Autonomous Growth of a Spatially Localized Supramolecular Hydrogel with Autocatalytic Ability

Autocatalysis and self‐assembly are key processes in developmental biology and are involved in the emergence of life. In the last decade both of these features were extensively investigated by chemists with the final goal to design synthetic living systems. Herein, we describe the autonomous growth of a self‐assembled soft material, that is, a supramolecular hydrogel, able to sustain its own formation through an autocatalytic mechanism that is not based on any template effect and emerges from a peptide (hydrogelator) self‐assembly. A domino sequence of events starts from an enzymatically triggered peptide generation followed by self‐assembly into catalytic nanofibers that induce and amplify their production over time, resulting in a 3D hydrogel network. A cascade is initiated by traces (10^?18 m ) of a trigger enzyme, which can be localized allowing for a spatial resolution of this autocatalytic buildup of hydrogel growth, an essential condition on the route towards further cell‐mimic designs.     

Control of Stem‐Cell Behavior by Fine Tuning the Supramolecular Assemblies of Low‐Molecular‐Weight Gelators

Controlling the behavior of stem cells through the supramolecular architecture of the extracellular matrix remains an important challenge in the culture of stem cells. Herein, we report on a new generation of low‐molecular‐weight gelators (LMWG) for the culture of isolated stem cells. The bola‐amphiphile structures derived from nucleolipids feature unique rheological and biological properties suitable for tissue engineering applications. The bola‐amphiphile‐based hydrogel scaffold exhibits the following essential properties: it is nontoxic, easy to handle, injectable, and features a biocompatible rheology. The reported glycosyl‐nucleoside bola‐amphiphiles (GNBA) are the first examples of LMWG that allow the culture of isolated stem cells in a gel matrix. The results (TEM observations and rheology) suggest that the supramolecular organizations of the matrix play a role in the behavior of stem cells in 3D environments.     

Self-Assembly of a Pyridine-Based Amphiphile Complexed with Regioisomeric Dihydroxy Naphthalenes into Supramolecular Nanotubes with Different Inner Diameters

A pyridine-based amphiphile complexed with 1,5-, 1,6-, 2,6-, or 2,7-dihydroxy naphthalene self-assembled in water to form nanotubes with inner diameters of 46, 38, 24, 18, and 11 nm in which the naphthalene molecules formed J-type aggregates. In contrast, the amphiphile complexed with 1,2-, 1,3-, 1,4-, 1,7-, 1,8-, or 2,3-dihydroxy naphthalene formed nanofibers in which the naphthalene molecules formed H-type aggregates. The inner diameter of the nanotubes strongly depended on the regioisomeric dihydroxy naphthalene. UV–vis, fluorescence, infrared spectroscopy, X-ray diffraction analysis, and differential scanning calorimetry showed that nanotubes with smaller inner diameters had weaker intermolecular hydrogen bonds between the tilted amphiphiles complexed with the naphthalene molecules within the membrane walls and showed larger Stokes shifts in the excimer fluorescence of the naphthalene moiety. These findings should be useful not only for fine-tuning the inner diameters of supramolecular nanotubes but also for controlling the aggregation states of functional aromatic molecules to generate nanostructures with useful optical and electronic properties in water.     

Fmoc-Dipeptide/Porphyrin Molar Ratio Dictates Energy Transfer Efficiency in Nanostructures Produced by Biocatalytic Co-Assembly

The controlled self-assembly of porphyrin derivatives (TCPP, tetrakis(4-carboxyphenyl)porphyrin) within Fmoc-protected (Fmoc=9-Fluorenylmethyloxycarbonyl) dipeptide (Fmoc-TL-NH₂) nanofibers is demonstrated. The biocatalytic co-assembly in aqueous medium generated an energy transfer hydrogel. Depending on the concentrations of porphyrin used, the resulting nanofibrous gels show two distinct regions of self-assembly behavior that is, integration of TCPP into nanostructures to produce two-component co-assembly fibers, or heterogeneous self-aggregation of TCPP within the self-assembled matrix observed at higher concentrations. The mode of assembly directly impacts on the energy transfer efficiency of these nanostructures. These results show that reversible biocatalytic co-assembly of structural and functional components enables fine-tuning of peptide/porphyrin energy transfer nanostructures.     

