Highly Controllable Ring–Chain Equilibrium in Quadruply Hydrogen Bonded Supramolecular Polymers

Organic-Cation Modulated Assembly Behaviors of a Ureidopyrimidone-Grafting Cluster

Ureidopyrimidone (UPy) is an important building block for constructing functional supramolecular polymers and soft materials based on their characteristic quadruple hydrogen bonds. While the evidence from the single-crystal X-ray diffraction data for the existence of linear hydrogen bonding has still been absent up to now. To obtain the crystals of UPy-containing molecules with high quality, enhanced rigidity and crystallinity are expected. Herein, an inorganic Anderson-Evans type cluster [Mn(OH₎₆Mo₆O₁₈]^3-, which can provide suitable stiffness and charge, is used as a linker to covalently anchor two UPy units. The prepared organic-inorganic polyanion with three negative charges has a linear architecture, which is prone to form an infinite one-dimensional structure based on the supramolecular forces. The results indicate that the combination models of UPy units can be conveniently modulated by organic counter cations with different sizes, and therefore three unreported models are observed under various conditions. The present study gives a unique understanding of the intermolecular interactions in UPy-based supramolecular polymers and also provides a simple tuning method, which benefits the construction of functional materials and the adjustment of their properties.

The Story of the Little Blue Box: A Tribute to Siegfried Hünig

The tetracationic cyclophane, cyclobis(paraquat-p-phenylene), also known as the little blue box, constitutes a modular receptor that has facilitated the discovery of many host-guest complexes and mechanically interlocked molecules during the past 35 years. Its versatility in binding small π-donors in its tetracationic state, as well as forming trisradical tricationic complexes with viologen radical cations in its doubly reduced bisradical dicationic state, renders it valuable for the construction of various stimuli-responsive materials. Since the first reports in 1988, the little blue box has been featured in over 500 publications in the literature. All this research activity would not have been possible without the seminal contributions carried out by Siegfried Hünig, who not only pioneered the syntheses of viologen-containing cyclophanes, but also revealed their rich redox chemistry in addition to their ability to undergo intramolecular π-dimerization. This Review describes how his pioneering research led to the design and synthesis of the little blue box, and how this redox-active host evolved into the key component of molecular shuttles, switches, and machines.

A Review on Synthesis Methods of Phyllosilicate- and Graphene-Filled Composite Hydrogels

This review discusses, in brief, the various synthetic methods of two widely-used nanofillers; phyllosilicate and graphene. Both are 2D fillers introduced into hydrogel matrices to achieve mechanical robustness and water uptake behavior. Both the fillers are inserted by physical and chemical gelation methods where most of the chemical gelation, i.e., covalent approaches, results in better physical properties compared to their physical gels. Physical gels occur due to supramolecular assembly, van der Waals interactions, electrostatic interactions, hydrophobic associations, and H-bonding. For chemical gelation, in situ radical triggered gelation mostly occurs.

Engineering Supramolecular Polymer Conformation for Efficient Carbon Nanotube Sorting

Supramolecular polymer sorting is a promising approach to separating single-walled carbon nanotubes (CNTs) by electronic type. Unlike conjugated polymers, they can be easily removed from the CNTs after sorting by breaking the supramolecular bonds, allowing for isolation of electronically pristine CNTs as well as facile recycling of the sorting polymer. However, little is understood about how supramolecular polymer properties affect CNT sorting. Herein, chain stoppers are used to engineer the conformation of a supramolecular sorting polymer, thereby elucidating the relationship between sorting efficacy and polymer conformation. Through NMR and UV-vis spectroscopy, small-angle X-ray scattering (SAXS), and thermodynamic modeling, it is shown that this supramolecular polymer exhibits ring-chain equilibrium, and that this equilibrium can be skewed toward chains by the addition of chain stoppers. Furthermore, by controlling the stopper-monomer ratio, the sorting yield can be doubled from 7% to 14% without compromising the semiconducting purity (>99%) or properties of sorted CNTs.

Reversible hydrogen-bonded polymerization regulated by allosteric metal templation

A stable quadruple hydrogen bonded cyclic dimer assisted by metal templation was successfully self-assembled and its reversible transformation to supramolecular polymer was investigated.

Ring-opening supramolecular polymerization controlled by orthogonal non-covalent interactions

The π–π interaction has been successfully utilized to orthogonally regulate the supramolecular polymerization driven by quadruple hydrogen bonding.

