Competitive Hydrogen Bonds Research Articles

Effect of water on CO2 capture and phase change in non-aqueous 1,4-butanediamine/ethylene glycol biphasic absorbents: Role of hydrogen bond competition

Non-aqueous liquid–solid biphasic absorbents show significant potential for reducing energy consumption in CO2 capture. However, the high hygroscopic nature of amine compounds and the approximately 10 % to 20 % water vapor in natural gas plants’ flue gases challenge their efficiency and stability. This study investigated water’s effects on the CO2 absorption/desorption performance, phase-change behavior, and products of the non-aqueous absorbent 1,4-Butanediamine (BDA)/ethylene glycol (EG). Experimental results show that water significantly impacts absorption/desorption performance. The maximum CO2 loading and regeneration efficiency were 1.4199 mol·mol−1 and 89.85 %, respectively. Water leads to the gradual disappearance of phase changes, with solid-phase CO2 loading decreasing from 0.008 to 0.004 mol·g−1. Quantitative NMR demonstrates that carbamates and CO32-/HCO3- are the main CO2-related products in aqueous systems, with their relative proportions affected by water content. Quantum chemical calculations and molecular dynamics simulations reveal that water enhances absorption efficiency by participating in the catalytic environment and reaction process. Water-induced hydrogen bonding competition is the leading cause of weakened interactions between species. Specifically, H-bonds between carbamate/protonated amines were decreased by 23.94 %. The enhanced solvation effect reduces aggregation of the key products, contributing to the gradual disappearance of phase changes. This study provides insights into water’s effect on non-aqueous biphasic absorbents at the molecular level, offering a theoretical foundation for the development and optimization of absorbents suitable for use with steam-containing flue gases.

3D cellulose scaffold with gradient pore structure controlled by hydrogen bond competition: Super-strength and multifunctional oil/water separation

Cellulose-based aerogels offer exceptional promise for oily wastewater treatment, but the challenge of low mechanical strength and limited application functions persists. Inspired by the graded porous structures in the animal skeleton and bamboo stem, we firstly report here a stepwise solvent diffusion-induced phase separation approach for constructing the gradient pore-density three-dimensional (3D) cellulose scaffold (GPDS). Benefiting from the regulation of competitive hydrogen bonding between the anti-solvents and the ionic liquid (IL) in cellulose solution, GPDS exhibits the decreased major channels size and increased minor pores amount gradually along the solvent diffusion direction. These endow GPDS with the characteristics of low density (0.019 g/cm) and super strength (high up to 870 KPa). The application of GPDS in the field of oil-water separation has achieved remarkable results, including oil/organic solvent absorption (13–25 g/gGPDS), immiscible oil-water mixture separation (high efficiency up to 99.8 %, flux > 2000 L/m2·h), and surfactant-stabilized oil-in-water emulsion (efficiency up to 97.7 %). Moreover, a simple hydrophobic treatment further realizes the efficient separation of water-in-oil emulsion (98.5 % efficiency). The as-fabricated GPDS accordingly achieves the multifunctional application in oil-water separation field. Thus, a new avenue is opened to construct 3D cellulose porous scaffold as adsorbent materials in oily wastewater treatment.

Competitive Intramolecular Hydrogen Bonding: Offering Molecules a Choice.

The conformational preferences of N-((6-methylpyridin-2-yl)carbamothioyl)benzamide were studied in solution, the gas phase and the solid state via a combination of NMR, density functional theory (DFT) and single crystal X-ray techniques. This acyl thiourea derivative can adopt two classes of low energy conformation, each stabilized by a different 6-membered intramolecular hydrogen bond (IHB) pseudoring. Analysis in different solvents revealed that the conformational preference of this molecule is polarity dependent, with increasingly polar environments yielding a higher proportion of the minor conformer containing an NH⋅⋅⋅N IHB. The calculated barrier to interconversion is consistent with dynamic behaviour at room temperature, despite the propensity of 6-membered IHB pseudorings to be static. This work demonstrates that introducing competitive IHB pathways can render static IHBs more dynamic and that such systems could have potential as chameleons in drug design.

