Highly fluorescent supramolecular gels with chirality transcription through hydrogen bonding

A highly fluorescent organogel with transparency was formed through a hydrogen (H)-bonding interaction between a non-fluorescent and achiral 2-(3',5'-bis-trifluoromethyl-biphenyl-4-yl)-3-(4-pyridin-4-yl-phenyl)-acrylonitrile (CN-TFMBPPE) monomer and chiral sergeant l-tartaric acid (TA) (or d-TA), with gel formation being accompanied by a drastic fluorescence enhancement as well as chirality induction.     

Side‐chain supramolecular polymers with induced supramolecular chirality through H‐bonding interactions

Side‐chain supramolecular polymers that show columnar mesomorphism have been prepared through H‐bonding interactions between a polyvinylpyridine polymer as H‐acceptor and different H‐donors derived from benzoic acid. These compounds have been designed according to a promesogenic structure, that is, either disk‐like or banana‐like, to promote stacking and therefore the formation of columnar arrangements. IR studies confirmed the formation of H‐bonds and demonstrated that the H‐bond intensity decreases upon increasing temperature. The mesophase organizations were studied by polarized optical microscopy, differential scanning calorimetry, and X‐ray diffraction. Associations containing poly‐3‐methyl‐4‐vinylpyridine showed supramolecular optical activity, as evidenced by circular dichroism studies on thin films. It is proposed that these supramolecular polymers adopt a helical structure that can be biased toward a given handedness by virtue of the configuration of the stereogenic centers in the peripheral tails of the acids. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5528–5541, 2008     

Chiral eighteen-component three-dimensional supramolecular entities stabilized by the hydrogen bonding and coordination interactions

A new class of chiral eighteen-component three-dimensional supramolecular entities has been assembled in toluene and chloroform from twelve zinc porphyrin-appended 2-(ethylamino)- pyrimido[4,5-b][1,8]naphthyridin-4(3H)-one monomers and six chiral bipyridyl compounds. The heterocyclic segments form two C₆-symmetric cyclic hexamers, which are stabilized by a well-established DDA-AAD hydrogen bonding motif, while the six chiral bispyridine ligands are coordinated to the corresponding zinc porphyrin units to give the two-layered architectures. The structures have been characterized by the ¹H NMR, UV-vis and circular dichroism experiments, which also reveals that, when the concentration of the monomers is high enough, the chiral supramolecular entity can be formed exclusively.     

Complementary quadruple hydrogen bonding in supramolecular copolymers

This paper describes a supramolecular copolymer based on quadruple hydrogen bonding between self-complementary ureido-pyrimidinones and complementary 2,7-diamido-1,8-naphthyridines. In contrast to previously reported polymer systems solely based on complementary hydrogen-bonding units, these polymers retain a high DP over a broad composition range.     

Dipolar interactions and hydrogen bonding in supramolecular aggregates: understanding cooperative phenomena for 1st hyperpolarizability

Weak intermolecular forces like dipolar interactions and hydrogen-bonding lead to a variety of different packing arrangements of molecules in crystals and self-assemblies. Such differences in the arrangements change the extent of excitonic splitting and excitation spectra in the multichromophore aggregates. In this tutorial review, the role of such interactions in fine tuning the linear and 1st non-linear optical (NLO) responses in molecular aggregates are discussed. The non-additivity of these optical properties arise specifically due to such cooperative interactions. Calculations performed on dimers, trimers and higher aggregates for model systems provide insights into the interaction mechanisms and strategies to enhance the 1st hyperpolarizabilities of pi-conjugated molecular assemblies. Flexible dipole orientations in the alkane bridged chromophores show odd-even variations in their second-harmonic responses that are explained through their dipolar interactions in different conformations. Parameters for the optical applications of molecules arranged in constrained geometry, like in Calix[n]arene, have been elucidated. We also highlight the recent developments in this field of research together with their future prospects.     

New supramolecular architectures based on hydrogen bonding

Heterocyclic compounds containing two and three adjacent hydrogen bond donor and acceptor sites in all possible arrangements were synthesized (see generalized structures shown below) to study and use their “base-pairing” capabilities. With two adjacent donor and acceptor groups there are three possible arrangements and these form two types of complexes (DA·AD and AA·DD). Three adjacent hydrogen bond donor and acceptor sites can be arranged in six different ways and these form three different complexes (ADA·DAD, AAD·DDA, and AAA·DDD).     

