Interfacial Hydrogen Bonds Research Articles

Structure of a nascent membrane protein as it folds on the BAM complex.

Mitochondria, chloroplasts, and Gram-negative bacteria are encased in a double layer of membranes. The outer membrane contains proteins with a β-barrel structure1,2. β-barrels are sheets of β-strands wrapped into a cylinder with the first strand hydrogen-bonded to the last strand. Conserved multi-subunit molecular machines fold and insert these proteins into the outer membrane3–5. One subunit of the machines is itself a β-barrel protein that plays a central role in folding other β-barrels. In Gram-negative bacteria, the β-barrel assembly machine (Bam) consists of the β-barrel protein BamA and four lipoproteins5–8. To understand how the Bam complex accelerates folding without using exogenous energy (e.g., ATP)9, we trapped folding intermediates on the machine. We report here the structure of the Bam complex folding BamA itself. The BamA catalyst (BamAM, for BamAmachine) forms an asymmetric hybrid β-barrel with the BamA substrate (BamAS). The N-terminal edge of BamAM has an antiparallel hydrogen-bonded interface with the C-terminal edge of BamAS, consistent with previous crosslinking studies10–12; the other edges of BamAM and BamAS are close to each other but curl inward and do not pair. Six hydrogen bonds in a membrane environment make the interface between the two proteins very stable. This stability allows folding but creates a high kinetic barrier to substrate release once folding has finished. Features at each end of the substrate overcome the barrier and promote release by stepwise exchange of hydrogen bonds. This mechanism of substrate-assisted product release explains how the Bam complex can stably associate with the substrate during folding and then turn over rapidly when folding is complete.

Design and synthesis of an amide-containing crosslinked network based on Diels-Alder chemistry for fully recyclable aramid fabric reinforced composites

Fiber reinforced thermoset composites (FRPCs) have received tremendous attention because of their merits of light weight, high modulus and high strength. However, the efficient recycling of the waste during the manufacturing and service life of FRPCs is still great challenge. This paper reports a newly designed dynamic crosslinked network based on Diels-Alder chemistry as matrix for fully recyclable aramid fabric reinforced composites. The DA network shows good thermomechanical properties owing to the incorporated aromatic amide bonds, and the overall performance can be readily tailored by adjusting the ratio of amide-containing component and flexible aliphatic component. The good reversibility of the DA network and highly efficient recovery of mechanical properties of recycled sample are confirmed. With optimized composition, the DA network exhibits good interfacial strength with aramid fiber that is comparable to that of widely used epoxy resin due to the interfacial hydrogen bonds among amide bonds between fiber and matrix. Moreover, the closed-loop recycling of both matrix and reinforced fabric without any other additive is also demonstrated. This paper presents the first report on recyclable aramid fiber reinforced composites and is expected to provide hints for future development of fully recyclable and high-performance FRPCs.

Polydopamine nanotube for dual bio-inspired strong, tough, and flame retarding composites

To realize green, light weight, strong, tough and additional functionalities in polymer composites is challenging and has attracted great attention recently. Nature has provided perfect models such as mussel and silk to guide the design and fabrication of manmade materials with these merits. Herein, two bio-inspired strategies are combined to construct a strong, tough, and flame retarding composites. Mussel-adhesive-inspired polydopamine nanotube (PDANT) with high aspect ratio is first prepared by using a readily removable ammonium molybdate nanowire as template. PDANT/poly(vinyl alcohol) (PVA) composites with abundant and arranged interfacial hydrogen bonds (H-bonds) that mimic the hierarchically and densely assembled H-bonds in nanocrystallines reinforced spider silk are then fabricated by solution casting. Tensile test reveals that these designs have significantly improved the strength and ductility of composites as compared to neat PVA and polydopamine nanoparticles reinforced PVA. Moreover, limiting oxygen index and vertical burning test indicate that PDANT could also act as excellent flame retardant to enhance the flame resistance of composites, owing to the percolation network of PDANT in matrix and the good radical scavenging ability of PDANT. Our finding underlines the great potential of PDANT as green alternative of inorganic nanotubes for strong, tough, and flame retarding polymer composites.