Compliant Iontronic Triboelectric Gels with Phase-Locked Structure Enabled by Competitive Hydrogen Bonding

HighlightsA bionic phase-locked structure-inspired iontronic triboelectric gel is proposed with good mechanical compliance for wearable haptic sensing applications.Competitive hydrogen bonding systems are constructed through polymer-solvent-nonsolvent interactions, and regeneration of polymers with weak hydrogen bond donors triggers controlled phase separation.Self-powered haptic skin constructed with iontronic triboelectric gel has a modulus (150.6 kPa) and stretchability (> 400%) similar to that of the human body, enabling fidelity transmission of haptic signals and precise recognition of sensing objects.

Dispersion Control over Molecule Cohesion: Exploiting and Dissecting the Tipping Power of Aromatic Rings.

ConspectusWe have learned over the past years how London dispersion forces can be effectively used to influence or even qualitatively tip the structure of aggregates and the conformation of single molecules. This happens despite the fact that single dispersion contacts are much weaker than competing polar forces. It is a classical case of strength by numbers, with the importance of London dispersion forces scaling with the system size. Knowledge about the tipping points, however difficult to attain, is necessary for a rational design of intermolecular forces. One requires a careful assessment of the competing interactions, either by sensitive spectroscopic techniques for the study of the isolated molecules and aggregates or by theoretical approaches. Of particular interest are the systems close to the tipping point, when dispersion interactions barely outweigh or approach the strength of the other interactions. Such subtle cases are important milestones for a scale-up to realistic multi-interaction situations encountered in the fields of life and materials science. In searching for examples that provide ideal competing interactions in complexes and small clusters, aromatic systems can offer a diverse set of molecules with a variation of dispersion and electrostatic forces that control the dominant and peripheral interactions. Our combined spectroscopic and theoretical investigations provide valuable insights into the balance of intermolecular forces because they typically allow us to switch the aromatic substituent on and off. High-resolution rotational spectroscopy serves as a benchmark for molecular structures, as correct calculations should be based on correct geometries. When discussing the competition with other noncovalent interactions, obvious competitors are directional hydrogen bonds. As a second counterweight to aryl interactions, we will discuss aurophilic/metallophilic interactions, which also have a strong stabilization with a small number of atoms involved. Vibrational spectroscopy is most sensitive to interactions of light atoms, and the competition of OH hydrogen bonds with dispersion forces in a molecular aggregate can be judged well by the OH stretching frequency. Experiments in the gas phase are ideal for gauging the accuracy of quantum chemical predictions free of solvent forces. A tight collaboration utilizing these three methods allows experiment vs experiment vs theory benchmarking of the overall influence of dispersion in molecular structures and energetics.

Ab initio investigation of the competition of pnicogen, halogen, and hydrogen bonds resulting from the interactions between cyanophosphine and hypohalous acids.

The complexes formed as a result of the interactions between cyanophosphine (CP, H2PCN) and hypohalous acid molecules (HOX, X = F, Cl, Br, and I) were studied by employing ab initio computations conducted at the MP2/aug-cc-pVTZ level. Three types of complexes were acquired (I, II, and III) as a result of the (O∙∙∙P) pnicogen bond, the (N∙∙∙H) hydrogen bond, and the (N∙∙∙X) halogen bond interaction, respectively. The results of harmonic vibrational frequency calculations with no imaginary frequencies confirmed the structures as minima. In addition, given the interaction energy of the complexes, hydrogen bond complexes of structure II have the highest stability compared to other structures. In all studied complexes, the strength of the interactions depended on the electronegativity of the halogen atoms. The characteristics and nature of the whole three types of complexes were examined and evaluated with natural bond orbital (NBO), atom in molecules (AIM), molecular electrostatic potential (MEP) maps, non-covalent interaction (NCI) index, and electron density difference (EDD) analyses. The optimization of all complexes and corresponding monomers was conducted through the ab initio method, employing the MP2 level along with the aug/cc-pVTZ basis set for all atoms, except for the iodine (I) atom, for which the aug-cc-pVTZ (PP) basis set was employed. Subsequent frequency calculations were executed to ascertain the minimum energy state of the complexes at the MP2 level and the aug/cc-pVTZ basis set, utilizing Gaussian09 software. The MEP maps of the monomers were generated using the analysis-surface suite (WFA-SAS) software package. To probe the orbital interactions within the studied complexes, NBO analysis was performed employing NBO software. The assessment of bond nature, topological features, and electron density values at critical points for the studied complexes was undertaken using AIMAll software. The NCI index was derived utilizing Multiwfn software, and its three-dimensional representation was rendered using VMD software.