Self-healing and shape memory functions exhibited by supramolecular liquid-crystalline networks formed by combination of hydrogen bonding interactions and coordination bonding

We here report a new approach to develop self-healing shape memory supramolecular liquid-crystalline (LC) networks through self-assembly of molecular building blocks via combination of hydrogen bonding and coordination bonding. We have designed and synthesized supramolecular LC polymers and networks based on the complexation of a forklike mesogenic ligand with Ag⁺ ions and carboxylic acids. Unidirectionally aligned fibers and free-standing films forming layered LC nanostructures have been obtained for the supramolecular LC networks. We have found that hybrid supramolecular LC networks formed through metal–ligand interactions and hydrogen bonding exhibit both self-healing properties and shape memory functions, while hydrogen-bonded LC networks only show self-healing properties. The combination of hydrogen bonds and metal–ligand interactions allows the tuning of intermolecular interactions and self-assembled structures, leading to the formation of the dynamic supramolecular LC materials. The new material design presented here has potential for the development of smart LC materials and functional LC membranes with tunable responsiveness.

New supramolecular hybrid liquid-crystalline networks exhibiting self-healing and shape memory properties are developed by self-assembly of small components through hydrogen bonding interactions and coordination bonding.     

Tetrathiafulvalene-hydroxyamides and -oxazolines: hydrogen bonding, chirality, and a radical cation salt

Racemic and enantiopure ethylenedithio-tetrathiafulvalene (EDT-TTF) derivatives featuring β-hydroxyamide or oxazoline (OX) groups bearing methyl or isopropyl substituents have been synthesized starting from the corresponding amino alcohols. Crystal structure analysis shows in the case of the racemic methyl-β-hydroxyamide donor the development of a unique hydrogen bond network, characterized by short CO?H-O and N-H?O-H intermolecular distances. The enantiopure (S)-EDT-TTF-methyl-OX crystallizes in the monoclinic non-centrosymmetric space group P2₁, whereas the isopropyl counterparts, (R)-and (S)-EDT-TTF-isopropyl-OX, crystallize in the orthorhombic non-centrosymmetric space group P2₁2₁2₁. All of them adopt a s-trans conformation in which TTF and oxazoline units are coplanar. Electrocrystallization experiments with the racemic EDT-TTF-methyl-OX, in the presence of (nBu₄)₂Mo₆Cl₁₄ as supporting electrolyte, afford a radical cation salt, formulated as [(±)-EDT-TTF-methyl-OX]₂Mo₆Cl₁₄, in which the donors associate in strong dimers, which further stack along the b direction to form quasi-homochiral helix-like ribbons.     

Self-assembly of supramolecular complexes based on hydrogen bonding

Self-assembly of hydrogen-bonding recognition complexes—2.5-bis(alkylamino)-1,4-benzoquinones were studied, and thermotropic liquid crystalline behavior of 2.5-bis(dodecylamino)-1,4-benzoquinone was further investigated. The obtained results showed that a ribbon-like backbone in this system plays an important role in keeping the layered supramolecular structure.     

Helical supramolecular aggregates based on ureidopyrimidinone quadruple hydrogen bonding

A series of mono- and bifunctional compounds 2-7, based on the ureido pyrimidinone quadruple hydrogen bonding unit, was prepared to study the mode of aggregation of these compounds in the bulk and in solution. Compounds 2-7 exhibit thermotropic liquid crystalline properties, as evidenced by differential scanning calorimetry and optical polarization microscopy. The presence of an ordered hexagonal discotic (D(ho)) phase of 2 a was confirmed by X-ray diffraction on an aligned sample. In chloroform, the bifunctional compounds form cyclic dimers at millimolar concentrations, and these dimers exist in equilibrium with linear species above a critical concentration, which may be from 6 mM to greater than 260 mM, depending on the structure of the spacer. Circular dichroism measurements in chloroform did not show a Cotton effect. Dodecane solutions of compounds 3, 4 b, and 7 b display a Cotton effect at the absorption band of the phenyl-pyrimidinone unit. Amplification of chirality was observed in mixtures of 7 a and 7 b, but not in mixtures of 4 a and 4 b, indicating that 7 a and 7 b form mixed polymeric aggregates with a helical architecture in dodecane solution, whereas 4 a and 4 b do not. The Cotton effect is lost upon increasing the temperature. Half of the helicity is lost at 25 degrees C for 3 and at 60 degrees C for 4 b, suggesting that 3, bearing the shorter spacer, forms less stable columns than 4 b. Compound 7 b loses half of its helicity at 45 degrees C. Compounds 2 b, 5, and 6 do not exhibit helical organization, as evidenced by the absence of Cotton effects.     

