Targeting bone with anionic macromolecules is a potent approach for the development of novel diagnostics and therapeutics for bone related diseases. A highly efficient modular synthesis of dendritic polyglycerol (dPG) polyanion dye conjugates, namely, sulfates, sulfonates, carboxylates, phosphates, phosphonates, and bisphosphonates via click chemistry is presented. By investigating the microarchitecture of stained bone sections with confocal laser scanning microscopy, the bisphosphonate, phosphonate, and phosphate functionalized polymers are identified as strongly penetrating compounds, whereas sulfates, sulfonates, and carboxylates reveal a weaker binding to hydroxyapatite (HA) but a more pronounced affinity toward collagen. In a quantitative HA binding assay, the affinity of the dPG sulfonate, sulfate, and carboxylate toward collagen and the exceptional high HA affinity of the phosphorous containing polyelectrolytes are validated. This shows the potential of dendritic polyphosphates and phosphonates as alternatives to the commonly employed bisphosphonate modification. In cytotoxicity studies with murine fibroblasts, the conjugates have no significant effect on the cell viability at 10^-5m. All polyanions are taken up into the cells within 24 h. The presented synthetic approach allows versatile extensions for preparing conjugates for selective bone imaging applications, tissue engineering, and drug delivery.

Herein, we report on the synthesis of PEG-1000-diethyl ester and 2-azido-propane-1,3-diol-based copolymers utilizing Novozym 435 (Candida antarctica lipase) using a biocatalytic method. The linear base copolymer was then functionalized with polyglycerol-based regular [G1.0] and [G2.0] dendrons and C₁₂/C₁₄ hydrophobic alkyl chains via an efficient “Click approach.” The resulting amphiphilic dendronized polymers form well-defined micelles in aqueous solutions. The transport behavior of these polymers was studied by using Nile red as a fluorescent model dye. The cytotoxicity profiles of a few representative polymers were evaluated, and the effect of hydrophobic alkyl chain length as well as the hydrophilic polyglycerol dendron's generation on the biocompatibility of polymeric systems was studied. Copyright © 2014 John Wiley & Sons, Ltd.

The synthesis and properties of four new ruthenium dyes for TiO₂-based dye-sensitized solar cells are presented. Bipyridine ligands with triarylamine or indoline moieties as donors, which differ both in the size of their conjugated π systems and in their hydrophobicity, have been introduced into thiocyanate (SCN)-free and SCN-containing complexes. The structural changes affect the absorption and electrochemical properties. Extension of the π conjugation leads to a shift in the absorption maximum to longer wavelengths, a broadening of the absorption spectra, and a decrease in the energy of the lowest unoccupied molecular orbital. The efficiency of TiO₂-based solar cells that have been sensitized with the new complexes is mainly affected by the adsorption behavior of the dyes. The SCN-containing complex with the less-substituted or extended donor outperforms the other dyes.

Die Proteinadsorption gilt als der wichtigste Faktor der Wechselwirkung zwischen polymeren Biomaterialien und Körperflüssigkeiten oder -gewebe. Die Haupteinflussfaktoren auf die Proteinadsorption sind wasservermittelte hydrophobe und Hydratationskräfte sowie elektrostatische Wechselwirkungen. Eine systematische Analyse verschiedener Monolagen führte zur Aufstellung allgemeiner Leitsätze, den sogenannten “Whitesides-Regeln”. Diese Konzepte wurden erfolgreich auf die Entwicklung verschiedener proteinresistenter Oberflächen angewendet und werden kontinuierlich weiterentwickelt, um das Verständnis von Protein-Material-Wechselwirkungen über die bisherigen Grenzen hinaus zu erweitern. Ebenso werden die Theorien zu Proteinadsorptionsmechanismen aufgrund der sich schnell entwickelnden analytischen Technologien fortlaufend verbessert. Ziel dieses Aufsatzes ist die Verbesserung der aufgestellten empirischen Leitlinien im Hinblick auf die theoretischen und analytischen Fortschritte. Dabei werden die aktuellen analytischen Methoden zur Untersuchung mechanistischer Hypothesen und Theorien zu Protein-Oberflächen-Wechselwirkungen besprochen. Ein besonderes Augenmerk liegt auf aktuellen Technologien im Bereich bioinerter und biospezifischer Beschichtungen und ihrer Anwendungen in der Biomedizin.

