Wir berichten über eine einfache Strategie zur Herstellung supramolekularer Copolymere an Goldoberflächen durch sukzessive Inkubation einer initiatorbeschichteten Oberfläche mit Lösungen aus gegensätzlich geladenen peptidischen Comonomeren. Ein ladungsreguliertes Wachstum des Polymers verlangsamt die Kinetik der Selbstorganisation in dem Maße, dass kinetisch gehemmte Copolymere im nahezu neutralen pH-Bereich gebildet werden. Auf diese Weise erreichen wir eine Kontrolle der Polymerarchitektur auf drei Ebenen: Die β-faltblattkodierte Peptidsequenz steuert eine Wachstumsrichtung der Polymere senkrecht zur Oberfläche, die Höhe der supramolekularen Copolymerbürsten wird durch den schrittweisen Aufbau des alternierenden Wachstums bestimmt, und eine Ortsauflösung in zwei Dimensionen wird mithilfe einer Mikrostrukturierung des Initiatormonomers erreicht. Die Programmierbarkeit der Polymerarchitektur ist besonders für die Entwicklung maßgeschneiderter Biomaterialien oder chiraler Grenzflächen für optoelektronische und sensorische Anwendungen von Interesse.

Die Synthese von vier zweizähnigen NHC-Thioether-Hybridliganden wird vorgestellt. Mit diesen Liganden modifizierte Palladium-Nanopartikel sind, in Abhängigkeit des verwendeten Liganden, in verschiedenen Lösungsmitteln stabil und zeigen eine hohe Chemoselektivität in der Hydrierung von Olefinen. Die Löslichkeit der Nanopartikel konnte je nach pH-Wert des Lösungsmittels mehrfach geschaltet werden. Röntgen-Photoelektronenspektroskopie (die eine feine Verschiebung in der Bindungsenergie zeigt) wurde als praktische Analysemethode zur Bestimmung des Bindungsmodus des NHC-Liganden identifiziert.

We report a facile strategy to grow supramolecular copolymers on Au surfaces by successively exposing a surface-anchored monomer to solutions of oppositely charged peptide comonomers. Charge regulation on the active chain end of the polymer sufficiently slows down the kinetics of the self-assembly process to produce kinetically trapped copolymers at near-neutral pH. We thereby achieve architectural control at three levels: The β-sheet sequences direct the polymerization away from the surface, the height of the supramolecular copolymer brushes is well-controlled by the stepwise nature of the alternating copolymer growth, and 2D spatial resolution is realized by using micropatterned initiating monomers. The programmable nature of the resulting architectures renders this concept attractive for the development of customized biomaterials or chiral interfaces for optoelectronics and sensor applications.

The synthesis of four different bidentate hybrid NHC-thioether ligands is presented. The corresponding palladium nanoparticles are stable in various solvents, depending on the ligand used, and show high chemoselectivity in the hydrogenation of olefins. The solubility of the nanoparticles can be switched multiple times depending on the pH value of the solvent. XPS analysis (which shows a subtle shift in the binding energy) was identified as a convenient tool to establish the binding mode of NHC ligands.

Triazolinedione (TAD) click reactions were combined with microcontact chemistry to print, erase, and reprint polymer brushes on surfaces. By patterning substrates with a TAD-tagged atom-transfer radical polymerization initiator (ATRP-TAD) and subsequent surface initiated ATRP, it was possible to graft micropatterned polymer brushes from both alkene- and indole-functionalized substrates. As a result of the dynamic nature of the Alder–ene adduct of TAD and indole at elevated temperatures, the polymer pattern could be erased while the regenerated indole substrate could be reused to print new patterns. To demonstrate the robustness of the methodology, the write–erase cycle was repeated four times.

Triazolindion-Click-Chemie und Mikrokontaktchemie wurden kombiniert, um Polymerbürsten auf Oberflächen zu drucken, zu löschen und anschließend erneut anzubinden. Die mikrostrukturierten Polymerbürsten wurden auf Alken- und Indol-Monoschichten gebildet, indem zuerst ein mit Triazolindion (TAD) substituierter Atomtransferradikalpolymerisationinitiator (ATRP-TAD) auf die Monoschichten gedruckt und anschließend eine oberflächeninitiierte Polymerisation durchgeführt wurde. Der dynamische Charakter des Alder-En-Addukts von TAD und Indol erlaubte es, die Polymerbürsten bei erhöhten Temperaturen von der Oberfläche zu löschen, während die regenerierten Indol-Monoschichten neu strukturiert wurden. Der Zyklus aus Schreiben und Löschen konnte vier Mal durchlaufen werden, wodurch die Robustheit der Methode bewiesen ist.

