Atomic modifications by synchrotron radiation at the calcite-ethanol interface.

This article reports on studies of the chemical alterations induced by synchrotron radiation at the calcite-ethanol interface, a simple model system for interfaces between minerals and more complex organic molecules containing OH groups. A combination of X-ray reflectivity and X-ray photoelectron spectroscopy of natural calcite, cleaved in distilled ethanol to obtain new clean interfaces, indicated that, during a 5 h period, the two top atomic layers of calcite, CaCO(3), transform into calcium oxide, CaO, by releasing CO(2). Also, the occupation of the first ordered layer of ethanol attached to calcite by hydrogen bonds almost doubles. Comparison between radiated and non-radiated areas of the same samples demonstrate that these effects are induced only by radiation and not caused by aging. These observations contribute to establishing a time limit for synchrotron experiments involving fluid-mineral interfaces where the polar OH group, as present in ethanol, plays a key role in their molecular structure and bonding. Also, the chemical evolution observed in the interface provides new insight into the behavior of some complex organic molecules involved in biomineralization processes.

Molecular ordering of ethanol at the calcite surface.

To produce biominerals, such as shells, bones, and teeth, living beings create organic compounds that control the growth of the solid phase. Investigating the atomic scale behavior of individual functional groups at the mineral-fluid interface provides fundamental information that is useful for constructing accurate predictive models for natural systems. Previous investigations of the activity of coccolith-associated polysaccharides (CAP) on calcite, using atomic force microscopy (AFM) [Henriksen, K., Young, J. R., Bown, P. R., and Stipp, S. L. S. Palentology 2004, 43 (Part 3), 725-743] and molecular dynamics (MD) modeling [Yang, M., Stipp, S. L. S., and Harding, J. H. Cryst. Growth Des. 2008, 8 (11), 4066-4074], have suggested that OH functional groups control polysaccharide attachment. The purpose of this work was to characterize, using X-ray reflectivity (XR) combined with molecular dynamics (MD) simulations, the structuring on calcite of a layer of the simplest carbon chain molecule that contains an OH group, ethanol (CH(3)-CH(2)-OH). We found evidence that EtOH forms a highly ordered structure at the calcite surface, where the first layer molecules bond with calcite. The ethanol molecules stand up perpendicularly at the interface or nearly so. As a consequence, the fatty, CH(3) ends form a new surface, about 6 Å from the termination of the bulk calcite, and beyond that, there is a thin gap where ethanol density is low. Following is a more disordered layer that is two to three ethanol molecules thick, about 14 Å, where density more resembles that of bulk liquid ethanol. The good agreement between theory and experiment gives confidence that a theoretical approach can offer information about behavior in more complex systems.

Widening social inequalities in mortality: the case of Barcelona, a southern European city.

OBJECTIVE: To analyse trends in mortality inequalities in Barcelona between 1983 and 1994 by comparing rates in those electoral wards with a low socioeconomic level and rates in the remaining wards. DESIGN: Mortality trends study. SETTING: The city of Barcelona (Spain). SUBJECTS: The study included all deaths among residents of the two groups of city wards. Details were obtained from death certificates. MAIN OUTCOME MEASURES: Age standardised mortality rates, age standardised rates of years of potential life lost, and age specific mortality rates in relation to cause of death, sex, and year were computed as well as the comparative mortality figure and the ratio of standardised rates of years of potential life lost. RESULTS: Rates of premature mortality increased from 5691.2 years of potential life lost per 100,000 inhabitants aged 1 to 70 years in 1983 to 7606.2 in 1994 in the low socioeconomic level wards, and from 3731.2 to 4236.9 in the other wards, showing an increase in inequalities over the 12 years, mostly due to AIDS and drug overdose as causes of death. Conversely, cerebrovascular disease showed a reduction in inequality over the same period. Overall mortality in the 15-44 age group widened the gap between both groups of wards. CONCLUSION: AIDS and drug overdose are emerging as the causes of death that are contributing to a substantial increase in social inequality in terms of premature mortality, an unreported observation in European urban areas.