Fibrils Emerging from Droplets: Molecular Guiding Principles behind Phase Transitions of a Short Peptide-Based Condensate Studied by Solid-State NMR.

Biochemical reactions occurring in highly crowded cellular environments require different means of control to ensure productivity and specificity. Compartmentalization of reagents by liquid-liquid phase separation is one of these means. However, extremely high local protein concentrations of up to 400 mg/ml can result in pathological aggregation into fibrillar amyloid structures, a phenomenon that has been linked to various neurodegenerative diseases. Despite its relevance, the process of liquid-to-solid transition inside condensates is still not well understood at the molecular level. We thus herein use small peptide derivatives that can undergo both liquid-liquid and subsequent liquid-to-solid phase transition as model systems to study both processes. Using solid-state nuclear magnetic resonance (NMR) and transmission electron microscopy (TEM), we compare the structure of condensed states of leucine, tryptophan and phenylalanine containing derivatives, distinguishing between liquid-like condensates, amorphous aggregates and fibrils, respectively. A structural model for the fibrils formed by the phenylalanine derivative was obtained by an NMR-based structure calculation. The fibrils are stabilised by hydrogen bonds and side-chain π-π interactions, which are likely much less pronounced or absent in the liquid and amorphous state. Such noncovalent interactions are equally important for the liquid-to-solid transition of proteins, particularly those related to neurodegenerative diseases.

Transvenous Lead Extraction in Pediatric Patients　- Is It the Same Procedure in Children as in Adults?

BACKGROUND: Cardiac implantable electronic devices (CIED) are very rare in the pediatric population. In children with CIED, transvenous lead extraction (TLE) is often necessary. The course and effects of TLE in children are different than in adults. Thus, this study determined the differences and specific characteristics of TLE in children vs. adults.Methods and Results: A post hoc analysis of TLE data in 63 children (age ≤18 years) and 2,659 adults (age ≥40 years) was performed. The 2 groups were compared with respect to risk factors, procedure complexity, and effectiveness. In children, the predominant pacing mode was a single chamber ventricular system and lead dysfunction was the main indication for lead extraction. The mean implant duration before TLE was longer in children (P=0.03), but the dwell time of the oldest extracted lead did not differ significantly between adults and children. The duration (P=0.006) and mean extraction time per lead (P<0.001) were longer in children, with more technical difficulties during TLE in the pediatric group (P<0.001). Major complications were more common, albeit not significantly, in children. Complete radiographic and procedural success were significantly lower in children (P<0.001). CONCLUSIONS: TLE in children is frequently more complex, time consuming, and arduous, and procedural success is more often lower. This is related to the formation of strong fibrous tissue surrounding the leads in pediatric patients.

Lead Extraction in Children and Young Adults: When is the Best Time for Lead/System Replacement?

The best strategy for lead management in children is a matter of debate, and our experiences are limited. This is a retrospective single-center study comparing difficulties and outcomes of transvenous lead extraction (TLE) implanted ich childhood and at age < 19 years (childhood-implanted-childhood-extracted, CICE) and at age < 19 (childhood-implanted-adulthood-extracted, CIAE). CICE patients-71 children (mean age 15.1 years) as compared to CIAE patients (114 adults (mean age 28.61 years) were more likely to have VVI than DDD pacemakers. Differences in implant duration (7.96 vs 14.08 years) appeared to be most important, but procedure complexity and outcomes also differed between the groups. Young adults with cardiac implantable electronic device implanted in childhood had more risk factors for major complications and underwent more complex procedures compared to children. Implant duration was significantly longer in CIAE patients than in children, being the most important factor that had an impact on patient safety and procedure complexity. CIAE patients were more likely to have prolonged operative duration and more complex procedures due to technical problems, and they were 2-3 times more likely to require second-line or advanced tools compared to children, but the rates of clinical and procedural success were comparable in both groups. The difference between the incidence of major complications between CICE and CIAE patients is very clear (MC 2.9 vs 7.0%, hemopericardium 1.4 vs 5.3% etc.), although statistically insignificant. Delay of lead extraction to adulthood seems to be a riskier option than planned TLE in children before growing up.

