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Since the discovery of the hydrated electron more than 40 years ago, a general consensus has emerged that the hydrated electron occupies a quasispherical cavity in liquid water. We simulated the electronic structure and dynamics of the hydrated electron using a rigorously derived pseudopotential to treat the electron-water interaction, which incorporates attractive oxygen and repulsive hydrogen features that have not been included in previous pseudopotentials. What emerged was a hydrated electron that did not reside in a cavity but instead occupied a approximately 1-nanometer-diameter region of enhanced water density. Both the calculated ground-state absorption spectrum and the excited-state spectral dynamics after simulated photoexcitation of this noncavity hydrated electron showed excellent agreement with experiment. The relaxation pathway involves a rapid internal conversion followed by slow ground-state cooling, the opposite of the mechanism implicated by simulations in which the hydrated electron occupies a cavity.

▪ Abstract  The electronic structure of conjugated polymers is of current interest because of the wide range of potential applications for such materials in optoelectronic devices. It is increasingly clear that the electronic properties of conjugated polymers depend sensitively on the physical conformation of the polymer chains and the way the chains pack together in films. This article reviews the evidence that interchain electronic species do form in conjugated polymer films, and that their number and chemical nature depend on processing conditions; the chain conformation, degree of interchain contact, and rate of energy transfer can be controlled by factors such as choice of solvent, polymer concentration, thermal annealing, presence of electrically charged side groups, and encapsulation of the polymer chains in mesoporous silica. Taken together, the results reconcile many contradictions in the literature and provide a prescription for the optimization of conjugated polymer film morphology for device applications.

The prevailing paradigm in subterranean ecology is that below‐ground food webs are simple, limited to one or two trophic levels, and composed of generalist species because of spatio‐temporally patchy food resources and pervasive energy limitation. This paradigm is based on relatively few studies of easily accessible, air‐filled caves. However, in some subterranean ecosystems, chemolithoautotrophy can subsidize or replace surface‐based allochthonous inputs of photosynthetically derived organic matter (OM) as a basal food resource and promote niche specialization and evolution of higher trophic levels. Consequently, the current subterranean trophic paradigm fails to account for variation in resources, trophic specialization, and food chain length in some subterranean ecosystems. We reevaluated the subterranean food web paradigm by examining spatial variation in the isotopic composition of basal food resources and consumers, food web structure, stygobiont species diversity, and chromophoric organic matter (CDOM), across a geochemical gradient in a large and complex groundwater system, the Edwards Aquifer in Central Texas (USA). Mean δ¹³C values of stygobiont communities become increasingly more negative along the gradient of photosynthetic OM sources near the aquifer recharge zone to chemolithoautotrophic OM sources closer to the freshwater‐saline water interface (FWSWI) between oxygenated freshwater and anoxic, sulfide‐rich saline water. Stygobiont community species richness declined with increasing distance from the FWSWI. Bayesian mixing models were used to estimate the relative importance of photosynthetic OM and chemolithoautotrophic OM for stygobiont communities at three biogeochemically distinct sites. The contribution of chemolithoautotrophic OM to consumers at these sites ranged between 25% and 69% of total OM utilized and comprised as much as 88% of the diet for one species. In addition, the food web adjacent to the FWSWI had greater trophic diversity when compared to the other two sites. Our results suggest that diverse OM sources and in situ, chemolithoautotrophic OM production can support complex groundwater food webs and increase species richness. Chemolithoautotrophy has been fundamental for the long‐term maintenance of species diversity, trophic complexity, and community stability in this subterranean ecosystem, especially during periods of decreased photosynthetic production and groundwater recharge that have occurred over geologic time scales.

For solution-phase chemical reactions, the solvent is often considered simply as a medium to allow the reactants to encounter each other by diffusion. Although examples of direct solvent effects on molecular solutes exist, such as the compression of solute bonding electrons due to Pauli repulsion interactions, the solvent is not usually considered a part of the chemical species of interest. We show, using quantum simulations of Na2, that when there are local specific interactions between a solute and solvent that are energetically on the same order as a hydrogen bond, the solvent controls not only the bond dynamics but also the chemical identity of the solute. In tetrahydrofuran, dative bonding interactions between the solvent and Na atoms lead to unique coordination states that must cross a free energy barrier of ~8 kBT—undergoing a chemical reaction—to interconvert. Each coordination state has its own dynamics and spectroscopic signatures, highlighting the importance of considering the solvent in the identity of condensed-phase chemical systems.

