A Double-Stranded Helix by Complexation of Two Polymer Chains with a Helical Supramolecular Assembly

A Metal-Free Helical Covalent Inorganic Polymer: Preparation, Crystal Structure and Optical Properties

Helical morphologies are widely observed in nature, however, it is very challenging to prepare artificial helical polymers. Especially, precisely understanding the structure information of artificial metal-free helical covalent inorganic polymers via single-crystal X-ray diffraction (SCXRD) analysis is rarely explored. Here, we successfully prepare a novel metal-free helical covalent inorganic polymer ({[Te(C6 H5 )2 ] [PO3 (OH)]}n , named CityU-10) by introducing angular anions (HOPO3 2- ) into traditional tellurium-oxygen chains. The dynamic reversibility of the reaction is realized through the introduction of organic tellurium precursor and the slow hydrolysis of polyphosphoric acid. High-quality and large-size single crystals of CityU-10 have been successfully characterized via SCXRD, where the same-handed helical inorganic polymer chains form a pseudo-two-dimensional layer via multiple hydrogen-bonding interactions. The left-handed layers and right-handed layers alternatively stack together through weak hydrogen bonds to form a three-dimensional supramolecular structure. The single crystals of CityU-10 are found to display promising optical properties with a large birefringence. Our results would offer new guidelines for designing and preparing new crystalline covalent polymers through tellurium-based chemistry.

Chiral template-induced porphyrin-based self-assembled materials for electrochemical chiral sensing

Chirality plays a key role in many fields of natural sciences as well as life sciences. Chiral materials are widely developed and used for electrochemical chiral recognition. In recent years, carbon quantum dots (CQDs) have been widely used as a novel carbon nanomaterial due to their excellent charge transfer properties, good biocompatibility, and low cost. The special structure of π-conjugated porphyrin attracts attention. Supramolecular self-assembly shows a way to construct chiral materials by self-assembling simple molecules into chiral composites. Herein, we demonstrate the self-assembly of achiral porphyrins induced by chiral carbon quantum dots assembled from L- and or D-tryptophan (L- and or D-Trp) with carbon quantum dots, resulting in 5,10,15,20-tetrakis (4-carboxyPheyl) (TCPP) self-assembled structure. The electrochemical chiral recognition of chiral self-assembled materials was studied using Phenylalanine (Phe) enantiomer as a chiral analyte. Electrochemical chiral recognition results showed that the chiral self-assembled materials induced by chiral templates have a good ability to discriminate Phe enantiomers. Therefore, this research provides a new idea for the synthesis of chiral composites and further expands applications to electrochemical chiral recognition.

DNA condensation and formation of ultrathin nanosheets via DNA assisted self-assembly of an amphiphilic fullerene derivative

DNA nanotechnology propose various assembly strategies to develop novel functional nanostructures utilizing unique interactions of DNA with small molecules, nanoparticles, polymers, and other biomolecules. Although, well defined nanostructures of DNA and amphiphilic small molecules were achieved through hybridization of covalently modified DNA, attaining precise organization of functional moieties through non-covalent interactions remain as a challenging task. Herein, we report mutually assisted assembly of an amphiphilic fullerene derivative and various DNA structures through non-covalent interactions, which leads to initial DNA condensation and subsequent assembly yielding ordered fullerene-DNA nanosheets. The molecular design of the cationic, amphiphilic fullerene derivative (FPy) ensures molecular solubility in the 10% DMSO-PBS buffer system and facile interactions with DNA through groove binding and electrostatic interactions of fullerene moiety and positively charged pyridinium moiety, respectively. The formation of FPy/DNA nanostructures were thoroughly investigated in the presence of λ-DNA, pBR322 plasmid DNA, and single and double stranded 20-mer oligonucleotides using UV-visible spectroscopy, AFM and TEM analysis. λ-DNA and pBR322 plasmid DNA readily condense in presence of FPy leading to micrometer sized few layer nanosheets with significant crystallinity due to ordered arrangement of fullerenes. Similarly, single and double stranded 20-mer oligonucleotides also interact efficiently with FPy and form highly crystalline nanosheets, signifying the role of electrostatic interaction and subsequent charge neutralization in the condensation triggered assembly. However, there is significant differences in the crystallinity and ordered arrangements of fullerenes between these two cases, where longer DNA form condensed structures and less ordered nanosheets while short oligonucleotides lead to more ordered and highly crystalline nanosheets, which could be attributed to the differential DNA condensation. Finally, we have demonstrated the addressability of the assembly using a cyanine modified single strand DNA, which also forms highly crystalline nanosheets and exhibit efficient quenching of the cyanine fluorescence upon self-assembly. These results open up new prospects in the development of functional DNA nanostructures through non-covalent interactions and hence have potential applications in the context of DNA nanotechnology.

