Internal Hydrogen Bond Research Articles

Predicting the Antifungal Activity of Small Organic Compounds on Aspergillus niger Mold using Molecular Dynamics Simulations.

Atomistic models of the plasma membrane of the pathogenic mold Aspergillus niger are developed. These models are described with an empirical molecular mechanical (MM) force field in combination with molecular dynamics (MD) simulations. The solvated plasma membrane models are brought into contact with 35 small organic compounds to observe their impact on a variety of membrane properties. All compounds are added at a constant total mass of 1% of the membrane mass. In addition, the ability of these compounds to inhibit the pathogenic cell growth of mold has been measured. Diffusion of compounds into the membrane model is readily observed during MD simulations. Changes in membrane properties found in simulations are not found to correlate with measured antifungal activities of compounds, suggesting that MD simulations of up to 1 μs are not sufficiently long to adequately describe compound-induced membrane disruption. However, properties related to the position and orientation of compounds relative to the membrane surface as well as hydrogen bonds formed between the compounds and the membrane show clear trends that correlate well with measured activities. A combination of these properties enables an activity prediction of compounds in good agreement with measurements. Activity is found predominantly for compounds that can be decomposed into a single continuous hydrophobic and hydrophilic moiety. Such active compounds can be energetically inserted most favorably into the membrane. These insertions destabilize the membrane by disrupting the internal membrane hydrogen bond network and by sliding between neighboring lipids, thereby separating them.

Exploring atmospheric nucleation processes: Hydration and fluoroalcoholic complexation of pyruvic acid.

This study examines the intermolecular interactions between small molecules and solvents, with a particular focus on pyruvic acid (PA). PA plays a significant role in biochemistry, astrochemistry, and atmospheric chemistry, particularly in aerosol particle formation. Previous studies on PA have been expanded upon by exploring its hydration and complexation with 2,2,2-trifluoroethanol (TFE). The clusters were generated using a supersonic expansion and characterized by broadband Fourier transform microwave spectroscopy. The structures of the clusters were identified by comparing the experimental results with high-level quantum-chemical computations. Among the possible isomers for the hydrated complex, the Tc-(H2O)2 kinetic complex, where PA exhibits an internal hydrogen bond, was favored over the Tt-(H2O)2 form, predicted to be the most stable conformer. Transitions from both the A and E internal rotation substates were observed exclusively in the dihydrate. The complex with TFE did not exhibit splitting due to the internal rotation of the methyl top. This is attributed to the presence of electronegative fluorine groups in TFE, stabilizing the complex through additional CH⋯F interactions, thereby hindering the internal rotation motion of the methyl top.

Lead-free semiconductor materials with high phase transition temperature: [1-Methylimidazole][SbBr4]

Semiconductor with structure phase change is a special multi-functional material, which plays an important role in the field of Solar Energy, information computing, sensor technology, artificial intelligence, etc. In this paper, the organic–inorganic lead-free semiconductor phase change material [1-Methylimidazole][SbBr4] (1) was successfully constructed. The IR, TGA, DSC, VT-PXRD, solid-state UV–vis spectroscopy and temperature dependence of dielectric constant were characterized and analysed. Single crystal X-ray diffraction shows that at 298 K, the space group is P21/c, the point group 2/m; an endothermic and exothermic peak appeared near 386 K and 367 K in the DSC heating–cooling cycles. Near the corresponding phase transition temperature point, compound 1 exhibits a significant reversible change in the dielectric platform. Interestingly, the band gap of compound 1 is about 2.53 eV. The existence of such interesting physical properties is closely related to the interaction between cations and anions in the molecule and the connection of internal hydrogen bonds. By constructing organic–inorganic hybrid semiconductor materials, we hope to obtain semiconductor materials with phase transition properties and actively explore and provide some ideas and support for the application of new high-tech materials.