Catalytic oxidation of carbon monoxide over copper oxide with interfering gases involved for industrial buildings: An experimental and theoretical study

With the intention of thoroughly eliminating carbon monoxide (CO) from indoor environment, it is one of the most promising methods of converting it into carbon dioxide (CO2) via catalytic oxidation processes. Therefore, in this study, catalytic oxidation mechanisms of CO over copper oxide (CuO) with interfering gases involved are investigated via theoretical calculations and experimental verification, which mainly include basic catalytic oxidation processes over CuO, effects of different interfering gases and analyses of thermodynamic features. According to results, catalytic oxidation of CO over CuO can be performed in three different routes and rate-determining transition-state (TS) energy barriers vary a lot from route to route at high temperature owing to different thermal stability. In the meantime, SO2, H2O and NO are theoretically proved to affect catalytic oxidation of CO via competitive adsorption, high oxidizability and hydrogen bonds, which are accompanied with different sensitivities to changes of temperature or temperature power exponents. In experiments, it is found that impurity of lattice planes and small specific surface areas in CuO are key to restricting catalytic oxidation performances. What is more, some extra chemical reactions in experiments (e.g. SO2 + O2 + CuO → CuSO4, NO + O2 + CO → CO2 + NO) caused by interfering gases colossally affect catalytic oxidation performances of CuO. The whole study provides crucial information for indoor air purification in industrial buildings by using cheap adsorbents/catalysts.

Effect of competitive interactions on the structure and properties of blends prepared from an industrial lignosulfonate polymer

To explore the possibility of applying lignin in practice, an industrial lignosulfonate (0–50 vol%) was blended with four ionomers. The concentrations of carboxyl and carboxylate groups were systematically varied in the ethylene-acrylic acid copolymers to study the competition of hydrogen and ionic bonds forming between the components. The mechanical properties of the blends were determined by tensile testing. The structure was investigated by scanning electron microscopy, while deformation and failure processes were studied by acoustic emission measurements and microscopy. Interfacial interactions were quantitatively characterized by analyzing local deformation processes and by evaluating the composition dependence of the tensile strength using appropriate models. Molecular dynamics simulations indicated that carboxylate groups preferably form clusters in the ionomer phase, consequently, the increasing degree of neutralization results in ionomers with more and more self-interactions of components deteriorating ionomer-lignin interactions. The novel combination of experiments, modeling, and simulation was done for the first time on such materials, and it pointed out that the role of hydrogen bonds is more critical in determining blend properties. Blends can be prepared for practical applications with a good combination of stiffness (0.8 GPa), tensile strength (22 MPa), and elongation-at-break (25 %) at 30 vol% lignosulfonate content and 33 % neutralization.

Ortho-pyridinyl anilines: A class of fluorescent chemoprobes for quantitatively visualizing proton donating ability

Proton donating ability is known to be a key factor during most chemical, physical, and biological processes; therefore, quantifying such an ability visibly is crucial for further research. However, there has long been a lack of excellent models to fulfil such a quantitative visualization. Here, we designed and synthesized a series of fluorescent chemoprobes based on ortho-pyridinyl anilines, whose fluorescence signal showed a quantitative relationship with its intermolecular hydrogen bond strength. On this basis, the proton donating ability of the external proton donors through competitive hydrogen bond formation could be shown quantitatively by virtue of the changes of the fluorescence.

