Hydrophobic Interface Research Articles

One-step construction of P(AM-DMDAAC)/GO aerogel evaporator with Janus wettability for stable solar-driven desalination

The interfacial solar evaporation, as a promising energy-efficient desalination technology, still urgently requires the development of efficiency and salt-resistance of the three-dimensional evaporators. Herein, Janus aerogels with macroporous air capsule structure were prepared by one-step hydrothermal self-assembly and freeze-drying treatment of dimethyldiallylammonium chloride acrylamide polymer-graphene colloidal solution, and then used for photothermal evaporation of high salt wastewater. The Janus P(AM-DMDAAC)/GO aerogels (PGA) exhibited asymmetric wettability and roughness at their upper and bottom surfaces, which are favorable for photothermal conversion at the hydrophobic interface and sufficient water supply at the hydrophilic interface. The evaporation rate of 3.65 kg m−2h−1 and the photothermal conversion efficiency of 98.9 % were obtained under 1.0 sun irradiation, which was attributed to the special three-dimensional structure of the Janus PGA. Benefited from the excellent water supply properties and the special air capsule framework, the as-obtained Janus PGA evaporator exhibited robust recyclability and durability in simulated seawater for 10 d without any salt crystallization. This study provides a simple strategy toward construct Janus aerogels with macroporous air capsule structure for solar evaporation and high-salinity wastewater treatment.

Effects of a plant cyclotide on conformational dynamics and destabilization of β-amyloid fibrils through molecular dynamics simulations.

Aggregation of β-amyloid (Aβ) peptide is one of the hallmarks of Alzheimer’s disease (AD) which results in chronic and progressive neurodegeneration of the brain. A recent study by our group have shown the ability of cyclic disulfide-rich peptides (“cyclotides”) isolated from a medicinal plant, Clitoria ternatea, to inhibit the aggregation of Aβ peptides and reduce oxidative stress caused by reactive oxygen species using in vivo models of transgenic Caenorhabditis elegans. In the present study, through extensive computational docking and multi-ns molecular dynamics (MD) simulation, we evaluated if cyclotides can stably bind to Aβ molecules and/or destabilize the Aβ fibril by preventing conformational changes from α-helical to β-sheet rich structures. We demonstrate that cyclotides bind effectively and stably to different forms of Aβ structures via hydrogen bonding and hydrophobic interactions. One of the conserved hydrophobic interface residues, Tyr10 was mutated to Ala and the impact of this virtual mutation was estimated by additional MD simulations for the wild-type (WT) and mutant protein-peptide complexes. A detailed MD simulation analyses revealed that cyclotides form hydrogen bonds with the toxic amyloid assemblies thereby weakening the inter-strand hydrogen bonds between the Aβ peptide. The φ-ѱ distribution map of residues in the cyclotide binding pocket that ideally adopt β-sheet conformation show deviation towards right-handed ɑ-helical (ɑR) conformation. This effect was similar to that observed for the Tyr10Ala mutant and doubly so, for the cyclotide bound form. It is therefore possible to hypothesise that the opening up of amyloid β-sheet is due to an unfolding process occurring in the Aβ caused by cyclotide binding and inhibition. Our current findings provide novel structural insights on the mode of interaction between cyclotides and Aβ fibrils and describe their anti-amyloid aggregation potential. This sheds light on the future of cyclotide-based drug design against protein aggregation, a hallmark event in many neurodegenerative diseases.

Fungicide itself as a trigger to facilely construct Hymexazol-Encapsulated polysaccharide supramolecular hydrogels with controllable rheological properties and reduced environmental risks