Nanoscale π-conjugated ladders

It is challenging to increase the rigidity of a macromolecule while maintaining solubility. Established strategies rely on templating by dendrons, or by encapsulation in macrocycles, and exploit supramolecular arrangements with limited robustness. Covalently bonded structures have entailed intramolecular coupling of units to resemble the structure of an alternating tread ladder with rungs composed of a covalent bond. We introduce a versatile concept of rigidification in which two rigid-rod polymer chains are repeatedly covalently associated along their contour by stiff molecular connectors. This approach yields almost perfect ladder structures with two well-defined π-conjugated rails and discretely spaced nanoscale rungs, easily visualized by scanning tunnelling microscopy. The enhancement of molecular rigidity is confirmed by the fluorescence depolarization dynamics and complemented by molecular-dynamics simulations. The covalent templating of the rods leads to self-rigidification that gives rise to intramolecular electronic coupling, enhancing excitonic coherence. The molecules are characterized by unprecedented excitonic mobility, giving rise to excitonic interactions on length scales exceeding 100 nm. Such interactions lead to deterministic single-photon emission from these giant rigid macromolecules, with potential implications for energy conversion in optoelectronic devices.

Retarded Solid-State Rotations of an Oval-Shaped Guest in a Deformed Cylinder with CH-π Arrays

Upon encapsulating an oval-shaped hydrocarbon guest, a cylindrical host deforms its shape to maximize intermolecular contacts. Structure-assembly relationship studies with a series of hydrocarbon guests disclosed the importance of molecular shapes and CH-π contacts. Multiple contacts and weak CH-π hydrogen bonds resulted in an optimal assembly; however, the shape deformation resulted in severe retardation of rotational motions in the crystal. Thus, unlike a circular guest, the oval-shaped guest did not change its orientation in the host. Unexpectedly, the planar guest did not affect the packing structure to form a double helix in intertwined host arrays.

Double helical conformation and extreme rigidity in a rodlike polyelectrolyte

The ubiquitous biomacromolecule DNA has an axial rigidity persistence length of ~50 nm, driven by its elegant double helical structure. While double and multiple helix structures appear widely in nature, only rarely are these found in synthetic non-chiral macromolecules. Here we report a double helical conformation in the densely charged aromatic polyamide poly(2,2′-disulfonyl-4,4′-benzidine terephthalamide) or PBDT. This double helix macromolecule represents one of the most rigid simple molecular structures known, exhibiting an extremely high axial persistence length (~1 micrometer). We present X-ray diffraction, NMR spectroscopy, and molecular dynamics (MD) simulations that reveal and confirm the double helical conformation. The discovery of this extreme rigidity in combination with high charge density gives insight into the self-assembly of molecular ionic composites with high mechanical modulus (~ 1 GPa) yet with liquid-like ion motions inside, and provides fodder for formation of other 1D-reinforced composites.

Double helix structures appear widely in nature, but only rarely in synthetic non-chiral macromolecules. Here the authors describe a double helix in a densely charged aromatic polyamide, which exhibits an axial rigidity persistence length of ~ 1 μm, much higher than that of DNA (~ 50 nm).

Double-helix PnLin chains: novel potential nonlinear optical materials

The structures, circular dichroism (CD) spectra and nonlinear optical (NLO) responses of a series of inorganic double-helix chains, P_nLi_n (n = 6–12), have been investigated using the quantum chemistry method.