Competition of hydrogen, tetrel, and halogen bonds in COCl2-HOX (X=F, Cl, Br, I) complexes

The present study investigates the competition between hydrogen, halogen, and tetrel bonds from the interaction of COCl2 with HOX using quantum chemistry simulations at the MP2/aug-cc-pVTZ computational level, in which five configurations were optimized, including adducts I –V. Two hydrogen bonds, two halogen bonds, and two tetrel bonds were obtained for five forms of adducts. The compounds were investigated using spectroscopic, geometry, and energy properties. Adduct I complexes are more stable than others, and adduct V halogen bonded complexes are more stable than adduct II complexes. These results are in agreement with their NBO and AIM results. The stabilization energy of the XB complexes depends on the nature of both the Lewis acid and base. The stretching frequency of the O–H bond in adducts I, II, III, and IV displayed a redshift, and a blue shift was observed in adduct V. The results for the O-X bond showed a blue shift in adducts I and III and a red shift in adducts II, IV, and V. The nature and characteristics of three types of interactions are investigated via NBO analysis and atoms in molecules (AIM).

Identification of and Mechanistic Insights into SARS-CoV-2 Main Protease Non-Covalent Inhibitors: An In-Silico Study.

The indispensable role of the SARS-CoV-2 main protease (Mpro) in the viral replication cycle and its dissimilarity to human proteases make Mpro a promising drug target. In order to identify the non-covalent Mpro inhibitors, we performed a comprehensive study using a combined computational strategy. We first screened the ZINC purchasable compound database using the pharmacophore model generated from the reference crystal structure of Mpro complexed with the inhibitor ML188. The hit compounds were then filtered by molecular docking and predicted parameters of drug-likeness and pharmacokinetics. The final molecular dynamics (MD) simulations identified three effective candidate inhibitors (ECIs) capable of maintaining binding within the substrate-binding cavity of Mpro. We further performed comparative analyses of the reference and effective complexes in terms of dynamics, thermodynamics, binding free energy (BFE), and interaction energies and modes. The results reveal that, when compared to the inter-molecular electrostatic forces/interactions, the inter-molecular van der Waals (vdW) forces/interactions are far more important in maintaining the association and determining the high affinity. Given the un-favorable effects of the inter-molecular electrostatic interactions-association destabilization by the competitive hydrogen bond (HB) interactions and the reduced binding affinity arising from the un-compensable increase in the electrostatic desolvation penalty-we suggest that enhancing the inter-molecular vdW interactions while avoiding introducing the deeply buried HBs may be a promising strategy in future inhibitor optimization.

Computational and experimental studies on the micellar morphology and emission mechanisms of AIE and H-bonding fluorescent composites.

In this work, we use density functional theory (DFT) calculated competitive hydrogen bonds and dissipative particle dynamics (DPD) simulated micellar structural information to uncover the CO2-expanded liquid (CXL)-aided self-assembled structure and emission mechanisms of the self-assembled fluorescent composites (SAFCs). Herein, the SAFCs are formed through the self assembly between diblock copolymer polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) blend and the dye molecule 4-(9-(2-(4-hydroxyphenyl)ethynyl)-7,10-diphenylfluoranthen-8-yl)phenol (4) in CO2-expanded toluene at 313.2 K and varied pressures. Firstly, from DPD simulation, we have demonstrated that the addition of CO2 to toluene favors both the expansion of the solvophobic P4VP phase and contraction of solvophilic PS chains, which facilitates the continuous morphological transitions of SAFCs from spherical micelles (3.0 MPa) through wormlike plus spherical micelles (4.0-4.8 MPa) to large vesicles (6.0-6.5 MPa) with pressure rise. Secondly, the DFT calculated bonding energies and IR spectra of the competitive hydrogen bonds help us to clarify the major type of hydrogen bonds determining the fluorescence (FL) performance of the SAFCs. Furthermore, we have revealed the SAFC emission mechanism via the pressure-tunable changes in the aggregation degrees and amount of hydrogen bonds involving 4 and P4VP chains. This work provides a good understanding for the morphology-property control of the self-assembled polymer composites in both microscopic and mesoscopic scales.