Hydrogels with porous networks have received considerable attention in cargo delivery systems due to the inherent versatile performances. However, ideal strategy that bioactive molecule itself spontaneously triggers natural polymers to form self-delivery hydrogels has been less exploited. Herein, the addition of hymexazol into the mixed aqueous solution of alginate and carboxymethyl chitosan can spontaneously trigger the formation of fungicide-encapsulated polysaccharide supramolecular hydrogels with controllable rheological properties and tunable multifunctionality. The hydrogels are three-dimensional porous network structures possessing shear-thinning, self-healing, and pH and ionic strength-responsive swelling properties. Furthermore, soils amended with hydrogel demonstrated enhanced water-holding and water-retention capacities. The hydrogels can not only decrease the leaching of hymexazol in soil, but also increase its retention capacity on hydrophobic interface, and significantly inhibit the fragmentation and rebound of the droplets on hydrophobic surface. More importantly, in addition to the good fungicidal activity, hydrogels can promote the sprouting of wheat seeds compared to the free hymexazol aqueous solution, demonstrating obvious biosafety to target plant through the gelation of active ingredient. This intriguing bioactive molecule itself-triggered self-delivery approach can bestow the active ingredient tunable multifunctionality without sacrificing the bioactivity, offering a promising and practical strategy for various application scenarios in sustainable agricultural practices.

Localized Hydrophobicity in Aqueous Zinc Electrolytes Improves Zinc Metal Reversibility.

The rechargeability of aqueous zinc metal batteries is plagued by parasitic reactions of the zinc metal anode and detrimental morphologies such as dendritic or dead zinc. To improve the zinc metal reversibility, hereby we report a new solution structure of aqueous electrolyte with hydroxyl-ion scavengers and hydrophobicity localized in solvent clusters. We show that although hydrophobicity sounds counterintuitive for an aqueous system, hydrophilic pockets may be encapsulated inside a hydrophobic outer layer, and a hydrophobic anode-electrolyte interface can be generated through the addition of a cation-philic, strongly anion-phobic, and OH--reactive diluent. The localized hydrophobicity enables less active water and less absorbed water on the Zn anode surface, which suppresses the parasitic water reduction; while the hydroxyl-ion-scavenging functionality further minimizes undesired passivation layer formation, thus leading to superior reversibility (an average Zn plating/stripping efficiency of 99.72% for 1000 cycles) and lifetime (80.6% capacity retention after 5000 cycles) of zinc batteries.

Three-phase interface of SnO2 nanoparticles loaded on hydrophobic MoS2 enhance photoelectrochemical N2 reduction

Photoelectrochemical nitrogen reduction (PEC NRR) provides a clean and sustainable method for the production of NH3 under environmental conditions. However, low reaction efficiency remains a major challenge due to the presence of competitive hydrogen evolution reactions (HER). Herein, nanocomposites (SNP/MSO) with three-phase interface were prepared by loading hydrophilic SnO2 nanoparticles (SNP) on hydrophobic MoS2 (MSO) obtained by surface modification with silicomolybdic acid. The hydrophobic interface eliminated the transport barrier of N2 in the liquid phase to the reaction center, inhibiting HER since the lowered contact area with the liquid proton. Meanwhile, the heterojunction structure formed between MSO and SNP accelerated the effective electron transfer. The synergistic effect of the triphase interface structure and electron transfer structure contributed to the high NH3 yield (19.6 μg h−1 mg−1) and FE (40.34%) of SNP/10MSO in the photoelectrochemical system. Compared with the nanocomposites (SNP/MSI) prepared by hydrophilic MoS2, FE was significantly increased by 10 percentage points.

Impact of Strain Relaxation on 2D Ruddlesden–Popper Perovskite Solar Cells

AbstractAlthough the photovoltaic performance of perovskite solar cells (PSCs) has reached the commercial standards, the unsatisfactory stability limits their further application. Hydrophobic interface and encapsulation can block the damage of water and oxygen, while the instability induced by intrinsic residual strain remains inevitable. Here, the residual strain in a two‐dimensional (2D) Ruddlesden–Popper (RP) perovskite film is investigated by X‐ray diffraction and atomic force microscopy. It's found that the spacer cations contribute to the residual strain even though they are not in the inorganic cages. Benefited from strain relaxation, the film quality is improved, leading to suppressed recombination, promoted charge transport and enhanced efficiency. More significantly, the strain‐released devices maintain 86 % of the initial efficiency after being kept in air with 85 % relative humidity (RH) for 1080 h, 82 % under maximum power point (MPP) tracking at 50 °C for 804 h and 86 % after continuous heating at 85 °C for 1080 h.

