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Molecular scaffolds that enable the combinatorial synthesis of new supramolecular building blocks are promising targets for the construction of functional molecular systems. Here, we report a supramolecular scaffold based on boroxine that enables the formation of chiral and ordered 1D supramolecular polymers, which can be easily functionalized for circularly polarized luminescence. The boroxine monomers are quantitatively synthesized in situ, both in bulk and in solution, from boronic acid precursors and cooperatively polymerize into 1D helical aggregates stabilized by threefold hydrogen‐bonding and π–π stacking. We then demonstrate amplification of asymmetry in the co‐assembly of chiral/achiral monomers and the co‐condensation of chiral/achiral precursors in classical and in situ sergeant‐and‐soldiers experiments, respectively, showing fast boronic acid exchange reactions occurring in the system. Remarkably, co‐condensation of pyrene boronic acid with a hydrogen‐bonding chiral boronic acid results in chiral pyrene aggregation with circularly polarized excimer emission and g‐values in the order of 10−3. Yet, the electron deficiency of boron in boroxine makes them chemically addressable by nucleophiles, but also sensitive to hydrolysis. With this sensitivity in mind, we provide first insights into the prospects offered by boroxine‐based supramolecular polymers to make chemically addressable, functional, and adaptive systems. [ABSTRACT FROM AUTHOR]

Despite the widespread use of microscopy techniques to characterize supramolecular polymers, the role of surfaces in the formation of these structures is unclear. Here we describe the epitaxial growth of intriguing 2D crystals of alkyl benzene‐1,3,5‐triscarboxamides formed by competitive attractive interactions with the mica surface. In contrast to the fibrous structure observed in apolar diluted solution, five‐fold twinned crystals or ribbon‐like structures are obtained on the mica surface. Moreover, these structures are still dynamic on the surface, being able to reorganize during the atomic force microscopy measurements. This work demonstrates that surface‐monomer interactions can be exploited to modulate the structure of 1D supramolecular polymers into 2D crystals. [ABSTRACT FROM AUTHOR]

Here, we report on the synthesis of discrete oligomers of alkyl‐bridged naphthalenediimides (NDIs) and study their molecular nanostructures both in bulk, in solution, and at the liquid‐solid interface. Via an iterative synthesis method, multiple NDI cores were bridged with short and saturated alkyl‐diamines (C3 and C12) or long and unsaturated alkyl‐diamines (u2C33 to u8C100) at their imide termini. The strong intermolecular interaction between the NDI cores was observed by probing their photophysical properties in solution. In bulk, the discrete NDI oligomers preferentially ordered in lamellar morphologies, irrespective of whether a saturated or unsaturated spacer was employed. Moreover, both the molecular architecture as well as the crystallization conditions play a significant role in the nanoscale ordering. The long unsaturated alkyl chains lead preferably to folded‐chain conformations while their saturated analogues form stretched arrangements. At the solution‐solid interface, well‐defined lamellar regions were observed. These results show that precision in chemical structure alone is not sufficient to reach well‐defined structures of discrete oligomers, but that it must be combined with precision in processing conditions. [ABSTRACT FROM AUTHOR]

Supramolecular copolymers have typically been studied in the extreme cases, such as self‐sorting or highly mixed copolymer systems, while the intermediate systems have been less understood. We have reported the temperature‐dependent microstructure in copolymers of triazine‐ and benzene‐derivatives based on charge‐transfer interactions with a highly alternating microstructure at low temperatures. Here, we investigate the temperature‐dependent copolymerization further and increase the complexity by combining triazine‐ and benzene‐derivatives with opposite preferred helicities. In this case, intercalation of the benzene‐derivative into the triazine‐derivative assemblies causes a helical inversion. The inversion of the net helicity was rationalized by comparing the mismatch penalties of the individual monomers, which indicated that the benzene‐derivative dictates the helical screw‐sense of the supramolecular copolymers. Surprisingly, this was not reflected in further investigations of slightly modified triazine‐ and benzene‐derivatives, thus highlighting that the outcome is a subtle balance between structural features, where small differences can be amplified due to the competitive nature of the interactions. Overall, these findings suggest that the temperature‐dependent microstructure of triazine‐ and benzene‐based supramolecular copolymers determines the copolymer helicity of the presented system in a similar way as the mixed majority‐rules phenomenon. [ABSTRACT FROM AUTHOR]

