Amplifier-Mediated Activation of Cell-Penetrating Peptides with Steroids: Multifunctional Anion Transporters for Fluorogenic Cholesterol Sensing in Eggs and Blood

Supramolecular Chemistry in the Biomembrane

The combination of supramolecular functional systems with biomolecular chemistry has been a fruitful exercise for decades, leading to a greater understanding of biomolecules and to a great variety of applications, for example, in drug delivery and sensing. Within these developments, the phospholipid bilayer membrane, surrounding live cells, with all its functions has also intrigued supramolecular chemists. Herein, recent efforts from the supramolecular chemistry community to mimic natural functions of lipid membranes, such as sensing, molecular recognition, membrane fusion, signal transduction, and gated transport, are reviewed.

Cationic dynamic covalent polymers for gene transfection

Dynamic covalent polymers have revealed strong potential in gene delivery, thanks to their versatile self-assembly, adaptive and responsive behaviors.

Covalent Surface Functionalization of Semiconducting Polymer Dots with β-Cyclodextrin for Fluorescent Ratiometric Assay of Cholesterol through Host-Guest Inclusion and FRET

Special functionalization of semiconducting polymer dots (Pdots) is highly desired to expand their applications in chemo/biosening. Herein, carboxyl-functionalized poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-{2,1',3}-thiadiazole)] dots covalently tagged with aminated β-cyclodextrin (NH₂-CD) have been designed to construct a ratiometric sensor for cholesterol (Cho). Using CD-Pdots as energy donors with rhodamine B (RB) as energy acceptors, a fluorescence resonance energy transfer (FRET) pair has been built because the host-guest interaction between RB and CD attached to Pdots brings donors and acceptors into close proximity. In the presence of Cho, the acceptors will depart from the donors because of the competitive inclusion interaction between Cho and RB with CD, resulting in the hindering of the FRET process between CD-Pdots and RB. On the basis of the turn-on fluorescence of CD-Pdots and turn-off fluorescence of RB, a sensitive ratiometric method for the determination of Cho in the concentration range from 25 to 350 nM with a detection limit of 4.9 nM was achieved. The proposed method was validated to determine free Cho in human serum samples with satisfactory results.

Cellular uptake: lessons from supramolecular organic chemistry

The objective of this Feature Article is to reflect on the importance of established and emerging principles of supramolecular organic chemistry to address one of the most persistent problems in life sciences. The main topic is dynamic covalent chemistry on cell surfaces, particularly disulfide exchange for thiol-mediated uptake. Examples of boronate and hydrazone exchange are added for contrast, comparison and completion. Of equal importance are the discussions of proximity effects in polyions and counterion hopping, and more recent highlights on ring tension and ion pair-π interactions. These lessons from supramolecular organic chemistry apply to cell-penetrating peptides, particularly the origin of "arginine magic" and the "pyrenebutyrate trick," and the currently emerging complementary "disulfide magic" with cell-penetrating poly(disulfide)s. They further extend to the voltage gating of neuronal potassium channels, gene transfection, and the delivery of siRNA. The collected examples illustrate that the input from conceptually innovative chemistry is essential to address the true challenges in biology beyond incremental progress and random screening.

Colorful surface architectures with three different types of dynamic covalent bonds: integration of anthocyanins, tritylium ions and flavins

Although they combine the best of covalent and non-covalent bonds, dynamic covalent bonds are usually not used together. Building on pioneering examples for functional systems with two orthogonal dynamic covalent bonds, we herein elaborate on multicomponent surface architectures that operate with three different types of dynamic covalent bonds. Disulfide exchange under basic conditions is used to grow single π stacks directly on oxide surfaces, hydrazone exchange under acidic conditions to add a second string or stack, and boronic-ester exchange under neutral conditions to build the third one. In this study, we show that this synthetic approach to complex systems provides access to emergent properties, as exemplified with ordered stacks of anthocyanins, pyrocatchol violet and riboflavins. The integration of anthocyanins, the central component of the pigments of plant flowers, is interesting to protect the blue flavylium cation against deprotonation, deplanarization and degradation. The integration of pyrocatchol violet is of interest to stabilize the blue, disfavored tritylium cation. The red riboflavin stacks are attractive because they generate high photocurrent. These colorful examples hint at the potential of synthetic methods that use three different types of dynamic covalent bonds in concert to build complex systems with emergent properties.

Planarizable push–pull oligothiophenes: in search of the perfect twist

The “twistome” of push–pull oligothiophenes is covered comprehensively. Particular emphasis is on the development of conceptually innovative fluorescent membrane probes.

