Encapsulation of divalent tetrahedral oxyanions of sulfur within the rigidified dimeric capsular assembly of a tripodal receptor: first crystallographic evidence of thiosulfate encapsulation within neutral receptor capsule

A simple tris(2-aminoethyl)amine based meta-chloro substituted tripodal thiourea receptor L has been extensively studied with two divalent oxyanions of sulfur, such as sulfate and thiosulfate, with identical dimensionality. The solid state crystal structure of the anion complexes with L reveal that the anions are encapsulated within the dimeric rigid capsular assembly of the receptor via N-Hanion interactions. To the best of our knowledge this is the first report on the encapsulation of thiosulfate within dimeric capsular assembly of a neutral receptor. The tight capsular sizes for both anion complexes are quite comparable, whereas the coordination mode of the anions and the hydrogen bonding parameters are significantly varied. The three dimensional solid state structural orientations of the capsular complexes are mainly governed by the ClCl (for thiosulfate complex) and ClS (for sulfate complex) halogen bonding interactions. The solution-state binding and encapsulation of oxyanions by N-Hanion hydrogen bonding has also been confirmed by quantitative (1)H NMR titration and 2D NOESY NMR experiments. Both the experiments confirm that in contradiction of 2?:?1 solid state binding, in solution the studied anions are bound within the pseudocavity of the receptor with 1?:?1 binding stoichiometry. Moreover, the change in chemical shifts of thiourea -NH protons and the binding constant values suggest the receptor-sulfate interaction is more energetically favorable compared to the receptor thiosulfate interaction.     

Water induced hydrophobic surface

A polyurethane coating is described that has hydrophilic wetting behavior when dry and hydrophobic when wet. A difference of approximately 25 degrees in advancing contact angles for dry (83 degrees ) and wet (108 degrees ) states is found by sessile drop and dynamic methods. The term "contraphilic" is suggested for this reversible change opposite customary amphiphilic behavior. Contraphilic behavior results from a soft block containing semifluorinated and 5,5-dimethyhydantoin segmers. Amide inter/intramolecular hydrogen bonding is proposed for the hydrophilic (dry) state, while surface-confined, amide-water hydrogen bonding "releases"semifluorinated groups, giving the hydrophobic state. Water-induced hydrophobic surfaces may lead to applications for easily switched wetting, such as in microfluidics.     

Double Hydrogen‐Bonding pH‐Sensitive Hydrogels Retaining High‐Strengths Over a Wide pH Range

Traditional pH‐sensitive hydrogels inevitably suffer strength deterioration while the responsive weak acid or base groups are in the ionized state. In this study, we report on a facile approach to fabricate a novel pH‐sensitive high‐strength hydrogel from copolymerization of two hydrogen‐bonding motif‐containing monomers, 3‐acrylamidophenylboronic acid and 2‐vinyl‐4,6‐diamino‐1,3,5‐triazine with a crosslinker N,N‐methylenebisacrylamide through hydrophilic optimization of the comonomer oligo(ethylene glycol) methacrylate. The double hydrogen bonding hydrogel exhibits both high tensile and compressive strengths over a broad pH range due to the unique ability to maintain at least one type of hydrogen‐bonding crosslink over the whole course of pH change.     

A molecular dynamics study of ethanol-water hydrogen bonding in binary structure I clathrate hydrate with CO2

Guest-host hydrogen bonding in clathrate hydrates occurs when in addition to the hydrophilic moiety which causes the molecule to form hydrates under high pressure-low temperature conditions, the guests contain a hydrophilic, hydrogen bonding functional group. In the presence of carbon dioxide, ethanol clathrate hydrate has been synthesized with 10% of large structure I (sI) cages occupied by ethanol. In this work, we use molecular dynamics simulations to study hydrogen bonding structure and dynamics in this binary sI clathrate hydrate in the temperature range of 100-250 K. We observe that ethanol forms long-lived (>500 ps) proton-donating and accepting hydrogen bonds with cage water molecules from both hexagonal and pentagonal faces of the large cages while maintaining the general cage integrity of the sI clathrate hydrate. The presence of the nondipolar CO(2) molecules stabilizes the hydrate phase, despite the strong and prevalent alcohol-water hydrogen bonding. The distortions of the large cages from the ideal form, the radial distribution functions of the guest-host interactions, and the ethanol guest dynamics are characterized in this study. In previous work through dielectric and NMR relaxation time studies, single crystal x-ray diffraction, and molecular dynamics simulations we have observed guest-water hydrogen bonding in structure II and structure H clathrate hydrates. The present work extends the observation of hydrogen bonding to structure I hydrates.     