Having external control over fundamental properties of polymers, such as their physical state, is a crucial yet challenging design criterion for smart materials. Liquifying polymers through photochemical events has significantly advanced various research lines. However, the opposite process of solidifying a polymer that is intrinsically in a liquid state reversibly with light is unattained. Herein, the light‐controlled liquid‐to‐solid transition of polysiloxanes is reported, which are decorated with a small number of azobenzene‐functionalized ureidopyrimidinone (Azo‐UPy) pendants. The UPy moieties toggle between intra‐ and intermolecular hydrogen bonding via trans→cis photoisomerization of the azobenzene. This transformation on the molecular level leads to the formation of strong supramolecular cross‐links, which, in turn, results in the macroscopic solidification of the material. The photoswitching event enables the post‐synthetic tailoring of the polymers' mechanical properties, thus providing an alternative to the addition of plasticizers or hardeners. Moreover, the adhesion strength of the photochromic material increases by a factor of 6 upon exposure to UV light. In situ illumination during rheological measurements reveals the delicate interplay between wavelength dependent penetration depth and photoswitching efficiency. This conceptually new (de)bonding on demand strategy paves the way for creating light‐responsive materials with exciting applications in temporal adhesion, recycling, lithography, and material processing. [ABSTRACT FROM AUTHOR]

When irradiating a molecular material containing photo‐isomerizable groups with pure circularly polarized light, a particular handedness may get imprinted into the material. To study the mechanism and kinetics of this process in situ and operando, we have developed a new chiroptical tool where the circular polarization of the incident circularly polarized light is monitored after transmission through the photoactive layer. Practical limits to the resolution and sensitivity of the measurements as well as its calibration are discussed. To aid interpretation of experimental results, we present kinetic Monte Carlo simulations on a model for the active material involving photo‐induced reorientation of molecules in a cholesteric organization. The simulations support the interpretation of a transient minimum in the degree of circular polarization of the transmitted light in terms of a nematic transient state during photo‐inversion of a cholesteric organization in the molecular material. [ABSTRACT FROM AUTHOR]

The desire to construct complex molecular systems is driven by the need for technological (r)evolution and our intrinsic curiosity to comprehend the origin of life. Supramolecular chemists tackle this challenge by combining covalent and noncovalent reactions leading to multicomponent systems with emerging complexity. However, this synthetic strategy often coincides with difficult preparation protocols and a narrow window of suitable conditions. Here, we report on unsuspected observations of our group that highlight the impact of subtle "irregularities" on supramolecular systems. Based on the effects of pathway complexity, minute amounts of water in organic solvents or small impurities in the supramolecular building block, we discuss potential pitfalls in the study of complex systems. This article is intended to draw attention to often overlooked details and to initiate an open discussion on the importance of reporting experimental details to increase reproducibility in supramolecular chemistry. [ABSTRACT FROM AUTHOR]

The combination of covalent and non‐covalent synthesis is omnipresent in nature and potentially enables access to new materials. Yet, the fundamental principles that govern such a synthesis are barely understood. Here, we demonstrate how even simple reaction mixtures behave surprisingly complex when covalent reactions are coupled to self‐assembly processes. Specifically, we study the reaction behavior of a system in which the in situ formation of discotic benzene‐1,3,5‐tricarboxamide (BTA) monomers is linked to an intertwined non‐covalent reaction network including self‐assembly into helical BTA polymers. This system shows an unexpected phase‐separation behavior in which an interplay of reactant/product concentrations, side‐products and solvent purity determines the system composition. We envision that these insights can bring us one step closer to how to design the synthesis of systems in a combined covalent/non‐covalent fashion. [ABSTRACT FROM AUTHOR]

Control over molecular motion is facilitated in materials with highly ordered nanoscale structures. Here we report on the fabrication of cholesteric liquid‐crystal networks by circularly polarized light irradiation, without the need for chiral dopant or plasticizer. The polymer network is obtained by photopolymerization of a smectic achiral diacrylate mesogen consisting of an azobenzene core and discrete oligodimethylsiloxane tails. The synchronous helical photoalignment and photopolymerization originate from the cooperative movement of the mesogens ordered in well‐defined responsive structures, together with the flexibility of the oligodimethylsiloxane blocks. The resulting thin films show excellent thermal stability and light‐induced memory features with reversible responses. Additionally, we demonstrate the fabrication of photo‐patterned films of liquid‐crystal networks with opposite helical senses. These findings provide a new method to make light‐controllable chiroptical materials with exciting applications in optics and photonics. [ABSTRACT FROM AUTHOR]

