Self-complementary Hydrogen Bonds Research Articles

Self-assembled Janus base nanotubes: chemistry and applications.

Janus base nanotubes are novel, self-assembled nanomaterials. Their original designs were inspired by DNA base pairs, and today a variety of chemistries has developed, distinguishing them as a new family of materials separate from DNA origami, carbon nanotubes, polymers, and lipids. This review article covers the principal examples of self-assembled Janus base nanotubes, which are driven by hydrogen-bond and π-π stacking interactions in aqueous environments. Specifically, self-complementary hydrogen bonds organize molecules into ordered arrays, forming macrocycles, while π-π interactions stack these structures to create tubular forms. This review elucidates the molecular interactions that govern the assembly of nanotubes and advances our understanding of nanoscale self-assembly in water.

High-performance polyurethane nanocomposites based on UPy-modified cellulose nanocrystals

Densely H-bonding assemblies are the key strategy found by nature to enhance the rupture strength of natural polymers without sacrificing their toughness, such as spider silk, while it still remains a great challenge using such intriguing strategy to prepare high-performance synthesized polymer or biopolymer enhanced polymer nanocomposites. To address this challenge, we report here a bio-inspired strategy using densely H-bonding assembly for facile fabrication of high performance polyurethane (PU) nanocomposites reinforced by hydroxyl-rich cellulose nanocrystals (CNCs) functionalized with 2-ureido-4-[1 H]-pyrimidinone motifs (CNC-UPy) containing self-complementary hydrogen bonds. These PU/CNC-UPy nanocomposites showed remarkably improved mechanical strength without sacrificing the elongation at break and toughness compared to pure PU matrix. Differential scanning calorimetry(DSC) results indicated that CNC-UPy could induce the formation of long range ordering of hard segment domains, due to the strong hydrogen bonding interactions between UPy motifs attached on CNC-UPy and PU matrix. Furthermore, wide angle X-ray diffraction (WAXD) measurements demonstrated that the strain-induced crystallization (SIC) was enhanced significantly by introducing CNC-UPy into PU, leading to a large stress at break. The enhanced interfacial H-bonding interactions between CNC and PU though UPy anchoring could overcome the inherent trade-off between the stiffness and toughness of polymer composites. The proposed bio-inspired strategy using densely H-bonding assembly will be with more extensive application prospects.

Crystal structure of the co-crystal salt 2-amino-6-bromo-pyridinium 2,3,5,6-tetra-fluoro-benzoate.

The asymmetric unit of the co-crystal salt 2-amino-6-bromo-pyridinium 2,3,5,6-tetra-fluoro-benzoate, C5H6BrN2 +·C7HF4O2 -, contains one pyridinium cation and one benzoate anion. In the crystal, the amino-pyridinium cationic unit forms two hydrogen bonds to the benzoate oxygen atoms in an R 2 2(8) motif. Two pyridinium benzoate units are hydrogen bonded through self-complementary hydrogen bonds between the second amine hydrogen and a carboxyl-ate O with a second R 2 2(8) motif to form a discrete hydrogen-bonded complex containing two 2-amino-6-bromo-pyridinium moieties and two 2,3,5,6-tetra-fluoro-benzoate moieties. The 2-amino-6-bromo-pyridinium moieties π-stack in a head-to-tail mode with a centroid-centroid separation of 3.7227 (12) Å and adjacent tetra-fluoro-benzoates also π-stack in a head-to-tail mode with a centroid-centroid separation of 3.6537 (13) Å.

Supramolecular Networks from Block Copolymers Based on Styrene and Isoprene Using Hydrogen Bonding Motifs-Part 1: Synthesis and Characterization.

The combination of controlled anionic polymerization and subsequent introduction of hydrogen bonding groups was established to form thermo-reversible, supramolecular networks. Several polyisoprene-block-polystyrene-block-polyisoprene (ISI) copolymers—with polystyrene (PS) as the main block, and consequently giving the decisive material characteristics—were synthesized. The novel modification approach to post-functionalize the polyisoprene (PI) end-blocks and to introduce different motifs, which are able to form self-complementary hydrogen bonds, was attained. In the first step, hydroxylation was accomplished using 9-borabicyclo[3.3.1]nonane. Starting from the hydroxylated polymer, esterification with succinic anhydride was implemented to form an ester group with carboxylic end-group (-O-CO-CH2-CH2-COOH). In a second approach, 1,1’-carbonyldiimidazole was used as coupling agent to introduce various types of diamines (diethylenetriamine, triethylentetramine, and 2,6-diaminopyridine) to prepare urethane groups with amine end-group (-O-CO-NH-R-NH2). 1H NMR spectroscopy was used to confirm the successful synthesis and to calculate the degree of functionalization Df. Differential scanning calorimetry (DSC) showed a difference of the glass transition temperature Tg between unfunctionalized and functionalized block copolymers, but no greater influence between the different types of modification, and thus, on the Tg of the PS block. In temperature dependent FTIR spectroscopy, reversible processes were observed.