In-situ polymerization of dual monomers for constructing a highly elastic PAA-co-PAM network enables efficient and stable Carbon-based perovskite solar cells

During the preparation of carbon-based perovskite solar cells, the external stress applied to the carbon paste inevitably compresses the perovskite lattice, potentially damaging its structure and generating defects. This poses a significant threat to the efficiency and stability of devices. Herein, a dual monomer irregular in-situ polymerization method was developed to form a highly elastic network (acrylamide-co-acrylic acid, PAA-co-PAM) within perovskite films, serving as both a ligament to passivate defects and a buffer to improve film stability under stress. The results demonstrated that multiple active sites of PAA-co-PAM could simultaneously passivate positive and negative defects, which improved charge transport efficiency, reduced nonradiative recombination, and prolonged lifetime of carriers. Meanwhile, the cross-linking network in PAA-co-PAM exhibits high elasticity due to both internal hydrogen bonds between monomers and external hydrogen bonds between monomers and perovskite, resulting in films with exceptional structural stability and mechanical resilience. Notably, the corresponding device achieved the power conversion efficiency of 15.39%. Moreover, the unencapsulated photovoltaic device passivated by the elastic network exhibits better storage stability and mechanical stability compared to the control devices. This work provides a new perspective and insight for comprehensively enhancing the stability of carbon-based perovskite solar cells.

Adsorption of oxytetracycline in hyporheic zone sediments mediated by microplastics: Experimental revelations and mechanistic insights

Microplastics (MPs), serving as carriers, possess a mediating effect on altering antibiotics (ATs) migration, yet this novel effect has not received due attention in the vulnerable hyporheic zones where surface water and groundwater converge. This study collected sediment layers from the typical hyporheic zone of the Weihe River, focusing on oxytetracycline (OTC) detected therein, and employed three types of MPs (polyethylene (PE), polypropylene (PP), and polymethyl methacrylate (PMMA) to establish various mediated adsorption systems. Through batch equilibrium adsorption experiments, morphological and spectroscopic characterizations combined with the impact of external environmental factors, the changes in OTC adsorption characteristics and the interactions before and after MPs mediation were systematically examined. The results indicate that MPs-mediated adsorption led to the formation of a rough, porous amorphous structure on the sediment surface, with potential internal hydrogen bonds. This exhibited an additional micropore diffusion step that delayed the adsorption kinetics equilibrium time, increased the isothermal maximum adsorption capacity along with desorption hysteresis effects, shifted thermodynamic enthalpy from physically dominated to semi-chemical adsorption participation, and resulted in an increased tendency towards disorder in entropy. The pH, ionic strength, and aging of MPs all affect the charge balance within the adsorption system, while MPs, OTC, and sediments can interact through the negative-charge-assisted hydrogen bond ((−)CAHB). The mediating effect of MPs stems from their role as receptors, facilitating the formation of (−)CAHB and thus crosslinking an amorphous structure available for OTC micropore filling. Compared to PE and PP, PMMA provides receptors through an additional free radical pathway, hence possessing a stronger mediating effect. These findings contribute to reevaluating the environmental fate of ATs and MPs from a new perspective, offering theoretical references for risk assessment and management of emerging pollutants.

Dibutylamide hydrophobic deep eutectic solvent used for selective extraction of Au(III) from hydrochloric acid medium

The effective and environmentally friendly recovery of gold from secondary resources has recently received increased attention. Hydrophobic deep eutectic solvent (HDES) composed of N,N-di-butylacetamide and 1-decanoic acid was used to construct the liquid-liquid extraction system to extract Au(III) from HCl medium. At first, DSC, TGA, FT-IR, and 1H NMR were used to describe the evidence of internal hydrogen bond interaction. The above evidence was verified in the molecular dynamics study of HDES. Then, a series of optimization experiments were carried out to investigate the extraction behaviors of HDES. Based on the results of optimization experiments, response surface method was used to explore the best experimental conditions and the results showed that HDES extracted 99% Au(III) under 0.56 mol/L HCl, 2.19 mol/L NaCl, and 5.83 mmol/L Au(III), and the maximum loading reached 77.0 mg/g. Further studies on the kinetics and thermodynamics of the extraction were used to propose an ion association mechanism. In addition, using 0.1 mol/L thiourea as the stripping agent, HDES displayed outstanding Au(III) selectivity and maintained the extraction efficiency in tests which involved 5-cycles. Overall, this study provides a green and efficient Au(III) recovery strategy for secondary resources.

