Double H-bonds Research Articles

Dual dynamic H-bonds crosslink side chains support a robust polysiloxane elastomer and its self-repairing and recycling properties

Owning excellent mechanical properties and mild repair conditions simultaneously has always been a paradox in the field of self-healing polysiloxane elastomer research. In this work, a robust polysiloxane elastomer with autonomic self-repairing at r. t. and recyclable properties was firstly designed and synthesized. The double strong H-bonds ensure the strength of the elastomer, while the urea bond with relatively weak bond energy also acts as a sacrifice bond to dissipate energy and further bolster the mechanical properties. Meanwhile the double dynamic bonds located in the side chain with stronger molecular activity ability help to get good self-healing performance. Additionally, the material that can be recycled by crushing/remolding and dissolving/remolding methods without compromising their mechanical robustness and self-repairing properties is environmentally friendly.

Double H-bonds multimer absorbent design for H2S absorption

A double H-bonds multimer absorbent for hydrogen sulfide (H2S) absorption was designed via intermolecular self-assembly using 1,8-Diazabicyclo-[5.4.0]-undec-7-ene (DBU) and ethylene glycol (EG) under the guidance of quantum chemical calculation (QCC). The formation mechanisms of multimer absorbents and the absorption mechanisms between those absorbents and H2S were explored by QCC and experiments. It was found that the formed multimer absorbent at the DBU/EG molar ratio of 1:2 has two intermolecular H-bonds with different strengths between DBU and EG, which can combine with H2S via strong intermolecular forces. Furthermore, the characteristics analysis of multimer absorbents and complexes confirmed the above mechanisms. Experimental results indicated that the DBU-2EG has a higher H2S solubility of 5.8 mol/kg multimer absorbent with a low viscosity value of 15.12 mPa·s at 25 °C and better regeneration performance. The multimer absorbent exhibits great potential in the H2S capture process.

Contrasting impact of phosphorus dissolution on the sorption of bisphenol A and carbamazepine by phosphorus-rich chars

Phosphorus (P)-rich chars produced by phosphoric-acid-assisted pyrolysis are promising carbonaceous remediation agents for soil pollution. Nevertheless, the potential of P species dissolution from P-rich chars has been ignored, and the impact of P dissolution on the sorption of hydrophobic compounds remains greatly unaddressed to date. Herein, the P species dissolution from wood-, cellulose-, and lignin-derived P-rich chars at 200–650 °C were investigated. P release capacity ranged from 0.2 to 0.3 mg·g−1 through cyclic dissolution and the maximum release capacity was 1.6 mg·g−1 through continuous dissolution. Enhanced P dissolution in soil experiment implies that P-rich char can be a potential P source. After P species dissolution, bisphenol A (BPA) sorption increased and carbamazepine (CBZ) sorption decreased onto P-rich chars. The enhanced π-π interaction facilitated BPA sorption, while the declined double charge-assisted H-bond ((±)CAHB) weakened CBZ sorption. Combined with DFT calculations, the binding energy (ΔE) supported the contrasting interfacial sorption processes. Apart from micropore-filling, the contribution of sorption mechanisms followed the sequence of (±)CAHB > π-π interaction > H-bonding. This work not only reveals that P-rich char can serve as a promising phosphatic fertilizer for soil improvement but also casts new light on the sorption mechanisms for hydrophobic compounds.

A DFT study of the interaction of aspirin, paracetamol and caffeine with one water molecule.

We have studied the interaction of water with three important analgesics, aspirin, paracetamol and caffeine using DFT calculations and FTIR-ATR spectroscopy. In our study, water is used as a probe molecule to reveal the various H-bonding sites on the electrostatic potential energy surface of the analgesics. We find that water forms a strong double H-bond with the COOH group of aspirin and that the oxygen of the ester group can become H-bond acceptors. Paracetamol forms the strongest H-bond with water at the hydroxyl group and weaker H-bonds with the C = O group and the N–H group. Caffeine forms the strongest H-bond with water at the top C = O group and can form additional H-bonds with the bottom C = O group and the nitrogen of the imidazole ring. These studies may help to better understand the solvation of these analgesics in water.Graphical abstract Supplementary InformationThe online version contains supplementary material available at 10.1007/s00894-022-05258-w.

