Strong H-bonds Research Articles

Hybrid cellulose-poly(4-vinylpyridine) adsorbents produced via ATRP and their application to target polyphenols in winemaking, olive oil production and almond processing residues

Hybrid cellulose-poly(4-vinylpyridine) particles (MCC-P(4VP)) were synthesized via ATRP grafting and used as adsorbents to target polyphenols in residues derived from winemaking, olive oil production and almond processing. These hybrid particles preserve good conditions to be used in continuous sorption/desorption processes and were assessed for the retention of polyphenols in solvent mixtures ranging from 0 to 100% water content. Other seven adsorbents were used in these assays, including three commercial resins and further materials synthesized in this research with 4VP.We show that the 4VP based adsorbents present a much higher average polyphenol retention in a broad range of working conditions, namely concerning the water content of the extract. This behavior stems from the strong binding capacity of the pyridyl functional group towards many polyphenols and excels with MCC-P(4VP) adsorbents when the hydrophobic interactions play a minor role.MCC-P(4VP) adsorbents were also used for purification and fractionation of polyphenols using simple sorption/desorption steps. A fraction enriched with the malvidin-3-O-glucoside anthocyanin was obtained from grape pomace. Fractions with high content of isorhamnetin-3-O-rutinoside were isolated from almond. Fractions enriched in secoiridoids and flavonoids were produced from olive mill wastewater while many phenolic alcohols and acids were removed. These results show the potential of the MCC-P(4VP) adsorbents to improve downstream processing of polyphenols and increase the biorefining efficiency, namely through the direct handling of organic extracts at high polyphenol concentration.This research also has disclosed the formation of a polymer population deviating from the expected homogeneous process in ATRP grafting. The partition of ATRP reactants between two regions in the homogeneous phase could be a source of some potentially interesting issues relevant to monomers presenting strong H-bond capability, such as 4VP. Thus, many future developments are possible for the designing of the functional materials here addressed, including the introduction of molecular recognition features.

Facile in situ fabrication of ZnO-embedded cellulose nanocomposite films with antibacterial properties and enhanced mechanical strength via hydrogen bonding interactions

Nano-ZnO were in situ prepared and permanently embedded in regenerated cellulose (RC) films by chemical precipitation to endow antibacterial of films and simultaneously strengthen tensile strength. ZnCl2 was selected as a promoter of 1-allyl-3-methylimidazolium chloride for cellulose dissolution and as a precursor for nano-ZnO synthesis. Zn2+-absorbed cellulose solution was reacted with NaOH under ultrasonic to obtain nano-ZnO embedded RC films. The results indicated that RC films treated with the longest sonication time, highest regeneration solution basicity, and highest cellulose concentration were demonstrated to be the most effective against S. aureus, which agreed well with the dense and homogeneous distribution of high content of nano-ZnO on the film surface. The nanocomposite films achieved particularly high mechanical strength of 202.0 MPa with improved thermal stability. Strong H-bonding formed between nano-ZnO and cellulose, which contributed to high tensile strength and thermal stability of films. This work affords a simple approach to prepare cellulose nanocomposite with outstanding performance for potential application in packaging.

Ammonium hexafluorosilicates as potential anti-caries agents: the problem of cation selection