Wir berichten über die Synthese, die Komplexierung und das Schalten in verschiedenen Umgebungen neuer difunktionaler Azobenzol-Oligoglycerin-Konjugate. Zunächst wurden die Schalter durch Wirt-Gast-Chemie an Goldoberflächen gekuppelt, und zwar über β-Cyclodextrin-Rezeptoren, die zuvor auf den entsprechenden Oberflächen immobilisiert worden waren, sowie eine Adamantylgruppe am Azobenzol. Das Isomerisierungsverhalten der amphiphilen Azobenzolderivate wurde in Lösung, auf Goldnanopartikeln und auf planaren Goldoberflächen untersucht. Durch die Bestrahlung mit Licht zweier Wellenlängen konnte die Benetzbarkeit der supramolekular funktionalisierten Oberflächen reversibel verändert werden. Zusätzlich zu den Photoisomerisierungsprozessen und den damit verbundenen Auswirkungen auf die Oberflächenfunktionalität wurde das thermische Rückschalten der cis-Isomere und ihrer Komplexe zur trans-Konfiguration beobachtet. So konnten thermische Halbwertszeiten der cis-Isomere errechnet werden, um eine Aussage über ihre Stabilität treffen zu können.

Ein neues Verfahren zur Herstellung multifunktionaler Materialbeschichtungen baut auf dendritischen, von Muscheln inspirierten Polymeren auf. Diese neuartigen Polymere beziehen nicht nur funktionelle Gruppen von Muschelfußproteinen (Mfps) ein, sondern weisen auch ähnliche Molekülgrößen und -strukturen wie Mfps auf. Die heteromultivalente Verankerung auf Substraten und Vernetzung in den Polymeren basieren auf einer hohen Konzentration von Brenzcatechin- und Aminogruppen. Das Molekulargewicht der Polymere liegt bei 10 kDa und ist somit vergleichbar mit demjenigen des am stärksten anhaftenden Muschelfußproteins, Mfp-5. Zudem befinden sich die funktionellen Gruppen sowohl bei den dendritischen Molekülen als auch in der Tertiärstruktur der Proteine an der Polymeroberfläche. Daher können diese bioinspirierten Polymere mit einer einfachen Tauchbeschichtung auf nahezu jedem Substrat rasch hochstabile Beschichtungsfilme bilden. Diese Methode ist genauso schnell wie die natürliche Verankerung der Muscheln.

Protein adsorption is considered to be the most important factor of the interaction between polymeric biomaterials and body fluids or tissues. Water-mediated hydrophobic and hydration forces as well as electrostatic interactions are believed to be the major factors of protein adsorption. A systematic analysis of various monolayer systems has resulted in general guidelines, the so-called “Whitesides rules”. These concepts have been successfully applied for designing various protein-resistant surfaces and are being studied to expand the understanding of protein–material interactions beyond existing limitations. Theories on the mechanisms of protein adsorption are constantly being improved due to the fast-developing analytical technologies. This Review is aimed at improving these empirical guidelines with regard to present theoretical and analytical advances. Current analytical methods to test mechanistic hypotheses and theories of protein–surface interactions will be discussed. Special focus will be given to state-of-the-art bioinert and biospecific coatings and their applications in biomedicine.

The synthesis, supramolecular complexation, and switching of new bifunctional azobenzene–oligoglycerol conjugates in different environments is reported. Through the formation of host–guest complexes with surface immobilized β-cyclodextrin receptors, the bifunctional switches were coupled to gold surfaces. The isomerization of the amphiphilic azobenzene derivatives was examined in solution, on gold nanoparticles, and on planar gold surfaces. The wettability of functionalized gold surfaces can be reversibly switched under light-illumination with two different wavelengths. Besides the photoisomerization processes and concomitant effects on functionality, the thermal cis to trans isomerization of the conjugates and their complexes was monitored. Thermal half-lives of the cis isomers were calculated for different environments. Surprisingly, the half-lives on gold nanoparticles were significantly smaller compared to planar gold surfaces.