Gold nanoparticles (Au NPs) with tailor-made structures and properties are highly desirable for applications in catalysis and sensing. In this context, surface modifications of Au NPs are of particular relevance. Herein, we present a sequential surface modification of Au NPs with Ag^I coordination complexes, which can be converted into Ag⁰-doped Au NPs by simple ligand-exchange reaction. The key innovative element of this surface modification is a multifunctional bioxazoline-based ligand that brings coordinated Ag^I into close proximity to the particle surface.

The development of an effective and general delivery method that can be applied to a large variety of structurally diverse biomolecules remains a bottleneck in modern drug therapy. Herein, we present a supramolecular system for the dynamic trapping and light-stimulated release of both DNA and proteins. Self-assembled ternary complexes act as nanoscale carriers, comprising vesicles of amphiphilic cyclodextrin, the target biomolecules and linker molecules with an azobenzene unit and a charged functionality. The non-covalent linker binds to the cyclodextrin by host–guest complexation with the azobenzene. Proteins or DNA are then bound to the functionalized vesicles through multivalent electrostatic attraction. The photoresponse of the host–guest complex allows a light-induced switch from the multivalent state that can bind the biomolecules to the low-affinity state of the free linker, thereby providing external control over the cargo release. The major advantage of this delivery approach is the wide variety of targets that can be addressed by multivalent electrostatic interaction, which we demonstrate on four types of DNA and six different proteins.

Für die Proteomik ist die einfache und effiziente Isolierung von Proteinen aus einer Mischung essenziell. Wir beschreiben hier einen supramolekularen Ansatz, um selektiv Proteine aus einer Proteinmischung einzufangen und mithilfe eines Magnetfeldes auszufällen. Dies geschieht durch die Bildung eines multivalenten selbstorganisierten Komplexes aus einer verdünnten Lösung der folgenden drei Komponenten: Cyclodextrin-beschichtete magnetische Nanopartikel, Adamantan- und Kohlenhydrat-funktionalisierte nichtkovalente Vernetzer und Lectine. Der selbstorganisierte ternäre Komplex wird im Magnetfeld ausgefällt und kann durch die Zugabe eines konkurrierenden Bindungspartners leicht wieder in Lösung gebracht werden. Wir zeigen, dass dieser supramolekulare Ansatz zur Aufreinigung von Proteinen mithilfe magnetischer Extraktion hoch selektiv und effizient erfolgt.

The easy and effective separation of proteins from a mixture is crucial in proteomics. A supramolecular method is described to selectively capture and precipitate one protein from a protein mixture upon application of a magnetic field. A multivalent complex self-assembles in a dilute aqueous solution of three components: magnetic nanoparticles capped with cyclodextrin, non-covalent cross-linkers with an adamantane and a carbohydrate moiety, and lectins. The self-assembled ternary complex is precipitated in a magnetic field and readily redispersed with the aid of a non-ionic surfactant and competitive binding agents. This strategy to purify proteins by supramolecular magnetic precipitation is highly selective and efficient.

Based on the combination of the unique features of both polyionic liquids and spherical colloidal crystals, a new class of inverse opaline spheres with a series of distinct properties was fabricated. It was found that such photonic spheres could not only be used as stimuli-responsive photonic microgels, but also serve as multifunctional microspheres that mimic the main characteristics of conventional molecules, including intrinsic optical properties, specific molecular recognition, reactivity and derivatization, and anisotropy.

