Hydrogen-bonding Behavior Research Articles

Photothermal-responsive lignin-based polyurethane with mechanically robust, fast self-healing, solid-state plasticity and shape-memory performance

In light of the depletion of petrochemical resources and increase in environmental pollution, there has been a significant focus on utilizing natural biomass, specifically lignin, to develop sustainable and functional materials. This research presents the development of a lignin-based polyurethane (DLPU) with photothermal-responsiveness by incorporating lignin and oxime-carbamate bonds into polyurethane network. The abundant hydrogen bonds between lignin and the polyurethane matrix, along with its cross-linked structure, contribute to DLPU's excellent mechanical strength (30.2 MPa) and toughness (118.7 MJ·m−3). Moreover, the excellent photothermal conversion ability of DLPU (54.4 %) activates dynamic reversible behavior of oxime-carbamate bonds and hydrogen bonds, thereby endowing DLPU with exceptional self-healing performance. After 15 min of near-infrared irradiation, DLPU achieves self-healing efficiencies of 96.0 % for tensile strength and 96.3 % for elongation at break. Additionally, DLPU exhibits photocontrolled solid-state plasticity as well as an excellent phototriggered shape-memory effect (70 s), with shape fixity and recovery ratios reaching 98.8 % and 95.3 %, respectively. By exploiting the spatial controllability and photothermal-responsiveness of DLPU, we demonstrate multi-dimensional responsive materials with self-healing and shape-shifting properties. This work not only promotes the development of multi-functional polyurethanes but also provides a pathway for the high-value utilization of lignin.

A dual dynamically cross-linked hydrogel promotes rheumatoid arthritis repair through ROS initiative regulation and microenvironment modulation-independent triptolide release

High oxidative stress and inflammatory cell infiltration are major causes of the persistent bone erosion and difficult tissue regeneration in rheumatoid arthritis (RA). Triptolide (TPL) has become a highly anticipated anti-rheumatic drug due to its excellent immunomodulatory and anti-inflammatory effects. However, the sudden drug accumulation caused by the binding of “stimulus-response” and “drug release” in a general smart delivery system is difficult to meet the shortcoming of extreme toxicity and the demand for long-term administration of TPL. Herein, we developed a dual dynamically cross-linked hydrogel (SPT@TPL), which demonstrated sensitive RA microenvironment regulation and microenvironment modulation-independent TPL release for 30 days. The abundant borate ester/tea polyphenol units in SPT@TPL possessed the capability to respond and regulate high reactive oxygen species (ROS) levels on-demand. Meanwhile, based on its dense dual crosslinked structure as well as the spontaneous healing behavior of numerous intermolecular hydrogen bonds formed after the breakage of borate ester, TPL could remain stable and slowly release under high ROS environments of RA, which dramatically reduced the risk of TPL exerting toxicity while maximized its long-term efficacy. Through the dual effects of ROS regulation and TPL sustained-release, SPT@TPL alleviated oxidative stress and reprogrammed macrophages into M2 phenotype, showing marked inhibition of inflammation and optimal regeneration of articular cartilage in RA rat model. In conclusion, this hydrogel platform with both microenvironment initiative regulation and TPL long-term sustained release provides a potential scheme for rheumatoid arthritis.

Probing the state of hydrogen in δ−AlOOH at mantle conditions with machine learning potential

Hydrous and nominally anhydrous minerals are a fundamental class of solids of enormous significance to geophysics. They are the water carriers in the deep geological water cycle and impact structural, elastic, plastic, and thermodynamic properties and phase relations in Earth's forming aggregates (rocks). They play a critical role in the geochemical and geophysical processes that shape the planet. Their complexity has prevented predictive calculations of their properties, but progress in materials simulations ushered by machine-learning potentials is transforming this state of affairs. Here, we adopt a hybrid approach that combines deep learning potentials (DPs) with the strongly constrained and appropriately normed meta-generalized gradient approximation functional to simulate a prototypical hydrous system. We illustrate the success of this approach to simulate δ−AlOOH (δ), a phase capable of transporting water down to near the core-mantle boundary of the Earth (∼2900km depth and ∼135GPa) in subducting slabs. A high-throughput sampling of phase space using molecular dynamics simulations with DPs sheds light on the hydrogen-bond behavior and proton diffusion at geophysical conditions. These simulations provide a pathway for a deeper understanding of these crucial components that shape Earth's internal state. Published by the American Physical Society 2024

Hydrogen-bonding behavior of amidines in helical structure.

