Dissymmetrical U‐Shaped π‐Stacked Supramolecular Assemblies by Using a Dinuclear CuI Clip with Organophosphorus Ligands and Monotopic Fully π‐Conjugated Ligands

Reactions between the U‐shaped binuclear Cu^I complex A that bears short metal–metal distances and the cyano‐capped monotopic π‐conjugated ligands 1 – 5 that carry gradually bulkier polyaromatic terminal fragments lead to the formation of π‐stacked supramolecular assemblies 6 – 10 , respectively, in yields of 50–80 %. These derivatives have been characterized by multinuclear NMR spectroscopic analysis and X‐ray diffraction studies. Their solid‐state structures show the selective formation of U‐shaped supramolecular assemblies in which two monotopic π‐conjugated systems present large ( 6 , 7 , and 9 ) or medium ( 8 and 10 ) intramolecular π overlap, thus revealing π–π interactions. These assemblies self‐organize into head‐to‐tail π‐stacked dimers that in turn self‐assemble to afford infinite columnar π stacks. The nature, extent, and complexity of the intermolecular contacts within the head‐to‐tail π‐stacked dimer depend on the nature of the terminal polyaromatic fragment carried by the cyano‐capped monotopic ligand, but it does not alter the result of the self‐assembling process. These results demonstrate that the dinuclear molecular clip A that bears short metal–metal distances allows selective supramolecular assembly processes driven by the formation of intra‐ and intermolecular short π–π interactions in the resulting self‐assembled structures; thus, demonstrating that their shape is not only dictated by the symmetry of the building blocks. This approach opens perspectives toward the formation of extended π‐stacked columns based on dissymmetrical and functional π‐conjugated systems.     

Dynamic Supramolecular Polymers Based on Benzene‐1,3,5‐tricarboxamides: The Influence of Amide Connectivity on Aggregate Stability and Amplification of Chirality

N‐Centred benzene‐1,3,5‐tricarboxamides (N‐BTAs) composed of chiral and achiral alkyl substituents were synthesised and their solid‐state behaviour and self‐assembly in dilute alkane solutions were investigated. A combination of differential scanning calorimetry (DSC), polarisation optical microscopy (POM) and X‐ray diffraction revealed that the chiral N‐BTA derivatives with branched 3,7‐dimethyloctanoyl chains were liquid crystalline and the mesophase was assigned as Col_ho. In contrast, N‐BTA derivatives with linear tetradecanoyl or octanoyl chains lacked a mesophase and were obtained as crystalline compounds. Variable‐temperature infrared spectroscopy showed the presence of threefold, intermolecular hydrogen bonding between neighbouring molecules in the mesophase of the chiral N‐BTAs. In the crystalline state at room temperature a more complicated packing between the molecules was observed. Ultraviolet and circular dichroism spectroscopy on dilute solutions of N‐BTAs revealed a cooperative self‐assembly behaviour of the N‐BTA molecules into supramolecular polymers with preferred helicity when chiral alkyl chains were present. Both the sergeants‐and‐soldiers as well as the majority‐rules principles were operative in stacks of N‐BTAs. In fact, the self‐assembly of N‐BTAs resembles closely that of their carbonyl (C?O)‐centred counterparts, with the exception that aggregation is weaker and amplification of chirality is less pronounced. The differences in the self‐assembly of N‐ and C?O‐BTAs were analysed by density functional theory (DFT) calculations. These reveal a substantially lower interaction energy between the monomeric units in the supramolecular polymers of N‐BTAs. The lower interaction energy is due to the higher energy penalty for rotation around the Ph? NH bond compared to the Ph? CO bond and the diminished magnitude of dipole–dipole interactions. Finally, we observed that mixed stacks are formed in dilute solution when mixing N‐BTAs and C?O BTAs.     