Pendant-Type Helicene Oligomers with p-Phenylene Ethynylene Main Chains: Synthesis, Reversible Formation of Ladderlike Bimolecular Aggregates, and Control of Intramolecular and Intermolecular Aggregation

Pendant-type (P)-helicene oligomers with p-phenylene ethynylene main chains up to a tetramer were synthesized by a building block method. The (P)-tetramer reversibly formed a ladderlike bimolecular aggregate upon cooling and disaggregated upon heating in (trifluoromethyl)benzene. Two bis(tetramer)s, in which two (P)-tetramers were connected by hexadecamethylene linkers, were also synthesized. The head-to-tail bis(tetramer) formed an intramolecular aggregate, and the head-to-head bis(tetramer) formed an intermolecular aggregate in toluene. The results suggest the antiparallel aggregation structure of the pendant-type (P)-tetramers. The structure of the linker was proven to be effective in controlling intramolecular and intermolecular aggregations.

Supramolecular Helical Systems: Helical Assemblies of Small Molecules, Foldamers, and Polymers with Chiral Amplification and Their Functions

In this review, we describe the recent advances in supramolecular helical assemblies formed from chiral and achiral small molecules, oligomers (foldamers), and helical and nonhelical polymers from the viewpoints of their formations with unique chiral phenomena, such as amplification of chirality during the dynamic helically assembled processes, properties, and specific functionalities, some of which have not been observed in or achieved by biological systems. In addition, a brief historical overview of the helical assemblies of small molecules and remarkable progress in the synthesis of single-stranded and multistranded helical foldamers and polymers, their properties, structures, and functions, mainly since 2009, will also be described.

Cooperative self-assembly of porphyrins with polymers possessing bioactive functions

This review covers recent research on design strategies for the cooperative self-assembly of porphyrins with polymers and its implementation as bioactive assembly.

Controllability of dynamic double helices: quantitative analysis of the inversion of a screw-sense preference upon complexation

We describe a quantitative analysis of the complexation-induced inversion of a screw-sense preference based on a conformationally dynamic double-helix structure in a macrocycle. The macrocycle is composed of two twisting units (terephthalamide), which are spaced by two strands (1,3-bis(phenylethynyl)benzene), and is designed to generate a double-helix structure through twisting about a C2 axis in a conrotatory manner. The attachment of chiral auxiliaries to the twisting units induces a helical preference for a particular sense of (M)- or (P)-helicity through the intramolecular transmission of chirality to dynamic double helices. The twisting unit can also act as a binding site for capturing a guest molecule, and, in a complexed state, the preferred screw sense of the dynamic double-helix structure is reversed to exhibit the contrary preference. We quantitatively monitored the complexation-induced inversion of the screw-sense preference using 1H NMR spectroscopy, which enabled us to observe independently two species with (M)- or (P)-helicity in both the absence and presence of a guest molecule. Inversion of the screw-sense preference was induced upon complexation with an achiral guest as well as a chiral guest.

Conductive porphyrin helix from ternary self-assembly systems

A helix with the ternary components of TPPS4, Zn(NO3)2 and C14DMAO is easily obtained in aqueous solution. It retains the characteristic fluorescence of the porphyrin and can be conductive when it bridges on a gold electrode, which provides potential applications in photochemistry and electrical devices.

A supramolecular ladder polymer prepared by hydrogen bonding-mediated self-assembly of a metallomacrocycle

A defect-free supramolecular ladder polymer was prepared by H-bond-mediated self-assembly of a metallocycle 1 as determined by NMR, viscometry and dynamic laser light scattering studies.

