Convenient Synthesis of 1 → 3 C-Branched Dendrons

In vivo deep-tissue microscopy with UCNP/Janus-dendrimers as imaging probes: resolution at depth and feasibility of ratiometric sensing

Lanthanide-based upconverting nanoparticles (UCNPs) are known for their remarkable ability to convert near-infrared energy into higher energy light, offering an attractive platform for construction of biological imaging probes. Here we focus on in vivo high-resolution microscopy - an application for which the opportunity to carry out excitation at low photon fluxes in non-linear regime makes UCNPs stand out among all multiphoton probes. To create biocompatible nanoparticles we employed Janus-type dendrimers as surface ligands, featuring multiple carboxylates on one 'face' of the molecule, polyethylene glycol (PEG) residues on another and Eriochrome Cyanine R dye as the core. The UCNP/Janus-dendrimers showed outstanding performance as vascular markers, allowing for depth-resolved mapping of individual capillaries in the mouse brain down to a remarkable depth of ∼1000 μm under continuous wave (CW) excitation with powers not exceeding 20 mW. Using a posteriori deconvolution, high-resolution images could be obtained even at high scanning speeds in spite of the blurring caused by the long luminescence lifetimes of the lanthanide ions. Secondly, the new UCNP/dendrimers allowed us to evaluate the feasibility of quantitative analyte imaging in vivo using a popular ratiometric UCNP-to-ligand excitation energy transfer (EET) scheme. Our results show that the ratio of UCNP emission bands, which for quantitative sensing should respond selectively to the analyte of interest, is also strongly affected by optical heterogeneities of the medium. On the other hand, the luminescence decay times of UCNPs, which are independent of the medium properties, are modulated via EET only insignificantly. As such, quantitative analyte sensing in biological tissues with UCNP-based probes still remains a challenge.

Nanoscale Amphiphilic Star-like Macromolecules with Carboxy-, Methoxy and Amine-terminated Chain Ends

Amphiphilic star-like macromolecules (ASMs) with chain ends terminating as methoxy-, carboxy and amine groups were synthesized for use as drug solubilization and delivery systems. Hydrophobic mucic acid derivatives were conjugated to the pentaerythritol tetraacrylate as the core molecule, then poly(ethylene glycol) chains with specific functionalized chain ends were attached. With respect to size in solution, the ASMs with longer alkyl chains (C12) in the core were slightly larger than polymers with shorter alkyl chains (C6), and the carboxy-terminated ASMs displayed slightly larger sizes than the methoxy and amine-terminated polymers. In aqueous solution, the ASMs maintained their nanosize, ranging from 20 to 40nm in diameter in solutions with pH values of 2, 7.4 and 9. The shorter C6 chain polymers displayed sizes that were independent of pH, whereas the longer chain polymers displayed a more pronounced response to pH changes. With respect to thermal properties, ASMs with larger hydrophobic cores had slightly lowered melting and crystallization temperatures. The methoxy-terminated ASMs have higher melting and crystallization temperatures (by 8°C) than the ASMs terminated with carboxy and amine functionalities.

Water-soluble perylenediimides: design concepts and biological applications

Water-soluble perylenediimides (PDIs) with high fluorescence intensity, photostability and biocompatibility have been successfully prepared and applied in the biological field.

Highly ordered dielectric mirrors via the self-assembly of dendronized block copolymers

Dendronized block copolymers were synthesized by ruthenium-mediated ring-opening methathesis polymerization of exo-norbornene functionalized dendrimer monomers, and their self-assembly to dielectric mirrors was investigated. The rigid-rod main-chain conformation of these polymers drastically lowers the energetic barrier for reorganization, enabling their rapid self-assembly to long-range, highly ordered nanostructures. The high fidelity of these dielectric mirrors is attributed to the uniform polymer architecture achieved from the construction of discrete dendritic repeat units. These materials exhibit light-reflecting properties due to the multilayer architecture, presenting an attractive bottom-up approach to efficient dielectric mirrors with narrow band gaps. The wavelength of reflectance scales linearly with block-copolymer molecular weight, ranging from the ultraviolet, through the visible, to the near-infrared. This allows for the modulation of photonic properties through synthetic control of the polymer molecular weight. This work represents a significant advancement in closing the gap between the precision obtained from top-down and bottom-up approaches.

Dendrimers functionalized with membrane-interacting peptides for viral inhibition

This contribution reports the synthesis of a poly(amide)-based dendrimer functionalized at the termini with a membrane-interacting peptide derived from the herpes simplex virus (HSV) type 1 glycoprotein H, namely gH625–644. This peptide has been shown to interact with model membranes and to inhibit viral infectivity. The peptidodendrimer inhibits both HSV-1 and HSV-2 at a very early stage of the entry process, most likely through an interaction with the viral envelope glycoproteins; thus, preventing the virus from coming into close contact with cellular membranes, a prerequisite of viral internalization. The 50% inhibitory concentration was 100 and 300 nM against HSV-1 and HSV-2 respectively, with no evidence of cell toxicity at these concentrations. These results show that the functionalization of a dendrimer with the peptide sequence derived from an HSV glycoprotein shows promising inhibitory activity towards viruses of the Herpesviridae family.