Amidines are an isostere of the amide bond and are completely unexplored in peptide secondary structure. This study marks the first investigation of the structural implications of amidines in folded helices. Amidines were found to engage in hydrogen-bonding interactions that are compatible with helical structure. The protic state of the amidine is also adaptive to local interactions, able to form stronger hydrogen bonds with proton donors or form the first example of a salt bridge along the peptide backbone to stabilize the C-terminus of the helical fold. The rationalization of this behavior was aided by our discovery that the basicity of amidines within peptide backbones can be significantly lower than previously assumed for small molecules. These findings compel investigation of amidines in peptide-drug design.

Pressure-Induced Aggregation of Associating Liquids as a Driving Force Enhancing Hydrogen Bond Cooperativity.

The behavior of hydrogen bonds under extreme pressure is still not well understood. Until now, the shift of the stretching vibration band of the X-H group (X = the donor atom) in infrared spectra has been attributed to the variation in the length of the covalent X-H bond. Herein, we combined infrared spectroscopy and X-ray diffraction experimental studies of two H-bonded liquid hexane derivatives, i.e., 2-ethyl-1-hexanol and 2-ethyl-1-hexylamine, in diamond anvil cells at pressures up to the GPa level, with molecular dynamics simulations covering similar thermodynamic conditions. Our findings revealed that the observed changes in the X-H stretching vibration bands under compression are not primarily due to H-bond shortening resulting from increased density but mainly due to cooperative enhancement of H-bonds caused by intensified molecular clustering. This sheds new light on the nature of H-bond interactions and the structure of liquid molecular systems under compression.

Molecular dynamics simulation of water condensation with nucleus under electromagnetic wave irradiation

The condensation process of water with different nuclei under electromagnetic wave irradiation was studied by molecular dynamics simulation. It was found that there is a different electric-field effect when the condensation nucleus was a small (NH4)2SO4 cluster than a CaCO3 nucleus. Through the analysis of the hydrogen-bond number, energy change, and dynamic behavior, we found that the effect of external electric field on the condensation process mainly comes from the change of potential energy caused by the dielectric response and there is a competition effect between the dielectric response and the dissolution in the system with (NH4)2SO4.

In Situ Lignin Modification Enabling Enhanced Interfibrillar Interactions in Lignocellulosic Nanomaterials toward Structural Applications

Lignocellulose nanopaper (LNP) assembled from lignocellulose nanofibrils (LCNFs) is an emerging eco-friendly structural material applicable to a variety of fields. Lignin serves as a crucial functional component in the LNP matrix; however, it negatively affects the interfacial hydrogen-bonding behaviors among LCNFs and consequently the inferior mechanical performance of LNP. In this study, a mild ozone-oxidation strategy was used to modify lignin macromolecules in situ without significant degradation of carbohydrate polymers (i.e., cellulose and hemicellulose) in LCNFs whereupon the interfacial hydrogen-bond energy was dramatically improved in the assembly and deformation process of LNP as validated by molecular dynamics simulation. Consequently, the lignin-modified LNP exhibited significantly enhanced tensile strength (from 83 to 140 MPa) and toughness (from 1.9 to 7.1 J/m3), which even surpassed those of conventional cellulose nanopaper. Benefiting from the well-preserved lignocellulosic structure, lignin-modified LNP maintained its inherent favorable water and thermal stability and intriguing optical performance, which supported our developed LNP to be a multifunctional structural material for diversified fields, for example, flexible electronic applications. Additionally, the estimated production cost for our developed LNP was approximately half of that for conventional cellulose nanopaper due to its significantly lower resource inputs such as the material, water, and energy. Overall, our study provides a site-specific macromolecular modulation strategy for the economically and environmentally feasible fabrication of high-performance lignocellulosic nanomaterials toward advanced structural applications.

Chirped pulse Fourier-transform microwave spectroscopy of alcohol and water tetramers.

In an effort to build towards quantitative models of alcohol:water microaggregation in liquid mixtures, the present works characterizes the energy landscape and structures of pure ethanol and mixed ethanol:water tetramers using Chirped Pulse Fourier-transform Microwave spectroscopy. Many conformers of each type of tetramer are available, and those with sufficiently strong dipole moments are experimentally examined. This analysis considers, but does not explicitly fit, the splitting of rotational states due to internal rotation of the methyl groups present, as well as utilizes isotopic substitution experiments to verify the conformer variations observed. Implications of the listed results include a suggestion of the stability of micro-aggregated structures as opposed to homogeneously mixed clusters, informing future work on characterization of larger clusters and any potential modeling of the hydrogen bond network at play.