Ethylene/1‐olefin copolymers made with supported metallocenes in slurry or gas‐phase polymerization are often less homogeneous than those made with the same unsupported metallocene in solution polymerization. In particular, their molecular weight distributions are broader, having polydispersities higher than two, and sometimes their chemical composition distributions may even be bimodal. In our previous publication, we developed a mathematical model to describe the polymerization kinetics and polymer microstructure of ethylene homopolymers made with a supported metallocene catalyst. In this article, we extended that model to also cover the copolymerization of ethylene and 1‐hexene with the same supported catalyst. The copolymerizations are performed in parallel semibatch reactors using a metallocene catalyst supported on an inorganic porous carrier. 1‐Hexene concentration and polymerization time are the factors changed to investigate this system. Modeling results show that, as for the ethylene homopolymerization case, a three‐site model is needed to describe the molecular weight distributions of the copolymers, but their chemical compositions can be described with a single set of reactivity ratios. A single set of parameters is also enough to describe the copolymerization kinetics with this supported catalyst. A new method is also developed and tested to estimate reactivity ratios under composition drift in this article. [ABSTRACT FROM AUTHOR]

During the XIXth century, France has been the theater of many discoveries in stereochemistry thanks to prestigious physicists, chemists, and crystallographers. Among them, Louis Pasteur is certainly the father of molecular chirality (the so‐called molecular dissymmetry), and because of the exceptionally favored conditions of his famous discovery on the resolution of tartrates, his findings have often been attributed to serendipity. But let us not forget that "in the fields of observation, chance only favors the prepared minds." [ABSTRACT FROM AUTHOR]

Recent investigations of supramolecular polymers based on chiral triphenylene‐2,6,10‐tricarboxamides (TTAs) showed how temperature‐induced changes in solvation can greatly influence the preferred helical conformation of the supramolecular polymers formed. Here, we combine chiral TTA with achiral copolymerization partners to further investigate temperature‐dependent solvation effects. Systematic variation of the system's composition shows clear impacts on the temperature window where the conformational change occurs. Further, simple chain length variations in the achiral comonomer greatly affect the ability to influence the conformational change in the copolymer, while the differences in the properties of the individual homopolymers are rather small. We herein highlight how subtle changes in the monomers can impact the observed copolymer properties drastically; an effect arising from the emerging complexity of multicomponent interactions in supramolecular copolymers with solvent‐solute interactions being more important than typically thought. [ABSTRACT FROM AUTHOR]

Despite the renewed interest in ion implantation doping of GaN, efficient electrical activation remains a challenge. The lattice location of 27Mg is investigated in GaN of different doping types as a function of implantation temperature and fluence at CERN's ISOLDE facility. The amphoteric nature of Mg is elucidated, i.e., the concurrent occupation of substitutional Ga and interstitial sites: following room temperature ultra‐low fluence (≈2 × 1010 cm−2) implantation, the interstitial fraction of Mg is highest (20–24%) in GaN pre‐doped with stable Mg during growth, and lowest (2–6%) in n‐GaN:Si, while undoped GaN shows an intermediate interstitial fraction of 10–12%. Both for p‐ and n‐GaN prolonged implantations cause interstitial 27Mg to approach the levels found for undoped GaN. Implanting above 400 °C progressively converts interstitial Mg to substitutional Ga sites due to the onset of Mg interstitial migration (estimated activation energy 1.5–2.3 eV) and combination with Ga vacancies. In all sample types, implantations above a fluence of 1014 cm−2 result in >95% substitutional Mg. Ion implantation is hence a very efficient method to introduce Mg into substitutional Ga sites, i.e., challenges toward high electrical activation of implanted Mg are not related to lack of substitutional incorporation. [ABSTRACT FROM AUTHOR]

The correlation between molecular structure and mechanism of supramolecular polymerizations is a topic of great interest, with a special focus on the pathway complexity of porphyrin assemblies. Their cooperative polymerization typically yields highly ordered, long 1D polymers and is driven by a combination of π‐stacking due to solvophobic effects and hydrogen bonding interactions. Subtle changes in molecular structure, however, have significant influence on the cooperativity factor and yield different aggregate types (J‐ versus H‐aggregates) of different lengths. In this study, the influence of amide connectivity on the self‐assembly behavior of porphyrin‐based supramolecular monomers was investigated. While in nonpolar solvents, C=O centered monomers readily assemble into helical supramolecular polymers via a cooperative mechanism, their NH centered counterparts form short, non‐helical J‐type aggregates via an isodesmic pathway. A combination of spectroscopy and density functional theory modelling sheds light on the molecular origins causing this stunning difference in assembly properties and demonstrates the importance of molecular connectivity in the design of supramolecular systems. Finally, their mutual interference in copolymerization experiments is presented. [ABSTRACT FROM AUTHOR]

