Self-assembled pi-nanotapes as donor scaffolds for selective and thermally gated fluorescence resonance energy transfer (FRET)

Self-assembled nanotapes of a few tailor-made oligo(p-phenylenevinylene)s (OPVs) have been prepared and used as supramolecular donor scaffold to study the fluorescence resonance energy transfer (FRET) to a suitable acceptor. In nonpolar solvents, FRET occurs with nearly 63-81% efficiency, exclusively from the self-assembled OPVs to entrapped Rhodamine B, resulting in the quenching of the donor emission with concomitant formation of the acceptor emission at 625 nm. The efficiency of FRET is considerably influenced by the ability of the OPVs to form the self-assembled aggregates and hence could be controlled by structural variation of the molecules, and polarity of the solvent. Most importantly, FRET could be controlled by temperature as a result of the thermally reversible self-assembly process. The FRET efficiency was significantly enhanced (ca. 90%) in a xerogel film of the OPV1 which is dispersed with relatively less amount of the acceptor (33 mol %), when compared to that of the aggregates in dodecane gel. FRET is not efficient in polar solvents due to weak self-organization of the chromophores. These results indicate that energy transfer occurs exclusively from the self-assembled donor and not directly from the individual donor molecules. The present study illustrates that the self-assembly of chromophores facilitates temperature and solvent controlled FRET within pi-conjugated nanostructures.     

Tunable self-assembled peptide amphiphile nanostructures

Peptide amphiphiles are capable of self-assembly into a diverse array of nanostructures including ribbons, tubes, and vesicles. However, the ability to select the morphology of the resulting structure is not well developed. We examined the influence of systematic changes in the number and type of hydrophobic and hydrophilic amino acids on the self-assembly of amphiphilic peptides. Variations in the morphology of self-assembled peptides of the form X(6)K(n) (X = alanine, valine, or leucine; K = lysine; n = 1-5) are investigated using a combination of transmission electron microscopy and dynamic light scattering measurements. The secondary structures of the peptides are determined using circular dichroism. Self-assembly is controlled through a combination of interactions between the hydrophobic segments of the peptide molecules and repulsive forces between the charged segments. Increasing the hydrophobicity of the peptide by changing X to a more lipophilic amino acid or decreasing the number of hydrophilic amino acids transforms the self-assembled nanostructures from vesicles to tubes and ribbons. Changes in the hydrophobicity of the peptides are reflected in changes in the critical micelle concentration observed using pyrene probe fluorescence analysis. Self-assembled materials formed from cationic peptide amphiphiles of this type display promise as carriers for insoluble molecules or negatively charged nucleic acids in drug or gene delivery applications.     

Controllable synthesis of conducting polypyrrole nanostructures

Wire-, ribbon-, and sphere-like nanostructures of polypyrrole have been synthesized by solution chemistry methods in the presence of various surfactants (anionic, cationic, or nonionic surfactant) with various oxidizing agents [ammonium persulfate (APS) or ferric chloride (FeCl3), respectively]. The surfactants and oxidizing agents used in this study have played a key role in tailoring the nanostructures of polypyrrole during the polymerization. It is inferred that the lamellar structures of a mesophase are formed by self-assembly between the cations of a long chain cationic surfactant [cetyltrimethylammonium bromide (CTAB) or dodeyltrimethylammonium bromide (DTAB)] and anions of oxidizing agent APS. These layered mesostructures are presumed to act as templates for the formation of wire- and ribbon-like polypyrrole nanostructures. In contrast, if a short chain cationic surfactant octyltrimethylammonium bromide (OTAB) or nonionic surfactant poly(ethylene glycol) mono-p-nonylphenyl ether (Opi-10) is used, sphere-like polypyrrole nanostructures are obtained, whichever of the oxidizing agents mentioned above is used. In this case, micelles resulting from self-assembly among surfactant molecules are envisaged to serve as the templates while the polymerization happens. It is also noted that, if anionic surfactant sodium dodeyl surfate (SDS) is used, no characteristic nanostructures of polypyrrole were observed. This may be attributed to the doping effect of anionic surfactants into the resulting polypyrrole chains, and as a result, micelles self-assembled among surfactant molecules are broken down during the polymerization. The effects of monomer concentration, surfactant concentration, and surfactant chain length on the morphologies of the resulting polypyrrole have been investigated in detail. The molecular structures, composition, and electrical properties of the nanostructured polypyrrole have also been investigated in this study.     

