Supramolecular Helical Structure Research Articles

Circularly polarized luminescence from cholesteric organic-inorganic hybrid silica films

Chiroptical functional materials with circularly polarized luminescence (CPL) properties have drawn increasing interest for their potential applications in optoelectronics and chiral sensing. However, the development of CPL materials with both large luminescence dissymmetry (glum) factors and high quantum yields (ΦF) in solid state is still a challenging task. In this work, organic–inorganic hybrid silica films have been prepared by the in-situ polycondensation of a cholesteric liquid-crystalline organosilane with the addition of a chiral dopant and an aggregation-induced emission (AIE)-active tetraphenylethene (TPE) derivative under an acidic condition. The resulting films emit bright CPL with the absolute glum values about 0.15, which were mainly caused by the long-range ordered supramolecular helical structure. It is found that the handedness of the CPL was dominated by the selective reflection of the cholesteric liquid crystal films.

Template synthesis, DNA binding, antimicrobial activity, Hirshfeld surface analysis, and 1D helical supramolecular structure of a novel binuclear copper(ii) Schiff base complex.

A new binuclear copper(ii) Schiff base complex [Cu2 L2− (NO3)2]·2CH3OH (1) [L = 2,6-bis((E)-(p-tolylimino)methyl)-4-methoxyphenol] was synthesized using a template method in which the tridentate N2O Schiff base ligand was derived from [1 + 2] condensation of 2,6-diformyl-4-methoxyphenol and p-methyl aniline in the presence of copper(ii) ions as the template agent. The X-ray diffraction analyses revealed that this complex crystallizes in the monoclinic system with space group P21/n. The most remarkable structural feature of 1 is that it contains two types of 1D right-handed helical chains. The molecules are linked by intermolecular hydrogen bonds and π⋯π interactions, then a 3D supramolecular network was constructed. Moreover, the intermolecular interactions on the crystal packing of 1 have been further studied using Hirshfeld surface analysis and corresponding 2D fingerprint plots. Binding interaction of this complex with calf thymus DNA (CT-DNA) has been investigated using absorption and emission studies, viscosity experiments and circular dichroism studies. Complex 1 shows significant binding to the DNA. The results of fluorescence spectroscopy and UV absorption spectroscopy, CD spectroscopy and viscosity indicated that this complex interacted with CT-DNA in a groove binding mode where the binding constant was 1.3 ± 0.2 × 104 L mol−1. Our fluorimeteric study showed that the reaction between 1 and CT-DNA was exothermic (ΔH = 59.6 kJ mol−1; ΔS = 268.79 J mol−1 K−1). Antibacterial activities of the complex were screened by the disc diffusion method against three Gram-positive bacteria (Staphylococcus aureus ATCC 25923, Enterococcus faecalis ATCC 23212 and S. epidermidis ATCC 34384), and three Gram-negative bacteria (Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853 and Klebsiella pneumonia ATCC 70063). The results indicated that this complex demonstrated acceptable antibacterial activities.

X⋅⋅⋅X Halogen Bond-Induced Supramolecular Helices.

The halogen bond is the attractive interaction between the electrophilic region of a halogen atom and the nucleophilic region of another molecular entity, emerging as a favorable manner to manipulate supramolecular chirality in self-assemblies. Engineering halogen bonded helical structures remains a challenge due to its sensitivity to solvent polarity and competitive forces like hydrogen bonds. Herein, we report a X⋅⋅⋅X (X=Cl, Br, I) type weak halogen bond that induces the formation and evolution of supramolecular helical structures both in solid and solution state. The π-conjugated phenylalanine derivatives with F, Cl, Br and I substitution self-assembled into 21 helical packing driven by hydrogen bond and halogen bond, respectively. The specific molecular geometries of π-conjugated amino acids gave rise to multiple noncovalent forces to stabilize the X⋅⋅⋅X halogen bond with small bond energies ranging from -0.69 to -1.49 kcal mol-1 . Halogen bond induced an opposite helicity compared to the fluorinated species, accompanied by the inversed circularly polarized luminescence.

