Although a linear relationship between the optical activity (normally the CD signal) and the enantiomeric excess (ee) of chiral auxiliaries has been the most commonly observed dependence in dynamic ...supramolecular helical aggregates, positive nonlinear CD–ee dependence, known as the “majority‐rules effect” (MRE), indicative of chiral amplification, has also been well documented and to some extent understood. In sharp contrast, the negative nonlinear CD–ee dependence has been much less reported and is not well understood. Here, the state of the art of both the positive and negative nonlinear CD–ee dependence in noncovalently bound supramolecular helical aggregates is summarized, with the hope that the vast examples of supramolecular aggregates showing positive nonlinear dependence, in terms of the methods of investigations, variations in the structure of the building block (single species or multiple species), and theoretical modeling using the mismatch penalty energy and helix reversal penalty energy, would help to guide the design of building blocks to form aggregates showing negative nonlinear dependence, and thus to understand the mechanisms. The potential applications of those functional supramolecular aggregates are also discussed.
The research progress of nonlinear CD–ee dependence in the dynamic supramolecular aggregates, positive and negative, is summarized from the viewpoint of their discoveries, experimental observations, theoretical descriptions, and applications, in a hope to facilitate a better understanding of supramolecular chirality and the fabrication of functional supramolecular chiral materials.
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Abstract The variation mechanism of blazars is a long-standing unresolved problem. In this work, we present a scenario to explain diverse variation phenomena for ON 231, where the jet emissions are ...composed of the flaring and the less variable components (most probably from the post-flaring blobs), and the variation is dominated by shock-in-jet instead of the Doppler effect. We perform correlation analysis for the multiwavelength light curves and find no significant correlations. For the optical band, ON 231 exhibits a harder when brighter (HWB) trend, and the trend seems to shift at different periods. Correspondingly, the correlation between the degree of polarization and flux exhibits a V-shaped behavior, and a similar translation relation during different periods is also found. These phenomena could be understood via the superposition of the flaring component and slowly varying background component. We also find that the slopes of the HWB trend become smaller at higher flux levels, which indicates the energy-dependent acceleration processes of the radiative particles. For the X-ray band, we discover a trend transition from HWB to softer when brighter (SWB) to HWB. We consider that the X-ray emission is composed of both the synchrotron tail and the synchrotron self-Compton components, which could be described by two log-parabolic functions. By varying the peak frequency, we reproduce the observed trend transition in a quantitative manner. For the γ -ray band, we find the SWB trend, which could be explained naturally if a very-high-energy γ -ray background component exists. Our study elucidates the variation mechanism of intermediate synchrotron-peaked BL Lac objects.
Understanding the incipient plastic mechanism in metals is critical for their associated mechanical properties. While heterogeneous dislocation nucleation from pre-existing defects constitutes the ...most prevalent onset mechanism of plasticity in the conventional solutions, such a scenario may break down in the recently emerging chemically-disordered high/medium entropy alloys (HEAs/MEAs), owing to their unique multiple-component feature and the inevitable inhomogeneity in local atomic environments. Here, classical molecular dynamics simulations and first-principles density functional theory calculations are carried out to study the atomic-scale mechanisms governing the incipient plasticity in a prototypical chemically complex face-centered cubic (fcc) CrCoNi MEA. Dislocation nucleation is found to occur preferentially at an energetically unstable defect cluster with body-centered cubic like (bcc-like) atomic environment as a precursor, after certain deformation before plasticity, which is in contrast with the usual mechanism of heterogeneous dislocation nucleation in the conventional solute solution metals. The minimum energy pathway of dislocation nucleation from a bcc precursor is discussed to rationalize the usual phenomenon. First-principles athermal quasi-static compression test validates the mechanism suggested by atomistic simulations. Further electronic structure analysis suggests that the local bcc-like defect cluster is related to the localized electronic behaviors of Cr atoms and the weak Cr-Cr bonding, which promote the dislocation nucleation and therefore the incipient plasticity of CrCoNi MEA. The atomic and electronic insights reported here highlight the significant role of local chemical order in determining the mechanical property, and shed light on the strategy of optimizing mechanical performance via tailoring composition and local atomic arrangement in the generic highly concentrated solutions.
