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

Pediatric Medication Noninitiation in Spain.

OBJECTIVES: To estimate medication noninitiation prevalence in the pediatric population and identify the explanatory factors underlying this behavior. METHODS: Observational study of patients (<18 years old) receiving at least 1 new prescription (28 pharmaceutical subgroups; July 2017 to June 2018) in Catalonia, Spain. A prescription was considered new when there was no prescription for the same pharmaceutical subgroup in the previous 6 months. Noninitiation occurred when a prescription was not filled within 1 month or 6 months (sensitivity analysis). Prevalence was estimated as the proportion of total prescriptions not initiated. To identify explanatory factors, a multivariable multilevel logistic regression model was used, and adjusted odds ratios were reported. RESULTS: Overall, 1 539 003 new prescriptions were issued to 715 895 children. The overall prevalence of 1-month noninitiation was 9.0% (ranging from 2.6% [oral antibiotics] to 21.5% [proton pump inhibitors]), and the prevalence of 6-month noninitiation was 8.5%. Noninitiation was higher in the youngest and oldest population groups, in children from families with a 0% copayment rate (vulnerable populations) and those with conditions from external causes. Out-of-pocket costs of drugs increased the odds of noninitiation. The odds of noninitiation were lower when the prescription was issued by a pediatrician (compared with a primary or secondary care clinician). CONCLUSIONS: The prevalence of noninitiation of medical treatments in pediatrics is high and varies according to patients' ages and medical groups. Results suggest that there are inequities in access to pharmacologic treatments in this population that must be taken into account by health care planners and providers

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

Understanding the Swelling Behavior of Modified Nanoclay Filler Particles in Water and Ethanol

Clay–polymer nanocomposite materials have gained much attention owing to their low weight ratio of filler to reinforcement properties, delivering lightweight yet resilient materials with excellent barrier properties to gas diffusion. An important process in their production is clay exfoliation, as maximum reinforcement and improvement of barrier properties occur when the clay mineral platelets are fully separated and dispersed through the polymer matrix with a preferred orientation. In this study we examine clay swelling—the first step leading to exfoliation—using molecular dynamics to generate solvation energetics, swelling curves, and atomic density profiles of three types of clay minerals—montmorillonite, vermiculite, and hectorite—with interlayer Na+ cations and/or three quaternary ammonium surfactants in water and ethanol. Analysis based on the provided simulations can help to distinguish between favorable and unfavorable swelling profiles of mineral/surfactant/solvent systems and therefore guide further research into this complex field