Anions Stabilize Each Other inside Macrocyclic Hosts.

Contrary to the simple expectations from Coulomb's law, Weinhold proposed that anions can stabilize each other as metastable dimers, yet experimental evidence for these species and their mutual stabilization is missing. We show that two bisulfate anions can form such dimers, which stabilize each other with self-complementary hydrogen bonds, by encapsulation inside a pair of cyanostar macrocycles. The resulting 2:2 complex of the bisulfate homodimer persists across all states of matter, including in solution. The bisulfate dimer's OH⋅⋅⋅O hydrogen bonding is seen in a 1 H NMR peak at 13.75 ppm, which is consistent with borderline-strong hydrogen bonds.

Bidirectional Singlet and Triplet Energy Transfer via the 2-Ureido-4[1H]-pyrimidinone Quadruple Hydrogen-Bonded Module

The bidirectional singlet–singlet and triplet–triplet energy transfer processes were observed for the first time within a noncovalent hydrogen-bonded module. For this purpose, 2-ureido-4[1H]-pyrimidinone quadruple hydrogen-bonds (UPy) functionalized BF2-chelated dipyrromethene (BODIPY-UPy) and iodinated BODIPY (I-BODIPY-UPy) were synthesized. These molecules formed energy donor–acceptor assembly through quadruple self-complementary hydrogen bonds, which demonstrated interesting photophysical properties. Spectroscopic studies in toluene solution revealed that selective excitation of BODIPY-UPy in the assembly resulted in efficient intra-assembly singlet energy transfer from excited BODIPY-UPy to I-BODIPY-UPy. This was followed by intersystem crossing of I-BODIPY-UPy from S1 to T1 and the backward triplet energy transfer from the I-BODIPY to BODIPY part. Time-resolved transient absorption spectroscopy confirmed that the triplet excited-state energy was distributed on both chromophores in the assembly. Density functional theory (DFT) calculations further validated the feasibility of energy transfer as well as two degenerate triplet states in the assembly. The present studies revealed that the bidirectional singlet–singlet and triplet–triplet energy transfer processes could be manipulated through the noncovalent quadruple hydrogen bonds. Studies on such a process in supramolecular assembly are of considerable importance in the elucidation of their possible function in natural photosystems and inspire applications in various fields such as luminescent materials, optoelectronic devices, photocatalysis, and photodynamic therapy.

Reinforcement of nanostructured organogels by hydrogen bonds

Reinforcing a micellar organogel by self-complementary hydrogen bonds.

Titin-mimicking polycyclic polymers with shape regeneration and healing properties

Polycyclic polymers made from cyclic (ABC)n-multiblock-copolymers that may undergo self-complementary hydrogen bonds within the individual rings show extraordinary material properties.

Hydrogen Bonding and Electron Transfer between Dimetal Paddlewheel Compounds Containing Pendant 2-Pyridone Functional Groups

The compounds M2(TiPB)3(HDON) (TiPB = 2,4,6-triisopropylbenzoic acid; H2DON = 2,7-dihdroxy-1,8-napthyridine; M = Mo (1a) or W (1b)) and Mo2(TiPB)2(O2CCH2Cl)(HDON) (1c) which contain a pendant 2-pyridone functional group have been prepared. These compounds are capable of forming self-complementary hydrogen bonds, resulting in the formation of "dimers of dimers" ([1a-c]2) in CH2Cl2 solutions. Electrochemical studies reveal two successive one-electron redox processes for [1a-c]2 in CH2Cl2 solutions that correspond to successive oxidations of the dimetal core, indicating stabilization of the mixed-valence state. Only small changes in the value of Kc are observed upon changing the ancillary ligand or metal, implying that proton coupled mixed valency is responsible for the stabilization. Dimethylsulfoxide (DMSO) disrupts the hydrogen bonding interactions in these compounds, and a single oxidation process is observed in DMSO which shifts to lower potential as the number of HDON ligands increases. Further substitution of carboxylate ligands with HDON leads to the formation of Mo2(TiPB)2(HDON)2 (2) and Mo2(HDON)4 (3), which adopt trans-1,1 and cis-2,2 regioisomers in the solid-state. (1)H NMR spectroscopy indicates that there are at least two regioisomers present in solution for both compounds. The lowest energy transition in the electronic absorption spectra of these compounds corresponds to a M2-δ → HDON-π* transition. The electrochemical, spectroscopic and structural results were rationalized with the aid of density functional theory (DFT) calculations.