超分子环糊精两亲分子

本文综述了“超分子环糊精两亲分子”的最新研究进展。超分子环糊精两亲分子主要包括疏水性修饰的环糊精衍生物(第一类)、环糊精衍生物与两亲分子的包合物(第二类)和环糊精衍生物与疏水性客体分子的包合物(第三类)。针对超分子环糊精两亲分子及其自组装体系的研究不但丰富了由诺贝尔化学奖得主Lehn等所提出的超分子化学的内涵,实现了多学科的交叉,而且在生物模拟、智能材料以及可控的、具有疗效的药物输运与缓释等领域具有潜在的应用前景。     

Co‐assembly of Polyoxometalates and Zwitterionic Amphiphiles into Supramolecular Hydrogels: From Crystalline Fibrillar to Amorphous Micellar Networks

Gelation mechanism is of utmost importance to the rational design of supramolecular hydrogelators. Although both kinetic and thermodynamic controlled self‐assembly processes have been widely studied in hydrogels, the formation relationship between crystalline and amorphous gel networks still remains ambiguous. Herein, a gelation transformation from a kinetic to a thermodynamic process was achieved by balancing the rigidity and flexibility of the inorganic–organic co‐assemblies. By using polyoxometalates and zwitterionic amphiphiles, the transition morphologies between crystalline and amorphous hydrogel networks were evidenced for the first time, as ordered wormlike micelles. Given the versatile applications of hydrogels in biological systems and materials science, these findings may highlight the potential of inorganic–organic binary supramolecular hydrogelators and fill in the blank between kinetic and thermodynamic controlled gelation processes.     

Pristine Carbon‐Nanotube‐Included Supramolecular Hydrogels with Tunable Viscoelastic Properties

Research investigations involving pristine carbon nanotubes (CNTs) and their applications in diversified fields have been gathering enormous impetus in recent times. One such emerging domain deals with the hybridization of CNTs within hydrogels to form soft nanocomposites with superior properties. However, till now, reports on the inclusion of pristine CNTs within low‐molecular‐weight hydrogels are very scarce due to their intrinsic feature of remaining in the bundled state and strong repulsive behavior to the aqueous milieu. Herein, the synthesis of a series of amino acid/dipeptide‐based amphiphilic hydrogelators having a quaternary ammonium/imidazolium moiety at the polar head and a C16 hydrocarbon chain as the hydrophobic segment is reported. The synthesized amphiphiles exhibited excellent hydrogelation (minimum gelation concentration (MGC) ≈0.7–5 % w/v) as well as single‐walled carbon nanotube (SWNT) dispersion ability in aqueous medium. Interestingly, the dispersed SWNTs were incorporated into the supramolecular hydrogel formed by amphiphiles with an imidazolium moiety at the polar end through complementary cation–π and π–π interactions. More importantly, the newly synthesized hydrogelators were able to accommodate a significantly high amount of pristine SWNTs (2–3.5 % w/v) at their MGCs without affecting the gelating properties. This is the first time that such a huge amount of SWNTs has been successfully incorporated within hydrogels. The efficient inclusion of SWNTs to develop soft nanocomposites was thoroughly investigated by spectroscopic and microscopic methods. Remarkably, the developed nanocomposites showed manifold enhancement (≈85‐fold) in their mechanical strength compared with native hydrogel without SWNTs. The viscoelastic properties of these nanocomposites were readily tuned by varying the amount of incorporated CNTs.     

Study on Dual Stimuli-Responsive Supramolecular Diblock Copolymers

In this paper, we report the synthesis and characterization of a new stimuli-responsive diblock polymer, i.e., methoxy poly (ethylene glycol)-block-Poly(N-isopropylacrylamide) (mPEG-b-PNIPAM), which belongs to the family of supramolecular amphiphiles. For this purpose, β-cyclodextrin (β-CD)-functionalized methoxy poly (ethylene glycol) (mPEG-CD) and adamantine (AD)-modified poly(N-isopropylacrylamide) (PNIPAM-AD) were synthesized. The diblock polymer mPEG-b-PNIPAM was then obtained by host–guest inclusion between mPEG-CD and PNIPAM-AD. The structure and molecular weight of the mPEG-b-PNIPAM was confirmed by ¹HNMR and GPC, respectively. Above the lower critical solution temperature (LCST), mPEG-b-PNIPAM can self-assemble into nano-structures in aqueous solutions with PNIPAM block as the core and mPEG block as the corona. The aggregation behavior of mPEG-b-PNIPAM were revealed by UV-vis, DLS measurements, and TEM observations. The mPEG-b-PNIPAM was further utilized to construct Dox@mPEG-b-PNIPAM micelles at 37°C in phosphate-buffered saline (PBS). No detectable amount of Dox was released from the micelles at 37°C. When cooling to 27°C or adding a competitive reagent, however, release of Dox from the micelles was observed.     