Chemical, photochemical and electrical stimuli are versatile possibilities to exert external control on self-assembled materials. Here, a trifunctional molecule that switches between an “adhesive” and a “non-adhesive” state in response to metal ions, or light, or oxidation is presented. To this end, an azobenzene–ferrocene conjugate with a flexible N,N′-bis(3-aminopropyl)ethylenediamine spacer was designed as a multistimuli-responsive guest molecule that can form inclusion complexes with β-cyclodextrin. In the absence of any stimulus the guest molecule induces reversible aggregation of host vesicles composed of amphiphilic β-cyclodextrin due to the formation of intervesicular inclusion complexes. In this case, the guest molecule operates as a noncovalent cross-linker for the host vesicles. In response to any of three external stimuli (metal ions, UV irradiation, or oxidation), the conformation of the guest molecule changes and its affinity for the host vesicles is strongly reduced, which results in the dissociation of intervesicular complexes. Upon elimination or reversal of the stimuli (sequestration of metal ion, visible irradiation, or reduction) the affinity of the guest molecules for the host vesicles is restored. The reversible cross-linking and aggregation of the cyclodextrin vesicles in dilute aqueous solution was confirmed by isothermal titration calorimetry (ITC), optical density measurements at 600 nm (OD₆₀₀), dynamic light scattering (DLS), ζ-potential measurements and cyclic voltammetry (CV). To the best of our knowledge, a dynamic supramolecular system based on a molecular switch that responds orthogonally to three different stimuli is unprecedented.

A broad spectrum of physiological processes is mediated by highly specific noncovalent interactions of carbohydrates and proteins. In a recent communication we identified several cyclic hexapeptides in a dynamic combinatorial library that interact selectively with carbohydrates with high binding constants in water. Herein, we report a detailed investigation of the noncovalent interaction of two cyclic hexapeptides (Cys-His-Cys (which we call HisHis) and Cys-Tyr-Cys (which we call TyrTyr)) with a selection of monosaccharides and disaccharides in aqueous solution. The parallel and antiparallel isomers of HisHis or TyrTyr were synthesized separately, and their interaction with monosaccharides and disaccharides in aqueous solution was studied by isothermal titration calorimetry, NMR spectroscopic titrations, and circular dichroism spectroscopy. From these measurements, we identified particularly stable complexes (K_a>1000 M⁻¹) of the parallel isomer of HisHis with N-acetylneuraminic acid and with methyl-α-D-galactopyranoside as well as of both isomers of TyrTyr with trehalose. To gain further insight into the structure of the peptide–carbohydrate complexes, structure prediction was performed using quantum chemical methods. The calculations confirm the selectivity observed in the experiments and indicate the formation of multiple intermolecular hydrogen bonds in the most stable complexes.

Basierend auf der Kombination der einzigartigen Eigenschaften von polyionischen Flüssigkeiten und kugelförmigen, kolloidalen Kristallen wurde eine neue Klasse von Opalkugeln mit einer Reihe besonderer Eigenschaften hergestellt. Diese photonischen Kugeln konnten nicht nur als responsive photonische Mikrogele verwendet werden, sondern auch als multifunktionelle Mikrokugeln, die die Haupteigenschaften herkömmlicher Moleküle wie optische Eigenschaften, spezifische molekulare Erkennung, Reaktivität, Derivatisierung und Anisotropie nachahmen.

Cyclodextrins are among the most popular host compounds in supramolecular chemistry. In this paper we describe a versatile approach to the multivalent functionalization of cyclodextrins by using photochemical thiol-alkene addition reactions (“thiol-ene click chemistry”). Starting from cyclodextrins allylated at the 2-OH, 3-OH and/or 6-OH positions, a range of thiols could be introduced in good to excellent yields. By using alkanethiols substituted with hydroxy, carboxylic acid, ester, protected amine, and tetraethyleneglycol groups, a broad variety of functionalized cyclodextrins was obtained. By using fluorinated alkanethiols, highly fluorinated cyclodextrins (up to 56 wt.-% of fluorine) were obtained in excellent yield.

Microcontact chemistry has been applied to patterned glass and silicon substrates by successive reaction of unprotected and monoprotected heterobifunctional linkers with alkene-terminated self-assembled monolayers (SAMs) to produce bi-, tri-, and tetrafunctional surfaces. Photochemical microcontact printing of an azide thiol linker followed by immobilization of an acid thiol linker on an undecenyl-terminated SAM results in a well-defined, micropatterned surface with terminal azide, acid, and alkene groups. Biologically relevant molecules (biotin, carbohydrates) have been selectively attached to the surface by means of orthogonal ligation chemistry, and the resulting microarrays display selective binding to fluorescently labeled proteins. An orthogonally addressable, tetrafunctional surface (azide, acid, alkene, and amine) can be prepared by an additional printing step of a tert-butyloxycarbonyl (Boc)-protected alkyne amine linker on the azide structures by using the copper(I)-catalyzed azide–alkyne Huisgen cycloaddition and subsequent removal of the protective group.

