Loading of Vesicles into Soft Amphiphilic Nanotubes using Osmosis

Aqueous Supramolecular Co-Assembly of Anionic and Cationic Photoresponsive Stiff-Stilbene Amphiphiles

Fabrication of macroscopic soft functional materials, such as macroscopic photoresponsive soft materials and artificial muscles, can be commonly prepared by charge screening of supramolecular assemblies with inorganic salt solutions using a shear-flow method. However, some of the charged end-groups of photoresponsive molecular amphiphiles cannot be stabilized with inorganic salt solutions to fabricate macroscopic soft materials. We design and synthesize stiff stilbene amphiphiles (SAs) functionalized with anionic phosphite and cationic quaternary ammonium end groups and determine their photochemical and supramolecular assembly properties. Supramolecular co-assembly of anionic and cationic nanotubes of SAs allows to transform into nanoribbons, confirmed by TEM, CAC, and Zeta potential measurements. Nanoribbons of anionic and cationic SAs can be prepared into macroscopic soft materials with inorganic salt solutions and surprisingly also with deionized water. The macroscopic soft material of anionic and cationic SAs can be stabilized at low concentration ∼5 mM. Meanwhile, the photoresponsiveness of the macroscopic soft materials is retained to provide macroscopic morphological change upon photoirradiation. These results exhibit the feasibility in fabrication of macroscopic functional soft materials from supramolecular assembly across multiple length-scale without help of inorganic salts and offer ample opportunity in developing future soft supramolecular robotic systems. This article is protected by copyright. All rights reserved.

Molecular photoswitches in aqueous environments

Molecular photoswitches enable dynamic control of processes with high spatiotemporal precision, using light as external stimulus, and hence are ideal tools for different research areas spanning from chemical biology to smart materials. Photoswitches are typically organic molecules that feature extended aromatic systems to make them responsive to (visible) light. However, this renders them inherently lipophilic, while water-solubility is of crucial importance to apply photoswitchable organic molecules in biological systems, like in the rapidly emerging field of photopharmacology. Several strategies for solubilizing organic molecules in water are known, but there are not yet clear rules for applying them to photoswitchable molecules. Importantly, rendering photoswitches water-soluble has a serious impact on both their photophysical and biological properties, which must be taken into consideration when designing new systems. Altogether, these aspects pose considerable challenges for successfully applying molecular photoswitches in aqueous systems, and in particular in biologically relevant media. In this review, we focus on fully water-soluble photoswitches, such as those used in biological environments, in both in vitro and in vivo studies. We discuss the design principles and prospects for water-soluble photoswitches to inspire and enable their future applications.

Self-Assembly of Photoresponsive Molecular Amphiphiles in Aqueous Media

Amphiphilic molecules, comprising hydrophobic and hydrophilic moieties and the intrinsic propensity to self-assemble in aqueous environment, sustain a fascinating spectrum of structures and functions ranging from biological membranes to ordinary soap. Facing the challenge to design responsive, adaptive, and out-of-equilibrium systems in water, the incorporation of photoresponsive motifs in amphiphilic molecular structures offers ample opportunity to design supramolecular systems that enables functional responses in water in a non-invasive way using light. Here, we discuss the design of photoresponsive molecular amphiphiles, their self-assembled structures in aqueous media and at air-water interfaces, and various approaches to arrive at adaptive and dynamic functions in isotropic and anisotropic systems, including motion at the air-water interface, foam formation, reversible nanoscale assembly, and artificial muscle function. Controlling the delicate interplay of structural design, self-assembling conditions and external stimuli, these responsive amphiphiles open several avenues towards application such as soft adaptive materials, controlled delivery or soft actuators, bridging a gap between artificial and natural dynamic systems.

Tuning of Morphology by Chirality in Self-Assembled Structures of Bis(Urea) Amphiphiles in Water

We present the synthesis and self‐assembly of a chiral bis(urea) amphiphile and show that chirality offers a remarkable level of control towards different morphologies. Upon self‐assembly in water, the molecular‐scale chiral information is translated to the mesoscopic level. Both enantiomers of the amphiphile self‐assemble into chiral twisted ribbons with opposite handedness, as supported by Cryo‐TEM and circular dichroism (CD) measurements. The system presents thermo‐responsive aggregation behavior and combined transmittance measurements, temperature‐dependent UV, CD, TEM, and micro‐differential scanning calorimetry (DSC) show that a ribbon‐to‐vesicles transition occurs upon heating. Remarkably, chirality allows easy control of morphology as the self‐assembly into distinct aggregates can be tuned by varying the enantiomeric excess of the amphiphile, giving access to flat sheets, helical ribbons, and twisted ribbons.