Peptide-based coacervates as biomimetic protocells.

Coacervates are condensed liquid-like droplets formed by liquid-liquid phase separation of molecules through multiple weak associative interactions. In recent years it has emerged that not only long polymers, but also short peptides are capable of forming simple and complex coacervates. The coacervate droplets they form act as compartments that sequester and concentrate a wide range of solutes, and their spontaneous formation make coacervates attractive protocell models. The main advantage of peptides as building blocks lies in the functional diversity of the amino acid residues, which allows for tailoring of the peptide's phase separation propensity, their selectivity in guest molecule uptake and the physicochemical and catalytic properties of the compartments. The aim of this tutorial review is to illustrate the recent developments in the field of peptide-based coacervates in a systematic way and to deduce the basic requirements for both simple and complex coacervation of peptides. We review a selection of peptide coacervates that illustrates the essentials of phase separation, the limitations, and the properties that make peptide coacervates biomimetic protocells. Finally, we provide some perspectives of this novel research field in the direction of active droplets, moving away from thermodynamic equilibrium.

Optical analysis of a solar thermochemical system with a rotating tower reflector and a receiver-reactor array.

We propose a concept of a rotating tower reflector (TR) in a beam-down optical system to alternate concentrated solar irradiation of an array of solar receiver-reactors, realizing multi-step solar thermochemical redox cycles. Optical and radiative characteristics of the proposed system are explored analytically and numerically by Monte-Carlo ray-tracing simulations. We study the effects of the system geometrical and optical parameters on the optical and radiative performance. TR axis is required to be tilted for accommodating the receiver-reactor array, resulting in reduced optical efficiency. We demonstrate that the annual optical efficiency of a baseline system with the receiver-reactor located south of the tower decreases from 46% to 37% for the axis tilt angle of TR increasing from 2° to 20°. The optical analysis conducted in this study provides a general formulation to enable predictions of required gain of thermal-to-chemical efficiency of the receiver-reactor array for obtaining improved overall solar-to-chemical efficiency of the solar thermochemical plant.

Optical analysis of a multi-aperture solar central receiver system for high-temperature concentrating solar applications.

A multi-aperture solar central receiver system is optically analyzed for increasing the net power to the receiver in a wide temperature range of 600-1800 K. A model system comprises a tower, a multi-aperture receiver with compound parabolic concentrators, and heliostat sub-fields. Optical modeling is performed using in-house developed Monte-Carlo ray-tracing programs. The heliostat sub-field geometrical configuration, the number of receiver apertures and optical properties of reflective surfaces are varied in the parametric study. Increasing the number of apertures from one to four increases the maximum net receiver power from 116 MW to 332 MW. The use of more than four apertures results in only limited further gain of the net receiver power but significantly decreases the overall optical efficiency and the solar-to-thermal efficiency. The optimal temperature for the maximized annual solar-to-exergy efficiency is found in the range of 1100-1200 K. This optimal temperature decreases slightly with an increasing number of apertures.

Activation of cell-penetrating peptide fragments by disulfide formation.

Three cell-penetrating peptides (CPPs), Tat, Pep-3 and penetratin, were split into two parts and each fragment was terminated with a cysteine residue, to allow disulfide bridge formation, as well as a fluorescent label, for visualization and quantitative analysis. After disulfide formation between two complementary CPP fragments, cellular uptake of the resulting conjugates was observed. As confirmed by in vitro experiments, the conjugated peptides showed uptake activity comparable to the native CPP sequences, while the truncated peptides were hardly active. Until now, this split CPP strategy has only been demonstrated for oligo-arginine CPPs, but here we demonstrate that it is also applicable to other cell-penetrating peptides. This wider applicability may help in the design of new activatable cell-penetrating peptides for, e.g., targeted drug delivery.

Fibrous Aggregates of Short Peptides Containing Two Distinct Aromatic Amino Acid Residues.

