Ice-Binding Proteins and Their Function.

Ice-binding proteins (IBPs) are a diverse class of proteins that assist organism survival in the presence of ice in cold climates. They have different origins in many organisms, including bacteria, fungi, algae, diatoms, plants, insects, and fish. This review covers the gamut of IBP structures and functions and the common features they use to bind ice. We discuss mechanisms by which IBPs adsorb to ice and interfere with its growth, evidence for their irreversible association with ice, and methods for enhancing the activity of IBPs. The applications of IBPs in the food industry, in cryopreservation, and in other technologies are vast, and we chart out some possibilities.

Transient Hysteresis in CDK4/6 Activity Underlies Passage of the Restriction Point in G1.

Cells escape the need for mitogens at a restriction point several hours before entering S phase. The restriction point has been proposed to result from CDK4/6 initiating partial Rb phosphorylation to trigger a bistable switch whereby cyclin E-CDK2 and Rb mutually reinforce each other to induce Rb hyperphosphorylation. Here, using single-cell analysis, we unexpectedly found that cyclin E/A-CDK activity can only maintain Rb hyperphosphorylation starting at the onset of S phase and that CDK4/6 activity, but not cyclin E/A-CDK activity, is required to hyperphosphorylate Rb throughout G1 phase. Mitogen removal in G1 results in a gradual loss of CDK4/6 activity with a high likelihood of cells sustaining Rb hyperphosphorylation until S phase, at which point cyclin E/A-CDK activity takes over. Thus, it is short-term memory, or transient hysteresis, in CDK4/6 activity following mitogen removal that sustains Rb hyperphosphorylation, demonstrating a probabilistic rather than an irreversible molecular mechanism underlying the restriction point.

On the engulfment of antifreeze proteins by ice.

Antifreeze proteins (AFPs) are remarkable biomolecules that suppress ice formation at trace concentrations. To inhibit ice growth, AFPs must not only bind to ice crystals, but also resist engulfment by ice. The highest supercooling, [Formula: see text], for which AFPs are able to resist engulfment is widely believed to scale as the inverse of the separation, [Formula: see text], between bound AFPs, whereas its dependence on the molecular characteristics of the AFP remains poorly understood. By using specialized molecular simulations and interfacial thermodynamics, here, we show that in contrast with conventional wisdom, [Formula: see text] scales as [Formula: see text] and not as [Formula: see text]. We further show that [Formula: see text] is proportional to AFP size and that diverse naturally occurring AFPs are optimal at resisting engulfment by ice. By facilitating the development of AFP structure-function relationships, we hope that our findings will pave the way for the rational design of AFPs.

Path-dependence of the Plio-Pleistocene glacial/interglacial cycles.

We find strong path dependence in the evolution of the Plio-Pleistocene glaciations using CLIMBER-2 Earth System Model simulations from the mid-Pliocene to modern preindustrial (3 My-0 My BP) driven by a gradual decrease in volcanic carbon dioxide outgassing and regolith removal from basal ice interaction. Path dependence and hysteresis are investigated by alternatively driving the model forward and backward in time. Initiating the model with preindustrial conditions and driving the model backward using time-reversed forcings, the increase in volcanic outgassing back-in-time (BIT) does not generate the high CO2 levels and relatively ice-free conditions of the late Pliocene seen in forward-in-time (FIT) simulations of the same model. This behavior appears to originate from nonlinearities and initial state dependence in the carbon cycle. A transition from low-amplitude sinusoidal obliquity (~41 ky) and precession (~23 ky) driven glacial/interglacial cycles to high-amplitude ~100 ky likely eccentricity-related sawtooth cycles seen between -1.25 My and -0.75 My BP (the Mid-Pleistocene transition or "MPT") in FIT simulations disappears in BIT integrations depending on the details of how the regolith removal process is treated. A transition toward depleted regolith and lowered atmospheric CO2 levels are both required to reproduce the MPT.

The oscillation of mitotic kinase governs cell cycle latches in mammalian cells.

