Electroluminescent networks via photo "click" chemistry

The use of thiol-ene click chemistry is demonstrated for the first time as a suitable method for cross-linking thin films of 4-phenylethenyl end-capped poly(fluorene). Cross-linking was accomplished by a simple, brief UV curing step at modest temperatures. This chemistry provides an advantage over similar schemes employed for cross-linking conjugated polymers since it does not require elevated temperature or produce potentially detrimental side products. Thiol-ene cross-linking was found to preserve the emissive color integrity of the poly(fluorene) films and allowed for facile photopatterning of the active polymer layer. Furthermore, the investigated cross-linking chemistry was shown to be fully compatible with fabrication of polymer light-emitting diodes (PLEDs) whose performance was comparable to noncross-linked devices. Multicolor PLEDs were also demonstrated by taking advantage of the photopatternability of the thiol-ene based system.     

Dendronized linear polymers via "click chemistry"

Dendronized linear polymers are prepared from dendritic azides and poly(vinylacetylene) using "click chemistry." The Cu(I)-catalyzed Huisgen [2 + 3] cycloaddition is quantitative up to the third generation.     

Surface modification of silicon nanowires via copper-free click chemistry

A two-step process based on copper-free click chemistry is described, by which the surface of silicon nanowires can be functionalized with specific organic substituents. A hydrogen-terminated nanowire surface is first primed with a monolayer of an α,ω-diyne and thereby turned into an alkyne-terminated, clickable platform, which is subsequently coupled with an overlayer of an organic azide carrying the desired terminal functionality. The reactive, electron-deficient character of the employed diyne enabled a quantitative coupling reaction at 50 °C without metal catalysis, which opens up a simple and versatile route for surface functionalization under mild conditions without any potentially harmful additives.     

A citric acid-derived ligand for modular functionalization of metal oxide surfaces via "click" chemistry

Citric acid is a widely used surface-modifying ligand for growth and processing of a variety of nanoparticles; however, the inability to easily prepare derivatives of this molecule has restricted the development of versatile chemistries for nanoparticle surface functionalization. Here, we report the design and synthesis of a citric acid derivative bearing an alkyne group and demonstrate that this molecule provides the ability to achieve stable, multidentate carboxylate binding to metal oxide nanoparticles, while also enabling subsequent multistep chemistry via the Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. The broad utility of this strategy for the modular functionalization of metal oxide surfaces was demonstrated by its application in the CuAAC modification of ZnO, Fe(2)O(3), TiO(2), and WO(3) nanoparticles.     

Polymer brushes grafted to "passivated" silicon substrates using click chemistry

We present herein a versatile method for grafting polymer brushes to passivated silicon surfaces based on the Cu(I)-catalyzed Huisgen 1,3-dipolar cycloaddition (click chemistry) of omega-azido polymers and alkynyl-functionalized silicon substrates. First, the "passivation" of the silicon substrates toward polymer adsorption was performed by the deposition of an alkyne functionalized self-assembled monolayer (SAM). Then, three tailor-made omega-azido linear brush precursors, i.e., PEG-N3, PMMA-N3, and PS-N3 (Mn approximately 20,000 g/mol), were grafted to alkyne-functionalized SAMs via click chemistry in tetrahydrofuran. The SAM, PEG, PMMA, and PS layers were characterized by ellipsometry, scanning probe microscopy, and water contact angle measurements. Results have shown that the grafting process follows the scaling laws developed for polymer brushes, with a significant dependence over the weight fraction of polymer in the grafting solution and the grafting time. The chemical nature of the brushes has only a weak influence on the click chemistry grafting reaction and morphologies observed, yielding polymer brushes with thickness of ca. 6 nm and grafting densities of ca. 0.2 chains/nm2. The examples developed herein have shown that this highly versatile and tunable approach can be extended to the grafting of a wide range of polymer (pseudo-) brushes to silicon substrates without changing the tethering strategy.     

