Direct functionalization of C-H bonds by electrophilic anions.

Alkanes and [B12X12]2- (X = Cl, Br) are both stable compounds which are difficult to functionalize. Here we demonstrate the formation of a boron-carbon bond between these substances in a two-step process. Fragmentation of [B12X12]2- in the gas phase generates highly reactive [B12X11]- ions which spontaneously react with alkanes. The reaction mechanism was investigated using tandem mass spectrometry and gas-phase vibrational spectroscopy combined with electronic structure calculations. [B12X11]- reacts by an electrophilic substitution of a proton in an alkane resulting in a B-C bond formation. The product is a dianionic [B12X11CnH2n+1]2- species, to which H+ is electrostatically bound. High-flux ion soft landing was performed to codeposit [B12X11]- and complex organic molecules (phthalates) in thin layers on surfaces. Molecular structure analysis of the product films revealed that C-H functionalization by [B12X11]- occurred in the presence of other more reactive functional groups. This observation demonstrates the utility of highly reactive fragment ions for selective bond formation processes and may pave the way for the use of gas-phase ion chemistry for the generation of complex molecular structures in the condensed phase.

Mechano-tunable chiral metasurfaces via colloidal assembly.

Dynamic control of circular polarization in chiral metasurfaces is being used in many photonic applications. However, simple fabrication routes to create chiral materials with considerable and fully tunable chiroptical responses at visible and near-infrared wavelengths are scarce. Here, we describe a scalable bottom-up approach to construct cross-stacked nanoparticle chain arrays that have a circular dichroism of up to 11°. Due to their layered design, the strong superchiral fields of the inter-layer region are accessible to chiral analytes, resulting in a tenfold enhanced sensitivity in a chiral sensing proof-of-concept experiment. In situ restacking and local mechanical compression enables full control over the entire set of circular dichroism characteristics, namely sign, magnitude and spectral position. Strain-induced reconfiguration opens up an intriguing route towards actively controlled pixel arrays using local deformation, which fosters continuous polarization engineering and multi-channel detection.

Troubling Aspects of the Trabecular Bone Score Adjustment for the Fracture Risk Assessment Tool (FRAX®).

The Fracture Risk Assessment Tool (FRAX®) is widely used to estimate the 10-year risk of hip fracture and major osteoporotic fracture (MOF, defined as a hip, humerus, wrist, or clinical vertebral fracture). In 2015, McCloskey and colleagues published an adjustment to FRAX® based on the trabecular bone score (TBS). In 2017, the adjustment was updated to use a different calculation for MOF when TBS was measured by Hologic in people assigned male sex at birth. However, this update occurred only on the website hosting FRAX® adjusted for TBS without any corresponding publication of the details of this update or its derivation or validation. In addition to this unpublished update, FRAX® adjusted for TBS also gives impossible results in certain situations, manifesting most clearly in people above a certain age who are at high 10-year risk. Further still, there are inexplicable divergences in the 10-year estimates of hip fracture between the equations published in 2015 and the estimates one obtains if using the website version, which manifest most clearly in people over 80 years old, even at lower 10-year risks. We call on the authors of the TBS adjustment to help the users of FRAX® and FRAX® adjusted for TBS by addressing these matters.

Retention and loss of PIT tags and surgically implanted devices in the Eurasian beaver.

BACKGROUND: Passive integrated transponder devices (PIT tags) are a valuable tool for individual identification of animals. Similarly, the surgical implantation of transmitters and bio-loggers can provide useful data on animal location, physiology and behavior. However, to avoid unnecessary recapture and related stress of study animals, PIT tags and bio-loggers should function reliably for long periods of time. Here, we evaluated the retention of PIT tags, and of very high frequency (VHF) transmitters and bio-loggers that were either implanted subcutaneously or into the peritoneal cavity of Eurasian beavers (Castor fiber). RESULTS: Over a 21-year period, we implanted PIT tags in 456 individuals and failed to detect a PIT tag at recapture in 30 cases, consisting of 26 individuals (6% of individuals). In all instances, we were still able to identify the individual due to the presence of unique ear tag numbers and tail scars. Moreover, we implanted 6 VHFs, 36 body temperature loggers and 21 heart rate loggers in 28 individuals, and experienced frequent loss of temperature loggers (at least 6 of 23 recaptured beavers) and heart rate loggers (10 of 18 recaptured beavers). No VHFs were lost in 2 recaptured beavers. CONCLUSIONS: Possible causes for PIT tag loss (or non-detection) were incorrect implantation, migration of the tag within the body, a foreign body reaction leading to ejection, or malfunctioning of the tag. We speculate that logger loss was related to a foreign body reaction, and that loggers were either rejected through the incision wound or, in the case of temperature loggers, possibly adhered and encapsulated to intestines, and then engulfed by the gastro-intestinal tract and ejected. We discuss animal welfare implications and give recommendations for future studies implanting bio-loggers into wildlife.