Impact of amide–amide hydrogen bonding on the stability of two nicotinamide complexes of silver(I)

The nicotinamide (pyridine-3-carboxamide, nia) complexes of silver(I), [Ag(nia)2(NO3)]·H2O (1), [Ag(nia)2(NO3)] (2), and {K[Ag(nia)2](NO3)2}n (3), were prepared and characterised by IR spectroscopy and TG/DTA thermal methods. The solid state structures of 2 and 3 were determined by single-crystal X-ray diffraction analysis. In both complexes two nicotinamide ligands are coordinated to silver(I) through the nitrogen atom of the pyridine ring in a near-linear fashion. In 2, additional coordination by two oxygen atoms of one nitrate group leads to the distorted tetrahedral coordination environment of silver(I). In 3, nitrate ions bridge potassium cations giving rise to a 2D coordination network which is further stabilised by cross-bridging of each two potassium atoms in [1 0 0] direction by complex cations, [Ag(nia)2]+. Despite different aggregation of 2 and 3 in the solid state, both complexes demonstrate quite similar thermal stability. The amide self-complementary hydrogen bonds appear to be the main driving force for establishing the crystal structures of both 2 and 3.

Triple-Shape Memory Polymers Based on Self-Complementary Hydrogen Bonding

Triple shape memory polymers (TSMPs) are a growing subset of a class of smart materials known as shape memory polymers, which are capable of changing shape and stiffness in response to a stimulus. A TSMP can change shapes twice and can fix two metastable shapes in addition to its permanent shape. In this work, a novel TSMP system comprised of both permanent covalent cross-links and supramolecular hydrogen bonding cross-links has been synthesized via a one-pot method. Triple shape properties arise from the combination of the glass transition of (meth)acrylate copolymers and the dissociation of self-complementary hydrogen bonding moieties, enabling broad and independent control of both glass transition temperature (T(g)) and cross-link density. Specifically, ureidopyrimidone methacrylate and a novel monomer, ureidopyrimidone acrylate, were copolymerized with various alkyl acrylates and bisphenol A ethoxylate diacrylate. Control of T(g) from 0 to 60 °C is demonstrated: concentration of hydrogen bonding moieties is varied from 0 to 40 wt %; concentration of the diacrylate is varied from 0 to 30 wt %. Toughness ranges from 0.06 to 0.14 MPa and is found to peak near 20 wt % of the supramolecular cross-linker. A widely tunable class of amorphous triple-shape memory polymers has been developed and characterized through dynamic and quasi-static thermomechanical testing to gain insights into the dynamics of supramolecular networks.

Synthesis and properties of thermoreversible crosslinking supramolecular polymer with weak multiple-hydrogen bonds and small chemical network sites from dimer acid, diamine and sulfonyl isocyanate

Thermoreversible crosslinking supramolecular polymers with weak hydrogen bonds were prepared from fatty dimer acids, diamines and sulfonyl isocyanate. The oligomers as backbones of supramolecular polymers have low molecular weights (5–7 repeating units). The hydrogen-bonding networks behave like elastic polymers with high rubber plateaus at high storage modulus, and have low melting temperature that is favoring the low temperature processing. The addition of sulfonyl isocyanate introduces the sulfonyl urethane groups (−O-CO-NH-SO2) that increase the diversity of self-complementary hydrogen bonds. However, the large bulk of sulfonyl groups (O = S = O) prolongs the distance of hydrogen bonds. The supromolecuar polymer with small chemical network sites has higher tensile length and Tm between the supromolecular polymers with sulfonyl groups.

A dinuclear oxo-bridged Fe(III) complex with tris(2-pyridylmethyl) amine: Structure and Hirshfeld surface analysis

A dinuclear Fe III complex [{Fe(TPA)Cl} 2O](ClO 4) 2·H 2O ( 1) where TPA is tris(2-pyridylmethyl)amine, has been synthesized and characterized by X-ray structural studies with a detailed analysis of Hirshfeld surfaces and fingerprint plots facilitating a comparison of intermolecular interactions in building different supramolecular architectures. Molecules of ( 1) are linked by self-complementary hydrogen bonds into two-dimensional framework, whose formation is readily analyzed in terms of substructures of lower dimensionality with finite zero dimensional dimeric units as the building blocks within the structure. The crystal packing is also stabilized by C–H⋯π and π–π stacking interactions and is responsible for the formation and strengthening of three dimensional supramolecular assembly. Investigation of intermolecular interactions and crystal packing via Hirshfeld surface analysis reveals that more than two-thirds of the close contacts are associated with weak interactions. The fingerprint plots demonstrate that these weak interactions are important for both local and crystal packing. A comparison of Hirshfeld surface in the complex with similar structure retrieved from the Cambridge Structural Database (CSD) has been presented.