Novel types of carborane-carrier hyaluronan derivatives via "click chemistry"

Two new HA derivatives bearing carborane rings were synthesized by click chemistry. The optimal conditions were assessed for the preparation of biocompatible boron carriers, potentially suitable for application in BNCT and capable of targeting the CD44 antigen. The new polymeric samples were characterized by means of NMR-spectroscopy techniques that gave degrees of 17 and 8% for HAAACB and HapACB, respectively. Both HAAACB and HApACB turned out to be nontoxic for colorectal, ovarian and bladder tumor cell lines, to disclose a specific interaction with the CD44 antigen as the native hyaluronan moiety, and to deliver boron-atom concentrations largely sufficient for BNCT therapy when accumulated in cancer cells.     

Efficient synthesis of multifunctional polymers via thiol-epoxy "click" chemistry

We demonstrate high efficiency and simplicity of the thiol-epoxy reaction towards preparation of a wide range of main-chain as well as end-chain multifunctional polymers.     

Magnetic nanoparticle assembly on surfaces using click chemistry

Controlled assembly of ferromagnetic nanoparticles on surfaces is of crucial importance for a range of spintronic and data storage applications. Here, we present a novel method for assembling monolayers of ferromagnetic FePt nanoparticles on silicon oxide substrates using "click chemistry". Reaction of alkyne-functionalized FePt nanoparticles with azide-terminated self-assembled monolayers (SAMs), on silicon oxide, leads to the irreversible attachment of magnetic nanoparticles to the surface via triazole linkers. Based on this covalent interaction, well-packed monolayers of FePt nanoparticles were prepared and nanoparticle patterns are generated on surfaces via microcontact printing (μCP).     

Phosphatidylcholine-derived bolaamphiphiles via click chemistry

The copper-catalyzed azide alkyne cycloaddition is employed to modify phosphatidylcholine precursors with sn-2 acyl chains containing terminal alkyne or azide groups. Although the reactions are conducted as biphasic dispersions, the yields are essentially quantitative. Bolaamphiphiles are formed by simply clicking together two phosphatidylcholine alkyne precursors to a central bisazide scaffold. The chemistry introduces polar 1,4-triazole units into the lipophilic region of the bilayer membrane, and the bolaamphiphiles do not form stable vesicles. [structure: see text].     

Copper-free click biofunctionalization of silicon nitride surfaces via strain-promoted alkyne-azide cycloaddition reactions

Cu-free "click" chemistry is explored on silicon nitride (Si(3)N(4)) surfaces as an effective way for oriented immobilization of biomolecules. An ω-unsaturated ester was grafted onto Si(3)N(4) using UV irradiation. Hydrolysis followed by carbodiimide-mediated activation yielded surface-bound active succinimidyl and pentafluorophenyl ester groups. These reactive surfaces were employed for the attachment of bicyclononyne with an amine spacer, which subsequently enabled room temperature strain-promoted azide-alkyne cycloaddition (SPAAC). This stepwise approach was characterized by means of static water contact angle, X-ray photoelectron spectroscopy, and fluorescence microscopy. The surface-bound SPAAC reaction was studied with both a fluorine-tagged azide and an azide-linked lactose, yielding hydrophobic and bioactive surfaces for which the presence of trace amounts of Cu ions would have been problematic. Additionally, patterning of the Si(3)N(4) surface using this metal-free click reaction with a fluorescent azide is shown. These results demonstrate the ability of the SPAAC as a generic tool for anchoring complex molecules onto a surface under extremely mild, namely ambient and metal-free, conditions in a clean and relatively fast manner.     