Malignant cells are able to survive and grow in detached conditions, despite the associated increase in reactive oxygen species; here a novel metabolic pathway used by cancer cells as they adapt to anchorage-independent growth is described. How detached cancer cells keep growing The paper describes a previously unknown mechanism by which cancer cells reprogram their metabolism to enable growth in three-dimensional spheroids. Detachment of cells from the extracellular matrix is normally inhibited by reactive oxygen species (ROS) that are released by detachment, but malignant cells can acquire the ability to survive and grow in detached conditions. Ralph DeBerardinis and colleagues demonstrate that cells in spheroids mitigate oxidative stress by generating citrate in the cytosol by IDH1-driven reductive glutamine metabolism. Cytosolic citrate is then taken up by the mitochondria where it participates in oxidative metabolism, leading to NADPH generation and suppression of mitochondrial ROS generation. Cells receive growth and survival stimuli through their attachment to an extracellular matrix (ECM) 1 . Overcoming the addiction to ECM-induced signals is required for anchorage-independent growth, a property of most malignant cells 2 . Detachment from ECM is associated with enhanced production of reactive oxygen species (ROS) owing to altered glucose metabolism 2 . Here we identify an unconventional pathway that supports redox homeostasis and growth during adaptation to anchorage independence. We observed that detachment from monolayer culture and growth as anchorage-independent tumour spheroids was accompanied by changes in both glucose and glutamine metabolism. Specifically, oxidation of both nutrients was suppressed in spheroids, whereas reductive formation of citrate from glutamine was enhanced. Reductive glutamine metabolism was highly dependent on cytosolic isocitrate dehydrogenase-1 (IDH1), because the activity was suppressed in cells homozygous null for IDH1 or treated with an IDH1 inhibitor. This activity occurred in absence of hypoxia, a well-known inducer of reductive metabolism. Rather, IDH1 mitigated mitochondrial ROS in spheroids, and suppressing IDH1 reduced spheroid growth through a mechanism requiring mitochondrial ROS. Isotope tracing revealed that in spheroids, isocitrate/citrate produced reductively in the cytosol could enter the mitochondria and participate in oxidative metabolism, including oxidation by IDH2. This generates NADPH in the mitochondria, enabling cells to mitigate mitochondrial ROS and maximize growth. Neither IDH1 nor IDH2 was necessary for monolayer growth, but deleting either one enhanced mitochondrial ROS and reduced spheroid size, as did deletion of the mitochondrial citrate transporter protein. Together, the data indicate that adaptation to anchorage independence requires a fundamental change in citrate metabolism, initiated by IDH1-dependent reductive carboxylation and culminating in suppression of mitochondrial ROS.

In 'Youngstown Sheet and Tube Co. v. Sawyer', Justice Black wrote that the Constitution limits the President's \"functions in the lawmaking process to the recommending of laws he thinks wise and the vetoing of laws he thinks bad.\" Article II, Section 3 of the Constitution is the source of the President's recommending function, stating that the President \"shall from time to time give to the Congress Information of the State of the Union, and recommend to their Consideration such Measures as he shall judge necessary and expedient . . . .\" Presidents dating back to George Washington have relied on the Recommendations Clause as a positive source of authority to make legislative recommendations to Congress. In an interesting twist, however, recent administrations have also frequently wielded it as a source of negative power to escape statutory requirements to provide information to Congress. Despite a great deal of scholarship and media commentary on executive power and the presidency, the active role of the Recommendations Clause in legislative politics as a source of negative presidential power has gone largely unexplored. This Comment sheds light on this important intersection of constitutional law and interbranch politics.

An important component of the hydrological niche involves the partitioning of water sources, but in landscapes characterized by shallow soils over fractured bedrock, root growth is highly constrained. We conducted a study to determine how physical constraints in the root zone affected the water use of three tree species that commonly coexist on the Edwards Plateau of central Texas; cedar elm (Ulmus crassifolia), live oak (Quercus fusiformis), and Ashe juniper (Juniperus ashei). The year of the study was unusually dry; minimum predawn water potentials measured in August were -8 MPa in juniper, less than -8 MPa in elm, and -5 MPa in oak. All year long, species used nearly identical water sources, based on stable isotope analysis of stem water. Sap flow velocities began to decline simultaneously in May, but the rate of decline was fastest for oak and slowest for juniper. Thus, species partitioned water by time when they could not partition water by source. Juniper lost 15—30 % of its stem hydraulic conductivity, while percent loss for oak was 70—75 %, and 90 % for elm. There was no tree mortality in the year of the study, but 2 years later, after an even more severe drought in 2011, we recorded 34, 14, 6, and 1 % mortality among oak, elm, juniper, and Texas persimmon (Diospyros texana), respectively. Among the study species, mortality rates ranked in the same order as the rate of sap flow decline in 2009. Among the angiosperms, mortality rates correlated with wood density, lending further support to the hypothesis that species with more cavitation-resistant xylem are more susceptible to catastrophic hydraulic failure under acute drought.