Guidelines for the assembly of hydrogen-bonded macrocycles

This article highlights selected examples on the synthesis of hydrogen-bonded macrocycles from ditopic molecules and analyze the main factors, often interrelated, that influence the equilibrium between ring and chain species.

Biomimetic folding of small organic molecules driven by multiple non-covalent interactions

The supramolecular self-folding of UPy-based monomers with low molecular weight driven by multiple non-covalent interactions has been developed.

Supramolecular crowns: a new class of cyclic hydrogen-bonded cavitands

A novel design of highly preorganized bicyclic monomers, based on quadruple hydrogen bonding motifs, is proposed to access noncovalent cavitands with large internal volumes and interesting shapes.

Photoresponsive supramolecular polymers based on quadruple hydrogen-bonding and a photochromic azobenzene motif

A photoresponsive quadruple hydrogen-bonded supramolecular polymer was constructed using photochromic azobenzene and ureidopyrimidinone motifs.

Supramolecular self-assemblies for bacterial cell agglutination driven by directional charge-transfer interactions

Two supramolecular amphiphiles are fabricated through directional charge-transfer interactions, which self-assemble into nanofibers and nanoribbons. Due to the existence of galactose on their surface, these self-assemblies act as a cell glue to agglutinate E. coli, benefiting from multivalent interactions.

An ATP/ATPase responsive supramolecular fluorescent hydrogel constructedviaelectrostatic interactions between poly(sodiump-styrenesulfonate) and a tetraphenylethene derivative

We report a supramolecular fluorescent hydrogel based on poly(sodiump-styrenesulfonate) and a tetraphenylethene derivative.

Intramolecular Hydrogen Bonding Involving Organic Fluorine: NMR Investigations Corroborated by DFT-Based Theoretical Calculations

The combined utility of many one and two dimensional NMR methodologies and DFT-based theoretical calculations have been exploited to detect the intramolecular hydrogen bond (HB) in number of different organic fluorine-containing derivatives of molecules, viz. benzanilides, hydrazides, imides, benzamides, and diphenyloxamides. The existence of two and three centered hydrogen bonds has been convincingly established in the investigated molecules. The NMR spectral parameters, viz., coupling mediated through hydrogen bond, one-bond NH scalar couplings, physical parameter dependent variation of chemical shifts of NH protons have paved the way for understanding the presence of hydrogen bond involving organic fluorine in all the investigated molecules. The experimental NMR findings are further corroborated by DFT-based theoretical calculations including NCI, QTAIM, MD simulations and NBO analysis. The monitoring of H/D exchange with NMR spectroscopy established the effect of intramolecular HB and the influence of electronegativity of various substituents on the chemical kinetics in the number of organic building blocks. The utility of DQ-SQ technique in determining the information about HB in various fluorine substituted molecules has been convincingly established.

Supramolecular Helical Nanofibers Formed by Achiral Monomers and Their Reversible Sol-Gel Transition

Well-defined supramolecular helical nanofibers have been constructed by a rationally designed achiral monomer in aqueous solution based on the 1:2 host-guest combination between cucurbit[8]uril and a 4,4'-bipyridin-1-ium chloride (BPY⁺ ) salt derivative. The formed nanostructures could be adjusted by varying the concentration of monomer from helical nanofibers to a pH-responsive hydrogel.

Controllable Supramolecular Polymerization Promoted by Host-Enhanced Photodimerization

In this letter, we report a new method of controllable supramolecular polymerization, taking advantage of host-enhanced photodimerization. The low-molecular-weight supramolecular oligomers were formed by noncovalent complexation between cucurbit[8]urils (CB[8]) and the bifunctional monomers (DBN) with Brooker's merocyanine moiety (MOED) on either end. Interestingly, when irradiated with UV light, the supramolecular oligomers could transform into supramolecular polymers with high molecular weight. The molecular weight of supramolecular polymers could be controlled by varying the irradiation time. It is highly anticipated that this work can enrich the methods on the modulation of supramolecular polymerization.