Negative friction and mobilities induced by friction fluctuation.

We study the transport phenomena of an inertial Brownian particle in a symmetric potential with periodicity, which is driven by an external time-periodic force and an external constant bias for both cases of the deterministic dynamics and the existence of friction coefficient fluctuations. For the deterministic case, it is shown that for suitable parameters, the existence of certain appropriate friction coefficients can enhance the transport of the particle, which may be interpreted as the negative friction coefficient; additionally, there coexist absolute, differential negative, and giant positive mobilities with increasing friction coefficients in the system. We analyze physical mechanisms hinted behind these findings via basins of attraction. For the existence of friction coefficient fluctuations, it is shown that the fluctuation can enhance or weaken, even eliminate these phenomena. We present the probability distribution of the particle's velocity to interpret these mobilities and the suitable parameters' regimes of these phenomena. In order to further understand the physical mechanism, we also study diffusions corresponding to these mobilities and find that for the small fluctuation, the negative friction appears, and there coexists absolute negative mobility, superdiffusion, and ballistic diffusion, whereas all of them vanish for the large fluctuation. Our findings may extensively exist in materials, including different defects, strains, the number of interfacial hydrogen bonds, the arrangements of ions, or graphite concentrations, which hints at the existence of different friction coefficients.

Structural Implications of Interfacial Hydrogen Bonding in Hydrated Wyoming-Montmorillonite Clay

Montmorillonite (MMT) clay—a layered porous nanomaterial used as seals in engineered waste containment barriers for spent nuclear fuel—adopts discrete hydration/swelling states depending upon surro...

Molecular Process of Gramicidin a Dimerization Determined with Milliseconds Atomistic Simulations and Machine Learning

Dimerization of cell membrane-associated proteins are critical in many fundamental cellular processes, including signal transmission and solute transport across the cell membranes. However, our current understanding of how lipid bilayer mediates the molecular process of cell membrane protein associations is limited. In this work, we have run over 1 millisecond unbiased atomistic molecular dynamics (MD) simulations and replica-exchange umbrella sampling simulations to understand the kinetic dimerization process of the mini-protein: gramicidin A. The millisecond unbiased MD simulations identified two different gA channel structures: the first channel structure is comparable to the NMR experimental structure (PDB: 1JNO), and it is characterized by a maximum number of 6 hydrogen bonds between the 1Val1-2Ala5, 1Ala3-2Ala3 and 1Ala5-2Val1 amino acid pairs at the monomer-monomer interface (called 6 HB channels). The second channel structure can only form a maximum number of 4 interfacial hydrogen bonds between the 1Val1-2Ala3 and 1Ala3-2Val1 (called 4 HB channels) due to the relative rotation of the two monomers by two amino acid positions. The two different channel structures were accurately predicted with the replica-exchange umbrella sampling simulations. Using unsupervised Hidden Markov Models and supervised supported vector machine methods to cluster the 60 million simulation snapshots, deeper insights into the molecular process were revealed and kinetic transitions in the gA dimerization process were evaluated. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. Release number: LLNL-ABS-791900-DRAFT

