Hydrogen-bonded Assemblies Research Articles

B(C6F5)3·H2O-Catalyzed N-H and C-H Functionalization of Aromatic Amines with Sulfoxonium Ylides under Metal-Free Conditions.

Hydrogen-bonded aggregates of B(C6F5)3 and water are proven as strong Brønsted acid catalysts, which have the advantages of low toxicity and broad compatibility. Sulfoxonium ylides are stable surrogates of diazo compounds, which participate in various reactions due to their versatile reactivity. Based on these characteristics, a strategy for C-N bond or C-C bond construction of aromatic amines with sulfoxonium ylides under metal-free catalytic conditions was established. This method has advantages of mild conditions and excellent yield, which is suitable for the N-H or C-H functionalization of various aromatic amine compounds.

Innovative strategy for the facile construction of active multifunctional coating on inert thermal insulation surface

Ethylene propylene diene monomer rubber is highly attractive as a thermal insulation material for solid rocket motors but is plagued by its inherent low wettability. Existing methods have been used to solve this problem by manually or mechanically sanding the surface, which is environmentally hazardous. Herein, a multifunctional composite coating is constructed on the surface of inert thermal insulation materials using a two-step low temperature plasma surface treatment via an efficient hydrogen-bonding assembly strategy. The resultant composite coating exhibits excellent adhesion to the inert thermal insulation substrate. Benefitting from this, the coating retained its superhydrophilicity after 80 abrasion cycles and 12 h of agitation scrubbing with saturated salt water. Due to the superhydrophilicity of the coating, a self-cleaning effect for oils of different viscosities on the surface can be achieved by the simple action of water. Besides the adiabatic performance tests showed that the average top surface temperature of the coated thermal insulation was 30.9 °C lower than that of the original thermal insulation. Char residue analysis showed that the coating formed a more complete char layer at high temperatures, resulting in improved adiabatic performance. Our work would afford a new frontier to fabricate solid rocket motor thermal insulation materials with excellent surface comprehensive properties in a simple, eco-friendly and sustainable way, opening new possibilities for the advancement of high-performance inert materials.

Hydrogen-bonded micelle assembly directed conjugated microporous polymers for nanospherical carbon frameworks towards dual-ion capacitors

Well-orchestrated carbon nanostructure with superb stable framework and high surface accessibility is crucial for zinc-ion hybrid capacitors (ZIHCs). Herein, a hydrogen-bonded micelle self-assembly strategy is proposed for morphology-controllable synthesis of conjugated microporous polymers (CMPs) derived carbon to boost zinc ion storage capability. In the strategy, F127 micellar assembly through intermolecular hydrogen bonds serves as structure-directed agents, directing CMPs’ oligomers grow into nanospherical assembly. The nanospherical carbon frameworks derived from CMPs (CNS-2) have shown maximized surface accessibility due to their plentiful tunable porosity and hierarchical porous structure with abundant mesoporous interconnected channels, and superb stability originating from CMPs’ robust framework, thus the CNS-2-based ZIHCs exhibit ultrahigh energy density of 163 Wh kg−1 and ultralong lifespan with 93 % capacity retention after 200, 000 cycles at 20 A g−1. Charged ion storage efficiency also lies in dual-ion alternate uptake of Zn2+ and CF3SO3− as well as chemical redox of Zn2+ with carbonyl/pyridine motifs forming O–Zn–N bonds. Maximized surface accessibility and dual-ion storage mechanism ensure excellent electrochemical performance. Thus, the hydrogen-bond-guide micelle self-assembly strategy has provided a facile way to design nanoarchitectures of CMPs derived carbon for advanced cathodes of ZIHCs.

Utilizing "Latent" Carbon: Repositioning Hydrogen-Bonded Synthons and Assemblies via Halogen Bonding to π-Systems.

Molecules bearing carboxylic acid, amide, and hydroxyl groups are ubiquitous in crystal engineering, where robust hydrogen-bonded synthons centred on these functionalities enable reliable crystal structure design. We now show that halogen bonding to the carbon π-system of such molecules, traditionally ignored in crystal engineering, permits the recognition and directional assembly of the resulting hydrogen-bonded structural subunits, leaving the archetypal hydrogen-bonded ring, ladder, and chain homosynthons intact, but repositioned in space. When applied to heteromolecular synthons, this enables rearranging more complex hydrogen-bonded motifs and the evolution of binary cocrystals into ternary ones through "latent" carbon-based recognition sites, demonstrating a rational approach to build higher-order solid-state supramolecular assemblies.