Synthetic ion transporters that work with anion-π interactions, halogen bonds, and anion-macrodipole interactions

The transport of ions and molecules across lipid bilayer membranes connects cells and cellular compartments with their environment. This biological process is central to a host of functions including signal transduction in neurons and the olfactory and gustatory sensing systems, the translocation of biosynthetic intermediates and products, and the uptake of nutrients, drugs, and probes. Biological transport systems are highly regulated and selectively respond to a broad range of physical and chemical stimulation. A large percentage of today's drugs and many antimicrobial or antifungal agents take advantage of these systems. Other biological transport systems are highly toxic, such as the anthrax toxin or melittin from bee venom. For more than three decades, organic and supramolecular chemists have been interested in developing new transport systems. Over time, curiosity about the basic design has evolved toward developing of responsive systems with applications in materials sciences and medicine. Our early contributions to this field focused on the introduction of new structural motifs with emphasis on rigid-rod scaffolds, artificial β-barrels, or π-stacks. Using these scaffolds, we have constructed selective systems that respond to voltage, pH, ligands, inhibitors, or light (multifunctional photosystems). We have described sensing applications that cover the three primary principles of sensor development: immunosensors that use aptamers, biosensors (an "artificial" tongue), and differential sensors (an "artificial" nose). In this Account, we focus on our recent interest in applying synthetic transport systems as analytical tools to identify the functional relevance of less common noncovalent interactions, anion-π interactions, halogen bonds, and anion-macrodipole interactions. Anion-π interactions, the poorly explored counterpart of cation-π interactions, occur in aromatic systems with a positive quadrupole moment, such as TNT or hexafluorobenzene. To observe these elusive interactions in action, we synthesized naphthalenediimide transporters of increasing π-acidity up to an unprecedented quadrupole moment of +39 Buckinghams and characterized these systems in comparison with tandem mass spectrometry and computational simulations. With π-acidic calixarenes and calixpyrroles, we have validated our results on anion-π interactions and initiated our studies of halogen bonds. Halogen bonds originate from the σ-hole that appears on top of electron-deficient iodines, bromines, and chlorines. Halogen-bond donors are ideal for anion transport because they are as strong and at least as directional as hydrogen-bond donors, but also hydrophobic. The discovery of the smallest possible organic anion transporter, trifluoroiodomethane, illustrates the power of halogen-bond donors. This molecule contains a single carbon atom and is a gas with a boiling point of -22 °C. Anion-macrodipole interactions, finally, differ significantly from anion-π interactions and halogen bonds because they are important in nature and cannot be studied with small molecules. We have used anion-transporting peptide/urea nanotubes to examine these interactions in synthetic transport systems. To facilitate the understanding of the described results, we also include an in-depth discussion of the meaning of Hill coefficients. The use of synthetic transport systems to catch less common noncovalent interactions at work is important because it helps to expand the collection of interactions available to create functional systems. Progress in this direction furthers fundamental knowledge and invites many different applications. For illustration, we briefly discuss how this knowledge could apply to the development of new catalysts.

Supramolecular self-assemblies as functional nanomaterials

In this review, we survey the diversity of structures and functions which are encountered in advanced self-assembled nanomaterials. We highlight their flourishing implementations in three active domains of applications: biomedical sciences, information technologies, and environmental sciences. Our main objective is to provide the reader with a concise and straightforward entry to this broad field by selecting the most recent and important research articles, supported by some more comprehensive reviews to introduce each topic. Overall, this compilation illustrates how, based on the rules of supramolecular chemistry, the bottom-up approach to design functional objects at the nanoscale is currently producing highly sophisticated materials oriented towards a growing number of applications with high societal impact.

Sensing applications of synthetic transport systems

This feature article offers a comprehensive account of a decade of research devoted to the combination of the grand sensing principles with synthetic transport systems that act in lipid bilayers. Differential sensing, that is pattern generation and pattern recognition, is exemplified with an artificial nose. The aptamer version of immunosensing is realized with sticky-end polymers of DNA double helices for both signal generation and signal transduction. Biosensing, that is the use of enzymes for signal generation, is exemplified first with an artificial tongue and then expanded to analytes such as cholesterol, phytate or polyphenols. Enjoyable also for the general reader, we hope that this account will inspire supramolecular organic as well as analytical, physical and biological chemists.

Recent synthetic transport systems

This critical review covers progress with synthetic transport systems, particularly ion channels and pores, between January 2006 and December 2009 in a comprehensive manner. This is the third part of a series launched in the year 2000, covering a rich collection of structural and functional motifs that should appeal to a broad audience of non-specialists, including to organic, biological, supramolecular and polymer chemists. Impressive breakthroughs have been achieved over the past four years in part because of a fruitful expansion toward new types of interactions, including metal-organic, π-π, aromatic electron donor-acceptor, anion-π or anion-macrodipole interactions as well as dynamic covalent bonds (169 references).

DNA aptamers as analyte-responsive cation transporters in fluorogenic vesicles: signal amplification by supramolecular polymerization

We report that single-stranded (ss) DNA aptamers can be activated by counterions such as dodecylguanidinium (DG) to act as transporters in fluorogenic vesicles. However, their activity is independent of the presence or absence of the analyte. Dimerization into ds-DNA helices increases activity in an overadditive manner. Duplex disassembly in response to analyte binding is thus detectable as inactivation. Shortened and mismatched antiaptamers destabilize the active duplex, reduce activity, and increase the sensitivity for the analyte. Supramolecular polymerization of aptamer/antiaptamer duplexes with "sticky ends" is shown to further increase activity without losses in sensitivity for the analyte. The results demonstrate that the principles of DNA nanotechnology are directly applicable to membrane based sensing systems with high precision and fidelity.