Unraveling the role of the homoarginine residue in antiplatelet drug eptifibatide in binding to the αIIbβ3 integrin receptor

Eptifibatide is an αIIbβ3 inhibitor that is currently used in the clinic. More than 10 scientific communications indicate that eptifibatide has a Lys-Gly-Asp or Arg-Gly-Asp sequence, while it actually has a hArg-Gly-Asp sequence. We aimed to unravel the importance of the homoarginine residue in eptifibatide in platelet activation and aggregation.Arg- and Lys-eptifibatide were synthesized by solid-phase peptide synthesis and measured in light transmission aggregometry, flow cytometry and whole blood thrombus formation under flow. Interactions of eptifibatide and its variants with αIIbβ3 integrin were studied using molecular dynamics simulations.Eptifibatide showed inhibition of collagen- and ADP-induced platelet aggregation, while Arg- and Lys-eptifibatide did not. Multiparameter assessment of thrombus formation showed suppressed platelet aggregate and fibrin formation upon eptifibatide treatment, in contrast to the other variants. Molecular dynamics simulations revealed that the hArg residue in eptifibatide is crucial to its activity, since the substitution of the hArg to Arg or Lys resulted in the inability to form double H-bonds with Asp224 in the αIIb chain of the αIIbβ3 receptor. The hArg is pivotal for the interaction of eptifibatide for the αIIbβ3 receptor and efficient inhibition of platelet aggregation.

A pH-responsive hyaluronic acid hydrogel for regulating the inflammation and remodeling of the ECM in diabetic wounds.

Diabetes is a universal disease in the world. In the wounds of diabetic individuals, chronic inflammation and an inefficient fibrogenic process hinder the formation and deposition of the ECM, which delays the process of wound healing. To reconstruct the ECM of a diabetic patient's wound, in this work, we designed a pH-responsive "Double H-bonds" (hydrogen bond and hydrazone bond) hyaluronic acid-collagen hydrogel. This hydrogel can be self-gelled quickly in neutral and alkaline environments. But the weakly acidic inflammatory environment of diabetic wounds may accelerate the degradation of the hydrogel and the release of metformin. The in vitro results showed that the hydrogel can enhance the adhesion and infiltration of fibroblasts while inhibiting the growth of macrophages. Meanwhile, metformin could be released and polarize macrophages from M1 to M2, thereby accelerating the migration of fibroblasts and the production of collagen in a high glucose environment. The in vivo results proved that this hydrogel could remodel the ECM in diabetic mice wounds.

Theoretical study of hydrogen-bond interactions of CO2 in organic absorbent 1,3-diphenylguanidine

Carbon capture and storage technology have been rapidly developed to reduce the carbon dioxide (CO2) emission into the environment. It has been found that the amine-based organic molecules could absorb CO2 efficiently and form the bicarbonate salts through hydrogen-bond (H-bond) interactions. Recently, the aqueous 1,3-diphenylguanidine (DPG) solution was developed to trap and convert CO2 to valuable chemicals under ambient conditions. However, how the DPG molecules interact with CO2 in an aqueous solution remains unclear. In this work, we perform molecular dynamics simulations to explore the atomistic details of CO2 in the aqueous DPG. The simulated results reveal that the protonated DPGH+ and the bicarbonate anions prefer to form complexes through different H-bond patterns. These double H-bonds are quite stable in thermodynamics, as indicated from the accurate density functional theory calculations. This study is helpful to understand the catalytic mechanism of CO2 conversion in the aqueous DPG.

Asymmetric Synthesis of 1,1,1-Triarylethanes by Chiral Imidodiphosphoric Acid Catalyzed Nucleophilic Addition of Pyrrole and Indoles to 3-Vinylindoles

Chiral imidodiphosphoric acids were employed as efficient catalysts in the enantioselective addition reaction of pyrrole and indoles to 3-vinylindoles. A series of optically active 1,1,1-triarylethmanes bearing quaternary stereocenters were synthesized in excellent yields (up to 99% yield) and enantioselectivities (up to 98% ee). Gram-scale reactions of 1i and 2a as well as 1o and 5a demonstrated the synthetic utility of this methodology. Control experiments showed that the formation of a double H-bond between the catalyst and substrates is necessary for an excellent outcome.

