Self-assembly of supra-amphiphiles based on dual charge-transfer interactions: from nanosheets to nanofibers

Gemini Surfactant-Induced Cysteine-Capped Copper Nanoclusters Self-Assembly with Enhanced Peroxidase-Like Activity and Colorimetric Glutathione Sensing

We have prepared a novel assembly with copper nanoclusters (CuNCs) and imidazolium-based gemini surfactants (different chain lengths). These novel mimic enzymes formed through the assembly of nanocluster-gemini surfactants have been utilized in creating colorimetric sensors to detect biomolecules. Yet, understanding the method for detecting glutathione (GSH) and its sensing mechanism using this specific assembly-based colorimetric sensor poses a significant challenge. Because of the role of surface ligands, the complexes of cysteine-capped CuNCs (Cys-CuNCs) and gemini surfactants exhibit strong amphiphilicity, enabling them to self-assemble like a molecular amphiphile. We have investigated the kinetics and catalytic capabilities of this Cys-CuNCs@gemini surfactant assembly through peroxidase-like activity. Additionally, a sensitive and simple-to-use colorimetric sensing approach for glutathione (GSH) is also disclosed here, demonstrating a low limit of detection, by using this peroxidase-like activity of Cys-CuNCs@gemini surfactant assemblies. Thus, the remarkable advantages of the Cys-CuNCs@gemini surfactant nanozyme make it suitable for the precise colorimetric detection of GSH, demonstrating excellent sensitivity and reliable selectivity. Additionally, it performs well in detecting GSH in various soft drinks.

Self-assembly solid-state enhanced fluorescence emission of GFP chromophore analogues: Formation of microsheets and microtubes oriented by molecular skeleton

The p-, m- and o-N,N-dimethylamino analogs of the green fluorescent protein (GFP) chromophore (denoted as p-DBHI, m-DBHI and o-DBHI) were synthesized by 2,3-cycloaddition. These three compounds were structurally characterized by NMR, HRMS and single crystal X-ray diffraction and were shown to be in the Z-form in both the solid phase and solution. Their fluorescence properties and self-assembly behaviors were investigated by UV-Vis, photoluminescence spectroscopy, fluorescence microscopy and scanning electron microscopy. They exhibited low fluorescence quantum yields in both protic and aprotic solvents, which was consistent with the reported results, and strong emissions in the solid state, thus exhibiting aggregation-induced emission (AIE) behaviors. By a solvent exchange method, the p-DBHI and o-DBHI were assembled into microsheets, while the m-DBHI was assembled into microtubule-like structures. The photoluminescence properties of the assemblies were compared with those of the pristine microcrystalline powders obtained by evaporation from organic solvents. The fluorescence quantum yields of the microcrystals obtained by self-assembly were recorded to 9.86 %, 3.37 % and 31.65 %, respectively, which were much higher than those of the corresponding pristine powders (4.71 %, 2.51 % and 17.03 %). This indicated that the fluorescence properties in the solid state depended on the morphologies of the particles.

Hydrogel Nanosheets Confined 2D Rhombic Ice: A New Platform Enhancing Chondrogenesis

