Molekulare Architektur und Funktion von polymeren orientierten Systemen – Modelle für das Studium von Organisation, Oberflächenerkennung und Dynamik bei Biomembranen

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.

Magnifying the Structural Components of Biomembranes: A Prototype for the Study of the Self-Assembly of Giant Lipids

How biomembranes are self-organized to perform their functions remains a pivotal issue in biological and chemical science. Understanding the self-assembly principles of lipid-like molecules hence becomes crucial. Herein, we report the mesostructural evolution of amphiphilic sphere-rod conjugates (giant lipids), and study the roles of geometric parameters (head-tail ratio and cross-sectional area) during this course. As a prototype system, giant lipids resemble natural lipidic molecules by capturing their essential features. The self-assembly behavior of two categories of giant lipids (I-shape and T-shape, a total of 8 molecules) is demonstrated. A rich variety of mesostructures is constructed in solution state and their molecular packing models are rationally understood. Giant lipids recast the phase behavior of natural lipids to a certain degree and the abundant self-assembled morphologies reveal distinct physiochemical behaviors when geometric parameters deviate from natural analogues.

Synthesis of π-Conjugated Benzocyclotrimers

Polycyclic aromatic hydrocarbons (PAHs), especially three branchphene benzocyclotrimers represent a series of molecules with intriguing physical and chemical properties. Benzocyclotrimers are also important precursors to construct fullerenes and graphenes. In this article, we review the recent progress in the preparation methods of π-conjugated benzocyclotrimers. In particular, cyclotrimerization reactions to construct varying shaped and edged benzocyclotrimers are illustrated. Various typical characterization methods for these materials, such as variable-temperature ¹ H-NMR, single crystal X-ray analysis, density functional theory (DFT) calculations and atomic force microscope (AFM) measurements are included for discussion.

Surface-Assisted Self-Assembly Strategies Leading to Supramolecular Hydrogels

Localized molecular self-assembly processes leading to the growth of nanostructures exclusively from the surface of a material is one of the great challenges in surface chemistry. In the last decade, several works have been reported on the ability of modified or unmodified surfaces to manage the self-assembly of low-molecular-weight hydrogelators (LMWH) resulting in localized supramolecular hydrogel coatings mainly based on nanofiber architectures. This Minireview highlights all strategies that have emerged recently to initiate and localize LMWH supramolecular hydrogel formation, their related fundamental issues and applications.

Chemically Locked Bicelles with High Thermal and Kinetic Stability

In situ polymerization of a bicellar mixture composed of a phospholipid and polymerizable surfactants afforded unprecedented stable bicelles. The polymerized composite showed an aligned phase over a wide thermal range (25 to >90 °C) with excellent (2)H quadrupole splitting of the solvent signal, thus implying versatility as an alignment medium for NMR studies. Crosslinking of the surfactants also brought favorable effects on the kinetic stability and alignment morphology of the bicelles. This system could thus offer a new class of scaffolds for biomembrane models.

Recruitment and Immobilization of a Fluorinated Biomarker Across an Interfacial Phospholipid Film using a Fluorocarbon Gas

Perfluorohexane gas when introduced in the air atmosphere above a film of phospholipid self-supported on an aqueous solution of C2F5-labeled compounds causes the recruitment and immobilization of the latter in the interfacial film. When the phospholipid forms a liquid-condensed Gibbs monolayer, which is the case for dipalmitoylphosphatidylcholine (DPPC), the C2F5-labeled molecule remains trapped in the monolayer after removal of F-hexane. Investigations involve bubble profile analysis tensiometry (Gibbs films), Langmuir monolayers and microbubble experiments. The new phenomenon was utilized to incorporate a hypoxia biomarker, a C2F5-labeled nitrosoimidazole (EF5), in microbubble shells. This finding opens perspectives in the delivery of fluorinated therapeutic molecules and biomarkers.