Interplay between anion-pi and hydrogen bonding interactions

The interplay between two important noncovalent interactions involving aromatic rings is studied by means of high level ab initio calculations. They demonstrate that synergistic effects are present in complexes where anion-pi and hydrogen bonding interactions coexist. These synergistic effects have been studied using the "atoms-in-molecules" theory and the Molecular Interaction Potential with polarization partition scheme. The present study examines how these two interactions mutually influence each other.     

The contribution of complementary hydrogen bonding to supramolecular structure

Two different types of complementary hydrogen bonding contribute to the formation and temperature dependent behavior of a pseudo[2]rotaxane dimer.     

Au3-to-Ag3 coordinate-covalent bonding and other supramolecular interactions with covalent bonding strength

An efficient strategy for designing charge-transfer complexes using coinage metal cyclic trinuclear complexes (CTCs) is described herein. Due to opposite quadrupolar electrostatic contributions from metal ions and ligand substituents, [Au(μ-Pz-(i-C₃H₇)₂)]₃·[Ag(μ-Tz-(n-C₃F₇)₂)]₃ (Pz = pyrazolate, Tz = triazolate) has been obtained and its structure verified by single crystal X-ray diffraction – representing the 1^st crystallographically-verified stacked adduct of monovalent coinage metal CTCs. Abundant supramolecular interactions with aggregate covalent bonding strength arise from a combination of M–M′ (Au → Ag), metal–π, π–π interactions and hydrogen bonding in this charge-transfer complex, according to density functional theory analyses, yielding a computed binding energy of 66 kcal mol⁻¹ between the two trimer moieties – a large value for intermolecular interactions between adjacent d¹⁰ centres (nearly doubling the value for a recently-claimed Au(i) → Cu(i) polar-covalent bond: Proc. Natl. Acad. Sci. U.S.A., 2017, 114, E5042) – which becomes 87 kcal mol⁻¹ with benzene stacking. Surprisingly, DFT analysis suggests that: (a) some other literature precedents should have attained a stacked product akin to the one herein, with similar or even higher binding energy; and (b) a high overall intertrimer bonding energy by inferior electrostatic assistance, underscoring genuine orbital overlap between M and M′ frontier molecular orbitals in such polar-covalent M–M′ bonds in this family of molecules. The Au → Ag bonding is reminiscent of classical Werner-type coordinate-covalent bonds such as H₃N: → Ag in [Ag(NH₃)₂]⁺, as demonstrated herein quantitatively. Solid-state and molecular modeling illustrate electron flow from the π-basic gold trimer to the π-acidic silver trimer with augmented contributions from ligand-to-ligand’ (LL′CT) and metal-to-ligand (MLCT) charge transfer.

A stacked Ag₃–Au₃ bonded (66 kcal mol⁻¹) complex obtained crystallographically exhibits charge-transfer characteristics arising from multiple cooperative supramolecular interactions.     

Chiral helicity induced by hydrogen bonding and chirality of podand histidyl moieties

[structure: see text] The single-crystal X-ray structure determination of N,N'-bis[(S)-(+)-1-methoxycarbonyl-2-(4-imidazolyl)ethyl]-2,6-pyridinedicarboxamide (L-BHisPA) and the D-isomer (D-BHisPA) derived from the corresponding chiral histidine revealed a left- and right-handed helical conformation, respectively, through intramolecular hydrogen bonding and chirality of the podand histidyl moieties. Furthermore, each helical molecule is connected by continuous intermolecular hydrogen bonds to afford a left- or right-handed helical assembly, respectively, in the crystal packing.     

The novel hydrogen bonding motifs and supramolecular patterns in 2,4-diaminopyrimidine-nitrobenzoate complexes

The crystal structures of the hydrogen-bonded, 1:1 molecular complexes of nitro (ortho, meta and para) benzoic acids with two 2,4-diaminopyrimidine derivatives (trimethoprim and pyrimethamine) have been investigated in detail (1-5). In all the crystal structures except pyrimethamine o-nitrobenzoate (3), the carboxylate group of the respective anions interacts with the protonated trimethoprim or pyrimethamine moiety in a linear fashion through a pair of N-H?O hydrogen bonds to form a cyclic hydrogen-bonded motif. This cyclic hydrogen-bonded motif is self-organized in different ways to get the novel types of hydrogen bonding motifs and supramolecular patterns. In the crystal structure of pyrimethamine o-nitrobenzoate (3), the chelating type of hydrogen bonding motif is self-organized to get a helical supramolecular pattern. In the crystal structures of both pyrimethamine m-nitrobezoate (4) and pyrimethamine p-nitrobenzoate (5), a novel type of an alternate arrangement of DADA (D represents donor and A represents acceptor) and DDAA arrays is present, resulting in the formation of hydrogen-bonded ladders.     