Nanoconfinement within flexible interfaces is a key step towards exploiting confinement effects in several biological and technological systems wherein flexible 2D materials are frequently utilized but are arduous to prepare. Hitherto unreported, the synthesis of 2D Hydrogel nanosheets (HNS) using a template- and catalyst-free process is developed representing a fertile ground for fundamental structure-property investigations. In due course of time, nucleating folds propagating along the edges trigger co-operative deformations of HNS generating regions of nanoconfinement within trapped water islands. These severely constricting surfaces force water molecules to pack within the nanoscale regime of HNS almost parallel to the surface bringing about phase transition into puckered rhombic ice with AA and AB Bernal stacking pattern, which was mostly restricted to Molecular dynamics (MD) studies so far. Interestingly, under high lateral pressure and spatial inhomogeneity within nanoscale confinement, bilayer rhombic ice structures were formed with an in-plane lattice spacing of 0.31 nm. In this work, a systematic exploration of rhombic ice formation within HNS has been delineated using High-resolution transmission electron microscopy (HRTEM), and its ultrathin morphology was examined using Atomic Force Microscopy (AFM). Scanning Electron Microscopy (SEM) images revealed high porosity while mechanical testing presented young's modulus of 155 kPa with ~84% deformation, whereas contact angle suggested high hydrophilicity. The combinations of nanosheets, porosity, nanoconfinement, hydrophilicity, and mechanical strength, motivated us to explore their application as a scaffold for cartilage regeneration, by inducing chondrogenesis of human Wharton Jelly derived mesenchymal stem cells (hWJ MSCs). HNS promoted the formation of cell aggregates giving higher number of spheroid formation and a marked expression of chondrogenic markers (ColI, ColII, ColX, ACAN and S-100), thereby providing some cues for guiding chondrogenic differentiation.

Digold(I) Thianthrenyl Complexes. Effect of Diphosphine Ligands on Molecular Structures in the Solid State and in Solution

A series of digold complexes possessing two thianthrenyl ligands, Au₂(Thi)₂(Ph₂P(CH₂) _n PPh₂) (Thi: 1-thianthrenyl; 1: n = 1, 2: n = 2, 3: n = 3, 4: n = 4), were prepared and characterized by crystallographic and spectroscopic measurements. X-ray crystallography of complexes 1 and 3 revealed U-shaped structures with short Au-Au distances [3.2171(3) Å and 3.0735(2) Å]. Complex 2 and three of the four structure-determined molecules of complex 4 showed structures without Au-Au contacts. UV-vis spectroscopic measurements of 1-4 and TD-DFT calculations of the two conformers of 1 revealed that complexes 1 and 3 in the solution phase contained conformers with Au(I)-Au(I) interactions in a much higher proportion than complexes 2 and 4. As a result, complexes with diphosphine ligands containing an odd number of methylene groups preferred structures with Au-Au interactions in the solid state and in solution. Oxidation of 1 with 2 equiv of PhICl₂ yielded a mixture of monomeric and dimeric thianthrenes and its dimer via ligand elimination and C-C coupling, respectively.

Responsive Interfacial Assemblies Based on Charge-Transfer Interactions

Charge transfer (CT) interactions have been widely used to construct supramolecular systems, such as functional nanostructures and gels. However, to date, there is no report on the generation of CT complexes at the liquid-liquid interface. Here, by using an electron-deficient acceptor dissolved in water and an electron-rich donor dissolved in oil, we present the in situ formation and assembly of CT complex surfactants (CTCSs) at the oil-water interface. With time, CTCSs can assemble into higher-order nanofilms with exceptional mechanical properties, allowing the stabilization of liquids and offering the possibility to structure liquids into nonequilibrium shapes. Moreover, due to the redox-responsiveness of the electron-deficient acceptor, the association and dissociation of CTCSs can be reversibly manipulated in a redox process, leading to the switchable assembly and disassembly of the resultant constructs.

Solvent-Directed Transformation of the Self-assembly and Optical Property of a Peptide-Appended Core-Substituted Naphthelenediimide and Selective Detection of Nitrite Ions in an Aqueous Medium