Spontaneous Self‐Assembly of γ‐Cyclodextrins in Dilute Solutions with Tunable Sizes and Thermodynamic Stability

The behavior in dilute solution of phosphate‐functionalized γ‐cyclodextrin macroanions with eight charges on the rim was explored. The hydrophilic macroions in mixed solvents show strong attraction between each other, mediated by the counterions, and consequently self‐assemble into blackberry‐type hollow spherical structures. Time‐resolved laser light scattering (LLS) measurements at high temperature ruled out the possibility of hydrogen bonding as the main driving force in the self‐assembly and indicated the good thermodynamic stability of assemblies regulated by the charge. The transition from single macroions to blackberries can be tuned by adjusting the content of organic solvent. The sizes of blackberries vary with the charge density of γ‐cyclodextrin by adjusting pH. It is the first report that pure cyclodextrins can generate supramolecular structures by themselves in dilute solution. The unique solution behavior of macroions provides a new opportunity to assemble cyclodextrin into functional materials and devices.     

Hydrogen‐bonded supramolecular polymers from derivatives of α‐amino‐ε‐caprolactam: A bio‐based material

Hydrogen‐bonded supramolecular polymers were prepared from the derivatives of α‐amino‐ε‐caprolactam (ACL), obtained from a renewable resource. Several self‐complimentary bis‐ or tetra‐caprolactam monomers were synthesized by varying the number of carbons of the spacer between the hydrogen‐bonding end groups. Physical properties of these hydrogen‐bonded polymers were clearly demonstrated by differential scanning colorimetry, solid‐state NMR, and X‐ray powder diffraction analyses. The supramolecular behavior was also supported by fiber formation from the melt for several of these compounds, and stable glassy materials were prepared from the physical mixtures of two different biscaprolactams. The self‐association ability of ACL was also used by incorporating ACL at the chain ends of low‐molecular weight Jeffamine (M_n = 900 g/mol) using urea and amide linkages. The transformation of this liquid oligomer at room temperature into a self‐standing, transparent film clearly showed the improvement in mechanical properties obtained by the introduction of terminal hydrogen‐bonding groups. Finally, the use of monomers with a functionality of four gave rise to network formation either alone or combination with bifunctional monomers. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Desymmetrization of 3,3′‐Bis(acylamino)‐2,2′‐bipyridine‐Based Discotics: The High Fidelity of Their Self‐Assembly Behavior in the Liquid‐Crystalline State and in Solution

Two novel nonsymmetrical disc‐shaped molecules 1 and 2 based on 3,3′‐bis(acylamino)‐2,2′‐bipyridine units were synthesized by means of a statistical approach. Discotic 1 possesses six chiral dihydrocitronellyl tails and one peripheral phenyl group, whereas discotic 2 possesses six linear dodecyloxy tails and one peripheral pyridyl group. Preorganization by strong intramolecular hydrogen bonding and subsequent aromatic interactions induce self‐assembly of the discotics. Liquid crystallinity of 1 and 2 was determined with the aid of polarized optical microscopy, differential scanning calorimetry, and X‐ray diffraction. Two columnar rectangular mesophases (Col_r) have been identified, whereas for C₃‐symmetrical derivatives only one Col_r mesophase has been found. 1 In solution, the molecularly dissolved state in chloroform was studied with ¹H NMR spectroscopy, whereas the self‐assembled state in apolar solution was examined with optical spectroscopy. Remarkably, these desymmetrized discotics, which lack one aliphatic wedge, behave similar to the symmetric parent compound. To prove that the stacking behavior of discotics 1 and 2 is similar to that of reported C₃‐symmetrical derivatives, a mixing experiment of chiral 1 with C₃‐symmetrical 13 has been undertaken; it has shown that they indeed belong to one type of self‐assembly. This helical J‐type self‐assembly was further confirmed with UV/Vis and photoluminescence (PL) spectroscopy. Eventually, disc 2 , functionalized with a hydrogen‐bonding acceptor moiety, might perform secondary interactions with molecules such as acids.     

