Trapped Water Molecules Research Articles

Role of Trapped Molecules at Sliding Contacts in Lattice-Resolved Friction.

Understanding atomic friction within a liquid environment is crucial for engineering friction mechanisms and characterizing surfaces. It has been suggested that the lattice resolution of friction force microscope in liquid environments stems from a dry contact state, with all liquid molecules expelled from the area of closest approach between the tip and substrate. Here, we revisit this assertion by performing in-depth friction force microscopy experiments and molecular dynamics simulations of the influence of surrounding water molecules on the dynamic behavior of the nanotribological contact between an amorphous SiO2 probe and a monolayer MoS2 substrate. An analysis of simulation and experimental stick-slip patterns demonstrates the entrapment of water molecules at the contact interface. These trapped water molecules behave as an integral component of the probe and participate in its interaction with the substrate, affecting the dynamics of the probe and preventing long slips. Significantly, surrounding water from the capillary or layer exhibits a replenishing effect, acting as a water reservoir during sliding. This phenomenon facilitates the preservation of lattice-scale resolution across a range of applied normal loads.

Microsyringe-assisted visual volume detection based on phase separation: the case of chymosin milk-clotting activity study.

The constantly diverse demand scenarios for rapid on-site analysis have put forward high requirements for developing low-cost and user-friendly visual detection methods. Therefore, developing a visual detection method with simple operation and intuitive results has important practical value in the field of analysis and detection, but it is also challenging. In this work, we propose a microsyringe-assisted visual volume detection method based on phase separation, and apply it to analyze the milk-clotting activity of chymosin. Chymosin can cause phase separation of milk with whey in the mobile phase and curd in the gel state. The network structures of casein in curd can trap water molecules, resulting in separation of whey from curd gradually. Therefore, the analysis of chymosin milk-clotting activity can be realized according to the volume of whey measured using a portable microsyringe. This method shows a good linear correlation when the concentration of chymosin ranges from 1.02 U L-1 to 1020 U L-1 and the limit of detection of this method for chymosin is calculated to be 0.03 U mL-1. This work successfully realizes the visual analysis of chymosin milk-clotting activity based on the enzyme-triggered phase separation. It also shows great promise to be applied in other phase separation-based detection systems with the advantages of high accuracy, great portability and user-friendliness.

Water Catchers within Sub-Nano Channels Promote Step-by-Step Zinc-Ion Dehydration Enable Highly Efficient Aqueous Zinc-Metal Batteries.

Zinc metal suffers from violent and long-lasting water-induced side reactions and uncontrollable dendritic Zn growth, which seriously reduce the coulombic efficiency (CE) and lifespan of aqueous zinc-metal batteries (AZMBs). To suppress the corresponding harmful effects of the highly active water, a stable zirconium-based metal-organic framework with water catchers decorated inside its sub-nano channels is used to protect Zn-metal. Water catchers within narrow channels can constantly trap water molecules from the solvated Zn-ions and facilitate step-by-step desolvation/dehydration, thereby promoting the formation of an aggregative electrolyte configuration, which consequently eliminates water-induced corrosion and side reactions. More importantly, the functionalized sub-nano channels also act as ion rectifiers and promote fast but even Zn-ions transport, thereby leading to a dendrite-free Zn metal. As a result, the protected Zn metal demonstrates an unprecedented cycling stability of more than 10000 h and an ultra-high average CE of 99.92% during 4000 cycles. More inspiringly, a practical NH4V4O10//Zn pouch-cell is fabricated and delivers a capacity of 98 mAh (under high cathode mass loading of 25.7mg cm-2) and preserves 86.2% capacity retention after 150 cycles. This new strategy in promoting highly reversible Zn metal anodes would spur the practical utilization of AZMBs.