The aim of the study was the assessment of the ability of short peptides to form aggregates under physiological conditions. The dipeptides studied were derived from different aromatic amino acids (heteroaromatic peptides). Tripeptides were obtained from two distinct aromatic amino acids and cysteine or methionine residue in the C-terminal, N-terminal, or central position. The ability of the peptides to form fibrous aggregates under physiological conditions was evaluated using three independent methods: the Congo Red assay, the Thioflavin T assay, and microscopic examinations using normal and polarized light. Materials potentially useful for regenerative medicine were selected based on their cytotoxicity to the endothelial cell line EA.hy 926 and physicochemical properties of films formed by peptides. The required parameters of biocompatibility were fulfilled by H-PheCysTrp-OH, H-PheCysTyr-OH, H-PheTyrMet-OH, and H-TrpTyr-OH.

Effect of non-stoichiometry on optical, radiative, and thermal characteristics of ceria undergoing reduction.

The complex refractive index of ceria has been determined at ambient temperature using variable angle spectroscopic ellipsometry for two chemical states-fully oxidized and partially reduced. The ellipsometric model is corroborated with complementary measurements of thickness, surface roughness, and chemical composition. Partially reduced ceria is shown to have a larger absorption index over a broad spectral range than fully oxidized ceria, including the visible and near IR regions. We use a simple model of a directly irradiated particle entrained in a gas flow to demonstrate the consequences of accounting for changes in chemical state when modeling ceria-based thermochemical process.

Search for Fibrous Aggregates Potentially Useful in Regenerative Medicine Formed under Physiological Conditions by Self-Assembling Short Peptides Containing Two Identical Aromatic Amino Acid Residues.

This study investigates the propensity of short peptides to self-organize and the influence of aggregates on cell cultures. The dipeptides were derived from both enantiomers of identical aromatic amino acids and tripeptides were prepared from two identical aromatic amino acids with one cysteine or methionine residue in the C-terminal, N-terminal, or central position. The formation or absence of fibrous structures under physiological conditions was established using Congo Red and Thioflavine T assays as well as by microscopic examination using normal and polarized light. The in vitro stability of the aggregates in buffered saline solution was assessed over 30 days. Materials with potential for use in regenerative medicine were selected based on the cytotoxicity of the peptides to the endothelial cell line EA.hy 926 and the wettability of the surfaces of the films, as well as using scanning electron microscopy. The criteria were fulfilled by H-dPhedPhe-OH, H-dCysdPhedPhe-OH, H-CysTyrTyr-OH, H-dPhedPhedCys-OH, H-TyrTyrMet-OH, and H-TyrMetTyr-OH. Our preliminary results suggest that the morphology and cell viability of L919 fibroblast cells do not depend on the stereochemistry of the self-organizing peptides.

Experimental and numerical characterization of a new 45 kWel multisource high-flux solar simulator.

The performance of a new high-flux solar simulator consisting of 18 × 2.5 kWel radiation modules has been evaluated. Grayscale images of the radiative flux distribution at the focus are acquired for each module individually using a water-cooled Lambertian target plate and a CCD camera. Raw images are corrected for dark current, normalized by the exposure time and calibrated with local absolute heat flux measurements to produce radiative flux maps with 180 µm resolution. The resulting measured peak flux is 1.0-1.5 ± 0.2 MW m-2 per radiation module and 21.7 ± 2 MW m-2 for the sum of all 18 radiation modules. Integrating the flux distribution for all 18 radiation modules over a circular area of 5 cm diameter yields a mean radiative flux of 3.8 MW m-2 and an incident radiative power of 7.5 kW. A Monte Carlo ray-tracing simulation of the simulator is calibrated with the experimental results. The agreement between experimental and numerical results is characterized in terms of a 4.2% difference in peak flux and correlation coefficients of 0.9990 and 0.9995 for the local and mean radial flux profiles, respectively. The best-fit simulation parameters include the lamp efficiency of 39.4% and the mirror surface error of 0.85 mrad.

Feature issue introduction: light, energy and the environment, 2015.

The feature issue highlights contributions from authors who presented their research at the OSA Light, Energy and the Environment Congress, held in Suzhou, China from 2 to 5 November, 2015.