Diamond nanowires: fabrication, structure, properties, and applications

C(sp(3) )C-bonded diamond nanowires are wide band gap semiconductors that exhibit a combination of superior properties such as negative electron affinity, chemical inertness, high Young's modulus, the highest hardness, and room-temperature thermal conductivity. The creation of 1D diamond nanowires with their giant surface-to-volume ratio enhancements makes it possible to control and enhance the fundamental properties of diamond. Although theoretical comparisons with carbon nanotubes have shown that diamond nanowires are energetically and mechanically viable structures, reproducibly synthesizing the crystalline diamond nanowires has remained challenging. We present a comprehensive, up-to-date review of diamond nanowires, including a discussion of their synthesis along with their structures, properties, and applications.

Mimicking biological membranes with programmable glycan ligands self-assembled from amphiphilic Janus glycodendrimers

An accelerated modular synthesis produced 18 amphiphilic Janus glycodendrimers with three different topologies formed from either two or one carbohydrate head groups or a mixed constellation with a noncarbohydrate hydrophilic arm. By simple injection of their THF solutions into water or buffer, all of the Janus compounds self-assembled into uniform, stable, and soft unilamellar vesicles, denoted glycodendrimersomes. The mixed constellation topology glycodendrimersomes were demonstrated to be most efficient in binding plant, bacterial, and human lectins. This evidence with biomedically relevant receptors offers a promising perspective for the application of such glycodendrimersomes in targeted drug delivery, vaccines, and other areas of nanomedicine.

Macroscopic supramolecular assembly of rigid building blocks through a flexible spacing coating

Macroscopic supramolecular assembly is a promising method for manufacturing macroscopic, ordered structures for tissue-engineering scaffolds. A flexible spacing coating is shown to overcome undesired surface and size effects and to enable assembly of macroscopic cubes with host/guest groups. The assembled pairs disassembled upon introduction of competitive guest molecules, thereby demonstrating a multivalent assembly mechanism.

Selective adhesion, lipid exchange and membrane-fusion processes between vesicles of various sizes bearing complementary molecular recognition groups

Equimolar mixtures of large unilamellar vesicles (LUVs) obtained from mixtures of egg lecithin and lipids containing complementary hydrogen bonding head groups (barbituric acid (BAR) and 2,4,6-triaminopyrimidine (TAP)) were shown to aggregate and fuse. These events have been studied in detail using electron microscopy and dynamic light scattering, and by fluorimetry using membrane or water-soluble fluorescence probes. It was shown that aggregation was followed by two competitive processes: a) lipid mixing leading to redispersion of the vesicles; b) fusion events generating much larger vesicles. In order to better understand the nature of the interaction, the effects of ionic strength and surface concentration of recognition lipids on the aggregation process were investigated by dynamic light scattering. Additionally, it was possible to inhibit the aggregation kinetics through addition of a soluble barbituric acid competitor. The study was extended to giant unilamellar vesicles (GUVs) to investigate the size effect and visualise the phenomena in situ. The interactions between complementary LUVs and GUVs or GUVs and GUVs were studied by optical microscopy using dual fluorescent labelling of both vesicle populations. A selective adhesion of LUVs onto GUVs was observed by electron and optical microscopies, whereas no aggregation took place in case of a GUV/GUV mixture. Furthermore, a fusion assay of GUV and LUV using the difference of size between GUV and LUV and calceine self-quenching showed that no mixing between the aqueous pools occured.

Hierarchical growth of fluorescent dye aggregates in water by fusion of segmented nanostructures

Dye aggregates are becoming increasingly attractive for diverse applications, in particular as organic electronic and sensor materials. However, the growth processes of such aggregates from molecular to small assemblies up to nanostructures is still not properly understood, limiting the design of materials' functional properties. Here we elucidate the supramolecular growth process for an outstanding class of functional dyes, perylene bisimides (PBIs), by transmission electron microscopy (TEM), cryogenic scanning electron microscopy (cryo-SEM), and atomic force microscopy (AFM). Our studies reveal a sequential growth of amphiphilic PBI dyes from nanorods into nanoribbons in water by fusion and fission processes. More intriguingly, the fluorescence observed for higher hierarchical order nanoribbons was enhanced relative to that of nanorods. Our results provide insight into the relationship between molecular, morphological, and functional properties of self-assembled organic materials.