Seasonality in surface weather results in seasonal temperature and humidity changes in caves. Ecological and physiological differences among trogloxenes, troglophiles, and troglobionts result in species-dependent responses to this variability. To investigate these responses, we conducted five biological inventories in a marble cave in the Sierra Nevada Range, California, USA between May and December 2010. The cave was divided into six quadrats and temperature was continuously logged in each (humidity was logged at the entrance and in the deep cave). With increasing distance from the entrance, temperature changes were increasingly attenuated and lagged relative to surface temperature. Linear regressions were created to determine the relationship between measured environmental variables and diversity for cavernicoles (troglobionts and troglophiles) and trogloxenes cave- wide and in the transition zone. Diversity for cavernicoles and trogloxenes peaked in the entrance and deep cave zones, respectively. Quadrat, date, 2-week antecedent temperature average, 2-week antecedent temperature range, and trogloxene abundance explained 76% of cavernicole diversity variability. Quadrat explained 55% of trogloxene diversity variability. In the transition zone, trogloxene abundance explained 26% of cavernicole variability and 2-week antecedent temperature and 2-week antecedent temperature range explained 40% of trogloxene variability. In the transition zone, trogloxene diversity was inversely related to 2-week antecedent temperature average and 2-week antecedent temperature range, suggesting that species were moving into the transition zone when temperature was most stable. In a CCA of cavernicoles distribution data and environmental variables, 35% of variation in species-specific distributions was attributable to quadrat, and non-significant percentages were explained by date and environmental variables. Differences in assemblage structure among quadrats were largely due to differences between distributions of trogloxenes and cavernicoles, but responses varied among species. Differences are likely due to ecological niche width, physiological constraints, and competition.

The hoverfly genus Tropidia Meigen, 1822, with the species T. scita (Harris, 1780), is recorded for the first time in the hoverfly fauna of Slovenia. This species was found at Draga ponds near Ig, Slovenia, on the 16th of June, 2024. With this new record, the number of hoverfly species in Slovenia has increased to 363. Rod Tropidia Meigen, 1822 z vrsto T. scita (Harris, 1780) je prvič zabeležen v favni muh trepetavk Slovenije. Ta vrsta je bila najdena 16. junija 2024 na ribnikih v Dragi pri Igu v Sloveniji. S tem novim zapisom se je število vrst muh trepetavk Slovenije povečalo na 363.

Hot drought is a climate phenomenon that has received much attention lately for its potential to disrupt forest function worldwide. A sharp increase in tree mortality associated with this climate pattern is often cast as a disturbance, in which high temperature is responsible for causing exceptional rates of mortality across species. The alternative interpretation is simply that drought kills trees species in a density-dependent manner, related to the water deficit experienced by individual trees. To evaluate the evidence for density-dependent vs. -independent dynamics, we conducted censuses on 30 m × 30 m plots across 30 sites in Ashe juniper (Juniperus ashei) woodlands on the Edwards Plateau of central Texas, USA, 4 years after the hot drought of 2011. We hypothesized that variation in crown mortality of the two most dominant species, Ashe juniper and live oak (Quercus virginiana and Q. fusiformis), could be attributed to tree size, stand density, precipitation amount and/or bedrock depth; factors we considered indicative of density (resource)-dependent dynamics. We further hypothesized that crown mortality in subordinate species and the occurrence of resprouting in trees whose crowns had died would be more strongly controlled by air temperature, vapor pressure deficit, or aspect, acting independently of density. Through model selection analysis, we identified the most parsimonious binomial regression models for crown death in Ashe juniper, live oak and the understory shrub Texas persimmon (Diospyros texana). In Ashe juniper populations, overall crown mortality was 20% and largely followed hypothesized patterns. Live oak had an overall crown mortality rate of 23%, which declined rather than increased with tree density, and no evidence that crown death was linked to atmospheric conditions. Further in support of hypotheses, crown mortality in Texas persimmon and resprouting in Ashe juniper and live oak were significantly affected by exposure to hot and dry conditions and not by density-dependent factors. A surprise finding was the positive effect of bedrock depth on crown mortality. Based on data analysis, we hypothesized that excess precipitation in 2010 was stored in the fractured bedrock below the soil horizon, especially on sites where the soil layer was thin. In the following drought year, this “rock-stored” water rescued larger Ashe juniper trees and live oak trees from crown death, presumably because they had roots in the fractured rock zone.