Cooperative Effect of a Classical and a Weak Hydrogen Bond for the Metal‐Induced Construction of a Self‐Assembled β‐Turn Mimic

A novel metal‐induced template for the self‐assembly of two independent phosphane ligands by means of unprecedented multiple noncovalent interactions (classical hydrogen bond, weak hydrogen bond, metal coordination, π‐stacking interaction) was developed and investigated. Our results address the importance and capability of weak hydrogen bonds (WHBs) as important attractive interactions in self‐assembling processes based on molecular recognition. Together with a classical hydrogen bond, WHBs may serve as promoters for the specific self‐assembly of complementary monomeric phosphane ligands into supramolecular hybrid structures. The formation of an intermolecular C? H???N hydrogen bond and its persistence in the solid state and in solution was studied by X‐ray crystal analysis, mass spectrometry and NMR spectroscopy analysis. Further evidence was demonstrated by DFT calculations, which gave specific geometric parameters for the proposed conformations and allowed us to estimate the energy involved in the hydrogen bonds that are responsible for the molecular recognition process. The presented template can be regarded as a new type of self‐assembled β‐turn mimic or supramolecular pseudo amino acid for the nucleation of β‐sheet structures when attached to oligopeptides.     

Cover Picture: Journal of the Chinese Chemical Society 2/2017

In this paper , the self‐assembly of supramolecular network of 5‐hydroxy‐6methyluracil (HMU) was investigated (colored in gray). It is found that the structural block of this system is dimer 1‐1 (a color fragment). The RDG analysis shows that the network structure of HMU is formed by medium‐strength hydrogen bonds (the intermolecular areas colored in blue). More details about this figure will be discussed by Dr. Regina Kh. Shayakhmetova and her group on page 143–152 in this issue.

     

Chiral self‐discrimination of the enantiomers of α‐phenylethylamine derivatives in proton NMR

Two types of chiral analytes, the urea and amide derivatives of α‐phenylethylamine, were prepared. The effect of inter‐molecular hydrogen‐bonding interaction on self‐discrimination of the enantiomers of analytes has been investigated using high‐resolution ¹H NMR. It was found that the urea derivatives with double‐hydrogen‐bonding interaction exhibit not only the stronger hydrogen‐bonding interaction but also better self‐recognition abilities than the amide derivatives (except for one bearing two NO₂ groups). The present results suggest that double‐hydrogen‐bonding interaction promotes the self‐discrimination ability of the chiral compounds. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis and self‐assembly behavior study of α,ω‐dicarboxyl‐poly(ethylene glycol)–permethyl‐6‐amino‐6‐deoxy‐β‐cyclodextrin‐monoamide: A new β‐cyclodextrin conjugate

A new type of amphiphilic macromolecule was synthesized through the attachment of a poly(ethylene glycol) chain to a permethyl‐amino‐β‐cyclodextrin ring. The structure of the product was studied with 1D and 2D NMR experiments and with MALDI‐TOF MS. The resulting comet‐shaped molecule showed self‐assembly behavior in polar solvents. The presence of supramolecular structures in aqueous media was detected with dynamic light scattering and proven also by 2D NOESY and DOSY experiments. The supramolecular structures that formed could serve as starting materials for new types of drug delivery bioconjugates containing two independent dopable sites, that is, the cyclodextrin ring and the core of the supramolecular structure. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5149–5155, 2007     

Highly accurate equilibrium structure of the C2h symmetric N1‐to‐O2 hydrogen‐bonded uracil‐dimer

The highly accurate ab initio equilibrium geometry of the hydrogen‐bonded uracil dimer is derived using a composite geometry extrapolation scheme based on all‐electron, complete basis set extrapolated Møller–Plesset perturbation theory using the jun‐pwCV[T,Q]Z basis sets combined with a valence CCSD(T)/cc‐pVTZ high‐level correction. Geometrical changes on dimerization are discussed and the performance of the several density functional approximations (among others SCAN, ωB97M‐V, DSD‐PBEP86‐D3(BJ), and DSD‐PBEP86‐NL) is evaluated. Orbital‐optimized MP2.5 is discussed as a reduced‐cost alternative to the CCSD(T) gradient in the composite scheme. A new reference interaction energy is calculated with explicitly correlated F12‐CCSD(T).     