Dynamic hydrogen bonds promote C–H functionalization driven by Cl− anion

Most of studies for hydrogen bonds focus on the static model especially between two polar atoms. In contrast, introducing the third polar atom may emerge the competitive hydrogen bonds, which would represent a distinct perspective to perturb the catalytic chemical transformation. Herein, we report quantum mechanics calculations and quasi-classical direct dynamics simulations that demonstrate a triangle form of proton accepters enabled by Cl− anion can afford diverse hydrogen bonds, which control the reactivity and selectivity of Rh catalyzed phenol functionalization. A redox mechanism for carbene insertions with notable ligand effect was discovered and supported by both calculations and the experimental kinetic isotopic effect. The quaternary ammonium additive can stabilize key oxonium ylide intermediates with O–H⋯Cl hydrogen bonds that inhibit the common O–H insertion and promote the carbene C–H insertion product. The nonclassical dynamic hydrogen bonds coupling with Rh complex dissociation may result in an intermediate shuttle of oxonium ylides, which unify the site-selective of the direct phenol functionalization.

Rational design of efficient deep eutectic solvents for HCl absorption through their competitive H-bonding interactions.

The design of an efficient absorbent is the premise for recovery and resource utilization of hydrogen chloride (HCl) from its industrial tail gases. Herein, a series of 1-butyl-3-methylimidazolium chloride (BmimCl) based-deep eutectic solvents (DESs) were designed and the solubility behavior for HCl was studied in terms of their structure, basicity, free volume, intermolecular interaction energy, and absorption enthalpy. The relationship between the interaction energy and the phase change in the HCl dissolution process was explored in detail. BmimCl-TAA (thioacetamide) (1 : 1) shows high reversible solubility due to its high free volume, suitable absorption enthalpy, and closer H-bonding (HB) interactions between BmimCl and TAA or HCl. The dissolution mechanism of HCl and the dynamic evolution of the HB network were verified by FT-IR and NMR spectra and quantum chemical calculations. The results show that it is the competitive HB interaction that promotes the dissolution of HCl, reduces the absorption enthalpy, and renders a reversible absorption. Compared with BmimCl, the absorption enthalpy of HCl in BmimCl-TAA (1 : 1) is reduced by 25% and the reversible solubility increased 150%. The reversible solubility of HCl in BmimCl-TAA (1 : 1) is as high as 0.51 g g-1 (1.76 mol mol-1) at 303.15 K and 101.3 kPa, and the absorbent can be regenerated facilely by heating under reduced pressure. This work provides new insights into the rational design of DES for efficient and reversible absorption of HCl and other polar gases.

High-pressure investigations on urea hydrogen peroxide

The effect of high-pressure on the crystal structure of urea hydrogen peroxide has been investigated to 30 GPa. Through in-situ Raman scattering and ADXRD measurements, a first-order phase transition is concluded at 2.5GPa, and the new phase is indexed to a triclinic phase using Rietveld refinement method. Further increase in pressure up to 30 GPa does not show any structural phase transition. From the Raman analysis, the irreversible phase transition should be correlated with the twist structure of urea in the adduct of urea and hydrogen peroxide as a result of the cooperation and competition of inter-molecular hydrogen bonds.

Effects of Oligomeric Procyanidins From Lotus Seedpod on the Retrogradation Properties of Rice Starch.

The extent of retrogradation strongly affects certain physical and cooking properties of rice starch (RS), which are important to consumers. In this study, oligomeric procyanidins from lotus seedpod (LSOPC) was prepared and used to investigate its inhibitory effect on RS retrogradation. Various structural changes of RS during retrogradation were characterized by differential scanning calorimetry, low field nuclear magnetic resonance, X-ray diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy. The results showed LSOPC could effectively retard both short- and long-term retrogradation of RS, and its inhibitory effect was dependent on the administered concentration of LSOPC. Molecule simulation revealed the interactions of RS and LSOPC, which indicated that the competition of hydrogen bonds between RS and LSOPC was the critical factor for anti-retrogradation. This inhibitory effect and mechanism of action of LSOPC could promote its applications in the field of starch anti-retrogradation.