Diverse Role of Solvents in Controlling Supramolecular Chirality

Supramolecular self-assembly stands for the spontaneous aggregation of small organic compounds or polymers into ordered structures at any scale. When being induced by inherent molecular chiral centers or ambient asymmetric factors, asymmetric spatial arrangement between building units shall occur, which is defined as supramolecular chirality. Except for molecular design, utilizing external stimulus factors to tune supramolecular chirality is a promising approach. In this Concept article, we particularly discuss the important role of solvents in manipulating the chirality of self-assembled systems. The impact of solvents on the chirality is generally based on three properties of solvents, i.e., chirality, polarity, and active coassembly with building blocks. Molecular self-assembly in chiral solvents could undergo the chirality transfer, exhibiting a chiral induction effect. Solvent polarity often determines intermolecular orientation. As a consequence, those building blocks with both polar and apolar segments might change their chirality depending on the solvent polarity. We elaborate the active participation of solvent molecules into ordered structures together with building blocks, where solvents and building blocks exhibit a coassembly manner. By specific treatments such as heating and cooling, solvents could be released or re-entrapped, allowing a smart control over supramolecular chirality. The solvent effect in manipulating two-dimensional chiral self-assemblies is then discussed. The perspective and future development in this research field are presented at last.     

Hierarchical Self-Assembled Photo-Responsive Tubisomes from a Cyclic Peptide-Bridged Amphiphilic Block Copolymer

Typically, the morphologies of the self-assembled nanostructures from block copolymers are limited to spherical micelles, wormlike micelles and vesicles. Now, a new generation of materials with unique shape and structures, cylindrical soft matter particles (tubisomes), are obtained from the hierarchical self-assembly of cyclic peptide-bridged amphiphilic diblock copolymers. The capacity of obtained photo-responsive tubisomes as potential drug carriers is evaluated. The supramolecular tubisomes pave an alternative way for fabricating polymeric tubular structures, and will expand the toolbox for the rational design of functional hierarchical nanostructures.     

Self-assembled lamellar nanostructures of wholly aromatic rod-rod-type block molecules

Wholly aromatic rod-rod type di- and triblock molecules, oligo(ether sulfone)-b-oligo(ether ketone)s (OES-OEK), were synthesized to study a solid-state self-assembled nanostructure. The OES and OEK segments in the block molecules form segregated crystalline domains. The energy-filtering transmission electron microscopy images revealed that the di- and triblock OES-OEK co-oligomers formed lamellar nanostructures with a periodicity of approximately 9 and 13 nm, respectively. [structure: see text].     

Functional supramolecular assemblies derived from dendritic building blocks

Control of the structure and function of self-assembled materials has been a significant issue in many areas of nanoscience. Among many different types of building blocks, dendritic ones have shown interesting self-assembly behaviour and functional performances due to their unique shape and multiple functionalities. Dendritic building blocks exhibit unique self-assembly behaviour in diverse environments such as aqueous and organic solutions, solid-liquid interfaces, and thermotropic solid conditions. Tuning the balance between hydrophilic and hydrophobic parts, as well as the external conditions for self-assembly, provides unique opportunities for control of supramolecular architectures. Furthermore, the introduction of suitable functional moieties into dendrons enables us to control self-assembly characteristics, allowing nanostructures to exhibit smart performances for electronic or biological applications. The self-assembly characteristics of amphiphilic dendrons under various conditions were investigated to elucidate how dendrons can assemble into nanoscopic structures and how these nanoassemblies exhibit unique properties. Well-defined nanostructures derived from self-assembly of dendrons provide an efficient approach for exhibition of unique functions at the nanoscale. This feature article describes the unique self-assembly characteristics of various types of dendritic building blocks and their potential applications as advanced materials.     