This study vividly displays the different self-assembling behavior and consequent tuning of the fluorescence property of a peptide-appended core-substituted naphthalenediimide (N1) in the aliphatic hydrocarbon solvents (n-hexane/n-decane/methyl cyclohexane) and in an aqueous medium within micelles. The N1 is highly fluorescent in the monomeric state and self-aggregates in a hydrocarbon solvent, exhibiting "H-type" or "face-to-face" stacking as indicated by a blue shift of absorption maxima in the UV-vis spectrum. In the H-aggregated state, the fluorescence emission of N1 changes to green from the yellow emission obtained in the monomeric state. In the presence of a micelle-forming surfactant, cetyl trimethylammonium bromide (CTAB), the N1 is found to be dispersed in a water medium. Interestingly, upon encapsulation of N1 into the micelle, the molecule alters its self-assembling pattern and optical property compared to its behavior in the hydrocarbon solvent. The N1 exhibits "edge-to-edge" stacking or J aggregates inside the micelle as indicated by the UV-vis spectroscopic study, which shows a red shift of the absorption maxima compared to that in the monomeric state. The fluorescence emission also differs in the water medium with the NDI derivative exhibiting red emission. FT-IR studies reveal that all amide NHs of N1 are hydrogen-bonded within the micelle (in the J-aggregated state), whereas both non-bonding and hydrogen-bonding amide NHs are present in the H-aggregated state. This is a wonderful example of solvent-mediated transformation of the aggregation pattern (from H to J) and solvatochromism of emission over a wide range from green in the H-aggregated state to yellow in the monomeric state and orangish-red in the J-aggregated state. Moreover, the J aggregate has been successfully utilized for selective and sensitive detection of nitrite ions in water even in the presence of other common anions (NO₃^-, SO₄^2-, HSO₄^-, CO₃^2-, and Cl^-).

Self-Assembly of Amphiphilic Copper Nanoclusters Driven by Cationic Surfactants

Amphiphilicity is an excellent physicochemical property, which is yet to be explored from traditional surfactants to nanoparticles. This article shows that the amphiphilicity of copper nanoclusters (CuNCs) can be readily tuned by electrostatic interactions with cationic surfactants and cetyltrimethylammonium cations (CTA⁺) with counterions Br^-, Cl^-, and C₇H₈O₃S^-. Due to the role of surface ligands, the complexes of glutathione-capped CuNCs (GSH-CuNCs) and the surfactants exhibit good amphiphilicity, which enables them to self-assemble like a molecular amphiphile. This could significantly increase the utility of metal nanoclusters in basic and applied research. As the concentration of the surfactant changes, the aggregates change from nanoparticles to network-like structures. After the formation of supramolecular self-assemblies by hydrophobic interactions, the enhancement of fluorescence intensity was observed, which can be ascribed to the suppression of intramolecular vibrations based on aggregation-induced emission (AIE) and combined with the compactness of GSH-CuNCs in self-assemblies. Our study provides a facile way to generate solid fluorescent materials with excellent fluorescence performance, which may find applications in light-emitting diodes (LEDs).

Uniform Nanowires Containing a Heterogeneousπ-Conjugated Core of Controlled Length, Composition and Morphology

In this work, it is demonstrated for the first time that heterojunction nanowires, consisting of a gradient and segmented-like heterogeneous π-conjugated core with controllable length, composition and morphology, can be generated by co-self-seeding of oligo(p-phenylene vinylene) (OPV)- and oligo(p-phenylene ethynylene) (OPE)-containing block copolymers in spite of different chain lengths and molecular conformation for OPE and OPV. More importantly, based on the understanding of the formation of heterogeneous core by the co-self-seeding approach, a "heating/cooling" seeded growth route was developed, by which linear and branched heterojunction nanowires containing a segmented heterogeneous π-conjugated core of controlled length, composition and morphology can be obtained. This work provides a versatile platform to generate heterojunction nanowires with excellent controllability in length, composition, and morphology.

Synergistic effect of hydrophobic and hydrogen bonding interaction-driven viologen-pyranine charge-transfer aggregates: adenosine monophosphate recognition