Insighting the inhibitory potential of novel modafinil drug derivatives against estrogen alpha (ERα) of breast cancer through a triple hybrid computational methodology

Breast cancer (Bca) is the prominent, most commonly detected, and the leading cause of mortality among women. Estrogen receptor alpha (ERα) is considered an important receptor for the proliferation of this disease and its blockage is necessary for the treatment of Bca. The purpose of the current study is to design novel potential inhibitors against ERα of Bca. We designed modafinil drug derivatives using quantum chemical methods. These newly designed derivatives were put under an in-silico investigation followed by molecular docking simulation, molecular dynamics simulation, and MMPBSA analysis to find novel inhibitors of ERα. Moreover, three reference anticancer drugs; tamoxifen, raloxifene, and toremifene are also studied against ERα of Bca. The spectroscopic and structural features of sulfoxide-based designed derivatives of modafinil drug M1((R)-2-(banzhydrylsulfinyl-N,N diethylacetamide) have been evaluated using different quantum chemical analyses. The findings of the current investigation demonstrate that all studied ligands exhibit the binding energy ranges (-5.3 to −5.8 Kcal/mol). The designed compounds showed effective hydrophobic (alkyl, π-alkyl, π-sigma, π-amide stacked, π-π T-shaped) interactions and hydrogen bond formation and are anticipated to be potential inhibitors against ERα. Additionally, designed derivatives have a good ADMET (absorption, distribution, metabolism, excretion, toxicity) profile and drug-likeness properties obeying RO5 without any toxicity. The stability profile of designed derivatives (M1-M6) was further validated by molecular dynamics (MD) simulation and calculate binding free energy by the MM-PBSA approach. All ligand–protein complexes showed structural stability over the 120 ns MD simulation time. The MD simulation of the complex system was carried out by RMSD (root-mean-square deviation) of C α atoms of ERα, RMSF (root mean square fluctuations), Rg (radius of gyration), SASA (solvent accessible surface area), and dynamic behavior of hydrogen bonds. The MD simulation results illustrate that RMSD for trajectories of designed derivative complexes over 120 ns are within the acceptable deviation range of ∼ 3 Å. The calculations of net binding free energy (ΔGbind) between the designed derivatives and their complexes are found to be −8.50 Kcal/mol (M1) at maximum and −5.197 Kcal/mol (M3) at a minimum among all derivatives. The outcomes of our current in-silico investigation will evoke the scientific community to carry out further in vivo and in vitro studies on designed modafinil derivatives that can be potential therapeutic drug candidates against ERα.

The effect of surface functional groups on the wettability of graphene oxide coated alumina substrate: Molecular dynamics simulations

In this article, molecular dynamic simulation was used to simulate the wetting process of graphene oxide coated alumina substrate. By changing the density of hydroxyl and epoxy groups on the surface of graphene oxide, the influence mechanism of two functional groups on the wetting process of water molecules was explored. From the simulation results, the increase of hydroxyl density can enhance the wettability of the substrate and reduce the wettability angle from 64.32° to 54.20°. By calculating the formation of the hydrogen bond in the wetting process, it is found that hydroxyl can significantly raise the hydrogen bond lifetime in the system. This increasing effect is particularly prominent in the observation of the hydrogen bond between water molecules and graphene oxide. The hydrogen bond lifetime increases from 2.20 ps to 12.77 ps. The result also reflects the reason why hydroxyl increases the wettability of the substrate. In addition, the increase of hydroxyl density also brings changes in hydrogen bond behavior and the number of hydrogen bonds. Under the condition of high epoxy density, most of the hydrogen bonds between water molecules and the substrate exist in the form of single hydrogen bonds, and the number is small. When the hydroxyl density increases, double-hydrogen bond, triple-hydrogen bond and single hydrogen bond appear in the model. In this process, the number of hydrogen bonds between the water droplet and the substrate is also increasing. Temperature is an important influence on the formation and lifetime of the hydrogen bond. High temperatures can promote the formation of the hydrogen bond between alumina and water molecules. In addition, it can also decrease the lifetime of all types of hydrogen bonds. Through the free energy perturbation theory, we get the free energy of different models in the wetting process. The results show that high hydroxyl density can improve the free energy of the wetting process, reduce the ability of spontaneous desorption and increase the stability of wetting. High temperatures can reduce the free energy and lead to the occurrence of desorption behavior. This article reveals the wetting mechanism of water molecules on graphene oxide coated alumina substrate, mainly reveals the influence of hydrogen bond and the change of free energy in the wetting process, which lays a theoretical foundation for the application of graphene oxide wetted coating on the aluminum alloy surface.

Assessment of Bioactivity-Modulating Pseudo-Ring Formation in Psilocin and Related Tryptamines.