Chiral tether-mediated stabilization and helix-sense control of complementary metallo-double helices

A series of novel PtII-linked double helices were prepared by inter- or intrastrand ligand-exchange reactions of the complementary duplexes composed of chiral or achiral amidine dimer and achiral carboxylic acid dimer strands joined by trans-PtII-acetylide complexes with PPh3 ligands using chiral and achiral chelating diphosphines. The structure and stability of the PtII-linked double helices were highly dependent on the diphosphine structures. An interstrand ligand exchange took place with chiral and achiral 1,3-diphosphine-based ligands, resulting in trans-PtII-bridged double helices, whose helical structures were quite stable even in dimethyl sulfoxide (DMSO) due to the interstrand cross-link, whereas a 1,2-diphosphine-based ligand produced non-cross-linked cis-PtII-linked duplexes, resulting from an intrastrand ligand-exchange that readily dissociated into single strands in DMSO. When enantiopure 1,3-diphosphine-based ligands were used, the resulting trans-PtII-bridged double helices adopted a preferred-handed helical sense biased by the chirality of the bridged diphosphines. Interestingly, the interstrand ligand exchange with racemic 1,3-diphosphine toward an optically-active PtII-linked duplex, composed of chiral amidine and achiral carboxylic acid strands, was found to proceed in a diastereoselective manner, thus forming complete homochiral trans-PtII-bridged double helices via a unique chiral self-sorting.

Progressive macromolecular self-assembly: from biomimetic chemistry to bio-inspired materials

Macromolecular self-assembly (MSA) has been an active and fruitful research field since the 1980s, especially in this new century, which is promoted by the remarkable developments in controlled radical polymerization in polymer chemistry, etc. and driven by the demands in bio-related investigations and applications. In this review, we try to summarize the trends and recent progress in MSA in relation to biomimetic chemistry and bio-inspired materials. Our paper covers representative achievements in the fabrication of artificial building blocks for life, cell-inspired biomimetic materials, and macromolecular assemblies mimicking the functions of natural materials and their applications. It is true that the current status of the deliberately designed and obtained nano-objects based on MSA including a variety of micelles, multicompartment vesicles, and some hybrid and complex nano-objects is at their very first stage to mimic nature, but significant and encouraging progress has been made in achieving a certain similarity in morphologies or properties to that of natural ones. Such achievements also demonstrate that MSA has played an important and irreplaceable role in the grand and long-standing research of biomimetic and bio-inspired materials, the future success of which depends on mutual and persistent efforts in polymer science, material science, supramolecular chemistry, and biology.

Programmed self-assembly of large π-conjugated molecules into electroactive one-dimensional nanostructures

Electroactive one-dimensional (1D) nano-objects possess inherent unidirectional charge and energy transport capabilities along with anisotropic absorption and emission of light, which are of great advantage for the development of nanometer-scale electronics and optoelectronics. In particular, molecular nanowires formed by self-assembly of π-conjugated molecules attract increasing attention for application in supramolecular electronics. This review introduces recent topics related to electroactive molecular nanowires. The nanowires are classified into four categories with respect to the electronic states of the constituent molecules: electron donors, acceptors, donor-acceptor pairs and miscellaneous molecules that display interesting electronic properties. Although many challenges still remain for practical use, state-of-the-art 1D supramolecular nanomaterials have already brought significant advances to both fundamental chemical sciences and technological applications.

New aspects of porphyrins and related compounds: self-assembled structures in two-dimensional molecular arrays

The advanced state of development of molecular design and synthetic chemistry of porphyrins and related molecules makes these compounds good candidates for technological appli cations, in which well characterized and designed structures and properties are required. In particular, 2-dimensional molecular level control of porphyrin array structures should reveal new aspects of nanotechnology. In this review, recent research on porphyrin assemblies, including 2-dimensional porphyrin arrays, is described with emphasis on phenol- and quinone-substituted tetrapyrrole units. A series of research aimed at developing strategies for preparation of porphyrin molecular arrays, where several novel aspects of molecular arrays, including phase transitions, ordered 2-D phase boundaries, and hydrogen-bonding networks, are introduced.

