Reversible Behavior Research Articles

An Anthracene-imidazoanthraquinone Conjugate Exhibiting Ratiometric Fluorescence Turn - On Behavior with CN- and F- Anions.

A new conjugate, 2-(4-(anthracen-9-yl) phenyl)-[1,2-d]imidazole-1H-anthraquninone (AQI) has been designed and synthesized as a molecular probe 4. The photophysical and electrochemical behavior of the probe in the absence and presence of different class of ions were examined in acetonitrile solution. The probe 4 with F- and CN- anions showed ratiometric fluorescence "turn - On" response due to variation in ICT processes. Cyclic voltammetry of probe exhibited reversible redox behavior wherein the band gap (Eg = 1240/lmax) of probe (DE = 3.220 eV) decreased (~ 2.583 eV) after the interaction with F- and CN- anions. The probe interacted with both anions in a 1:1 stoichiometry with good binding constants (KF- = 2.05×106 M-1 and KCN- = 1.46×106 M-1) and limit of detection/quantification (LOD/LOQ) in nM range. The probable complexes, 4+F-/CN- upon interaction with trifluoroacetic (TFA) acid showed reversible behavior. The out emission of probe upon providing F- and TFA as a chemical inputs mimic the function of a memory device, write-read-erase-read functions and a molecular keypad lock system. The probe upon interaction with both F- and CN- anions showed a naked-eye sensitive color change in solution and on test paper strips. Also, the probe showed sensitivity to detect the F- in toothpaste.

A reconfigurable memristor diode based on a CuInP2S6/graphene lateral heterojunction.

The conventional reconfiguration of transistors requires an additional independent terminal for controllable gate input, which complicates the device structure and makes circuit integration difficult. In this work, we propose a reconfigurable diode based on a 2D layered copper indium thiophosphate (CIPS) and graphene (Gr) van der Waals lateral heterojunction, exhibiting distinctively bias-dependent reconfiguration. The reconfiguration characteristics include reversible memristive behaviors with a current on/off ratio of about 103 and switchable rectifying polarity with a rectifying ratio of up to 3 × 103. This reconfigurable mechanism arises from the lateral bias-induced migration of Cu+ ions, effectively modulating the barrier height at the CIPS and Gr interface. This work provides a simplified reconfigurable solution for electrostatically modulated circuits.

Dynamic supramolecular snub cubes.

Mimicking the superstructures and properties of spherical biological encapsulants such as viral capsids1 and ferritin2 offers viable pathways to understand their chiral assemblies and functional roles in living systems. However, stereospecific assembly of artificial polyhedra with mechanical properties and guest-binding attributes akin to biological encapsulants remains a formidable challenge. Here we report the stereospecific assembly of dynamic supramolecular snub cubes from 12 helical macrocycles, which are held together by 144 weak C-H hydrogen bonds3. The enantiomerically pure snub cubes, which have external diameters of 5.1 nm, contain 2,712 atoms and chiral cavities with volumes of 6,215 Å3. The stereospecific assembly of left- and right-handed snub cubes was achieved by means of a hierarchical chirality transfer protocol4, which was streamlined by diastereoselective crystallization. In addition to their reversible photochromic behaviour, the snub cubes exhibit photocontrollable elasticity and hardness in their crystalline states. The snub cubes can accommodate numerous small guest molecules simultaneously and encapsulate two different guest molecules separately inside the uniquely distinct compartments in their frameworks. This research expands the scope of artificial supramolecular assemblies to imitate the chiral superstructures, dynamic features and binding properties of spherical biomacromolecules and also establishes a protocol for construction of crystalline materials with photocontrollable mechanical properties.

Confined phase behavior of subcritical carbon dioxide in nanoporous media: the effects of pore size and temperature.

