Study of ligand substituent effects on the rate and stereoselectivity of lactide polymerization using aluminum salen-type initiators.

A series of aluminum salen-type complexes [where salen is N,N′-bis(salicylaldimine)-1,2-ethylenediamine] bearing ligands that differ in their steric and electronic properties have been synthesized and investigated for the polymerization of rac-lactide. X-ray crystal structures on key precatalysts reveal metal coordination geometries intermediate between trigonal bipyramidal and square-based pyramidal. Both the phenoxy substituents and the backbone linker have a significant influence over the polymerization. Electron-withdrawing groups attached to the phenoxy donor generally gave an increased polymerization rate, whereas large ortho substituents generally slowed down the polymerization. The vast majority of the initiators afforded polylactide with an isotactic bias; only one exhibited a bias toward heteroselectivity. Isoselectivity generally increases with increased flexibility of the backbone linker, which is presumed to be better able to accommodate any potential steric clashes between the propagating polymer chain, the inserting monomer unit, and the substituents on the phenoxy donor

‘I was there from the start’: The identity maintenance strategies used by fans to combat the threat of losing

On-field performances are a key, yet uncontrollable, determinant of team identification. In this research, we explore how fans of a new team, with an overwhelming loss to win ratio, maintain a positive social identity. Qualitative data gathered from 20 semi-structured interviews were used to address this research objective. Our findings indicated fans use social creativity and social mobility strategies to help preserve a positive and distinctive group identity. In the absence of success, fans evaluated the group on dimensions that reflected positively on, and emphasised the distinctiveness of, group membership. Fans also sought to increase their status in the group to increase the positivity of this association. We use these findings to extend understanding of social identity theory and provide recommendations for sport organisations with unfavourable performance records. Recommendations are themed around highlighting the unique nature of the group and and favourable status comparisons between members of the in-group

Recent progress in organic solar cells based on small molecules

We report on a series of organic solar cells based on heterojunetions of oligothiophene derivatives with varying chain length and C60 fullerenes. Devices arc based on cither p-i-n or p-i-i structure. In the first the intrinsic photovoltaic active layer is sandwiched between a p-typc and n-typc doped organic wide-gap layer for hole and electron transport respectively. In the latter the electron transport layer is replaced by a thin layer of wide-gap material as exciton blocker. Through optimization of transport and absorber layers we are able to reach in devices with single heterojunetions an open circuit voltage Voc of about 1V, a short circuit current density Jsc of about 5.6mA/cm2 and a fill factor FF above 50% under an AM1.5 illumination with 1000W/m2. However, still only a small part of the available solar spectrum is used. Thus, based on these materials stacked solar cells have been made to further improve the light absorption. The thickness of each layer is optimized using optical simulations to match the currents delivered by each of the solar cells in the stack. Through the incorporation of a very efficient recombination zone between the stacked solar cells the resulting Voc nearly reaches the sum of the Voc of the two serially connected solar cells

An experimental search for an explanation of the difference between beam and bottle neutron lifetime measurements

The past two decades have yielded several new measurements and reanalysis of older measurements of the neutron lifetime. These have led to a 4.4 standard deviation discrepancy between the most precise measurements of the neutron decay rate producing protons in cold neutron beams and the most precise lifetime measured in neutron storage experiments. Here we publish an analysis of the recently published UCN aimed a searching for an explanation of this difference using the model proposed by Koch and Hummel

Amphotericin B-loaded nanoparticles for local treatment of cutaneous leishmaniasis