The mammalian cell cycle alternates between two phases - S-G2-M with high levels of A- and B-type cyclins (CycA and CycB, respectively) bound to cyclin-dependent kinases (CDKs), and G1 with persistent degradation of CycA and CycB by an activated anaphase promoting complex/cyclosome (APC/C) bound to Cdh1 (also known as FZR1 in mammals; denoted APC/C:Cdh1). Because CDKs phosphorylate and inactivate Cdh1, these two phases are mutually exclusive. This 'toggle switch' is flipped from G1 to S by cyclin-E bound to a CDK (CycE:CDK), which is not degraded by APC/C:Cdh1, and from M to G1 by Cdc20-bound APC/C (APC/C:Cdc20), which is not inactivated by CycA:CDK or CycB:CDK. After flipping the switch, cyclin E is degraded and APC/C:Cdc20 is inactivated. Combining mathematical modelling with single-cell timelapse imaging, we show that dysregulation of CycB:CDK disrupts strict alternation of the G1-S and M-G1 switches. Inhibition of CycB:CDK results in Cdc20-independent Cdh1 'endocycles', and sustained activity of CycB:CDK drives Cdh1-independent Cdc20 endocycles. Our model provides a mechanistic explanation for how whole-genome doubling can arise, a common event in tumorigenesis that can drive tumour evolution.

Elastic heterogeneity governs asymmetric adsorption-desorption in a soft porous crystal.

Metal-organic frameworks (MOFs), which possess a high degree of crystallinity and a large surface area with tunable inorganic nodes and organic linkers, exhibit high stimuli-responsiveness and molecular adsorption selectivity that enable various applications. The adsorption in MOFs changes the crystalline structure and elastic moduli. Thus, the coexistence of adsorbed/desorbed sites makes the host matrices elastically heterogeneous. However, the role of elastic heterogeneity in the adsorption-desorption transition has been overlooked. Here, we show the asymmetric role of elastic heterogeneity in the adsorption-desorption transition. We construct a minimal model incorporating adsorption-induced lattice expansion/contraction and an increase/decrease in the elastic moduli. We find that the transition is hindered by the entropic and energetic effects which become asymmetric in the adsorption process and desorption process, leading to the strong hysteretic nature of the transition. Furthermore, the adsorbed/desorbed sites exhibit spatially heterogeneous domain formation, implying that the domain morphology and interfacial area between adsorbed/desorbed sites can be controlled by elastic heterogeneity. Our results provide a theoretical guideline for designing soft porous crystals with tunable adsorption hysteresis and the dispersion and domain morphology of adsorbates using elastic heterogeneity.

In vitro cell cycle oscillations exhibit a robust and hysteretic response to changes in cytoplasmic density.

Cells control the properties of the cytoplasm to ensure proper functioning of biochemical processes. Recent studies showed that cytoplasmic density varies in both physiological and pathological states of cells undergoing growth, division, differentiation, apoptosis, senescence, and metabolic starvation. Little is known about how cellular processes cope with these cytoplasmic variations. Here, we study how a cell cycle oscillator comprising cyclin-dependent kinase (Cdk1) responds to changes in cytoplasmic density by systematically diluting or concentrating cycling Xenopus egg extracts in cell-like microfluidic droplets. We found that the cell cycle maintains robust oscillations over a wide range of deviations from the endogenous density: as low as 0.2× to more than 1.22× relative cytoplasmic density (RCD). A further dilution or concentration from these values arrested the system in a low or high steady state of Cdk1 activity, respectively. Interestingly, diluting an arrested cytoplasm of 1.22× RCD recovers oscillations at lower than 1× RCD. Thus, the cell cycle switches reversibly between oscillatory and stable steady states at distinct thresholds depending on the direction of tuning, forming a hysteresis loop. We propose a mathematical model which recapitulates these observations and predicts that the Cdk1/Wee1/Cdc25 positive feedback loops do not contribute to the observed robustness, supported by experiments. Our system can be applied to study how cytoplasmic density affects other cellular processes.

A Time-Domain Perspective on the Structural and Electronic Response in Epitaxial Ferroelectric Thin Films on Silicon.