Impact of Strain Relaxation on 2D Ruddlesden-Popper Perovskite Solar Cells.

Although the photovoltaic performance of perovskite solar cells (PSCs) has reached the commercial standards, the unsatisfactory stability limits their further application. Hydrophobic interface and encapsulation can block the damage of water and oxygen, while the instability induced by intrinsic residual strain remains inevitable. Here, the residual strain in a two-dimensional (2D) Ruddlesden-Popper (RP) perovskite film is investigated by X-ray diffraction and atomic force microscopy. It's found that the spacer cations contribute to the residual strain even though they are not in the inorganic cages. Benefited from strain relaxation, the film quality is improved, leading to suppressed recombination, promoted charge transport and enhanced efficiency. More significantly, the strain-released devices maintain 86 % of the initial efficiency after being kept in air with 85 % relative humidity (RH) for 1080 h, 82 % under maximum power point (MPP) tracking at 50 °C for 804 h and 86 % after continuous heating at 85 °C for 1080 h.

Synoeca‐MP: New insights into its mechanism of action by using NMR and molecular dynamics simulations approach

AbstractSynoeca‐MP is a 14‐residue amidated peptide, belongs to the mastoparan family and it is found in the venom of the wasp Synoeca surinama and has antibacterial and antifungal activity. The low cytotoxicity of the peptide also makes it an excellent candidate for drug development. To better understand its selectivity and interaction with the membrane, the peptide behavior in membrane‐like environments was studied here and the peptide structure in SDS micelles was determined by NMR spectroscopy. The behavior of the peptide in hydrophobic media and in different pH ranges was studied by CD spectroscopy. The incorporation of residues into the anionic micelles was studied by hydrogen‐deuterium exchange. The peptide stability and insertion in the micelles was studied by molecular dynamics simulations. Synoeca‐MP, bound to SDS micelles, exhibits a partial α‐helix conformation, with the first five residues and the last two unfolded. H/D exchange showed that the peptide has a slow exchange rate. After 164 h, four residues had not yet completed H/D substitution, suggesting parallel alignment of the peptide with the micelle, mainly due to the hydrophobic interface. This may indicate a carpet interaction model of the peptide with micelles. The molecular simulation study of peptide showed that the peptide consists of a well‐folded alpha‐helix core and unfolded extremities, which are responsible for the nature of the peptide interaction. The biophysical analyses can improve the atomic understanding of the mode of action of the peptide and help in future improvements of the peptide for clinical usage.

Realizing highly stable zinc-ion batteries via electrolyte engineering with adsorbed molecular protective layer

Uncontrolled dendrites, corrosion and passivation of Zn metal seriously limit the development of Zn-ion batteries (ZIBs). Electrolyte engineering with various additives is a promising approach due to its high operability and significant effects. Herein, we report a low-cost and high-effective cysteamine (CS) as the additive to achieve dendrite-free ZIBs. Dendrite-free ZIBs with CS as the organic additive can prevent direct contact of Zn with water through a dynamic adsorption layer and desolvation of [Zn(H2O)6]2+. The optimized electrolyte also shows advantages in re-regulating the Zn ion fluxes and holding the steady hydrophobic interface during the electrochemical process to alleviate water decomposition and anode corrosion during cycling. CS employed as the additive enables stable Zn plating and stripping over 1360 h at the current density of 1 mA cm−2 and the capacity of 1 mAh cm−2. The Zn/diquinoxalino [2,3-a:2′,3′-c] phenazine (HATN) and Zn/Mn-doped V2O5 (MVO) full cells with CS as the additive exhibits ultra-high Coulombic efficiency (CE, 100 ± 0.3%) as well as long cycling performance at the current density of 1 A g−1. This work will provide a novel experimental approach in understanding the dendrite-suppression mechanism and pave a way to construct electrolyte engineering for ZIBs.

Acidic pH Promotes Refolding and Macroscopic Assembly of Amyloid β (16-22) Peptides at the Air-Water Interface.