In Situ Self-Assembled J-Aggregate Nanofibers of Glycosylated Aza-BODIPY for Synergetic Cell Membrane Disruption and Type I Photodynamic Therapy

The in situ self-assembly of exogenous molecules is a powerful strategy for manipulating cellular behavior. However, the direct self-assembly of photochemically inert constituents into supramolecular nano-photosensitizers (PSs) within cancer cells for precise photodynamic therapy (PDT) remains a challenge. Herein, we developed a glycosylated Aza-BODIPY compound ( LMBP ) capable of self-assembling into J-aggregate nanofibers in situ for cell membrane destruction and type I PDT. LMBP selectively entered human hepatocellular carcinoma HepG2 cells and subsequently self-assembled into intracellular J-aggregate nanovesicles and nanofibers through supramolecular interactions. Detailed studies revealed that these J-aggregate nanostructures generated superoxide radicals (O₂⁻⋅) exclusively through photoinduced electron transfer, thus enabling effective PDT. Furthermore, the intracellular nanofibers exhibited an aggregation-induced retention effect, which resulted in selective toxicity to HepG2 cells by disrupting their cellular membranes and synergizing with PDT for powerful tumor suppression efficacy in vivo.     

Theoretical Study on Electronic and Charge Transfer Properties of Oligo[8]thiophene and Its Circular,Hooped, and Helical Derivatives

The novel linear, circular, hooped, and helical molecules based on oligo[8]thio- phene were theoretically studied for the applications of charge transfer devices. To investigate the influence of topology for oligo[8]thiophene derivatives, the geometry structures, frontier molecular orbital （FMO） energies, charge transport properties, and stability property were predicted by density functional theory methods. The calculated results reported herein show that the oligo[8]thiophene derivative with linear structure has smaller energy gap, and fused oligo[8]thiophene derivative with circular structure has the smallest reorganization energy among the designed molecules. We have also studied the stability properties of the designed molecules, and oligo[8]thiophene derivatives are more stable tharJ the fused oligo[8]thiophene derivatives.     

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 seque nce with less than three residues.As β-sheet supramolecular secondary structures have been discovered in solidstate 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-te rminal 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 structure s 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.     

Morphology transformation via pH-triggered self-assembly of peptides

Three flexible peptides (P1: (C(17)H(35)CO-NH-GRGDG)(2)KG; P2: (Fmoc-GRGDG)(2)KG; P3: (CH(3)CO-NH-GRGDG)(2)KG) self-assembled to form a variety of morphologically distinct assemblies at different pHs. P1 formed nanofibers at pH 3, then self-assembled into nanospheres with pH up to 6 and further changed to lamellar structures when the pH value was further increased to 10. P2 aggregated into an entwined network structure at pH 3, and then self-assembled into well-defined nanospheres, lamellar structures, and vesicles via adjusting the pH value. However, P3 did not self-assemble into well-ordered nanostructures, presumably due to the absence of a large hydrophobic group. The varying self-assembly behaviors of the peptides at different pHs are attributed to molecular conformational changes. These self-assembled supramolecular materials might contribute to the development of new peptide-based biomaterials.     