Distance-based lateral flow biosensor for the quantitative detection of bacterial endotoxin

Bacterial endotoxin (a type of lipopolysaccharide, LPS) that acts as the strongest immune stimulant exhibits high toxicity to human health. The golden standard detection methods rely heavily on the use of a large amount of tachypleus amebocyte lysate (TAL) reagents, extracted from the unique blue blood of legally protected horseshoe crabs. Herein, a cost-effective distance-based lateral flow (D-LAF) sensor is demonstrated for the first time based on the coagulation cascade process of TAL induced by endotoxin, which causes the generation of gel-state TAL. The gelation process can increase the amount of trapped water molecules and shorten the lateral flow distance of the remaining free water on the pH paper. The water flow distance is directly correlated to the concentration of endotoxin. Noteworthy, the D-LAF sensor allows the detection of endotoxin with the reduced dosage of TAL reagents than the golden standard detection methods. The detection limit of endotoxin is calculated to be 0.0742 EU/mL. This method can be applied to the detection of endotoxin in real samples such as household water and clinical injection solution with excellent performance comparable to the commercial ELISA kit.

Ionic Covalent Organic Framework as a Dual Functional Sensor for Temperature and Humidity.

Visual sensing of humidity and temperature by solids plays an important role in the everyday life and in industrial processes. Due to their hydrophobic nature, most covalent organic framework (COF) sensors often exhibit poor optical response when exposed to moisture. To overcome this challenge, the optical response is set out to improve, to moisture by incorporating H-bonding ionic functionalities into the COF network. A highly sensitive COF, consisting of guanidinium and diformylpyridine linkers (TG-DFP), capable of detecting changes in temperature and moisture content is fabricated. The hydrophilic nature of the framework enables enhanced water uptake, allowing the trapped water molecules to form a large number of hydrogen bonds. Despite the presence of non-emissive building blocks, the H-bonds restrict internal bond rotation within the COF, leading to reversible fluorescence and solid-state optical hydrochromism in response to relative humidity and temperature.

Nucleate boiling enhancement on hybrid graphene-nanoplatelets/carbon nanotubes coatings for light-emitting diode cooling

This study explores the remarkable enhancement of light-emitting diode (LED) cooling through nucleate boiling using hybrid coatings of graphene-nanoplatelets (GNP) and carbon nanotubes (CNT). The introduction of oxygenated functional groups in the cured GNP and CNT coatings fosters improved hydrophilicity, promoting water intercalation within the nanostructures. The hybrid cured GNP/CNT coating demonstrates superior nucleate boiling performance compared to individual cured GNP and CNT coatings, owing to complementary mechanisms. Cured CNT facilitate efficient water permeation by enabling water molecules to infiltrate through their inner cores and intertwining tube spaces, while cured GNP offer an escape route for trapped water molecules and absorbed latent heat due to their layer-by-layer arrangement of graphene sheets with broadened interlayers. As compared to the bare copper surface, the LED cooled using the hybrid cured GNP/CNT coating exhibits a maximum temperature drop of 20.7 °C and an enhancement up to 1212 % in heat transfer coefficient, surpassing the cured GNP and CNT coatings. Moreover, the hybrid cured GNP/CNT coating improves the LED illuminance by 16.6 %, validating its potency in improving cooling performance. These findings highlight the potential of GNP/CNT hybrid coatings in advancing nucleate boiling cooling technologies and offer valuable insights into optimizing LED performance for high-quality lighting solutions.

Water molecules in boron nitride interlayer space: ice and hydrolysis in super confinement.

Development of nano-sized channels and filters in the recent years has made the role of water immensely important as water molecules affect their performance and durability. Here, we take advantage of molecular dynamics and density functional theory methods to demonstrate the shift in behavior of water molecules confined between hexagonal boron nitride (HBN) sheets spaced at 3.0 to 6.5 Å. Our results demonstrate that lower interlayer spaces cause higher amounts of charge transferred between the species, while at extreme degrees of confinement, these interactions cause the disintegration of trapped water molecules. Consequently, the inner face of the HBN sheets is functionalized with hydroxyl groups, releasing hydrogens in the form of protons that travel the interlayer space by Grotthuss mechanism. This is the first-hand evidence of a mechanical form of hydrolysis that corresponds with a nucleophilic attack (on boron atoms) to relieve water from extreme confined conditions. This process unveils a previously unknown behavior of water within extremely confined spaces and reveals new considerations concerning nanofilters and nanochannels.