Amine-functionalized metal organic framework@graphene oxide as filler in PAEK-containing carboxyl group membrane for ultrafiltration with ultra-high permeability and strong fouling resistance

Achieving high fouling resistance and permeability using membrane separation technology in water treatment processes remains a challenge. In this work, a novel mixed matrix membrane (PAEK-COOH/UiO-66-NH2@GO) with superb fouling resistance and high permeability was prepared by the nonsolvent induced phase separation method, by in-situ growth of UiO-66-NH2 on graphene oxide (GO) layer, and by preparing hydrophilic poly(arylene ether ketone) (PAEK) containing carboxyl groups (PAEK-COOH). On the basis of the structure and performance analysis of the mixed matrix membrane (MMMs), the maximum water flux reached 591.25 L·m–2·h–1 for PAEK-COOH/UiO-66-NH2@GO, while the retention rate for bovine serum albumin increased from 85.40% to 94.87%. As the loading gradually increased, the hydrophilicity of the MMMs increased, significantly enhancing their fouling resistance. The strongest anti-fouling ability observed was 94.74%, which was 2.02 times greater than that of the pure membrane. At the same time, the MMMs contained internal amide and hydrogen bonds during the preparation process, forming a cross-linked structure, which further enhanced the mechanical strength and chemical stability. In summary, the MMMs with high retention rate, strong permeability, and anti-fouling ability were successfully prepared.

Facet engineering of minerals for effective oil-water separation

Minerals have been growing as an emerging ‘hot’ topic in separating water-in-oil emulsions. Whether the intrinsic structure of minerals could precisely regulate water–mineral interactions for enhancing emulsions separation efficiency is still ambiguous. Here, taking half-hydrated gypsum as a case, this study reveals the crystal facet-dependent potential mechanism of minerals in water-in-oil emulsions separation. We show that the (204) facet of half-hydrated gypsum is more susceptible to water-induced degradation and hydration reaction. With combined experimental and theoretical studies, the facet-dependent mechanism for oil–water separation are revealed; the (204) facet that exhibited weak internal hydrogen bond and strong binding energy with water accelerated the dissolution and recrystallization of half-hydrated gypsum, thus enhancing oil–water separation efficiency. Through engineering, half-hydrated gypsum with a higher surface fraction of the (204) facet achieved much higher separation efficiency (99.9%), surpassing those of minerals in disclosed literature. This investigation not only contributes significantly to the comprehension of interactions at the minerals-water interface but also illuminates novel perspectives and avenues for the utilization of facet engineering in advancing research on mineral surface properties.

The shape of water - how cluster formation explains the hydrophobic effect

The hydrophobic effect is a particular characteristic of water, which in its pure form exhibits more anomalous properties than any other known liquid. A unifying molecular scale origin of these observations has been sought for decades. Here, we show that thermodynamically driven formation of water clusters in water simultaneously explains the hydrophobic effect and water’s anomalous properties. Our unifying first-principles based model for water cluster formation predicts the correct thermodynamics of organic molecule solvation in water as well as surfactant self-assembly. Our model provides an intuitive explanation that water as a whole becomes more hydrophobic as temperature decreases, because higher concentrations of clusters favour internal hydrogen bonds, which leads to fewer opportunities for interactions with solutes.

