N-H Bond Dissociation Enthalpies and Facile H Atom Transfers for Early Intermediates of Fe-N and Fe-CN Reductions.

Fe-mediated biological nitrogen fixation is thought to proceed via either a sequence of proton and electron transfer steps, concerted H atom transfer steps, or some combination thereof. Regardless of the specifics and whether the intimate mechanism for N-to-NH conversion involves a distal pathway, an alternating pathway, or some hybrid of these limiting scenarios, Fe-NH intermediates are implicated that feature reactive N-H bonds. Thermodynamic knowledge of the N-H bond strengths of such species is scant, and is especially difficult to obtain for the most reactive early stage candidate intermediates (e.

Sensitivity of El Niño intensity and timing to preceding subsurface heat magnitude.

Despite extensive ongoing efforts on improving the long-term prediction of El Niño-Southern Oscillation, the predictability in state-of-the-art operational schemes remains limited by factors such as the spring barrier and the influence of atmospheric winds. Recent research suggests that the 2014/15 El Niño (EN) event was stalled as a result of an unusually strong basin-wide easterly wind burst in June, which led to the discharge of a large fraction of the subsurface ocean heat. Here we use observational records and numerical experiments to explore the sensitivity of EN to the magnitude of the heat buildup occurring in the ocean subsurface 21 months in advance.

What does recent neuroscience tell us about criminal responsibility?

A defendant is criminally responsible for his action only if he is shown to have engaged in a guilty act- (eg for larceny, voluntarily taking someone else's property without permission)-while possessing a guilty mind- (eg knowing that he had taken someone else's property without permission, intending not to return it)-and lacking affirmative defenses (eg the insanity defense or self-defense). We therefore first review neuroscientific studies that bear on the nature of voluntary action, and so could, potentially, tell us something of importance about the of crimes. Then we look at studies of intention, perception of risk, and other mental states that matter to the of crimes.

The physiology of growth arrest: uniting molecular and environmental microbiology.

Most bacteria spend the majority of their time in prolonged states of very low metabolic activity and little or no growth, in which electron donors, electron acceptors and/or nutrients are limited, but cells are poised to undergo rapid division cycles when resources become available. These non-growing states are far less studied than other growth states, which leaves many questions regarding basic bacterial physiology unanswered. In this Review, we discuss findings from a small but diverse set of systems that have been used to investigate how growth-arrested bacteria adjust metabolism, regulate transcription and translation, and maintain their chromosomes.

A Synthetic Single-Site Fe Nitrogenase: High Turnover, Freeze-Quench (57)Fe Mössbauer Data, and a Hydride Resting State.

The mechanisms of the few known molecular nitrogen-fixing systems, including nitrogenase enzymes, are of much interest but are not fully understood. We recently reported that Fe-N2 complexes of tetradentate P3(E) ligands (E = B, C) generate catalytic yields of NH3 under an atmosphere of N2 with acid and reductant at low temperatures. Here we show that these Fe catalysts are unexpectedly robust and retain activity after multiple reloadings.

An Fe-N₂ Complex That Generates Hydrazine and Ammonia via Fe═NNH₂: Demonstrating a Hybrid Distal-to-Alternating Pathway for N₂ Reduction.

Biological N2 fixation to NH3 may proceed at one or more Fe sites in the active-site cofactors of nitrogenases. Modeling individual e(-)/H(+) transfer steps of iron-ligated N2 in well-defined synthetic systems is hence of much interest but remains a significant challenge. While iron complexes have been recently discovered that catalyze the formation of NH3 from N2, mechanistic details remain uncertain.

Asymmetric copper-catalyzed C-N cross-couplings induced by visible light.

Despite a well-developed and growing body of work in copper catalysis, the potential of copper to serve as a photocatalyst remains underexplored. Here we describe a photoinduced copper-catalyzed method for coupling readily available racemic tertiary alkyl chloride electrophiles with amines to generate fully substituted stereocenters with high enantioselectivity. The reaction proceeds at -40°C under excitation by a blue light-emitting diode and benefits from the use of a single, Earth-abundant transition metal acting as both the photocatalyst and the source of asymmetric induction.