Global “Interface‐Space” Dual‐Modulation by Functional Supramolecules Organic Frameworks on Aqueous Zinc‐Ion Batteries

AbstractThe uneven zinc‐ion flux and interfacial contact between the anode and electrolyte trigger malignant dendrites and byproducts, significantly hindering the practical application of zinc‐metal batteries. Herein, a H‐bonded supramolecular organic framework (HSOF) is proposed to help regulate Zn2+ flux and stabilize interfacial chemistry. The self‐assembled supermolecule structures by in‐plane H‐bond networks firmly trap water molecules to assist Zn2+ de‐solvation and block interfacial corrosion. The abundant polar groups provide strong guidance for Zn2+ distribution, ensuring homogeneous, and rapid ion transport‐deposition kinetics. Meanwhile, the π–π stacked space‐layout structure affords preferred Zn(002) plane stacking for smooth and flat growth. Benefiting from these advantages, the HSOFs are employed on Zn surface for interfacial adjustment and on separator decoration for spatial manipulation, successfully realizing an overall “interface‐space” dual‐regulation effect. It delivers over 3000 h for the HSOF@Zn anode in symmetric cell and up to 5000 h for HSOF‐decorated separator in Zn||Zn symmetric cell, respectively. The HSOF@Zn||V2O5 full cell with the HSOF‐decorated separator demonstrates enhanced capacity retention of 92.7% after 2500 cycles at 5 A g−1. The full cell can be easily scaled up into a pouch cell, which still has a capacity retention rate of 94% after 1000 cycles.

A multifunctional MXene-porous polydopamine interface for stable and dendrite-free zinc metal batteries

Aqueous zinc ion batteries are regarded one of the most promising next generation battery technologies for safe and low-cost energy storage applications. However, the inevitable dendrites growth and detrimental side reactions for Zn metal anodes in aqueous electrolytes induce short cycle life, low coulombic efficiencies, and cell failure. Here we propose to construct a MXene-porous polydopamine (MPP) interfacial layer on the Zn metal surface. The abundant functional groups in MPP can effectively trap water molecules to suppress their corrosion to Zn metal, indicating the desolvation and anticorrosion functions. Combined experimental and simulation results show that MPP layers can also lower the nucleation overpotentials and homogenize the electric field distribution and Zn ion flux, which ensure the horizontal and dendrite-free Zn metal deposition. The MPP-Zn electrodes exhibit an exceptionally long cycle life of over 1000 h (10 times that of bare Zn) and excellent high-rate capabilities in (a)symmetric cells. When the optimal Zn anodes were coupled with NH4V4O10 cathodes, the Zn metal full cells presented a remarkable capacity of 368 mAh g−1 and negligible capacity degradations after 300 cycles, which rivals the state-of-the-art performance in literature. The multifunction-in-one concept in this work would spur the development of practical Zn metal batteries.

Insight on the mechanism of hexagonal pyrrhotite depression by starch during flotation

Polysaccharides such as gelatinized starch have been largely employed to depress specific minerals during froth flotation. In this study, two samples of caustic gelatinized starch (paste starches) with different molecular weights (MW) were used as depressants for hexagonal pyrrhotite. There is an increasing interest in finding more environmentally friendly strategies to depress hexagonal pyrrhotite since this mineral is one major gangue minerals in nickeferrous ore deposits, for instance. The mechanism of adsorption of paste starches on hexagonal pyrrhotite was evaluated by different techniques. Equilibrium adsorption tests suggested that the adsorption is dependent on the depressant molecular weight if it is used in high concentrations. The sequence of conditioning also showed to be relevant. Pre-adsorbed collector highly influenced the adsorption of higher MW paste starch. Langmuir and Brunauer–Emmett–Teller (BET) model fittings of adsorption data in combination with Quartz Crystal Microbalance with Dissipation (QCM-D) results demonstrated a looser packing density of the higher MW paste starch. This conformation provides more room for water molecules within this depressant’s chains. Since trapped water molecules may generate a repulsive hydration force to air bubbles near the mineral surface, pyrrhotite conditioned with the high MW paste starch showed a lower flotation recovery. Higher hydration levels of the higher MW paste starch were also proven by Atomic Force Microscopy (AFM) tests, and indirectly quantified in the contact angle measurements (Washburn method). Although the higher MW paste starch adsorbs less, this depressant still provides a higher surface wettability. This study has reinforced the importance in considering the molecular size of a polysaccharide for sulfide mineral depression.