Formation of a Polypseudorotaxane via Self‐Assembly of γ‐Cyclodextrin with Poly(N‐isopropylacrylamide)

A polypseudorotaxane (PPR) comprising γ‐cyclodextrin (γ‐CD) as host molecules and poly(N‐isopropylacrylamide) (PNIPAM) as a guest polymer is prepared via self‐assembly in aqueous solution. Due to the bulky pendant isopropylamide group, PNIPAM exhibits size‐selectivity toward self‐assembly with α‐, β‐, and γ‐CDs. It can fit into the cavity of γ‐CD to give rise to a PPR, but cannot pass through α‐CD and β‐CD under the same conditions. The ratio of the number of γ‐CD molecules to entrapped NIPAM repeat units is kept at 1:2.2 or 1:2.4, determined by ¹H NMR spectroscopy and TGA analysis, respectively, indicating that there are more than 2 but less than 3 NIPAM repeat units included by one γ‐CD molecule. This finding opens new avenues to PPR‐based supramolecular polymers to be used as solid, stimuli‐responsive materials.     

Solvent‐Induced Helical Assembly and Reversible Chiroptical Switching of Chiral Cyclic‐Dipeptide‐Functionalized Naphthalenediimides

Understanding the roles of various parameters in orchestrating the preferential chiral molecular organization in supramolecular self‐assembly processes is of great significance in designing novel molecular functional systems. Cyclic dipeptide (CDP) chiral auxiliary‐functionalized naphthalenediimides (NCDPs 1 – 6 ) have been prepared and their chiral self‐assembly properties have been investigated. Detailed photophysical and circular dichroism (CD) studies have unveiled the crucial role of the solvent in the chiral aggregation of these NCDPs. NCDPs 1 – 3 form supramolecular helical assemblies and exhibit remarkable chiroptical switching behaviour (M‐ to P‐type) depending on the solvent composition of HFIP and DMSO. The strong influence of solvent composition on the supramolecular chirality of NCDPs has been further corroborated by concentration and solid‐state thin‐film CD studies. The chiroptical switching between supramolecular aggregates of opposite helicity (M and P) has been found to be reversible, and can be achieved through cycles of solvent removal and redissolution in solvent mixtures of specific composition. The control molecular systems (NCDPs 4 – 6 ), with an achiral or D ‐isomer second amino acid in the CDP auxiliary, did not show chiral aggregation properties. The substantial roles of hydrogen bonding and π–π interactions in the assembly of the NCDPs have been validated through nuclear magnetic resonance (NMR), photophysical, and computational studies. Quantum chemical calculations at the ab initio, semiempirical, and density functional theory levels have been performed on model systems to understand the stabilities of the right (P‐) and left (M‐) handed helical supramolecular assemblies and the nature of the intermolecular interactions. This study emphasizes the role of CDP chiral auxiliaries on the solvent‐induced helical assembly and reversible chiroptical switching of naphthalenediimides.     

Cyano‐Functionalized Triarylamines on Coinage Metal Surfaces: Interplay of Intermolecular and Molecule–Substrate Interactions

The self‐assembly of cyano‐functionalized triarylamine derivatives on Cu(111), Ag(111) and Au(111) was studied by means of scanning tunnelling microscopy, low‐energy electron diffraction, X‐ray photoelectron spectroscopy and density functional theory calculations. Different bonding motifs, such as antiparallel dipolar coupling, hydrogen bonding and metal coordination, were observed. Whereas on Ag(111) only one hexagonally close‐packed pattern stabilized by hydrogen bonding is observed, on Au(111) two different partially porous phases are present at submonolayer coverage, stabilized by dipolar coupling, hydrogen bonding and metal coordination. In contrast to the self‐assembly on Ag(111) and Au(111), for which large islands are formed, on Cu(111), only small patches of hexagonally close‐packed networks stabilized by metal coordination and areas of disordered molecules are found. The significant variety in the molecular self‐assembly of the cyano‐functionalized triarylamine derivatives on these coinage metal surfaces is explained by differences in molecular mobility and the subtle interplay between intermolecular and molecule–substrate interactions.     