Amphiphilic Carbazole‐Containing Compounds with Lower Critical Solution Temperature Behavior for Supramolecular Self‐Assembly and Solution‐Processable Resistive Memories

The self‐organization and resistive memory performances of a series of newly synthesized water‐soluble amphiphilic carbazole derivatives have been explored. Temperature‐dependent UV/Vis absorption spectroscopy has been conducted to study the isodesmic self‐assembly mechanism of the carbazole‐containing compounds. This class of compounds also exhibits interesting lower critical solution temperature properties, which are sensitive to concentration and ionic additives. One of the compounds has been solution‐processed and utilized as an active material in the engineering of resistive memory devices, exhibiting a switching voltage of about 3.9 V, a constant ON/OFF current ratio of 10⁶, and a long retention time of 10⁴ s. The present work demonstrates the versatile potential applications of water‐soluble amphiphilic carbazole‐containing compounds in supramolecular chemistry and resistive memory devices.     

Tunable Supramolecular Assembly and Photoswitchable Conversion of Cyclodextrin/Diphenylalanine-Based 1D and 2D Nanostructures

A photocontrolled, interconvertible supramolecular 2D-nanosheet/1D-nanotube system was constructed through the supramolecular assembly of adamantanyl-modified diphenylalanine with azobenzene-bridged bis(β-cyclodextrin). The nanosheet exhibited a greater fluorescence enhancement effect than the nanotube. Significantly, these nanosheets and nanotubes could interconvert via the photocontrolled trans/cis isomerization of azobenzene linkers in bis(β-cyclodextrin), and this photo-switchable one-dimensional/two-dimensional morphological interconversion was reversible and recyclable. This enables convenient routes to highly ordered nanostructures with various morphologies and dimensions that can be controlled by external stimuli.     

From Peptide Nucleic Acids to Supramolecular Structures of Nucleic Acid Derivatives

Nucleic acids play a pivotal role in life processes. The endeavours to shed light on the essential properties of these intriguing building blocks led us to the synthesis of different analogues and the investigation of their properties. First various peptide nucleic acid monomers and oligomers have been synthesized, using an Fmoc/acyl protecting group strategy, and their properties studied. The serendipitous discovery of a side reaction of coupling agents led us to the elaboration of a peptide sequencing method. The capricious behaviour of guanine derivatives spurred the determination of their substitution pattern using ¹³C, ¹⁵N NMR, and mass spectrometric methods. The properties of guanines initiated the logical transition to the study of supramolecular systems composed of purine analogues. Thus, xanthine and uracil derivatives have been obtained and their supramolecular self-assembly properties scrutinized in gas, solid, and liquid states and at solid-liquid interfaces.     

Sequential Assembly of Mutually Interactive Supramolecular Hydrogels and Fabrication of Multi-Domain Materials

A two-component self-sorting hydrogel based on acylhydrazide and carboxylic acid derivatives of 1,3:2,4-dibenzylidene-d -sorbitol (DBS-CONHNH₂ and DBS-COOH) is reported. A heating–cooling cycle induces the self-assembly of DBS-CONHNH₂, followed by the self-assembly of DBS-COOH induced by decreasing pH. Although the networks are formed sequentially, there is spectroscopic evidence of interactions between them, which impact on the mechanical properties and significantly enhance the ability of these low-molecular-weight gelators (LMWGs) to form gels when mixed. The DBS-COOH network can be switched “off” and “on” within the two-component gel through a pH change. By using a photo-acid generator, the two-component gel can be prepared combining the thermal trigger with photo-irradiation. Photo-patterned self-assembly of DBS-COOH within a pre-formed DBS-CONHNH₂ gel under a mask yields spatially controlled multi-domain gels. Different gel domains can have different functions, for example, controlling the rate of release of heparin incorporated into the gel, or directing gold nanoparticle assembly. Such photo-patterned multi-component hydrogels have potential applications in regenerative medicine or bio-nano-electronics.     