Probing Water Dissociation and Oxygen Replacement on Partially Oxygen-Covered Cu(111) by Reflection Absorption Infrared Spectroscopy.

The presence of chemisorbed oxygen on the Cu(111) surface is known to strongly reduce the activation barrier for water dissociation as compared to bare Cu(111). Here, we present direct experimental evidence for the hydrogen abstraction mechanism responsible for the facile H2O dissociation on an O/Cu(111) surface using reflection absorption infrared spectroscopy (RAIRS) in combination with isotopically labeled reactants. We also observe that chemisorbed hydroxyl species produced by water dissociation on the O/Cu(111) surface undergo an efficient hydrogen atom transfer from trapped water molecules, leading to the rapid replacement of the initial oxygen isotope coverage and the detection of only a single hydroxyl isotopologue on the surface, in apparent contradiction with the hydrogen abstraction mechanism. In the presence of Cu2O oxide islands on the O/Cu(111) surface, water dissociation occurs selectively at the edges of those islands, leading to the self-assembly of isotopically ordered structures.

PREPARATION OF FE-DOPED ZINC OXYSULFIDE (Fe-Zn(O,S)) WITH SURFACE DEFECT FOR HYDROGEN EVOLUTION REACTION

In this study, Fe-doped Zn(O,S) has been successfully fabricated by a one-step preparation process using chemical wet method. The Fe-doped Zn(O,S) photocatalysts were studied by varying the content of Fe dopant. The characterizations of Fe-doped Zn(O,S) were carried out by SEM and XRD analyses to determine the morphology and phase of samples. Furthermore, the optical and electrochemical properties were characterized through EIS, TPC, DRS and PL analyses. Briefly, Zn(O,S) with 5% Fe amount exhibited the most optimum condition as compared to other Fe amounts in which it showed better charge separation with the hydrogen evolution amount of 29000 mikromol/g in 10% EtOH solution. Lastly, the proposed mechanism is initially by the trapping of water molecules in the oxygen vacancy (defect) in Fe-Zn(O,S) sample followed by the reduction to generate hydrogen (H2) gas via the intermediate of proton (H+).

Constructing tough bilayer hydrogel with excellent lubrication performance for load-bearing application

Numerous strategies have been proposed to improve the strength and stiffness of hydrogels, which significantly sacrificed water content, thereby compromising lubrication properties. Hence, it remains challenging to develop elastic and strong hydrogels with excellent lubrication properties for a wide range of applications. Inspired by the stratified structure of natural bio-tissues, the mechanically strong bilayer hydrogels comprising of soft lubricating layer and hard load-bearing layer were prepared. The top porous structure could trap water molecules to achieve low friction (COF∼0.009) under a heavily loaded condition of 5 N (contact stress∼2.5 MPa), while the bottom layer provided excellent load-bearing capacity. The bilayer hydrogel with high mechanical strength, superior lubrication and excellent wear-resistance properties has considerable potential in joint replacement and tissue scaffold.

Probing a Hydrogen-π Interaction Involving a Trapped Water Molecule in the Solid State.