X⋅⋅⋅X Halogen Bond‐Induced Supramolecular Helices

AbstractThe halogen bond is the attractive interaction between the electrophilic region of a halogen atom and the nucleophilic region of another molecular entity, emerging as a favorable manner to manipulate supramolecular chirality in self‐assemblies. Engineering halogen bonded helical structures remains a challenge due to its sensitivity to solvent polarity and competitive forces like hydrogen bonds. Herein, we report a X⋅⋅⋅X (X=Cl, Br, I) type weak halogen bond that induces the formation and evolution of supramolecular helical structures both in solid and solution state. The π‐conjugated phenylalanine derivatives with F, Cl, Br and I substitution self‐assembled into 21 helical packing driven by hydrogen bond and halogen bond, respectively. The specific molecular geometries of π‐conjugated amino acids gave rise to multiple noncovalent forces to stabilize the X⋅⋅⋅X halogen bond with small bond energies ranging from −0.69 to −1.49 kcal mol−1. Halogen bond induced an opposite helicity compared to the fluorinated species, accompanied by the inversed circularly polarized luminescence.

The role of hydroxyl group of ethanol in the self-assembly of pharmaceutical cocrystal of myricetin with 4,4′-bipyridine

In order to further explore the role that hydroxyl plays in synthesizing and improving physicochemical properties of pharmaceutical cocrystals of flavonoids, an unreported pharmaceutical cocrystal (MYR·BPY·EtOH) of myricetin (MYR) with 4,4′-bipyridine (BPY) has been synthesized and characterized. However, something unexpected happened. MYR·BPY·EtOH is a cocrystal with supramolecular helical structure which is different from the supramolecular layered structure of MYR·BPY·H2O that we have reported on. This may be due to the O9-H9···O6 hydrogen bond, which was formed by the hydroxyl of the ethanol molecule and the 6-oxygen atoms of the MYR, maintains the cocrystal helical structure. Additionally, MYR·BPY·EtOH shows better solubility in comparison to pure MYR and MYR·BPY·H2O. but the hygroscopic stability of MYR·BPY·EtOH and MYR·BPY·H2O are lower than that of pure MYR. It may be compared with planar MYR and layered-structured MYR·BPY·H2O, helically-structured MYR·BPY·EtOH is more likely to allow water molecules to enter. This study implies that we should not ignore the influential that hydroxyl groups of solvent molecules have on the structures and properties of flavonoid pharmaceutical cocrystals when considering the influence of hydroxyl groups of the A, B, and C rings of flavonoid on the cocrystal structure of flavonoids.

Mechano‐Optical Response of Novel Polymer Composites Based on Elastic Polyurethane Matrix Filled with Low‐Molar‐Mass Cholesteric Droplets

AbstractAmong the various types of liquid crystalline (LC) structures, the cholesteric mesophase attracts special attention in view of helical supramolecular structure determining their specific optical properties. The helix pitch of cholesteric liquid crystals is very sensitive to mechanical stress, resulting in change of their optical properties and position of selective light reflection peak. Here, films of polymer‐dispersed cholesteric liquid crystals based on polyurethane elastomer are prepared and studied. Liquid crystal mixtures based on chiral cholesterol derivatives are uniformly dispersed in the form of micrometer‐sized droplets in an elastomeric matrix. A significant mechano‐optical response of the composites under the action of deformation is demonstrated, and the change in the position of the selective light reflection band during mechanical stress is studied in detail. A shift in the selective light reflection peak by 100 nm or more is found. This process is accompanied by color transformations of brightly colored films. Such materials can be promising for creating stress and deformation sensors, ripple and bending sensors, and other technical devices.

Molecular Conformation of Bent-Core Molecules Affected by Chiral Side Chains Dictates Polymorphism and Chirality in Organic Nano- and Microfilaments.