Understanding the role of non-covalent interactions that dictate and fine-tune the direction of self-assembly of functional molecules is crucial for developing stimuli responsive materials. Herein, we systematically designed and synthesized viologen derivatives with hydrophobic dodecyl chains and alkyl carboxylic acid functionalities. The complementary electronic and electrostatic counterpart of viologens was chosen as pyranine. Viologens comprising of a hydrophobic dodecyl chain on one terminal and hydrogen bonding alkyl carboxylic acid on the other (V1 and V2) underwent aggregation to a varying extent upon interaction with pyranine. The length of the alkyl carboxylic acid had a greater impact on the nature and morphology of the aggregates. Control molecules (V3 and V4) in which 4,4'-bipyridine was symmetrically quaternized with alkyl carboxylic acids did not aggregate upon interaction with pyranine. The delicate balance existing between the hydrophobicity of the dodecyl chains and the intermolecular hydrogen bonding interaction between the alkyl carboxylic acid groups in V1 or V2 of the corresponding charge transfer (CT) complexes was instrumental in driving the aggregation. The CT aggregates of [V1-Pyr] and [V2-Pyr] exhibited excellent stability in water which disaggregated at physiological pH. We emphasize on the importance of synergy between hydrophobic and hydrogen bonding interactions in reinforcing each other to drive the supramolecular aggregation of the CT complexes. Such pH dependent CT aggregates are of importance as scaffolds in pH controlled drug release. In the present study, the CT aggregates were evaluated for adenosine nucleotide recognition in water; [V1-Pyr] and [V2-Pyr] exhibited selective response towards adenosine monophosphate via deprotonation induced dissolution of aggregates in water leading to emission enhancement.

Multiple-Responsive Hierarchical Self-Assemblies of a Smart Supramolecular Complex: Regulation of Noncovalent Interactions

We herein report a smart amphiphilic supramolecular complex ([MimA-EDA-MimA]@[DBS]₂) with stimuli-responsive self-assembly, constructed by 3-(3-formyl-4-hydroxybenzyl)-1-methylimidazolium chloride (MimACl), sodium dodecyl benzene sulfonate (SDBS), and ethylenediamine (EDA). The self-assembly of [MimA-EDA-MimA]@[DBS]₂ shows triple-sensitivities in response to pH, concentration, and salt. At a low pH, only micelles are formed, which can transform into vesicles spontaneously when the pH increases to 11.8. Vesicles can gradually fuse into vesicle clusters and elongated assemblies with increasing concentration of [MimA-EDA-MimA]@[DBS]₂. Chainlike aggregates, ringlike aggregates, or giant vesicles can be formed by adding inorganic salts (i.e., NaCl and NaNO₃), which could be derived from the membrane fusion of vesicles. The noncovalent interactions, including π-π stacking, hydrogen bonding, and electrostatic interactions, were found to be responsible for the topology evolution of assemblies. Thus, it provides an opportunity to construct smart materials through the regulation of the role of noncovalent interactions in self-assembly.

Supramolecular self-assemblies for bacterial cell agglutination driven by directional charge-transfer interactions

Two supramolecular amphiphiles are fabricated through directional charge-transfer interactions, which self-assemble into nanofibers and nanoribbons. Due to the existence of galactose on their surface, these self-assemblies act as a cell glue to agglutinate E. coli, benefiting from multivalent interactions.

The sensitivity of donor - acceptor charge transfer to molecular geometry in DAN - NDI based supramolecular flower-like self-assemblies

A charge-transfer (CT) complex self-assembled from an electron acceptor (NDI-EA: naphthalene diimide with appended diamine) and an electron donor (DAN: phosphonic acid-appended dialkoxynapthalene) in aqueous medium. The aromatic core of the NDI and the structure of DAN1 were designed to optimize the dispersive interactions (π-π and van der Waals interactions) in the DAN1–NDI-EA self-assembly, while the amino groups of NDI also interact with the phosphonic acid of DAN1 via electrostatic forces. This arrangement prevented crystallization and favored the directional growth of 3D flower nanostructures. This molecular geometry that is necessary for charge transfer to occur was further evidenced by using a mismatching DAN2 structure. The flower-shaped assembly was visualized by scanning electron and transmission electron microscopy. The formation of the CT complex was determined by UV-vis and cyclic voltammetry and the photoinduced electron transfer to produce the radical ion pair was examined by femtosecond laser transient absorption spectroscopic measurements.

