Interplay of Depletion Forces and Biomolecular Recognition in the Hierarchical Assembly of Supramolecular Tubes

Crowding effects have a profound impact on the hierarchical organization of cellular architectures. In the fields of systems chemistry and soft matter, this effect has not received much attention so far. Here, it is explored how poly(ethylene glycol) (PEG) as a crowding agent invokes depletion forces that act on synthetic supramolecular tubes. Hence, supramolecular tubes are pushed from their random orientation into hierarchically assembled bundles due to the PEG-induced crowded environment. The resulting morphology of formed bundled architectures can be tuned by the concentrations of both the supramolecular tubes and the PEG. The introduction of biotin groups at the surface of the tubes allows the engineering of biotin–streptavidin crosslinks between them. The order of introducing PEG and streptavidin in the system further affects the formed hierarchical assemblies, as well as their resistance toward dilution. The strategy described here provides a new route to establish hierarchically organized supramolecular architectures, combining crowding and specific biomolecular interactions, which shows the potential for controlling the structure of supramolecular materials and other soft matter systems.</p

Multivalent Noncovalent Interfacing and Cross-Linking of Supramolecular Tubes

Natural supramolecular filaments have the ability to cross-link with each other and to interface with the cellular membrane via biomolecular noncovalent interactions. This behavior allows them to form complex networks within as well as outside the cell, i.e., the cytoskeleton and the extracellular matrix, respectively. The potential of artificial supramolecular polymers to interact through specific noncovalent interactions has so far only seen limited exploration due to the dynamic nature of supramolecular interactions. Here, a system of synthetic supramolecular tubes that cross-link forming supramolecular networks, and at the same time bind to biomimetic surfaces by the aid of noncovalent streptavidin–biotin linkages, is demonstrated. The architecture of the networks can be engineered by controlling the density of the biotin moiety at the exterior of the tubes as well as by the concentration of the streptavidin. The presented strategy provides a pathway for designing adjustable artificial supramolecular superstructures, which can potentially yield more complex biomimetic adaptive materials

Spectroscopic Contrast of Diarylethene Molecules on Octanethiol Monolayer

We present a systematic scanning tunneling microscopy (STM) study of bias-dependent imaging of disulfur diarylethene (2S-DE) molecules on octanethiol (C8) monolayer at room temperature. In a rigid confinement of the C8 matrix, we did not observe any significant variation in the appearance of the 2S-DE. On the contrary, a reversal in the apparent height of the 2S-DE was present when the molecule was situated on a gold vacancy island. We attributed this finding to the presence of a new electronic state that became accessible for a tunneling event. In addition, the C8 surface structure underwent a reversible phase transformation from root 3 x root 3 R30 degrees hexagonal to c(4x2) square superlattice when the bias voltage was reduced from -825 mV to -425 mV or vice versa. Under a finite bias voltage, an appreciable topographic variation of the 2S-DE signature was demonstrated for the first time. This finding can be ascribed to a finite overlap of the associated wave functions that occurred between the tip state and the 2S-DE molecular energy level. We believe that physical insight on the bias-dependent imaging of organic molecules on solid surface is important towards the advancement of molecular electronics-based devices

Photoswitchable architecture transformation of a DNA-hybrid assembly at the microscopic and macroscopic scale

Molecular recognition-driven self-assembly employing single-stranded DNA (ssDNA) as a template is a promising approach to access complex architectures from simple building blocks. Oligonucleotide-based nanotechnology and soft-materials benefit from the high information storage density, self-correction, and memory function of DNA. Here we control these beneficial properties with light in a photoresponsive biohybrid hydrogel, adding an extra level of function to the system. An ssDNA template was combined with a complementary photo-responsive unit to reversibly switch between various functional states of the supramolecular assembly using a combination of light and heat. We studied the structural response of the hydrogel at both the microscopic and macroscopic scale using a combination of UV-vis absorption and CD spectroscopy, as well as fluorescence, transmission electron, and atomic force microscopy. The hydrogels grown from these supramolecular self-assembly systems show remarkable shape-memory properties and imprinting shape-behavior while the macroscopic shape of the materials obtained can be further manipulated by irradiation

Light-fuelled reversible expansion of spiropyran-based vesicles in water

We present the design and synthesis of spiropyran-based dynamic vesicles, for which the building block is the amphiphilic merocyanine isomer. Under irradiation with visible light, the photo-conversion of the protonated and charged merocyanine to the neutral spiropyran form leads to the transient and reversible expansion of these vesicles.</p

Light-fuelled reversible expansion of spiropyran-based vesicles in water

We present the design and synthesis of spiropyran-based dynamic vesicles, for which the building block is the amphiphilic merocyanine isomer. Under irradiation with visible light, the photo-conversion of the protonated and charged merocyanine to the neutral spiropyran form leads to the transient and reversible expansion of these vesicles

Bicomponent H-Bonded Porous Molecular Networks at the Liquid–Solid Interface: What Is the Influence of Preorganization in Solution?

Tailoring the architecture of porous two-dimensional networks formed by molecules is essential for developing functional materials with low dimensionality. Here we present bicomponent porous networks with tunable pore-sizes that were formed by self-assembly of hydrogen-bonding molecules at the liquid/graphite interface. Scanning tunneling microscopy investigations demonstrate the formation and coexistence of three polymorphs. It is found that the occurrence of these polymorphs depends critically on the surface coverage. Further on, atomic force microscopy measurements, spectroscopic studies, and dynamic light scattering investigations show the propensity of one of the two molecular components to form aggregates beyond the monolayer. We discuss how these preorganized aggregates in solution may affect the self-assembly at the interfac