Slip pulse and resonance of the Kathmandu basin during the 2015 Gorkha earthquake, Nepal.

Detailed geodetic imaging of earthquake ruptures enhances our understanding of earthquake physics and associated ground shaking. The 25 April 2015 moment magnitude 7.8 earthquake in Gorkha, Nepal was the first large continental megathrust rupture to have occurred beneath a high-rate (5-hertz) Global Positioning System (GPS) network.

HOLMES: The electron capture decay of [Formula: see text]Ho to measure the electron neutrino mass with sub-eV sensitivity.

The European Research Council has recently funded HOLMES, a new experiment to directly measure the neutrino mass. HOLMES will perform a calorimetric measurement of the energy released in the decay of [Formula: see text]Ho. The calorimetric measurement eliminates systematic uncertainties arising from the use of external beta sources, as in experiments with beta spectrometers.

Realizing the potential of synthetic biology.

Synthetic biology, despite still being in its infancy, is increasingly providing valuable information for applications in the clinic, the biotechnology industry and in basic molecular research. Both its unique potential and the challenges it presents have brought together the expertise of an eclectic group of scientists, from cell biologists to engineers. In this Viewpoint article, five experts discuss their views on the future of synthetic biology, on its main achievements in basic and applied science, and on the bioethical issues that are associated with the design of new biological systems.

Local relative density modulates failure and strength in vertically aligned carbon nanotubes.

Micromechanical experiments, image analysis, and theoretical modeling revealed that local failure events and compressive stresses of vertically aligned carbon nanotubes (VACNTs) were uniquely linked to relative density gradients. Edge detection analysis of systematically obtained scanning electron micrographs was used to quantify a microstructural figure-of-merit related to relative local density along VACNT heights. Sequential bottom-to-top buckling and hardening in stress-strain response were observed in samples with smaller relative density at the bottom.

Higher recovery and better energy dissipation at faster strain rates in carbon nanotube bundles: an in-situ study.

We report mechanical behavior and strain rate dependence of recoverability and energy dissipation in vertically aligned carbon nanotube (VACNT) bundles subjected to quasi-static uniaxial compression. We observe three distinct regimes in their stress-strain curves for all explored strain rates from 4 × 10(-2) down to 4 × 10(-4)/sec: (1) a short initial elastic section followed by (2) a sloped plateau with characteristic wavy features corresponding to buckle formation and (3) densification characterized by rapid stress increase. Load-unload cycles reveal a stiffer response and virtually 100% recoverability at faster strain rates of 0.

Electron cryotomography of bacterial cells.

While much is already known about the basic metabolism of bacterial cells, many fundamental questions are still surprisingly unanswered, including for instance how they generate and maintain specific cell shapes, establish polarity, segregate their genomes, and divide. In order to understand these phenomena, imaging technologies are needed that bridge the resolution gap between fluorescence light microscopy and higher-resolution methods such as X-ray crystallography and NMR spectroscopy. Electron cryotomography (ECT) is an emerging technology that does just this, allowing the ultrastructure of cells to be visualized in a near-native state, in three dimensions (3D), with "macromolecular" resolution (approximately 4nm).

Analysis of the performance of the software/hardware product MyDiaBase+RxChecker for assessing treatment regimens.

In 2008, the Action to Control Cardiovascular Risk in Diabetes trial was halted due to an unexpected number of deaths in the intensive treatment group (aiming for hemoglobin A1c levels less than 6%). Hypoglycemic episodes were thought by some to be a contributing cause, underscoring again the challenge of maintaining tight control while avoiding dangerous excursions into hypoglycemic territory. Albisser and colleagues present a set of articles in this issue of Journal of Diabetes Science and Technology that describe a clinical product developed specifically for this timeless clinical conundrum.