In the last decade, ammonium hexafluorosilicate (AHFS) and ammonium hexafluorosilicates with biologically active cations (AHBAC), which have certain advantages over traditional fluoride medicinal substances, have been actively studied as anti-caries agents. In particular, an important feature of the action of AHFS is its ability to cause prolonged occlusion of the dentinal tubules with a precipitate of calcium fluoride; when using AHBAС there is a possibility of strengthening the anti-caries activity of the substance due to the pharmacological potential of the cation.
 The purpose of the review is to analyze the effects of the cation on the physicochemical properties and biological activity of ammonium hexafluorosilicates as potential anti-caries agents.
 Research methods – bibliosemantic, content analysis.
 It was drew the attention to the peculiarity of the AHBAC structure: salt structures are formed on the basis of systems of strong interionic H-bonds, mainly of the NH···F type, which have a significant effect on the properties of hexafluorosilicates in the crystalline state and their behavior in solutions. It was demonstrated the non-trivial nature of the change of solubility in water of AHBAC with heterocyclic and aromatic cations, which consists in the decrease of solubility with increasing number of hydrophilic fragments in the structure of cations. Adequate 2D QSPR models for interpretation and virtual screening of AHBAC water solubility have been constructed. Accounting for the effect of H-bonds on the solubility of AHBAC was detailed. It was assumed that the process of hydrolysis of AHBAC in aqueous solutions can be stimulated by elongation of the Si–F anion bonds due to the effects of H-bonds. It is shown that the thermal stability of AHBAC with pyridinium cations symbatically correlates with the number of strong and medium H-bonds in salt structures.
 The action of the pharmacological effects of the cation on the biological activity of AHBAC is manifested in the form of an increase in the caries-prophylactic efficacy of AHBAC in comparison with a similar effect of AHFS. Attempts to establish a relationship between the anti-caries activity of AHBAC and a certain pharmacological action of the cation have led to mixed results. This obviously reflects the complex mechanism of the influence of the biological activity of the cation on the caries-prophylactic efficacy of hexafluorosilicates, which is not limited to any one, albeit dominant, type of activity.

Fatigue behaviors of physical hydrogels based on hydrogen bonds

Physical hydrogels, composed of non-covalently crosslinking three dimensional polymer networks and a large amount of water, have drawn much attention due to their excellent mechanical properties such as high toughness, self-healing, self-recovery, and shape-memory. But the fatigue behaviors of physical hydrogels, especially the role of non-covalent bonds in the fatigue process, have not been well studied. Here we study fatigue damage and fatigue fracture of two kinds of physical hydrogels based on hydrogen bonding (H-bonding): poly(vinyl alcohol)/poly(acrylic acid) (PVA/PAA) gels with weak H-bonding (weak gels) and PVA/PAA-LiCl gels with strong H-bonding (strong gels). For the fatigue damage of uncut samples, both the weak and strong gels are fatigue strengthened in small deformation by stretch-induced H-bonding rearrangement, but are fatigue damaged in large deformation by chain sliding. For the fatigue fracture of precut samples, both the weak and strong gels show no measurable fatigue threshold, but the strong gel can mitigate crack growth. These results reveal the intrinsically weak non-covalent bonds cannot effectively increase the fatigue resistance of physical hydrogels. This work provides a deep perspective for developing novel anti-fatigue hydrogels.

Pillar[5]arene-Derived endo-Functionalized Molecular Tube for Mimicking Protein-Ligand Interactions.

Artificial tubular molecular pockets bearing polar functionalities on their inner surface are useful model systems for understanding the mechanisms of protein-ligand interactions in living systems. We herein report a pillar[5]arene-derived molecular tube, [P4-(OH)BPO], whose endo conformational isomer endo-[P4-(OH)BPO] possesses an inwardly pointing hydrogen-bond (H-bond) donor (OH) in its deep cavity and a strong H-bond acceptor (C═O) on its predominantly hydrophobic inner surface, rendering it a perfect protein binding pocket mimetic. A fragment-based drug design model was established using endo-[P4-(OH)BPO] and a library of various shape-complementary fragment ligands (1-38). On the basis of the binding affinity data for "fragment-pocket" complexes G⊂endo-[P4-(OH)BPO] (G = 1-38), two rationally designed "lead molecules" (39 and 40) were identified as being able to enhance binding affinity significantly by forming H-bonds with both the donor and acceptor of endo-[P4-(OH)BPO]. The described work opens new avenues for developing pillar[n]arene-derived protein binding pocket-mimetic systems for studies of protein-ligand interactions and mechanisms of enzymatic reactions.