ParaCEST MRI contrast agents capable of derivatization via"click" chemistry

A comprehensive series of lanthanide chelates has been prepared with a tetrapropargyl DOTAM type ligand. The complexes have been characterized by a combination of (1)H NMR, single-crystal X-ray crystallography, CEST and relaxation studies and have also been evaluated for potential use as paramagnetic chemical exchange saturation transfer (ParaCEST) contrast agents in magnetic resonance imaging (MRI). We demonstrate the functionalization of several chelates by means of alkyne-azide "click" chemistry in which a glucosyl azide is used to produce a tetra-substituted carbohydrate-decorated lanthanide complex. The carbohydrate periphery of the chelates has a potent influence on the CEST properties as described herein.     

PEGylation of porous silicon using click chemistry

Porous silicon has received considerable interest in recent years in a range of biomedical applications, with its performance determined by surface chemistry. In this work, we investigate the PEGylation of porous silicon wafers using click chemistry. The porous silicon wafer surface chemistry was monitored at each stage of the reaction via photoacoustic Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, whereas sessile drop contact angle and model protein adsorption measurements were used to characterize the final PEGylated surface. This work highlights the simplicity of click-chemistry-based functionalization in tailoring the porous silicon surface chemistry and controlling protein-porous silicon interactions.     

Thermally curable polyvinylchloride via click chemistry

Novel side‐chain benzoxazine functional polyvinylchloride (PVC‐Benzoxazine) was synthesized by using “Click Chemistry” strategy. First, approximately 10% of chloro groups of PVC were converted to azido groups by using NaN₃ in N,N‐dimethylformamide. Propargyl benzoxazine was prepared independently by a ring closure reaction between p‐propargyloxy aniline, paraformaldehyde, and phenol. Finally, azidofunctionalized PVC was coupled to propargyl benzoxazine with high efficiency by click chemistry. The spectral and thermal analysis confirmed the presence of benzoxazine functionality in the resulting polymer. It is shown that PVC containing benzoxazine undergoes thermally activated curing in the absence of any catalyst forming PVC thermoset with high thermal stability. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3512–3518, 2008     

Biotinylated thermoresponsive core cross-linked nanoparticles via RAFT polymerization and "click" chemistry

A straightforward approach to the synthesis of "clickable" thermoresponsive core cross-linked (CCL) nanoparticles was developed. This approach was based on reversible addition-fragmentation chain transfer (RAFT) radical cross-linking polymerization of styrene and divinylbenzene with azide-functionalized poly(N-isopropylacrylamide) (PNIPAM-N(3)) as macro chain transfer agent in a selective solvent. Spherical nanoparticles with a diameter of 12nm were obtained after 24h polymerization. When the lyophilized CCL nanoparticles were dispersed in THF, spherical nanoparticles were observed, confirming the stability of CCL nanoparticles. The transmission electron microscopy (TEM) studies demonstrated that spherical nanoparticles and wormlike structure coexisted in the aqueous solution. The CCL nanoparticles have a lower critical solution temperature (LCST) at about 29.6°C, a little lower than that of PNIPAM homopolymer. Biotin molecules were conjugated to the surface of CCL nanoparticles via "click" chemistry in aqueous media. After bioconjugation, the LCST shifted to 28.3°C. The bioavailability of biotin to protein avidin was evaluated by a 4'-hydroxyazobenzene-2-carboxylic acid/avidin (HABA/avidin) binding assay and TEM.     

2D assembly of non-interacting magnetic iron oxide nanoparticles via"click" chemistry

Azide-terminated magnetic iron oxide nanoparticles have been assembled in 2D on alkyne-terminated self-assembled monolayers (SAMs) by the copper(i) catalyzed alkyne-azide cycloaddition (CuAAC) "click" reaction; the kinetics of the reaction is an important parameter to control the interparticle distance and thus the dipolar interactions.     