Computational models of heart pumping efficiencies based on contraction waves in spiral elastic bands.

We present a framework for modeling biological pumping organs based on coupled spiral elastic band geometries and active wave-propagating excitation mechanisms. Two pumping mechanisms are considered in detail by way of example: one of a simple tube, which represents a embryonic fish heart and another more complicated structure with the potential to model the adult human heart. Through finite element modeling different elastic contractions are induced in the band.

The social brain: neural basis of social knowledge.

Social cognition in humans is distinguished by psychological processes that allow us to make inferences about what is going on inside other people-their intentions, feelings, and thoughts. Some of these processes likely account for aspects of human social behavior that are unique, such as our culture and civilization. Most schemes divide social information processing into those processes that are relatively automatic and driven by the stimuli, versus those that are more deliberative and controlled, and sensitive to context and strategy.

Physiology in phylogeny: modeling of mechanical driving forces in cardiac development.

This article explores the heart phylogeny, the development of the heart from embryonic to adult shape. For the shape change from tubular to four-chamber to be initiated, a mechanical twist needs to be present in the embryonic heart tube. The helical shape of the muscle fibers in the embryonic heart is a necessary but not a sufficient condition for the transformation to occur.

Nonequilibrium phase transitions in cuprates observed by ultrafast electron crystallography.

Nonequilibrium phase transitions, which are defined by the formation of macroscopic transient domains, are optically dark and cannot be observed through conventional temperature- or pressure-change studies. We have directly determined the structural dynamics of such a nonequilibrium phase transition in a cuprate superconductor. Ultrafast electron crystallography with the use of a tilted optical geometry technique afforded the necessary atomic-scale spatial and temporal resolutions.

An inward-facing conformation of a putative metal-chelate-type ABC transporter.

The crystal structure of a putative metal-chelate-type adenosine triphosphate (ATP)-binding cassette (ABC) transporter encoded by genes HI1470 and HI1471 of Haemophilus influenzae has been solved at 2.4 angstrom resolution. The permeation pathway exhibits an inward-facing conformation, in contrast to the outward-facing state previously observed for the homologous vitamin B12 importer BtuCD.

Laboratory earthquakes along inhomogeneous faults: directionality and supershear.

We report on the experimental observation of spontaneously nucleated ruptures occurring on frictionally held bimaterial interfaces with small amounts of wave speed mismatch. Rupture is always found to be asymmetric bilateral. In one direction, rupture always propagates at the generalized Rayleigh wave speed, whereas in the opposite direction it is subshear or it transitions to supershear.

Laboratory earthquakes: the sub-Rayleigh-to-supershear rupture transition.

We report on the experimental observation of spontaneously nucleated supershear rupture and on the visualization of sub-Rayleigh-to-supershear rupture transitions in frictionally held interfaces. The laboratory experiments mimic natural earthquakes. The results suggest that under certain conditions supershear rupture propagation can be facilitated during large earthquake events.

Role of predicted metalloprotease motif of Jab1/Csn5 in cleavage of Nedd8 from Cul1.

COP9 signalosome (CSN) cleaves the ubiquitin-like protein Nedd8 from the Cul1 subunit of SCF ubiquitin ligases. The Jab1/MPN domain metalloenzyme (JAMM) motif in the Jab1/Csn5 subunit was found to underlie CSN's Nedd8 isopeptidase activity. JAMM is found in proteins from archaea, bacteria, and eukaryotes, including the Rpn11 subunit of the 26S proteasome.

Receptor-mediated endocytosis of poly(acrylic acid)-conjugated liposomes by macrophages.

The uptake characteristics of negatively-charged liposomes made by conjugation of poly(acrylic acid) (PAA) were studied with respect to cultured RAW macrophages. The PAA-conjugated liposomes were internalized and digested in an acidic compartment at a much faster rate than the unmodified phosphatidylcholine (PC) liposomes. After incubation for 18 h, an over 5-fold increase in the uptake of PC liposomes was obtained by PAA conjugation.