Cryoprotectants Disrupt Hydrogen-Bond Networks at the Lipid-Water Interface

Cryoprotectant agents (CPAs) are mixtures of small organic compounds used to inhibit ice-crystal growth during cell and tissue freezing and storage, but these compounds can be themselves toxic to cells. Increased membrane permeability, caused by partial disruption of lipid-lipid interactions, combined with dehydration, have been hypothesized to be the main driver of cell toxicity, but the specific interactions between lipids and cryoprotectants are poorly understood. In this study, we investigate the effects of dimethyl sulfoxide (DMSO) on phosphatidylcholine bilayers. We have measured ultrafast two-dimensional infrared (2D IR) spectra of the ester carbonyl vibrations to directly probe the interfacial hydrogen bond networks. Our measurements directly quantify the picosecond hydrogen bond lifetimes at the ester carbonyl positions. Spectra are interpreted at an atomistic level using molecular dynamics simulations, which are in semi-quantitative agreement with experiment. Our results show that biologically relevant cryoprotectant concentrations (<20 mol%), partially dehydrate the interface, but surprisingly, hydrogen-bond lifetimes are non-monotonic with increasing concentration: 1. Low DMSO concentrations (<10%) severely disrupt the otherwise ice-like interfacial hydrogen bond networks, without altering the lipid-lipid interactions, leading to faster overall hydrogen bond dynamics at the ester carbonyls. 2. Above >10 mol%, dynamics become slower as a result of dehydration, more rigid H-bond conformations, trapped water, and stronger headgroup-headgroup interactions. Together, these results provide an atomistic foundation for understanding the complex effects of cryoprotectants on lipid membranes, showing that different effects dictate the properties of membranes within various cryoprotectant concentration regimes.

Poly(vinyl acetate)-coated jute fabric reinforced polyester composite with enhanced mechanical performance: Interfacial hydrogen bond and autohesion mechanism

The current research was conducted to determine the effect of pre-heating and coating of jute fabric with poly(vinyl acetate) for the improvement of the mechanical performance of jute fabric reinforced unsaturated polyester resin composite. Six different types of composites were manufactured through the implementation of hand lay-up method. The application level of 200 g of poly(vinyl acetate) per square meter of jute fabric leads to enhanced mechanical property of the composite. The optimum dose of coating showed improvement of 31%, 42.1%, and 35.7% in tensile strength, interlaminar shear strength, and flexural strength respectively in juxtaposition to preheated and untreated jute fabric-based the composite, whereas impact strength gained 59.7%. Such considerable increase in the mechanical performance is the result of strong interfacial adhesion ascribed to autohesion of unsaturated polyester resin with poly(vinyl acetate) and building of hydrogen bond between jute and poly(vinyl acetate) as supported by Fourier transform infrared spectroscopy. The optical microscopy of cross-sections of each sample revealed the homogeneity and distribution of coating thicknesses of poly(vinyl acetate). The characterisation of fractured surfaces of composite under tensile loading was carried out by scanning electron micrograph. The thermal behaviour of composite samples was examined by differential scanning calorimetry. The degree of curing of composite samples was typically found to be 72%. Water absorption reduced to its half by the virtue of gradual decrease in void content from 9.52% to 4.87%.

Interfacial Hydrogen-Bonding Dynamics in Surface-Facilitated Dehydrogenation of Water on TiO2(110).

Molecular-level understanding of the dehydrogenation of interfacial water molecules on metal oxides and their interactive nature relies on the ability to track the motion of light and small hydrogen atoms, which is known to be difficult. Here, we report precise measurements of the surface-facilitated water dehydrogenation process at terminal Ti sites of TiO2(110) using scanning tunneling microscopy. Our measured hydrogen-bond dynamics of H2O and D2O reveal that the vibrational and electronic excitations dominate the sequential transfer of two H (D) atoms from a H2O (D2O) molecule to adjacent surface oxygen sites, manifesting the active participation of the oxide surface in the dehydrogenation processes. Our results show that, at the stoichiometric Ti5c sites, individual H2O molecules are energetically less stable than the dissociative form, where a barrier is expected to be as small as approximately 70-120 meV on the basis of our experimental and theoretical results. Moreover, our results reveal that interfacial hydrogen bonds can effectively assist H atom transfer and exchange across the surface. The revealed quantitative hydrogen-bond dynamics provide a new atomistic mechanism for water interactions on metal oxides in general.

