6 research outputs found
Uncovering the ElectronâPhonon Interplay and Dynamical EnergyâDissipation Mechanisms of Hot Carriers in Hybrid Lead Halide Perovskites
The discovery of slow hot carrier cooling in hybrid organicâinorganic lead halide perovskites (HOIPs) has provided exciting prospects for efficient solar cells that can overcome the ShockleyâQueisser limit. Questions still loom over how electronâphonon interactions differ from traditional polar semiconductors. Herein, the electronâphonon coupling (EPC) strength of common perovskite films (MAPbBr3, MAPbI3, CsPbI3, and FAPbBr3) is obtained using transient absorption spectroscopy by analyzing the hot carrier cooling thermodynamics via a simplified twoâtemperature model. Density function theory calculations are numerically performed at relevant electronâtemperatures to confirm experiments. Further, the variation of carrierâtemperature over a large range of carrierâdensities in HOIPs is analyzed, and an âSâshapedâ dependence of the initial carrierâtemperature to carrierâdensity is reported. The phenomenon is attributed to the dominance of the large polaron screening and the destabilization effect which causes an increasingâdecreasing fluctuation in temperature at low excitation powers ; and a hotâphonon bottleneck which effectively increases the carrier temperature at higher carrierâdensities. The turning point in the relationship is indicative of the critical Mott density related to the nonmetalâmetal transition. The EPC analysis provides a novel perspective to quantify the energy transfer in HOIPs, electronâlattice subsystem, and the complicated screeningâbottleneck interplay is comprehensively described, resolving the existing experimental contradictions
Assaying Environmental Nickel Toxicity Using Model Nematodes
Although nickel exposure results in allergic reactions, respiratory conditions, and cancer in humans and rodents, the ramifications of excess nickel in the environment for animal and human health remain largely undescribed. Nickel and other cationic metals travel through waterways and bind to soils and sediments. To evaluate the potential toxic effects of nickel at environmental contaminant levels (8.9-7,600 Ôg Ni/g dry weight of sediment and 50-800 Ôg NiCl2/L of water), we conducted assays using two cosmopolitan nematodes, Caenorhabditis elegans and Pristionchus pacificus. We assayed the effects of both sediment-bound and aqueous nickel upon animal growth, developmental survival, lifespan, and fecundity. Uncontaminated sediments were collected from sites in the Midwestern United States and spiked with a range of nickel concentrations. We found that nickel-spiked sediment substantially impairs both survival from larval to adult stages and adult longevity in a concentration-dependent manner. Further, while aqueous nickel showed no adverse effects on either survivorship or longevity, we observed a significant decrease in fecundity, indicating that aqueous nickel could have a negative impact on nematode physiology. Intriguingly, C. elegans and P. pacificus exhibit similar, but not identical, responses to nickel exposure. Moreover, P. pacificus could be tested successfully in sediments inhospitable to C. elegans. Our results add to a growing body of literature documenting the impact of nickel on animal physiology, and suggest that environmental toxicological studies could gain an advantage by widening their repertoire of nematode species
Selenite-mediated production of superoxide radical anions in A549 cancer cells is accompanied by a selective increase in SOD1 concentration, enhanced apoptosis and Se-Cu bonding
Selenite may exert its cytotoxic effects against cancer cells via the generation of reactive oxygen species (ROS). We investigated sources of, and the cellular response to, superoxide radical anion (O2 ·â) generated in human A549 lung cancer cells after treatment with selenite. A temporal delay was observed between selenite treatment and increases in O2 ·â production and biomarkers of apoptosis/necrosis, indicating that the reduction of selenite by the glutathione reductase/NADPH system (yielding O2 ·â) is a minor contributor to ROS production under these conditions. By contrast, mitochondrial and NADPH oxidase O2 ·â generation were the major contributors. Treatment with a ROS scavenger [poly(ethylene glycol)-conjugated superoxide dismutase (SOD) or sodium 4,5-dihydroxybenzene-1,3-disulfonate] 20 h after the initial selenite treatment inhibited both ROS generation and apoptosis determined at 24 h. In addition, SOD1 was selectively upregulated and its perinuclear cytoplasmic distribution was colocalised with the cellular distribution of selenium. Interestingly, messenger RNA for manganese superoxide dismutase, catalase, inducible haem oxygenase 1 and glutathione peroxidase either remained unchanged or showed a delayed response to selenite treatment. Colocalisation of Cu and Se in these cells (Weekley et al. in J. Am. Chem. Soc. 133:18272â18279, 2011) potentially results from the formation of a CuâSe species, as indicated by Cu K-edge extended X-ray absorption fine structure spectra. Overall, SOD1 is upregulated in response to selenite-mediated ROS generation, and this likely leads to an accumulation of toxic hydrogen peroxide that is temporally related to decreased cancer cell viability. Increased expression of SOD1 gene/protein coupled with formation of a CuâSe species may explain the colocalisation of Cu and Se observed in these cells.Claire M. Weekley, Gloria Jeong, Michael E. Tierney, Farjaneh Hossain, Aung Min Maw, Anu Shanu, Hugh H. Harris, Paul K. Wittin