Self-assembly of amphiphiles with terthiophene and tripeptide segments into helical nanostructures

We previously reported a class of tripeptide amphiphiles known as peptide lipids that self-assemble into one-dimensional nanostructures with superhelical twisting. The pitch of this supramolecular twisting is controlled directly through sterics in the molecular structure of hydrophobic segments. In this work we study the supramolecular behavior of these nanoscale helices by substituting with a terthiophene conjugated segment of potential electronic interest and also through variations in the stereochemistry of the tripeptide. This terthiophene peptide lipid was shown to self-assemble into one-dimensional helical nanofibers with a regular diameter of 9±1 nm and helical pitch of 65±6 nm, and also found to form hierarchical double- and triple-stranded helices, which could be associated with terthiophene J-aggregate interactions among fibers. For stereochemical effects, we compared four diastereomers in the tripeptide sequence using l-glutamic acid and l- and d-alanine residues to probe their ability to control supramolecular organization. Interestingly, we found by atomic force microscopy that the LLD diastereomers formed cylindrical nanofibers without any twisting, whereas LDD diastereomeric segments self-assembled into helical nanofibers with a pitch of 40±6 nm. LDL diastereomeric segments formed, on the other hand, aggregates without any regular shape. We propose that these profound effects of chirality with amino acid sequence are related to changes in the β-sheet sub-structure within the nanofibers.     

Hybrid Soft Nanomaterials Composed of DNA Microspheres and Supramolecular Nanostructures of Semi-artificial Glycopeptides

Aqueous hybrid soft nanomaterials consisting of plural supramolecular architectures with a high degree of segregation (orthogonal coexistence) and precise hierarchy at the nano- and microscales, which are reminiscent of complex biomolecular systems, have attracted increasing attention. Remarkable progress has been witnessed in the construction of DNA nanostructures obtained by rational sequence design and supramolecular nanostructures of peptide derivatives through self-assembly under aqueous conditions. However, orthogonal self-assembly of DNA nanostructures and supramolecular nanostructures of peptide derivatives in a single medium has not yet been explored in detail. In this study, DNA microspheres, which can be obtained from three single-stranded DNAs, and three different supramolecular nanostructures (helical nanofibers, straight nanoribbons, and flowerlike microaggregates) of semi-artificial glycopeptides were simultaneously constructed in a single medium by a simple thermal annealing process, which gives rise to hybrid soft nanomaterials. Fluorescence imaging with selective staining of each supramolecular nanostructure uncovered the orthogonal coexistence of these structures with only marginal impact on their morphology. Additionally, the biostimuli-responsive degradation propensity of each supramolecular architecture is retained, and this may allow the construction of active soft nanomaterials exhibiting intelligent biofunctions.     

Synthesis and self-assembly of oligomers containing cruciform 9,10-bis(arylethynyl)anthracene unit: formation of supramolecular nanostructures based on rod-length-dependent organization

Conjugated rod-coil molecules, incorporating flexible and rigid blocks, have a strong affinity to self-organize into various supramolecular nanostructures in the bulk state.In this study, we report synthesized oligomers containing cruciform 9,10-bis(arylethynyl)anthracene units and characterized their self-assembly behavior. The molecular structures were characterized with ¹H, ¹³C NMR, and matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectroscopy. An investigation of the supramolecular nanostructures of these molecules using differential scanning calorimetry, thermal polarized optical microscopy, and small-angle X-ray scattering revealed that the rod length of coil-rod-coil molecules with identical rod to coil volume ratios dramatically influences self-assembly behavior in the bulk state. Molecules 2 and 3 with relatively longer rod lengths self-assemble into lamellar structures in the solid state, whereas, molecules 1 and 4 self-assemble into two-dimensional (2-D) oblique columnar structures in the liquid crystalline phase, in addition, on heating, molecule 1 transforms from the oblique columnar phase to the nematic phase.     