This operando study of epitaxial ferroelectric Pb(Zr0.48Ti0.52)O3 capacitors on silicon substrates studies their structural response via synchrotron-based time-resolved X-ray diffraction during hysteresis-loop measurements in the 2-200 kHz range. At high frequencies, the polarization hysteresis loop is rounded and the classical butterfly-like strain hysteresis acquires a flat dumbbell shape. We explain these observations from a time-domain perspective: The polarization and structural motion within the unit cell are coupled to the strain by the piezoelectric effect and limited by domain wall velocity. The solution of this coupled oscillator system is derived experimentally from the simultaneously measured electronic and structural data. The driving stress σFE(t) is calculated as the product of the measured voltage U(t) and polarization P(t). Unlike the electrical variables, σFE(t) and η(t) of the ferroelectric oscillate at twice the frequency of the applied electrical field. We model the measured frequency-dependent phase shift between η(t) and σFE(t).

MXene Crosslinked Hydrogels with Low Hysteresis Conferred by Sliding Tangle Island Strategy.

Single-network hydrogels are often too fragile to withstand mechanical loading, whereas double-network hydrogels typically exhibit significant hysteresis during cyclic stretching-releasing process due to the presence of a sacrificial network. Consequently, it is a considerable challenge for designing hydrogels that are both low in hysteresis and high in toughness for applications requiring dynamic mechanical loads. Herein, the study introduced a novel "sliding tangle island" strategy for creating tough and low-hysteresis hydrogels, which are prepared through in situ polymerization of highly concentrated acrylamides (AM) to form numerous entanglements within the MXene spacing without any chemical crosslinker. The MXene entangled with long polyacrylamide (PAM) chains to form tangle island that served as a relay station to transmit stress to neighboring molecular chains. This mechanism helps alleviate stress concentration and enhances energy dissipation efficiency, thereby reducing mechanical hysteresis. The resulting hydrogel exhibited exceptional properties, including high stretchability (≈900%), low hysteresis (less than 7%), high toughness (1.34 MJ m-3), and excellent sensing performance to rival the commercial hydrogel electrode. Therefore, this work sheds light on feasible design of energy dissipation structure to reduce the hysteresis of the composite hydrogels.

3D Printing of Thermo-Mechano-Responsive Photoluminescent Noncovalent Cross-Linked Ionogels with High-Stretchability and Ultralow-Hysteresis for Wearable Ionotronics and Anti-Counterfeiting.

Ionogel has recently emerged as a promising ionotronic material due to its good ionic conductivity and flexibility. However, low stretchability and significant hysteresis under long-term loading limit their mechanical stability and repeatability. Developing ultralow hysteresis ionogels with high stretchability is of great significance. Here, a simple and effective strategy is developed to fabricate highly stretchable and ultralow-hysteresis noncovalent cross-linked ionogels based on phase separation by 3D printing of 2-hydroxypropyl acrylate (HPA) in 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4). Ingeniously, the sea-island structure of the physically cross-linked network constructed by the smaller nanodomains and larger nanodomain clusters significantly minimizes the energy dissipation, endowing these ionogels with remarkable stretchability (>1000%), ultra-low hysteresis (as low as 0.2%), excellent temperature tolerance (-33-317 °C), extraordinary ionic conductivity (up to 1.7 mS cm-1), and outstanding durability (5000 cycles). Moreover, due to the formation of nanophase separation and cross-linking structure, the as-prepared ionogels exhibit unique thermochromic and multiple photoluminescent properties, which can synergistically be applied for anti-counterfeiting and encrypting. Importantly, flexible thermo-mechano-multimodal visual ionotronic sensors for strain and temperature sensing with highly stable and reproducible electrical response over 20 000 cycles are fabricated, showing synergistically optical and electrical output performances.

On the Low-Pressure Hysteresis (LPH) in Gas Sorption Isotherms of Porous Carbons.