Probing the interaction mode in hydrophilic interaction chromatography

This work aims at characterizing interactions between a select set of probes and 22 hydrophilic and polar commercial stationary phases, to develop an understanding of the relationship between the chemical properties of those phases and their interplay with the eluent and solutes in hydrophilic interaction chromatography. "Hydrophilic interaction" is a somewhat inexact term, and an attempt was therefore made to characterize the interactions involved in HILIC as hydrophilic, hydrophobic, electrostatic, hydrogen bonding, dipole-dipole, π-π interaction, and shape-selectivity. Each specific interaction was quantified from the separation factors of a pair of similar substances of which one had properties promoting the interaction mode being probed while the other did not. The effects of particle size and pore size of the phases on retention and selectivity were also studied. The phases investigated covered a wide range of surface functional groups including zwitterionic (sulfobetaine and phosphocholine), neutral (amide and hydroxyl), cationic (amine), and anionic (sulfonic acid and silanol). Principal component analysis of the data showed that partitioning was a dominating mechanism for uncharged solutes in HILIC. However, correlations between functional groups and interactions were also observed, which confirms that the HILIC retention mechanism is partly contributed by adsorption mechanisms involving electrostatic interaction and multipoint hydrogen bonding. Phases with smaller pore diameters yielded longer retention of solutes, but did not significantly change the column selectivities. The particle diameter had no significant effect, neither on retention, nor on the selectivities. An increased water content in the eluent reduced the multipoint hydrogen bonding interactions, while an increased electrolyte concentration lowered the selectivities of the tested columns and made their interaction patterns more similar.     

Stimuli‐responsive polymer nanocomposites based on styrene‐butadiene rubber and bacterial cellulose whiskers

Water‐induced mechanically adaptive rubber nanocomposites were prepared by mixing bacterial cellulose whiskers (BCWs) suspension with styrene‐butadiene rubber (SBR) latex, followed by evaporation method. The structure, morphology, dynamic mechanical properties, water stimuli‐responsive behavior, and biodegradability of SBR/BCWs nanocomposite films were investigated. The results showed that the hydrophilic whiskers had a significant reinforcement effect on the storage modulus of SBR matrix, which originated from the formation of a rigid three‐dimensional filler network within matrix by strong hydrogen bonding between whiskers. The SBR/BCWs nanocomposites showed pronounced water stimuli‐responsive behavior compared with neat SBR. The storage modulus of SBR/BCWs nanocomposite could be decreased by 99.2% after equilibrium water swelling. This remarkable water‐triggered modulus change is attributed to the disentanglement of BCWs network via competitive hydrogen bonding with water.     

Water makes it hydrophobic: contraphilic wetting for polyurethanes with soft blocks having semifluorinated and 5,5-dimethylhydantoin side chains

A series of polyurethanes with novel copolymer soft blocks display a new surface phenomenon, contraphilic wetting, in which the dry surface is hydrophilic and the wetted surface is hydrophobic. A precursor polymer was prepared with copolymer soft blocks containing semifluorinated (trifluoroethoxy, 3FOx, or pentafluoropropoxy, 5FOx) and bromomethyl functional pendant groups with 2:1, 1:1, and 1:2 semifluorinated/bromomethyl ratios. The hard block consists of isophorone diisocyanate (IPDI) and 1,4-butanediol (BD). 5,5-Dimethylhydantoin was introduced by the substitution of Br via reaction-on-polymer. The composition, structure, and percent of 5,5-dimethylhydantoin substitution for both the precursor and the 5,5-dimethylhydantoin-substituted polyurethanes were analyzed by 1H NMR. The difference between the advancing contact angle on the wetted surface and that on the dry surface (deltaC) is highest (38 degrees ) for the polyurethane with the highest ratio of semifluorinated/hydantoin soft block side chains. A model is proposed according to which contraphilic wetting is driven enthalpically by hydrogen bonding. For the dry surface, hydrogen bonding of 5,5-dimethylhydantoin amide carbonyl groups to methylene hydrogens of semifluorinated groups disrupts the normal surface concentration of semifluorinated groups, whereas the geometric arrangement of hydantoin N-H results in availability for hydrogen bonding with water. Upon exposure to water, amide groups switch from hydrogen bonding to -CH2CF2CF3 to stronger hydrogen bonding with water. As a result, semifluorinated groups are "released", and the surface becomes hydrophobic. Drying the coating (50 degrees C) reversibly restores hydrophilic character. Coatings stored at ambient temperature and humidity have deltaC values intermediate between dry and wet states.     