Supramolecular elastomers with high strength and low toxicity are suitable for safety protection

Elastomer with high strength and toughness, temperature resistance and low smoke toxicity have shown great application prospects in the field of safety protection. In order to meet the needs of high strength, high toughness and smoke toxicity safety, a high-strength structural elastomer is formed by introducing the integration of hard skeleton and soft elastomer, that is, two-dimensional black phosphorus with high flame retardant efficiency and bimetallic hydroxide with catalytic detoxification (BP-MA-LDH) as the hard skeleton, based on the special combination of internal hydrogen bonds. High strength supramolecular poly(Urethane) (SPU) elastomer was manufactured by molecular design. The high strength and toughness SPU elastomer also has a tensile strength of 53.77 Ma and a elongation at break of 715.26 %. The addition of 2.0 wt% BP-MA-LDH reduces the heat release rate of SPU by 58.84 % and the smoke production release by 61.54 %. In terms of flue gas toxicity inhibition, Fractional Effective Dose was used to evaluate the flue gas toxicity of elastomer composites, and the release of CO, HCN, oxynitride and other toxic gases were greatly reduced. The synthetic performance of SPU elastomer composites in strengthening and toughening, smoke suppression and toxicity reduction is much better than that reported by peers.

Crystal structure and characterization of a new lanthanide coordination polymer, [Pr2(pydc)(phth)2(H2O)3]·H2O

A new lanthanide coordination polymer, poly[[triaquabis(μ4-phthalato)(μ3-pyridine-2,5-dicarboxylato)dipraseodymium] monohydrate], {[Pr2(C7H3NO4)2(C8H4O4)(H2O)3]·H2O} n or {[Pr2(phth)2(pydc)(H2O)3]·H2O} n , (pydc2− = pyridine-2,5-dicarboxylate and phth2− = phthalate) was synthesized and characterized, revealing the structure to be an assembly of di-periodic {Pr2(pydc)(phth)2(H2O)3} n layers. Each layer is built up by edge-sharing {Pr2N2O14} and {Pr2O16} dimers, which are connected through a new coordination mode of pydc2− and phth2−. These layers are stabilized by internal hydrogen bonds and π–π interactions. In addition, a three-dimensional supramolecular framework is built by interlayer hydrogen-bonding interactions involving the non-coordinated water molecule. Thermogravimetric analysis shows that the title compound is thermally stable up to 400°C.

Switching the proton-coupled electron transfer mechanism for non-canonical tyrosine residues in a de novo protein.

The proton-coupled electron transfer (PCET) reactions of tyrosine (Y) are instrumental to many redox reactions in nature. This study investigates how the local environment and the thermodynamic properties of Y influence its PCET characteristics. Herein, 2- and 4-mercaptophenol (MP) are placed in the well-folded α3C protein (forming 2MP-α3C and 4MP-α3C) and oxidized by external light-generated [Ru(L)3]3+ complexes. The resulting neutral radicals are long-lived (>100 s) with distinct optical and EPR spectra. Calculated spin-density distributions are similar to canonical Y˙ and display very little spin on the S-S bridge that ligates the MPs to C32 inside the protein. With 2MP-α3C and 4MP-α3C we probe how proton transfer (PT) affects the PCET rate constants and mechanisms by varying the degree of solvent exposure or the potential to form an internal hydrogen bond. Solution NMR ensemble structures confirmed our intended design by displaying a major difference in the phenol OH solvent accessible surface area (≤∼2% for 2MP and 30-40% for 4MP). Additionally, 2MP-C32 is within hydrogen bonding distance to a nearby glutamate (average O-O distance is 3.2 ± 0.5 Å), which is suggested also by quantum mechanical/molecular mechanical (QM/MM) molecular dynamics simulations. Neither increased exposure of the phenol OH to solvent (buffered water), nor the internal hydrogen bond, was found to significantly affect the PCET rates. However, the lower phenol pKa values associated with the MP-α3C proteins compared to α3Y provided a sufficient change in PT driving force to alter the PCET mechanism. The PCET mechanism for 2MP-α3C and 4MP-α3C with moderately strong oxidants was predominantly step-wise PTET for pH values, but changed to concerted PCET at neutral pH values and below when a stronger oxidant was used, as found previously for α3Y. This shows how the balance of ET and PT driving forces is critical for controlling PCET mechanisms. The presented results improve our general understanding of amino-acid based PCET in enzymes.

