Rational Fabrication of Multiple Dimensional Assemblies from Tryptophan-Based Racemate

Fabricating structural complex assemblies from simple amino acid-based derivatives is attracting great research interests due to their easy accessibility and preparation. However, the morphological regulation of racemates (an equimolar mixture of enantiomers) were largely overlooked. In this work, through rational modulation of kinetic and thermodynamic parameters, we achieved multiple dimensional architectures employing tryptophan-based racemate (RPWM). Upon assembling, 1D bundled nanofibers, 2D lamellar nanostructure and 3D urchin-like microflowers could be obtained depending on the solvents used. The corresponding morphology evolutions were successfully illustrated by changing the enantiomeric excess (ee) value. Moreover, for RPWM, uniform 0D nanospheres were formed in H 2 O under 4 ℃, which could spontaneously convert into lamella under ambient temperature. Taking advantages of its temperature-responsive phase change behavior, RPWM assemblies exhibited excellent removal efficiency for organic dye RhB, and could be reused for several consecutive cycles without significant changes in its removal performance. Taken together, it's rational to envision that the engineering of racemates assembly pathways can greatly increase the robustness in a wide variety of supramolecular materials and further lead to their blooming versatile applications.

Driving force balance-the "identity card" of supramolecules in a self-sorting multicomponent assembly system

Contrary to the popular belief that multicomponent assembly systems will theoretically co-assemble under the same type of driving forces, two distinct assembly modes from a system composed of two chemically similar supramolecules were demonstrated in this work. Although with exactly the same driving forces, molecule-level self-sorting unexpectedly occurred in this two-component system made of polyhedral oligomeric silsesquioxane (POSS) core-based supramolecules with one and eight lysine derivative arms. From the experiments, it was concluded that instead of driving force types, driving force counterpoise plays a vital role here, which we called "identity card hypothesis". The hypothesis suggests that two highly similar components show high affinity for the same molecules through the differentiated "identity card"-like balance of driving forces induced by the difference in the molecular spatial shape, which has never been reported before.

Salt-effect enhanced hollow-fiber liquid-phase microextraction of glutathione in human saliva followed by miniaturized capillary electrophoresis with amperometric detection

A hollow-fiber liquid-phase microextraction (HF-LPME) method was established for purification and enrichment of glutathione (GSH) in human saliva followed by a miniaturized capillary electrophoresis with amperometric detection system (mini-CE-AD). Based on regulating isoelectric point and increasing salt effect to modify donor phase, HF-LPME could provide high enrichment efficiency for GSH up to 471 times, and the extract was directly injected for mini-CE-AD analysis. The salt-effect enhanced HF-LPME/mini-CE-AD method has been successfully applied to saliva analysis, and acceptable LOD (0.46 ng/mL, S/N = 3) and recoveries (92.7-101.3%) could be obtained in saliva matrix. The sample pretreatment of this developed method was simple and required no derivatization, providing a potential alternative for non-invasive fluid analysis using portable instrument.

Chirality on dendrimers: “roll booster” of the molecule-level self-sorting assembly in two-component supramolecular gel system

Chirality-induced recognition-promoted thermodynamic phase separation and different rate-kinetically controlled assembly helps molecule-level self-sorting emerge in a dendritic multicomponent gel.

A controllable etching supramolecular hydrogel based on metal ions

We report an interesting gel-etching system in which a gel can be etched with corresponding etching rates and color changes when different types of etching molecules are added to the gel. This gel system may have wide potential application in molecular recognition, pre-packaged, as well as other functional materials.

How should multicomponent supramolecular gels be characterised?

We discuss the current state of characterising multicomponent low molecular weight gels across all length scales, and the effectiveness of the different techniques that have been used.

