A close examination of the structure and dynamics of HC(NH2)2PbI3 by MD simulations and group theory

International audienceThe formamidinium lead iodide hybrid perovskite is studied using first principles molecular dynamics simulations and further analyzed using group theory. The simulations are performed on large supercells containing 768 atoms under isothermal and fully anisotropic isobaric conditions. Two trajectories, one at 300 K and another at 450 K, were extended for over 50 ps in order to perform a detailed assessment of the rotational dynamic of the organic cations. The characteristic rotations of the cation are analyzed by defining two rotation axes. It is found that the formamidinium molecules rotate preferentially around the direction parallel to the line connecting the two nitrogen atoms. The rotational dynamics shows some characteristics already observed in methylammonium lead iodide, like a heterogeneous dynamic at room temperature that disappears at 450 K. The orientational probability of the molecules is explored in terms of an expansion in cubic harmonics up to the 12 th order. It reveals a strong directionality at room temperature that relaxes when increasing the temperature. These findings are further rationalized using Landau and group theories suggesting a mixed displacive/order-disorder structural instability at lower temperatures

Hydrogen bonding and orientation effects on the accommodation of methylamine at the air-water interface

Methylamine is an abundant amine compound detected in the atmosphere which can affect the nature of atmospheric aerosol surfaces, changing their chemical and optical properties. Molecular dynamics simulation results show that methylamine accommodation on water is close to unity with the hydrophilic head group solvated in the interfacial environment and the methyl group pointing into the air phase. A detailed analysis of the hydrogen bond network indicates stronger hydrogen bonds between water and the primary amine group at the interface, suggesting that atmospheric trace gases will likely react with the methyl group instead of the solvated amine site. These findings suggest new chemical pathways for methylamine acting on atmospheric aerosols in which the methyl group is the site of orientation specific chemistry involving its conversion into a carbonyl site providing hydrophilic groups for uptake of additional water. This conversion may explain the tendency of aged organic aerosols to form cloud condensation nuclei. At the same time, formation of NH2 radical and formaldehyde is suggested to be a new source for NH2 radicals at aerosol surfaces, other than by reaction of absorbed NH3. The results have general implications for the chemistry of other amphiphilic organics, amines in particular, at the surface of atmospherically relevant aerosol

Cambio climático y salud: estudio comparativo de la morbilidad en tres zonas de la ciudad de Bahía Blanca

Los extremos térmicos siempre estuvieron asociados a una mayor morbi-mortalidad, impactando mas en los extremos de la vida, en los niveles socioeconómicos bajos y en las personas con enfermedad previa, dependiendo de las características regionales. Los cambios climáticos pronosticados, causarían un aumento de la morbi-mortalidad por causa del calor, disminución de la mortalidad por frío en zonas templadas, un incremento de las enfermedades contagiosas por inundaciones o por influencia sobre los vectores y efectos sobre la salud causados por el desplazamiento de la población. Las antroponosis y zoonosis, directase indirectas, podrían incrementarse según las regiones. Se vería afectada la interacción entre los parámetros meteorológicos y los contaminantes naturales y antropogénicos; esto podría desencadenar y/o agravar enfermedades respiratorias y cardiovasculares.Universidad Nacional de La Plat

Hydrogen bonding and orientation effects on the accommodation of methylamine at the air-water interface

Methylamine is an abundant amine compound detected in the atmosphere which can affect the nature of atmospheric aerosol surfaces, changing their chemical and optical properties. Molecular dynamics simulation results show that methylamine accommodation on water is close to unity with the hydrophilic head group solvated in the interfacial environment and the methyl group pointing into the air phase. A detailed analysis of the hydrogen bond network indicates stronger hydrogen bonds between water and the primary amine group at the interface, suggesting that atmospheric trace gases will likely react with the methyl group instead of the solvated amine site. These findings suggest new chemical pathways for methylamine acting on atmospheric aerosols in which the methyl group is the site of orientation specific chemistry involving its conversion into a carbonyl site providing hydrophilic groups for uptake of additional water. This conversion may explain the tendency of aged organic aerosols to form cloud condensation nuclei. At the same time, formation of NH2 radical and formaldehyde is suggested to be a new source for NH2 radicals at aerosol surfaces, other than by reaction of absorbed NH3. The results have general implications for the chemistry of other amphiphilic organics, amines in particular, at the surface of atmospherically relevant aerosol

Utilization of medicines in a program of primary health care in rural- marginal populations

Se determinaron indicadores básicos del uso de medicamentos en Atención Primaria de Salud (APS) en un programa solidario y se implementaron estrategias de Atención Farmacéutica para mejorar la calidad de la dispensación y la educación sanitaria, asegurando el suministro de medicamentos esenciales a una población rural-marginal de Argentina. Se analizaron las prescripciones médicas siguiendo parámetros de la Organización Mundial de la Salud (OMS) sobre el uso de medicamentos, mediante la determinación de tres indicadores básicos: las prácticas de prescripción, la asistencia al paciente y los factores específicos del servicio de Farmacia. El lugar de realización fue la zona rural de Cachi Yaco (Córdoba). La utilización de los indicadores básicos OMS fue una herramienta simple que permitió evaluar con rapidez y seguridad aspectos importantes de la APS. El trabajo coordinado y comprometido de los distintos profesionales del equipo de salud, alumnos y voluntarios, permitió satisfacer en un alto porcentaje el acceso a medicamentos esta comunidad.The aim of this work was to determine the basic indicators of medicines in Primary Health Care (PHC) in a social program, and to implement the strategies of Pharmaceutical Care in order to improve the quality of the dispensation and sanitary education, thus assuring the supply of essential medicines in rural-marginal populations. The method chosen was to apply the parameters of the World Health Organization (WHO) to determine three basic indicators: the practice of prescription, the assistance to the patient and the specific factors of the pharmaceutical service. The place of the study was Cachi Yaco in the province of Córdoba, Argentina. The utilization of the basic indicators of the WHO were a simple tool that allowed us to evaluate quickly important safety aspects of the pharmaceutical practice in the field of the PHC. Using coordinated work of the professionals, students and volunteers, the access to medicines in this community was realized in an efficient way.Colegio de Farmacéuticos de la Provincia de Buenos Aire