A rapid and universal approach for multifunctional material coatings was developed based on a mussel-inspired dendritic polymer. This new kind of polymer mimics not only the functional groups of mussel foot proteins (mfps) but also their molecular weight and molecular structure. The large number of catechol and amine groups set the basis for heteromultivalent anchoring and crosslinking. The molecular weight reaches 10 kDa, which is similar to the most adhesive mussel foot protein mfp-5. Also, the dendritic structure exposes its functional groups on the surface like the folded proteins. As a result, a very stable coating can be prepared on virtually any type of material surface within 10 min by a simple dip-coating method, which is as fast as the formation of mussel byssal threads in nature.

Four new water-soluble polyglycerol-dendronized perylene, terrylene, and quaterrylene bisimides have been synthesized and characterized with respect to their optical properties in polar organic solvents and water by using UV/Vis and fluorescence spectroscopy. All of these dyes were highly soluble in water, but the size of the chosen polyglycerol dendron was only sufficient to completely suppress dye aggregation for the core-unsubstituted perylene derivative. Their high solubility in water and their absorption and emission wavelengths up to the NIR region make the core-unsubstituted perylene and terrylene bisimides ideal candidates for applications in bioimaging, whilst the lack of fluorescence for quaterrylene bisimide in all polar solvents does not warrant further investigation of this chromophore in fluorescence and imaging applications. Likewise, tuning of the emission of rylene bisimides towards longer wavelengths by employing electron-donating bay substituents is not a promising strategy, owing to the lower fluorescence quantum yields in polar solvents and, in particular, in water.

pH-Spaltbare zellbeladene Mikrogele mit exzellenten Langzeitüberlebensraten wurden durch Kombination bioorthogonaler spannungsvermittelter Azid-Alkin-Cycloaddition (SPAAC) und Tröpfchen-basierter Mikrofluidik hergestellt. Poly(ethylenglycol)dicyclooctin und dendritisches Poly(glycerinazid) fungierten als bioinerte Mikrogelbausteine. Die Azid-Konjugation erfolgte mithilfe unterschiedlicher säurelabiler Benzacetallinker, wodurch eine präzise Steuerung der Abbaukinetik im interessanten pH-Bereich zwischen 4.5 und 7.4 ermöglicht wurde. Hierdurch konnte eine pH-gesteuerte Freisetzung der verkapselten Zellen auf Abruf erreicht werden, ohne ihre Überlebensrate oder Ausspreizung zu beeinträchtigen. Folglich können die Mikrogelpartikel für die temporäre Verkapselung von Zellen verwendet werden, wobei sich die Zellen während der Verkapselung studieren und manipulieren lassen. Anschließend können die Zellen durch Zersetzung des Mikrogelgerüstes isoliert und freigesetzt werden.

pH-Cleavable cell-laden microgels with excellent long-term viabilities were fabricated by combining bioorthogonal strain-promoted azide–alkyne cycloaddition (SPAAC) and droplet-based microfluidics. Poly(ethylene glycol)dicyclooctyne and dendritic poly(glycerol azide) served as bioinert hydrogel precursors. Azide conjugation was performed using different substituted acid-labile benzacetal linkers that allowed precise control of the microgel degradation kinetics in the interesting pH range between 4.5 and 7.4. By this means, a pH-controlled release of the encapsulated cells was achieved upon demand with no effect on cell viability and spreading. As a result, the microgel particles can be used for temporary cell encapsulation, allowing the cells to be studied and manipulated during the encapsulation and then be isolated and harvested by decomposition of the microgel scaffolds.

Multivalent interactions can be applied universally for a targeted strengthening of an interaction between different interfaces or molecules. The binding partners form cooperative, multiple receptor–ligand interactions that are based on individually weak, noncovalent bonds and are thus generally reversible. Hence, multi- and polyvalent interactions play a decisive role in biological systems for recognition, adhesion, and signal processes. The scientific and practical realization of this principle will be demonstrated by the development of simple artificial and theoretical models, from natural systems to functional, application-oriented systems. In a systematic review of scaffold architectures, the underlying effects and control options will be demonstrated, and suggestions will be given for designing effective multivalent binding systems, as well as for polyvalent therapeutics.