Cellulose nanocrystal/plant oil polymer composites with hydrophobicity, humidity-sensitivity, and high wet strength

The preparation of high-performance cellulose nanocrystals (CNCs)/plant oil-derived polymer composites is still a challenge, due to their poor compatibility. Here, by designing amide groups and epoxy groups on sunflower oil derived polymers, appropriate interfacial hydrogen bond interactions between the polymers and CNCs were constructed, where CNCs were homogenously dispersed in polymer matrix. Tensile tests and DMA results revealed that the incorporation of CNCs into sunflower oil derived epoxy polymers significantly enhanced the tensile strength and storage modulus. More importantly, nanocomposites with 50 wt% CNCs are still hydrophobic, which not only show a fast and reversible humidity induced modulus switch, but also exhibit high wet strength (19.9 MPa) after equilibrium water adsorption. The present work revealed that proper designed CNCs/plant oil polymer nanocomposites are good candidates for high performance and functional materials, which are able to replace petroleum-based materials in various fields.

Parallel Homochiral and Anti-Parallel Heterochiral Hydrogen-Bonding Interfaces in Multi-Helical Abiotic Foldamers.

A hydrogen‐bonding interface between helical aromatic oligoamide foldamers has been designed to promote the folding of a helix‐turn‐helix motif with a head‐to‐tail arrangement of two helices of opposite handedness. This design complements an earlier helix‐turn‐helix motif with a head‐to‐head arrangement of two helices of identical handedness interface. The two motifs were shown to have comparable stability and were combined in a unimolecular tetra‐helix fold constituting the largest abiotic tertiary structure to date.

Preparation and Performance of Silica/ESBR Nanocomposites Modified by Bio-Based Dibutyl Itaconate

Ester-functionalized styrene-butadiene rubber (dibutyl itaconate-styrene-butadiene rubber) (D-ESBR) was synthesized by low-temperature emulsion polymerization using dibutyl itaconate (DBI) as a modified monomer containing ester groups. Nonpetroleum-based silica with hydroxy groups was used as a filler to enhance the D-ESBR, which can provide excellent mechanical properties, low rolling resistance, and high wet skid resistance. During the preparation of the silica/D-ESBR nanocomposites, a hydrogen-bonding interface was formed between the hydroxy groups on the surface of silica and the ester groups in the D-ESBR macromolecules. As the content of ester groups in the D-ESBR increases, the dispersion of silica in the nanocomposites is gradually improved, which was verified by rubber process analyzer (RPA) and scanning electron microscopy (SEM). Overall mechanical properties of the silica/D-ESBR modified with 5 wt % DBI were improved and became superior to that of the non-modified nanocomposite. Compared with the non-modified silica/D-ESBR, the DBI modified silica/D-ESBR exhibited a lower tan δ value at 60 °C and comparable tan δ value at 0 °C, indicating that the DBI modified silica/D-ESBR had lower rolling resistance without sacrificing wet skid resistance.

Interaction Mechanisms of Insensitive Explosive FOX-7 and Graphene Oxides from Ab Initio Calculations.

Energetic material–graphene oxide (EM–GO) composites exhibit excellent thermal stability and insensitivity to mechanical stimuli. The interfacial interactions play an important role in affecting the structural and electrical properties of EM–GO composites. FOX-7 crystal with a wave-shaped layer structure is an ideal prototype system for matching with oxygen-rich GO monolayers to form FOX-7–GO composites. Here, we conducted a systematic investigation on FOX-7–GO composites by dispersion-corrected density functional approach. Our results revealed that there exists relatively strong interaction in the FOX-7–GO interface, which stems from the synergistic effect of interfacial charge transfer and hydrogen bonds. The electronic structure analyses demonstrated that GO can hybridize with FOX-7 to reduce charge accumulation on the FOX-7 surface. These theoretical results are useful for clarifying the interfacial effects on the sensitivity of FOX-7–GO composites.

Interfacial H-Bond Dynamics in Reverse Micelles: The Role of Surfactant Heterogeneity.

