Solvent Dependence of Lateral Charge Transfer in a Porphyrin Monolayer

Lateral charge transport in a redox-active monolayer can be utilized for solar energy harvesting. A model porphyrin system was chosen to study the influence of the solvent on lateral hole hopping, which plays a crucial role in the charge-transfer kinetics. We examined the influence of water, acetonitrile, and propylene carbonate as solvents. Hole-hopping lifetimes varied by nearly three orders of magnitude among solvents, ranging from 3 ns in water to 2800 ns in propylene carbonate, and increased nonlinearly as a function of added acetonitrile in aqueous solvent mixtures. These results elucidate the important roles of solvation, molecular packing dynamics, and lateral charge-transfer mechanisms that have implications for all dye-sensitized photoelectrochemical device designs

Gut microbiota disturbance during helminth infection: can it affect cognition and behaviour of children?

Background: Bidirectional signalling between the brain and the gastrointestinal tract is regulated at neural, hormonal, and immunological levels. Recent studies have shown that helminth infections can alter the normal gut microbiota. Studies have also shown that the gut microbiota is instrumental in the normal development, maturation and function of the brain. The pathophysiological pathways by which helminth infections contribute to altered cognitive function remain poorly understood. Discussion: We put forward the hypothesis that gastrointestinal infections with parasitic worms, such as helminths, induce an imbalance of the gut-brain axis, which, in turn, can detrimentally manifest in brain development. Factors supporting this hypothesis are: 1) research focusing on intelligence and school performance in school-aged children has shown helminth infections to be associated with cognitive impairment, 2) disturbances in gut microbiota have been shown to be associated with important cognitive developmental effects, and 3) helminth infections have been shown to alter the gut microbiota structure. Evidence on the complex interactions between extrinsic (parasite) and intrinsic (host-derived) factors has been synthesised and discussed. Summary: While evidence in favour of the helminth-gut microbiota-central nervous system hypothesis is circumstantial, it would be unwise to rule it out as a possible mechanism by which gastrointestinal helminth infections induce childhood cognitive morbidity. Further empirical studies are necessary to test an indirect effect of helminth infections on the modulation of mood and behaviour through its effects on the gut microbiota

Bobwhite Response to Cattle Grazing in South Texas

Range management practices to improve habitat for wildlife by reducing brush and increasing herbaceous plants, coupled with reduced stocking rates, can lead to dense stands of dominant grasses, such as four-flower trichloris (Trichloris pluriflora). This monoculture of trichloris creates dense vegetation unsuitable for northern bobwhite (Colinus virginianus; hereafter, bobwhite), reduces plant species diversity, and alters ecosystem functions. The objectives of this study are to 1) evaluate the effects of a proper cattle grazing regime to improve bobwhite habitat and 2) develop a management guide documenting how cattle grazing can be used as a tool to reduce the density and cover of dominant grasses and thereby allow higher plant species richness. The study is taking place in Duval County, Texas, USA, between 2 pastures with a combined area of 2,500 ha. One pasture serves as the control (1,337 ha) while the other (1,109 ha) is grazed to maintain a stubble height of 30–40 cm. We placed 10 grazing exclosures and 10 25-m transects within each treatment to determine botanical composition and cover. Double sampling is conducted monthly to determine forage standing crop. Forage standing crop, plant species richness, total ground cover, and forage utilization will be estimated. We hypothesize that 1) the grazed pasture will contain more bobwhites than the nongrazed pasture, 2) plant species richness will be greater in the grazed pasture, and 3) grazing will reduce the cover of trichloris. In 2020, plant species richness varied among sampling periods and was recorded as 7.5 species/transect and 4.8 species/transect higher in the nongrazed control compared to the grazed pasture in June and August, respectively. After the end of the first year of grazing, however, there was no statistical difference in plant species richness between the 2 pastures, a result that does not coincide with our second hypothesis. Litter cover did not vary among sampling periods in the nongrazed pasture but changed in the grazed pasture. Litter cover was 9.4%, 14.3%, 14.6%, and 8.9% higher in the grazed pasture than in the nongrazed pasture in May, August, September, and December 2020, respectively. Bare ground cover changed throughout sampling periods in the nongrazed and grazed pastures. Bare ground cover was 22%, 18%, and 22% higher in the grazed pasture than in the nongrazed pasture in May, September, and December 2020, respectively. Trichloris cover did not change throughout the sampling period in the grazed pasture but varied in the nongrazed pasture. Trichloris cover was 31%, 20%, 37.5%, and 35.3% higher in the nongrazed pasture than in the grazed pasture in May, August, September, and December 2020, respectively; these results support our third hypothesis. We began the cattle grazing in May 2020 with a herd of 228 mother cows placed in the grazing treatment. After 109 days of grazing, the pasture reached the target stubble height and the herd was removed. In 2021 we began grazing in June with a herd of 337 stocker calves. Vegetation growth outpaced what the calves could eat, so we removed them after 56 days and added 300 bred cows. These mother cows grazed for another 96 days until the current utilization rate was met. We completed aerial surveys for both 2020 and 2021, and the results indicate that bobwhite density on the grazed pasture was about 80% higher in 2020 and 25% higher in 2021 compared to the nongrazed pasture. These findings are consistent with our first hypothesis. In theory, by reducing the trichloris cover and increasing bare ground, we are creating more usable space for bobwhites; consequently, we are recording more bobwhites in the grazed pasture. The results are preliminary, but our study has the potential to shed light on bobwhite responses to proper cattle grazing and in turn to inform decisions about managing bobwhite habitat across South Texas