Self-Assembly of Supramolecular Polymers from β-Strand Peptidomimetic−Poly(ethylene oxide) Hybrids

The use of hydrogen-bonding β-strand peptidomimetics for the preparation of supramolecular polymers is described here. The β-strand mimics were selected for their ability to form hydrogen bonds on only one face of the strand, allowing for controlled assembly into linear polymers. Alkyne-functionalized peptidomimetics with the capacity to form either four, six, or eight self-complementary hydrogen bonds were synthesized and conjugated to both termini of low molecular weight (MW) α,ω-diazidopoly(ethylene glycol). The assembly of these polymers into higher MW supramolecular polymers was investigated by multiangle light scattering, dynamic light scattering, and circular dichroism. It was found that the eight-hydrogen-bonding system was required for the significant formation of high MW assemblies and that the degree of assembly was dependent on the polymer concentration as well as the solvent. Thus, these peptidomimetics provide a new platform for the development of supramolecular polymers with the promise to ...

Establishing Amide···Amide Reliability and Synthon Transferability in the Supramolecular Assembly of Metal-Containing One-Dimensional Architectures

On the basis of a combination of new structural data (eleven single-crystal structure determinations are presented) and information from the Cambridge Structural Database, it has been shown that self-complementary hydrogen-bond based amide...amide dimers can be relied upon as effective supramolecular synthons for the assembly and organization of acac- and paddle-wheel complexes of a variety of metal(II) ions. The targeted molecular recognition event and intended extended one-dimensional motif appear with a supramolecular yield of 78% (a total of 28 structures were examined). Despite the fact that the hydrogen bonds that give rise to the R2(2)(8) motif can be disrupted by both carboxylate- and acac-ligands, as well as by solvent molecules, they remain remarkably resilient and therefore represent useful synthetic tools in inorganic crystal engineering.

Controlled Ring-Opening Polymerization Initiated via Self-Complementary Hydrogen-Bonding Units

Controlled anionic ring-opening polymerization of ϵ-caprolactone (ϵ-CL) in toluene using self-complementary quadruple hydrogen bonding array 2-ureido-4[1H]-pyrimidinone (UPy)-functionalized initiators with stannous(II) octanoate has been achieved to yield UPy−poly(ϵ-caprolactone) chains capable of undergoing supramolecular self-assembly. Molecular weights of these polymers varied from 2000 to 20 000 g/mol and were determined using 1H NMR end-group analysis as well as gel permeation chromatography. Furthermore, using Ubbelohde solution viscometry, samples demonstrated a marked increase in viscosity-average molecular weight when measured in chloroform, indicating that the UPy chain ends are in a dimerized form when compared to polymer solutions in dimethylformamide (DMF).

Complex Formation between a Nucleobase and Tetracyanoquinodimethane Derivatives: Crystal Structures and Transport Properties of Charge-Transfer Solids of Cytosine

Abstract Reaction between cytosine, a nucleobase, in methanol and several 7,7,8,8-tetracyanoquinodimethane derivatives (R-TCNQ) in acetonitrile yielded three kinds of ionic solids; (I) insulators composed of methoxy-substituted R-TCNQ anions, (II) semiconducting fully ionic R-TCNQ radical anion salts, and (III) conductive partially ionic or mixed-valent R-TCNQ radical anion salts. Electronic and chemical structures of these products were characterized by optical and magnetic measurements, and structural and elemental analyses. Cation units in all products were found to be protonated cytosine species. Crystal structures were determined for methoxy-substituted anion salts (R = F4 and H) in Group I and R-TCNQ radical anion salts (R = H and Et2) in Group II with hemiprotonated cytosine pairs formed by triple self-complementary hydrogen bonds. They established one-dimensional hemiprotonated cytosine ribbons by double complementary hydrogen bonds. Hydrogen bonds between cytosine and R-TCNQ anions exhibited high potential to regulate molecular arrangements producing a segregated layered structure and uniform arrangement of R-TCNQ radical anion columns stable down to low temperature. The partially ionic salt of MeTCNQ in Group III exhibited metallic behavior and the highest conductivity of 10+1 S cm−1 so far observed for charge-transfer complexes based on biological molecules.