This study investigates the effect of confinement on the phase behavior of carbon dioxide (CO2) and its implications for storage in nanometer-scale pores. A patented gravimetric apparatus was employed to experimentally measure the adsorption and desorption isotherms at varying pore sizes and temperatures. The isotherms were generated at temperatures below the critical point of CO2 (from -23.1 to 20 °C) using mesoporous material MCM-41 with pore sizes of 6, 8, 10, and 12 nm. The capillary condensation and bulk saturation pressures were measured from the adsorption isotherms for each pore size and temperature. Meanwhile, the evaporation pressures under confinement were determined from the desorption branches. The experimentally measured bulk saturation and dew point pressures were successfully compared against the NIST data, confirming the accuracy of measurements. All isotherms showed reversible behavior, exhibiting no adsorption-desorption hysteresis, indicating that all temperatures studied here were above the hysteresis critical temperature. For all pore sizes, the amount of CO2 adsorbed in confined spaces decreased with ascending temperatures. Furthermore, the CO2 uptake during capillary condensation showed an inverse correlation with the pore size; smaller pores adsorbed more CO2 due to the higher interaction strength with pore walls than larger counterparts. Furthermore, the results provide an in-depth understanding of the effect of pore size and temperature on the equilibrium behavior of CO2 molecules in confined and bulk spaces of porous media. The results from the present study can significantly aid the storage applications of CO2 in a wide range of natural and synthetic porous materials.

The effect of retained austenite on austenite reversion behavior and corresponding mechanical properties of Ti-Mo precipitation hardening stainless steels

The effect of retained austenite on austenite reversion behavior and corresponding mechanical properties of Ti-Mo precipitation hardening stainless steels

Manipulating Toughness and Microstructure in Polyelectrolyte Complex Hydrogels with Competitive Surfactant Micelles.

Polyelectrolyte complex (PEC) hydrogels provide a promising strategy to develop a class of physically cross-linked networks characterized by exceptional toughness and self-healing properties. However, the precise control of the microstructure and the enhancement of mechanical properties still pose challenges in the field of PEC hydrogels. Herein, we propose a strategy to manipulate the structure of PEC with competitively charged surfactant micelles, leveraging the spatially confined surface charge and excluded volume effects to overcome coacervation issues associated with the PEC, thus achieving a simple one-step preparation of macroscopically uniform and tough PEC hydrogels. Specifically, polyelectrolyte complex/surfactant micelle (PEC-SM) hybrid hydrogels were prepared by one-step copolymerization of chitosan (CS)/acrylic acid/cetyltrimethylammonium bromide (CTAB) micelles. The content of CTAB micelles was found to continuously modulate both the structure and the mechanical properties of the resulting PEC-SM hydrogel network. On one hand, reversible deformation-recovery behavior exhibited by CTAB cavity micelles through hydrophobic interactions efficiently dissipates energy; on the other hand, competition between CS chains and CTAB micelles for electrostatic binding sites with poly(acrylic acid), along with excluded volume effects of CTAB micelles, imparts a hierarchical structure upon the PEC-SM hydrogel. Rheology provided detailed insights into the viscoelastic behaviors of PEC-SM hydrogels at varying CTAB concentrations. The intermolecular interaction and heterogeneous network structure of physically cross-linked PEC-SM hydrogels with CTAB micelles were elucidated by solid-state nuclear magnetic resonance (NMR) spectroscopy. On the basis of rheology and NMR results, complemented by other characterization analyses, the physical illustration of the PEC-SM hybrid hydrogel network structure regulated by competitive surfactant micelles is presented. This work offers valuable in-depth insight into polyelectrolyte complexation and provides a foundation for the development of robust PEC hydrogel materials.

