Binding Energy Evaluation Platform: A Database of Quantum Chemical Binding Energy Distributions for the Astrochemical Community

The quality of astrochemical models is highly dependent on reliable binding energy (BE) values that consider the morphological and energetic variety of binding sites on the surface of ice-grain mantles. Here, we present the Binding Energy Evaluation Platform (BEEP) and database that, using quantum chemical methods, produces full BE distributions of molecules bound to an amorphous solid water (ASW) surface model. BEEP is highly automatized and allows one to sample binding sites on a set of water clusters and to compute accurate BEs. Using our protocol, we computed 21 BE distributions of interstellar molecules and radicals on an amorphized set of 15–18 water clusters of 22 molecules each. The distributions contain between 225 and 250 unique binding sites. We apply a Gaussian fit and report the mean and standard deviation for each distribution. We compare with existing experimental results and find that the low- and high-coverage experimental BEs coincide well with the high-BE tail and mean value of our distributions, respectively. Previously reported single BE theoretical values are broadly in line with ours, even though in some cases significant differences can be appreciated. We show how the use of different BE values impacts a typical problem in astrophysics, such as the computation of snow lines in protoplanetary disks. BEEP will be publicly released so that the database can be expanded to other molecules or ice models in a community effort

A novel framework for studying the impact of binding energy distributions on the chemistry of dust grains

The evaporation of molecules from dust grains is crucial to understanding some key aspects of the star- and the planet-formation processes. During the heating phase, the presence of young protostellar objects induces molecules to evaporate from the dust surface into the gas phase, enhancing its chemical complexity. Similarly, in circumstellar discs, the position of the so-called snow lines is determined by evaporation, with important consequences for the formation of planets. The amount of molecules that are desorbed depends on the interaction between the species and the grain surface, which is controlled by the binding energy. Recent theoretical and experimental works point towards a distribution of values for this parameter instead of the single value often employed in astrochemical models.We present a new "multi-binding energy" framework to assess the effects that a distribution of binding energies has on the amount of species bound to the grains. We find that the efficiency of the surface chemistry is significantly influenced by this process, with crucial consequences on the theoretical estimates of the desorbed species

A novel framework to study the impact of binding energy distributions on the chemistry of dust grains

The evaporation of molecules from dust grains is crucial to understand some key aspects of the star- and the planet-formation processes. During the warm-up phase the presence of young protostellar objects induces molecules to evaporate from the dust surface into the gas phase, enhancing its chemical complexity. Similarly, in circumstellar disks, the position of the so-called snow-lines is determined by evaporation, with important consequences for the formation of planets. The amount of molecules that are desorbed depends on the interaction between the species and the grain surface, which is controlled by the binding energy. Recent theoretical and experimental works point towards a distribution of values for this parameter instead of the single value often employed in astrochemical models.We present here a new "multi-binding energy" framework, to assess the effects that a distribution of binding energies has on the amount of species bound to the grains. We find that the efficiency of the surface chemistry is significantly influenced by this process with crucial consequences on the theoretical estimates of the desorbed species.Comment: Accepted A&

Sphingomyelin Functions as a Novel Receptor for Helicobacter pylori VacA

The vacuolating cytotoxin (VacA) of the gastric pathogen Helicobacter pylori binds and enters epithelial cells, ultimately resulting in cellular vacuolation. Several host factors have been reported to be important for VacA function, but none of these have been demonstrated to be essential for toxin binding to the plasma membrane. Thus, the identity of cell surface receptors critical for both toxin binding and function has remained elusive. Here, we identify VacA as the first bacterial virulence factor that exploits the important plasma membrane sphingolipid, sphingomyelin (SM), as a cellular receptor. Depletion of plasma membrane SM with sphingomyelinase inhibited VacA-mediated vacuolation and significantly reduced the sensitivity of HeLa cells, as well as several other cell lines, to VacA. Further analysis revealed that SM is critical for VacA interactions with the plasma membrane. Restoring plasma membrane SM in cells previously depleted of SM was sufficient to rescue both toxin vacuolation activity and plasma membrane binding. VacA association with detergent-resistant membranes was inhibited in cells pretreated with SMase C, indicating the importance of SM for VacA association with lipid raft microdomains. Finally, VacA bound to SM in an in vitro ELISA assay in a manner competitively inhibited by lysenin, a known SM-binding protein. Our results suggest a model where VacA may exploit the capacity of SM to preferentially partition into lipid rafts in order to access the raft-associated cellular machinery previously shown to be required for toxin entry into host cells

Algunas consideraciones sobre el acceso de los pobres a la tierra en las grandes ciudades de América Latina

Incluye BibliografíaIntenta despejar ciertos mitos encerrados en la planificación para que las recomendaciones sobre políticas de tierra urbana conduzcan a eliminar barreras que se oponen al acceso de los pobres a la tierra

Acceso de los pobres a la tierra en las grandes ciudades de America Latina

Incluye Bibliografí