The understanding and the application of reversible covalent reactions and coordination chemistry together with the proper design of the molecular frameworks, allow to achieve not only well‐defined output architectures but also different grades of complex behavior. In this work, the dynamic nature of the helical systems offers an additional level of complexity by combining self‐sorting on two levels: 1) the build‐up of the ligand strand constituents from their components through dynamic covalent chemistry; 2) the assembly of the helicates from the ligands and the metal cations through dynamic metallo‐supramolecular chemistry. The information encoded in the ligands constituent molecule was read differently (and accurately at the same time) by metal cations that varied in the coordination algorithms. It enabled the selective formation of a specific type of helicates from a wide library of helicates formed by the possible combination of subcomponents. Ligands containing dynamic tridentate and/or bidentate binding motifs in the same strand were studied to explore the helicates self‐assembly with appropriate metal cations. [ABSTRACT FROM AUTHOR]

The design and the characterization of supramolecular additives to control the chain length of benzene‐1,3,5‐tricarboxamide (BTA) cooperative supramolecular polymers under thermodynamic equilibrium is unraveled. These additives act as chain cappers of supramolecular polymers and feature one face as reactive as the BTA discotic to interact strongly with the polymer end, whereas the other face is nonreactive and therefore impedes further polymerization. Such a design requires fine tuning of the conformational preorganization of the amides and the steric hindrance of the motif. The chain cappers studied are monotopic derivatives of BTA, modified by partial N‐methylation of the amides or by positioning of a bulky cyclotriveratrylene cage on one face of the BTA unit. This study not only clarifies the interplay between structural variations and supramolecular interactions, but it also highlights the necessity to combine orthogonal characterization methods, spectroscopy and light scattering, to elucidate the structures and compositions of supramolecular systems. [ABSTRACT FROM AUTHOR]

The supramolecular folding of amphiphilic heterograft copolymers equipped with dendritic pendants is investigated using a combination of proton nuclear magnetic resonance (1H NMR) spectroscopy, small‐angle X‐ray scattering, and circular dichroism spectroscopy. Hereto, the linear poly(ethylene glycol) pendants normally used to convey water compatibility are partially substituted with branched analogues. For one set of copolymers, second‐generation polyglycerol dendrons are directly attached to the polymer backbone, while for the other a hydrophilic linker is placed in between. The results show that the branching of the hydrophilic pendants affects the local structure of the folded copolymer but does not influence the overall conformation and single‐chain character of the folded copolymers in solution. All copolymers fold into 4–5 nm single‐chain polymeric nanoparticles with a very compact spherical morphology, independent of the dendritic content of the copolymer. Intriguingly, the incorporation of the dendritic pendants affects the formation of a structured interior even at low incorporation ratios. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 411–421 The supramolecular folding of amphiphilic heterograft copolymers equipped with dendritic pendants is investigated. Hereto, the linear poly(ethylene glycol) pendants normally used to convey water‐compatibility are partially substituted with branched analogues. The results show that the branching of the hydrophilic pendants affects the local structure of the folded copolymer but does not influence the overall conformation and single‐chain character of the folded copolymers in solution. [ABSTRACT FROM AUTHOR]

Abstract: The first three insertion steps of propylene for isoselective metallocenes from the one‐carbon‐bridged cyclopentadienyl–fluorenyl {Cp/Flu} and silicon‐bridged ansa‐bis(indenyl) {SBI} families were computed by using a theoretical method implementing the B3PW91 functional in combination with solvent corrections incorporated with the Solvation Model based on Density (SMD) continuum model. For C1‐symmetric {Cp/Flu}‐type metallocenes, two mechanisms of stereocontrol were validated theoretically: more facile and more stereoselective chain “stationary” insertion (or site epimerization backskip) and less stereoselective alternating mechanisms. For the C2‐symmetric {SBI}‐type system, the computation results were in complete agreement with the sole operating chain migratory insertion mechanism. The thermochemical data obtained through the study were used to predict microstructures of polypropylenes by using three‐parameter and one‐parameter statistical models for the two metallocene systems, respectively. The calculated meso/rac pentad distributions were found to be in good agreement with those determined experimentally for isotactic polypropylene samples obtained at different polymerization temperatures. [ABSTRACT FROM AUTHOR]

