University of Granada | Perez-Jimenez R.,Columbia University | And 4 more authors.
Structure | Year: 2013

Summary Little is known about the evolution of protein structures and the degree of protein structure conservation over planetary time scales. Here, we report the X-ray crystal structures of seven laboratory resurrections of Precambrian thioredoxins dating up to approximately four billion years ago. Despite considerable sequence differences compared with extant enzymes, the ancestral proteins display the canonical thioredoxin fold, whereas only small structural changes have occurred over four billion years. This remarkable degree of structure conservation since a time near the last common ancestor of life supports a punctuated-equilibrium model of structure evolution in which the generation of new folds occurs over comparatively short periods and is followed by long periods of structural stasis. © 2013 Elsevier Ltd.

Oliva S.R.,University of Seville | Mingorance M.D.,Instituto Andaluz Of Ciencias Of La Tierra | Leidi E.O.,IRNAS CSIC
Journal of Environmental Monitoring | Year: 2011

The influence of silicon on responses to copper excess was studied in plants of Erica andevalensis. Plantlets were grown in nutrient solutions containing two Cu (1 and 500 M) and three Si concentrations (0, 0.5 and 1 mM). Plant growth, water content, and mineral nutrient concentration were determined. Plants grown with 500 M Cu showed differences in growth and shoot water content depending on Si supply. The addition of 1 mM Si in high-Cu nutrient solutions significantly improved plant growth and reduced water loss preventing plant death related to Cu-excess. Silicon supply reduced significantly leaf Cu concentration (up to 32%) and increased Cu concentration in roots. Phytoliths isolated from leaves were analysed by scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy. Such phytoliths consisted in silica deposits associated with Cu and other elements (K, Ca, P). Improvement by Si of Cu tolerance in E. andevalensis was clearly related to the inhibition of Cu upward transport. The leaf phytoliths formed in Si-treated plants might have some contribution to tolerance by Cu immobilisation and inactivation. © 2011 The Royal Society of Chemistry.

Kellermeier M.,University of Konstanz | Colfen H.,University of Konstanz | Garcia-Ruiz J.M.,Instituto Andaluz Of Ciencias Of La Tierra
European Journal of Inorganic Chemistry | Year: 2012

Biomineralization can afford crystal frameworks of great diversity and utmost complexity, frequently featuring hierarchical structures and morphologies beyond any crystallographic restrictions. The formation of such architectures is usually directed by organic molecules or matrices, which modify crystallization in a deliberate manner. Their influence often leads to sinuous forms, which, by intuition, suggest the presence of life and distinguish these minerals from their inanimate, mostly euhedral counterparts. However, such a strict distinction does not hold. In fact, smooth curvature and higher-order structuring can occur also in purely inorganic environments: simply by precipitating alkaline earth carbonates in silica-containing media, aggregates of highly oriented carbonate nanocrystals can be obtained that display striking noncrystallographic morphologies such as regular helicoids. Thereby, individual crystallites as well as the entire assembly are sheathed by amorphous silica, thus giving a composite material with various levels of hierarchy. These exceptional forms, called "silica biomorphs", self-assemble through a bottom-up process, which relies on local variations in the conditions and is driven by a pH-based coupling of the carbonate and silicate. Here, we review recent progress in the field of silica biomorphs with particular focus on their mechanism of formation, provide insight into structural details at different length scales, and discuss implications of these biomimetic crystal aggregates for both primitive life detection and materials science. When crystallized in the presence of silica, alkaline earth carbonates can self-assemble into elaborate nanoparticle superstructures showing curved morphologies and a level of hierarchy reminiscent of biominerals. This review summarizes recent work on these so-called silica biomorphs, focusing on structural aspects and the underlying mechanism of formation. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Sleutel M.,Vrije Universiteit Brussel | Lutsko J.,Free University of Colombia | Van Driessche A.E.S.,Vrije Universiteit Brussel | Duran-Olivencia M.A.,Instituto Andaluz Of Ciencias Of La Tierra | Maes D.,Vrije Universiteit Brussel
Nature Communications | Year: 2015

It is widely accepted that many phase transitions do not follow nucleation pathways as envisaged by the classical nucleation theory. Many substances can traverse intermediate states before arriving at the stable phase. The apparent ubiquity of multi-step nucleation has made the inverse question relevant: does multistep nucleation always dominate single-step pathways? Here we provide an explicit example of the classical nucleation mechanism for a system known to exhibit the characteristics of multi-step nucleation. Molecular resolution atomic force microscopy imaging of the two-dimensional nucleation of the protein glucose isomerase demonstrates that the interior of subcritical clusters is in the same state as the crystalline bulk phase. Our data show that despite having all the characteristics typically associated with rich phase behaviour, glucose isomerase 2D crystals are formed classically. These observations illustrate the resurfacing importance of the classical nucleation theory by re-validating some of the key assumptions that have been recently questioned. © 2014 Macmillan Publishers Limited. All rights reserved.

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