Development of structural complexity by liquid-crystal self-assembly

Since the discovery of the liquid-crystalline state of matter 125 years ago, this field has developed into a scientific area with many facets. This Review presents recent developments in the molecular design and self-assembly of liquid crystals. The focus is on new exciting soft-matter structures distinct from the usually observed nematic, smectic, and columnar phases. These new structures have enhanced complexity, including multicompartment and cellular structures, periodic and quasiperiodic arrays of spheres, and new emergent properties, such as ferroelctricity and spontaneous achiral symmetry-breaking. Comparisons are made with developments in related fields, such as self-assembled monolayers, multiblock copolymers, and nanoparticle arrays. Measures of structural complexity used herein are the size of the lattice, the number of distinct compartments, the dimensionality, and the logic depth of the resulting supramolecular structures.

Molecular assemblies of perylene bisimide dyes in water

Perylene bisimides are among the most valuable functional dyes and have numerous potential applications. As a result of their chemical robustness, photostability, and outstanding optical and electronic properties, these dyes have been applied as pigments, fluorescence sensors, and n-semiconductors in organic electronics and photovoltaics. Moreover, the extended quadrupolar π system of this class of dyes has facilitated the construction of numerous supramolecular architectures with fascinating photophysical properties. However, the supramolecular approach to the formation of perylene bisimide aggregates has been restricted mostly to organic media. Pleasingly, considerable progress has been made in the last few years in developing water-soluble perylene bisimides and their application in aqueous media. This Review provides an up-to-date overview on the self-assembly of perylene bisimides through π-π interactions in aqueous media. Synthetic strategies for the preparation of water-soluble perylene bisimides and the influence of water on the π-π stacking of perylene bisimides as well as the resulting applications are discussed.

Docetaxel nanotechnology in anticancer therapy

Taxanes have been recognized as a family of very efficient anticancer drugs, but the formulation in use for the two main taxanes-Taxol for paclitaxel and Taxotere for docetaxel-have shown dramatic side effects. Whereas several new formulations for paclitaxel have recently appeared, such as Abraxane and others currently in various phases of clinical trials, there is no new formulation in clinical trials for the other main taxane, docetaxel, except BIND-014, a polymeric nanoparticle, which recently entered phase I clinical testing. Therefore, we review herein the state of the art and recent abundance in published results of academic approaches toward nanotechnology-based drug-delivery systems containing nanocarriers and targeting agents for docetaxel formulations. These efforts will certainly enrich the spectrum of docetaxel treatments in the near future. Taxotere's systemic toxicity, low water solubility, and other side effects are significant problems that must be overcome. To avoid the limitations of docetaxel in clinical use, researchers have developed efficient drug-delivery assemblies that consist of a nanocarrier, a targeting agent, and the drug. A wide variety of such engineered nanosystems have been shown to transport and eventually vectorize docetaxel more efficiently than Taxotere in vitro, in vivo, and in pre-clinical administration. Recent progress in drug vectorization has involved a combined therapy and diagnostic ("theranostic") approach in a single drug-delivery vector and could significantly improve the efficiency of such an anticancer drug as well as other drug types.

Modular design in natural and biomimetic soft materials

Under eons of evolutionary and environmental pressure, biological systems have developed strong and lightweight peptide-based polymeric materials by using the 20 naturally occurring amino acids as principal monomeric units. These materials outperform their man-made counterparts in the following ways: 1) multifunctionality/tunability, 2) adaptability/stimuli-responsiveness, 3) synthesis and processing under ambient and aqueous conditions, and 4) recyclability and biodegradability. The universal design strategy that affords these advanced properties involves "bottom-up" synthesis and modular, hierarchical organization both within and across multiple length-scales. The field of "biomimicry"-elucidating and co-opting nature's basic material design principles and molecular building blocks-is rapidly evolving. This Review describes what has been discovered about the structure and molecular mechanisms of natural polymeric materials, as well as the progress towards synthetic "mimics" of these remarkable systems.