Multivalente Wechselwirkungen können universell zur gezielten Bindungsverstärkung zwischen verschiedenen Grenzflächen oder Molekülen genutzt werden. Die Bindungspartner bilden dabei kooperativ multiple Rezeptor-Ligand-Wechselwirkungen, die auf einzelnen schwachen, nichtkovalenten Bindungen basieren und daher prinzipiell reversibel sind. Daher spielen multi- und polyvalente Wechselwirkungen in biologischen Systemen eine entscheidende Rolle für Erkennungs-, Adhäsions- und Signalprozesse. Die wissenschaftliche und praktische Etablierung dieses Prinzips wird anhand der Entwicklung von natürlichen Systemen über einfache artifizielle und theoretische Modelle hin zu anwendungsorientierten funktionalen Systemen demonstriert. Anhand eines systematischen Überblicks über Gerüstarchitekturen werden die zugrunde liegenden Wirk- und Steuerungsmöglichkeiten aufgezeigt und Designvorschläge für möglichst effektive multivalente Bindungspartner bis hin zu polyvalenten Therapeutika aufgezeigt.

A series of nonionic amphiphiles derived from polyglycerol dendrons were studied for their ability to solubilize and isolate single-walled carbon nanotubes. The amphiphiles possessed differently sized polar head groups, hydrophobic tail units, and various aromatic and non-aromatic groups between the head and tail groups. Absorbance analysis revealed that amphiphiles with anchor groups derived from pyrene were far inferior to those that possessed simple linear aliphatic tail groups. Absorbance and near-infrared fluorescence analyses revealed a weak dependence on the dendron size of the head group, but a strong positive trend in suspended nanotube density and fluorescence intensity for amphiphiles with longer tail units. Variations in the moieties linking the head and tail groups led to a range of effects on the suspensions, with linkers imparting flexibility and a bent shape that gave improved performance overall. This was illustrated most dramatically by a pair of benzamide-containing amphiphiles, the para isomer of which showed evidence in the fluorescence data of increased nanotube aggregate formation when compared with the meta isomer. In addition, statistical AFM was used to illustrate more directly the microscopic differences between amphiphiles that were effective at nanotube bundle disruption and those that were not.

The non-specific adsorption of proteins to surfaces in contact with biofluids constitutes a major problem in the biomedical and biotechnological field, due to the initiation of biofilm formation and the resulting improper function of devices. Therefore, non-fouling surfaces modified with poly(ethylene glycol) (PEG) are usually applied. In this study, we report the synthesis of triethoxysilane modified glycerol based polymers of linear and branched architecture for the preparation of covalently attached monolayers on glass. Evaluation of the biocompatibility of these surfaces was performed in comparison to bare non-coated glass, hydrophobic hexadecane modified glass, and mPEG modified glass as the controls. Protein adsorption of BSA and fibrinogen (1 mg · mL⁻¹ in PBS) after 4 and 24 h immersion was reduced by more than 96 and 90%, respectively, compared to the adsorption on bare glass substrates. In addition, mouse NIH-3T3 fibroblast cells showed only marginal adhesion on the polyglycerol and mPEG coated slides after 3 and 7 d incubation in cell suspension, which demonstrates the long-term stability of the applied glass coatings. The non-adhesive properties of these coatings were further reflected in bacterial adhesion tests of Escherichia coli K12 and three clinically relevant Gram-positive and negative strains (Staphylococcus aureus, Pseudomonas aeruginosa, and Aeromonas hydrophila), since linear polyglycerol (LPG(OH)), linear poly(methyl glycerol) (LPG(OMe)), and hyperbranched polyglycerol (HPG) reduced the adhesion for all tested strains by more than 99% compared to bare glass. Therefore, polyglycerol derivatives present an excellent non-fouling surface coating as an alternative to PEG with feasibility for surface modification of various substrates.