Rational design of an argon-binding superelectrophilic anion.

Chemically binding to argon (Ar) at room temperature has remained the privilege of the most reactive electrophiles, all of which are cationic (or even dicationic) in nature. Herein, we report a concept for the rational design of anionic superelectrophiles that are composed of a strong electrophilic center firmly embedded in a negatively charged framework of exceptional stability. To validate our concept, we synthesized the percyano-dodecoborate [B12(CN)12]2-, the electronically most stable dianion ever investigated experimentally. It serves as a precursor for the generation of the monoanion [B12(CN)11]-, which indeed spontaneously binds Ar at 298 K. Our mass spectrometric and spectroscopic studies are accompanied by high-level computational investigations including a bonding analysis of the exceptional B-Ar bond. The detection and characterization of this highly reactive, structurally stable anionic superelectrophile starts another chapter in the metal-free activation of particularly inert compounds and elements.

Tuning the pore structure of templated mesoporous poly(melamine-co-formaldehyde) particles toward diclofenac removal.

The increasing demand and implementation of pharmaceutics poses severe risk to different aquatic species as detectable contaminant in almost every surface water worldwide. Diclofenac (DCF) as one of the most common used analgesics was investigated as contaminant to be removed by adsorption onto nanoporous poly(melamine-co-formaldehyde) (PMF) particles featuring a very high amount of nitrogen functionalities. To achieve a high specific surface area (up to 416 m2/g) and a tunable pore system by hard templating, four different SiO2 nanoparticles were used as template. Differences in the pore formation and achieved pore structure were elucidated. For the first time, the adsorption of DCF onto PMF was tested. In batch adsorption experiments, impactful adsorption capacities as high as 76 µmol/g were achieved and complete removal at initial concentrations of 2 mg/L DCF. Differences in the connectivity and the micropore structure were decisive for uptake in low concentrations and the achieved adsorption capacity, respectively. As the presented PMF particles can be easily synthesized with the monomers formaldehyde and melamine combined with colloidal silica as sacrificial template and water as green solvent, this material presents a viable adsorbent for the removal of DCF at a larger scale. Our study further indicates a high potential for the removal of other pharmaceuticals.

Identification of a Two-Coordinate Iron(I)-Oxalate Complex.

Exotic oxidation states of the first-row transition metals have recently attracted much interest. In order to investigate the oxidation states of a series of iron-oxalate complexes, an aqueous solution of iron(III) nitrate and oxalic acid was studied by infrared free liquid matrix-assisted laser desorption/ionization as well as ionspray mass spectrometry. Here, we show that iron is not only detected in its common oxidation states +II and +III, but also in its unusual oxidation state +I, detectable in both positive-ion and in negative-ion modes, respectively. Vibrational spectra of the gas phase anionic iron oxalate complexes [FeIII (C2 O4 )2 ]- , [FeII (C2 O4 )CO2 ]- , and [FeI (C2 O4 )]- were measured by means of infrared photodissociation spectroscopy and their structures were assigned by comparison to anharmonic vibrational spectra based on second-order perturbation theory.

Host defense or parasite cue: Skin secretions mediate interactions between amphibians and their parasites.

Amphibian skin secretions (substances produced by the amphibian plus microbiota) plausibly act as a first line of defense against parasite/pathogen attack, but may also provide chemical cues for pathogens. To clarify the role of skin secretions in host-parasite interactions, we conducted experiments using cane toads (Rhinella marina) and their lungworms (Rhabdias pseudosphaerocephala) from the range-core and invasion-front of the introduced anurans' range in Australia. Depending on the geographical area, toad skin secretions can reduce the longevity and infection success of parasite larvae, or attract lungworm larvae and enhance their infection success. These striking differences between the two regions were due both to differential responses of the larvae, and differential effects of the skin secretions. Our data suggest that skin secretions play an important role in host-parasite interactions in anurans, and that the arms race between a host and parasite can rapidly generate spatial variation in critical features of that interaction.

