Radu A. Gropeanu

pH-Responsive quantum dots via an albumin polymer surface coating.

Multifunctional peptide-polymer hybrid materials have been applied as efficient and biocompatible quantum-dot coating materials. Significant pH responsiveness (e.g., an influence of the pH on the quantum yields of the peptide-polymer/QDs) was found and is attributed to conformational rearrangements of the peptide backbone.

Antibacterial Strategies from the Sea: Polymer-Bound Cl-Catechols for Prevention of Biofilm Formation

Inspired by the amino acid 2-chloro-4,5-dihydroxyphenylalanine (Cl-DOPA), present in the composition of the proteinaceous glue of the sandcastle worm Phragmatopoma californica, a simple strategy is presented to confer antifouling properties to polymer surfaces using (but not releasing) a bioinspired biocide. Cl-Dopamine is used to functionalize polymer materials and hydrogel films easily, to prevent biofilm formation on them.

Fluorescent Core/Shell Nanoparticles for Specific Cell-Nucleus Staining†

The highly fluorescent perylene-3,4,9,10-tetracarboxdiimide (PDI) chromophore is a popular dye and pigment because of its excellent chemical, thermal, and photochemical stability. Due to these outstanding properties, there have been several successful applications of PDI chromophores in various fields. Water-soluble and fluorescent PDI dyes have been used in biological applications such as the in vitro staining of cells and proteins. The combination of water solubility and high fluorescence quantum yield still represents a challenging goal since PDI dyes have a strong tendency to form aggregates in aqueous solution even at very low concentrations. Water solubility and high fluorescence quantum yields of ionic PDIs were obtained by introducing positively or negatively charged substituents into the bay region of the chromophore. Although these ionic PDIs penetrate the cytoplasmic membrane of living cells, the synthesis of PDIs with specific binding properties to subcellular compartments has not yet been achieved. Recently, the preparation of core/shell nanoparticles with high structural perfection, water-solubility, and biocompatibility has been reported. However, the synthesis and biological characterization of fluorescent core/shell nanoparticles with specific biological applications have not been demonstrated. Herein we describe a novel water-soluble, negatively charged PDI derivative that specifically labels the cell nucleus by strong binding to positively charged nuclear proteins, thus allowing their application as a fluorescent dye in pathological and histochemical studies. The core/shell nanoparticle (Figure 1, P1) consists of a central PDI chromophore, a rigid first-generation polyphenylene dendrimer scaffold for suppressing aggregation of the central PDI chromophore in aqueous media and a polymer shell with multiple carboxylic acid groups for inducing water solubility and biological specificity. The synthetic strategy towards P1 is shown in Scheme 1, starting from the previously

Fine-tuning DNA/albumin polyelectrolyte interactions to produce the efficient transfection agent cBSA-147

We present the preparation and isolation of different chemically modified BSA species with varying numbers of primary amino groups at the surface. Highly cationic albumin proteins with increased numbers of amino groups were achieved and complex formation with plasmid DNA was carefully investigated. We compare the transfection results, polyelectrolyte complexes morphologies with their impact on complex stabilities, cytotoxicities and DNA accessibility. This knowledge-driven approach led to the identification of the efficient non-viral DNA delivery agent cBSA-147, which showed high transfection efficacies and stability.

Photoactivatable Caged Cyclic RGD Peptide for Triggering Integrin Binding and Cell Adhesion to Surfaces

We report the synthesis and properties of a photoactivatable caged RGD peptide and its application for phototriggering integrin‐ and cell‐binding to surfaces. We analysed in detail 1) the differences in the integrin‐binding affinity of the caged and uncaged forms by quartz crystal microbalance (QCM) studies, 2) the efficiency and yield of the photolytic uncaging reaction, 3) the biocompatibility of the photolysis by‐products and irradiation conditions, 4) the possibility of site, temporal and density control of integrin‐binding and therefore human cell attachment, and 5) the possibility of in situ generation of cell patterns and cell gradients by controlling the UV exposure. These studies provide a clear picture of the potential and limitations of caged RGD for integrin‐mediated cell adhesion and demonstrate the application of this approach to the control and study of cell interactions and responses.

