Characteristics of six new para-fluorophenylalanine resistant loci of Aspergillus nidulans.

Characteristics of six new para-fluorophenylalanine resistant loci of Aspergillus nidulans

Domain inhibition linked low activity of Phe-tRNA synthetase for para-fluorophenylalanine in a mutant of Aspergillus nidulans

A number of different mechanisms for p-fluorophenylalanine (FPA) resistance have been described in Aspergillus nidulans. We present data on a new locus for FPA resistance and its biochemical change. Before this report, 20 FPA resistant loci conferring resistance to this amino acid analogue have been identified by us (Tiwary et al. 1987 Curr. Microbiol. 15:305-311) and two by Kinghorn and Pateman (1975 J. Gen. Microbiol. 86:174-184). These mutations have been mapped on five out of eight linkage groups of A. nidulans, there being no report of any mapping of FPA resistant loci on linkage groups III,IV or VII. A new class of FPA resistant mutants exhibiting a reduced level of phenylalanyl-tRNA synthetase was identified in a selection scheme using nitrate as the nitrogen source (Tiwary et al. 1987 Mol. Gen. Genet. 209:164-169). We have slightly modified the technique for the selection of analogue resistant mutants by substituting aspartic acid (25 mM) for sodium nitrate (0.6%) as the nitrogen source in the Czapek-Dox medium in the presence of 30 mg/ml FPA. A higher rate of survival was found on medium containing aspartate than nitrate

Case Report: Potential Arsenic Toxicosis Secondary to Herbal Kelp Supplement

CONTEXT: Medicinal use of dietary herbal supplements can cause inadvertent arsenic toxicosis. CASE PRESENTATION: A 54-year-old woman was referred to the University of California, Davis, Occupational Medicine Clinic with a 2-year history of worsening alopecia and memory loss. She also reported having a rash, increasing fatigue, nausea, and vomiting, disabling her to the point where she could no longer work full-time. A thorough exposure history revealed that she took daily kelp supplements. A urine sample showed an arsenic level of 83.6 μg/g creatinine (normal < 50 μg/g creatinine). A sample from her kelp supplements contained 8.5 mg/kg (ppm) arsenic. Within weeks of discontinuing the supplements, her symptoms resolved and arsenic blood and urine levels were undetectable. DISCUSSION: To evaluate the extent of arsenic contamination in commercially available kelp, we analyzed nine samples randomly obtained from local health food stores. Eight of the nine samples showed detectable levels of arsenic higher than the Food and Drug Administration tolerance level of 0.5 to 2 ppm for certain food products. None of the supplements contained information regarding the possibility of contamination with arsenic or other heavy metals. The 1994 Dietary Supplement Health and Education Act (DSHEA) has changed the way dietary herbal therapies are marketed and regulated in the United States. Less regulation of dietary herbal therapies will make inadvertent toxicities a more frequent occurrence. RELEVANCE TO CLINICAL PRACTICE: Clinicians should be aware of the potential for heavy metal toxicity due to chronic use of dietary herbal supplements. Inquiring about use of dietary supplements is an important element of the medical history

A thermally-invariant, additively manufactured, high-power graphene resistor for flexible electronics

Solution processed two-dimensional (2D) layered materials and their integration with additive manufacturing techniques, such as ink-jet printing, is a facile approach for incorporating these exotic materials into device platforms for flexible electronics. In this work, graphene ink formulations are successfully utilized toward the design and fabrication of high-power resistive structures that are printed on both rigid and flexible substrates and have the potential to deliver close to 10 W of power. A near-flat, negative temperature coefficient of resistivity (TCR) is measured with an activation energy E a ~ 2.4 meV for electron hopping, which is 100×  lower compared to E a values for high TCR materials. The TCR and E a values are amongst the lowest reported for 2D layered material systems. The thermal-invariance of resistivity for such high-power graphene printed resistors is attractive for applications, for example to provide a stable heating source for flexible electronics over extreme thermal environments. The transport characteristics of the ink-jet printed features is modeled as a composite structure in order to explain the thermal response which appears to be mediated via defects in the sonicated graphite, and correlates well to inferences made from Raman spectroscopy and transmission electron microscopy analysis conducted on the printed graphene structures. In order to fabricate such functional structures with ink-jet printing, the active nozzle number, printing passes, and annealing conditions are shown to play an important role to determine line resolution, and also dictate the morphological and electronic transport characteristics of the printed graphene features

High-K dielectric sulfur-selenium alloys.

Upcoming advancements in flexible technology require mechanically compliant dielectric materials. Current dielectrics have either high dielectric constant, K (e.g., metal oxides) or good flexibility (e.g., polymers). Here, we achieve a golden mean of these properties and obtain a lightweight, viscoelastic, high-K dielectric material by combining two nonpolar, brittle constituents, namely, sulfur (S) and selenium (Se). This S-Se alloy retains polymer-like mechanical flexibility along with a dielectric strength (40 kV/mm) and a high dielectric constant (K = 74 at 1 MHz) similar to those of established metal oxides. Our theoretical model suggests that the principal reason is the strong dipole moment generated due to the unique structural orientation between S and Se atoms. The S-Se alloys can bridge the chasm between mechanically soft and high-K dielectric materials toward several flexible device applications