Competitive Hydrogen Bonding and Unprecedented Polymorphism in Selected Chiral Phosphorylated Thioureas

New racemic and enantiopure N-phosphorylated thioureas bearing 1-phenylethyl or tetrahydronaphthalenyl fragments were synthesized. According to NMR data assisted by DFT calculations, the preferred conformation is stabilized by an intramolecular hydrogen bond. This form in solution is in equilibrium with dimeric N–H···S hydrogen-bonded associates, the population depending on the concentration. In the crystalline phase the low-energy conformation with an intramolecular H-bond is realized only in the racemic tetrahydronaphthalenyl derivative. In most crystals various types of intermolecular hydrogen bonding are observed, accompanied by the formation of infinite linear chains or helical structures. Due to the conformational lability of compounds and competitive intermolecular H-bonding, multiple polymorphic modifications are formed. Therefore, crystallization of enantiopure 1-phenylethyl derivatives from various solvents results in concomitant polymorphs at room temperature. One of them undergoes reversible two-step phase transitions from the high-symmetry I41 space group (Z′ = 1, no disorder) via the P41 space group (Z′ = 6) to the monoclinic P21 space group (Z′ = 16) accompanied by drastic concerted conformational changes. Notably, the optimization of the crystal packing is observed upon phase transitions with a gradual reduction of the void space in the unit cell from 4.5% to 0.8%. This is a rare case of several high-Z′ polymorphs for one compound, with chirality playing an important role.

Competitive tetrel bond and hydrogen bond in benzaldehyde-CO2: characterization via rotational spectroscopy.

The rotational spectrum of the 1 : 1 benzaldehyde-CO2 complex has been investigated using pulsed-jet Fourier transform microwave spectroscopy complemented with quantum chemical calculations. Two isomers, both characterized by one C⋯O tetrel bond (n → π* interaction) and one C-H⋯O hydrogen bond (n → σ* interaction), have been observed in the pulsed jet. Competition between the tetrel bond and the hydrogen bond has been disclosed by natural bond orbital analysis: isomer I is characterized by one dominating OCCO2⋯O tetrel bond (12.6 kJ mol-1) and a secondary (C-H)formyl⋯O hydrogen bond (2.2 kJ mol-1); by contrast, in isomer II the (C-H)phenyl⋯O hydrogen bond (7.6 kJ mol-1) becomes the dominant bond, while the OCCO2⋯O tetrel bond (5.8 kJ mol-1) becomes much weaker with respect to that of isomer I. Using intensity measurements the relative population ratio of the two isomers was estimated to be NI/NII ≈ 2/1.

Polyol and sugar osmolytes can shorten protein hydrogen bonds to modulate function

Polyol and sugar osmolytes are commonly used in therapeutic protein formulations. How they may affect protein structure and function is an important question. In this work, through NMR measurements, we show that glycerol and sorbitol (polyols), as well as glucose (sugar), can shorten protein backbone hydrogen bonds. The hydrogen bond shortening is also captured by molecular dynamics simulations, which suggest a hydrogen bond competition mechanism. Specifically, osmolytes weaken hydrogen bonds between the protein and solvent to strengthen those within the protein. Although the hydrogen bond change is small, with the average experimental cross hydrogen bond 3hJNC′ coupling of two proteins GB3 and TTHA increased by ~ 0.01 Hz by the three osmolytes (160 g/L), its effect on protein function should not be overlooked. This is exemplified by the PDZ3−peptide binding where several intermolecular hydrogen bonds are formed and osmolytes shift the equilibrium towards the bound state.

Mucus-Inspired Supramolecular Adhesives with Oil-Regulated Molecular Configurations and Long-Lasting Antibacterial Properties.

Inspired by mucus, which provides an ideal supramolecular model and whose fluid-like (viscous) and solid-like (elastic) behaviors can be adjusted to meet different physiological requirements, we report oil-regulated supramolecular adhesives by the co-assembly of polyurea oligomers and carvacrol oils. The adhesive is crosslinked by weak but abundant hydrogen bonds, which can be regulated by the incorporated carvacrol oils through the competition of intermolecular hydrogen bonds, presenting a unique set of mucus-mimicking features including oil-regulated mechanics, processability, reusable adhesivity, and extreme longevity in both air and water. Owing to the intrinsic bactericidal effect of the carvacrol oils, the developed adhesives can serve as potent antibacterial coatings with both rapid contact killing (99.9% killing within 15 min) and long-term controlled release abilities (up to 70 days), enabling versatile antibacterial applications in diverse conditions. We envision that these adhesives will be useful in buildings and architectures, community and public facilities, food storage and packaging technologies, functional textiles, and practical biomedical fields.