A competitive photoresponsive supramolecular system is formed in a dilute aqueous solution of three components: vesicles of amphiphilic α-cyclodextrin host 1 a, divalent p-methylphenyl guest 2 or divalent p-methylbenzamide guest 3, and photoresponsive azobenzene monovalent guest 5. Guests 2 and 3 form weak inclusion complexes with 1 a (K_a≈10² M⁻¹), whereas azobenzene guest 5 forms a strong inclusion complex (K_a≈10⁴ M⁻¹), provided it is in the trans state. The aggregation and adhesion of vesicles of host 1 a is mediated by guest 2 (or 3) due to the formation of multiple intervesicular noncovalent links, as confirmed by using isothermal titration calorimetry (ITC), optical density measurements at 600 nm (OD600), dynamic light scattering (DLS), and cryogenic transmission electron microscopy (cryo-TEM). The addition of excess monovalent guest trans-5 to vesicles of 1 a aggregated by divalent guest 2 (or 3) causes the dispersion of vesicles of 1 a because trans-5 displaces 2 (as well as 3) from the vesicle surface. Upon UV irradiation of a dilute ternary mixture of vesicles of 1 a, guest 2 (or 3), and competitor trans-5, compound trans-5 isomerizes to cis-5, and renewed aggregation of vesicles of 1 a by guest 2 (or 3) occurs because 2 (as well as 3) displaces cis-5 from the vesicle surface. Subsequent visible irradiation causes the redispersion of vesicles of 1 a because cis-5 reisomerizes into trans-5, which again displaces guest 2 (or 3) from the vesicle surface. In this way, the competitive photoresponsive aggregation and dispersion of vesicles can be repeated for several cycles.

The aggregation of β-cyclodextrin vesicles can be induced by an adamantyl-substituted zwitterionic guanidiniocarbonylpyrrole carboxylate guest molecule (1). Upon addition of 1 to the cyclodextrin vesicles at neutral pH, the vesicles aggregate (but do not fuse), as shown by using UV/Vis and fluorescence spectroscopy, dynamic light scattering, ζ-potential measurements, cryogenic transmission electron microscopy, and atomic force microscopy. Aggregation of the vesicles is induced by a twofold supramolecular interaction. First, the adamantyl group of 1 forms an inclusion complex with β-cyclodextrin. Second, at neutral pH the guanidiniocarbonylpyrrole carboxylate zwitterion dimerizes through the formation of hydrogen-bonded ion pairs. Because the dimerization of 1 depends on the zwitterionic protonation state of 1, the aggregation of the cyclodextrin vesicles is also pH dependent; the cyclodextrin vesicles do not interact at pH 5 or 9, at which 1 is either cationic or anionic and, therefore, not self-complementary. These observations are consistent with molecular recognition of the vesicles through a combination of two different supramolecular interactions, that is, host–guest inclusion and dimerization of zwitterions, at the bilayer membrane surface.

An artificial glycocalix self-assembles when unilamellar bilayer vesicles of amphiphilic β-cyclodextrins are decorated with maltose and lactose by host–guest interactions. To this end, maltose and lactose were conjugated with adamantane through a tetra(ethyleneglycol) spacer. Both carbohydrate–adamantane conjugates strongly bind to β-cyclodextrin (K_a≈4×10⁴ M⁻¹). The maltose-decorated vesicles readily agglutinate (aggregate) in the presence of the lectin concanavalin A, whereas the lactose-decorated vesicles agglutinate in the presence of peanut agglutinin. The orthogonal multivalent interaction in the ternary system of host vesicles, guest carbohydrates, and lectins was investigated by using isothermal titration calorimetry, dynamic light scattering, UV/Vis spectroscopy, and cryogenic transmission electron microscopy. It was shown that agglutination is reversible, and the noncovalent interaction can be suppressed and eliminated by the addition of competitive inhibitors, such as D-glucose or β-cyclodextrin. Also, it was shown that agglutination depends on the surface coverage of carbohydrates on the vesicles.