The cis–trans isomerisation of N-benzylideneaniline (NBA) and derivatives containing a central CN bond has been investigated experimentally and theoretically. Eight different NBA molecules in three different solvents were irradiated to enforce a photochemical transcis isomerisation and the kinetics of the thermal backreaction cistrans were determined by NMR spectroscopy measurements in the temperature range between 193 and 288 K. Theoretical calculations using density functional theory and Eyring transition-state theory were carried out for 12 different NBA species in the gas phase and three different solvents to compute thermal isomerisation rates of the thermal back reaction. While the computed absolute rates are too large, they reveal and explain experimental trends. Time-dependent density functional theory provides optical spectra for vertical transitions and excitation energy differences between trans and cis forms. Together with isomerisation rates, the latter can be used to identify “optimal switches” with good photochromicity and reasonable thermal stability.

The estrogen receptor binding affinities of bivalent raloxifene ligands tethered by flexible spacers of different lengths have been evaluated in vitro. Two bivalent binding modes, intra- and intermolecular, were hypothesized to explain their different binding properties. The binding affinities of these bivalent ligands in an aqueous environment are influenced by their conformations, which can be determined by 2D NMR and UV spectral methods. Moreover, computer modeling and simulations were performed to explain the binding modes of these bivalent ligands and to estimate the conformational entropy difference between their unbound and bound states. It was found that bivalent ligands tethered by long spacers had weaker binding affinities because of the shielding of the binding moieties that results from their folded conformations; those tethered by short spacers had stronger affinities because they exposed their ligands to the receptor.

We describe the synthesis of multivalent mannose derivatives by using hyperbranched polyglycerols (hPG) as a scaffold with different linker structures. Grafting of protected mannose (Man) units is achieved by using Cu^I-catalyzed Huisgen click chemistry with either an anomeric azide or propargyl ether onto complementarily functionalized alkyne or azido polymer surfaces. NMR spectroscopy, dynamic light scattering (DLS), IR spectroscopy, size-exclusion chromatography (SEC), and elemental analysis have been used to characterize the hPG–Man compounds. The surface availability and bioactivity of Man-modified polymers were evaluated by using a competitive surface plasmon resonance (SPR)-based binding assay by interactions of the glycopolymers with concanavalin A (Con A), a lectin that binds mannose containing molecules. The results indicated that the novel glycoarchitectures presented in this work are efficient inhibitors of Con A–mannose recognition and resulted in inhibitor concentrations (mean IC₅₀) from the micro- to the nanomolar range, whereas the corresponding monovalent mannoside (methyl-Man) requires millimolar concentrations. The results provide an interesting structure–activity relationship for libraries of materials that differ in the linkage of the sugar moiety presented on a biocompatible polyglycerol scaffold.

We describe the synthesis of a series of sialic acid-conjugated, polyglycerol-based nanoparticles with diameters in the range of 1–100 nm. Particle sizes were varied along with the degree of functionalization to match the corresponding virus size and receptor multiplicity in order to achieve maximum efficiency. To build up these architectures, we used biocompatible, hyperbranched polyglycerols as scaffolds and recently developed polyglycerol-based nanogels, the sizes of which can be varied between 2–4 nm and 40–100 nm, respectively. We demonstrate here that such multivalent nanoparticles inhibit influenza A virus cell binding and fusion and consequently infectivity. The potential of multivalency is evident from larger particles showing very efficient inhibition of viral infection up to 80 %. Indeed, both the size of the nanoparticle and the amount of ligand density are important determinants of inhibition efficiency. The inhibitory activity of the tested polymeric nanoparticles drastically increased with size. Particles with similar dimensions to the virus (50–100 nm) are exceedingly effective. We also observed a saturation point in degree of surface functionalization (i.e. ligand density), above which inhibition was not significantly improved. Our study emphasizes the importance of matching particle sizes and ligand densities to mimic biological surfaces and improve interactions; this is a vital concept underlying multivalent interactions.