Environment-Adaptive Coassembly/Self-Sorting and Stimulus-Responsiveness Transfer Based on Cholesterol Building Blocks

Manipulating the property transfer in nanosystems is a challenging task since it requires switchable molecular packing such as separate aggregation (self-sorting) or synergistic aggregation (coassembly). Herein, a unique manipulation of self-sorting/coassembly aggregation and the observation of switchable stimulus-responsiveness transfer in a two component self-assembly system are reported. Two building blocks bearing the same cholesterol group give versatile topological structures in polar and nonpolar solvents. One building block (cholesterol conjugated cynanostilbene, CCS) consists of cholesterol conjugated with a cynanostilbene unit, and the other one (C₁₀CN) is comprised of cholesterol connected with a naphthalimide group having a flexible long alkyl chain. Their assemblies including gel, crystalline plates, and vesicles are obtained. In gel and crystalline plate phases, the self-sorting behavior dominates, while synergistic coassembly occurs in vesicle phase. Since CCS having the cyanostilbene group can respond to the light irradiation, it undergoes light-induced chiral amplification. C₁₀CN is thermally responsive, whereby its supramolecular chirality is inversed upon heating. In coassembled vesicles, it is interestingly observed that their responsiveness can be transferred by each other, i.e., the C₁₀CN segment is sensitive to the light irradiation, while CCS is thermoresponsive. This unprecedented behavior of the property transfer may shine a light to the precise fabrication of smart materials.

Understanding Pathway Complexity of Organic Micro/Nanofiber Growth in Hydrogen-Bonded Coassembly of Aromatic Amino Acids

Rational engineering of one-dimensional (1D) self-assembled aggregates to produce desired materials for versatile functions remains a challenge. In this work, we report the noncovalent modulation of 1D aggregates at the micro/nanoscale using a coassembly protocol. Aromatic amino acids were employed as the model building blocks, and melamine (Mm) behaves as a modulator to form coassembly arrays with aromatic amino acids selectively. The selective self-assembly behavior between aromatic amino acids and Mm allows distinguishing and detecting Mm and aromatic amino acids from their analogues in macroscopic and microscopic scales. Dimensions and sizes of fibrous aggregates prepared from different amino acids show two opposite pathways from pristine assemblies to coassemblies induced by the addition of Mm. This pathway complexity could be controlled by the molecular conformation determined by α-positioned substituents. The developed hypothesis presents an excellent expansibility to other substrates, which may guide us to rationally design and screen 1D materials with different dimensions and sizes including the production of high-quality self-standing hydrogels.

Facile Stimuli-Responsive Transformation of Vesicle to Nanofiber to Supramolecular Gel via ω-Amino Acid-Based Dynamic Covalent Chemistry

This paper reports an interesting type of self-assembly systems based on dynamic covalent bonds. The systems are pH-responsible and reversible, which could be utilized for controlling the morphology transformation of the assemblies. In alkaline conditions, the amine group of 11-aminoundecanoic acid (AUA) can connect with the aldehyde group of benzaldehyde (BA) or 1-naphthaledhyde (NA) by dynamic covalent bond to form a small organic building block accompanied by the morphological transformation from vesicles to fibers. When pH is lowered to a neutral value, the dynamic covalent bonds (imine bonds) can be hydrolyzed, leading to the dissociation of fibers and appearance of spherical aggregates. The transformation was confirmed reversible as fibers appeared again when the pH was changed back to alkaline value. In addition, a reversibly controlled gel was designed based on the nanofiber formation. NaCl, which is capable of greatly enhance the nanofiber density and cross-linking, was used to induce the growth of free-standing gel from free-flowing nanofiber system, and the resultant gel was proven to be pH-reversible.

Selective Metal-Ion-Mediated Vesicle Adhesion Based on Dynamic Self-Organization of a Pyrene-Appended Glutamic Acid

Vesicles with dynamic membranes provide an ideal model system for investigating biological membrane activities, whereby vesicle aggregation behaviors including adhesion, fusion, fission, and membrane contraction/extension have attracted much attention. In this work we utilize an aromatic amino acid (pyrene-appended glutamic acid, PGlu) to prepare nanovesicles that aggregate to form vesicle clusters selectively induced by Fe(3+) or Cu(2+), and the vesicles transform into irregular nano-objects when interacting with Al(3+). Vesicle clusters have better stability than pristine vesicles, which hinders the spontaneous morphological transformation from vesicles into lamellar nanosheets with long incubation period. The difference between complexation of Fe(3+) and Al(3+) with vesicles was studied by various techniques. On the basis of metal ion-vesicle interactions, this self-assembled nanovesicle system also behaves as an effective fluorescent sensor for Fe(3+) and Al(3+), which cause fluorescence quenching and enhanced excimer emission, respectively.