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Optical sensors that respond to enantiomeric excess of chiral analytes are highly demanded in chirality related research fields and demonstrate their potential in many applications, for example, ...screening of asymmetric reaction products. Most sensors developed so far are small molecules. This
Tutorial Review
covers recent advances in chirality sensing systems that are different from the traditional small molecule-based sensors, by using macrocycles, synthetic oligomers/polymers, supramolecular polymers and nanoparticles as the sensors, in which supramolecular interactions operate.
Recent advances in four classes of non-small-molecule based chirality sensors are reviewed.
Diffusion in the traditional single-crystalline solids is usually dynamically homogeneous characterized by a single-value or two characteristic activation energies. However, such a scenario breaks ...down at atomic-scale in the recently advanced high-entropy alloys, which are of unique structural features with multi-principal elements randomly occupying on lattice sites that induces strikingly local chemical heterogeneity. Here we uncover and decouple the possible dynamic heterogeneity accommodating the lattice diffusion in an archetypical high-entropy Cantor alloy CoCrFeMnNi via combined molecular statics, molecular dynamics, and a saddle-point sampling method. Wide distribution of vacancy formation energies and migration energies are revealed. We propose a single-vacancy and a vacancy-saturated model, respectively, to set up possible lower bound and upper bound of diffusivities. The models define a possible range of activation energies for the lattice diffusion in high-entropy alloys, which are comparable to experimental data. Finally, we argue that the conventional hypothesis of diffusion activation energy estimated from Arrhenius equation as the sum of the vacancy formation energy and migration energy becomes intractable in high-entropy alloys. These atomic-scale insights into diffusion heterogeneity, in contrast to the classical theory of homogeneous diffusion in conventional solid solutions, highlight the complexity of diffusion pathways and the intimate correlation between chemical, topological disorder and dynamic heterogeneity in the generic complex concentrated alloys.
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A significant challenge in creating supramolecular materials is that conjugating molecular functionalities to building blocks often results in dissociation or undesired morphological transformation ...of their assemblies. Here we present a facile strategy to preserve structurally labile peptide assemblies after molecular modification of the self‐assembling peptides. Sheet‐forming peptides are designed to afford a staggered alignment with the segments bearing chemical modification sites protruding from the sheet surfaces. The staggered assembly allows for simultaneous separation of attached molecules from each other and from the underlying assembly motifs. Strikingly, using PEGs as the external molecules, PEG400‐ and PEG700‐peptide conjugates directly self‐associate into nanosheets with the PEG chains localized on the sheet surfaces. In contrast, the sheet formation based on in‐register lateral packing of peptides does not recur upon the peptide PEGylation. This strategy allows for fabrication of densely modified assemblies with a variety of molecules, as demonstrated using biotin (hydrophobic molecule), c(RGDfK) (cyclic pentapeptide), and nucleic acid aptamer (negatively charged ssDNA). The staggered co‐assembly also enables extended tunability of the amount/density of surface molecules, as exemplified by screening ligand‐appended assemblies for cell targeting. This study paves the way for functionalization of historically challenging fragile assemblies while maintaining their overall morphology.
We present a unique way to preserve structurally labile nanosheets after conjugation of a variety of molecules to the self‐assembling peptides. The sheet‐forming peptides afford a staggered alignment for simultaneous separation of external molecules from each other and from the underlying assembly motifs. This strategy allows the functionalization of historically challenging fragile assemblies while maintaining their overall morphology.
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8.