Effects of grain boundary phases on recoil loops by in situ observation of magnetization behavior in nanocrystalline PrNd–Fe–B magnets

The grain boundary phase (GBP) has a significant influence on the magnetization behavior in nanocrystalline PrNd–Fe–B magnets. The current study demonstrates that reversible/irreversible magnetization behavior and the phenomenon of open recoil loops are related to both the nature of GBPs and the magnetization state by in situ observation. The optimization of GBPs nature (increase the volume fraction and improve the composition of GBPs) leads to the suppression of reversible magnetization behavior and the phenomenon of open recoil loops at low fields. Since the asymmetric magnetic domain structure appears only at low cycle fields, the openness phenomenon originates from the weak pinning grain boundaries (GBs). In addition, optimization of the GBPs also enhances pinning strength and uniformity, which contributes to the domain walls being pinned in the GBs at higher external fields. At this moment, the domain wall is dominated by irreversible magnetization behavior, and the openness phenomenon disappears. This proves that the coercivity mechanism is transformed from inhomogeneously weak pinning to homogeneously strong pinning with the optimization of GBPs. Consequently, the coercivity and squareness factor are significantly enhanced. This study sheds light on the understanding of the effects of GBP's nature on recoil loops and coercivity mechanism, and it also provides significant guidance for the development of advanced permanent magnets.

Anisotropic Strain Evolution of Layered LiNi0.5Co0.2Mn0.3O2 Cathode in Formation Cycle.

The formation process plays a key role in developing long life and high energy density materials, during which the phase transition, strain evolution, and structural self-adaption interact rationally with each other to produce a qualified electrode for Li-ion batteries (LIBs). Taking the layered LiNi0.5Co0.2Mn0.3O2 cathode as an example, the substantial structural changes, both in the bulk and at the surface are thoroughly documented during the formation cycle. Upon initial charging, different phases emerge continuously, resulting in lattice mismatches, inhomogeneous strain, and microstructural distortions. The irreversible loss of lattice oxygen, combined with the spontaneous cation mixing and the formation of rock-salt phase at the surface, contributes to the initial capacity loss. As a self-adjustment process, this initial capacity loss facilitates the development of a robust LixNi0.5Co0.2Mn0.3O2 electrode by relieving internal strain and stabilizing the rippled layered structure, thereby ensuring highly reversible electrochemical behavior in subsequent cycles. These findings lay a solid foundation for the design and optimization of layered cathodes for rechargeable batteries.

Regioregular Poly(p‐phenylene iminoborane): A Strictly Alternating BN‐Isostere of Poly(p‐phenylene vinylene) with Stimuli‐Responsive Behavior

AbstractIncorporation of BN units into π‐conjugated organic compounds, as substitutes for specific CC couples, often leads to new hybrid materials with modified physical and chemical properties. Poly(p‐phenylene iminoborane)s are derived from well‐known poly(p‐phenylene vinylene) (PPV) by replacement of the vinylene groups by B=N linking units. Herein, an unprecedented poly(p‐phenylene iminoborane) is presented that features a strictly alternating sequence of BN units along the main chain. The synthesis thereof was achieved by AB‐type polymerization of a monomer featuring an N and a B terminus. Monodisperse oligomers with up to three BN units in the chain were additionally prepared and structurally characterized. Associated with the introduction of a dipole in the regioregular backbone structure, they display notable fluorescence already in solution and large Stokes shifts, distinct from their previously reported BBNN‐sequenced congeners. All compounds show aggregation‐induced emission enhancement (AIEE) properties. Computational studies provided evidence for emission from either locally excited (LE) or twisted intramolecular charge transfer (TICT) states. These processes can be optionally addressed by various stimuli, giving rise to dual emission, solvatochromic, thermochromic, and reversible mechanochromic behavior.

Regioregular Poly(p-phenylene iminoborane): A Strictly Alternating BN-Isostere of Poly(p-phenylene vinylene) with Stimuli-Responsive Behavior.