Relevance of π-Backbonding for the Reactivity of Electrophilic Anions [B12 X11 ]- (X=F, Cl, Br, I, CN).

Electrophilic anions of type [B12 X11 ]- posses a vacant positive boron binding site within the anion. In a comparatitve experimental and theoretical study, the reactivity of [B12 X11 ]- with X=F, Cl, Br, I, CN is characterized towards different nucleophiles: (i) noble gases (NGs) as σ-donors and (ii) CO/N2 as σ-donor-π-acceptors. Temperature-dependent formation of [B12 X11 NG]- indicates the enthalpy order (X=CN)>(X=Cl)≈(X=Br)>(X=I)≈(X=F) almost independent of the NG in good agreement with calculated trends. The observed order is explained by an interplay of the electron deficiency of the vacant boron site in [B12 X11 ]- and steric effects. The binding of CO and N2 to [B12 X11 ]- is significantly stronger. The B3LYP 0 K attachment enthapies follow the order (X=F)>(X=CN)>(X=Cl)>(X=Br)>(X=I), in contrast to the NG series. The bonding motifs of [B12 X11 CO]- and [B12 X11 N2 ]- were characterized using cryogenic ion trap vibrational spectroscopy by focusing on the CO and N2 stretching frequencies ν C O and ν N 2 , respectively. Observed shifts of ν C O and ν N 2 are explained by an interplay between electrostatic effects (blue shift), due to the positive partial charge, and by π-backdonation (red shift). Energy decomposition analysis and analysis of natural orbitals for chemical valence support all conclusions based on the experimental results. This establishes a rational understanding of [B12 X11 ]- reactivety dependent on the substituent X and provides first systematic data on π-backdonation from delocalized σ-electron systems of closo-borate anions.

Online Monitoring of Isomeric Reaction Intermediates.

Ephemeral intermediates often hold the key to a more detailed understanding of chemical reaction pathways. Online methods to unambiguously identify the structure of such molecular entities, in particular in the presence of multiple isomers, are scarce. This paper presents a methodology that allows real-time monitoring of isomeric solution-phase reaction intermediates of continuous-flow reactions by coupling a microfluidic chip-reactor to a cryogenic ion trap triple mass spectrometer. The technique combines the excellent reaction control associated with microfluidic chips with the unique specificity and sensitivity of infrared photodissociation (IRPD) spectroscopy, which allows for an unambiguous structural assignment of gaseous ions based on their IR fingerprint. It represents a valuable extension to the instrumentation for online-analysis of reactive intermediates and proves particularly valuable whenever the sensitivity of NMR is not sufficient. After a brief description of the experimental approach, illustrative examples are provided to highlight the application of the chip-IRPD setup for mechanistic studies, particularly for stereoselective processes. The article concludes with an outlook on future challenges and perspectives.

Understanding spatio-temporal patterns of deer-vehicle collisions to improve roadkill mitigation.

Vehicles collide with hundreds of thousands of deer on European roads each year. This leads to animal deaths and suffering, economic damage and risks for human safety, making the reduction of road mortality a major field in conservation biology. In order to successfully reduce roadkill, we need improved knowledge regarding spatio-temporal patterns of deer-vehicle collisions (DVCs) on a landscape scale. Here, we analyzed >85,000 DVCs collected over 17 years in Denmark to investigate changes in the number of DVCs over time and to find spatio-temporal patterns of DVC occurrence. We used a use-availability design - originally developed for habitat selection analyses - to compare DVCs involving roe deer (Capreolus capreolus), red deer (Cervus elaphus) and fallow deer (Dama dama) with random road locations on a landscape scale. This approach enabled us to combine temporal (seasonal and diel variation), spatial (land cover, road density and type) and other relevant variables (deer population density, traffic, and deer activity) within the same analysis. We found that factors related to infrastructure and land cover were most important in explaining patterns of DVCs, but seasonal and diel changes, deer activity, and population density were also important in predicting the occurrence of DVCs. Importantly, patterns of DVCs were largely similar between the three deer species, with more DVCs occurring at intermediate traffic density, increasing forest cover, during dusk and dawn, and with increasing deer activity and population density. The strong and consistent patterns found here will allow the development of flexible mitigation measures. We propose that our findings could be used to develop a spatio-temporally flexible warning system for smartphones and navigation systems that is based on existing map providers, making it a widely available and cheap mitigation measure.