High sensitivity determination of sweetener glycyrrhizic acid by triple-wavelength overlapping resonance Rayleigh scattering method and its analytical application

Under suitable acidic conditions, the triphenylmethane cationic dyes ethyl violet (EV) and crystal violet (CV) can form hydrogen-bonded cationic supramolecular aggregates with water molecules, respectively. Upon the addition of glycyrrhizic acid (GZA), these hydrogen-bonded cationic supramolecular aggregates undergo ionic association reactions with GZA, leading to the forming of new ion-associated hydrogen-bonded supramolecular aggregates. By optimizing the reaction conditions, two novel systems for the determination of GZA were developed using the triple-wavelength overlapping resonance Rayleigh scattering (TWO-RRS) technique. The enhancement observed in these systems was proportional to the concentration of GZA within a specific range. The linear ranges for these systems were 0.05–0.55 μg/mL, with limits of detection (LOD) at 0.016 μg/mL and 0.011 μg/mL, respectively. The standard addition method was employed to determine the content of GZA in actual samples. This study presents a new and valuable method for the determination of GZA, a sweetener.

Influence of Copper Surface Orientation on the Hydrogen-Bonded Assembly of 2-Methylbenzimidazole Molecules: A Comparative Study

Influence of Copper Surface Orientation on the Hydrogen-Bonded Assembly of 2-Methylbenzimidazole Molecules: A Comparative Study

Switchable supramolecular helices for asymmetric stereodivergent catalysis

Despite recent developments on the design of dynamic catalysts, none of them have been exploited for the in-situ control of multiple stereogenic centers in a single molecular scaffold. We report herein that it is possible to obtain in majority any amongst the four possible stereoisomers of an amino alcohol by means of a switchable asymmetric catalyst built on supramolecular helices. Hydrogen-bonded assemblies between a benzene-1,3,5-tricarboxamide (BTA) achiral phosphine ligand coordinated to copper and a chiral BTA comonomer are engaged in a copper-hydride catalyzed hydrosilylation and hydroamination cascade process. The nature of the product stereoisomer is related to the handedness of the helices and can thus be directed in a predictable way by changing the nature of the major enantiomer of the BTA comonomer present in the assemblies. The strategy allows all stereoisomers to be obtained one-pot with similar selectivities by conducting the cascade reaction in a concomitant manner, i.e. without inverting the handedness of the helices, or sequentially, i.e. by switching the handedness of the supramolecular helices between the hydrosilylation and hydroamination steps. Supramolecular helical catalysts appear as a unique and versatile platform to control the configuration of molecules or polymers embedding several stereogenic centers.

Biomimetic Hydrogen-Bonded G ⋅ C ⋅ G ⋅ C Quadruplex within a Tetraphenylethene-Based Octacationic Spirobicycle in Water.

In biological systems, nucleotide quadruplexes (such as G-quadruplexes) in DNA and RNA that are held together by multiple hydrogen bonds play a crucial functional role. The biomimetic formation of these hydrogen-bonded quadruplexes captured by artificial systems in water poses a significant challenge but can offer valuable insights into these complex functional structures. Herein, we report the formation of biomimetic hydrogen-bonded G ⋅ C ⋅ G ⋅ C quadruplex captured by a tetraphenylethene (TPE) based octacationic spirobicycle (1). The spirobicyclic compound possesses a three-dimensional (3D) crossing dual-cavity structure, which enables the encapsulation of four d(GpC) dinucleotide molecules, thereby realizing 1 : 4 host-guest complexation in water. The X-ray structure reveals that four d(GpC) molecules further form a two-layer G ⋅ C ⋅ G ⋅ C quadruplex with Watson-Crick hydrogen bonds, which are stabilized within the dual hydrophobic cavities of 1 through the cooperative non-covalent interactions of hydrogen bonds, CH⋅⋅⋅π interactions, and hydrophobic effect. Due to the dynamically-rotational propeller chirality of TPE units, 1 with adaptive chirality can further serve as a chiroptical sensor to exhibit opposite Cotton effects with mirror-image CD spectra for the pH-dependent hydrogen-bonded assemblies of d(GpC) including the Watson-Crick G ⋅ C ⋅ G ⋅ C (pH 9.22) and Hoogsteen G ⋅ C+ ⋅ G ⋅ C+ (pH 5.74) quartets through the host-guest chirality transfer in water.