ABSTRACT: Liquid crystal polymer networks (LCNs) lead the research geared toward macroscopic motion of materials. These actuators are molecularly programed to adapt their shape in response to external stimuli. Non‐photo‐responsive thin films of LCNs covered with heat absorbers (e.g., graphene or ink) are shown to continuously oscillate when exposed to light. The motion is governed by the heat dissipated at the film surface and the anisotropic thermal deformation of the network. The influence of the LC molecular alignment, the film thickness, and the LC matrix on the macroscopic motion is analyzed to probe the limits of the system. The insights gained from these experiments provide not only guidelines to create actuators by photo‐thermal or pure photo‐effects but also a simple method to generate mechanical oscillators for soft robotics and automated systems. © 2018 The Authors. Journal of Polymer Science Part A: Polymer Chemistry Published by Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 1331–1336 [ABSTRACT FROM AUTHOR]

Summary: In trans persons on gender‐affirming hormonal treatment, a decrease (in trans women) or increase (in trans men) in hematocrit is often observed. Reference ranges for evaluation of hematocrit levels in trans persons have not been established. This prospective cohort study is part of the European Network for the Investigation of Gender Incongruence (ENIGI). At the Ghent and Amsterdam sites, we included 625 hormone‐naïve trans persons. Gender‐affirming hormonal treatment was initiated at the first visit. In trans men, serum hematocrit (Hct) levels increased during the first year (+4.9 Hct %, 95% CI 3.82–5.25), with the most pronounced increase during the first 3 months (+2.7 Hct %, 95% CI 1.94–3.29). Trans men receiving testosterone esters had a larger increase in serum hematocrit levels compared to trans men receiving testosterone undecanoate (Δ 0.8 Hct %). Of 192 trans men, 22 (11.5%) developed serum hematocrit levels ≥50.0%. Trans men on testosterone undecanoate were less likely to develop hematocrit levels ≥50% or ≥52%, compared to trans men on testosterone esters, and were less likely to develop hematocrit levels ≥50%, compared to trans men on testosterone gel. In trans women, serum hematocrit had dropped by 4.1 Hct % (95% CI 3.50–4.37) after 3 months, after which only small decreases were observed. In conclusion, serum hematocrit levels can be found in the reference range of the perceived gender as from 3 months after the initiation of gender‐affirming hormonal treatment. [ABSTRACT FROM AUTHOR]

Materials with highly ordered molecular arrangements have the capacity to display unique properties derived from their nanoscale structure. Here, the synthesis and characterization of azobenzene (AZO)-functionalized siloxane oligomers of discrete length that form photoswitchable supramolecular materials are described. Specifically, synergy between phase segregation and azobenzene crystallization leads to the self-assembly of an exfoliated 2D crystal that becomes isotropic upon photoisomerization with UV light. Consequently, the material undergoes a rapid athermal solid-to-liquid transition which can be reversed using blue light due to the unexpectedly fast 2D crystallization that is facilitated by phase segregation. In contrast, enabling telechelic supramolecular polymerization through hydrogen bonding inhibits azobenzene crystallization, and nanostructured pastes with well-ordered morphologies are obtained based on phase segregation alone, thus demonstrating block copolymer-like behavior. Therefore, by tailoring the balance of self-assembly forces in the azobenzene-functionalized siloxane oligomers, fast and reversible phase-changing materials can be engineered with various mechanical properties for applications in photolithography or switchable adhesion to lubricant properties. [ABSTRACT FROM AUTHOR]

We report on the fabrication of a rewritable and reprogrammable dual-photoresponsive liquid crystalline-based actuator containing an azomerocyanine dye that can be locally converted into the hydroxyazopyridinium form by acid treatment. Each dye absorbs at a different wavelength giving access to programmable actuators, the folding of which can be controlled by using different colors of light. The acidic patterning is reversible and allows the erasing and rewriting of patterns in the polymer film, giving access to reusable, adjustable soft actuators. [ABSTRACT FROM AUTHOR]