An In Silico Evaluation of Molecular Interaction Between Antimicrobial Peptide Subtilosin A of Bacillus subtilis with Virulent Proteins of Aeromonas hydrophila

Subtilosin A, a cyclic peptide from Bacillus subtilis is known for its antimicrobial activity against a diverse range of bacteria. Herein, we report the specific interaction between subtilosin A against virulent proteins of Aeromonas hydrophila through in silico analysis. Aeromonas toxic proteins such as aerolysin and hemolysin were selected from the non-redundant database. The hemolysin protein was designed by homology modelling tool, and it was validated using Ramachandran plot. Then subtilosin A and target toxin proteins were energy minimized for further docking study. The whole docking experiments were done using antibody mode in Cluspro. Subtilosin A building an active interaction with Aeromonas toxins through H-bonds and protein–protein docking analysis revealed that the hemolysin has 6 H-bond interaction towards the antimicrobial target protein subtilosin A than aerolysin, which has 9 H-bonds. The most favourable interacting residues of subtilosin A are Thr6, Cys13, Ile19, Pro20, Asp21, Phe22, Glu23 and Gly35 involving in the strong H-bond formation and proceeds to inhibition of toxin. Hence, the study confirmed that the subtilosin A has more antimicrobial activity to inhibit the Aeromonas toxins by interacting with their binding site residues for preventing extracellular cleavage.

N-carbamate protected amino acid derived guanidine organocatalysts

We report the preparation of a range of N -protected amino acid derived guanidine organocatalysts and their application to the Michael addition of 2-hydroxy-1,4-napthoquinone to β-nitrostyrene, achieving a maximum ee of 26%. Whilst these catalysts gave poor ees, the structural variation together with the X-ray crystallographic study of the intra- and intermolecular hydrogen bonding reported suggest that the C 2 -symmetric catalysts are lead compounds for the further development of this methodology. • N -protected amino acid derived guanidine organocatalysts were prepared.. • A Michael addition of 2-hydroxy-1,4-napthoquinone to β-nitrostyrene was achieved in 26% ee. • X-ray analysis suggested strong intramolecular H-bonds between carbamate carbonyls and guanidine N-H’s.

Controlling Light-Induced Proton Transfer from the GFP Chromophore.

Green Fluorescent Protein (GFP) is known to undergo excited-state proton transfer (ESPT). Formation of a short H-bond favors ultrafast ESPT in GFP-like proteins, such as the GFP S65T/H148D mutant, but the detailed mechanism and its quantum nature remain to be resolved. Here we study in vacuo, light-induced proton transfer from the GFP chromophore in hydrogen-bonded complexes with two anionic proton acceptors, I- and deprotonated trichloroacetic acid (TCA- ). We address the role of the strong H-bond and the quantum mechanical proton-density distribution in the excited state, which determines the proton-transfer probability. Our study shows that chemical modifications to the molecular network drastically change the proton-transfer probability and it can become strongly wavelength dependent. The proton-transfer branching ratio is found to be 60 % for the TCA complex and 10 % for the iodide complex, being highly dependent on the photon energy in the latter case. Using high-level ab initio calculations, we show that light-induced proton transfer takes place in S1 , revealing intrinsic photoacid properties of the isolated GFP chromophore in strongly bound H-bonded complexes. ESPT is found to be very sensitive to the topography of the highly anharmonic potential in S1 , depending on the quantum-density distribution upon vibrational excitation. We also show that the S1 potential-energy surface, and hence excited-state proton transfer, can be controlled by altering the chromophore microenvironment.

Hydration structure of flat and stepped MgO surfaces.

We investigate the solvation structure of flat and stepped MgO(001) in neutral liquid water using ab initio molecular dynamics based on a hybrid density functional with dispersion corrections. Our simulations show that the MgO surface is covered by a densely packed layer of mixed intact and dissociated adsorbed water molecules in a planar arrangement with strong intermolecular H-bonds. The water dissociation fractions in this layer are >20% and >30% on the flat and stepped surfaces, respectively. Slightly above the first water layer, we observe metastable OH groups perpendicular to the interface, similar to those reported in low temperature studies of water monolayers on MgO. These species receive hydrogen bonds from four nearby water molecules in the first layer and have their hydrophobic H end directed toward bulk water, while their associated protons are bound to surface oxygens. The formation of these OH species is attributed to the strong basicity of the MgO surface and can be relevant for understanding various phenomena from morphology evolution and growth of (nano)crystalline MgO particles to heterogeneous catalysis.