Psilocybin (1) is the major alkaloid found in psychedelic mushrooms and acts as a prodrug to psilocin (2, 4‐hydroxy‐N,N‐dimethyltryptamine), a potent psychedelic that exerts remarkable alteration of human consciousness. In contrast, the positional isomer bufotenin (7, 5‐hydroxy‐N,N‐dimethyltryptamine) differs significantly in its reported pharmacology. A series of experiments was designed to explore chemical differences between 2 and 7 and specifically to test the hypothesis that the C‐4 hydroxy group of 2 significantly influences the observed physical and chemical properties through pseudo‐ring formation via an intramolecular hydrogen bond (IMHB). NMR spectroscopy, accompanied by quantum chemical calculations, was employed to compare hydrogen bond behavior in 4‐ and 5‐hydroxylated tryptamines. The results provide evidence for a pseudo‐ring in 2 and that sidechain/hydroxyl interactions in 4‐hydroxytryptamines influence their oxidation kinetics. We conclude that the propensity to form IMHBs leads to a higher number of uncharged species that easily cross the blood‐brain barrier, compared to 7 and other 5‐hydroxytryptamines, which cannot form IMHBs. Our work helps understand a fundamental aspect of the pharmacology of 2 and should support efforts to introduce it (via the prodrug 1) as an urgently needed therapeutic against major depressive disorder.

Molecular dynamics study of hydrogen bond in peptide membrane at 150–300 K

In this work, we develop molecular dynamics simulations to investigate the structural and dynamic behavior of hydrogen bonds in A6X-type peptide structures (X = D, K, and R) in the range of temperature from 150 K to 300 K. Our results show a strong structural dependence of the hydrogen bonds with the mobility of the peptides in the membrane. Such dependence can impact the formation of hydration channels in the membrane structure. Our results show that the hydrogen bond network becomes dynamic at temperatures above 240 K which makes the membrane structure more organized, with a uniform stacking of β-sheets. The density of hydrogen bonds in these materials shows up to 16–24 hydrogen bonds per nm3, which characterizes such structures with a dense and robust mesh of interactions. Our results also show that the dynamic of the hydrogen-bond network has a dependence on the polar head of the A6X peptide (X = D, K, or R).

An extended COSMO-SAC method for the prediction of carboxylic acid solubility

The COSMO-SAC model provides a convenient method for predicting the phase behavior of components with minimal information about molecules using quantum-mechanical principles. During the past few years, several researchers tried to improve the prediction capability with modifications to hydrogen bonding terms and other methods of calculation. In this contribution, we focused on carboxylic acid groups, which may exhibit different hydrogen-bond behavior as compared with alcohols. The calculation scheme in COSMO-SAC (2017 version) was slightly modified to encompass a hydrogen-bond term specifc to carboxylic acid groups. The parameters for the extended COSMO-SAC model were fitted using 559 data points. The characteristics of the extended model were investigated for the prediction capability of binary solubility, ternary solubility, and vapor-liquid equilibrium data. The results show that the extension correctly predicts the phase behavior of mixtures containing carboxylic acids.

Understanding of Competitive Hydrogen Bond Behavior of Imidazolium-Based Ionic Liquid Mixture around Single-Walled Carbon Nanotubes

Here we have performed molecular dynamics simulations to investigate the structures, dynamics, and hydrogen bonds (HBs) of the imidazolium-based ionic liquid (IL) mixture containing equimolar 1-eth...

Study on the unsaturated hydrogen bond behavior of bio-based polyamide 56

AbstractIn this paper, the unsaturated hydrogen bonds (H-bonds) of the bio-based polyamide 56 (PA56) with an odd-even unit structure were analyzed by infrared spectroscopy. It was proved that the bio-based PA56 had less saturated H-bonds, which became attenuated and blue-shifted at the temperature exceeding 260°C. Besides, as H-bond was decayed and broken, new unsaturated H-bonds readily formed. Moreover, the experimental results obtained strongly indicate that the unsaturated H-bonds of bio-based polyamide 56 could react with polar metal oxides. Besides, the intercalation of montmorillonite was found to have a significant influence on the hydrogen bond between polymer chains.

Aromatic Foldamers Recognizing Saccharides to Form Chiral Helices

New meta-arylene ethynylene foldamers were developed by employing pyridine and phenol units. These demonstrated interesting properties related to the hydrogen-bonding behavior of the arylene units. Pyridine-acetylene-phenol foldamers showed improved saccharide recognition abilities compared with pyridine-acetylene foldamers with no phenol units. Solid-liquid extraction could be achieved due to the strong binding. Hydrocarbon stapling by alkene metathesis under templation was attempted, and the helical structure was efficiently stabilized. Phenol-acetylene oligomers spontaneously formed helical structures via intramolecular hydrogen bonding. The helical sense could be biased by adding chiral amines.