Characterizing the hydrogen bond structure and dynamics at surfactant interfaces is essential for understanding how microscopic interactions translate to bulk microemulsion properties. Heterogeneous blends containing tens or hundreds of surfactants are common in the industry, but the most fundamental studies have been carried out on micelles composed of a single surfactant species. Therefore, the effect of surfactant heterogeneity on the interfacial structure and dynamics remains poorly understood. Here, we use ultrafast two-dimensional infrared spectroscopy and molecular dynamics simulations to characterize sub-picosecond solvation dynamics as a function of the surfactant composition in ∼120 nm water-in-oil reverse micelles. We probe the ester carbonyl vibrations of nonionic sorbitan surfactants, which are located precisely at the interface between the polar and nonpolar regions, and as such, report on the interfacial water dynamics. We show a 7% increase in hydrogen bond populations together with a 37% slowdown of interfacial hydrogen bond dynamics in heterogeneous mixtures containing hundreds of species, compared to more uniform compositions. Simulations, which are in semiquantitative agreement with experiments, indicate that structural diversity leads to decreased packing efficiency, which in turn drives water further into the otherwise hydrophobic region. Interestingly, this increase in hydration is accompanied by a slowdown of dynamics, indicating that water molecules solvating surfactants are conformationally constrained. These studies demonstrate that the composition and heterogeneity are key factors in determining interfacial properties.

Understanding the interfacial interactions of bioinspired chitosan-calcite nanocomposites by first principles molecular dynamics simulations and experimental FT-IR spectroscopy

The interfacial structures and bonding mechanism of the adsorption of chitosan monomers (GlcN and GlcNAc) on calcite (104) surface are investigated using first principles molecular dynamics simulations. It is revealed that the strong coordination CaO bonds are formed between five-fold coordinated Ca atoms on calcite surface and O atoms of hydroxyl groups (OH) and acetyl groups of chitosan in the chitosan-calcite nanocomposites, improving the chemical compatibility between organic and inorganic phases at the interface in the natural occurring nacre. Although, the presence of interfacial hydrogen bonds is also confirmed by analyzing the valence electron density difference in terms of induced dipole, the evolution of the equilibrium adsorption geometry is found to be mainly governed interfacial CaO coordination bonds. The amide group (NH2) of chitosan binds with calcite at the interface mainly through the formation of weak hydrogen bond. The predicted interfacial electronic structure can be either conductive (GlcNAc) or insulating (GlcN). The frequencies of the characteristic peaks in the calculated total and partial vibrational densities of states of GlcN/calcite systems are found to be in agreement with the FT-IR spectrum of the experimentally prepared chitosan-calcite nanocomposites, crucially validating the modelling structures and computational methodology employed in current work. Theoretical results strongly indicate that the peculiar adsorption in FT-IR spectrum at 2500 cm−1 is related to the presence of free GlcN molecule due to the hydrolysis of chitosan in aqueous solution.

"On Water" Catalytic Aldol Reaction between Isatins and Acetophenones: Interfacial Hydrogen Bonding and Enamine Mechanism.

"On water" catalytic aldol reaction catalyzed by polyetheramine (D230) has been developed for easy access to 3-substituted 3-hydroxyindolin-2-ones through the reaction between various substituted isatins and acetophenones/cyclic ketones in high yields under room temperature. Systematic mechanism investigation uncovers the secret for the on water catalytic aldol reaction: comparison of the heterogeneous and homogeneous reaction circumstances with yields of 95 and 20%, respectively, indicates the on-water reaction dominating; interfacial hydrogen bonding between isatin with H2O is tested based on the downfield shift of the C2 and C3's 13C NMR signals when water was added to the CDCl3 solution of isatin; Lewis base polyetheramine D230 catalyzes the aldol reaction via the enamine mechanism verified by in situ NMR and ESI-MS analysis.

Direct Evidence of Interfacial Hydrogen Bonding in Proton-Electron Concerted 2D Organic Bilayer on Au Substrate

Direct Evidence of Interfacial Hydrogen Bonding in Proton-Electron Concerted 2D Organic Bilayer on Au Substrate

Hydration and Orientation of Carbonyl Groups in Oppositely Charged Lipid Monolayers on Water.