Cu(II) Ion-Responsive Self-Assembly Based on a Water-Soluble Pillar[5]arene and a Rhodamine B-Containing Amphiphile in Aqueous Media

Cu(II) ion-responsive self-assembly in aqueous media was achieved based on a water-soluble pillar[5]arene host and a rhodamine B-containing amphiphile guest. The host-guest complex acted as a supra-amphiphile and self-assembled into vesicles. After addition of Cu(II), vesicles turned into solid nanoparticles, accompanied by the color change of the solution from colorless to red and a fluorescence "on" phenomenon.

First report of charge-transfer induced heat-set hydrogel. Structural insights and remarkable properties

The remarkable ability of a charge-transfer (CT) complex prepared from a pyrene-based donor (Py-D) and a naphthalenediimide-based acceptor (NDI-A) led to the formation of a deep-violet in color, transparent hydrogel at room temperature (RT-gel). Simultaneously, the RT-gel was diluted beyond its critical gelator concentration (CGC) to obtain a transparent sol. Very interestingly, the resultant sol, on heating above 70 °C, transformed into a heat-set gel instantaneously with a hitherto unknown CGC value. Detailed studies revealed the smaller globular aggregates of the RT-gels fuse to form giant globules upon heating, which, in turn, resulted in heat-set gelation through further aggregation. The thermoresponsive property of Py-D alone and 1 : 1 Py-D : NDI-A CT complex was investigated in detail which revealed the hydrophobic collapse of the oxyethylene chains of the CT complex upon heating was mainly responsible for heat-set gelation. Thixotropy, injectability, as well as stimuli responsiveness of the RT-gels were also addressed. In contrast, heat-set gel did not show thixotropic behavior. The X-ray diffraction (XRD) patterns of the xerogel depicted lamellar packing of the CT stacks in the gel phase. Single crystal XRD studies further evidenced the 1 : 1 mixed CT stack formation in the lamellae and also ruled out orthogonal hydrogen bonding possibilities among the hydrazide unit in the CT gel although such interaction was observed in a single crystal of NDI-A alone. In addition, a Ag(+)-ion triggered metallogelation of NDI-A and nematic liquid-crystalline property of Py-D were also observed.

Self-assembly of fluorescent diimidazolium salts: tailor properties of the aggregates changing alkyl chain features

Self assembly of fluorescent diimidazolium NDI salts showed properties of aggregates changing with alkyl chain length, with an odd–even effect.

Dual-responsive self-assembly of a bola-type supra-amphiphile constructed from a new pillar[6]arene-based recognition motif in water and its application in controlled release

A new host–guest system based on a water-soluble pillar[6]arene (WP6) was designed and its application in the construction of dual-responsive self-assembly of a bola-type supra-amphiphile and application in controlled release was achieved.

Pillar[10]arene-based host–guest complexation promoted self-assembly: from nanoparticles to uniform giant vesicles

A novel host-guest recognition motif between a water-soluble pillar[10]arene and pyrene derivative was established and further applied in the fabrication of a pH-responsive supra-amphiphile.

Tetraphenylethene-containing supramolecular hyperbranched polymers: aggregation-induced emission by supramolecular polymerization in aqueous solution

Supramolecular hyperbranched polymers have been constructed, by using host-enhanced π–π interactions between CB[8] and a TPE derivative, with aggregation-induced emission.

Flower-like supramolecular self-assembly of phosphonic acid appended naphthalene diimide and melamine

Diverse supramolecular assemblies ranging from nanometres to micrometers of small aromatic π-conjugated functional molecules have attracted enormous research interest in light of their applications in optoelectronics, chemosensors, nanotechnology, biotechnology and biomedicines. Here we study the mechanism of the formation of a flower-shaped supramolecular structure of phosphonic acid appended naphthalene diimide with melamine. The flower-shaped assembly formation was visualised by scanning electron microscope (SEM) and transmission electron microscopy (TEM) imaging, furthermore, XRD and DLS used to determined mode of aggregation. Characteristically, phosphonic acid-substituted at imide position of NDIs possess two important properties resulting in the formation of controlled flower-like nanostructures: (i) the aromatic core of the NDI which is designed to optimize the dispersive interactions (π-π stacking and van der Waals interactions) between the cores within a construct and (ii) phosphonic acid of NDI interact with malamine through molecular recognition i.e. strong hydrogen-bonding (H-bonding). We believe such arrangements prevent crystallization and favour the directional growth of flower-like nanostructure in 3D fashion. These works demonstrate that complex self-assembly can indeed be attained through hierarchical non-covalent interactions of two components. Furthermore, flower-like structures built from molecular recognition by these molecules indicate their potential in other fields if combined with other chemical entities.