Dendritic Star Polymers for Efficient DNA Binding and Stimulus-Dependent DNA Release

Water-soluble core-shell star polymers consisting of a dendritic polyphenylene core and an outer shell containing a defined number of amino groups have been synthesized via atom transfer radical polymerization (ATRP). All macromolecules efficiently interacted with a diverse set of DNA fragments, and stable complexes were formed and visualized by atomic force microscopy. The observed tight binding of DNA, which was found in the sub-nanomolar range, was mainly attributed to strong electrostatic interactions. Complex stoichiometries between the polyelectrolytes were controlled via the number of amino groups of the star polymers, and well-defined nanoscopic architectures were formed. DNA was released from the complexes after treatment with high concentrations of sodium chloride in aqueous solution. Such star polymers, which allow the binding and release of DNA, represent attractive candidates for the development of novel anion-exchange resins for DNA purification or as nonviral vector systems for gene delivery.

New photolabile BAPTA-based Ca2+ cages with improved photorelease.

The efficient synthesis, physicochemical and photolytical properties of a photoactivable BAPTA-based Ca(2+) cage containing two photosensitive o-nitrobenzhydryl groups attached to the aromatic core are described. Ca(2+) release in living cells was evaluated. The double substitution with the chromophores caused a significant improvement of the Ca(2+) release properties of nitr-T versus singly substituted reported nitr-x derivatives without compromising Ca(2+)/Mg(2+) selectivity or pH insensitivity. Our results demonstrate a general strategy to improve light-triggered Ca(2+) release which may result in more efficient, selective, and pH-insensitive photolabile Ca(2+) chelators.

Photopatterned antibodies for selective cell attachment

We present a phototriggerable system that allows for the spatiotemporal controlled attachment of selected cell types to a biomaterial using immobilized antibodies that specifically target individual cell phenotypes. o-Nitrobenzyl caged biotin was used to functionalize chitosan membranes and mediate site-specific coupling of streptavidin and biotinylated antibodies after light activation. The ability of this system to capture and immobilize specific cells on a surface was tested using endothelial-specific biotinylated antibodies and nonspecific ones as controls. Homogeneous patterned monolayers of human umbilical vein endothelial cells were obtained on CD31-functionalized surfaces. This is a simple and generic approach that is applicable to other ligands, materials, and cell types and shows the flexibility of caged ligands to trigger and control the interaction between cells and biomaterials.

Tailored Albumin-based Copolymers for Receptor-Mediated Delivery of Perylenediimide Guest Molecules

The synthesis of a novel and multifunctional copolymer based on a human serum albumin backbone bearing several folic acid as well as PEO groups was presented. In solution, this side-chain copolymer adopts a globular architecture and about five molecules of the water-insoluble chromophore PDI were successfully incorporated into these micelles for receptor-mediated cell uptake investigations. A significant uptake of these bioconjugates via receptor-mediated endocytosis was detected for cells expressing folic acid receptors in the cell membrane. These novel albumin-based copolymers could serve as efficient and biocompatible carrier systems facilitating the directed delivery of lipophilic drug molecules into cancer cells and they allow investigating vesicle formation and trafficking even at the single molecule level.

Functional Layers for Zn II Ion Detection: From Molecular Design to Optical Fiber Sensors

We report on the synthesis of a novel perylene monoimide derivative that shows high response and selectivity for zinc ion detection. The complexation of Zn(2+) by the dye is followed by FD-MS, (1)H NMR, UV-vis spectroscopy, and isothermal titration calorimetry. Quantum chemical calculations are performed to gain further insight into the electronic processes responsible for the spectroscopic changes observed upon complexation. Finally, the perylene dye is incorporated in a sol-gel silica layer coated on optical fibers that are then used for Zn(2+) detection in aqueous solution.