The application of nanotechnology in medicine and pharmaceuticals is a rapidly advancing field that is quickly gaining acceptance and recognition as an independent area of research called “nanomedicine”. Urgent needs in this field, however, are biocompatible and bioactive materials for antifouling surfaces and nanoparticles for drug delivery. Therefore, extensive attention has been given to the design and development of new macromolecular structures. Among the various polymeric architectures, dendritic (“treelike”) polymers have experienced an exponential development due to their highly branched, multifunctional, and well-defined structures. This Review describes the diverse syntheses and biomedical applications of dendritic polyglycerols (PGs). These polymers exhibit good chemical stability and inertness under biological conditions and are highly biocompatible. Oligoglycerols and their fatty acid esters are FDA-approved and are already being used in a variety of consumer applications, e.g., cosmetics and toiletries, food industries, cleaning and softening agents, pharmaceuticals, polymers and polymer additives, printing photographing materials, and electronics. Herein, we present the current status of dendritic PGs as functional dendritic architectures with particular focus on their application in nanomedicine, in drug, dye, and gene delivery, as well as in regenerative medicine in the form of non-fouling surfaces and matrix materials.

In this paper we describe disulfide containing, polyglycerol nanogels as a new class of biodegradable materials. These nanoparticles are prepared in inverse miniemulsion via an acid catalyzed ring-opening polyaddition of disulfide containing polyols and polyepoxides. Varying conditions allow us to tune particle size and disulfide content within the polymer network; particles can be prepared with narrow polydispersities and diameters in the range from 25 to 350 nm. Particle degradation under reductive intracellular conditions is studied by various analytical techniques. Gel permeation chromatography indicates that final degradation products have relatively low molecular weights (≤ 5 kDa). In addition, studies in cell culture show these nanoscale materials to be highly biocompatible. Dye-labelled nanogels are shown by optical microscopy techniques to readily internalize into cells by endocytotic mechanisms. This study highlights the great potential of these particles to function as sophisticated nanotransporters that deliver cargo to a certain tissue or cell target and then biodegrade into smaller fragments which would be cleared from the body by the kidney. (with ≈ 30 kDa molecular weight cut off)

In this paper we present the asymmetric hydrogenation of α-keto esters with platinum nanoparticles homogeneously stabilized in dendritic core-multishell architectures. The main focus lies on recycling and metal leaching, because little is reported so far about these aspects. It is shown that the stabilizing polymer allows for the efficient modification of the Pt surface with the chiral alkaloid cinchonidine, thereby inducing enantioselectivity and enhancing the reaction rate in the asymmetric hydrogenation of ethyl pyruvate. After optimization of the reaction conditions 63% ee for (R)-ethyl lactate was obtained. During recycling it was found that this value could even be increased upon ultrafiltration of the catalyst prior to use. Recycling was accomplished for 10 cycles with stable activity and enantioselectivity (∼73% ee) in the first eight runs. Aggregation of the initially well dispersed nanoparticles was observed by transmission electron microscope (TEM) analysis, leading to reduced conversion after the 8^th cycle, but metal leaching into the product has been observed only in the very first run.

This paper describes the behavior of various generations of polyglycerol dendrimers that contain a perfluorinated shell. The aggregation in organic solvents is based on supramolecular fluorous–fluorous interactions, which can be described by means of ¹⁹F NMR spectroscopy. In order to study the interaction and aggregation phenomena of dendrimers with perfluorinated shell and perfluoro-tagged guest molecules we investigated [G3.5]-dendrimer with a perfluorinated shell in the presence of perfluoro-tagged disperse red. Noteworthy, the interaction intensities varied in an unexpected manner depending on the equivalents of perfluoro-tagged guest molecules added to the dendrimers in solution which then formed supramolecular complexes based on fluorous–fluorous interactions. We found that these complexes aggregated around residual air in the solvent to form stable micron-sized bubbles. Their sizes correlated with the interaction intensities measured for certain dendrimer–guest molecule ratios. Degassing of the solutions led to a quasi phase separation between organic and fluorous phase, whereby the dendrimers formed the fluorous phases. Regassing the sample with air afforded bubbles of the initial size again.