Super-assembled highly compressible and flexible cellulose aerogels for methylene blue removal from water

Physical adsorption is a common method to solve the contamination of methylene blue in dyeing wastewater. As a kind of adsorption material, cellulose aerogels with high porosity and surface areas have great potential application in methylene blue removal. However, the week hydrogen bonding between cellulose nanofibers making the cellulose aerogels with the poor mechanical properties and can be easily destroyed during adsorption. Hence, the preparation of cellulose aerogels with high mechanical strength is still a great challenge. Here, we report a robust super-assembly strategy to fabricate cellulose aerogels by combining cellulose nanofibers with PVA and M-K10. The resulting cellulose aerogels not only has a robust chemically cross-linked network, but also has strong H-bonds, which greatly enhance the mechanical properties. The resulting cellulose aerogels possess a low density of 19.32 mg/cm3. Furthermore, the cellulose aerogel shows 93% shape recovery under 60% strain (9.5 kPa under 60% strain) after 100 cycles, showing excellent mechanical property. The adsorption capacity of cellulose aerogel to methylene blue solution of 20 mg/L is 2.28 mg/g and the adsorption kinetics and adsorption isotherms have also been studied. Pseudo-second-order kinetic model and Freundlich isotherm model are more acceptable for indicating the adsorption process of methylene blue on the cellulose aerogel. Thus, this compressible and durable cellulose aerogel is a very prospective material for dyeing wastewater cleanup.

Ionic Liquid-Assisted Alignment of Corn Straw Microcrystalline Cellulose Aerogels with Low Tortuosity Channels for Salt-Assistance Solar Steam Evaporators.

The development of a highly salt-resistant solar evaporator with long-term energy conversion is essential for practical solar desalination. Herein, we first report the ionic liquid-assisted alignment of corn straw-based microcrystalline and oxidized microcrystalline cellulose for preparation of biomass aerogel (abbreviated as CSMCA and CSOMCA) evaporators with low tortuosity channels for salt-assistance solar steam generation. By coating of carbonized cornstalk nanoparticles onto CSMCA and CSOMCA as light-absorbing layers (named C-CSMCA and C-CSOMCA), the light absorption of C-CSMCA and C-CSOMCA reaches 92 and 95%, respectively. The formation of strong H-bonding between pyranoid rings of cellulose in the presence of the ionic liquid would result in a reorientation of microcrystalline cellulose, which makes it possible to create vertically aligned channels of CSMCA and CSOMCA after replacement of solvents, followed by freeze drying. Combined with their low thermal conductivity (0.037 and 0.043 W m-1 K-1), high porosity, and intrinsic superhydrophilicity, C-CSMCA and C-CSOMCA exhibit high evaporation rates (1.44 and 1.36 kg m-2 h-1) and excellent energy conversion efficiencies (88 and 84%). In particular, bearing with vertically aligned channels, C-CSMCA and C-CSOMCA possess excellent salt tolerance for solar desalination due to a rapid resolving and return of the crystalline salt into water, for example, no surface salt crystallization for C-CSMCA after 20 days of continuous evaporation. Moreover, both C-CSMCA and C-CSOMCA have excellent sewage treatment capacity and can efficiently absorb dyes and heavy-metal ions in water bodies, showing great potential in actual desalination and sewage treatment based on their cost-effective, simple, scalable, and green manufacture.