The carbonyl groups of glycerolipid monolayers on water play an important role in the formation of the interfacial hydrogen bond network, which in turn influences the interactions of lipids with, for example, metabolites. As the frequency of the carbonyl absorption band strongly depends on the hydration state of the lipid headgroups, the carbonyl band is a sensitive reporter of changes in the headgroup environment. Here, we use phase-resolved sum frequency generation spectroscopy to obtain information about the orientation and hydration of the carbonyl groups in lipid monolayers. We find that there are two distinct carbonyl moieties in the lipid monolayers, oppositely oriented relative to the surface plane, that experience substantially different hydrogen-bonding environments.

Fabrication of mesoporous SiO2@SLS composite to remove organic pollutants: hydrogen bond-induced intriguing changes of solubility

Because biomass lignin shows good adsorption activity, its derivatives such as alkali lignin and kraft lignin have been applied in water treatment; however, sodium lignosulfonate (SLS), mainly limited by its high water solubility, is not applicable in this respect. In this work, we fabricated SiO2@SLS mesoporous adsorbent using a facile solution coating method by one step. SLS coating SiO2 enables the former to be “separated” from water, accomplishing the soluble to insoluble conversion. This change makes the composite more suitable and efficient to remove organic pollutants from water than the SLS precursor. It is found that interfacial hydrogen bonds play a significant role in the conversion, which is further corroborated by density functional theory calculations. Various characterizations show that SiO2@SLS is composed of uniform particles around 80 nm in size. Abundant mesopores with diameters ranging from 2 to 3 nm are found on the surface of SiO2@SLS nanoparticles. The specific surface areas of SiO2@SLS were measured between 293.4 and 33.2 m2 g−1, depending on the SLS amount used in the preparing process. Originating from the bio-adsorbent lignin precursor, the SiO2@SLS composite shows excellent adsorption property. Representatively, SiO2@SLS-0.6 is able to efficiently remove methylene blue (MB), almost twice as much as SiO2-0 does; its adsorption capacity (Qm) reaches 206.2 mg g−1 according to the Langmuir model fitting; notably, SiO2@SLS-0.6 works very well even in a high-concentration MB solution (50 mg L−1), showing removal efficiencies at 90.0% (within 1 h) and 99.9% (720 h, i.e., 30 days). Plus having remarkable adsorption stability, our composite SiO2@SLS is anticipated to be promising in application of polluted water treatment.

Hydrogen-bonding power interfacial load transfer of carbon fabric/polypyrrole composite pseudosupercapacitor electrode with improved electrochemical stability

The design of a strong interface interaction is a critical issue to improve the electrochemical stability of polypyrrole (PPy) composite electrodes. In the natural world, hydrogen bond that powers the load transfer can be observed in spider silk. The challenges are to achieve interfacial hydrogen bond interaction to stiff the PPy to help the effective load transfer and alleviate the swelling/shrinkage of PPy chains. Here, a composite electrode was prepared by pyrrole (Py) vapor deposition on the air-plasma-activated carbon fabric (PCF) surface. The X-ray photoelectron spectroscopy and fourier transformed infrared spectroscopy results showed that the COOH groups appearing on the PCF and hydrogen bonds can be formed on the interface of PCF/PPy. Interfacial shear strength (IFSS) and scanning electronic microscope determined hydrogen bond on the interface of PCF/PPy enhance the adhesion and power the load transfer process from PPy to carbon fiber. These interfacial hydrogen bonds severed as adhesion points helped the load transfer effectively to the substrate and decreased the contact resistance, preventing the damage of PPy chains and improving electrochemical performances of PCF/PPy as the electrode for pseudosupercapacitor. The PCF/PPy supercapacitor showed excellent cycling stability (93% capacitance retention after 4000 cycles), while CF/PPy showed poor cycling stability (74% after 4000 cycles). The idea of hydrogen bond powered electrochemical stability can be of reference for the researchers to improve the cycling stability of other conductive polymers that are widely used in high-performance supercapacitor.