Dynamic Assemblies of Molecular Motor Amphiphiles Control Macroscopic Foam Properties

Stimuli-responsive supramolecular assemblies controlling macroscopic transformations with high structural fluidity, i.e., foam properties, have attractive prospects for applications in soft materials ranging from biomedical systems to industrial processes, e.g., textile coloring. However, identifying the key processes for the amplification of molecular motion to a macroscopic level response is of fundamental importance for exerting the full potential of macroscopic structural transformations by external stimuli. Herein, we demonstrate the control of dynamic supramolecular assemblies in aqueous media and as a consequence their macroscopic foam properties, e.g., foamability and foam stability, by large geometrical transformations of dual light/heat stimuli-responsive molecular motor amphiphiles. Detailed insight into the reversible photoisomerization and thermal helix inversion at the molecular level, supramolecular assembly transformations at the microscopic level, and the stimuli-responsive foam properties at the macroscopic level, as determined by UV-vis absorption and NMR spectroscopies, electron microscopy, and foamability and in situ surface tension measurements, is presented. By selective use of external stimuli, e.g., light or heat, multiple states and properties of macroscopic foams can be controlled with very dilute aqueous solutions of the motor amphiphiles (0.2 weight%), demonstrating the potential of multiple stimuli-responsive supramolecular systems based on an identical molecular amphiphile and providing opportunities for future soft materials.

A Technical Introduction to Transmission Electron Microscopy for Soft-Matter: Imaging, Possibilities, Choices, and Technical Developments

With a significant role in material sciences, physics, (soft matter) chemistry, and biology, the transmission electron microscope is one of the most widely applied structural analysis tool to date. It has the power to visualize almost everything from the micrometer to the angstrom scale. Technical developments keep opening doors to new fields of research by improving aspects such as sample preservation, detector performance, computational power, and workflow automation. For more than half a century, and continuing into the future, electron microscopy has been, and is, a cornerstone methodology in science. Herein, the technical considerations of imaging with electrons in terms of optics, technology, samples and processing, and targeted soft materials are summarized. Furthermore, recent advances and their potential for application to soft matter chemistry are highlighted.

Diselenide-Containing Polymeric Vesicles with Osmotic Pressure Response

Mechanophore is a kind of functional group that can undergo chemical reactions when given mechanical force stimuli. In this paper, osmotic pressure was used as an external force to trigger a diselenide exchange reaction. A diselenide bond containing block polymer capable of self-assembling to a vesicle structure and an ester bond containing a counterpart were synthesized in this study. When NaCl was added into the solution to generate the osmotic pressure difference inside and outside vesicles, diselenide containing vesicles were ruptured, while the ester bond counterpart stayed still. Further investigation into the chemical composition of both vesicles indicated the occurrence of the diselenide exchange reaction. The osmotic pressure response of the diselenide bond enriched the diselenide dynamic covalent chemistry and offers a potential application in a controlled release system.

Transmission Electron Microscopy as a Tool for the Characterization of Soft Materials: Application and Interpretation

Transmission electron microscopy (TEM) provides direct structural information on nano-structured materials and is popular as a characterization tool in soft matter and supramolecular chemistry. However, technical aspects of sample preparation are overlooked and erroneous image interpretations are regularly encountered in the literature. There are three most commonly used TEM methods as we derived from literature: drying, staining and cryo-TEM, which are explained here with respect to their application, limitations and interpretation. Since soft matter chemistry relies on a lot of indirect evidence, the role of TEM for the correct evaluation of the nature of an assembly is very large. Mistakes in application and interpretation can therefore have enormous impact on the quality of present and future studies. We provide helpful background information of these three techniques, the information that can and cannot be derived from them and provide assistance in selecting the right technique for soft matter imaging. This essay warns against the use of drying and explains why. In general cryo-TEM is by far the best suited method and many mistakes and over-interpretations can be avoided by the use of this technique.

End-capping of amphiphilic nanotubes with phospholipid vesicles: impact of the phospholipid on the cap formation and vesicle loading under osmotic conditions

Soft amphiphilic nanotubes are capped with vesicles comprised of either overall neutral, zwitterionic phospholipids, or those that carry a net charge. The phase transition temperature of the zwitterionic phospholipids plays a crucial role in the phase separation that leads to the end-capped nanotubes. The cationic vesicle caps can be loaded into the nanotubes via osmosis whereas the anionic vesicle caps are stable under hyper-osmotic conditions. Furthermore, no additional salt needs to be added for the cationic vesicle caps to induce the loading of the vesicles into the nanotubes due to the presence of counterions.