Biomimetic and environmentally friendly self-assembly behavior of melamine onto the surface of black phosphorus nanosheets: Constructing advanced P/N-containing nano flame retardants

Herein, inspired by the hierarchical structure within the biological protein, we adjust the temperature of the aqueous solution to control the unfolding and reconstitution of hydrogen bonds among melamine (MA) molecules, thus preparing MA-functionalized black phosphorus (MA@BP) nanosheets. As confirmed by the first-principles calculations, melamine can spontaneously adsorb onto the surface of BP nanosheets and enhance the interfacial interactions between BP nanosheets and thermoplastic polyurethane (TPU) matrix. Compared to pure BP nanosheets, MA@BP nanosheets present more efficient suppression effects in heat release and toxic CO production. Besides, due to the photo-thermal conversion effect of BP nanosheets, TPU-MA@BP-2.0 presents an equilibrium temperature of ∼ 80 °C under simulated sunlight of 1.0 kW/m2 and a significant solar de-icing performance. The solve-free and hydrogen-bond assembly method not only solves the lack problem of functional groups for the functionalization of BP nanosheets, but also develops a flame-retardant and photo-thermal polymer nanocomposite applied in various occasions.

Self-adhesive and self-healing hydrogel dressings based on quaternary ammonium chitosan and host-guest interacted silk fibroin

Skin is susceptible to varying degrees of injury from external forces, heat, disease, and chemical corrosion. Wound dressings using tissue engineering principles can accelerate skin tissue repair, relieve patient pain, and reduce the formation of scars. In this study, the self-adhesive and self-healing hydrogel dressings based on quaternary ammonium chitosan (QCS), β-cyclodextrin-modified silk fibroin (CD-SF), and adamantane-modified silk fibroin (AD-SF), that was designed. The formed hydrogels not only based on the host-guest interactions between CD-SF as host polymer and AD-SF as guest polymer, also the hydrogen-bonding assembly from QCS was combined. The successful synthesis of QCS, CD-SF, and AD-SF was established using Fourier Transform Infrared spectroscopy (FT-IR) and 1H nuclear magnetic resonance (1H NMR) spectroscopy. The obtained QCS/CD-SF/AD-SF (QCA) hydrogels displayed self-adhesive, self-healing, and mechanical properties. The hydrogels exhibited antibacterial performance, combating typical Gram-negative bacteria Escherichia coli (E. coli) and Gram-positive bacteria Staphylococcus aureus (S. aureus). Further, CCK-8 assay by incubating hydrogels with NIH-3T3 cells and optical microscope inspection of cell morphology indicates the excellent cytocompatibility of the hydrogels. The designed QCA hydrogel with antibacterial properties and biocompatibility have great potential as wound dressings for wound healing treatment.

Development of photoluminescent hydrogen-bonded frameworks based on pyromellitic diimide-tethered carboxylic acid hosts and multi-bonding solvent guests

Supramolecular aspects of multi-component hydrogen-bonded assemblies constructed by the combinations of pyromellitic diimide-tethered carboxylic acids and some multiple hydrogen-bonded donor/acceptor solvent molecules are studied.

Hydrogen-bonded assemblies of iron(II) spin crossover complexes.