This study investigates the origin of low-pressure hysteresis (LPH) in the adsorption and desorption of three different probe molecules: carbon dioxide, nitrogen, and argon, across various adsorption temperatures (from cryogenic to room temperature), and within five different carbon materials: synthetic carbons (pristine and one post-synthetically oxidized) and natural coal. Significant attention is dedicated to elucidating LPH in oxidized samples outgassed at various temperatures (120-350 °C). Experimental results show that insufficient outgassing temperature can lead to unreliable data due to artificial LPH and significantly underestimated textural properties, primarily caused by porosity blockage from substances like moisture. Conversely, in samples where heteroatoms have a stabilizing effect on texture, such as natural coal, careful consideration of outgassing temperature is crucial due to the risk of thermal degradation. Other factors contributing to LPH are adsorption temperature, and especially, kinetic limitations at cryogenic temperatures for cellulose-based carbons. Minor factors responsible for LPH are the physical state of the sample (monolith vs powder) and the flexibility of the porous system, both studied by carbon dioxide sorption. This study constitutes an important piece in the evaluation of LPH, providing practical recommendations and underlining the importance of experimental design, with implications for further research in this complex field.

Hysteresis-Free, Elastic, and Tough Hydrogel with Stretch-Rate Independence and High Stability in Physiological Conditions.

Many existing synthetic hydrogels are inappropriate for repetitive motions because of large hysteresis, and their mechanical properties in warm and saline physiological conditions remain understudied. In this study, a stretch-rate-independent, hysteresis-free, elastic, and tough nanocomposite hydrogel that can maintain its mechanical properties in phosphate-buffered saline of 37 °C similar to warm and saline conditions of the human body is developed. The strength, stiffness, and toughness of the hydrogel are simultaneously reinforced by biomimetic silica nanoparticles with a surface of embedded circular polyamine chains. Such distinctive surfaces form robust interfacial interactions by local topological folding/entanglement with the polymer chains of the matrix. Load transfer from the soft polymer matrix to stiff nanoparticles, along with the elastic sliding/unfolding/disentanglement of polymer chains, overcomes the traditional trade-off between strength/stiffness and toughness and allows for hysteresis-free, strain-rate-independent, and elastic behavior. This robust reinforcement is sustained in warm phosphate-buffered saline. These properties demonstrate the application potential of the developed hydrogel as a soft, elastic, and tough bio-strain sensor that can detect dynamic motions across various deformation speeds and ranges. The findings provide a simple yet effective approach to developing practical hydrogels with a desirable combination of strength/stiffness and toughness, in a fully swollen and equilibrated state.

Ionic Bonding Without Directionality Facilitates Efficient Interfacial Bridging for Perovskite Solar Cells.

Interface passivation through Lewis acid-base coordinate chemistry in perovskite solar cells (PSCs) is a universal strategy to reduce interface defects and hinder ion migration. However, the formation of coordinate covalent bonding demands strict directional alignment of coordinating atoms. Undoubtedly, this limits the selected range of the interface passivation molecules, because a successful molecular bridge between charge transport layer and perovskite bottom interface needs a well-placed molecular orientation. In this study, it is discovered that potassium ions can migrate to the hollow sites of multiple iodine ions from perovskite to form K-Ix ionic bonding, and the ionic bonds without directionality can support molecular backbone rotation to facilitate polar sites (carboxyl groups) chelating Pb at the bottom perovskite interface, finally forming a closed-loop bonding structure. The synergy of coordinate and ionic bonding significantly reduces interface defects, changes electric field distribution, and immobilizes iodine at the perovskite bottom interface, resulting in eliminating the hysteresis effect and enhancing the performance of PSCs. As a result, the corresponding devices achieve a high efficiency exceeding 24.5% (0.09 cm2), and a mini-module with 21% efficiency (12.4 cm2). These findings provide guidelines for designing molecular bridging strategies at the buried interface of PSCs.

Achieving a Rapid Na+ Migration and Highly Reversible Phase Transition of NASICON for Sodium-Ion Batteries with Suppressed Voltage Hysteresis and Ultralong Lifespan.