Optics of solar central receiver systems: a review.

This article reviews the state of the art in optical design, modeling and characterization of solar central receiver systems.

Effect of surface radiative properties of a CO(2) sorbent particle on its interactions with high-flux solar irradiation.

A thermal transport phenomena model for the decomposition of a CO2 sorbent particle under concentrated solar irradiation is used to evaluate four approximate engineering models for the surface radiative properties of the particle. The radiative property models are formulated by considering the solid-phase to be opaque or semi-transparent and the size of the surface features to be either smaller or larger than the incident irradiation wavelength. Time to complete decomposition of the particle and maximum surface temperature in simulations employing the four models differ by approximately 2% and 0.5%, respectively.

Effect of pore-level geometry on far-field radiative properties of three-dimensionally ordered macroporous ceria particle.

The effects of pore size on direction-averaged radiative properties of three-dimensionally ordered macroporous (3DOM) cerium dioxide (ceria) particles are investigated in the spectral range of 0.3-10 µm. The particles are of spherical shape and contain interconnected pores in a face-centered cubic lattice arrangement. The porous particle is modeled as a three-dimensional array of interacting dipoles using the discrete dipole approximation (DDA). The validity of the Lorenz-Mie theory to predict far-field radiative properties of a quasi-homogeneous particle with the effective optical properties obtained using the volume-averaging theory (VAT) is demonstrated. Direction-averaged extinction, scattering, and absorption efficiency factors as well as the scattering asymmetry factor are determined as a function of the pore size for a particle of 1 µm diameter and as a function of the particle size for pores of 400 nm diameter. The overlapping ordered pores in the 3DOM particles and the boundary effects in the presence of pores of size comparable to that of the particle are shown to affect the radiative properties in the ultraviolet to near-infrared spectral ranges. The effects of the 3DOM pore-level features on the far-field radiative properties are not captured by the Lorenz-Mie theory combined with VAT. Consequently, the use of advanced modeling tools such as DDA is necessary. In the mid- and far-infrared spectral ranges, the effects of 3DOM pore-level features on the far-field radiative properties diminish and the approach combining the Lorenz-Mie theory and VAT is shown to be accurate.

Scalable nano-architecture for stable near-blackbody solar absorption at high temperatures.

Light trapping enhancement by nanostructures is ubiquitous in engineering applications, for example, in improving highly-efficient concentrating solar thermal (CST) technologies. However, most nano-engineered coatings and metasurfaces are not scalable to large surfaces ( > 100 m2) and are unstable at elevated temperatures ( > 850 °C), hindering their wide-spread adoption in CST. Here, we propose a scalable layer nano-architecture that can significantly enhance the solar absorption of an arbitrary material. Our electromagnetics modelling predicts that the absorptance of cutting-edge light-absorbers can be further enhanced by more than 70%, i.e. relative improvement towards blackbody absorption from a baseline value without the nano-architecture. Experimentally, the nano-architecture yields a solar absorber that is 35% optically closer to a blackbody, even after long-term (1000 h) high-temperature (900 °C) ageing in air. A stable solar absorptance of more than 97.88 ± 0.14% is achieved, to the best of our knowledge, the highest so far reported for these extreme ageing conditions. The scalability of the layer nano-architecture is further demonstrated with a drone-assisted deposition, paving the way towards a simple yet significant solar absorptance boosting and maintenance method for existing and newly developed CST absorbing materials.

Biomolecular condensates can both accelerate and suppress aggregation of α-synuclein.

Biomolecular condensates present in cells can fundamentally affect the aggregation of amyloidogenic proteins and play a role in the regulation of this process. While liquid-liquid phase separation of amyloidogenic proteins by themselves can act as an alternative nucleation pathway, interaction of partly disordered aggregation-prone proteins with preexisting condensates that act as localization centers could be a far more general mechanism of altering their aggregation behavior. Here, we show that so-called host biomolecular condensates can both accelerate and slow down amyloid formation. We study the amyloidogenic protein α-synuclein and two truncated α-synuclein variants in the presence of three types of condensates composed of nonaggregating peptides, RNA, or ATP. Our results demonstrate that condensates can markedly speed up amyloid formation when proteins localize to their interface. However, condensates can also significantly suppress aggregation by sequestering and stabilizing amyloidogenic proteins, thereby providing living cells with a possible protection mechanism against amyloid formation.