Structure, Spectroscopy, and Electrochemistry of Manganese(I) and Rhenium(I) Quinoline Oximes

Reactions of α- and β-diimine quinoline aldoximes with Mn(I) and Re(I) tricarbonyl halides afford quinoline oxime complexes. Both Mn(I) and Re(I) complexes experience severe geometric strain due to ligand steric interactions: 6-membered metallocycles exhibit more pronounced distortions than 5-membered ones, consistent with density functional theory structural analyses. Such distortions likely also affect reactivity patterns, as evidenced by Re(I)-induced deoximation of a quinoline variant containing a CF_3-ketoxime

Structure, Spectroscopy, and Electrochemistry of Manganese(I) and Rhenium(I) Quinoline Oximes

Reactions of α- and β-diimine quinoline aldoximes with Mn(I) and Re(I) tricarbonyl halides afford quinoline oxime complexes. Both Mn(I) and Re(I) complexes experience severe geometric strain due to ligand steric interactions: 6-membered metallocycles exhibit more pronounced distortions than 5-membered ones, consistent with density functional theory structural analyses. Such distortions likely also affect reactivity patterns, as evidenced by Re(I)-induced deoximation of a quinoline variant containing a CF_3-ketoxime

A photo- and electrochemically-active porphyrin–fullerene dyad electropolymer

A hole- and electron-conducting polymer has been prepared by electropolymerization of aporphyrin–fullerene monomer. The porphyrin units are linked by aminophenyl groups to form a linear chain in which the porphyrin is an integral part of the polymer backbone. The absorption spectrum of a film formed on indium-tin-oxide-coated glass resembles that of a model porphyrin–fullerene dyad, but with significant peak broadening. The film demonstrates a first oxidation potential of 0.75 V vs. SCE, corresponding to oxidation of the porphyrin polymer, and a first reduction potential of -0.63 V vs. SCE, corresponding to fullerene reduction. Time-resolved fluorescence studies show that the porphyrin first excited singlet state is strongly quenched by photoinduced electron transfer to fullerene. Transient absorption investigations reveal that excitation generates mobile charge carriers that recombine by both geminate and nongeminate pathways over a large range of time scales. Similar studies on a related polymer that lacks the fullerene component show complex, laser-intensity-dependent photoinduced electron transfer behavior. The properties of the porphyrin–fullerene electropolymer suggest that it maybe useful in organic photovoltaic applications, wherein light absorption leads to charge separationwithin picoseconds in a “molecular heterojunction” with no requirement for exciton migration.Fil: Gervaldo, Miguel Andres. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados; ArgentinaFil: Liddell, Paul A.. Arizona State University; Estados UnidosFil: Kodis, Gerdenis. Arizona State University; Estados UnidosFil: Brennan, Bradley J.. Arizona State University; Estados UnidosFil: Johnson, Christopher R.. Arizona State University; Estados UnidosFil: Bridgewater, James W.. Arizona State University; Estados UnidosFil: Moore, Ana L.. Arizona State University; Estados UnidosFil: Moore, Thomas A.. Arizona State University; Estados UnidosFil: Gust, Devens. Arizona State University; Estados Unido