The paper reports on the synthesis, crystal structure, thermal and magnetic properties of spin crossover (SCO) salts containing the [Fe(bpp)2]2+ cation (bpp = 2,6-bis(pyrazol-3-yl)pyridine) and different rigid polycarboxylate anions, such as anthracene-9,10-dicarboxylate (ADC), benzene-1,3,5-tricarboxylate (BTC) and biphenyl-4,4'-dicarboxylate (BPDC). Compound [Fe(bpp)2](ADC)·9H2O (1) shows a porous hydrogen-bonded structure with water molecules sitting in the channels. It contains low-spin (LS) Fe2+ cations that undergo crossover to the high-spin (HS) state upon dehydration. Anhydrous 1 remains HS on cooling at low temperatures. A similar magnetic behaviour is obtained for the partially protonated BTC salt [Fe(bpp)2](HBTC)·5H2O (2), showing a spin change concomitant with dehydration to a HS phase that undergoes gradual and partial SCO on cooling, affecting 25% of the Fe2+ cations. Instead, the BPDC salt [Fe(bpp)2](BPDC)·5H2O (3) has a ground HS state in its fully hydrated form.

Self-Assembly of N-Rich Triimidazoles on Ag(111): Mixing the Pleasures and Pains of Epitaxy and Strain.

In the present report, homochiral hydrogen-bonded assemblies of heavily N-doped (C9H6N6) heterocyclic triimidazole (TT) molecules on an Ag(111) substrate were investigated using scanning tunneling microscopy (STM) and low energy electron diffraction (LEED) techniques. The planar and prochiral TT molecules, which exhibit a threefold rotation symmetry and lack mirror symmetry when assembled on the substrate, carry multiple hydrogen-bonding donor and acceptor functionalities, inevitably leading to the formation of hexameric two-dimensionally extended assemblies that can be either homo- (RR/SS) or heterochiral (RS). Experimental STM data showing well-ordered homochiral domains and experimental LEED data are consistent with simulations assuming the R19.1° overlayer on the Ag(111) lattice. Importantly, we report the unexpected coincidence of spontaneous resolution with the condensation of neighboring islands in adjacent "Janus pairs". The islands are connected by a characteristic fault zone, an observation that we discuss in the context of the fairly symmetric molecule and its propensity to compromise and benefit from interisland bonding at the expense of lattice mismatches and strain in the defect zone. We relate this to the close to triangular shape and the substantial but weak bonding scheme beyond van der Waals (vdW) of the TT molecules, which is due to the three N-containing five-membered imidazole rings. Density functional theory (DFT) calculations show clear energetic differences between homochiral and heterochiral pairwise interactions, clearly supporting the experimental results.

Hydrogen-Bonding Assembly Meets Anion Coordination Chemistry: Framework Shaping and Polarity Tuning for Xenon/Krypton Separation.

Hybrid hydrogen-bonded (H-bonded) frameworks built from charged components or metallotectons offer diverse guest-framework interactions for target-specific separations. We present here a study to systematically explore the coordination chemistry of monovalent halide anions, i.e., F- , Cl- , Br- , and I- , with the aim to develop hybrid H-bond synthons that enable the controllable construction of microporous H-bonded frameworks exhibiting fine-tunable surface polarity within the adaptive cavities for realistic xenon/krypton (Xe/Kr) separation. The spherical halide anions, especially Cl- , Br- , and I- , are found to readily participate in the charge-assisted H-bonding assembly with well-defined coordination behaviors, resulting in robust frameworks bearing open halide anions within the distinctive 1D pore channels. The activated frameworks show preferential binding towards Xe (IAST Xe/Kr selectivity ca. 10.5) because of the enhanced polarizability and the pore confinement effect. Specifically, dynamic column Xe/Kr separation with a record-high separation factor (SF=7.0) among H-bonded frameworks was achieved, facilitating an efficient Xe/Kr separation in dilute, CO2 -containing gas streams exactly mimicking the off-gas of spent nuclear fuel (SNF) reprocessing.

Water-Assisted Programmable Assembly of Flexible and Self-Standing Janus Membranes.