Highly linear self-assembled porphyrin wires

An efficient noncovalent assembly process involving high geometrical control was applied to a linear bis(imidazolyl zinc porphyrin) 7Zn, bearing C(18) substitutents, to generate linear multiporphyrin wires. The association process is based on imidazole recognition within the cavity of the phenanthroline-strapped zinc porphyrin. In chlorinated solvents, discrete soluble oligomers were obtained after (7Zn)(n) was end-capped with a terminal single imidazolyl zinc porphyrin derivative 4Zn. These soluble species, as well as their destabilization in the presence of protic solvents, were studied by UV-visible and time-resolved luminescence. In the solid state, assemblies as long as 480 nm, which corresponds to 190 iterative units or a total of 380 porphyrins, were observed by atomic force microscopy measurements on mica. The length and linearity of the porphyrin wires obtained illustrate the potential of phenanthroline-strapped porphyrins for the directional control of self-assembly processes.

Rational construction of perylene bisimide columnar superstructures with a biased helical sense

Discotic supramolecular complexes bearing six perylene bisimide (PBI) chromophores were prepared by mixing monotopically triple-hydrogen-bonding melamines equipped with two PBI chromophores and two 3,7-dimethyloctyl chiral handles with tritopically triple-hydrogen-bonding cyanuric acid (CA). UV/Vis and fluorescence titration experiments demonstrated that the discotic complexes were formed in methylcyclohexane by the 3:1 complexation between the melamines and CA. TEM and AFM studies revealed that the complexes hierarchically organize into fibrous columnar assemblies, which eventually results in the formation of organogels. Circular dichroism (CD) and flash-photolysis time resolved microwave conductivity measurements revealed the presence of extended chiral stacks of PBI chromophores within the columns. The anisotropy factors of the columnar assemblies are remarkably high (g=1.5×10(-3)) when considering the presence of only one 3,7-dimethyloctyl chiral handle per perylene chromophore, suggesting that the columnar structures have a biased helical sense. The fact that the chiral centers are located inside the discotic complexes rather than at their peripheries might be unique structural property responsible for the rather strong optical activities for the assemblies of this chromophore. The effective transcription of the molecular chirality to the extended columnar assemblies through the formation of unique discotic complexes enables the expression of "majority-rules" chiral amplification effect, which is unprecedented for the supramolecular assemblies of PBIs.

Synthesis and function of double-stranded helical polymers and oligomers

The design and synthesis of artificial helical polymers and oligomers has attracted much interest, in connection with fascinating biological helices and their sophisticated functions as well as possible applications in novel chiral materials. The last half-century has seen a significant advancement in the synthesis of single-stranded helical polymers and oligomers, since the discovery of the helical structure of isotactic polypropylene. In contrast, the chemistry of double-stranded helical counterparts is still premature. This paper highlights our recent achievements in the synthesis, structures, and functions of double-stranded helical polymers and oligomers, stressing an important role of supramolecular chemistry in the design and synthesis of double helices with a controlled helical sense.

ssPNA templated assembly of oligo(p-phenylenevinylene)s

A single-stranded oligothymine peptide nucleic acid (PNA) was used as a template for the assembly of a chiral oligo(p-phenylenevinylene) diaminotriazine derivative (OPV) in methylcyclohexane (MCH) revealing nanostructures in which the size is controlled by the template.

Lyomesophases of C3-symmetrical bipyridine-based discs in alkanes: an X-ray diffraction study

The importance of the role of alkane solvents in the self-assembly process of pi-conjugated molecules is well recognized but hardly understood. Here we present our results on the X-ray diffraction studies that we conducted to gain insight into the supramolecular structure of mixtures of a bipyridine-based molecule (1) with alkanes. Independent of the alkane used (linear or branched), above x(w) > 0.06 (with x(w) being the weight fraction of 1) the mixtures show lyotropic liquid-crystalline behavior. The nature of the lyomesophase depends only on x(w) and not on the nature of the alkane (linear or branched). A columnar rectangular phase is present when x(w) > 0.66. Upon dilution of 1, a columnar hexagonal phase is assigned first (0.50 < x(w) < 0.65), and finally a columnar nematic phase is observed when x(w) < 0.50. Concentration-dependent SAXD measurements revealed that the dilution of 1 can be viewed as a swelling process. First, solvent molecules occupy space between the columns formed by 1, which are not disrupted. This process can quantitatively be described by a 2D swelling model. Only at lower concentrations does 3D swelling start as the columns start breaking into shorter fragments.