Heterogenized Iridium Water-Oxidation Catalyst from a Silatrane Precursor

A pentamethylcyclopentadienyl (Cp*) iridium water-oxidation precatalyst was modified to include a silatrane functional group for covalent attachment to metal oxide semiconductor surfaces. The heterogenized catalyst was found to perform electrochemically driven water oxidation at an overpotential of 462 mV with a turnover number of 304 and turnover frequency of 0.035 s^(–1) in a 0.1 M KNO3 electrolyte at pH 5.8. Computational modeling of the experimental IR spectra suggests that the catalyst retains its Cp* group during the first hour of catalysis and likely remains monomeric

Analytical Methods for Discriminating Stardust in Aerogel Capture Media

Comet 81P/Wild 2's serendipitous orbit change to the inner solar system in 1974 offered researchers a rare opportunity to sample cometary material from the Kuiper belt, a repository of material left over from solar system formation {approx}4.6 Gyr ago. NASA's Stardust mission intercepted the comet in January 2004 and returned with material collected from its tail in January 2006. The cometary material, consisting of particles ranging from 10 microns down to <2 nm, was collected in aerogel, a very low density ({approx}3 mg/cm cm3) silica foam, to minimize the effects of deceleration from 6.1 km/s. The entire deceleration track is extracted from the aerogel block as a pyramidal shape known as a keystone which can be mapped using x-ray fluorescence prior to extraction of terminal or intermediate particles for other analyses. One goal of the track mapping is to determine the bulk composition of the cometary material returned. Unfortunately, although the aerogel is predominantly SiO{sub 2}, there are sufficient quantities of trace elements similar to those expected in the cometary material to require sophisticated discrimination techniques in order to decide whether a fluorescence map pixel contains only aerogel or both aerogel and cometary material. We have developed a dual threshold analysis approach for better distinguishing cometary material from aerogel contaminants and have applied it to five Stardust impact tracks and terminal particles. Here, we present aspects of the dual threshold approach and demonstrate its impact on track composition for one track

First X-ray Fluorescence MicroCT Results from Micrometeorites at SSRL

X-ray fluorescence microCT (computed tomography) is a novel technique that allows non-destructive determination of the 3D distribution of chemical elements inside a sample. This is especially important in samples for which sectioning is undesirable either due to the risk of contamination or the requirement for further analysis by different characterization techniques. Developments made by third generation synchrotron facilities and laboratory X-ray focusing systems have made these kinds of measurements more attractive by significantly reducing scan times and beam size. First results from the x-ray fluorescence microCT experiments performed at SSRL beamline 6-2 are reported here. Beamline 6-2 is a 54 pole wiggler that uses a two mirror optical system for focusing the x-rays onto a virtual source slit which is then reimaged with a set of KB mirrors to a (2 x 4) {micro}{sup 2} beam spot. An energy dispersive fluorescence detector is located in plane at 90 degrees to the incident beam to reduce the scattering contribution. A PIN diode located behind the sample simultaneously measures the x-ray attenuation in the sample. Several porous micrometeorite samples were measured and the reconstructed element density distribution including self-absorption correction is presented. Ultimately, this system will be used to analyze particles from the coma of comet Wild-2 and fresh interstellar dust particles both of which were collected during the NASA Stardust mission

A framework for monitoring the safety of water services: from measurements to security

The sustainable developments goals (SDGs) introduced monitoring of drinking water quality to the international development agenda. At present, Escherichia coli are the primary measure by which we evaluate the safety of drinking water from an infectious disease perspective. Here, we propose and apply a framework to reflect on the purposes of and approaches to monitoring drinking water safety. To deliver SDG 6.1, universal access to safe drinking water, a new approach to monitoring is needed. At present, we rely heavily on single measures of E. coli contamination to meet a normative definition of safety. Achieving and sustaining universal access to safe drinking water will require monitoring that can inform decision making on whether services are managed to ensure safety and security of access