The coupling between molecular conformation and chirality is a cornerstone in the construction of supramolecular helical structures of small molecules across various length scales. Inspired by biological systems, conformational preselection and control in artificial helical molecules, polymers, and aggregates has guided various applications in optics, photonics, and chiral sorting among others, which are frequently based on an inherent chirality amplification through processes such as templating and self-assembly. The so-called B4 nano- or microfilament phase formed by some bent-shaped molecules is an exemplary case for such chirality amplification across length scales, best illustrated by the formation of distinct nano- or microscopic chiral morphologies controlled by molecular conformation. Introduction of one or more chiral centers in the aliphatic side chains led to the discovery of homochiral helical nanofilament, helical microfilament, and heliconical-layered nanocylinder morphologies. Herein, we demonstrate how a priori calculations of the molecular conformation affected by chiral side chains are used to design bent-shaped molecules that self-assemble into chiral nano- and microfilament as well as nanocylinder conglomerates despite the homochiral nature of the molecules. Furthermore, relocation of the chiral center leads to formation of helical as well as flat nanoribbons. Self-consistent data sets from polarized optical as well as scanning and transmission electron microscopy, thin-film and solution circular dichroism spectropolarimetry, and synchrotron-based X-ray diffraction experiments support the progressive and predictable change in morphology controlled by structural changes in the chiral side chains. The formation of these morphologies is discussed in light of the diminishing effects of molecular chirality as the chain length increases or as the chiral center is moved away from the core-chain juncture. The type of phase (B1-columnar or B4) and morphology of the nano- or microfilaments generated can further be controlled by sample treatment conditions such as by the cooling rate from the isotropic melt or by the presence of an organic solvent in the ensuing colloidal dispersions. We show that these nanoscale morphologies can then organize into a wealth of two- and three-dimensional shapes and structures ranging from flower blossoms to fiber mats formed by intersecting flat nanoribbons.

Pearl-inspired polymer films with chiral nematic and multi-lamellar structures

ABSTRACT Structural coloured materials have been widely found in nature. More and more artificial materials were created based on structural colour. However, fabrication of polymer films with pearly lustre remains a challenging task. Herein, a strategy is reported to prepare broadband reflection polymer films based on the fluorophilic association. A monomer with a perfluorooctyl chain is synthesised. After photo-crosslinking a mixture of a chiral nematic liquid crystal and the fluorinated monomer, broadband reflection film with pearly lustre is obtained. The broadband reflection originates from the broad distribution of the helical pitch. The pearly lustre is caused by the periodically ordered layers formed by the microphase separation between hydrocarbon and fluorocarbon chains.A strategy for the preparation of color liquid crystal polymer film with pearly luster is developed. The Bragg-reflection color originates from the supramolecular helical structure of the cholesteric liquid crystal and the pearly luster originates from the multilayer structure formed by the fluorocarbon/hydrocarbon microphase separation

Structure–mechanical property relationship of a pentapeptide crystal

A peptide having miniature (P)310/α-helix conformation, forms intermolecular H-bonded supramolecular helical bundle structure which further self-assembled to interdigited supramolecular sheet-like structure that eventually from the brittle crystal.

Helical secondary structures and supramolecular tilted chirality in N-terminal aryl amino acids with diversified optical activities

Helix structures at atomic/molecular level have not been found in self-assembled peptide sequence with less than three residues. As β-sheet supramolecular secondary structures have been discovered in solid-state amino acids, we here report the conjugation of simple N-terminal aryl protecting group could give rise to helical supramolecular secondary structures in solid-state, which determines the optical activities of the adjacent aryl groups. The carboxylic acid-involved asymmetric H-bonds in N-terminal aryl amino acids induce the emergence of super-helical structures of amino acid residues and aryl groups. In most cases, supramolecular tilted chirality of aryl groups is opposite to that of amino acid sequences, of which handedness and helical pitch are determined by the H-bond modalities. Determining correlation between supramolecular tilted chirality of aryl segments and their chiroptical activities is firstly unveiled, which was verified by the computational results based on density functional theory. Most aryl amino acids self-assembled by nanoprecipitation method via crystallization induced self-assembly into rigid one-dimensional microstructures with ultra-high Young’s modulus. This study reveals the generic existence of chiral supramolecular structures in aggregated amino acid derivatives and gives an in-depth investigation into the structural-property relationships, which could guide the rational design and screening of chiroptical supramolecular materials.

Perylene diimide derivative via ionic self-assembly: helical supramolecular structure and selective detection of ATP

The novel PDI complex can be self-assembled into a helical supramolecular structure. Moreover, the solution of the complex can also realize the visual detection of ATP.

Pentapeptide Nanoreactor as a Platform for Halogenations, Diels-Alder Reaction, and Morita-Baylis-Hillman Reaction.