The detection and characterization of trapped water molecules in chemical entities and biomacromolecules remains a challenging task for solid materials. We herein present proton-detected solid-state Nuclear Magnetic Resonance (NMR) experiments at 100 kHz magic-angle spinning and at high static magnetic-field strengths (28.2 T) enabling the detection of a single water molecule fixed in the calix[4]arene cavity of a lanthanide complex by a combination of three types of non-covalent interactions. The water proton resonances are detected at a chemical-shift value close to zero ppm, which we further confirm by quantum-chemical calculations. Density Functional Theory calculations pinpoint to the sensitivity of the proton chemical-shift value for hydrogen-π interactions. Our study highlights how proton-detected solid-state NMR is turning into the method-of-choice in probing weak non-covalent interactions driving a whole branch of molecular-recognition events in chemistry and biology.

Untersuchung einer Wasserstoff‐π Wechselwirkung in einem eingeschlossenen Wassermolekül im Festkörper

AbstractDer Nachweis und die Charakterisierung von eingeschlossenen Wassermolekülen in chemischen Gebilden und Biomakromolekülen ist weiterhin eine Herausforderung für feste Materialien. Wir präsentieren hier Protonen‐detektierte Festkörper‐Kernspinresonanzspektroskopie (NMR) Experimente bei Rotationsfrequenzen von 100 kHz um den magischen Winkel und bei hohen statischen Magnetfeldstärken (28.2 T), die den Nachweis eines einzelnen Wassermoleküls ermöglichen, das im Calix[4]aren‐Hohlraum eines Lanthan‐Komplexes durch eine Kombination von drei Arten nicht‐kovalenter Wechselwirkungen fixiert ist. Die Protonenresonanzen des Wassers werden bei einer chemischen Verschiebung nahe Null ppm nachgewiesen, was wir durch quantenchemische Berechnungen bestätigen. Berechnungen mit der Dichtefunktionaltheorie zeigen, wie empfindlich der Wert der chemischen Verschiebung der Protonen auf Wasserstoff‐π‐Wechselwirkungen reagiert. Unsere Studie unterstreicht, wie sich die Protonen‐detektierte Festkörper NMR zur Methode der Wahl für die Untersuchung schwacher nicht‐kovalenter Wechselwirkungen entwickelt, die einen ganzen Zweig molekularer Erkennungsvorgänge in der Chemie und Biologie bestimmen.

Role of supramolecular polymers in photo-actuation of spiropyran hydrogels.

Supramolecular-covalent hybrid polymers have been shown to be interesting systems to generate robotic functions in soft materials in response to external stimuli. In recent work supramolecular components were found to enhance the speed of reversible bending deformations and locomotion when exposed to light. The role of morphology in the supramolecular phases integrated into these hybrid materials remains unclear. We report here on supramolecular-covalent hybrid materials that incorporate either high-aspect-ratio peptide amphiphile (PA) ribbons and fibers, or low-aspect-ratio spherical peptide amphiphile micelles into photo-active spiropyran polymeric matrices. We found that the high-aspect-ratio morphologies not only play a significant role in providing mechanical reinforcement to the matrix but also enhance photo-actuation for both light driven volumetric contraction and expansion of spiropyran hydrogels. Molecular dynamics simulations indicate that water within the high-aspect-ratio supramolecular polymers exhibits a faster draining rate as compared to those in spherical micelles, which suggests that the high-aspect-ratio supramolecular polymers effectively facilitate the transport of trapped water molecules by functioning as channels and therefore enhancing actuation of the hybrid system. Our simulations provide a useful strategy for the design of new functional hybrid architectures and materials with the aim of accelerating response and enhancing actuation by facilitating water diffusion at the nanoscopic level.

Synthesis of Open‐Cage Fullerenes Containing a H‐Bond between the Encapsulated Water Molecule and the Amide Moiety on the Rim of the Orifice

AbstractFurther hydrolysis of an open‐cage fullerene derivative with an epoxy moiety on the rim of the orifice led to the formation of a new open‐cage fullerene with a 17‐membered orifice and an amide group directly above the orifice. The water encapsulation ratio in the new open‐cage compound reached 100 % as a result of heating with water at 80 °C. The amide group above the orifice completely blocks the opening and forms H‐bond with the trapped water molecule. Single crystal X‐ray structure shows that the bond length between the trapped water oxygen and the amide oxygen is 2.859 Å. The H‐bond energy is about −3.83 kcal/mol as shown by theoretical calculation.

