Time filter

Source Type

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.

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.

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.

Duarte C.M.,CSIC - Mediterranean Institute for Advanced Studies | Duarte C.M.,University of Western Australia | Regaudie-De-Gioux A.,CSIC - Mediterranean Institute for Advanced Studies | Regaudie-De-Gioux A.,Spanish Oceanographic Institute | And 4 more authors.
Annual Review of Marine Science | Year: 2013

Incubation (in vitro) and incubation-free (in situ) methods, each with their own advantages and limitations, have been used to derive estimates of net community metabolism in the oligotrophic subtropical gyres of the open ocean. The hypothesis that heterotrophic communities are prevalent in most oligotrophic regions is consistent with the available evidence and supported by scaling relationships showing that heterotrophic communities prevail in areas of low gross primary production, low chlorophyll a, and warm water, conditions found in the oligotrophic ocean. Heterotrophic metabolism can prevail where heterotrophic activity is subsidized by organic carbon inputs from the continental shelf or the atmosphere and from nonphotosynthetic autotrophic and mixotrophic metabolic pathways. The growth of the oli-gotrophic regions is likely to be tilting the metabolic balance of the ocean toward a greater prevalence of heterotrophic communities. © 2013 by Annual Reviews. All rights reserved.

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.

Lutsko J.F.,Free University of Colombia | Duran-Olivencia M.A.,Instituto Andaluz Of Ciencias Of La Tierra
Journal of Chemical Physics | Year: 2013

It is shown that diffusion-limited classical nucleation theory (CNT) can be recovered as a simple limit of the recently proposed dynamical theory of nucleation based on fluctuating hydrodynamics [J. F. Lutsko, J. Chem. Phys. 136, 034509 (2012)]10.1063/1.3677191. The same framework is also used to construct a more realistic theory in which clusters have finite interfacial width. When applied to the dilute solution/dense solution transition in globular proteins, it is found that the extension gives corrections to the nucleation rate even for the case of small supersaturations due to changes in the monomer distribution function and to the excess free energy. It is also found that the monomer attachment/detachment picture breaks down at high supersaturations corresponding to clusters smaller than about 100 molecules. The results also confirm the usual assumption that most important corrections to CNT can be achieved by means of improved estimates of the free energy barrier. The theory also illustrates two topics that have received considerable attention in the recent literature on nucleation: the importance sub-dominant corrections to the capillary model for the free energy and of the correct choice of the reaction coordinate. © 2013 AIP Publishing LLC.

Lutsko J.F.,Free University of Colombia | Duran-Olivencia M.A.,Instituto Andaluz Of Ciencias Of La Tierra
Journal of Physics Condensed Matter | Year: 2015

A two-variable stochastic model for diffusion-limited nucleation is developed using a formalism derived from fluctuating hydrodynamics. The model is a direct generalization of the standard classical nucleation theory (CNT). The nucleation rate and pathway are calculated in the weak-noise approximation and are shown to be in good agreement with direct numerical simulations for the weak-solution/strong-solution transition in globular proteins. We find that CNT underestimates the time needed for the formation of a critical cluster by two orders of magnitude and that this discrepancy is due to the more complex dynamics of the two variable model and not, as often is assumed, a result of errors in the estimation of the free energy barrier. © 2015 IOP Publishing Ltd.

Duran-Olivencia M.A.,Instituto Andaluz Of Ciencias Of La Tierra | Lutsko J.F.,Free University of Colombia
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2015

Classical nucleation theory has been recently reformulated based on fluctuating hydrodynamics [J. F. Lutsko and M. A. Durán-Olivencia, Classical nucleation theory from a dynamical approach to nucleation, J. Chem. Phys. 138, 244908 (2013).JCPSA60021-960610.1063/1.4811490]. The present work extends this effort to the case of nucleation in confined systems such as small pores and vesicles. The finite available mass imposes a maximal supercritical cluster size and prohibits nucleation altogether if the system is too small. We quantity the effect of system size on the nucleation rate. We also discuss the effect of relaxing the capillary-model assumption of zero interfacial width resulting in significant changes in the nucleation barrier and nucleation rate. © 2015 American Physical Society.

Caballero E.,Instituto Andaluz Of Ciencias Of La Tierra | Jimenez de Cisneros C.,Instituto Andaluz Of Ciencias Of La Tierra
Chemie der Erde - Geochemistry | Year: 2011

The aim of this study is to determine the isotopic composition (δ18O and δ2H) of interstitial water in bentonites. The study had been carried out from adsorbed vapour in homoionic bentonites. We have worked with the fraction <20μm of a bentonite from Serrata de Níjar (Almería, Spain). Homoionic sodium and calcium bentonites were prepared as well as variable quantities of exchangeable Na/Ca (75Ca/25Na; 50Ca/50Na; 25Ca/75Na), by mixing pure sodium and calcium suspensions in the appropriate quantities. To carry out the hydration of the samples, every one of them was previously dried at 300°C overnight, they were subjected to controlled saturation conditions in an atmosphere of different relative humidity and at a constant temperature of 20°C, until equilibrium was achieved. The different vapour pressures were: P/Po=0.05; P/Po=0.078; P/Po=0.15; P/Po=0.32; P/Po=0.45; P/Po=0.63; P/Po=0.8; P/Po=1, obtained from the saturated solutions of different salts or sulphuric acid. The saturation water was extracted for isotopic analysis from an aliquot of a saturated sample. The technique used was vacuum extraction based on a modification of the one described by Araguás-Araguás et al. (1995). The differentiation between the isotopes of 18O and 2H from interstitial water in the bentonite samples, depending on the different relative humidity, may affect the ions diffusion in the interstitial solutions, since in those from low relative humidities, there could be a higher diffusion velocity as they are formed by molecules of light isotopes, versus interstitial solutions from higher relative humidities or those near saturation. This fact should be taken into account in studies on cation and solute transport from these solutions inside bentonite, even though it is important to continue studying and corroborating it with a larger number of solutions isotopically marked. © 2011.

Loading Instituto Andaluz Of Ciencias Of La Tierra collaborators
Loading Instituto Andaluz Of Ciencias Of La Tierra collaborators