Dendrimer functionalization with a membrane-interacting domain of herpes simplex virus type 1: towards intracellular delivery

A poly(amide)-based dendrimer was synthesized and functionalized with the membrane-interacting peptide gH(625-644) (gH625) derived from the herpes simplex virus type 1 (HSV-1) envelope glycoprotein H, which has previously been shown to assist in delivering large cargoes across the cellular membrane. We demonstrate that the attachment of the gH625 peptide sequence to the termini of a dendrimer allows the conjugate to penetrate into the cellular matrix, whereas the unfunctionalized dendrimer is excluded from translocation. The peptide-functionalized dendrimer is rapidly taken into the cells mainly through a non-active translocation mechanism. Our results suggest that the presented peptidodendrimeric scaffold may be a promising material for efficient drug delivery.

Chemiluminescence change of polyphenol dendrimers with different core molecules

Second generation polyphenol dendrimers (PDs) with different core molecules were synthesized, and their chemiluminescence (CL) was measured by reacting the PDs with H2O2 under alkaline conditions. All of the PDs showed a strong CL, more than 120-fold greater than that of gallic acid. Various CL intensities of the PDs were obtained using different core molecules in the PDs. The distance between each dendron in the PD structure is crucial in the PD CL intensity.

Multifunctionalization of dendrimers through orthogonal transformations

A straightforward methodology for the synthesis of multifunctionalized dendrimers that is based on an orthogonal functionalization strategy has been developed. Polyamide-based dendrimers that possess both a single aldehyde and a single azide moiety on their periphery have been synthesized by using a convergent synthetic strategy. These dendrimers can be functionalized quantitatively with small organic and biological molecules that contain hydrazide and/or alkyne groups in which each functional moiety is completely specific for its complementary motif. This orthogonal functionalization strategy has the potential to be used to synthesize multifunctional dendrimers for a variety of applications, which range from targeted biological delivery vehicles to optical materials.

New dendrimers containing a single cobaltocenium unit covalently attached to the apical position of Newkome dendrons: electrochemistry and guest binding interactions with cucurbit[7]uril

Two new dendrimer series were prepared and characterized. These dendrimers contain a single bis(cyclopentadienyl)cobalt(III) (cobaltocenium, Cob+) unit covalently attached to the apical (focal) position of Newkome-type dendrons, ranging in size from first to third generation. The dendrimers in the first series (1ECob+-3ECob+) are hydrophobic and have 3, 9, and 27 tert-butyl esters on their peripheries, whereas the dendrimers in the second series (1Cob+-3Cob+) are hydrophilic with 3, 9, and 27 carboxylic acid groups on their surfaces, respectively. In voltammetric experiments, all dendrimers showed the expected one-electron reversible reduction of the cobaltocenium center, and the heterogeneous rate of electron transfer decreased with generation in both dendrimer series. The host-guest binding interactions between water-soluble dendrimers 1Cob+-3Cob+ and the cucurbit[7]uril (CB7) host were investigated using 1H NMR spectroscopy, MALDI-TOF mass spectrometry, and electrochemical techniques. The association equilibrium constants (K) for all dendrimer guests were significantly lower than that measured for the inclusion complex between underivatized Cob+ and CB7 (K = 5.7 x 10(9) M(-1)). Nonetheless, among the three dendrimers surveyed, the second-generation dendrimer, 2Cob+, afforded optimum stabilization for the CB7 inclusion complex.

Multivalent glycomimetics: synthesis of nonavalent mannoside clusters with variation of spacer properties

Oligosaccharide mimetics are important tools in the glycosciences. In this work, we have employed spaced glycodendrons for the synthesis of oligomannoside mimetics. Starting from a number of trivalent, branched molecular wedges, the preparation of nonavalent cluster mannosides was accomplished, which were varied with regard to the chemical characteristics of their spacer moieties and spacer lengths. For ligation of the various trivalent dendrons to the nonavalent target molecules peptide coupling was employed.

Dendron-Tethered and Templated CdS Quantum Dots on Single-Walled Carbon Nanotubes

CdS nanoparticles on the surface of single-walled carbon nanotubes (SWNTs) were templated and stabilized through the initial attachment of 1 --> 3 C-branched amide-based dendrons and were both photophysically and morphologically characterized. The CdS clusters were shown to be ca. 1.4 nm in diameter as calculated from their optical absorption spectra and exhibited reduced fluorescence emission intensity at 434 nm compared to that of CdS quantum dots stabilized by untethered dendrons due to partial emission quenching by the SWNT. Unchanged UV absorption behavior of these materials indicated that they are stable > 90 days at 25 degrees C.

Design, Synthesis, and Characterization of Conifer-Shaped Dendritic Architectures

An elongated structural design leading to more conical-shaped dendritic architectures by using a combination of 1-->3, 1-->(2+1), and 1-->(2+1 Me) C-branched monomers is presented. Synthesis of the conifer-shaped macromolecule was achieved by reaction between isocyanate 20 and amine 26 in dry CH2Cl2. A resultant extended focal adamantane-modified dendron was deprotected to generate the water-soluble product, which was subsequently complexed with beta-cyclodextrin in D2O to create the desired tree-like product. Host-guest interactions of the adamantane moiety with the beta-cyclodextrin cavity were monitored by 1H NMR spectroscopy. All monomers, key intermediates, and final products were fully characterized by 1H and 13C NMR spectroscopy, ESI or MALDI-TOF mass spectrometry, and IR spectroscopy.