Incorporation of BN units into π-conjugated organic compounds, as substitutes for specific CC couples, often leads to new hybrid materials with modified physical and chemical properties. Poly(p-phenylene iminoborane)s are derived from well-known poly(p-phenylene vinylene) (PPV) by replacement of the vinylene groups by B=N linking units. Herein, an unprecedented poly(p-phenylene iminoborane) is presented that features a strictly alternating sequence of BN units along the main chain. The synthesis thereof was achieved by AB-type polymerization of a monomer featuring an N and a B terminus. Monodisperse oligomers with up to three BN units in the chain were additionally prepared and structurally characterized. Associated with the introduction of a dipole in the regioregular backbone structure, they display notable fluorescence already in solution and large Stokes shifts, distinct from their previously reported BBNN-sequenced congeners. All compounds show aggregation-induced emission enhancement (AIEE) properties. Computational studies provided evidence for emission from either locally excited (LE) or twisted intramolecular charge transfer (TICT) states. These processes can be optionally addressed by various stimuli, giving rise to dual emission, solvatochromic, thermochromic, and reversible mechanochromic behavior.

Magnetization reversal of perpendicular magnetic anisotropy multilayers on polymeric substrates for flexible spintronics applications

Earlier demonstrations of spintronic functionality on flexible substrates have highlighted the potential for spintronics in flexible electronics applications. However, for device applications, the relationship between global magnetization reversal, as measured by hysteresis, and the local reversal processes of nucleation and growth of magnetic domains need to be understood for magnetic systems on flexible substrates. This study compares the local magnetization reversal behavior of perpendicularly magnetized Pt/CoFeB/Pt and Pt/Co/Pt on rigid and flexible polymeric substrates using magneto-optical Kerr effect magnetometry and microscopy. It is shown that while the magnetic hysteresis is comparable, the local details of the nucleation and field driven reversal are quite different and are attributed to the greater variability of the surface structures of the polymeric substrates, which has implications for consistency in device performance.

A reversible positive and negative photoconductivity behavior modulated by polarization effect

Negative photoconductive devices exhibit a significant reduction in conductivity under illumination, enabling high-contrast optical modulation and promising great potential in optics. In this study, an ITO/BFCO/TiO2/FTO device was simply fabricated through a synergistic application of sol-gel and magnetron sputtering techniques. Interestingly, the ferroelectric polarization can be reversibly modulated by a low bias voltage in the ITO/BFCO/TiO2/FTO device, thereby exhibiting bipolar voltage dependent reversible behavior of positive and negative photoconductivity. This mechanism has been discussed, where the combined effect of illumination and applied voltage induces internal polarization reversal in Bi2FeCrO6, leading to a transition in the resistance state from low to high. This transition results in an elevation of the energy band, thereby impeding the migration of charge carriers. Additionally, femtosecond laser transient absorption spectroscopy reveals redshift in the initial absorption peak, indicating changes in the band structure induced by illumination, crucial for understanding carrier dynamics in a non-equilibrium state.

Reversal behavior and stability of spin textures with different topologies in ultrathin films

Reversal behavior and stability of spin textures with different topologies in ultrathin films

Twistocaloric effect versus elastocaloric effect in shape memory alloys for low-force mechanocaloric design

Abstract The mechanocaloric effect refers to the reversible thermal effect under an external mechanical field and includes the elastocaloric effect (under the uniaxial stress field) and the twistocaloric effect (under the torsional stress field). In mechanocaloric designs, the elastocaloric effect has been the mainstream of the field with an emphasis on enhancing the performance of the elastocaloric materials and implementing them into elastocaloric systems. The twistocaloric effect has been recognized in materials implementation and exhibits the potential of miniaturized design. In this report, we compare the elastocaloric effect to the twistocaloric effect in the aspects of 1) superelastic behaviors including the critical transformation stress, transformation plateau, and transformation hysteresis, 2) reversible thermal behaviors, and 3) distribution of stress and temperature. We have provided the threshold of applied force for the twistocaloric effect under a combined set of strain and strain rates. Compared to the elastocaloric effect, the twistocaloric effect requires less force for the comparable temperature change and at a similar level of applied force generates a higher temperature change. To capture the distribution of the mechanical and thermal fields, we have conducted simulation and in-situ experiments to drive insights into the low-field activated transformation process in twistocaloric design compared to elastocaloric design. These results provide mechanical and thermal information on comparing the elastocaloric and twistocaloric effects and can facilitate the advanced mechanocaloric design for solid-state cooling technologies.