Inversion of supramolecular chirality in bichromophoric perylene bisimides: influence of temperature and ultrasound

The supramolecular helicity in the self-assembled nanostructures of two perylene bisimide bichromophoric systems could be controlled by varying the preparatory methods. The self-assembly of the compounds under different conditions was investigated in detail by using absorption, fluorescence, CD, FTIR, XRD, TEM, and SEM techniques. These studies reveal that the heating-cooling method results in aggregates with ordered molecular packing and enhanced optical chirality. Ultrasonication leads to molecular aggregates with less ordered packing wherein the supramolecular chirality was reversed relative to the sample prepared via a heating-cooling method. This heating-cooling method proved to be superior in terms of nanofiber synthesis, yielding fibers with extended length and a prominent helical twist. At higher concentration, both compounds exhibited a gelation property in benzonitrile. The tunable chiroptical properties in these supramolecular systems make them potential candidates for applications in the field of optical and electronic device fabrication based on organic nanostructures.

Supra-amphiphiles: a new bridge between colloidal science and supramolecular chemistry

In addition to conventional amphiphiles, an emerging research area is supra-amphiphiles, which are constructed on the basis of noncovalent interactions and dynamic covalent bonds. In this feature article, we have provided a general introduction to the concept, design principles, and topologies of supra-amphiphiles, starting from some rationally tailored building blocks. In addition, we highlight some progress in the functional assembly of supra-amphiphiles, such as responsive nanoscale carriers, antibacterial and antitumor agents, fluorescent-based chemical sensors, and enzyme mimics. The supra-amphiphile is a new bridge between colloidal science and supramolecular chemistry, and it is a field where we can make full use of our imaginative power.

Supra-amphiphilic aggregates formed by p-sulfonatocalix[4]arenes and the antipsychotic drug chlorpromazine

We report here a supramolecular strategy to directly assemble the small molecular antipsychotic drug chlorpromazine (CPZ) into nanostructures, induced by p-sulfonatocalix[4]arene (SC4A) and p-sulfonatocalix[4]arene tetraheptyl ether (SC4AH), with high drug loading efficiencies of 61% and 46%, respectively. The binary host-guest assembly process was monitored using optical transmittance measurements, and the size and morphology of these two kinds of supra-amphiphilic assemblies were identified using a combination of light scattering and high-resolution transmission electron microscopy, which showed solid spherical micelles. This strategy presents new opportunities for the development of high loading drug-containing carriers with easy processability for drug delivery.

Mono-molecule-layer nano-ribbons formed by self-assembly of bolaamphiphiles

Amphiphilic molecules generally tend to organize spontaneously into spherical or cylindrical micelles/vesicles in appropriate liquid media and conditions, and seldom form two dimensional (2D) planar structures with a regular shape, due to their energetically unfavorable state. Herein, the self-assembly of a new bolaamphiphile bearing a bistriazole-pyrene unit leads to the formation of mono-molecule-layer nano-ribbons. The π-π stacking interaction between the rigid bistriazole-pyrene units and electrostatic screening contributed by the aromatic counterion tosyl groups are responsible for the 2D alignment of the molecules in the aggregate. Partial replacement of the tosyl groups causes a reduction in the width of the nano-ribbons and the coordination of triazole with Pd2+ ions results in the collapse of the self-assembled structure. This study supplies new clues for fabricating molecular level 2D nanostructures by bottom-up supramolecular assembly.