The present paper focuses on the study of the effectiveness of the sacrificial cladding using polymeric foam as crushable core to reduce the delivered blast energy using a simplified structure. The latter consists of a simply supported steel beam under a localized blast load. The tested sacrificial cladding has a cross-sectional area of 80 × 80 mm2. The effect of the front plate mass and the crushable core properties (plateau stress and thickness) is studied. Three polymeric foams are investigated: (a) the expanded polystyrene foam (PS13) with a density of 13 kg/m3, (b) the closed-cell polyurethane (PU30) with a density of 30 kg/m3, and (c) the open-cell polyurethane (PU50) with a density of 50 kg/m3. Four front plate masses are used: 144, 188, 336, and 495 g. All possible combinations are tested to determine their absorption capacity. The obtained results show that the absorption capability increases by increasing the front plate mass, the plateau stress, and the thickness of the crushable core. The open-cell polyurethane PU50 performs better. Disintegration problems are observed on the expanded polystyrene PS13 after the end of the compression process. [ABSTRACT FROM AUTHOR]

We report the case of a patient on chronic hemodialysis treatment with paroxysms of severe arterial hypertension accompanied by tachycardia, pallor, sweating and tremor. Measurement of plasma catecholamines revealed norepinephrine level of 4625 pg/mL (reference range 191-225 pg/mL), epinephrine level of 1035 pg/mL (58-76 pg/mL) and dopamine level of 148 pg/mL (50-100 pg/mL). MRI showed a left adrenal mass of 2 cm. After the patient was started on an alpha-1 adrenergic receptor blocker, she underwent a left adrenalectomy. Anatomopathological examination confirmed the diagnosis of pheochromocytoma. Although urinary testing is not possible in anuric hemodialysis patients, diagnosis of pheochromocytoma can be made through measurement of plasma free metanephrines and/or plasma catecholamines. [ABSTRACT FROM AUTHOR]

A diffuse reflectance infrared Fourier-transform (DRIFT) study has been conducted at 373 K and 1 bar on an industrial Cr/Ti/SiO2 Phillips-type catalyst modified with, and without, triethylaluminium (TEAl) as co-catalyst. The reaction rate of the polymerization of ethylene, as monitored by the increase in the methylene stretching band of the growing polyethylene (PE), has been investigated as a function of the titanium content. After an initial period of mixed kinetics, with the reaction rate significantly higher for the TEAl-modified catalysts compared with the non-modified catalysts, the polymerization proceeded as a pseudo-zero-order reaction with a reaction rate that increased as a function of titanium loading. Furthermore, it was found that the higher Ti loading caused the appearance of more acidic hydroxyl groups and modified the Cr sites by making them more Lewis acidic, ultimately shortening the induction time and increasing the initial polymerization rate. [ABSTRACT FROM AUTHOR]

Multiferroic superlattices consisting of 15 double layers BaTiO3-BiFeO3 show a very high magnetoelectric voltage coefficient αME of up to 49 V cm−1 Oe−1 at 300 K, measured at 1 kHz with zero direct current (DC) bias magnetic field. However, the microscopic origins of such high αME values, and the temperature and DC magnetic field dependencies of αME are not understood up to now. Therefore, in this study two superlattices grown at high/low oxygen partial pressures having high/low αME values, respectively, are compared. While at high growth pressure the strain contrast in high-resolution transmission electron microscopy images is limited to few layers at the substrate interface, the low-pressure sample shows much more pronounced microstrain. This is additionally visualized in Fourier transformed images, and the out-of-plane lattice parameter of the single BaTiO3 layer is increased near the interface. In addition to a low density of oxygen vacancies, it seems to be important to avoid micromechanical clamping of the 2D single-phase nanolayers of the multiferroic BaTiO3-BiFeO3 superlattices to achieve high magnetoelectric coupling. [ABSTRACT FROM AUTHOR]

The functionality and electronic properties of metal/ferroelectric systems rely heavily on the chemical and structural properties of the interface. The isotope sensitive technique of nuclear resonant scattering is used to selectively study the chemistry and magnetic state of the Fe/BaTiO3 interface. An electric polarity-dependent modification of the metal/ferroelectric oxide interface has been systematically observed. The results show that the interface can be oxidized or reduced by inverting the polarity of the electric field applied across the interface above a threshold field value of ±400 kV m−1. Remarkably, the final interface state depends on the polarization history of the system. Based on these results, a model for the electric field induced ion transport at the Fe/BaTiO3 interface has been suggested. Such subtle structural changes at the interface deteriorate the magnetoelectric coupling. However, for certain applications where an oxide layer is required at metal/ferroelectric oxide interfaces, the electric fields can be used to control interdiffusion processes. [ABSTRACT FROM AUTHOR]