Subtle Molecular Engineering around Flavin core for Stimuli-Responsive Solid-State Luminophore.

The present manuscript discusses the design, synthesis, and stimuli-responsive solid-state properties of two novel flavin analogues, Phenyl Flavin (PhFl) and Pyridinyl Flavin (PyFl), featuring covalently linked phenyl and pyridinyl rings to isoalloxazine. Stimuli-responsive properties of PhFl and PyFl were examined, where PyFl displayed more pronounced and reversible emissive behavior in the solid state in response to external stimuli. To elucidate the mechanism underlying the mode for switching behavior, single crystal- and powder-X-ray diffraction, as well as differential scanning calorimetry studies, were performed. Furthermore, a simple dip-in method was used to demonstrate its usage as ink free rewritable material.

Reversible Degradation Phenomenon in PEMWE Cells: An Experimental and Modeling Study

In proton exchange membrane water electrolysis (PEMWE) systems, voltage cycles dropping below a threshold are associated with reversible performance improvements, which remain poorly understood despite being documented in literature. The distinction between reversible and irreversible performance changes is crucial for accurate degradation assessments. One approach in literature to explain this behavior is the oxidation and reduction of iridium. Iridium-based electrocatalyst activity and stability in PEMWE hinge on their oxidation state, influenced by the applied voltage. Yet, full-cell PEMWE dynamic performance remains underexplored, with a focus typically on stability rather than activity. This study systematically investigates reversible performance behavior in PEMWE cells using Ir-black as an anodic catalyst. Results reveal a recovery effect when the low voltage level drops below 1.5 V, with further enhancements observed as the voltage decreases, even with a short holding time of 0.1 s. This reversible recovery is primarily driven by improved anode reaction kinetics, likely due to changing iridium oxidation states, and is supported by alignment between the experimental data and a dynamic model that links iridium oxidation/reduction processes to performance metrics. This model allows distinguishing between reversible and irreversible effects and enables the derivation of optimized operation schemes utilizing the recovery effect.

Biochemically plausible models of habituation for single-cell learning.

The ability to learn is typically attributed to animals with brains. However, the apparently simplest form of learning, habituation, in which a steadily decreasing response is exhibited to a repeated stimulus, is found not only in animals but also in single-cell organisms and individual mammalian cells. Habituation has been codified from studies in both invertebrate and vertebrate animals as having ten characteristic hallmarks, seven of which involve a single stimulus. Here, we show by mathematical modeling that simple molecular networks, based on plausible biochemistry with common motifs of negative feedback and incoherent feedforward, can robustly exhibit all single-stimulus hallmarks. The models reveal how the hallmarks arise from underlying properties of timescale separation and reversal behavior of memory variables, and they reconcile opposing views of frequency and intensity sensitivity expressed within the neuroscience and cognitive science traditions. Our results suggest that individual cells may exhibit habituation behavior as rich as that which has been codified in multi-cellular animals with central nervous systems and that the relative simplicity of the biomolecular level may enhance our understanding of the mechanisms of learning.

N-methyl-D-aspartate Receptors and Depression: Linking Psychopharmacology, Pathology and Physiology in a Unifying Hypothesis for the Epigenetic Code of Neural Plasticity