Sodium ion batteries have attracted great attention for large scale energy storage devices to replace lithium-ion batteries. As a promising polyanionic cathode material of sodium-ion batteries, Na3V2(PO4)2F3 (NVPF) belonging to NASICON exhibits large gap space and excellent structural stability, leading to a high energy density and ultralong cycle lifespan. To improve its stability and Na ion mobility, K+ cations are introduced into NVPF crystal as in situ partial substitution for Na+. The influence of K+ in situ substitution on crystal structure, electronic properties, kinetic properties, and electrochemical performance of NVPF are investigated. Through ex situ examination, it turns out that K+ occupied Na1 ion, in which the K+ does not participate in the charge-discharge process and plays a pillar role in improving the mobility of Na+. Moreover, the doping of K+ cation can reduce the bandgap energy and improve the electronic conductivity. Besides, the optimal K+ doping concentration in N0.92K0.08VPF/C is found so as to achieve rapid Na+ migration and reversible phase transition. The specific capacity of N0.92K0.08VPF/C is as high as 128.8 mAh g-1 at 0.2 C, and at 10 C its rate performance is excellent, which shows a capacity of 113.3 mAh g-1.

Measuring magnetic hysteresis curves with polarized soft X-ray resonant reflectivity.

Calculations and measurements of polarization-dependent soft X-ray scattering intensity are presented during a magnetic hysteresis cycle. It is confirmed that the dependence of the intensity on the magnetic moment can be linear, quadratic or a combination of both, depending on the polarization of the incident X-ray beam and the direction of the magnetic moment. With a linearly polarized beam, the scattered intensity will have a purely quadratic dependence on the magnetic moment when the magnetic moment is parallel to the scattering plane. However, with the magnetic moment perpendicular to the scattering plane, there is also a linear component. This means that, when measuring the hysteresis with linear polarization during a hysteresis cycle, the intensity will be an even function of the applied field when the change in the magnetic moment (and field) is confined within the scattering plane but becomes more complicated when the magnetic moment is out of the scattering plane. Furthermore, with circular polarization, the dependence of the scattered intensity on the moment is a combination of linear and quadratic. With the moment parallel to the scattering plane, the linear component changes with the helicity of the incident beam. Surprisingly, in stark contrast to absorption studies, even when the magnetic moment is perpendicular to the scattering plane there is still a dependence on the moment with a linear component. This linear component is completely independent of the helicity of the beam, meaning that the hysteresis loops will not be inverted with helicity.

Engineered Compounds to Control Ice Nucleation and Recrystallization.

One of the greatest concerns in the subzero storage of cells, tissues, and organs is the ability to control the nucleation or recrystallization of ice. In nature, evidence of these processes, which aid in sustaining internal temperatures below the physiologic freezing point for extended periods of time, is apparent in freeze-avoidant and freeze-tolerant organisms. After decades of studying these proteins, we now have easily accessible compounds and materials capable of recapitulating the mechanisms seen in nature for biopreser-vation applications. The output from this burgeoning area of research can interact synergistically with other novel developments in the field of cryobiology, making it an opportune time for a review on this topic.

Temperature-Modulated Reversible Clustering of Gold Nanorods Driven by Small Surface Ligands.

Temperature-modulated colloidal phase of plasmonic nanoparticles is a convenient playground for resettable soft-actuators or colorimetric sensors. To render reversible clustering under temperature change, bulky ligands are required, especially if anisotropic morphologies are of interest. This study showcases thermoresponsive gold nanorods by employing small surface ligands, bis (p-sulfonatophenyl) phenyl-phosphine dihydrate dipotassium salt (BSPP) and native cationic surfactant. Temperature-dependent analysis in real-time allowed to describe the structural features (interparticle distance and cluster size) as well as thermal parameters, melting and freezing temperatures. These findings suggest that neither covalent Au-S bonds nor bulky ligands are required to obtain a robust thermoresponsive system based on anisotropic gold nanoparticles, paving the way to stimuli-responsive nanoparticles with a wide range of sizes and geometries.

Post-device Dimethylamine Treatment Enables Stable and Efficient Perovskite Solar Cells.