Mechanism of Annihilation-Delayed Fluorescence of 7-Azaindole in Cyclohexane Solution

Spectral and kinetic characteristics of annihilation-delayed fluorescence (ADF) of 7-azaindole in cyclohexane solution were measured at room temperature. Two bands with maxima at 345 and 480 nm were observed in the ADF spectrum. The short-wavelength band was interpreted as ADF of dimers formed by dipole–dipole interactions of molecules in excited singlet and ground states that were populated by triplet–triplet annihilation (TTA) of monomers. The long-wavelength band was attributed to ADF of dimer-tautomers formed by a double H-bond and double proton transfer. Excited singlet states of dimer-tautomers were populated by mixed annihilation of monomer and dimer-tautomer triplet states. Decay kinetics of monomer and dimer-tautomer triplet states were determined mainly by TTA processes.

Adjusting the acidity of sulfonated organocatalyst for the one-pot production of 5-ethoxymethylfurfural from fructose

A novel sulfonated organocatalyst bearing stable double H-bonds shows high catalytic performance and good reusability for the tandem production of 5-ethoxymethylfurfural (EMF), a biofuel candidate, from biomass-derived fructose.

Guanidinium cation–water clusters

The gas-phase structure, stabilities, and vibrational stretching frequencies of hydrated guanidinium cation (Gdm+Wn, n = 1–6) have been calculated using ab initio and density functional theory methods. It is found from the optimized geometries of various clusters that water molecules interact with the Gdm+ through double H-bond (N–H···O) acceptor model. Evidences reveal that the sequential binding energies of Gdm+Wn clusters are similar to that of hydration of monovalent alkali metal ions and isoelectronic protonated carbonic acid. The calculated binding energy of the clusters increases with the increase in the number of water molecule. Results elicit that the stability of completely and symmetrically hydrated clusters is the highest when compared to that of partially and asymmetrically hydrated ones. It is interesting to note from the findings that the symmetrically hydrated Gdm+W6 cluster forms a tripod structure. The AIM theory provides useful information about different types of H-bonding interactions present in the hydrated Gdm+.

Direction-dependent secondary bonds and their stepwise melting in a uracil-based molecular crystal studied by infrared spectroscopy and theoretical modeling

Three types of supramolecular interactions are identified in the three crystallographic directions in crystals of 1,4-bis[(1-hexylurac-6-yl) ethynyl]benzene, a uracil-based molecule with a linear backbone. These three interactions, characterized by their strongest component, are: intermolecular double H-bonds along the molecular axis, London dispersion interaction of hexyl chains connecting these linear assemblies, and π–π stacking of the aromatic rings perpendicular to the molecular planes. On heating, two transitions happen, disordering of hexyl chains at 473 K, followed by H-bond melting at 534 K. The nature of the bonds and transitions was established by matrix-isolation and temperature-dependent infrared spectroscopy and supported by theoretical computations.

Light-Responsive Self-Assembled Materials by Supramolecular Post-Functionalization via Hydrogen Bonding of Amphiphilic Block Copolymers

A new class of light-responsive supramolecular amphiphilic block copolymers (BCs) based on the association through multiple H-bonding between 4-isobutyloxyazobenzene motifs and 2,6-diacylaminepyridine units is reported. Block copolymers containing 2,6-diacylaminopyridine side units, as hydrophobic block, and poly(ethylene glycol), as a hydrophilic segment, were functionalized with either a carboxylic acid azodendron, via double H-bonding, or a thymine azobenzene, via triple H-bonding. The structural and thermal characterization of these supramolecular azo-copolymers in bulk and solution is presented. The work emphasizes the self-assembly of these supramolecular polymers in water and the study of their UV-light responsive properties by UV–vis spectroscopy, dynamic light scattering (DLS), transmission electron microscopy (TEM), and synchrotron small-angle X-ray (SAXS). The present noncovalent postpolymerization functionalization strategy has provided stable self-assemblies in water with light responsive pro...

Crystal structures of di- and tri-hydrochlorides of 1,4,7-triazaheptane

Four protonated 1,4,8,11-tetraazacyclotetradecane has been characterized as nitrates to show expanded ring structure due to charge repulsion[1]. However, linier polyamine, 1,4,7-triazaheptane (diethylentriamine=dien) gave di-hydrochloride(1) and tri-hydrochloride(2) and their single crystal structures were examined. In the compound 1, the terminal N atoms are protonated as expected but the dien takes U-shaped conformation with forming double H-bond to a Cl- ion at the terminals and the central nitrogen forms another H-bond to the other Cl- ion, as shown in the figure. The dien takes linear conformation in the compound 2 as expected.