A pentapeptide nanoreactor has been designed and synthesized as a platform to carry out the traditional organic reactions such as bromination, iodination, cycloaddition, and condensation reactions. The pentapeptide Boc–Phe–Phe–Aib–Phe–Phe–OMe with a supramolecular helical structure and π-rich channel provides nanoconfinements and thus facilitates the organic reactions. Bromination and iodination of aniline take place without any halogen carrier (Lewis acid) in the pentapeptide platform. Iodination produced p-iodoaniline only. The Diels–Alder reaction between furan and maleic anhydride increased 2-fold in the pentapeptide platform and the Morita–Baylis–Hillman reaction of benzaldehyde and ethyl acrylate in methanol enhanced 1.5-fold.

Parity Violation in Supramolecular Aggregation: Insights from Optoelectronic Properties

In the contemporary science, it is believed that supramolecular chiral structures (left‐ or right‐handed) emanating from enantiomeric (L‐ or D‐enantiomers) chiral building blocks would have identical physical and chemical properties. Here, PBI derivatives with chiral L‐phenylalanine and D‐phenylalanine at the imide positions have been synthesized and designated as PPAL and PPAD. Surprisingly, the chiral perylenebisimide (PBI) derivatives containing PPAL and PPAD self‐assemble to mirror image helical supramolecular structures showing dissymmetric energy states. They also exhibit different optoelectronic characteristics in the supramolecular aggregated state in chlorinated solvents. These studies indicate parity violation in supramolecular aggregated state and it may provide great impetus in understanding the origin of the evolutionary conserved L‐amino acids in nature.

Design of an Amphiphilic Perylene Diimide for Optical Recognition of Anticancer Drug through a Chirality-Induced Helical Structure.

Introduction of chirality into a supramolecular self-assembly system plays an indispensable role in attaining specific molecular recognition ability. Herein, a chiral anticancer drug 5'-deoxy-5-fluorouridine (5'DFU) was explored for inducing the self-assembly of a cationic perylene diimide derivative containing boronic acid groups (PDI-PBA) into a highly ordered right-handed helical structure. As a result, PDI-PBA exhibited a molecular recognition ability towards 5'DFU among other cis-diols and anticancer drugs. With the help of a dynamic covalent bond and favorable hydrogen-bonding interactions, chirality transfer from chiral 5'DFU to achiral PDI-PBA breaks down the strong π-π stacking of PDI-PBA and makes it reorganize into highly ordered helical supramolecular structures. This work provides an insight into chiral anticancer drug tuning interactions of π-chromophores and the inducement of hierarchical self-assembly to achieve specific molecular recognition.

Hierarchy of Asymmetry in Chiral Supramolecular Polymers: Toward Functional, Helical Supramolecular Structures.

The formation of helical structures through the supramolecular polymerization of a variety of self-assembling units is reviewed. These scaffolds are usually obtained by efficient transfer or amplification of chirality phenomena, in which the starting self-assembling molecules possess different elements of asymmetry, such as point or axial chirality. Relevant examples of helical supramolecular structures investigated under thermodynamic control are reviewed, and the helical outcome of remarkable examples of chiral entities obtained through kinetic control are also highlighted. Finally, selected examples of flexible macroscopic chirality and catalysis are described to illustrate the applicability of helical aggregates.

Researches on the construction of supramolecular helical chains in crystallized β-alaninium sulfate/ perchlorate compounds

A new compound, (H2L)2SO4 (1) (HL = β-alanine), was synthesized and studied based on X-ray single crystal diffraction analysis. β-alanine molecular displays two kinds of molecule torsion geometries (I and II) in compound 1, which construct supramolecular Z-shaped chains and supramolecular helical chains respectively. Based on our understanding of the helical packing mechanism of β-alanine in compound 1, we predicted and found supramolecular helical chains in another compound H2LClO4 (2) for the first time, although the crystal data of compound 2 has been reported previously. The way of simple β-alanine self-organizing into supramolecular helical chains was discussed in detail by comparing the structure of the compound 1 and compound 2, which may be important for understanding the way of simple molecules self-organizing into supramolecular helical structure and offers a good case for achiral ligands to construct supramolecular helical chains.