Assembly by amyloid-beta (Aβ) peptides is vital for various neurodegenerative diseases. The process can be accelerated by hydrophobic interfaces such as the cell membrane interface and the air–water interface. Elucidating the assembly mechanism for Aβ peptides at hydrophobic interface requires knowledge of the microscopic structure of interfacial peptides. Here we combine scanning force microscopy, sum-frequency generation spectroscopy, and metadynamics simulations to probe the structure of the central fragment of Aβ peptides at the air–water interface. We find that the structure of interfacial peptides depends on pH: at neutral pH, the peptides adopt a less folded, bending motif by forming intra-hydrogen bonds; at acidic pH, the peptides refold into extended β-strand fibril conformation, which further promotes their macroscopic assembly. The conformational transition of interfacial peptides is driven by the reduced hydrogen bonds, both with water and within peptides, resulting from the protonation of acidic glutamic acid side chains.

Preparation of micro-convex rough interface carbon aerogels with cellulose-lithium bromide (LiBr) molten salt hydrate gelled system and application of oil-water separation

As a novel nanoporous carbon material with high porosity, large specific surface area, excellent electrical conductivity and high temperature resistance, carbon aerogels have broad application prospects in the fields of catalyst carriers, energy storage and adsorption materials. In this work, the hydrophobic micro-convex rough interface cellulose carbon aerogels (CCAs) were fabricated via carbonization of cellulose-lithium bromide (LiBr) molten salt hydrate gelled system. The prepared CCAs shows a low density (0.016–0.023 g/cm3), high porosity (98.9–99.2 %), superior hydrophobicity (water contact angle over 135°) and excellent absorption of different oils and organic solvents. The absorption ability of CCAs 1.0-T800 for different oils and organic solvents can be 25–55 times its own weight. More importantly, the CCAs adsorbent can be reused by simple absorption/distillation method and still kept high-efficiency oil absorption capacity and excellent hydrophobicity after 5 absorption/elution cycles, displaying recyclability and robust stability. This study provides a green and facile way to fabrication of cellulose II carbon aerogels for application in spilled oil recovery, and exhibited highly promising as an economical, efficient and safe adsorbent for wastewater treatment.

Structural insight into apelin receptor-G protein stoichiometry.

The technique of cryogenic-electron microscopy (cryo-EM) has revolutionized the field of membrane protein structure and function with a focus on the dominantly observed molecular species. This report describes the structural characterization of a fully active human apelin receptor (APJR) complexed with heterotrimeric G protein observed in both 2:1 and 1:1 stoichiometric ratios. We use cryo-EM single-particle analysis to determine the structural details of both species from the same sample preparation. Protein preparations, in the presence of the endogenous peptide ligand ELA or a synthetic small molecule, both demonstrate these mixed stoichiometric states. Structural differences in G protein engagement between dimeric and monomeric APJR suggest a role for the stoichiometry of G protein-coupled receptor- (GPCR-)G protein coupling on downstream signaling and receptor pharmacology. Furthermore, a small, hydrophobic dimer interface provides a starting framework for additional class A GPCR dimerization studies. Together, these findings uncover a mechanism of versatile regulation through oligomerization by which GPCRs can modulate their signaling.

Engineered Design of the E-Helix Structure on Ferritin Nanoparticles.