Insights into hydrogen bonding and stacking interactions in cellulose

In this quantum chemical study, we explore hydrogen bonding (H-bonding) and stacking interactions in different crystalline cellulose allomorphs; namely, cellulose I(β) and cellulose III(I). We consider a model system representing a cellulose crystalline core made from six cellobiose units arranged in three layers with two chains per layer. We calculate the contributions of intrasheet and intersheet interactions to the structure and stability in both cellulose I(β) and cellulose III(I) crystalline cores. Reference structures for this study were generated from molecular dynamics simulations of water-solvated cellulose I(β) and III(I) fibrils. A systematic analysis of various conformations describing different mutual orientations of cellobiose units is performed using the hybrid density functional theory with the M06-2X with 6-31+G(d,p) basis sets. We dissect the nature of the forces that stabilize the cellulose I(β) and cellulose III(I) crystalline cores and quantify the relative strength of H-bonding and stacking interactions. Our calculations demonstrate that individual H-bonding interactions are stronger in cellulose I(β) than in cellulose III(I); however, the total H-bonding contribution to stabilization is larger in cellulose III(I) because of the highly cooperative nature of the H-bonding network. In addition, we observe a significant contribution from cooperative stacking interactions to the stabilization of cellulose I(β). The theory of atoms-in-molecules (AIM) has been employed to characterize and quantify these intermolecular interactions. AIM analyses highlight the role of nonconventional CH···O H-bonding in the cellulose assemblies. Finally, we calculate molecular electrostatic potential maps for the cellulose allomorphs that capture the differences in chemical reactivity of the systems considered in our study.     

The role of hydrogen bonding in water-metal interactions

The hydrogen bond interaction between water molecules adsorbed on a Pd <111> surface, a nucleator of two dimensional ordered water arrays at low temperatures, is studied using density functional theory calculations. The role of the exchange and correlation density functional in the characterization of both the hydrogen bond and the water-metal interaction is analyzed in detail. The effect of non local correlations using the van der Waals density functional proposed by Dion et al. [M. Dion, H. Rydberg, E. Schr?der, D. C. Langreth and B. I. Lundqvist, Phys. Rev. Lett., 2004, 92, 246401] is also studied. We conclude that the choice of this potential is critical in determining the cohesive energy of water-metal complexes. We show that the interaction between water molecules and the metal surface is as sensitive to the density functional choice as hydrogen bonds between water molecules are. The reason for this is that the two interactions are very similar in nature. We make a detailed analogy between the water-water bond in the water dimer and the water-Pd bond at the Pd <111> surface. Our results show a strong similarity between these two interactions and based on this we describe the water-Pd bond as a hydrogen bond type interaction. These results demonstrate the need to obtain an accurate and reliable representation of the hydrogen bond interaction in density functional theory.     

One-pot synthesis of supramolecular polymer containing quadruple hydrogen bonding units

A facile, efficient technique was built to synthesize a supramolecular material containing quadruple hydrogen bonding sites. The current approach presented here involves a single-step reaction between the amine of precursor, e.g. methyl isocytosine (MIC) and the epoxy group of polymer, e.g. poly(ethylene glycol diglycidyl ether) (PEG DGE, M_n = 526 g/mol, as verified using ¹H NMR and FT-IR spectroscopy. Wide angle X-ray scattering (WAXS), UV/visible spectroscopy and differential scanning calorimeter (DSC) clearly show that the product is not a simple mixture of two components, but the supramolecular polymer containing quadruple hydrogen bonding sites. Complex melt viscosities reveal that mechanical properties of the supramolecular polymer are enhanced by more than 10⁴ times compared to the pristine low molecular weight polymer, giving rise to the significant change of physical state from liquid to solid. Current approach also illustrates an advantageous route because it does not need the selective use of monofunctionalized precursor and not produce a dead, difunctionalized precursor.