Liquefaction of water on the hydrophobic surface of black phosphorene: A reactive molecular dynamics simulation

Numerous empirical and computational studies have been undertaken on the phenomenon of liquefaction on hydrophilic surfaces. However, recent experiments have demonstrated that some of the hydrophobic surfaces, e.g., black phosphorene, have the capacity for water vapor liquefaction. The current study uses reactive molecular dynamics simulation to model the water vapor molecules' conversion to the liquid water cluster on black phosphorene. First, some simulations are performed in the presence of one, two, and numerous water molecules on the black phosphorene surface, and their structures and dynamics are investigated. Afterward, the growth and formation mechanism of the water cluster on the surface is studied. According to the results, due to the difference in the energy level of the two zigzag and armchair directions of the black phosphorene, the trapped water molecule in the zigzag direction acts as the initial nucleus of the water molecule accumulation. The presence of other water molecules provides the opportunity for the water clusters' growth via the intermolecular hydrogen bonds of water molecules. To study the structure and dynamics of water molecules on the black phosphorene surface, the molecules' orientation and molecular dipole moment, the water molecules’ dipole moment profile, the mass center displacement of water molecules, hydrogen bonds, and their stability were calculated.

Metal-free catalysis for efficient reduction of 4-nitrophenol by graphene quantum dots controlled by the surface trapped water molecules

We report the synthesis of environment-friendly and water-soluble metal-free functional carbon materials, graphene quantum dots (GQDs), applied as catalysts for efficient reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in aqueous solution at room temperature and ambient condition. The one-pot and easily synthesized GQDs show excellent variation in catalytic property in reducing 4-NP. While the unprotected GQDs demonstrate relatively slow conversion of 4-NP to 4-AP, the protein-protected and thiolate-coated GQDs show enhancement in the reduction rate by two orders of magnitude. The heterogeneous catalytic activity by the three variants of GQDs appears to depend on the extent of core surface-trapped water molecules.

An injectable, naproxen-conjugated, supramolecular hydrogel with ultra-low critical gelation concentration-prepared from a known folate receptor ligand.

Short peptides capped on the N-terminus with aromatic groups are often able to form supramolecular hydrogels-self-assembled networks of fibrils able to trap water molecules. Typically, these hydrogelators can form stiff gels at concentrations of 0.1 to 1.0 wt%-i.e. they consist of mainly water. The properties of these soft materials mimic those of the extracellular matrix (ECM) of biological tissue and therefore they have found many biomedical uses in tissue engineering, wound healing, drug delivery, biosensing and bioprinting applications. In drug delivery strategies related to cancer therapy, injectable hydrogels can serve as a depot formulation, where a sustained release of the chemotherapeutic from near the tumour site allows reduced doses and, therefore, decreased side effects. To further target cancer cells, folic acid-conjugated hydrogels and nanostructures are often sought, to exploit the overexpression of folate receptors on cancer cells-an approach which can allow the selective cellular uptake of an encapsulated drug. In this present study, two known dipeptide folate receptor ligands (1 and 2) recently identified from a screen of a DNA-encoded compound library, were synthesised and investigated for their hydrogelation ability and cytotoxicity. Compound 1, containing a naproxen capping group, rapidly forms hydrogels at concentrations as low as 0.03 wt%-one of the lowest critical gelation concentrations (CGCs) known for a supramolecular hydrogelator. In contrast, compound 2, which contains a 3-indolepropionic acid capping group, was unable to form hydrogels under a range of conditions and concentrations, instead forming nanospheres with diameters of 0.5 μm. Hydrogels of 1 were characterised by STEM microscopy, rheology, fluorescence spectroscopy and circular dichroism. Both compounds 1 and 2 had no impact on the proliferation of kerotinocytes (HaCaT cells) at concentrations up to 100 μM. Compound 1, containing the NSAID, was tested for anti-inflammatory activity in a human cyclooxygenase-1/2 model. The rate of the release of model drug compounds from within hydrogels of 1 was also investigated.