The nonspecific interaction of proteins with surfaces in contact with biofluids leads to adverse problems and is prevented by a biocompatible surface coating. The current benchmark material among such coatings is poly(ethylene glycol) (PEG). Herein, we report on the synthesis of linear polyglycerol derivatives as promising alternatives to PEG. Therefore, gold surfaces as a model system are functionalized with a self-assembled monolayer (SAM) by a two-step anhydride coupling and a direct thiol immobilization of linear poly(methyl glycerol) and polyglycerol. Surface plasmon resonance (SPR) spectroscopy reveals both types of functionalized surfaces to be as resistant as PEG towards the adsorption of the test proteins fibrinogen, pepsin, albumin, and lysozyme. Moreover, linear polyglycerols adsorb even less proteins from human plasma than a PEG-modified surface. Additional cell adhesion experiments on linear poly(methyl glycerol) and polyglycerol-modified surfaces show comparable cell resistance as for a PEG-modified surface. Also, in the case of long-term stability, high cell resistance is observed for all samples in medium. Additional in vitro cell-toxicity tests add to the argument that linear poly(methyl glycerol) and polyglycerol are strong candidates for promising alternatives to PEG, which can easily be modified for biocompatible functionalization of other surfaces.

Core–multishell architectures are a new approach to homogeneously stabilize metal nanoparticles for harsh conditions. Herein, we present the synthesis and stabilization of Pt nanoparticles in dendritic core–multishell polymers and their application in hydrogenation reactions. The successful recycling of the catalyst was demonstrated for the hydrogenation of methyl crotonate 1 and was either achieved by ultrafiltration or in a two-phase system for at least 14 cycles. Thereby, the total turnover number (TON) was increased to 22 000. In the recycling experiments, low metal leaching into the product (as low as 0.3 ppm) was detected. Additionally, the selective hydrogenation of isophorone 3 was investigated and selectivities of 99:1 for CC versus CO hydrogenation were achieved.

We present the synthesis of symmetrical (pyrrolidine-salen)Cr^III complexes immobilized on hyperbranched polyglycerol 1 through linkers of different lengths and their application in the asymmetric ring-opening of meso-epoxides. This reaction proceeded through a cooperative bimetallic mechanism and for the polymeric catalysts a positive dendritic effect with regard to the reaction rate was found. In addition, the introduction of long linkers (C6, C10, and C18) forced the favored head-to-tail orientation of two catalyst molecules and led to greater enantioselectivity with ee values of 48 % (cyclohexene oxide) and 64 % (cyclopentene oxide) for the ring-opening of meso-epoxides with TMSN₃ catalyzed by hPG-C10-CrCl (13). The soluble polyglycerol-supported catalyst was recovered five times by dialysis to afford similar activities and a 10 % increase in the enantioselectivity.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

A new water-soluble polyglycerol derivative functionalized with N-heterocyclic carbene palladium complexes was prepared and applied as catalyst for Suzuki cross-coupling reactions in water. The complex displays a metal loading of around 65 metal centers per dendrimeric molecule, which is estimated to contain 130 chelating groups and thus corresponds approximately to the formation of 2:1 NHC/metal complexes. Monomeric analogues were also synthesized to validate the reactivity of the dendritic catalyst. Both types of catalysts were tested with various aryl bromides and arylboronic acids. Turnover frequencies of up to 2586 h⁻¹at 80 °C were observed with the dendritic catalyst along with turnover numbers of up to 59 000, which are among the highest turnover numbers reported for polymer-supported catalysts in neat water. The dendritic catalyst could be used (reused) in five consecutive reactions without loss in activity.

Dendrimers are an important class of polymeric materials for a broad range of applications in which monodispersity and multivalency are of interest. Here we report on a highly efficient synthetic route towards bifunctional polyglycerol dendrons on a multigram scale. Commercially available triglycerol (1), which is highly biocompatible, was used as starting material. By applying Williamson ether synthesis followed by an ozonolysis/reduction procedure, glycerol-based dendrons up to the fourth generation were prepared. The obtained products have a reactive core, which was further functionalized to the corresponding monoazido derivatives. By applying copper(I)-catalyzed 1,3-dipolar cycloaddition, so-called “click” coupling, a library of core–shell architectures was prepared. After removal of the 1,2-diol protecting groups, water-soluble core–shell architectures 24–27 of different generations were obtained in high yields. In the structure–transport relationship with Nile red we observe a clear dependence on core size and generation of the polyglycerol dendrons.