Insertion of an immunogenic epitope at the C-terminus of ferritin has shown the potential to produce a stable and efficacious vaccine. There is however limited understanding of how C-terminus insertion affects ferritin protein stability. The E-helix at the C-terminus has attracted interest because there are contradictory reports as to whether it has a role in protein stabilization. Here, we report, for the first time, combining molecular dynamics simulation (MDS) with experiment to engineer the design of the E-helix at the C-terminus of engineered human ferritin heavy chain (F1) inserted with Epstein-Barr nuclear antigen 1 (EBNA1, E1) and flexible linker (L3) residues (to afford F1L3E1). Hot spots on the E-helix of the C-terminus were predicted by MDS at aa 167 (Glu) and aa 171 (Asp). Five (5) variants of F1L3E1 were constructed by considering hot spots and alteration of electrostatic or hydrophobic interfaces, namely, (1) C1, hot spots substituted with noncharged residue Gln; (2) C2, hot spots substituted with positively charged residue Arg; (3) C3, hydrophobic residues substituted with the most hydrophobic residues Val and Ile; (4) C4, hydrophobic residues substituted with the most hydrophilic residues Gln and Asn; and (5) C5, a heptad repeat structure in the E-helix disrupted by substituting "a" and "d" heptad residues with noncharged polar residue Gln. It was found that the E-helix is essential to maintain integrated protein stability and that changing the hydrophobic interface (C3 and C4) had more significant effects on protein folding and stability than changing the electrostatic interface (C1 and C2). It was confirmed by both MDS and experiment that variants C1, C2, and C5 were able to fold to form stable conformational structures with protein surface hydrophobicity similar to that of F1L3E1. However, they are less thermally stable than F1L3E1. Significant changes in hydrophobicity drove significant protein aggregation for variants C3 and C4. It is concluded that the molecular design of the C-terminus in engineered ferritin, especially the E-helix, is important to ensure the epitope-based chimeric vaccine is safe (aggregate free) and efficacious.

Structural basis of the bHLH domains of MyoD-E47 heterodimer

The basic helix-loop-helix (bHLH) family is one of the most conserved transcription factor families that plays an important role in regulating cell growth, differentiation and tissue development. Typically, members of this family form homo- or heterodimers to recognize specific motifs and activate transcription. MyoD is a vital transcription factor that regulates muscle cell differentiation. However, it is necessary for MyoD to form a heterodimer with E-proteins to activate transcription. Even though the crystal structure of the MyoD homodimer has been determined, the structure of the MyoD heterodimer in complex with the E-box protein remains unclear. In this study, we determined the crystal structure of the bHLH domain of the MyoD-E47 heterodimer at 2.05 Å. Our structural analysis revealed that MyoD interacts with E47 through a hydrophobic interface. Moreover, we confirmed that heterodimerization could enhance the binding affinity of MyoD to E-box sequences. Our results provide new structural insights into the heterodimer of MyoD and E-box protein, suggesting the molecular mechanism of transcription activation of MyoD upon binding to E-box protein.

Temperature-induced hydrophobicity transition of MXene membrane for directly preparing W/O emulsions

Although hydrophilic membranes are desired for reducing resistance to water permeation, hydrophilic surfaces are not used in the water-in-oil (W/O) membrane emulsification process because water spreads on the hydrophilic surface without forming droplets. Here, we report that a hydrophilic ceramic membrane can form a hydrophobic interface in diesel at a higher temperature; interestingly, the experiments show that the contact angle increases when the temperature rises. The hydrophilic membrane surface evolves into a hydrophobic interface, particularly near the boiling point of water, resulting in a water contact angle of 147.5° ± 1.2°. This work established a method for preparing W/O monodispersed emulsions by direct emulsification of hydrophilic ceramic membranes at a temperature close to the boiling point of water. Additionally, it made high flux of membrane emulsification of monodispersed W/O emulsions possible, which satisfied the industrial requirements of fluidized catalytic cracking in the petrochemical industry.

Influence of effective polarization on ion and water interactions within a biomimetic nanopore

Interactions between ions and water at hydrophobic interfaces within ion channels and nanopores are suggested to play a key role in the movement of ions across biological membranes. Previous molecular-dynamics simulations have shown that anion affinity for aqueous/hydrophobic interfaces can be markedly influenced by including polarization effects through an electronic continuum correction. Here, we designed a model biomimetic nanopore to imitate the polar pore openings and hydrophobic gating regions found in pentameric ligand-gated ion channels. Molecular-dynamics simulations were then performed using both a non-polarizable force field and the electronic-continuum-correction method to investigate the behavior of water, Na+, and Cl- ions confined within the hydrophobic region of the nanopore. Number-density distributions revealed preferential Cl- adsorption to the hydrophobic pore walls, with this interfacial layer largely devoid of Na+. Free-energy profiles for Na+ and Cl- permeating the pore also display an energy-barrier reduction associated with the localization of Cl- to this hydrophobic interface, and the hydration-number profiles reflect a corresponding reduction in the first hydration shell of Cl-. Crucially, these ion effects were only observed through inclusion of effective polarization, which therefore suggests that polarizability may be essential for an accurate description for the behavior of ions and water within hydrophobic nanoscale pores, especially those that conduct Cl-.