α‐Halogenoacetanilides as Hydrogen‐Bonding Organocatalysts that Activate Carbonyl Bonds: Fluorine versus Chlorine and Bromine

α-Halogenoacetanilides (X=F, Cl, Br) were examined as H-bonding organocatalysts designed for the double activation of CO bonds through NH and CH donor groups. Depending on the halide substituents, the double H-bond involved a nonconventional CH⋅⋅⋅O interaction with either a HCXn (n=1-2, X=Cl, Br) or a HCAr bond (X=F), as shown in the solid-state crystal structures and by molecular modeling. In addition, the catalytic properties of α-halogenoacetanilides were evaluated in the ring-opening polymerization of lactide, in the presence of a tertiary amine as cocatalyst. The α-dichloro- and α-dibromoacetanilides containing electron-deficient aromatic groups afforded the most attractive double H-bonding properties towards CO bonds, with a NH⋅⋅⋅O⋅⋅⋅HCX2 interaction.

Hydrogen Bond and Proton Transport in Acid–Base Complexes and Amphoteric Molecules by Density Functional Theory Calculations and 1H and 31P Nuclear Magnetic Resonance Spectroscopy

Intermolecular and intramolecular hydrogen bond (H-bond) and proton transport in acid-base complexes and amphoteric molecules consisting of phosphonic acid groups and nitrogenous heterocyclic rings are investigated by density functional theory calculations and (1)H NMR and (31)P NMR spectroscopy. It is concluded that a phosphonic acid group can act both as H-bond donor and H-bond acceptor, while an imine nitrogen atom can only act as H-bond acceptor and an amine group as H-bond donor. And the intramolecular H-bond is weaker than the intermolecular H-bond attributing to configurational restriction. In addition, the strongest H-bond interaction is observed between a phosphonic acid and a 1H-indazole because of the formation of double H-bonds. The (1)H NMR and (31)P NMR chemical shifts for the acid-base complexes are consistent with the density functional theory calculations. From the (1)H NMR chemical shifts, fast proton exchange is observed between a phosphonic acid and 1H-benzimidazole or 1H-indazole. Finally, it is proposed that polymeric material tethered with 1H-benzimidazole or 1H-indazole rings is a favorable component for high-temperature proton exchange membranes based on acid-base complexes or acid-base amphoteric molecules.

Exploration of Charge-Transfer Solids Utilizing Nucleobases: Nanoarchitectures by Hydrogen-Bonds in the Ionic Assemblies of Guanine and TCNQ Derivatives

We studied formation and structural characteristics of charge-transfer solids of 9-n-butylguanine (BuG) with fluorinated tetracyanoquinodimethane derivatives (FnTCNQ, n = 4, 2, and 1). Complex formation in a methanol (MeOH)-containing solvent generated two types of salts composed of either a methoxy-substituted anion or a fully ionic anion radical of FnTCNQ. In all anion radical salts, BuG existed as a protonated or a hemiprotonated species, BuGH+ or (BuG)(BuGH+), respectively, and formed hydrogen-bonded (H-bonded) assemblies. In these BuGH+ assemblies, FnTCNQ•– molecules were fixed and aligned periodically, providing H-bonded polycationic templates. In (BuGH+)(F4TCNQ•–), BuGH+ dimers by complementary H-bonds formed a two-dimensional (2D) polycationic sheet. The F4TCNQ•– face-to-face dimers formed a one-dimensional (1D) segregated column aided by formation of H-bonds with BuGH+. In (BuGH+)(F2TCNQ•–)(MeOH), BuGH+ dimers by complementary double H-bonds formed a 1D polycationic ribbon supported by MeOH-media...