Janus membranes with asymmetric wettability have been considered cutting-edge for energy/environmental-sustainable applications like water/fog harvester, breathable skin, and smart sensor; however, technical challenges in fabrication and accurate regulation of asymmetric wettability limit their development. Herein, by using water-assisted hydrogen-bonded (H-bonded) assembly of small molecules at water/oil interface, a facile strategy is proposed for one-step fabrication of membranes with well-regulable asymmetric wettability. Asymmetric orderly patterns, beneficial for mass transport based on abundant high-permeability sites and large surface area, are constructed on opposite membrane surfaces. Upon tuning water-assisted H-bonding via H-sites/configuration design and temperature/pH modulation, double-hydrophobic, double-hydrophilic, and hydrophobic-hydrophilic membranes are facilely fabricated. The Janus membranes show smart vapor-responsive curling and unidirectional water transport with promising flux of 1158±25Lm-2 h-1 under natural gravity and 31500±670L·(m-2 h-1 bar-1 ) at negative pressure. This bottom-up approach offers a feasible-to-scalable avenue to precise-manipulation of Janus membranes for advanced applications, providing an effective pathway for developing tailor-made self-assembled nanomaterials.

CHNO - Formylnitrene, Cyanic, Isocyanic, Fulminic, and Isofulminic Acids and their Interrelationships at DFT and CASPT2 Levels of Theory.

Fulminic and cyanic acids played a decisive role in the conception of isomerism 200 years ago. Cyanic (HOCN), isocyanic (HNCO), and fulminic (HCNO) acids have been detected in several interstellar sources, but isofulminic acid (HONC) is little known. Here we examine the interrelationships between the four acids and formylnitrene, HC(O)N, at the CASPT2 and three DFT levels. Formylnitrene has a triplet ground state, T0, a closed shell singlet (CSS), S0, and an open-shell singlet (OSS), S1, lying ∼7 and 27 kcal/mol above T0, respectively. The CSS is weakly stabilized by a 12 kcal/mol bond between the N and the O atoms. A conical intersection 12 kcal/mol above T0 permits easy T0-S0 interchange. Formyl azide and formylnitrene (T0 and S0) are isomerized thermally to HNCO. HOCN is best obtained via dissociation of the nitrene (or of HNCO) to H• + NCO• radicals ∼46 kcal/mol above the T0 nitrene. Isofulminic acid, HONC, isomerizes readily to cyanic acid, HOCN, in thermal and photochemical reactions. Fulminic acid, HCNO, can isomerize to HNCO via CSS formylnitrene. Easy tautomerization prevents the preparation of HOCN in quantity. The barrier to isomerization is strongly reduced in small hydrogen-bonded aggregates so that trace amounts of HOCN can exist in equilibrium with HNCO.

Hydrogen-Bonded Polymer Nanomedicine with AIE Characteristic for Intelligent Cancer Therapy.

One of the major goals of biomedical science is to pioneer advanced strategies toward precise and smart medicine. Hydrogen-bonding (H-bonding) assembly incorporated with an aggregation-induced emission (AIE) capability can serve as a powerful tool for developing supramolecular nanomedicine with clear tumor imaging and smart therapeutic performance. We here report a H-bonded polymeric nanoformulation with an AIE characteristic toward smart antitumor therapy. To do so, we first design a structurally novel tetraphenylethylene (TPE)-based H-bonding theranostic prodrug, TPE-(FUA)4, characterized by four chemotherapeutic fluorouracil-1-acetic acid (FUA) moieties arched to the TPE core. A six-arm star-shaped amphiphilic polymer vehicle, P(DAP-co-OEGEA)6, is prepared, bearing hydrophilic and biocompatible POEGEA (poly(oligo (ethylene glycol) ethyl acrylate) segments, along with a hydrophobic and H-bonding PDAP (poly(diaminopyridine acrylamide)) segment. Thanks to the establishment of the DAP/FUA H-bonding association, incorporating the TPE-(FUA)4 prodrug to the P(DAP-co-OEGEA)6 vehicle can yield H-bond cross-linked nanoparticles with interpenetrating networks. For the first time, AIE luminogens are interwoven into a six-arm star-shaped polymer via an intrinsic H-bonding array of the chemotherapeutic agent FUA, thus imposing an effective restriction of TPE molecular rotations. Concomitantly, encapsulated photothermal agent (IR780) via a hydrophobic interaction facilitates the formation of nanoassemblies, TPE-(FUA)4/IR780@P(DAP-co-OEGEA)6, featuring synergistic cancer chemo/photothermal therapy (CT/PTT). Our study can contribute a practical solution to fulfill biomedical requirements with a conductive advance in precision nanomedicine.