Peptide amphiphile nanofibers with conjugated polydiacetylene backbones in their core

The coupling of electronic and biological functionality through self-assembly is an interesting target in supramolecular chemistry. We report here on a set of diacetylene-derivatized peptide amphiphiles (PAs) that react to form conjugated polydiacetylene backbones following self-assembly into cylindrical nanofibers. The polymerization reaction yields highly conjugated backbones when the peptidic segment of the PAs has a linear, as opposed to a branched, architecture. Given the topotactic nature of the polymerization, these results suggest that a high degree of internal order exists in the supramolecular nanofibers formed by the linear PA. On the basis of microscopy, the formation of a polydiacetylene backbone to covalently connect the beta-sheets that help form the fibers does not disrupt the fiber shape. Interestingly, we observe the appearance of a polydiacetylene (PDA) circular dichroism band at 547 nm in linear PA nanofibers suggesting the conjugated backbone in the core of the nanostructures is twisted. We believe this CD signal is due to chiral induction by the beta-sheets, which are normally twisted in helical fashion. Heating and cooling shows simultaneous changes in beta-sheet and conjugated backbone structure, indicating they are both correlated. At the same time, poor polymerization in nanofibers formed by branched PAs indicates that less internal order exists in these nanostructures and, as expected, then a circular dichroism signal is not observed for the conjugated backbone. The general variety of materials investigated here has the obvious potential to couple electronic properties and in vitro bioactivity. Furthermore, the polymerization of monomers in peptide amphiphile assemblies by a rigid conjugated backbone also leads to mechanical robustness and insolubility, two properties that may be important for the patterning of these materials at the cellular scale.     

Morphology controlled self-assembled nanostructures of sandwich mixed (phthalocyaninato)(porphyrinato) europium triple-deckers. Effect of hydrogen bonding on tuning the intermolecular interaction

A series of five novel sandwich-type mixed (phthalocyaninato)(porphyrinato) europium triple-decker complexes with different numbers of hydroxyl groups at the meso-substituted phenyl groups of porphyrin ligand 1-5 have been designed, synthesized, and characterized. Their self-assembly properties, in particular the effects of the number and positions of hydroxyl groups on the morphology of self-assembled nanostructures of these triple-decker complexes, have been comparatively and systematically studied. Competition and cooperation between the intermolecular pi-pi interaction and hydrogen bonding in the direction perpendicular to the pi-pi interaction direction for different compounds were revealed to result in nanostructures with a different morphology from nanoleafs for 1, nanoribbons for 2, nanosheets for 3, and curved nanosheets for 4 and to spherical shapes for 5. The IR and X-ray diffraction (XRD) results reveal that, in the nanostructures of triple-decker 2 as well as 3-5, a dimeric supramolecular structure was formed through an intermolecular hydrogen bond between two triple-decker molecules, which as the building block self-assembles into the target nanostructures. Electronic absorption spectroscopic results on the self-assembled nanostructures reveal the H-aggregate nature in the nanoleafs and nanoribbons formed from triple-deckers 1 and 2 due to the dominant pi-pi intermolecular interaction between triple-decker molecules, but the J-aggregate nature in the curved nanosheets and spherical shapes of 4 and 5 depending on the dominant hydrogen bonding interaction in cooperation with pi-pi interaction among the triple-decker molecules. Electronic absorption and XRD investigation clearly reveal the decrease in the pi-pi interaction and increase in the hydrogen bonding interaction among triple-decker molecules in the nanostructures along with the increase of hydroxyl number in the order of 1-5. The present result appears to represent the first effort toward realization of controlling and tuning the morphology of self-assembled nanostructures of sandwich tetrapyrrole rare earth complexes through molecular design and synthesis.     

Assembly of peptide–thiophene conjugates: the influence of peptide content and location

Biomolecule-directed self-assembly of π-conjugated oligomers has attracted great attention in the past decade. In this contribution, two conjugates composed of quaterthiophene and tetrapeptide (Gly-Val-Gly-Val) were synthesised, namely peptide–thiophene–peptide (PTP) and thiophene–peptide–thiophene (TPT), to investigate the influence of peptide content ratio and its location in the molecular structures on the nanostructures and properties of the assemblies. Both conjugates formed organogels consisting of left-handed twisted nanostructures; however, anti-parallel β-sheets were observed in PTP while parallel β-sheets were obtained for TPT, although in both cases oligothiophenes adopted an H-like stacking mode. Obvious solvent-induced supramolecular chirality inversion from the oligothiophene segment was observed for PTP while such phenomenon was not clear for TPT. PTP and TPT gels also showed different stabilities towards temperature increase, as evidenced by variable-temperature circular dichroism study. From the data, it is suggested that the rational design of the location and ratio of peptide plays a key role in constructing materials with determined properties based on peptide–thiophene conjugates.     