基于超分子环糊精两亲分子的敏感型囊泡体系

敏感型囊泡可初步概括为由两亲分子通过非共价键构筑的、对外界的刺激具有特色响应性的一类新型囊泡体系。由"超分子环糊精两亲分子"自组装形成的囊泡体系是该类体系中重要的一类。本文重点介绍了环糊精参与的"超分子环糊精两亲分子"囊泡体系的研究进展。以与环糊精复合的化合物结构类型不同进行分类,介绍了该类囊泡体系的制备以及该体系在医药工程、新型"智能"材料以及生物模拟等方面的潜在应用;结合现阶段的研究状况,对该类囊泡体系的发展前景进行了展望。     

Nanostructured Micelle Nanotubes Self-Assembled from Dinucleobase Monomers in Water

Despite the central importance of aqueous amphiphile assemblies in science and industry, the size and shape of these nano-objects is often difficult to control with accuracy owing to the non-directional nature of the hydrophobic interactions that sustain them. Here, using a bioinspired strategy that consists of programming an amphiphile with shielded directional Watson–Crick hydrogen-bonding functions, its self-assembly in water was guided toward a novel family of chiral micelle nanotubes with partially filled lipophilic pores of about 2 nm in diameter. Moreover, these tailored nanotubes are successfully demonstrated to extract and host molecules that are complementary in size and chemical affinity.     

Nanostructured Micelle Nanotubes Self‐Assembled from Dinucleobase Monomers in Water

Despite the central importance of aqueous amphiphile assemblies in science and industry, the size and shape of these nano‐objects is often difficult to control with accuracy owing to the non‐directional nature of the hydrophobic interactions that sustain them. Here, using a bioinspired strategy that consists of programming an amphiphile with shielded directional Watson–Crick hydrogen‐bonding functions, its self‐assembly in water was guided toward a novel family of chiral micelle nanotubes with partially filled lipophilic pores of about 2 nm in diameter. Moreover, these tailored nanotubes are successfully demonstrated to extract and host molecules that are complementary in size and chemical affinity.     

Elasticity‐Dependent Fast Underwater Adhesion Demonstrated by Macroscopic Supramolecular Assembly

Macroscopic supramolecular assembly (MSA) is a recent development in supramolecular chemistry to associate visible building blocks through non‐covalent interactions in a multivalent manner. Although various substrates (e.g. hydrogels, rigid materials) have been used, a general design rule of building blocks in MSA systems and interpretation of the assembly mechanism are lacking and are required. Herein we design three model systems with varied elastic modulus and correlated the MSA probability with the elasticity. Based on the effects of substrate deformability on multivalency, we have proposed an elastic‐modulus‐dependent rule that building blocks below a critical modulus of 2.5 MPa can achieve MSA for the used host/guest system. Moreover, this MSA rule applies well to the design of materials for fast underwater adhesion: Soft substrates (0.5 MPa) can achieve underwater adhesion within 10 s with one order of magnitude higher strength than that of rigid substrates (2.5 MPa).     

Supramolecular Diblock Copolymers Featuring Well‐defined Telechelic Building Blocks

We report supramolecular AB diblock copolymers comprised of well‐defined telechelic building blocks. Helical motifs, formed via reversible addition‐fragmentation chain‐transfer (RAFT) or anionic polymerization, are assembled with coil‐forming and sheet‐featuring blocks obtained via atom‐transfer radical polymerization (ATRP) or ring‐opening metathesis polymerization (ROMP). Interpolymer hydrogen bonding or metal‐coordination achieves dynamic diblock architectures featuring hybrid topologies of coils, helices, and/or π‐stacked sheets that, on a basic level, mimic protein structural motifs in fully synthetic systems. The intrinsic properties of each block (e.g., circular dichroism and fluorescence) remain unaffected in the wake of self‐assembly. This strategy to develop complex synthetic polymer scaffolds from functional building blocks is significant in a field striving to produce architectures reminiscent of biosynthesis, yet fully synthetic in nature. This is the first plug‐and‐play approach to fabricate hybrid π‐sheet/helix, π‐sheet/coil, and helix/coil architectures via directional self‐assembly.