Direct Nanoscale Characterization of Deep Levels in AgCuInGaSe2 Using Electron Energy‐Loss Spectroscopy in the Scanning Transmission Electron Microscope

A new experimental framework for the characterization of defects in semiconductors is demonstrated. Through the direct, energy‐resolved correlation of three analytical techniques spanning six orders of magnitude in spatial resolution, a critical mid‐bandgap electronic trap level (E_V + 0.56 eV) within Ag_0.2Cu_0.8In_1?xGa_xSe₂ is traced to its nanoscale physical location and chemical source. This is achieved through a stepwise, site‐specific correlated characterization workflow consisting of device‐scale (≈1 mm²) deep level transient spectroscopy (DLTS) to survey the traps present, scanning probe–based DLTS (scanning‐DLTS) for mesoscale‐resolved (hundreds of nanometers) mapping of the target trap state's spatial distribution, and scanning transmission electron microscope based electron energy‐loss spectroscopy (STEM‐EELS) and X‐ray energy‐dispersive spectroscopy for nanoscale energy‐, structure, and chemical‐resolved investigation of the defect source. This first demonstration of the direct observation of sub‐bandgap defect levels via STEM‐EELS, combined with the DLTS methods, provides strong evidence that the long‐suspected Cu_In/Ga substitutional defects are indeed the most likely source of the E_V + 0.56 eV trap state and serves as a key example of this approach for the fundamental identification of defects within semiconductors, in general.     

Nature-inspired pyrrolo[2,3-d]pyrimidines targeting the histamine H3 receptor

Inspired by marine compounds the derivatization of the natural pyrrolo[2,3-d]pyrimidine lead scaffold led to a series of novel compounds targeting the histamine H₃ receptor. The focus was set on improved binding towards the receptor and to establish an initial structure-activity relationship for this compound class based on the lead structure (compound V, K_i value of 126 nM). As highest binding affinities were found with 1,4-bipiperidines as basic part of the ligands, further optimization was focused on 4-([1,4′-bipiperidin]-1′-yl)-pyrrolo[2,3-d]pyrimidines. Related pyrrolo[2,3-d]pyrimidines that were isolated from marine sponges like 4-amino-5-bromopyrrolo[2,3-d]pyrimidine (compound III), showed variations in halogenation pattern, though in a next step the impact of halogenation at 2-position was evaluated. The chloro variations did not improve the affinity compared to the dehalogenated compounds. However, the simultaneous introduction of lipophilic cores with electron-withdrawing substitution patterns in 7-position and dehalogenation at 2-position (11b, 12b) resulted in compounds with significantly higher binding affinities (K_i values of 7 nM and 6 nM, respectively) than the initial lead structure compound V. The presented structures allow for a reasonable structure-activity relationship of pyrrolo[2,3-d]pyrimidines as histamine H₃ receptor ligands and yielded novel lead structures within the natural compound library against this target.     

A life cycle assessment of Agaricus bisporus mushroom production in the USA

The International Journal of Life Cycle Assessment - Stakeholders across the food product supply chain are increasingly interested in understanding the environmental effects of food production....     

Incidence and tracking of Escherichia coli O157:H7 in a major produce production region in California

Fresh vegetables have become associated with outbreaks caused by Escherichia coli O157:H7 (EcO157). Between 1995-2006, 22 produce outbreaks were documented in the United States, with nearly half traced to lettuce or spinach grown in California. Outbreaks between 2002 and 2006 induced investigations of possible sources of pre-harvest contamination on implicated farms in the Salinas and San Juan valleys of California, and a survey of the Salinas watershed. EcO157 was isolated at least once from 15 of 22 different watershed sites over a 19 month period. The incidence of EcO157 increased significantly when heavy rain caused an increased flow rate in the rivers. Approximately 1000 EcO157 isolates obtained from cultures of>100 individual samples were typed using Multi-Locus Variable-number-tandem-repeat Analysis (MLVA) to assist in identifying potential fate and transport of EcO157 in this region. A subset of these environmental isolates were typed by Pulse Field Gel Electrophoresis (PFGE) in order to make comparisons with human clinical isolates associated with outbreak and sporadic illness. Recurrence of identical and closely related EcO157 strains from specific locations in the Salinas and San Juan valleys suggests that transport of the pathogen is usually restricted. In a preliminary study, EcO157 was detected in water at multiple locations in a low-flow creek only within 135 meters of a point source. However, possible transport up to 32 km was detected during periods of higher water flow associated with flooding. During the 2006 baby spinach outbreak investigation, transport was also detected where water was unlikely to be involved. These results indicate that contamination of the environment is a dynamic process involving multiple sources and methods of transport. Intensive studies of the sources, incidence, fate and transport of EcO157 near produce production are required to determine the mechanisms of pre-harvest contamination and potential risks for human illness.     

Application of conformationally restricted peptidomimetics to modeling the bound conformation of peptide antagonists with the IL-1 receptor

A collection of complementary peptide caricatures that closely mimic low-energy (presumably highly populated) conformations of amino acids of interest would constitute a valuable tool set to study the interactions of small peptide ligands with their biological targets. Our general strategy for the design, synthesis and application of peptidomimetics is presented. An illustration of how structural information from mimetics combined with cutting edge biophysical data can be used to derive a model for the bound conformation of an 11-mer peptide antagonist with the IL-1 receptor is given.