Supramolecular Capsule Based on Complementary Adenine-Thymine Base Pairing

The harmonious effect of multiple hydrogen bonds plays an essential role in the molecular recognition of many biological systems including well-known cases such as the assembly of duplex DNA and the second structure of proteins. In a similar way, multiple hydrogen bonds have been used in the construction of molecular receptors, onedimensional linear aggregates, two-dimensional planar aggregates, and three-dimensional assemblies. Recently, three-dimensional, self-assembled structures have been designed and synthesized based on self-complementary hydrogen bonds. Only a few artificial systems, however, have utilized DNA-like, complementary, purinepyrimidine base pairing for the construction of selfassembled superstructures. This is because the interaction of adenine (Ade)-thymine (Thy) [or Ade-uridine (Uri)] is too weak (Ka ≈ 10 M−1 in CDCl3), and because cytosine (Cyt) and guanine (Gua) are notoriously hard to handle due to their poor solubility in organic solvents, despite the strong interaction of Cyt-Gua (Ka ≈ 10 M−1 in CDCl3). In spite of these limitations, several groups have tried to achieve the desired molecular assemblies by using Ade-Thy [or AdeUri] or Cyt-Gua base pairing interactions. In this report, we describe the self-assembly of a threedimensional superstructure by using the complementary base-pairing motif. We introduced four Ade and four Thy units into a resorcin[4]arene cavitand, and constructed a selfassembled molecular capsule via multiple hydrogen bonds between the four Ade-Thy pairs in a nonpolar organic solvent (Figure 1). Construction of three-dimensional molecular assemblies requires that the complementary binding partners meet each other with an appropriate curvature of the hydrogen-bond directionality. In order for the two binding partners to associate with each other by hydrogen bonds, we chose a rather long linker, namely the mercaptopropyl group (vide infra). 9-(3-Mercaptopropyl)Ade 1b and 1-(3-Mercaptopropyl)Thy 2b were synthesized from their thiouronium salts (Scheme 1). Treatment of Ade with 1-bromo-3-chloropropane in the presence of NaH gave 9-(3-chloropropyl)Ade 1a. Refluxing EtOH solution of 1a and thiourea and sequential treatment with sodium hydroxide afforded 1b. 1(3-Bromopropyl)Thy 2a was also prepared as shown in Scheme 1. First, Thy was silylated by using hexamethyldisilazane (HMDS) and a catalytic amount of chlorotrimethylsilane (TMSCl). Then, a reaction of the silylated Thy with 1,3-dibromopropane gave 2a. The last step for the synthesis of 2b was the same as that of 1b. Resorcin[4]arene tetramethylbromide 3 was synthesized using Cram’s method. The coupling of 3 and 1b (or 2b) was achieved by a typical SN2 reaction (Scheme 2). The formation of the self-assembled supramolecular heterodimer between 4a and 4b was investigated by H

Syntheses, structures and thermal properties of two new copper(II) melamine complexes

The reactions of melamine with CuCl 2 · 2H 2O and Cu(OAc) 2 · H 2O in boiling methanol afforded the complexes Cu 2Cl 2(μ-Cl)(μ-OCH 3)(CH 3OH) 2(MA) 2 · 2Et 2O (MA = melamine), 1, and [Cu(η 1-OAc)(μ-OCH 3)(MA)] 2 · 0.33H 2O, 2, respectively, which were characterized by single crystal X-ray crystallography. The molecules of these two complexes are interlinked by the N–H⋯N self-complementary hydrogen bonds and N–H⋯X (X = Cl or O) interactions to form 2-D molecular sheets and a 3-D porous structure, respectively. Complex 2 shows both hexagonal and triangular pores constrained by the N–H⋯N self-complementary hydrogen bonds. Thermal gravimetric analyses (TGA) were carried out to investigate their thermal properties.

N,N′,N′′-Tris(p-methoxyphenyl)phosphoric triamide

The title compound, C(21)H(24)N(3)O(4)P, is a self-complementary hydrogen-bond (HB) building unit, with (P=)O as the primary HB acceptor and N-H as the HB donor. Each of the four crystallographically distinct and nearly parallel molecules of the unit cell has a net dipole moment along the P=O bond direction and all of the dipoles are directed in the same general crystallographic direction. Head-to-tail N-H...O=P double-HB strands stack adjacent molecules into one-dimensional infinite polar columns. Each polar column is a 2(1) helix and all columns are essentially parallel, resulting in polar order throughout the entire crystal.