Fracture universality in amorphous nanowires Zhao, Kun; Wang, Yun-Jiang; Cao, Penghui
Journal of the mechanics and physics of solids,
April 2023, 2023-04-00, Volume:
173
Journal Article
Peer reviewed
Open access
Crystalline nanowires exhibiting a wide range of size-dependent fracture and failure modes have been extensively studied, yet the fracture behaviors of amorphous materials and their size dependence ...remain elusive. Here extensive atomistic simulations are performed to reveal the deformation and fracture behaviors in a broad class of amorphous nanowires with varying sizes, including CuZr, CuZrAl, FeP, Si, and a ductile Lennard-Jones system. It is found that the fracture strain ɛf increases with nanowire length L but decreases with diameter D, which exhibits a linear relationship with the diameter-to-length ratio as ɛf∝D/L, —a scaling law valid in these five distinct glassy systems understudied. We develop a theoretical model, capturing the size of plastic zone at plastic yielding and its vital role in governing the final fracture strain, which shows an agreement with the simulation data. By taking into account the intrinsic atomic-level ideal strain, remarkably, all the size-dependent fracture strain data collapse, signifying the universality of fracture nature in a broad range of glassy materials.
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The prevalence of cardiovascular disease (CVD) has been rising due to sedentary lifestyles and unhealthy dietary patterns. Peroxisome proliferator-activated receptor α (PPARα) is a nuclear receptor ...regulating multiple biological processes, such as lipid metabolism and inflammatory response critical to cardiovascular homeostasis. Healthy endothelial cells (ECs) lining the lumen of blood vessels maintains vascular homeostasis, where endothelial dysfunction associated with increased oxidative stress and inflammation triggers the pathogenesis of CVD. PPARα activation decreases endothelial inflammation and senescence, contributing to improved vascular function and reduced risk of atherosclerosis. Phenotypic switch and inflammation of vascular smooth muscle cells (VSMCs) exacerbate vascular dysfunction and atherogenesis, in which PPARα activation improves VSMC homeostasis. Different immune cells participate in the progression of vascular inflammation and atherosclerosis. PPARα in immune cells plays a critical role in immunological events, such as monocyte/macrophage adhesion and infiltration, macrophage polarization, dendritic cell (DC) embedment, T cell activation, and B cell differentiation. Cardiomyocyte dysfunction, a major risk factor for heart failure, can also be alleviated by PPARα activation through maintaining cardiac mitochondrial stability and inhibiting cardiac lipid accumulation, oxidative stress, inflammation, and fibrosis. This review discusses the current understanding and future perspectives on the role of PPARα in the regulation of the cardiovascular system as well as the clinical application of PPARα ligands.
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Spinel LiNi0.5Mn1.5O4 (LNMO), high‐voltage and high‐power density, is a very promising cathode candidate. Nevertheless, its lack of cycling stability has historically been long accepted as an ...inherent issue. Based on the above problem, a strategy is initiated to directly address Mn dissolution and unstable interface structure. A beneficial solid‐phase reaction occurs at the LNMO interface, transforming the spinel phase into two functional phases. One is the layered phase that provides electrochemical activity and supports charge transport. The other is the rock‐salt like phase induced by Li/Mn exchange that can inhibit the dissolution of Mn and provide inert protection. The Li/Mn exchange structure increases the diffusion energy barriers of Mn, which restrains the loss of Mn, proven by the bond valence sum calculation. The two phases are modulated successfully at the LNMO interface to balance the stable material structure and excellent charge transfer, obtaining a sample with excellent electrochemical performance. The capacity retention rate of modified LNMO is 15% higher than that of the pristine sample after 500 cycles. The preparation method does not utilize any dopants or coatings and can play a guiding role in addressing issues regarding structural stability and electrochemical performance for cathode materials.
The spinel phase transforms into a layered phase and a rock‐salt like phase at the LiNi0.5Mn1.5O4 interface by an intrinsic method. The rock‐salt like phase induced by Li/Mn exchange can inhibit the dissolution of Mn and the Jahn‐Teller distortion. Through interface phase modulation, the capacity retention is increased by 15%.
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