Cyclic oxygen exchange capacity of Ce-doped V2O5 materials for syngas production via high-temperature thermochemical-looping reforming of methane.

Synthesis gas production via solar thermochemical reduction-oxidation reactions is a promising pathway towards sustainable carbon-neutral fuels. The redox capability of oxygen carriers with considerable thermal and chemical stability is highly desirable. In this study, we report Ce-doped V2O5 structures for high-temperature thermochemical-looping reforming of methane coupled to H2O and CO2 splitting reactions. Incorporation of fractional amounts of large cerium cations induces a V5+ to V3+ transition and partially forms a segregated CeVO4 phase. More importantly, the effective combination of efficient ion mobility of cerium and high oxygen exchange capacity of vanadia achieves synergic and cyclable redox performance during the thermochemical reactions, whereas the pure vanadia powders undergo melting and show non-cyclic redox behaviour. These materials achieve noteworthy syngas production rates of up to 500 mmol molV -1 min-1 during the long-term stability test of 100 CO2 splitting cycles. Interestingly, the cerium ions are mobile between the lattice and the surface of the Ce-doped vanadia powders during the repeated reduction and oxidation reactions and contribute towards the cyclic syngas production. However, this also causes the formation of the CeVO4 phase in Ce-rich powders, which increases the H2/CO ratios and lowers fuel selectivity, which can be controlled by optimizing the cerium concentration. These findings are noteworthy towards the experimental approach of evaluating the oxygen carriers with the help of advanced characterization techniques.

A short peptide synthon for liquid-liquid phase separation.

Liquid-liquid phase separation of disordered proteins has emerged as a ubiquitous route to membraneless compartments in living cells, and similar coacervates may have played a role when the first cells formed. However, existing coacervates are typically made of multiple macromolecular components, and designing short peptide analogues capable of self-coacervation has proven difficult. Here we present a short peptide synthon for phase separation, made of only two dipeptide stickers linked via a flexible, hydrophilic spacer. These small-molecule compounds self-coacervate into micrometre-sized liquid droplets at sub-millimolar concentrations, which retain up to 75 wt% water. The design is general and we derive guidelines for the required sticker hydrophobicity and spacer polarity. To illustrate their potential as protocells, we create a disulfide-linked derivative that undergoes reversible compartmentalization controlled by redox chemistry. The resulting coacervates sequester and melt nucleic acids, and act as microreactors that catalyse two different anabolic reactions yielding molecules of increasing complexity. This provides a stepping stone for new coacervate-based protocells made of single peptide species.

A High-Efficiency Wavelength-Tunable Monolayer LED with Hybrid Continuous-Pulsed Injection.

High-efficiency and wavelength-tunable light-emitting diode (LED) devices will play an important role in future advanced optoelectronic systems. Traditional semiconductor LED devices typically have a fixed emission wavelength that is determined by the energy of the emission states. Here, a novel high-efficiency and wavelength-tunable monolayer WS2 LED device, which operates in the hybrid mode of continuous-pulsed injection, is developed. This hybrid injection enables highly enhanced emission efficiency (>20 times) and effective size of emission area (>5 times) at room temperature. The emission wavelength of the WS2 monolayer LED device can be tuned over more than 40 nm by driving AC voltages, from exciton emission to trion emission, and further to defect emission. The quantum efficiency of defect electroluminescence (EL) emission is measured to be more than 24.5 times larger than that from free exciton and trion EL emission. The separate carrier injection in the LED also demonstrates advantages in allowing defect species to be visualized and distinguished in real space. Those defects are assigned to be negatively charged defects. The results open a new route to develop high-performance and wavelength-tunable LED devices for future advanced optoelectronic applications.