Facile decoration of functionalized single-wall carbon nanotubes with phthalocyanines via "click chemistry"

We describe the functionalization of single-wall carbon nanotubes (SWNTs) with 4-(2-trimethylsilyl)ethynylaniline and the subsequent attachment of a zinc-phthalocyanine (ZnPc) derivative using the reliable Huisgen 1,3-dipolar cycloaddition. The motivation of this study was the preparation of a nanotube-based platform which allows the facile fabrication of more complex functional nanometer-scale structures, such as a SWNT-ZnPc hybrid. The nanotube derivatives described here were fully characterized by a combination of analytical techniques such as Raman, absorption and emission spectroscopy, atomic force and scanning electron microscopy (AFM and SEM), and thermogravimetric analysis (TGA). The SWNT-ZnPc nanoconjugate was also investigated with a series of steady-state and time-resolved spectroscopy experiments, and a photoinduced communication between the two photoactive components (i.e., SWNT and ZnPc) was identified. Such beneficial features lead to monochromatic internal photoconversion efficiencies of 17.3% when the SWNT-ZnPc hybrid material was tested as photoactive material in an ITO photoanode.     

Design and characterization of an electrochemical peptide-based sensor fabricated via"click" chemistry

We report an electrochemical peptide-based sensor fabricated via'click' chemistry for detection of anti-p24 antibodies. Our results also allude to a signaling mechanism similar to that of the linear probe electrochemical DNA sensor.     

Functional polyisobutylenes via a click chemistry approach

1‐(ω‐Azidoalkyl)pyrrolyl‐terminated polyisobutylene (PIB) was successfully synthesized both by substitution of the terminal halide of 1‐(ω‐haloalkyl)pyrrolyl‐terminated PIB with sodium azide and by in situ quenching of quasiliving PIB with a 1‐(ω‐azidoalkyl)pyrrole. Azide substitution of the terminal halide was carried out in 50/50 heptane/DMF at 90 °C for 24 h using excess azide. The 1‐(ω‐haloalkyl)pyrrolyl‐PIB precursors included 1‐(2‐chloroethyl)pyrrolyl‐PIB, 1‐(2‐bromoethyl)pyrrolyl‐PIB, and 1‐(3‐bromopropyl)pyrrolyl‐PIB. In situ quenching involved direct addition of 1‐(2‐azidoethyl)pyrrole to quasiliving PIB initiated from 5‐tert‐butyl‐1,3‐di(1‐chloro‐1‐methylethyl)benzene (bDCC)/TiCl₄ at ?70 °C in hexane/CH₃Cl (60/40, v/v). ¹H NMR analysis of the quenched product revealed mixed isomeric end groups in which PIB was attached at either C₂ or C₃ of the pyrrole ring (C₂/C₃ = 0.40/0.60). SEC indicated the absence of coupled PIB under optimized conditions, confirming exclusive mono‐substitution on each pyrrole ring. 1‐(3‐Azidopropyl)pyrrolyl‐PIB was reacted in modular fashion with various functional alkynes, propargyl alcohol, propargyl acrylate, glycidyl propargyl ether, and 3‐dimethylamino‐1‐propyne, via a Huisgen 1,3‐dipolar cycloaddition (Click) reaction, using Cu(I)Br/N,N,N′,N″,N″‐pentamethyldiethylenetriamine or bromtris(triphenylphosphine)Cu(I) as catalyst. The reactions were quantitative and produced PIBs bearing terminal hydroxyl, acrylate, glycidyl, or dimethylaminomethyl groups attached via exclusively four‐substituted triazole linkages. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2533–2545, 2010     

Synthesis of functionalized bisphosphonates via click chemistry

An efficient general synthetic approach giving the possibility for facile, rapid and cheap access to a wide range of novel nitrogen-bisphosphonates (N-BPs) as potent drug candidates, based on the reaction of mono- and bis-propargyl-substituted bisphosphonates with a variety of azides under Cu(i) catalysis ("click" methodology), has been developed. The method allows the incorporation of two functionalities into the N-BP molecule simultaneously, as well as to ligate in situ two N-BPs to one another via the one-pot reaction of organic dibromides with propargyl-substituted bisphosphonates, generating both the diazide and Cu(I) moieties.