Bond-strengthening in staphylococcal adhesion to hydrophilic and hydrophobic surfaces using atomic force microscopy

Time-dependent bacterial adhesion forces of four strains of Staphylococcus epidermidis to hydrophobic and hydrophilic surfaces were investigated. Initial adhesion forces differed significantly between the two surfaces and hovered around -0.4 nN. No unambiguous effect of substratum surface hydrophobicity on initial adhesion forces for the four different S. epidermidis strains was observed. Over time, strengthening of the adhesion forces was virtually absent on hydrophobic dimethyldichlorosilane (DDS)-coated glass, although in a few cases multiple adhesion peaks developed in the retract curves. Bond-strengthening on hydrophilic glass occurred within 5-35 s to maximum adhesion forces of -1.9 +/- 0.7 nN and was concurrent with the development of multiple adhesion peaks upon retract. Poisson analysis of the multiple adhesion peaks allowed separation of contributions of hydrogen bonding from other nonspecific interaction forces and revealed a force contribution of -0.8 nN for hydrogen bonding and +0.3 nN for other nonspecific interaction forces. Time-dependent bacterial adhesion forces were comparable for all four staphylococcal strains. It is concluded that, on DDS-coated glass, the hydrophobic effect causes instantaneous adhesion, while strengthening of the bonds on hydrophilic glass is dominated by noninstantaneous hydrogen bond formation.     

Polymorphism of l‐Tryptophan

A new polymorph of l ‐tryptophan was prepared through crystallization from the gas phase, with structure determination carried out directly from powder XRD data augmented by periodic DFT‐D calculations. The new polymorph (denoted β) and the previously reported polymorph (denoted α) are both based on alternating hydrophilic and hydrophobic layers, but with substantially different hydrogen‐bonding arrangements. The β polymorph exhibits the energetically favourable l 2‐l 2 hydrogen‐bonding arrangement, which is unprecedented for amino acids with aromatic side chains. The specific molecular conformations adopted in the β polymorph facilitate this hydrogen‐bonding scheme while avoiding steric conflict of the side chains.     

Hydrophilic carbon nanotube membrane enhanced interfacial evaporation for desalination

Carbon nanotube-based(CNT-based) interfacial evaporation material is one of the most potential materials for solar desalination. Here, we studied the evaporation rate of the CNT-based membranes with different hydrophilic and hydrophobic chemical modified surfaces using molecular dynamic simulations.We found that the hydrogen bonding density among water molecules at the interface is a key factor in enhancing the evaporation rate. For a hydrophilic CNT-based membrane, the strong interactions betwe...     

Tuning One‐Dimensional Nanostructures of Bola‐Like Peptide Amphiphiles by Varying the Hydrophilic Amino Acids

By combining experimental measurements and computer simulations, we here show that for the bola‐like peptide amphiphiles XI₄X, where X=K, R, and H, the hydrophilic amino acid substitutions have little effect on the β‐sheet hydrogen‐bonding between peptide backbones. Whereas all of the peptides self‐assemble into one dimensional (1D) nanostructures with completely different morphologies, that is, nanotubes and helical nanoribbons for KI₄K, flat and multilayered nanoribbons for HI₄H, and twisted and bilayered nanoribbons for RI₄R. These different 1D morphologies can be explained by the distinct stacking degrees and modes of the three peptide β‐sheets along the x‐direction (width) and the z‐direction (height), which microscopically originate from the hydrogen‐bonding ability of the sheets to solvent molecules and the pairing of hydrophilic amino acid side chains between β‐sheet monolayers through stacking interactions and hydrogen bonding. These different 1D nanostructures have distinct surface chemistry and functions, with great potential in various applications exploiting the respective properties of these hydrophilic amino acids.     