The incorporation of organic ligands via post-device treatment is an effective strategy to improve the stability of perovskite solar cells (PSCs). Although the active area is protected by metal electrode under post-treatment, the aggression of post-treatment ligands into active area cannot be avoided thoroughly. Unfortunately, the size of long-chain amines is too large, and the three-dimensional (3D) perovskite cannot maintain its 3D perovskite structure once the cation substitution occurs during the post-treatment. Despite that the low-dimensional (LD) perovskites are beneficial to stability, long-chain amines are harmful to carrier transport in PSCs. Here, we introduce dimethylamine (DMA), a slightly oversized cation that can be doped into 3D perovskite structure, for post-device treatment to improve the efficiency and stability of PSCs. After exposure to DMA gas, the inactive area of Cs/FA/MA mixed cation perovskite device that is not covered by metal electrode is converted into LD perovskite, passivating the defects of 3D perovskite in the active region, suppressing non-radiation recombination and ion migration. As a result, we achieved a power conversion efficiency (PCE) of 22.29 % with negligible hysteresis and better stability after DMA post-treatment, which is much higher than that (20.40 %) of the control device.

Effects of gamma-ray irradiation on material and electrical properties of AlN gate dielectric on 4H-SiC.

This article investigates the radiation effects on as-deposited and annealed AlN films on 4H-SiC substrates under gamma-rays. The AlN films are prepared using plasma-enhanced-atomic-layer-deposition on an n-type 4H-SiC substrate. The AlN/4H-SiC MIS structure is subjected to gamma-ray irradiation with total doses of 0, 300, and 600 krad(Si). Physical, chemical, and electrical methods were employed to study the variations in surface morphology, charge transport, and interfacial trapping characteristics induced by irradiation. After 300 krad(Si) irradiation, the as-deposited and annealed samples exhibit their highest root mean square values of 0.917 nm and 1.190 nm, respectively, which is attributed to N vacancy defects induced by irradiation. Under irradiation, the flatband voltage (Vfb) of the as-deposited sample shifts from 2.24 to 0.78 V, while the annealed sample shifts from 1.18 to 2.16 V. X-ray photoelectron spectrum analysis reveals the decomposition of O-related defects in the as-deposited AlN and the formation of Al(NOx)ycompounds in the annealed sample. Furthermore, the space-charge-limits-conduction (SCLC) in the as-deposited sample is enhanced after radiation, while the barrier height of the annealed sample decreases from 1.12 to 0.84 eV, accompanied by the occurrence of the SCLC. The physical mechanism of the degradation of electrical performance in irradiated devices is the introduction of defects like N vacancies and O-related defects like Al(NOx)y. These findings provide valuable insights for SiC power devices in space applications.

Defining ferroelectric characteristics with reversible piezoresponse: PUND switching spectroscopy PFM characterization.

Detecting ferroelectricity at micro- and nanoscales is crucial for advanced nanomaterials and materials with complicated topography. Switching spectroscopy piezoresponse force microscopy (SSPFM), which involves measuring piezoelectric hysteresis loops via a scanning probe microscopy tip, is a widely accepted approach to characterize polarization reversal at the local scale and confirm ferroelectricity. However, the local hysteresis loops acquired through this method often exhibit unpredictable shapes, a phenomenon often attributed to the influence of parasitic factors such as electrostatic forces and current flow. Our research has uncovered that the deviation in hysteresis loop shapes can be caused by spontaneous backswitching occurring after polarization reversal. Moreover, we've determined that the extent of this effect can be exacerbated when employing inappropriate SSPFM waveform parameters, including duration, frequency, and AC voltage amplitude. Notably, the conventional 'pulse-mode' SSPFM method has been found to intensify spontaneous backswitching. In response to these challenges, we have redesigned SSPFM approach by introducing the positive up-negative down (PUND) method within the 'step-mode' SSPFM. This modification allows for effective probing of local piezoelectric hysteresis loops in ferroelectrics with reversible piezoresponse while removing undesirable electrostatic contribution. This advancement extends the applicability of the technique to a diverse range of ferroelectrics, including semiconductor ferroelectrics and relaxors, promising a more reliable and accurate characterization of their properties.