Light and cucurbit[7]uril complexation dual-responsiveness of a cyanostilbene-based self-assembled system

A cyanostilbene-based amphiphile (CS) was synthesized, which could self-assemble into non-emissive bilayer vesicles and ultra-thin ribbons. Cucurbit[7]uril (CB[7]) could form an inclusion complex with CS with a significant hypochrome effect, giving a strong blue emission from non-emissive species. CS underwent photoisomerization induced by light irradiation, which allowed the membrane contraction into smaller vesicles.

Tuning of gel morphology with supramolecular chirality amplification using a solvent strategy based on an Fmoc-amino acid building block

The self-assembly of an aromatic amino acid affords diverse aggregates from flat nanofibers to twist nanofibers with tunable supramolecular chirality.

Controllable self-assemblies of sodium benzoate in different solvent environments

Sodium benzoate is an important and widely used food additive, however, it's self-assembly properties in diverse solvents have been rarely studied. Here, we systematically report its various self-assemblies in different solvents environments.

Remarkable viscoelasticity in mixtures of cyclodextrins and nonionic surfactants

We report the effect of native cyclodextrins (α, β, and γ) and selected derivatives in modulating the self-assembly of the nonionic surfactant polyoxyethylene cholesteryl ether (ChEO10) and its mixtures with triethylene glycol monododecyl ether (C12EO3), which form wormlike micelles. Cyclodextrins (CDs) generally induce micellar breakup through a host-guest interaction with surfactants; instead, we show that a constructive effect, leading to gel formation, is obtained with specific CDs and that the widely invoked host-guest interaction may not be the only key to the association. When added to wormlike micelles of ChEO10 and C12EO3, native β-CD, 2-hydroxyethyl-β-CD (HEBCD), and a sulfated sodium salt of β-CD (SULFBCD) induce a substantial increase of the viscoelasticity, while methylated CDs rupture the micelles, leading to a loss of the viscosity, and the other CDs studied (native α- and γ- and hydroxypropylated CDs) show a weak interaction. Most remarkably, the addition of HEBCD or SULFBCD to pure ChEO10 solutions (which are low-viscosity, Newtonian fluids of small, ellipsoidal micelles) induces the formation of transparent gels. The combination of small-angle neutron scattering, dynamic light scattering, and cryo-TEM reveals that both CDs drive the elongation of ChEO10 aggregates into an entangled network of wormlike micelles. (1)H NMR and fluorescence spectroscopy demonstrate the formation of inclusion complexes between ChEO10 and methylated CDs, consistent with the demicellization observed. Instead, HEBCD forms a weak complex with ChEO10, while no complex is detected with SULFBCD. This shows that inclusion complex formation is not the determinant event leading to micellar growth. HEBCD:ChEO10 complex, which coexists with the aggregated surfactant, could act as a cosurfactant with a different headgroup area. For SULFBCD, intermolecular interactions via the external surface of the CD may be more relevant.

Reversible pH-responsive helical nanoribbons formed using camptothecin

The natural antitumor drug camptothecin was found to self-assemble into helical nanoribbons in aqueous solution. The formation and disappearance of the helical nanoribbons can be tuned reversibly through changing the pH value of the solution.

Self-assembly of folic acid/melamine complexes with hierarchy levels: from membranes to porous spherulites and networks

Utilizing the self-assembly of folic acid/melamine complexes in water, we realized the construction of spherulites and networks with porous structure from membrane growth and folding.