Uncompetitive NMDAR (N-methyl-D-aspartate receptor) antagonists restore impaired neural plasticity, reverse depressive-like behavior in animal models, and relieve major depressive disorder (MDD) in humans. This review integrates recent findings from in silico, in vitro, in vivo, and human studies of uncompetitive NMDAR antagonists into the extensive body of knowledge on NMDARs and neural plasticity. Uncompetitive NMDAR antagonists are activity-dependent channel blockers that preferentially target hyperactive GluN2D subtypes because these subtypes are most sensitive to activation by low concentrations of extracellular glutamate and are more likely activated by certain pathological agonists and allosteric modulators. Hyperactivity of GluN2D subtypes in specific neural circuits may underlie the pathophysiology of MDD. We hypothesize that neural plasticity is epigenetically regulated by precise Ca2+ quanta entering cells via NMDARs. Stimuli reach receptor cells (specialized cells that detect specific types of stimuli and convert them into electrical signals) and change their membrane potential, regulating glutamate release in the synaptic cleft. Free glutamate binds ionotropic glutamatergic receptors regulating NMDAR-mediated Ca2+ influx. Quanta of Ca2+ via NMDARs activate enzymatic pathways, epigenetically regulating synaptic protein homeostasis and synaptic receptor expression; thereby, Ca2+ quanta via NMDARs control the balance between long-term potentiation and long-term depression. This NMDAR Ca2+ quantal hypothesis for the epigenetic code of neural plasticity integrates recent psychopharmacology findings into established physiological and pathological mechanisms of brain function.

The role of morphological adaptability in Vibrio cholerae's motility.

This study highlights the enhanced motility of filamentous Vibrio cholerae in viscous environments, an adaptation that may provide a survival advantage in the human gastrointestinal tract. By demonstrating increased reversal behavior at mucin interfaces, filamentous V. cholerae cells exhibit a superior ability to penetrate the mucus layer, which is crucial for effective colonization and infection. Filamentous cells in bile-supplemented media further underscores their potential role in disease pathogenesis. These findings offer critical insights into the morphological flexibility of V. cholerae and its potential implications for infection dynamics, paving the way for more effective strategies in managing and preventing cholera outbreaks.

Reversible Performance Dynamics in PEM Water Electrolysis: An Electrochemical Study

In Proton Exchange Membrane Water Electrolysis (PEMWE) systems, a notable phenomenon occurs following voltage transitions from low to high, such as after a shutdown and subsequent startup: the cell performance initially improves, higher currents are achieved, then gradually returns to baseline (s. Figure 1). This reversible performance behavior remains poorly understood despite documentation in the literature, see e.g., ref. [1, 2], and laboratory observations. However, distinguishing between reversible and irreversible performance losses is essential for accurate degradation assessments, emphasizing the need for detailed exploration of the underlying mechanisms.The activity and stability of iridium-based electrocatalysts, crucial for the oxygen evolution reaction (OER) within PEMWE systems, depend on their iridium oxidation state, which varies with the applied voltage. While studies typically explore these oxidation state changes in aqueous model systems such as rotating disk electrodes (RDE) and scanning flow cells (SFC), the focus is often more on stability than on activity changes [2]. However, the current understanding of the catalysts' dynamic performance in PEMWE full-cell configurations remains incomplete.In this study, a systematic experimental investigation of the reversible performance behavior of PEMWE cells was conducted. Tests were performed with single PEM water electrolysis cells with an active area of 4 cm², using a Nafion™ 115 catalyst-coated membrane. The anode and cathode loadings were 2.0 mgIr/cm² and 1.0 mgPt/cm², respectively. The voltage-driven experiments aimed to identify the voltage level that triggers performance recovery, evaluate the significance of this improvement depending on the low-voltage level, and assess how the duration of low-voltage phases affects recovery.The results demonstrated that a recovery effect occurred once the low-voltage level dropped below 1.5 V, with further enhancements in recovery observed as the voltage continued to decrease. This effect was evident even with a brief holding time of 0.1 s at the lower voltage level. The reversible recovery is primarily driven by increased kinetics, likely influenced by voltage-dependent changes in iridium oxidation states. These observations are strongly supported by a robust alignment between the experimental data and a novel dynamic 0D model, which links iridium oxidation/reduction processes to performance metrics.By investigating the dynamic behavior of iridium-based electrocatalysts in full-cell configurations, this research enriches the understanding of reversible performance phenomena in PEMWE cells. It provides an essential foundation for future studies to understand the mechanisms behind these reversible phenomena.We gratefully acknowledge the financial support of the HyThroughGen project (BMBF 03HY108C) and the Deriel project (BMBF 03HY122A).