Intramolecular hydrogen bonds involving organic fluorine in the derivatives of hydrazides: an NMR investigation substantiated by DFT based theoretical calculations

The rare examples of intramolecular hydrogen bonds (HB) of the type the N-H∙∙∙F-C, detected in a low polarity solvent in the derivatives of hydrazides, by utilizing one and two-dimensional solution state multinuclear NMR techniques, are reported. The observation of through-space couplings, such as, (1h)JFH, and (1h)JFN, provides direct evidence for the existence of intra-molecular HB. Solvent induced perturbations and the variable temperature NMR experiments unambiguously establish the presence of intramolecular HB. The existence of multiple conformers in some of the investigated molecules is also revealed by two dimensional HOESY and (15)N-(1)H HSQC experiments. The (1)H DOSY experimental results discard any possibility of self or cross dimerization of the molecules. The derived NMR experimental results are further substantiated by Density Function Theory (DFT) based Non Covalent Interaction (NCI), and Quantum Theory of Atom in Molecule (QTAIM) calculations. The NCI calculations served as a very sensitive tool for detection of non-covalent interactions and also confirm the presence of bifurcated HBs.

Supramolecular Construction of Multifluorescent Gels: Interfacial Assembly of Discrete Fluorescent Gels through Multiple Hydrogen Bonding

Multifluorescent supramolecular gels with complex structures are constructed from discrete fluorescent gels, which serve as the building blocks, through hydrogen bonding interactions at interfaces. The multifluorescent gel can realize rapid healing within only ≈100 s.

A supramolecular brush polymer via the self-assembly of bridged tris(β-cyclodextrin) with a porphyrin derivative and its magnetic resonance imaging

Accurate imaging of soft tissues is one of the ultimate goals in biomedical imaging. Different imaging modalities can improve their disadvantages, and promote the imaging ability. However, once an imaging agent has been prepared, it is usually hard to adjust it according to the actual needs. Herein, we developed a supramolecular brush polymer (SBP) as a versatile imaging agent platform. The SBP platform (SBPP) is constructed by the intermolecular inclusion complexation of bridged tris(β-cyclodextrin) (1) with Mn(iii)-porphyrin-bearing poly(ethylene glycol) (PEG) side chains (Mn(iii)-TPP), and can further bind other functional groups by host-guest interactions of cyclodextrin and adamantine. The SBPP is characterized by UV/vis absorption spectroscopy, NMR, dynamic light scattering (DLS), atomic force microscopy (AFM) and transmission electron microscopy (TEM). We demonstrated that this SBPP not only has no cellular toxicity against NIH 3T3 cells in in vitro cell experiments, but it also shows an efficient enhanced T₁ relaxivity in in vitro MR imaging experiments. When used as multifunctional imaging agents, different imaging probes and/or targeting agents can be introduced to this SBPP as needed through simple host-guest interactions. In in vitro imaging experiments, it shows accurate imaging of different kinds of cancer cells by choosing on-demand targeting agents. These results suggest a promising strategy for engineering multifunctional imaging agents with SBPs.

Organic fluorine involved intramolecular hydrogen bonds in the derivatives of imides: NMR evidence corroborated by DFT based theoretical calculations

The rare occurrence of intramolecular hydrogen bonds (HBs) of the type N–H⋯F–C is detected in the derivatives of imides in a low polarity solvent by using multi-dimensional and multinuclear NMR experiments.

The construction of supramolecular polymers through anion bridging: from frustrated hydrogen-bonding networks to well-ordered linear arrays

The construction of supramolecular polymers has been realized by converting random hydrogen-bonding networks into well-ordered linear hydrogen-bonding arrays through an anion-bridging strategy.

A fluorescent supramolecular polymer with aggregation induced emission (AIE) properties formed by crown ether-based host–guest interactions

A fluorescent supramolecular polymer with aggregation induced emission properties was constructed and applied in the detection of Pd²⁺ ions.

A pillar[5]arene-fused cryptand: from orthogonal self-assembly to supramolecular polymer

A supramolecular polymer based on a novel pillar[5]arene-fused cryptand host was successfully constructed by the orthogonal self-assembly of two host–guest interactions.

Shear-modulus investigations of monohydroxy alcohols: evidence for a short-chain-polymer rheological response

Liquids composed of small-molecule monohydroxy alcohols are demonstrated to display rheological behavior typical for oligomeric chains. This observation was made possible by rheological experiments in which more than seven decades in frequency and more than five decades on the mechanical modulus scale are covered. The singly hydrogen-bonded monohydroxy alcohols were chosen because they display significant, but surprisingly poorly understood effects of intermolecular association. Based on the present shear study, one can apply theoretical concepts of polymer science to understand the anomalous physical behavior of a wide range of hydrogen-bonded liquids.