Self-association as a solubility limiting factor of riboflavin in aqueous media.

Single crystal X-ray diffraction analysis of needle shaped riboflavin (RF) crystals revealed π-stacking of RF's isoalloxazine units (distance: 3.643-3.313 Å) with syn-orientated ribityl chains. In line with this, classical molecular dynamics (MD) (400 ns) using an isobaric-isothermal (NPT) ensemble of eight RF in a water box (〈V〉 ∼ 508.62 nm3, 〈p〉 = 1.11 bar) revealed anti-aligned aggregation of RF in water (COM-distance: 4 Å). Comparing umbrella sampling for the separation of two RF molecules to the separation of two lumichrome molecules, the similar mean potential force for the separation of RF and lumichrome (22.8 kJ mol-1; 24.4 kJ mol-1) proved dispersive interactions as the origin of RF's aggregation. Though stacking of RF is the major water-solubility limiting factor, the conformation of RF's ribityl chain may alter the solubility in water. Both, MD (in water) and COSMO-RS (in water continuum) predicted that conformations of RF with an extended ribityl chain are thermodynamically preferred over any conformations with internal hydrogen bonds between hydroxyl groups and nitrogen/oxygen atoms of the pyrimidine moiety of the flavin ring. Interestingly, COSMO-RS predicted the solubility of the extended conformation to be significantly lower than the latter leading to the very low average solubility of RF. Nuclear Overhauser effect measurements (NOESY) of the structurally related sodium riboflavin 5'-monophosphate (RF-PO4) in deuterium oxide confirmed π-stacking of the isoalloxazine rings. In conformity with the 350 times higher water-solubility of RF-PO4, NOESY also indicated a contorted conformation of the ribityl phosphate chain, whereas, for RF, indications for a contorted chain were not observed.

Pressure-induced structural evolution to a nearly perfect kagome lattice in β-Mn2(OH)3Cl nanosheets

The frustrated magnets exhibiting kagome geometries and the investigation of their structure-property relationships have garnered substantial attention as potential candidates for quantum spin liquid (QSL). In this study, β-Mn2(OH)3Cl nanosheets with distorted kagome geometries were synthesized via a solid-state reaction, and low-temperature magnetic measurements revealed a spin-glass-like magnetic phase transition around 40 K in the frustrated β-Mn2(OH)3Cl. A pressure-induced structural phase transition was further realized by employing in situ synchrotron X-ray diffraction, leading to a hexagonal crystal structure with a nearly perfect kagome lattice of magnetic Mn2+ ions. High-pressure Raman and UV–vis absorption measurements indicates that the topological evolution can be attributed to the synergistic effects of pressure driven internal hydrogen bonds and the intrinsic Jahn-Teller effects. This study provides a strategy for synthesizing candidate compounds of QSL and sheds light on the mechanism underlying the topological evolution of kagome lattices under high pressure.

Highly Adhesive and Self-Healing Zwitterionic Hydrogels as Antibacterial Coatings for Medical Devices.

Bacterial infection of medical devices has caused incalculable losses to maintenance costs and health care. A single coating with antibacterial function cannot guarantee the long-term use of the device, because the coating will be damaged and fall off during reuse. To solve this problem, the development of coatings with high adhesion and self-healing ability is a wise direction. In this paper, a multifunctional polyzwitterionic antibacterial hydrogel coating (PZG) composed of amphozwitterion monomer, anionic monomer, and quaternary ammonium cationic monomer was synthesized by dipping UV photoinitiated polymerization. The structure of PZGs was characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. Ascribing to the hydrogel internal electrostatic interaction, hydrogen bond, and cation-π interaction, the obtained PZGs exhibited high ductility (>1200% strain) and appropriate strength (>189 kPa). Remarkably, PZGs could also adhere firmly on different substrates through noncovalent interaction, and their adhesion could be controlled by adjusting the amount of zwitterionic. Reversible physical interactions in polymer networks endowed hydrogels with excellent self-healing properties. In addition, PZGs exhibit good antibacterial activity and biocompatibility due to the synergistic effect of quaternary ammonium cation and amphozwitterion monomer. This work provides a multifunctional antibacterial coating for medical equipment and has broad application prospects in the biomedical field.