Hydrogen-bonded monolayers and interdigitated multilayers at the air-water interface

Crystalline monolayers of octadecylsulfonate amphiphiles (C18S) separated by hydrophilic guanidinium (G) spacer molecules were formed at the air-water interface at a surface coverage that was consistent with that expected for a fully condensed monolayer self-assembled by hydrogen bonding between the G ions and the sulfonate groups. The surface pressure-area isotherms reflected reinforcement of this monolayer by hydrogen bonding between the G ions and the sulfonate groups, and grazing incidence X-ray diffraction (GIXD) measurements, performed in-situ at the air-water interface, revealed substantial tilt of the alkyl hydrophobes (t = 49 degrees with respect to the surface normal), which allowed the close packing of the C18 chains needed for a stable crystalline monolayer. This property contrasts with behavior observed previously for monolayers of hexadecylbiphenylsulfonate (C16BPS) and G, which only formed crystallites upon compression, accompanied by ejection of the G ions from the air-water interface. Upon compression to higher surface pressures, GIXD revealed that the highly tilted (G)C18S monolayer crystallites transformed to a self-interdigitated (G)C18S crystalline multilayer accompanied by a new crystalline monolayer phase with slightly tilted alkyl chains and disordered sulfonate headgroups. This transformation was dependent on the rate of compression, suggesting kinetic limitations for the "zipper-like" transformation from the crystalline monolayer to the self-interdigitated (G)C18S crystalline multilayer.     

Induction of periodic nanostructures in polythiophene films through block copolymer templating

A new class of periodically nanostructured polythiophene materials with high regularity and numerous morphologies is prepared through the cooperative self‐assembly of polythiophene derivatives with a templating block copolymer (BCP) and poly(1,4‐isoprene)‐block‐poly(methacrylic acid) (PMA). The selection of the hydrophilic and aprotic triethylene glycol (TEG) group as side chains on polythiophene and the use of hydrophilic and protic PMA are crucial to producing well‐ordered nanostructures in polythiophene films, as it enables selective coassembly within the hydrophilic domain through hydrogen bonding. The composite films are shown to have formed hexagonally packed cylinders with 28 nm periodicities based on small‐angle X‐ray scattering and transmission electron microscopy. The formation of hydrogen bonding is revealed by a shift in the carbonyl peak of PMA in the Fourier transform infrared spectra of the composite film relative to the neat film. This suggests that the TEG‐functionalized polythiophene selectively incorporates into PMA. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 1105–1112     

Hydrogen‐Bonding Toughened Hydrogels and Emerging CO2‐Responsive Shape Memory Effect

A double hydrogen bonding (DHB) hydrogel is constructed by copolymerization of 2‐vinyl‐4,6‐diamino‐1,3,5‐triazine (hydrophobic hydrogen bonding monomer) and N,N‐dimethylacrylamide (hydrophilic hydrogen bonding monomer) with polyethylene glycol diacrylates. The DHB hydrogels demonstrate tunable robust mechanical properties by varying the ratio of hydrogen bonding monomer or crosslinker. Importantly, because of synergistic energy dissipating mechanism of strong diaminotriazine (DAT) hydrogen bonding and weak amide hydrogen bonding, the DHB hydrogels exhibit high toughness (up to 2.32 kJ m⁻²), meanwhile maintaining 0.7 MPa tensile strength, 130% elongation at break, and 8.3 MPa compressive strength. Moreover, rehydration can help to recover the mechanical properties of the cyclic loaded–unloaded gels. Attractively, the DHB hydrogels are responsive to CO₂ in water, and demonstrate unprecedented CO₂‐triggered shape memory behavior owing to the reversible destruction and reconstruction of DAT hydrogen bonding upon passing and degassing CO₂ without introducing external acid. The CO₂ triggering mechanism may point out a new approach to fabricate shape memory hydrogels.     