Constructing Hydrophobic Interface with Close-Packed Coordination Supramolecular Network for Long-Cycling and Dendrite-Free Zn-Metal Batteries.

Commercialization of aqueous zinc-metal batteries remains unrealistic due to the substantial dendrite growth and side reaction issues on the zinc anodes. It is highly demanded to develop easy-to-handle approaches for constructing stable, dense, as well as homogeneous solid anode/electrolyte interfaces. Herein, the authors construct the zinc anode interface with a close-packed Zn-TSA (TSA = thiosalicylate) coordination supramolecular network through the facile and up-scalable wet-chemical method. The hydrophobic Zn-TSA network can block solvated water and establish a solid-state diffusion barrier to well-distribute the interfacial Zn2+ , thus inhibiting hydrogen evolution and zinc dendrite growth on the anode. Meanwhile, the Zn-TSA network induces the formation of a uniform and stable solid electrolyte interphase composed of multiple inorganic-organic compounds. This denser structure can accommodate and self-heal the crack/degradation of the anode interphase associated with the repeated volume changes, and suppress the generation of detrimental by-product, Znx (OTF- )y (OH)2x-y ·nH2 O. Such a rationally fabricated anode/electrolyte interface further endows the assembled symmetric cells with superior plating/stripping stability for over 2000 h without dendrite formation (at 1mA cm-2 and 1 mAh cm-2 ). Furthermore, this zinc anode has practical application in the Zn-MoS2 and Zn-V2 O5 full cells. This study provides a new train of thought for constructing the dense interface of zinc-metal anode.

How the Hydrophobic Interface between a Perfluorosulfonic Acid Polymer and Water Vapor Controls Membrane Hydration

How the Hydrophobic Interface between a Perfluorosulfonic Acid Polymer and Water Vapor Controls Membrane Hydration

Nature of a H2O Molecule Confined in the Hydrophobic Interface between the Heme and G-Quartet Planes in a Heme–DNA Complex

Heme binds selectively to the 3'-terminal G-quartet of all parallel G-quadruplex DNAs to form stable heme-DNA complexes. Interestingly, the heme-DNA complexes exhibit various spectroscopic and functional properties similar to those of hemoproteins. Since the nature of the axial ligands is crucial in determining the physicochemical properties of heme, identification and characterization of the axial ligands in a heme-DNA complex are essential to elucidate the structure-function relationship in the complex. NMR studies of a complex possessing a low-spin ferric heme with a water molecule (H2O) and cyanide ion (CN-) as the axial ligands allowed detailed characterization of the physicochemical nature of the axial H2O ligand. We found that the in-plane asymmetry of the heme electronic structure of the complex is not largely affected by the axial H2O coordination, indicating that the H2O confined in the hydrophobic interface between the heme and G-quartet planes of the complex rotates about the coordination bond with respect to the heme. The effect of the hydrogen(H)/deuterium(D) isotope replacement of the axial H2O on the heme electronic structure was manifested in the isotope shifts of paramagnetically shifted heme methyl proton signals of the complex in such a manner that three resolved peaks associated with axial H2O, HDO, and D2O were observed for each of the heme methyl proton signals. These findings provide not only the basis for an understanding of the nature of the unique axial H2O but also an insight into the molecular mechanism responsible for the control of the heme reactivity in the heme-DNA complex.

Anti‐Corrosion for Reversible Zinc Anode via a Hydrophobic Interface in Aqueous Zinc Batteries (Adv. Energy Mater. 9/2022)

Aqueous Zinc Batteries The study of the reversible zinc metal anode is significant in the context of energy storage in aqueous zinc batteries. In article number 2103557, Li Tao, Jian Cui, Hao Wang and co-authors report the use of quaternary ammonium cationic surfactants as aqueous electrolyte additives forming a self-consistent hydrophobic interface to block corrosion by water and modulate zinc deposition.