Hydrogen bonding catalysis by water in epoxide ring opening reaction

Water can act as catalyst is perhaps the most intriguing property reported of this molecule in the last decade. However, despite being an integral part of many enzyme structures, the role of water in catalyzing enzymatic reactions remains sparsely studied. In a recent study, we have shown that the epoxide ring opening in aspartate proteases follows a two-step process involving water. In this work, we attempt to unravel the electronic basis of the co-catalytic role of water in the epoxide ring opening reaction by employing high-level quantum mechanical calculations at M06-2X/6-31+G(d,p) level of accuracy. Our computed electron density and its reduced gradient show that water anchor the reactant molecules through strong H-bond bridges. In addition, the strong ionizing power of water allows better charge delocalization to stabilize the transition states and oxyanion intermediate. Electrostatic analyses suggest greater charge transfer from the aspartates to the epoxide in the transition state, which is found to be exergonic in nature rendering a low-barrier reaction compared to a control system where water was omitted in the reaction field. This elucidated mechanism at electronic level could promote further research to search for the co-catalytic role of water in other enzymes.

Study on Typical Diarylurea Drugs or Derivatives in Cocrystallizing with Strong H-Bond Acceptor DMSO.

Diarylureas are widely used in self-assembly and supramolecular chemistry owing to their outstanding characteristics as both H-bond donors and acceptors. Unfortunately, this bonding property is rarely applied in the development of urea-containing drugs. Herein, seven related dimethyl sulfoxide (DMSO) complexes were screened from 12 substrates involving sorafenib and regorafenib, mainly considering the substitution effect following a robust procedure. All complexes were structurally confirmed by spectroscopic means and thermal analysis. Specially, five cocrystals with three deuterated, named sorafenib·DMSO, donafenib·DMSO, deuregorafenib·DMSO, 6·DMSO, and 7·DMSO were obtained. The crystal structures revealed that all host molecules consistently bonded with DMSO in intermolecular interaction in a 1:1 stoichiometry. However, further comparison with documented DMSO complexes and parent motifs presented some arrangement diversities especially for 6·DMSO which offered a counter-example to previous rules. Major changes in the orientation of meta-substituents and the packing stability for sorafenib·DMSO and deuregorafenib·DMSO were rationalized by theory analysis and computational energy calculation. Cumulative data implied that the planarization of two aryl planes in diarylureas may play a crucial role in cocrystallization. Also, a polymorph study bridged the transformation between these ureas and their DMSO complexes.

Anti-HIV-drug and phyto-flavonoid combination against SARS-CoV-2: a molecular docking-simulation base assessment

At the health emergence, no such potent prophylactic therapy is available to control the deadly emerged Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2). However, existing antiviral, anti-inflammatory, antimalarial drugs is the only option against SARS-CoV-2, but it may be harmful to patients without more clinical evidence. As an alternative solution, we proposed a newer hypothesis using the selective 10 potent anti-HIV drugs and flavonoid class of phytochemicals from previous reports to use in combination against SARS-CoV-2. Primarily, 10 anti-HIV protease inhibitor drugs and 10 phyto-flavonoids as ligands in molecular docking study against the putative target, the SARS-CoV-2-main protease (Mpro) ID: 6Y2E), as an essential enzyme in viral genome replication. According to molecular docking and drug-ability scores of each ligand, the anti-HIV drug, the darunavir (with a docking score, −10.25 kcal/mol and drug-likeness rating, 0.60) and the quercetin-3-rhamnoside (with a docking score, −10.90 kcal/mol and drug-likeness rating, 0.82) were selected for further analysis in combined effect. Perceptibly, the combined ‘anti-HIV drug and phyto-flavonoid’ docking complex has actively interacted with eight strong H-bonds with stability, briefly elucidated through RMRD-, RMSF- Rg-plots and MM/PBSA-binding energy calculation during 100 ns than the individual against SARS-CoV-2-Mpro. Thus, the ‘anti-HIV-drug-phyto-flavonoid’ combination therapy could be used against SARS-CoV-2 after some experimental validation. Communicated by Ramaswamy H. Sarma

Distinct Tetracyanoquinodimethane Derivatives: Enhanced Fluorescence in Solutions and Unprecedented Cation Recognition in the Solid State.