Substrate‐Induced Dimerization Assembly of Chiral Macrocycle Catalysts toward Cooperative Asymmetric Catalysis

An artificial system of substrate‐induced dimerization assembly of chiral macrocycle catalysts enables a highly cooperative hydrogen‐bonding activation network for efficient enantioselective transformation. These macrocycles contain two thiourea and two chiral diamine moieties and dimerize with sulfate to form a sandwich‐like assembly. The macrocycles then adopt an extended conformation and reciprocally complement the hydrogen‐bonding interaction sites. Inspired by the guest‐induced dynamic assembly, these macrocycles catalyze the decarboxylative Mannich reaction of cyclic aldimines containing a sulfamate heading group. The imine substrate can be activated toward nucleophilic attack of β‐ketoacid by a cooperative hydrogen‐bonding network enabled by sulfamate‐induced dimerization assembly of the macrocycle catalysts. Highly efficient (>95 % yield in most cases) and enantioselective (up to 97.5:2.5 er) transformation of a variety of substrates using only 5 mol % macrocycle was achieved.     

Recognition of Hydrophilic Cyclic Compounds by a Water-Soluble Cavitand

A water-soluble deep cavitand bearing amides on the upper rim and trimethyl ammonium groups on the feet was synthesized. The open-ended cavity is stabilized by the intramolecular hydrogen bonds formed between the adjacent amides, and the introduction of trimethylammonium imparts to the cavitand good solubility in water. The cavitand exhibits high binding affinity and selectivity to hydrophilic molecules in water. With certain guests, such as cyclohexyl alcohols, amines and acids, the recognition involves the synergistic action of hydrogen bonding with hydrophobic effects. The binding phenomena are interpreted in terms of a fixed solvent cage presented by the host to the guest.     

Solvent-mediated folding of a doubly charged anion

The microsolvation of the suberate dianion, -O2C(CH2)6CO2-, with two separate charge centers was studied by photoelectron spectroscopy and molecular dynamics simulation one solvent molecule at a time for up to 20 waters. It is shown that the two negative charges are solvated in the linear suberate alternately. As the solvent number increases, the negative charges are screened and a conformation change occurs at 16 waters, where the cooperative hydrogen bonding of water is large enough to overcome the Coulomb repulsion and pull the two negative charges closer through a water bridge. This conformation change, revealed both from the experiment and from the simulation, is a manifestation of the hydrophilic and hydrophobic forces at the molecular level.     

Hydrogen-Bonded Complexes of Fluorophenylacetylenes: To Fluoresce or Not?

The hydrogen-bonded complexes of fluorophenylacetylenesexhibit unusual and interesting fluorescence turn ON/OFF behaviour following excitation to ¹ππ* (S₁) state. The fluorescence switching behaviour can be realized by (i) “change in the intermolecular structure, (ii) change in the position of fluorine substitution and (iii) change in the hydrogen bonding partner or a combination thereof. Experiments indicate that the ≡C−H⋅⋅⋅X (X=O, N) hydrogen bonding with the acetylenic group plays a pivotal role in this switching behaviour. Intriguingly, weaker ≡C−H⋅⋅⋅X hydrogen bonding leads to fluorescence OFF state, which is turned ON by stronger hydrogen bonding. The observed fluorescence this switching behaviour is rationalized on the basis of a phenomenological model which suggests a coupling between the initially excited S₁ state and a dark S_n state in the Franck-Condon region with limited window controlled by the ≡C−H⋅⋅⋅X hydrogen bonding as a crucial parameter. Such fluorescence switching behaviour in hydrogen-bonded complexes is unprecedented and these intriguing results hopefully will stimulate theoreticians to test ′state of the art′ theories to explain these observations in a consistent manner.     

An Easy Access to Organic Salt‐Based Stimuli‐Responsive and Multifunctional Supramolecular Hydrogels

By exploiting orthogonal hydrogen bonding involving supramolecular synthons and hydrophobic/hydrophilic interactions, a new series of simple organic salt based hydrogelators derived from pyrene butyric acid and its β‐alanine amide derivative, and various primary amines has been achieved. The hydrogels were characterised by microscopy, table‐top rheology and dynamic rheology. FTIR, variable‐temperature ¹H NMR and emission spectroscopy established the role of various supramolecular interactions such as hydrogen bonding and π–π stacking in hydrogelation. Single‐crystal X‐ray diffraction (SXRD) studies supported the conclusion that orthogonal hydrogen bonding involving amide–amide and primary ammonium monocarboxylate (PAM) synthons indeed played a crucial role in hydrogelation. The hydrogels were found to be stimuli‐responsive and were capable of sensing ammonia and adsorbing water‐soluble dye (methylene blue). All the hydrogelators were biocompatible (MTT assay in RAW 264.7 cells), indicating their suitability for use in drug delivery.