The effect of the shape of a mesogenic group on the structure of supramolecular aggregates based on wedge-shaped and cone-shaped dendrons

This review addresses the key principles underlying the formation of liquid crystalline phases based on wedge-shaped and cone-shaped dendrons of different chemical nature. Despite rich phase diversity of the above systems, the development of a mesophase can be reliably predicted by the geometric model, which compares the shape of a wedge dendron with the radial density distribution in the relevant Voronoi polyhedra. 2D columnar phases formed by chiral [7]-heterohelicene molecules with long aliphatic side chains are described in detail. The as-formed columnar aggregates are shown to possess a helical 132 symmetry and are composed of thirteen blocks, and each block involves six molecules. In this case, the internal structure of the first-level (lower) supramolecular aggregate appears to be different from that of the helical supramolecular structure.

Discotic liquid crystals of transition metal complexes 56: Synthesis of mesogenic phthalocyanine-fullerene dyads and influence of the substitution position of alkoxy chains and the kind of terminal groups on appearance of the helical supramolecular structure

We have synthesized twelve novel discotic columnar liquid crystals based on a phenoxy-group-substituted phthalocyaninato copper(II) complex having the same alkoxy chain of C[Formula: see text]H[Formula: see text]O at different positions in the phenoxy group: the parent compounds {0a~0c-16}and the OH-substituted compounds {3a~3c-16}, the OFBA-substituted compounds {2a~2c-16}and the C[Formula: see text]-substituted dyads {1a~1c-16}. The letters of a, b and c mean substitution positions of C[Formula: see text]H[Formula: see text]O group at [Formula: see text], [Formula: see text] and [Formula: see text], respectively. We have investigated the influence of both substitution position of the alkoxy chains and the kind of terminal groups (OH, OFBA and C[Formula: see text] on the mesomorphism and the helical supramolecular structure, by using DSC, POM and temperature-variable small angle X-ray diffraction measurements. As a result, an additional big peak (Peak H) tends to appear at around 2[Formula: see text] = 1.1[Formula: see text] in the X-ray diffraction patterns only for the dyads {1a~1c-16}but not for the other compounds, {0a~0c-16}, {3a~3c-16}and {2a~2c-16}, regardless of the substitution positions of the alkoxy group. Moreover, we revealed that both the m-substituted derivative 1a-16 and the m,p-substituted derivative 1c-16 gave Peak H, but that only the p-substituted derivative 1b-16 did not give Peak H among these three dyads {1a~1c-16}. From the temperature-variable small angle X-ray diffraction measurements for the m,p-substituted derivative 1c-16 using two different sample preparation methods, we proved that the Peak H originates from a helical pitch of fullerenes. We also pointed out that the m-substituted long alkoxy chains are at least needed to form the helical supramolecular structure in the present (PhO)[Formula: see text]PcM-C[Formula: see text]-based dyads.

Helical supramolecular self-assembly by prolamide thymidine/uridine analogues

ABSTRACTThis report describes the syntheses of rationally designed non-sugar nucleoside as prolamide nucleosides which contain prolyl ring and pyrimidine nucleobases (uracil/thymine) via acetamide bonds. These nucleosides have propensity to form distinctive self-assembly supramolecular helical structures ubiquitously through Watson-Crick/reverse type of hydrogen bonding with nucleobases. Moreover, the prolyl acetamide backbone groups- carbonyl (-C = O) and hydroxyl (-OH) group, are also involved in strengthening of self-assembled helical structures. Importantly, both prolamide thymidine and prolamide uridine have shown two distinctive helical structural patterns, in spite of containing the same backbone. Hence thymine and uracil moieties of prolamide nucleosides are responsible for unique supramolecular helical structural architectures.

The Breaking of Symmetry Leads to Chirality in Cucurbituril-Type Hosts

Cucurbituril-type hosts are highly symmetric, but there are means to break their symmetry. This review will present examples from three directions of induction of chirality in or by cucurbituril-type hosts: first, through the incorporation of stereogenic elements into host molecules; second, through complexation with achiral guests, which leads to axial supramolecular chirality and helical structures; third, through the formation of complexes with chiral guests in multi-molecule complexes and induction of supramolecular chirality. In addition, a list of chiral guests used in binding studies with cucurbiturils is collected. We would envision that encouraged by the outlined examples of outstanding applications of chiral cucurbituril-supramolecular systems, the boundaries of chiral applications of cucurbiturils would be widened.