Causes and consequences of inverse density-dependent territorial behaviour and aggression in a monogamous mammal.

Territoriality is an important process shaping population dynamics, and the defence of a territory is crucial for individuals to increase the duration of territory occupancy and, consequently, reproductive success. However, little is known about how the frequency of territory intrusions and subsequent territorial behaviours and aggression by territory owners are affected by external factors, such as population density. This is important because it can affect mate change (the replacement of one pair member) and dispersal, a key ecological process. The aim of this study was to investigate the behavioural and spatial response of territory owners to intruder pressure as a function of population density in a territorial, monogamous mammal, the Eurasian beaver (Castor fiber). Using a combination of GPS technology, scent experiments, camera trap data and tail scar observations from an individual-based long-term study, we investigated the factors influencing spatial movement patterns by territory owners in response to a simulated intruder and the factors affecting territory intrusions. We found consistent inverse density-dependent patterns in territorial behaviours and evidence of conspecific aggression. At lower densities, territory owners detected more simulated intrusions, showed more territorial reactions and experienced increased conspecific aggression as indicated by tail scars, suggesting increased intruder pressure. Inverse density-dependent territorial behaviour and aggression suggest a potential mechanistic link between inverse density-dependent natal dispersal and mate change. At low population densities, increased dispersal amplifies intruder pressure, leading to the observed increases in territorial behaviours, conspecific aggression and previously observed mate turnover, which in turn might increase natal dispersal. Our study demonstrates how population density can affect the behaviour and space use of individuals, which is important for territory occupancy and fitness.

Unravelling the configuration of transient ortho-quinone methides by combining microfluidics with gas phase vibrational spectroscopy.

The alkylidene double bond configuration of transient ortho-quinone methides (o-QMs) is studied by cryogenic ion trap vibrational spectroscopy. To this end, o-QMs are formed from ortho-hydroxy benzhydryl alcohols in a Brønsted acid mediated dehydration reaction on a microfluidic chip reactor and the E/Z isomer ratio is determined by comparing the measured gas phase mid-infrared fingerprints with the predicted harmonic spectra from density functional theory calculations. Control over the stereochemistry is achieved by exploiting steric repulsion interactions between the substituents adjacent to the formal double bond of the o-QMs. Attempts to manipulate the ratio of the E- and Z-isomers by varying the reaction conditions were unsuccessful. This observation suggests a low isomerization barrier and hence shorter equilibration times with respect to the on-chip residence time. The fluxional character of the formal double bond is confirmed in 13C-labelling experiments, which reveal a substantially red-shifted CC stretching frequency characteristic for extended, conjugated π-systems.

Direct Observation of Plasmon Band Formation and Delocalization in Quasi-Infinite Nanoparticle Chains.

Chains of metallic nanoparticles sustain strongly confined surface plasmons with relatively low dielectric losses. To exploit these properties in applications, such as waveguides, the fabrication of long chains of low disorder and a thorough understanding of the plasmon-mode properties, such as dispersion relations, are indispensable. Here, we use a wrinkled template for directed self-assembly to assemble chains of gold nanoparticles. With this up-scalable method, chain lengths from two particles (140 nm) to 20 particles (1500 nm) and beyond can be fabricated. Electron energy-loss spectroscopy supported by boundary element simulations, finite-difference time-domain, and a simplified dipole coupling model reveal the evolution of a band of plasmonic waveguide modes from degenerated single-particle modes in detail. In striking difference from plasmonic rod-like structures, the plasmon band is confined in excitation energy, which allows light manipulations below the diffraction limit. The non-degenerated surface plasmon modes show suppressed radiative losses for efficient energy propagation over a distance of 1500 nm.

Joining Microfluidics with Infrared Photodissociation: Online Monitoring of Isomeric Flow-Reaction Intermediates.

A cryogenic ion trap vibrational spectrometer is combined with a microfluidic chip reactor in a proof-of-principle experiment on the Hantzsch cyclization reaction forming 2-amino-4-phenyl thiazole from phenacyl bromide and thiourea. First, the composition of the reaction solution is characterized using electrospray-ionization mass spectrometry combined with two-color infrared photodissociation (IRPD) spectroscopy. The latter yields isomer-specific vibrational spectra of the reaction intermediates and products. A comparison to results from electronic structure calculations then allows for an unambiguous structural assignment and molecular-level insights into the reaction mechanism. Subsequently, we demonstrate that isomeric and isobaric ions can be selectively monitored online with low process time, i.e., using a single IRPD wavelength per isomer, as the chip reaction parameters are varied.