Hydrogen bond and internal rotations barrier: DFT study on heavier group-14 analogues of formamide

A theoretical study on heavier group-14 substituting effect on the essential property of formamide, strong hydrogen bond with water and internal rotational barrier was performed within the framework of natural bond orbital (NBO) analysis and based on the density functional theory calculation. For heavier group-14 analogues of formamide (YHONH2, Y = Si, Ge and Sn), the nN–πY=O conjugation strength does not always reduce as Y becomes heavier, for example, silaformamide and germaformamide have similar strength of delocalization. Heavier formamides prefer being H-bond donors to form FYO–H2O complexes to being H-bond acceptors to form FYH–H2O complexes. The NEDA analysis indicates that H-bond energies of FYO–H2O complexes increase as moving down group 14 due to concurrently stronger charge transfer (CT) and electrostatic attraction and for the FYH–H2O complexes H-bond strengths are similar. The model of CTs from FYO to H2O differs from that at FYH–H2O complexes, which are contributed not only by aligning lone-pair orbital of O but also by another lone-pair orbital. At two lowest lying excited states (the triplet and S1 excited states), formamide and its heavier analogues form double H-bonds with H2O molecule at the same time. The barrier heights of internal rotation become gradually low from C to Sn, formamide (15.73 kcal/mol) > silaformamide (11.73 kcal/mol) > germaformamide (9.45 kcal/mol) > stannaformamide (7.50 kcal/mol) at the CCSD(T)/aug-cc-pVTZ//B3LYP/cc-pVTZ level. NBO analysis indicates that the barrier does not only come from the nNπ*YO conjugation, and for heavier analogues of formamide, the nNσ*YO hyperconjugation effect and steric effect considerably contribute to the overall rotational barrier. Copyright © 2013 John Wiley & Sons, Ltd.

Intrinsic molecular characteristics of inhibiting STAT3 activation and dimerization through targeting the phosphotyrosine binding site within the SH2 domain—A molecular dynamics study

STAT3 is activated by various cytokines and growth factors through phosphorylation of Tyr-705 (pY-STAT3); pY-STAT3 plays a key role in numerous cellular processes such as cell growth and apoptosis resistance. Increased levels of pY-STAT3 have been observed in many cancers and have been associated with poor prognosis. The STAT3 SH2 domain is required for two essential steps in STAT3 activation: recruitment of latent STAT3 to the activated, kinase-containing receptor complex, which leads to its phosphorylation on Tyr-705, and STAT3 tail-to-tail dimerization. Structure-based drug design has been used to identify small-molecule inhibitors that target the STAT3 SH2 domain with the goal of developing potent anti-cancer drugs. However, the few small-molecule STAT3 inhibitors reported to date have, at best, moderate potency, blocking STAT3 activation with IC50s in the 5–10μM range. One reason for this modest success may be the highly flexible nature of the STAT3 SH2 domain, which results in unreliable modeled structures of the STAT3 SH2 domain bound by inhibitors that are based on X-ray crystallography. In order to improve structure-based drug design, it will be helpful to examine the protein dynamics of the STAT3 SH2 and its structural details in the context of the STAT3 dimer, unbound monomer, and ligand-bound monomers. Here, we performed homology modeling, flexible docking, and molecular dynamics (MD) simulations on the STAT3 SH2 domain alone and in a complex with a STAT3 partner (STAT3 dimer), a phosphotyrosyl peptide derived from gp130, and the peptidomimetic CJ-887. The STAT3 dimer and the STAT3-gp130 peptide complexes share many features, including the H-bond network that binds the phosphorylated tyrosine, the double H-bonds between the binding peptide chain and residue 636–638 backbones, and hydrophobic contacts between the binding residue side chains and the SH2 domain. The gp130 peptide-binding system contains an extra H-bond network by virtue of its Gln-908 side chain being engaged by the STAT3 Gln-644 side chain and the Glu-638 backbone carbonyl. Furthermore, MD simulation (1-μs) of the ligand-free STAT3 monomer indicates that the phosphotyrosine binding pocket and nearby regions are stable in the absence of ligand binding although the extended parts of the SH2 domain are considerably flexible. The structural details in the CJ-887 binding are largely similar to those of the gp130-binding system but extra H-bonds and hydrophobic contacts are identified that may contribute to its increased binding affinity. These findings provide new support at the atomic level to the design and optimization of novel non-peptide STAT3 inhibitors, especially organic molecules obeying Lipinski’s rule of five.

Enhanced catalytic activity of titanosilicates controlled by hydrogen-bonding interactions

A typical volcano-shaped curve has been found in heterogeneous catalytic systems containing titanosilicates for the first time. A new reactive intermediate with double H-bonds is proposed. Systematic results clearly evidence another H-bond formed between the high-electronegativity atom of the H-bond acceptor and the H(end) atom of Ti-Oα-Oβ-H(end).