A triethylaluminium(TEAl)-modified Phillips ethylene polymerisation Cr/Ti/SiO2 catalyst has been developed with two distinct active regions positioned respectively in the inner core and outer shell of the catalyst particle. DRIFTS, EPR, UV-Vis-NIR DRS, STXM, SEM-EDX and GPC-IR studies revealed that the catalyst produces simultaneously two different polymers, i.e., low molecular weight linear-chain polyethylene in the Ti-abundant catalyst particle shell and high molecular weight short-chain branched polyethylene in the Ti-scarce catalyst particle core. Co-monomers for the short-chain branched polymer were generated in situ within the TEAl-impregnated confined space of the Ti-scarce catalyst particle core in close proximity to the active sites that produced the high molecular weight polymer. These results demonstrate that the catalyst particle architecture directly affects polymer composition, offering the perspective of making high-performance polyethylene from a single reactor system using this modified Phillips catalyst. [ABSTRACT FROM AUTHOR]

The displacement of molecular structures from their thermodynamically most stable state by imposition of various types of electronic and conformational constraints generates highly strained entities that tend to release the accumulated strain energy by undergoing either structural changes or chemical reactions. The latter case amounts to strain-induced reactivity (SIR) that may enforce specific chemical transformations. A particular case concerns dynamic covalent chemistry which may present SIR, whereby reversible reactions are activated by coupling to a high-energy state. We herewith describe such a dynamic covalent chemical (DCC) system involving the reversible imine formation reaction. It is based on the formation of strained macrocyclic bis-imine metal complexes in which the macrocyclic ligand is in a high energy form enforced by the coordination of the metal cation. Subsequent demetallation generates a highly strained free macrocycle that releases its accumulated strain energy by hydrolysis and reassembly into a resting state. Specifically, the metal-templated condensation of a dialdehyde with a linear diamine leads to a bis-imine [1+1]-macrocyclic complex in which the macrocyclic ligand is in a coordination-enforced strained conformation. Removal of the metal cation by a competing ligand yields a highly reactive [1+1]-macrocycle, which then undergoes hydrolysis to transient non-cyclic aminoaldehyde species, which then recondense to a strain-free [2+2]-macrocyclic resting state. The process can be monitored by 1H NMR spectroscopy. Energy differences between different conformational states have been evaluated by Hartree-Fock (HF) computations. One may note that the stabilisation of high-energy molecular forms by metal ion coordination followed by removal of the latter, offers a general procedure for producing out-of-equilibrium molecular states, the fate of which may then be examined, in particular when coupled to dynamic covalent chemical processes. [ABSTRACT FROM AUTHOR]

ABSTRACT A homozygous missense mutation (c.822 G> C) was found in the gene encoding the mitochondrial asparaginyl-t RNA synthetase ( NARS2) in two siblings born to consanguineous parents. These siblings presented with different phenotypes: one had mild intellectual disability and epilepsy in childhood, whereas the other had severe myopathy. Biochemical analysis of the oxidative phosphorylation ( OXPHOS) complexes in both siblings revealed a combined complex I and IV deficiency in skeletal muscle. In-gel activity staining after blue native-polyacrylamide gel electrophoresis confirmed the decreased activity of complex I and IV, and, in addition, showed the presence of complex V subcomplexes. Considering the consanguineous descent, homozygosity mapping and whole-exome sequencing were combined revealing the presence of one single missense mutation in the shared homozygous region. The c.822 G> C variant affects the 3′ splice site of exon 7, leading to skipping of the whole exon 7 and a part of exon 8 in the NARS2 m RNA. In EBV-transformed lymphoblasts, a specific decrease in the amount of charged mt-t RNAAsn was demonstrated as compared with controls. This confirmed the pathogenic nature of the variant. To conclude, the reported variant in NARS2 results in a combined OXPHOS complex deficiency involving complex I and IV, making NARS2 a new member of disease-associated aaRS2. [ABSTRACT FROM AUTHOR]