Theoretical investigation on the mechanism and kinetics of the OH•‒initiated atmospheric degradation of p-chloroaniline: Addition of [formula omitted] and isomerization of peroxy radicals

Atmospheric oxidation of the p-chloroaniline-OH• adduct [C6H4ClNH2–OH]• (AD-C2) by ∑g−3O2 and internal isomerization processes of peroxy radical [C6H4ClNH2–OH]•-O2 are theoretically investigated at the M06-2X/aug-cc-pVTZ and CBS-QB3//M06-2X/aug-cc-pVTZ level of theories. Potential energy surfaces (PESs) for the most efficient pathways indicated that the oxidation process begins via the complexation of individual reactants in syn mode forming PRCy-iOO-syn (y = 2,5) in an exothermic and endogenic step. The syn mode addition is favored over the anti one due to the formation of internal hydrogen bond between the hydroxyl and peroxy groups. Formation of new C5–OO bond in PRCy-iOO-syn complex is an unimolecular process which is exothermic and exoergic. This pathway is predominated over other internal conversions due to the presence of stronger intramolecular hydrogen bond. Cyclization of the produced [C6H4ClNH2–OH]•-O2 peroxy radical AD-C2-5OO-syn into the bicyclic peroxy radical AD-C2-5,6OO-syn is the last step which is strongly endothermic and endogenic. The rate coefficients are calculated by means of the RRKM theory over the temperature range 250–350 K and at a pressure range of 0.1 bar to the high-pressure limit. The RRKM rate coefficients at the M06-2X/aug-cc-pVTZ level for the first bimolecular and last unimolecular steps are in order of 10−16 cm3 molecule−1 s−1 and 10−7 s−1, respectively, while the obtained rate coefficients at the CBS-QB3//M06-2X/aug-cc-pVTZ are overestimated about two order of magnitude.

CrMP-Sol database: classification, bioinformatic analyses and comparison of cancer-related membrane proteins and their water-soluble variant designs

Membrane proteins are critical mediators for tumor progression and present enormous therapeutic potentials. Although gene profiling can identify their cancer-specific signatures, systematic correlations between protein functions and tumor-related mechanisms are still unclear. We present here the CrMP-Sol database (https://bio-gateway.aigene.org.cn/g/CrMP), which aims to breach the gap between the two. Machine learning was used to extract key functional descriptions for protein visualization in the 3D-space, where spatial distributions provide function-based predictive connections between proteins and cancer types. CrMP-Sol also presents QTY-enabled water-soluble designs to facilitate native membrane protein studies despite natural hydrophobicity. Five examples with varying transmembrane helices in different categories were used to demonstrate the feasibility. Native and redesigned proteins exhibited highly similar characteristics, predicted structures and binding pockets, and slightly different docking poses against known ligands, although task-specific designs are still required for proteins more susceptible to internal hydrogen bond formations. The database can accelerate therapeutic developments and biotechnological applications of cancer-related membrane proteins.