Tetracyanoquinodimethane (TCNQ) is known to react with various amines to generate substituted TCNQ derivatives with remarkable optical and nonlinear optical characteristics. The choice of amine plays a crucial role in the outcome of molecular material attributes. Especially, mono/di-substituted TCNQ’s possessing strong fluorescence in solutions than solids are deficient. Furthermore, cation recognition in the solid-state TCNQ derivatives is yet undetermined. In this article, we present solution-enhanced fluorescence and exclusive solid-state recognition of K+ ion achieved through the selection of 4-(4-aminophenyl)morpholin-3-one (APM) having considerable π-conjugation and carbonyl (C=O) functionality, particularly in the ring. TCNQ when reacted with APM, in a single-step reaction, resulted in two well-defined distinct compounds, namely, 7,7-bis(4-(4-aminophenyl)morpholin-3-ono)dicyanoquinodimethane (BAPMDQ [1], yellow) and 7,7,8-(4-(4-aminophenyl)morpholin-3-ono)tricyanoquinodimethane (APMTQ [2], red), with increased fluorescence intensity in solutions than their solids. Crystal structure investigation revealed extensive C–H−π interactions and strong H-bonding in [1], whereas moderate to weak interactions in [2]. Surprisingly, simple mechanical grinding during KBr pellet preparation with [1, 2] triggered unidentified cation recognition with a profound color change (in ∼1 min) detected by the naked eye, accompanied by a drastic enhancement of fluorescence, proposed due to the presence of carbonyl functionality, noncovalent intermolecular interactions, and molecular assemblies in [1, 2] solids. Cation recognition was also noted with various other salts as well (KCl, KI, KSCN, NH4Cl, NH4Br, etc.). Currently, the recognition mechanism of K+ ion in [1, 2] is demonstrated by the strong electrostatic interaction of K+ ion with CO and simultaneously cation−π interaction of K+ with the phenyl ring of APM, supported by experimental and computational studies. Computational analysis also revealed that a strong cation−π interaction occurred between the K+ ion and the phenyl ring (APM) in [2] than in [1] (ΔGbinding calculated as ∼16.3 and ∼25.2 kcal mol–1 for [1] and [2], respectively) providing additional binding free energy. Thus, both electrostatic and cation−π interactions lead to the recognition. Scanning electron microscopy of drop-cast films showed microcrystalline “roses” in [1] and micro/nano “aggregates” in [2]. Optical band gap (∼3.565 eV) indicated [1, 2] as wide-band-gap materials. The current study demonstrates fascinating novel products obtained by single-pot reaction, resulting in contrasting optical properties in solutions and experiencing cation recognition capability exclusively in the solid state.

Crossover from hydrogen to chemical bonding.

Hydrogen bonds (H-bonds) can be interpreted as a classical electrostatic interaction or as a covalent chemical bond if the interaction is strong enough. As a result, short strong H-bonds exist at an intersection between qualitatively different bonding descriptions, with few experimental methods to understand this dichotomy. The [F-H-F]- ion represents a bare short H-bond, whose distinctive vibrational potential in water is revealed with femtosecond two-dimensional infrared spectroscopy. It shows the superharmonic behavior of the proton motion, which is strongly coupled to the donor-acceptor stretching and disappears on H-bond bending. In combination with high-level quantum-chemical calculations, we demonstrate a distinct crossover in spectroscopic properties from conventional to short strong H-bonds, which identify where hydrogen bonding ends and chemical bonding begins.