Ultranarrow Second-Harmonic Resonances in Hybrid Plasmon-Fiber Cavities.

We demonstrate second-harmonic generation with ultranarrow resonances in hybrid plasmon-fiber cavities, formed by depositing single-crystalline gold nanorods onto the surface of tapered microfibers with diameters in the range of 1.7-1.8 µm. The localized surface plasmon mode of the single gold nanorod efficiently couples with a whispering gallery mode of the fiber, resulting in a very narrow hybrid plasmon-fiber resonance with a high quality factor Q of up to 250. When illuminated with a tunable 100 fs laser, a sharp SHG peak narrower than half of the spectral width of the impinging laser emerges, superimposed on a broad multiphoton photoluminescence background. The enhancement of the SHG peak of the hybrid system is typically 1000-fold when compared to that of a single gold nanorod alone. Tuning the laser over the hybrid resonance enables second-harmonic spectroscopy and yields an ultranarrow line width as small as 6.4 nm. We determine the second-harmonic signal to rise with the square of the laser power, while the multiphoton photoluminescence background rises with powers between 4 and 6, indicating a very efficient higher-order process. A coupled anharmonic oscillator model is able to describe the linear as well as second-harmonic resonances very well. Our work will open the door to the simultaneous utilization of narrow whispering gallery resonances together with high plasmonic near-field enhancement and should allow for nonlinear sensing and extremely efficient nonlinear light generation from ultrasmall volumes.

DNA-Assembled Plasmonic Waveguides for Nanoscale Light Propagation to a Fluorescent Nanodiamond.

Plasmonic waveguides consisting of metal nanoparticle chains can localize and guide light well below the diffraction limit, but high propagation losses due to lithography-limited large interparticle spacing have impeded practical applications. Here, we demonstrate that DNA-origami-based self-assembly of monocrystalline gold nanoparticles allows the interparticle spacing to be decreased to ∼2 nm, thus reducing propagation losses to 0.8 dB per 50 nm at a deep subwavelength confinement of 62 nm (∼λ/10). We characterize the individual waveguides with nanometer-scale resolution by electron energy-loss spectroscopy. Light propagation toward a fluorescent nanodiamond is directly visualized by cathodoluminescence imaging spectroscopy on a single-device level, thereby realizing nanoscale light manipulation and energy conversion. Simulations suggest that longitudinal plasmon modes arising from the narrow gaps are responsible for the efficient waveguiding. With this scalable DNA origami approach, micrometer-long propagation lengths could be achieved, enabling applications in information technology, sensing, and quantum optics.

Probing the propensity of perchlorate anions for surface solvation by infrared photodissociation spectroscopy.

We investigate the perchlorate anion, ClO4-, microhydrated with up to eight water molecules using infrared photodissociation (IRPD) spectroscopy aided by density functional theory computations. The features observed in the IRPD spectra of D2-tagged ClO4-(H2O)n with n = 0-8 in the O-H stretching (2800-3800 cm-1) and fingerprint (800-1800 cm-1) spectral ranges are assigned to vibrational modes of the solvent, i.e., free and hydrogen-bonded O-H stretching and H2O bending modes, and of the solute, i.e., perchlorate stretching modes. The splitting of the triply degenerate antisymmetric stretching mode in the bare ClO4- (1102 cm-1) upon microhydration directly reports on the symmetry of the local solvation network, while the red-shift of the hydrogen-bonded O-H stretching bands in comparison to those of free O-H oscillators (>3700 cm-1) reflects the strength of the anion-water (3550-3650 cm-1) and water-water (3240-3540 cm-1) hydrogen bonds. The stronger water-water interaction leads to an early onset of water-water hydrogen bond formation (n = 2) and eventually asymmetric solvation of ClO4-, evidenced by the population of the second and third hydration shells at n = 5 and n = 8, respectively, before the first hydration shell is completed. The present study provides a bottom-up view of the initial stages of hydrogen-bond network formation around a high surface propensity anion, and these insights are discussed in the context of recent results obtained for the water-vapor interface of perchlorate solutions.