Healable, degradable polyurethane elastomers with excellent mechanical properties based on multiple hydrogen bonds

AbstractDue to its comprehensive properties, polyurethane elastomer (PU) plays a vital role in ships, construction, transportation facilities, and other fields. However, it is challenging to design polyurethane elastomer materials with good mechanical properties, self‐healing ability, and degradable ability. Herein, a kind of polyurethane elastomer based on multiple hydrogen bond crosslinking was successfully synthesized by using polycaprolactone with substantial crystallization as a soft chain segment and introducing adipic dihydrazide (ADH) and U2‐diol (a ureido‐pyrimidinone with two hydroxyl groups at the end) to achieve ordered hydrogen bond assembly design and control. The elastomer has good tensile strength, healability, degradability, and solubility. The maximum tensile strength and toughness of the prepared polyurethane elastomer (PUAD) were 46.34 MPa and 687.66 MJ/m3, respectively. With the increase of U2‐diol content, the self‐repair efficiency was greatly enhanced. After seven repair cycles, the self‐repair efficiency can still reach 66.88%. In addition, the bacterial degradation test using Pseudomonas aeruginosa as a strain showed that PUAD film had excellent degradability. The dissolution test with N,N‐dimethylformamide (DMF) as solvent showed that the tensile strength was almost unchanged after three dissolutions.

Mechanochemical Mediated Coexistence of B←N Coordination and Hydrogen Bonding.

Mechanochemistry afforded a photoactive cocrystal via coexisting (B)O-H⋅⋅⋅N hydrogen bonds and B←N coordination. Specifically, solvent-free mechanochemical ball mill grinding and liquid-assisted grinding of a boronic acid and an alkene resulted in mixtures of hydrogen-bonded and coordinated complexes akin to mixtures of noncovalent complexes that can be obtained in solution in equilibria processes. The alkenes of the hydrogen-bonded assembly undergo an intermolecular [2+2] photodimerization in quantitative conversion, effectively reporting the outcome of the self-assembly processes. Our results suggest that interplay involving noncovalent bonds subjected to mechanochemical conditions can lead to functional solids where, in the current case, the structure composed of the weaker hydrogen bonding interactions predominates.

Systematic Exploration of Structural Topologies in Hydrogen-Bonded Supramolecular Assemblies of Citric Acid with Different Heterocyclic Compounds.

Hydrogen-bonded supramolecular assemblies of citric acid, CA, with some heterocyclic compounds (N-donor and N-oxide)-acridine (acr), phenazine (phenz), 1,10-phenanthroline (110phen), 1,7-phenanthroline (17phen), 4,7-phenanthroline (47phen), 1,4-diazabicyclo[2.2.2]octane (dabco), and 4,4'-bipyridyl-N,N'-dioxide (bpydo)-have been reported. Among these, only the N-donors phenz and N-oxide (bpydo) form neutral co-crystals, while the others form salts owing to the deprotonation of -COOH. Thus, depending on the nature of the aggregate (salt/co-crystal), recognition between the co-formers is established through O-H···N/N+-H···O/N+H···O-heteromeric hydrogen bonding. Additionally, CA molecules establish homomeric interactions mediated by O-H···O hydrogen bonds. Moreover, CA forms a cyclic network with the co-formers or on its own, with a noteworthy feature of formation of host-guest networks in the assemblies with acr and phenz (solvated). In the assembly of acr, the CA molecules form a host network and captivate acr molecules as guest species, while in the case of phenz assembly, both the co-formers together encapsulate the solvent in the channels. However, the observed cyclic networks in the other structures form three-dimensional topologies in the form of ladders, a sandwich, lamellar layers, and interpenetrated networks. The structural features of the ensembles are evaluated unequivocally by the single-crystal X-ray diffraction method, while the homogeneity and phase purity are evaluated by using the powder X-ray diffraction method and differential scanning calorimetry. Further, conformational analysis of CA molecules reveals three types of conformations-T-shape (type I), syn-anti (type II), and syn (type III) as also observed in the literature for other CA co-crystals. In addition, the strength of the intermolecular interactions is quantified by performing Hirshfeld analysis.