The nature of short hydrogen bonds

Chemical Physics Hydrogen bonding (H-bonding) unquestionably plays an important role in chemical and biological systems and is responsible for some of their unusual properties. Strong, short H-bonds constitute a separate class that, owing to their elusive characterization, has remained a point of contention over the past several decades. Using femtosecond two-dimensional infrared spectroscopy in conjunction with quantum chemical calculations, Dereka et al. demonstrate a powerful way to investigate the nature of short H-bonding (see the Perspective by Bonn and Hunger). Their quantitative characterization of multiple coupled motions in the model system of bifluoride anion [F-H-F]− in aqueous solution reveals several distinctive features of a crossover from conventional to short, strong H-bonding. Science , this issue p. [160][1] see also p. [123][2] [1]: /lookup/doi/10.1126/science.abe1951 [2]: /lookup/doi/10.1126/science.abf3543

Self-assembly and Nano scaled Ni (II) Coordination Complex as an Efficient Catalyst and Luminescent Sensor

Design of the structure of nanosized photo-catalysts is an interesting research area to achieve high performance of their catalytic property. Nano-scaled single crystals of {[Ni(EN)4(NCS)2]} coordination complex (EN = ethyl nicotinate), CC1 and the nano-sized particles, CC1\ are synthesized by self-assembly and ultrasonic radiation methods, respectively. The structure comprises two crystallographically different and chemically identical Ni atoms adopting [NiN6] octahedron geometry. The structure of CC1 propagates via 1D-zegzag chains which extend in 3D- fashion via strong H-bonds. The chemical structure and morphology of CC1 and CC1\ are characterized by single crystal and powder X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and spectroscopic methods. The heterogeneous catalytic and photo-catalytic activity of CC1 and CC1\ exhibit very efficient catalytic activity towards degradation of indigo carmine dye (IC) within very short times under UV-light or ultrasonic radiation. The good limit of detection and the high quenching efficiency of CC1 towards selective quantitative fdetermination of nitrobenzene (NB) and Fe3+ ions support its behavior as an efficient luminescent sensor.

Theoretical and Experimental Insights into the Self-Assembly and Ion Response Mechanisms of Tripodal Quinolinamido-Based Supramolecular Organogels.

The exploration and understanding of self-assembly and stimuli-responsive mechanisms of supramolecular systems are of fundamental importance for researchers to plan syntheses reasonably. Herein, the self-assembly and ions responsive mechanisms of a tripodal quinolinamido-based supramolecular organogel (TBT-gel) were investigated through experiments and theoretical calculations including independent gradient model (IGM), localized orbitals locator (LOL) and hole-electron theory. According to these studies, the self-assembly mechanism of TBT-gel was based on strong threefold H-bonding and π-π interactions, which induced the TBT forming helical, one-dimensional supramolecular polymer. After addition of Fe3+ into the TBT-gel, the one-dimensional supramolecular polymer had been crosslinked by the Fe3+ through coordination interaction and formed a metallogel (TBT-Fe-gel). Interestingly, the TBT-gel showed selective fluorescent response for Fe3+ and F- based on a competitive coordination mechanism. Moreover, the study on fluorescence responsive mechanism of TBT-gel for Fe3+ and F- implied the ICT mode governs both the electron excitation and de-excitation processes. The calculated results were in agreement with the corresponding experimental results. Notably, the quantum chemical calculations provided a deep understanding and visualized presentation of the assembly and stimuli-responsive mechanisms.

A shape-persistent arylene ethynylene macrocycle with a multiple acetamide modified cavity: synthesis and gelation

A new arylene ethynylene macrocycle (AEM) molecule bearing endo-acetamide groups was obtained by a Pd/Cu mediated homo-coupling reaction. Introducing tetraethylene glycol ether as a linkage between two C-shaped fragments substantially improved the final cyclization yield (30%). Concentration-dependent 1HNMR experiments indicated that strong aggregates formed through H-bonds were observed for this new macrocycle with amide groups in solution. And also, this macrocycle was fluorescent in solution and showed a highly selective fluorescence quenching response toward the highly toxic Hg2+. More importantly, this macrocycle could induce gelation of several solvents. Significantly, an interesting aggregation-induced enhanced emission (AIEE) behavior was observed for this macrocycle upon gelation. Both SEM and TEM investigations revealed that nanoporous structures existed in the xerogels. This study offers a new molecular design approach to develop fluorescent gels from planar AEM molecules with a functional cavity.