Bifunctional hydrophobic deep eutectic solvents for selective recovery of Sm and Co from waste SmCo permanent magnets

The application of hydrophobic deep eutectic solvent (HDES) to single-use separation of valuable metal ions in waste samarium-cobalt permanent magnets has been a significant challenge. Trioctylphosphine oxide and 3-benzoyl-1,1,1-trifluoroacetone were combined to prepare a bifunctional HDES that was investigated for green, efficient and safe recovery Sm and Co. Firstly, internal hydrogen bond interaction was verified by DSC, TGA, NMR, FT-IR and molecular dynamics study. Then, a various of optimization experiments were carried out to discovery extraction behaviors on different metal ions. The findings indicated that the acidity has a significant impact on the effectiveness of the extraction process. The maximum extraction capacities were measured as 98.8 g/L Sm(III), 64.8 g/L Co(II), 52.4 g/L, Fe(III) and 75.1 g/L Cu(II), respectively. After that, combined with UV–vis, FT-IR and XPS, the neutral complex extraction mechanism was proposed. Finally, the competitive extraction experiments at different acidity provided the theoretical underpinnings for a three-stage separation strategy that, through acidity control and the use of various stripping agents, was able to efficiently recover 97.8% Sm(III), 99.1% Co(II), 99.5% Fe(III) and 95.6% Cu(II). The whole recycling process has no need additional organic solvents, enabling cleaner and sustainable engineering production.

Fentanyl and the Fluorinated Fentanyl Derivative NFEPP Elicit Distinct Hydrogen-Bond Dynamics of the Opioid Receptor.

The development of safe therapeutics to manage pain is of central interest for biomedical applications. The fluorinated fentanyl derivative N-(3-fluoro-1-phenethylpiperidin-4-yl)-N-phenylpropionamide (NFEPP) is potentially a safer alternative to fentanyl because unlike fentanyl─which binds to the μ-opioid receptor (MOR) at both physiological and acidic pH─NFEPP might bind to the MOR only at acidic pH typical of inflamed tissue. Knowledge of the protonation-coupled dynamics of the receptor-drug interactions is thus required to understand the molecular mechanism by which receptor activation initiates cell signaling to silence pain. To this end, here we have carried out extensive atomistic simulations of the MOR in different protonation states, in the absence of opioid drugs, and in the presence of fentanyl vs NFEPP. We used graph-based analyses to characterize internal hydrogen-bond networks that could contribute to the activation of the MOR. We find that fentanyl and NFEPP prefer distinct binding poses and that, in their binding poses, fentanyl and NFEPP partake in distinct internal hydrogen-bond networks, leading to the cytoplasmic G-protein-binding region. Moreover, the protonation state of functionally important aspartic and histidine side chains impacts hydrogen-bond networks that extend throughout the receptor, such that the ligand-bound MOR presents at its cytoplasmic G-protein-binding side, a hydrogen-bonding environment where dynamics depend on whether fentanyl or NFEPP is bound, and on the protonation state of specific MOR groups. The exquisite sensitivity of the internal protein-water hydrogen-bond network to the protonation state and to details of the drug binding could enable the MOR to elicit distinct pH- and opioid-dependent responses at its cytoplasmic G-protein-binding site.

Construction and mechanism study of lignin-based polyurethane with high strength and high self-healing properties

Lignin is a natural polymer with abundant functional groups with great application prospects in lignin-based polyurethane elastomers with self-healing abilities. In this study, a lignin self-healing polyurethane (PUDA-L) was specially designed using lignin as the raw material of polyurethane, combining lignin with Diels-Alder (DA) bond and hydrogen bonds. The experimental results showed that PUDA-L was prepared with good thermal stability, fatigue resistance, shape memory effect, excellent mechanical strength, and self-healing ability by partially replacing the crosslinking agents with bio-based lignin and hydroxylated modified lignin to increase the hydroxyl content. Polyurethane has a tensile strength of up to 29 MPa and an elongation at break of up to 500 %. The excellent self-healing ability of PUDA-L originates from the internal DA bonds and cross-linked hydrogen bonds. After the dumbbell sample was fused and heated at 130 °C for 4 h, the elastomer could be completely healed, the tensile strength was restored to 29 MPa, and the self-healing efficiency was up to 100 %. The developed PUDA-L elastomer has promising applications in sensors and smart skins.