Camouflaged carborane amphiphiles: synthesis and self-assembly

A series of amphiphilic amine hydrochloride salts of B-polymethylated (camouflaged) (aminoalkyl)- and bis(aminoalkyl)carboranes have been designed and synthesized in high yield for the purpose of constructing novel carborane-based nanomaterials. Due to the distinct separation of the hydrophobic and hydrophilic regions within each salt, the mono- and disubstituted amphiphiles spontaneously self-assembled upon sonication into rod-shape micro/nanostructures in aqueous solutions. The effects of concentration, method of dispersion, solvent, chain length, counterion, ionic charge, and underlying carborane cage structure on the formation of the these rod products were investigated. The microrods have been studied by transmission electron microscopy (TEM), optical microscopy, X-ray powder diffraction (XRD), thermogravimetric/differential thermal analysis (TG/DTA), and FTIR. For the first time, this work clearly demonstrates the self-assembly of B-polymethylated carboranes into supramolecular structures.     

[60]富勒烯的超分子自组装研究进展

超分子自组装是发展超分子电子学的重要途径。随着纳米科学和技术的迅速发展,自组装技术已成功地应用于纳米尺度物质的维数、形貌和功能等的调控。作为构筑分子水平上一维、二维、三维有序功能结构和高有序分子聚集态结构的关键技术,超分子自组装技术有力地推动了具有优良光、电、磁性能的分子材料和纳米功能材料更深层次的研究。本文综述了超分子自组装在富勒烯科学领域的基础研究和应用,特别是对有利于自组织和自组装功能的富勒烯基衍生物的设计与合成、超分子作用力引导的具有特定结构的分子体系的可控自组装、以及富勒烯分子聚集态结构材料的光物理过程、超分子中电子转移和能量转移现象进行了描述;并对卟啉、四硫富瓦烯、碗烯和杯芳烃等一系列富π电子化合物和大环主体分子等包含[60]富勒烯的主体化合物的超分子作用和超分自组装体以及通过氢键、π-π作用、静电力和范德华力和金属配位作用形成的[60]富勒烯超分子自组装体进行了总结,对未来发展进行了展望。     

Chiral amphiphilic self-assembled alpha,alpha'-linked quinque-, sexi-, and septithiophenes: synthesis, stability and odd-even effects

The synthesis, characterization, and self-assembly in butanol of a series of well-defined alpha,alpha'-linked quinqui-, sexi-, and septithiophenes substituted, via ester links at their termini, by chiral oligo(ethylene oxide) chains carrying an alpha, beta, delta, and epsilon methyl, respectively, are reported. Studies of the self-assembly of these molecules using UV/visible absorption, luminescence, and circular dichroism spectroscopies reveal, for the sexithiophene case, that the magnitude of the observed Cotton effect in the aggregates diminishes progressively as the chiral substituent is moved away from the thiophene segment. The stability of the assemblies increases with the length of the oligothiophene and as the substituent chiral unit is moved away from the aromatic core, being greatest for the unsubstituted case. The sign of the Cotton effect alternates in an "odd/even" manner as the position of the chiral substituent is moved along the oligo(ethylene oxide) chain and on going from the quinquethiophene to the septithiophene having the same side chain. Atomic force microscopy on materials deposited from solution on an aluminum or glass surface and optical measurements show that capsules are formed from the oligothiophenes with H-type packing of the aromatic segments.