Light irradiation of the molecular photoswitch 1- E causes isomerization into the 1- Z configuration stabilized by an internal hydrogen bond. 1- E bears aldehyde groups allowing for dynamic covalent reaction with linear diamines. On photoinduced E/ Z shape switching of 1 in presence of diamines, the system undergoes interconversion between two states, a non-cyclic oligomeric one and a macrocyclic one, corresponding respectively to the E and Z configurations of 1. With a mixture of linear α,ω-diamines, 1- E yields non-selective dynamic oligomers by random incorporation of diamine components. Photoswitching to the 1- Z form leads to constitutional adaptation with preferential formation of the macrocycle incorporating the best suited diamine, H2N(CH2)7NH2. In presence of metal cations, the E form switches from its unbound W shape to its coordinated U shape and yields the macrocycle resulting from the selective incorporation of the diamine H2NCH2CH2OCH2CH2NH2 that contains an additional O coordination site. Taken together, the results obtained describe constitutional adaptation in a triple state system: an oligomeric one and two different macrocyclic ones generated in response to two orthogonal agents, a physical stimulus, light, or a chemical effector, metal cations. These three states present, towards the incorporation of diamine components, respectively no selection, photoselection and metalloselection. [ABSTRACT FROM AUTHOR]

Sequential multiple Eu ion implantations at low fluence (1×1013 cm-2 at 300 keV) and subsequent rapid thermal annealing (RTA) steps (30 s at 1000 °C or 1100 °C) were performed on high quality nominally undoped GaN films grown by metal organic chemical vapour deposition (MOCVD) and medium quality GaN:Mg grown by hydride vapour phase epitaxy (HVPE). Compared to samples implanted in a single step, multiple implantation/annealing shows only marginal structural improvement for the MOCVD samples, but a significant improvement of crystal quality and optical activation of Eu was achieved in the HVPE films. This improvement is attributed to the lower crystalline quality of the starting material, which probably enhances the diffusion of defects and acts to facilitate the annealing of implantation damage and the effective incorporation of the Eu ions in the crystal structure. Optical activation of Eu3+ ions in the HVPE samples was further improved by high temperature and high pressure annealing (HTHP) up to 1400 °C. After HTHP annealing the main room temperature cathodo- and photoluminescence line in Mg-doped samples lies at ∼ 619 nm, characteristic of a known Mg-related Eu3+ centre, while after RTA treatment the dominant line lies at ∼ 622 nm, typical for undoped GaN:Eu. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Composite multiferroics are a new class of material where magneto-electric coupling is achieved by creating an interface between a ferromagnetic and a ferroelectric compound. The challenge of understanding the chemical and magnetic properties of such interface is a key to achieve good magneto-electric coupling. The unique possibilities offered by isotope sensitive techniques are used to selectively investigate the interface's chemistry and magnetism in Fe/BaTiO3 and Fe/LiNbO3 systems during the application of an electric field. With a large enough electric field, a strong oxidation of Fe is triggered, which creates a magnetically dead interface. This leads to an irreversible decrease of the magneto-electric coupling properties. Material parameters are identified that determine under which electric field the interface may be modified. The results are confirmed on the two systems and are expected to be widespread in this new class of hybrid material. [ABSTRACT FROM AUTHOR]

Lift-off protocols for thin films for improved extended X-ray absorption fine structure (EXAFS) measurements are presented. Using wet chemical etching of the substrate or the interlayer between the thin film and the substrate, stand-alone high-quality micrometer-thin films are obtained. Protocols for the single-crystalline semiconductors GeSi, InGaAs, InGaP, InP and GaAs, the amorphous semiconductors GaAs, GeSi and InP and the dielectric materials SiO2 and Si3N4 are presented. The removal of the substrate and the ability to stack the thin films yield benefits for EXAFS experiments in transmission as well as in fluorescence mode. Several cases are presented where this improved sample preparation procedure results in higher-quality EXAFS data compared with conventional sample preparation methods. This lift-off procedure can also be advantageous for other experimental techniques ( e.g. small-angle X-ray scattering) that benefit from removing undesired contributions from the substrate. [ABSTRACT FROM AUTHOR]

The capabilities of artificial neural networks (ANNs) have been investigated for the analysis of nuclear resonant scattering (NRS) data obtained at a synchrotron source. The major advantage of ANNs over conventional analysis methods is that, after an initial training phase, the analysis is fully automatic and practically instantaneous, which allows for a direct intervention of the experimentalist on- site. This is particularly interesting for NRS experiments, where large amounts of data are obtained in very short time intervals and where the conventional analysis method may become quite time-consuming and complicated. To test the capability of ANNs for the automation of the NRS data analysis, a neural network was trained and applied to the specific case of an Fe/Cr multilayer. It was shown how the hyperfine field parameters of the system could be extracted from the experimental NRS spectra. The reliability and accuracy of the ANN was verified by comparing the output of the network with the results obtained by conventional data analysis. [ABSTRACT FROM AUTHOR]