Asymmetric Hydrogenation of Olefins Using Chiral Crabtree-type Catalysts : Scope and Limitations

AuthorCount:4;Other funders:Nordic Energy Research (N-INNER II); Spanish Government CTQ2010-15835;  Catalan Government 2009SGR116 ICREA; Foundation through the ICREA Academia awards  </p

Acción antibacteriana in vitro de dentífricos sin flúor frente a cepas de Streptococcus mutans

Introducción: Los dentífricos con ingredientes activos previenen la caries dental en niños. Objetivo: Determinar la actividad antibacteriana in vitro de tres dentífricos sin flúor y dos soluciones control frente a cepas estándares de Streptococccus mutans. Métodos: Se realizó un estudio transversal, prospectivo y experimental a doble ciego. Se utilizó agar tripticasa de soya con el método de difusión a 37 °C durante 24 h. Se observó el tamaño de los halos de crecimiento inhibitorio en cada grupo. El análisis de los datos se realizó con el software SPSS15, mediante pruebas estadísticas de corroboración de distribución gaussiana de Shapiro-Wilk, prueba de Kruskal-Wallis y de Mann-Whitney. Resultados: El diámetro de inhibición en gluconato de clorhexidina al 0,12 % fue de 26,69 mm (± 1,85), en el agua destilada de 6 mm (± 0) y para las pastas dentífricas de 6 mm (± 0) y 22,93 mm (± 3,39). Al comparar los diámetros obtenidos por la acción del gluconato de clorhexidina 0,12 % y del agua destilada con los dentífricos libre de flúor, sólo en uno de los casos se obtuvieron diferencias estadísticamente significativas (p< 0,05). Conclusiones: No todos los dentífricos para la higiene bucal del bebé estudiados presentan actividad antibacteriana frente a la cepa de Streptococcus mutans ATCC 25175

Chiral ferrocene-based P,S ligands for Ir-catalyzed hydrogenation of minimally functionalized olefins. Scope and limitations

International audienceA family of 12 modular ferrocenyl planar chiral phosphine-thioethers (P,S) has been studied in the asymmetric hydrogenation of minimally functionalized alkenes. These ligands differ by the substituent on sulfur or by the linker between the ferrocene moiety and the sulfur atom (no linker, methylene or methyl substituted methylene linker bearing an additional element of chirality). The cationic iridium(cod) complexes of the different P,S ligands have been efficiently synthesized. For the majority of the ligands, coordination yielded only a single diastereoisomer with full control of the absolute configuration on sulfur. The different iridium complexes have been used in the hydrogenation of various di, tri, and tetrasubstituted minimally functionalized olefins. Conversions and enantioselectivities are highly dependent on the ligand and substrate structure. Full conversions and low-to-excellent enantioselectivities could be obtained (maximum ee from 14 to 94% for 1,1-disubsituted alkenes, from 17 to 99% for trisubstituted olefins, and 34% for the tetrasubstituted alkene)

Pituitary Cell Turnover: From Adult Stem Cell Recruitment through Differentiation to Death

The recent demonstration using genetic tracing that in the adult pituitary stem cells are normally recruited from the niche in the marginal zone and differentiate into secretory cells in the adenopituitary has elegantly confirmed the proposal made when the pituitary stem cell niche was first discovered 5 years ago. Some of the early controversies have also been resolved. However, many questions remain, such as which are the markers that make a pituitary stem cell truly unique and the exact mechanisms that trigger recruitment from the niche. Little is known about the processes of commitment and differentiation once a stem cell has left the niche. Moreover, the acceptance that pituitary cells are renewed by stem cells implies the existence of regulated mechanisms of cell death in differentiated cells which must themselves be explained. The demonstration of an apoptotic pathway mediated by RET/caspase 3/Pit-1/Arf/p53 in normal somatotrophs is therefore an important step towards understanding how pituitary cell number is regulated. Further work will elucidate how the rates of the three processes of cell renewal, differentiation and apoptosis are balanced in tissue homeostasis after birth, but altered in pituitary hyperplasia in response to physiological stimuli such as puberty and lactation. Thus, we can aim to understand the mechanisms underlying human disease due to insufficient (hypopituitarism) or excess (pituitary tumor) cell numbers. (C) 2015 S. Karger AG, Base