Halogen‐Bond‐Mediated Assembly of a Single‐Component Supramolecular Triangle and an Enantiomeric Pair of Double Helices from 2‐(Iodoethynyl)pyridine Derivatives

Construction of single‐component supramolecular triangle and unprecedented spontaneous resolution of pairs of intertwined supramolecular 3₁‐ and 3₂‐double helices by the self‐assembly of achiral 2‐(iodoethynyl)pyridine and its derivatives have been achieved through intermolecular ethynyl C?I????N halogen bonds in the crystalline state. Fine‐tuning of the molecular structure of the achiral monomer and choice of solvents for crystallization have a dominant effect on the resultant supramolecular architectures.     

Melamine driven supramolecular self‐assembly of nucleobase derivatives in water

Water‐soluble supramolecular polymers, especially made up of biomolecules, are ideally suited to build new biomaterials that can mimic or interact with dynamic, biological environments. Here, two derivatives from thymine (T), that is N‐[2‐(3,4‐Dihydro‐5‐methyl‐2,4‐dioxo‐1(2H)‐pyrimidinyl)acetyl]‐L‐phenylalanine (T‐phe) and N‐(2‐Aminoethyl)‐3,4‐dihydro‐5‐methyl‐2,4‐dioxo‐1(2H)‐pyrimidineacetamide (T‐NH₂) were synthesized. Then the optimal condition for self‐assembly of T‐phe and T‐NH₂ driven by melamine (M) was explored. It was observed that M/T kept at 1:3 with equivalent T‐phe and T‐NH₂ under neutral environment resulted in long fibers (>1 μm) with extremely high aspect ratios, which suggested that electrostatic and π‐stacking interactions could be effectively orchestrated by hydrogen bonds to direct the hierarchical assembly. Furthermore, hydrogels were spontaneously generated with a concentrated solution of T‐phe, T‐NH₂, and M due to the fibril entanglement. Given its biomimetic nature and efficient self‐assembly process, this newly developed supramolecular polymer stacked by tetrameric structures represented an innovative concept and pathway for novel bio‐inspired materials. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 789–796     

Self‐Assembly through Coordination and π‐Stacking: Controlled Switching of Circularly Polarized Luminescence

Multiple noncovalent interactions can drive self‐assembly through different pathways. Here, by coordination‐assisted changes in π‐stacking modes between chromophores in pyrene‐conjugated histidine (PyHis), a self‐assembly system with reversible and inversed switching of supramolecular chirality, as well as circularly polarized luminescence (CPL) is described. It was found that l ‐PyHis self‐assembled into nanofibers showing P‐chirality and right‐handed CPL. Upon Zn^II coordination, the nanofibers changed into nanospheres with M‐chirality, as well as left‐handed CPL. The process is reversible and the M‐chirality can change to P‐chirality by removing the Zn^II ions. Experimental and theoretical models unequivocally revealed that the cooperation of metal coordination and π‐stacking modes are responsible the reversible switching of supramolecular chirality. This work not only provides insight into how multiple noncovalent interactions regulate self‐assembly pathways.     