Cutaneous leishmaniasis (CL) is an infectious, parasitic disease caused by the protozoan Leishmania. Amphotericin B (AMB) is a macrolide polyene antibiotic presenting potent antifungal and antileishmanial activity, but due to poor water solubility at physiological pH, side effects, and toxicity, its therapeutic efficiency is limited. In the present study, poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) loaded with AMB were generated to reduce drug toxicity and facilitate localized delivery over a prolonged time. AMB NPs were characterized for particle size, zeta potential, polydispersity index, and degree of aggregation. In vitro assessments demonstrated its sustained activity against Leishmania major promastigotes and parasite-infected macrophages. A single intralesional administration to infected BALB/c mice revealed that AMB NPs were more effective than AMB deoxycholate in terms of reducing lesion area. Taken together, these findings suggest thatAMB NPs improve AMB delivery and can be used for local treatment of CL.This research was funded by the GIP program of the Deutsche Forschungsgemeinschaft (DFG) German Research Foundation. EZ wish to acknowledge the financial support of the RBNI-The Russell Berrie Nanotechnology Institute at the Technion. CLJ holds the Michael and Penny Feiwel Chair of Dermatology

Increased Infarct Wall Thickness by a Bio-Inert Material Is Insufficient to Prevent Negative Left Ventricular Remodeling after Myocardial Infarction

Several injectable materials have been shown to preserve or improve cardiac function as well as prevent or slow left ventricular (LV) remodeling post-myocardial infarction (MI). However, it is unclear as to whether it is the structural support or the bioactivity of these polymers that lead to beneficial effects. Herein, we examine how passive structural enhancement of the LV wall by an increase in wall thickness affects cardiac function post-MI using a bio-inert, non-degradable synthetic polymer in an effort to better understand the mechanisms by which injectable materials affect LV remodeling.Poly(ethylene glycol) (PEG) gels of storage modulus G' = 0.5±0.1 kPa were injected and polymerized in situ one week after total occlusion of the left coronary artery in female Sprague Dawley rats. The animals were imaged using magnetic resonance imaging (MRI) at 7±1 day(s) post-MI as a baseline and again post-injection 49±4 days after MI. Infarct wall thickness was statistically increased in PEG gel injected vs. control animals (p<0.01). However, animals in the polymer and control groups showed decreases in cardiac function in terms of end diastolic volume, end systolic volume and ejection fraction compared to baseline (p<0.01). The cellular response to injection was also similar in both groups.The results of this study demonstrate that passive structural reinforcement alone was insufficient to prevent post-MI remodeling, suggesting that bioactivity and/or cell infiltration due to degradation of injectable materials are likely playing a key role in the preservation of cardiac function, thus providing a deeper understanding of the influencing properties of biomaterials necessary to prevent post-MI negative remodeling

Delivery modulation in silica mesoporous supports via alkyl chain pore outlet decoration

This article focuses on the study of the release rate in a family of modified silica mesoporous supports. A collection of solids containing ethyl, butyl, hexyl, octyl, decyl, octadecyl, docosyl, and triacontyl groups anchored on the pore outlets of mesoporous MCM-41 has been prepared and characterized. Controlled release from pore voids has been studied through the delivery of the dye complex tris(2,2¿-bipyridyl)ruthenium(II). Delivery rates were found to be dependent on the alkyl chain length anchored on the pore outlets of the mesoporous scaffolding. Moreover, release rates follow a Higuchi diffusion model, and Higuchi constants for the different hybrid solids have been calculated. A decrease of the Higuchi constants was observed as the alkyl chain used to tune the release profile is longer, confirming the effect that the different alkyl chains anchored into the pore mouths exerted on the delivery of the cargo. Furthermore, to better understand the relation between pore outlets decoration and release rate, studies using molecular dynamics simulations employing force-field methods have been carried out. A good agreement between the calculations and the experimental observations was observed.Financial support from the Spanish Government (projects MAT2009-14564-C04-01 and MAT2009-14564-C04-04) and the Generalitat Valencia (project PROMETEO/2009/016) is gratefully acknowledged.Aznar Gimeno, E.; Sancenón Galarza, F.; Marcos Martínez, MD.; Martínez Mañez, R.; Stroeve, P.; Cano, J.; Amoros Del Toro, P. (2012). Delivery modulation in silica mesoporous supports via alkyl chain pore outlet decoration. Langmuir. 28:2986-2996. https://doi.org/10.1021/la204438jS298629962