Characterization of Nucleobases in Broadband Terahertz Spectra from 0.5 to 10 THz with the Air-Biased-Coherent-Detection Technique.

Terahertz time-domain spectroscopy (THz-TDS) is an effective coherent detection technique for deeply understanding the structures and functions of biomolecules. However, generally not full information in the whole THz range can be obtained due to the limited detection bandwidth (usually less than 5 THz) of the traditional THz-TDS systems. In this paper, effective THz absorption spectra in 0.5–10 THz range of five typical nucleobases of DNA/RNA are characterized with a super broadband THz detection technique, called the air-biased- coherent-detection (THz-ABCD) technique. Few unexpected characteristic absorption peaks appeared in the low-frequency region and meanwhile a series of anticipated characteristic absorption peaks are found in the high-frequency region. The fingerprint spectra of these nucleobases are helpful for further analysis on the vibration and twisting behavior of hydrogen bonds, van der Waals and electrostatic forces etc. between and within DNA/RNA biomolecules.

Molecular Dynamics Investigations of Dibutyl-phosphoric Acid-Parameterization and Dimerization.

A reparameterized molecular dynamics force field for dibutyl-phosphoric acid (HDBP) has been developed. Parameterization was done using the general Amber force field, as a starting point. The density and dipole moment of bulk phase simulations compare well to that of known experimental values, and the heat of vaporization is comparable to an estimated empirical value. All values have been optimized to within 4%. The newly optimized force field was validated against the self-diffusion coefficient, matching experimental data to within 18%, which is a significant improvement compared to the nonoptimized force field. Further, a potential of mean force study was carried out to understand the behavior of hydrogen bonds in HDBP dimers. This required the determination of hydrogen bonding criteria that captures the behavior of the HDBP dimer and is reported in this work as well.

Monitoring Coil-Globule Transitions of Thermoresponsive Polymers by Using NMR Solvent Relaxation.

Thermoresponsive polymers exhibit coil-globule transition in aqueous solution where the polymer undergoes transition from the coil-like morphology to a globular form with the change of temperature. Such transitions also reflect changes in the solvent dynamics captured by various spectroscopic methods. In this work, we construct a phenomenological model to capture the dynamics of the NMR relaxation of water molecules of an aqueous solution of thermoresponsive polymers that are known to form hydrogen bonds with the solvent water molecules. The model relies on the behavior of the polymer-solvent hydrogen bonds and the sharing of rotational kinetic energy of water molecules in the vicinity of the polymer chain and the bulk. This is shown to provide a direct estimate of the fractional change of the polymer-water hydrogen bonds across lower critical solution temperature from NMR relaxation data of solvent water along with a reliable estimate of the transition temperature. In addition, it also provides a measure of the dispersion of the strengths of these hydrogen bonds. We exemplify the validity of this model by successfully fitting the experimental data to show that the extracted parameters provide significant insights into the role played by the hydrogen bonds in the process. The possible extension of this model to solvents that form no hydrogen bonds with the polymers is also discussed.

Exploring Chimeric Calix[4]tetrolarene Molecular Scaffolds: Theoretical Investigations.

The structure and spectral characteristics of the chimeric mixture of calixarene and pyrogallolarene (usually referred to as calix[4]tetrolarene) and its derivatives are studied employing the M06-2X-based density functional theory. Different conformers, viz., cone, partial cone, 1,2-alternate, and 1,3-alternate, were identified as the stationary point structures on their potential energy surfaces. Among these, the symmetric C4 v cone conformer is found to be energetically favorable, which can be attributed to the cyclic array of hydrogen-bonding network in the calix[4]tetrolarene or its thia analogue. The substitution of methoxy groups at the upper rims of calix[4]tetrol- and thicalix[4]tetrol-arenes significantly influences the cooperative hydrogen-bonding network and conformational behavior of these hosts. The methoxy-substituted macrocycles show lowering in symmetry from C4 v to C2 v, engendering the pinched cone conformer to be the lowest energy structure. The enhanced solubility of the modified calix[4]tetrolarene macrocycles has been further explained from diminutive cooperative hydrogen bonding in its top rim compared to the pyrogallolarene, which is evidenced from the quantum theory of atoms in molecule and noncovalent interaction reduce density gradient method. Discernibly, the underlying cooperative hydrogen bonding emerges its signature in the characteristic vibrational patterns of the calixarene-based molecular scaffolds. The chemical shift parameters in their 1H NMR spectra have further been characterized.