基于柔性多齿吡啶胺配体和顺丁烯二酸铜组装的两种新型超分子配合物研究

Two novel supramolecular complexes, [Cu（bopapa）（mal）]·H2O·CH3OH （1） and {[Cu（bopapap）]（Hmal）2}·2H2O （2） [bpapa = bis-[6-（2-pyridylamino）pyrid-2-yl]amine, bpapap = 2,6-bis-[6-（pyrid-2-ylamino）pyrid-2-ylamino]- pyridine, mal=maleate dianion] were rationally designed and synthesized based on flexible multidentate ligands and copper（Ⅱ） maleate. Complexes 1 and 2 were all characterized by elemental analysis, spectroscopic techniques, thermal analysis and single crystal X-ray diffraction analysis. Complex 1 is of an infinite 3-D supramolecular framework constructed by 2-D sheets to contain 1-D helical chains formed by intermolecular hydrogen bond inter- actions between the non-coordinated oxygen atoms from maleate and nitrogen atoms from amino groups of bpapa. Complex 2 also takes a 3-D supramolecular structure, which is built from 2-D rhombic sheets produced by sequential dimer units. Interestingly, three pairs of symmetrical hydrogen bonds generate these dimer units.     

Host–Guest Binding‐Site‐Tunable Self‐Assembly of Stimuli‐Responsive Supramolecular Polymers

Despite the remarkable progress made in controllable self‐assembly of stimuli‐responsive supramolecular polymers (SSPs), a basic issue that has not been consideration to date is the essential binding site. The noncovalent binding sites, which connect the building blocks and endow supramolecular polymers with their ability to respond to stimuli, are expected to strongly affect the self‐assembly of SSPs. Herein, the design and synthesis of a dual‐stimuli thermo‐ and photoresponsive Y‐shaped supramolecular polymer (SSP2) with two adjacent β‐cyclodextrin/azobenzene (β‐CD/Azo) binding sites, and another SSP (SSP1) with similar building blocks, but only one β‐CD/Azo binding site as a control, are described. Upon gradually increasing the polymer solution temperature or irradiating with UV light, SSP2 self‐assemblies with a higher binding‐site distribution density; exhibits a flower‐like morphology, smaller size, and more stable dynamic aggregation process; and greater controllability for drug‐release behavior than those observed with SSP1 self‐assemblies. The host–guest binding‐site‐tunable self‐assembly was attributed to the positive cooperativity generated among adjacent binding sites on the surfaces of SSP2 self‐assemblies. This work is beneficial for precisely controlling the structural parameters and controlled release function of SSP self‐assemblies.     

Biocomplementary interaction behavior in DNA‐like and RNA‐like polymers

A series of nucleobased polymers and copolymers were synthesized through atom transfer radical polymerization (ATRP). Biocomplementary DNA‐ and RNA‐like supramolecular complexes are formed in dilute DMSO solution through nucleobase recognition. ¹H NMR titration studies of these complexes in CDCl₃ indicated that thymine‐adenine (T‐A) and uracil‐adenine (U‐A) complexes form rapidly on the NMR time scale with high association constants (up to 534 and 671 M^–1, respectively) and result in significant T_g increase. WAXD and differential scanning calorimetry analyzes in the bulk state indicate the presence of highly physical cross‐linked structures and provide further details into the nature of the self‐assembly of these systems. Furthermore, this study is of discussion on the difference in the hydrogen bond strength between T‐A and U‐A base pairs within polymer systems, indicating that the strength of hydrogen bonds in RNA U‐A pairs is stronger than that in DNA T‐A base pairs. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6388–6395, 2009     

Poly(dimethylsiloxane)‐based polymer organogelators with L‐lysine derivatives as a organogelation‐causing segment

New poly(dimethylsiloxane)‐based polymer organogelators with L ‐lysine derivatives were synthesized on the basis of synthetically simple procedure, and their organogelation abilities were investigated. These polymer organogelators have a good organogelation ability and form organogels in many organic solvents. In the organogels, polymer gelators constructed a mesoporous structure with a pore size of about 1 μm formed by entanglement of the self‐assembled nanofibers. The L ‐lysine derivatives in the polymer gelators functioned as a gelation‐causing segment and the organogelation was induced by self‐assembly of the L ‐lysine segments through a hydrogen bonding interaction. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3817–3824, 2006